EP1890831B1 - Process for producing a gearing of sintermaterial - Google Patents

Description

The present invention relates to a method for producing a toothing from sintered material.

Sintered gear elements such as gears made by powder metallurgy are used in some areas. However, creating a suitable production of sintered components due to the powder, its behavior and its properties with regard to some technical fields of application compared to conventional solid materials creates problems.

From the doctoral thesis " New methods for increasing the load capacity of sintered gears ", Gert Kotthoff, Shaker Verlag, volume 23/2003, ISBN 3-8322-2125-5 Theoretical basics, investigations and attempts to model the manufacture of a gear from powder metal using surface rolling to densify a toothing of the gear emerge.

From the GB 2 250 227 A shows a device for producing a gearwheel starting from a preform.

Out LSSigl et al., "Evolution of Gear Quality in Helical PM Gears during Processing", Powder Metallurgy World Congress & Exhibition (Euro PM2004), October 17-21, Vienna, Austria, XP009176190 , a powder-metallurgically manufactured gear for a transmission is known.

Out WO 02/43897 A a method and a device for producing a gear from sintered material are known.

The object of the present invention is to enable an improvement in the production of a toothing from sintered material.

This object is achieved by a method for producing a toothing from a sintered material with the features of claim 1. Advantageous refinements and developments are specified in the respective dependent claims. The characteristics given in the description can be general as well as special can be linked to other features for further training. In particular, the examples given with their respective characteristics are not to be interpreted restrictively. Rather, the features specified there can also be linked to other features from other examples or from the general description.

A preform can be used for the production of a toothing from sintered material, the preform having a negative oversize. The negative oversize is preferably arranged at least on one flank of a tooth of the toothing. In particular, the negative oversize can run asymmetrically along the flank.

A further development provides that a negative oversize is to be carried out on each flank of a tooth. For example, a tooth at the same height has a first negative oversize on a first flank and a second negative oversize on a second flank, the first and second flanks being asymmetrical to one another.

The negative oversize is preferably arranged between a head region of the tooth and an oversize on a flank of the tooth. In addition, the negative oversize can be arranged in a corner region of the tooth base. There is also the possibility that the toothing has different flank slopes at the same height of the tooth, at least on one tooth.

In addition to an external toothing or other type of toothing, surface compaction is also carried out on a toothing that is an internal toothing. Finally, the preform becomes a surface-compacted gear.

According to the invention, a method for producing a toothing from a sintered material is provided, wherein a preform is assigned at least one negative oversize, determined by means of iterative calculation, which is at least partially filled by displacement of the sintered material when the toothing is surface-densified. A measurement material adjacent to the negative measurement is preferably displaced into the negative measurement. The preform can be surface-compacted into the desired final shape, with optional hardening and / or surface finishing. This can be done before or after surface compaction. Honing and grinding can be considered as finishing.

The negative oversize is preferably designed using an iterative calculation, in which a simulation of the surface compaction on the preform determines whether the shape of the adjacent oversize is designed such that d the negative oversize can be smoothed towards the desired final contour. For this purpose, a machine is provided for the calculation and / or for the execution of a surface compression of a toothing, wherein a calculated kinematics can be included, by means of which a negative allowance on a flank of the toothing can be smoothed to a desired final contour via the surface compression.

In a further development of the method for producing an at least partially surface-hardened metal toothing element, which has a compressed sintered material, a preform of the toothing element is produced with a locally selective allowance based on a final dimension of the toothing element and rolled to the final dimension by means of at least one rolling tool, the Gear element is compacted locally at least in the region of at least one flank and / or a foot of a tooth of the tooth element to produce a compressed edge layer on a surface.

A gear element is, for example, a gear, a rack, a cam, a P-rotor, a ring gear, a chain gear or the like. The compacted sintered material is produced in particular using powder metallurgy processes. For example, a metal powder is sintered under pressure in connection with a heat treatment. Furthermore, metal powder, for example, is injection molded in connection with plastic and, in particular, is sintered under a pressure, preferably with a heat treatment. For the shaping of a sintered workpiece, in particular a sintered shape is used which has at least almost the final dimension of the toothing element to be produced. The workpiece resulting directly from the sintering process is preferably used as the preform. In another variant, however, at least one further surface processing step can also be followed. The preform has an oversize, which is to be understood as the difference to a final dimension, the difference being preferably defined pointwise perpendicular to the surface.

As a rolling tool, for example, a roller is used which is equipped with a toothing which can be brought into engagement with the toothing of the toothing element. Such a rolling tool is in particular under pressure on a Rolled surface of the gear element. In particular, two or more such rolling tools are preferably used simultaneously. For example, a gear wheel to be produced can be arranged centrally between two rolling tools. By delivering both rolling tools, surface compaction of the sintered material of the toothing can then be brought about. In general, for example, such a manufacturing process starts Takeya et al, "Surface Rolling of Sintered Gears," SAE 1982 World Congress, Technical Paper 820234 forth. Also from DE 33 250 37 , out US 4,059,879 , out EP 0 552 272 A1 , out EP 1 268 102 A1 , out US 5,729,822 , out US 5,711,187 , out US 5,884,527 , out US 5,754,937 , out US 6,193,927 , out EP 0 600 421 A1 , out GB 2,250,227 Different manufacturing processes, sintered materials, tools, the sequence of the compression and devices for sintered gears emerge, which can also be used adapted to the invention. Reference is made to the above publications in accordance with the scope of this disclosure.

For example, it is also possible to use a first rolling tool under a first pressure, essentially for rough contour rolling, and then a second rolling tool under a second pressure to achieve the surface compaction to be set in a targeted manner.

The locally selective oversize is in particular dimensioned such that the toothing element is compacted in a locally varying manner on a surface at least in the area of at least one flank or additionally of a foot of a tooth of the toothing element. A full density is preferably achieved within the compressed outer layer, the full density preferably being understood in relation to a density of a comparable powder-forged tooth. For example, a preform made of a sintered material in a core has a density of at least 6.8 d / cm ³ , preferably of at least 7.1 g / cm ³ and in particular of at least 7.3 g / cm ³ . In the compacted surface layer, the preform has, for example, a density of at least 7.7 g / cm ³ , preferably of at least 7.8 g / cm ³ , which corresponds to the density of a powder-forged preform made of the same material. A strength curve that is suitable for the stress is particularly advantageously achieved. Furthermore, with a locally variable and stress-appropriate density profile, a highly stressable sintered toothing is preferably provided. The density profile can have a greater degree of density over a larger area, in particular in the areas subject to higher stress, in comparison to immediately adjacent areas of lower load. By determining an optimized dimension, a toothing produced in this way can also be economically produced in a few steps.

According to one embodiment, the differently compacted edge layer is also produced over a different allowance along a flank and / or tooth base of the preform. For example, it is provided that a depth of the compressed edge layer, viewed perpendicular to the surface, has a maximum density at approximately the location of a maximum stress. This can, for example, be halfway up the tooth and decrease continuously to zero in relation to the tooth head and the tooth base. In particular, to avoid pitting, it is provided, for example, that a particularly high compression in the sintered material is set in a range between 20% and 30%, in particular between 23% and 25%, below the rolling circle. However, other courses can also be provided. In particular, when designing a compression profile, a force profile on a tooth flank of the toothing element is taken into account in its intended use. For example, the forces occurring on the teeth of a gearwheel in a transmission are used and the resulting comparison stress curves below the surface are used. This procedure is also possible with other gears.

It is particularly advantageous if an oversize on a first flank of the tooth is chosen differently than on a second flank of the tooth. In this case, in particular a direction of force transmission is taken into account in the intended use of a toothing element. In the case of a gearwheel in a transmission, for example, this takes into account the fact that, depending on a direction of rotation in the direction of rotation, different forces occur on the tooth flanks than against the direction of rotation. Furthermore, a different compression due to a direction of rotation of a rolling tool can be compensated for. The oversizes are preferably chosen such that after a compression process, an identical compression profile results along the first and the second tooth flank.

For example, to avoid stress cracks in a tooth base or tooth base area, a locally compressed surface layer is also sought in these areas. It is particularly expedient if an asymmetrical oversize is selected in a tooth base. For example, a left tooth root area has a different compression depth than a right tooth root. In particular, between two Teeth a preferably continuous variation of a depth of an edge layer can be provided by a corresponding variation of the allowance.

When designing a toothing, a different, in particular asymmetrical dimension is preferably provided not only with respect to one flank, but preferably with respect to two flanks lying opposite one another. In addition, a different dimension is provided in the tooth base, which is preferably asymmetrical. Tooth flanks and tooth feet of a toothing can each be asymmetrical. In this case, the oversize is not only to be understood as the provision of additional material. Rather, this also includes an undersize. This is to be understood to mean that less sintered material is provided in a zone than would have to be provided in relation to an end contour after a processing step. The undersize determined ensures, for example, that no undesired elevations occur when sintered material is displaced. The undersize therefore represents an area of a preform with a toothing that is to be filled in by displacement of sintered material.

In addition, there is the possibility of providing different pressure angles on a tooth of a tooth system. The pressure angle of the one flank of the tooth can thus deviate by at least 15% from the pressure angle of the other flank of the tooth.

In one embodiment it is provided that at least 20 μm below a surface of a first flank of the tooth, a density that is 2% to at least 15% higher than on a second flank of the tooth is generated at the same height. A density is preferably achieved on the first flank of the tooth which corresponds at least approximately to the density achieved for a powder-forged toothing element, whereas the second flank has a lower density. For example, at a density in a range between 7.2 g / cm ³ and 7.7 g / cm ³ is set an edge, while in the corresponding region of the second flank has a density between 7.5 g / cm ³ and 7.82 g / cm ^{3 is} set. In particular, this takes into account, for example, different loads on the two tooth flanks that are dependent on the direction of rotation. A requirement-oriented elasticity and hardness curve is preferably achieved. This furthermore preferably reduces noise development, for example in a transmission.

Furthermore, it is provided that a local oversize on a first flank of the tooth is chosen to be at least 10% larger than an oversize on a second flank of the tooth at the same height. In a first variant it is achieved, for example, that an identical compression profile is achieved on the first and the second tooth flank due to different pressurization during compression depending on the direction of rotation. In a further variant, for example, a different compression profile is achieved on the first and the second tooth flank. In particular, different maximum densities, their depths as well as their location in relation to the height of the toothing can be set specifically.

It is particularly expedient if an amount of a maximum local oversize is at least 15 μm, preferably at least 100 μm and particularly preferably at least 400 μm. If the density of the preform is in a range between 7.2 g / cm ³ and 7.5 g / cm ³ , a maximum allowance between 20 and 150 μm is preferably provided. If the density of the preform is between 6.7 g / cm ³ and 7.2 g / cm ³ , a maximum allowance between 50 μm and 500 μm is preferably used. An oversize can also be negative locally, taking into account, for example, a lateral redistribution of material. Lateral redistribution can occur by flowing material as a result of a rolling process. In particular, an at least locally negative oversize can be provided, which is locally below the final dimension. The negative oversize is preferably at most 100 microns. According to one embodiment, the negative oversize is at most less than 50 μm and in particular less than 20 μm. In particular, the maximum negative oversize is in a range between 100 µm and 20 µm.
A compression is preferably achieved which reaches a depth of between 1 mm and 1.5 mm at least in a region of a tooth flank of the toothing. The compression in the tooth base, however, can be lower. According to one embodiment, the maximum depth of compression of a tooth flank is at least 6 times greater than a maximum depth of compression in a region of the associated tooth base. This allows the toothing to have sufficient strength on the one hand, but on the other hand also maintain a certain deformability. This prevents tooth breakage.

In one embodiment of the method it is provided that the preform and the rolling tool are rolled onto one another until a final shaping movement is generated between the toothing element produced thereby and the rolling tool. This is used, for example, to manufacture gear wheels that are in engagement with one another. Preference is given to the rolling tool during the rolling process a distance between the rolling tool and preform is reduced. Accordingly, a rolling pressure is set or adjusted in particular. In addition to the possibility of force control, path control can also be implemented on the machine. In addition, there is the possibility of providing a combination of force and displacement control in the manufacture of the toothing. A pure path control can also take place in one section of the production and a pure force control in another section of the production. These can also alternate several times.

In a further embodiment it is provided that a cycloidal and / or involute toothing is created between the preform and the rolling tool by means of the rolling movement.

In addition to gear elements in the sense of gear wheels, other gear elements can also be produced. For example, it is provided that a cam is produced as the toothing element. In particular, a cam can be produced such as is used, for example, for the mechanical actuation of an adjusting device, for example for adjusting a valve or the like. A locally varied compression of an edge layer on a flank of a cam preferably provides an improved strength profile with less susceptibility to wear.

A further improvement in surface hardening can be achieved in particular in that the method for producing an at least partially surface-compressed metal toothing element comprises a thermal and / or chemical surface hardening process.

In a first variant, case hardening, for example, is used as the thermal and / or chemical hardening process. In addition to increasing the hardness, tension is preferably reduced. In a further variant, for example, a carbonitriding process is used. Furthermore, a nitriding or nitrocaborating process as well as a boriding process can be used. In particular, a reduction in tension is also achieved in these processes in connection with a heat treatment. The hardening can also be influenced by adjusting the prevailing pressure. For example, a vacuum can be set, especially when case hardening is carried out. There is also the possibility of induction hardening.

According to one embodiment, the hardening is carried out only partially, for example only in the area of the toothing.

In a preferred variant, it is provided that a method for producing an at least partially surface-hardened metal toothing element, which has a compressed sintered material, comprises the steps "cold or hot pressing, sintering, dimension and surface compaction rolls and case hardening". For example, a metal powder is first cold-pressed in a mold which has at least approximately the final dimension of the toothing element to be produced. In a second step, for example, the sintering process takes place under the action of heat with or without the action of pressure. The dimensional and surface compaction is then preferably carried out by means of rollers. As already mentioned above, dimension and surface compaction rolling is preferably carried out simultaneously using at least two rolling tools. This can be followed by hardening, in particular case hardening, which enables the surface to be hardened further.

• gemischte Pulver (admixed powders): Zum Beispiel Eisenpulver wird mit anderen vorzugsweise elementaren Pulvern gemischt. Zum Beispiel:
  • Ancorsteel 1000+1,5-3,5 w/o Cu + 0,6-1,1 w/o Graphit + 0,5-1,2 w/o Schmiermittel
  • Ancorsteel 1000B+1,5-2,2 w/o Ni + 0.4-0,9 w/o Graphit + 0,6-1,1 w/o Schmiermittel
• teilweise legierte Pulver (partially alloyed, diffusion alloyed powders): Ein Pulver bei dem der oder die Legierungsbestandteile metallurgisch mit elementarem Pulver oder vorlegiertem Pulver verbunden sind. Zum Beispiel: Distaloy AB, Distaloy 4600A, Distaloy AE, Distaloy 4800A
• vorlegierte Pulver (pre-alloyed powders): Pulver aus zwei oder mehr Elementen, die während der Pulverherstellung legiert werden, wobei die Pulverpartikel gleichverteilt werden. Zum Beispiel: Ancorsteel 4600V, Ancorsteel 2000, Ancorsteel 86, Ancorsteel 150HP
• Hybridlegierung (hybrid alloy): vorlegierte oder partiell legierte Pulver mit elementaren oder eisenlegierten Zugaben, die vermischt werden, um die gewünschte Materialzusammenstellung zu erhalten. Zum Beispiel:
  • Ancorsteel 85P+1,5-2,5 w/o Ni + 0,4-0,8 w/o Graphit + 0,55-1,1 w/o Schmierzusatz
  • Distaloy AE + 1,5-2,5 w/o Ni + 0,4-0,8 w/o Graphit + 0,55-0,95 Schmierzusatz
  • Ancorsteel 85HP + 1,1-1,6 w/o FeMn + 0,35-0,65 w/o Graphit + 0,6-0,95 Schmierzusatz

1. 1. Das Werkstück weist eine Kerndichte zwischen 6,5 und 7,5 g/cm³ auf. Die Oberflächendichte beträgt mehr als 7,5 g/cm³. Eine maximale Dichte wird bis zu einer Tiefe von 0,1 mm erzeugt.
   Ausgangsmaterialien für die Vorform sind sintermetallische Pulver, insbesondere vorlegierte Materialien, partiell legierte Materialien oder Hybridlegierungen.
   Mit einem vorlegiertem Material wird ein Kaltverpressen, ein Sintern in einem Temperaturbereich zwischen 1100°C und 1150°C, ein Oberflächenverdichten, ein Einsatzhärten und ein anschließendes Schleifen vorgenommen, um eine Endform eines Werkstücks mit Verzahnung zu erzielen.
   Mit einem partiell legierten metallischem Sintermaterial wird ein Warmpressen bei einer Pressentemperatur in einem Bereich zwischen 50°C und 80°C, ein Hochtemperatursintern in einem Bereich vorzugsweise zwischen 1250° C und 1280°C, ein Oberflächenverdichten, ein anschließendes Vakuum-Einsatzhärten und ein Honen durchgeführt, um eine Endform eines Werkstücks mit Verzahnung zu erzielen.
   Mit einem Sintermaterial aufweisen eine Hybridlegierung wird ein Warmpressen ausgeführt, bei dem vorzugsweise das Pulver und das Werkzeug erhitzt sind. Vorzugsweise sind diese in einem Bereich zwischen 120°C und 150° aufgeheizt. Anschließend erfolgte ein Sinterschritt, beispielsweise als Hochtemperatursintern, ein Oberflächenverdichten und anschließend Induktionshärten. Eine Nachbehandlung kann beispielsweise entfallen.
2. 2. Die Vorform ist pulvergeschmiedet. Diese Vorform wird zumindest teilweise im Bereich der Zahnflanken und/oder des Zahnfußes oberflächenverdichtet. Eine Kerndichte des Werkstücks beträgt zwischen 5,7 g/cm³ und 7,7 g/cm³. Eine Oberflächendichte im Bereich der beträgt mehr als 7,8 g/cm³, wobei vorzugsweise in diesem Bereich alle verbliebenen Poren an der Oberfläche verschlossen sind. Es kann jedoch auch eine Maximaldichte bis zu einer Tiefe von 1,5 mm erzeugt werden.
   Ein Herstellungsverfahren kann wie folgt ablaufen: Wahl des Pulvermaterials, Kaltpressen des Pulvermaterials, Sintern vorzugsweise mit einer Temperatur um ca. 1120°C, anschließen Schmieden, vorzugsweise bei einer Temperatur um die 1000°C, eventuelles Entfernen einer Oxidationsschicht, Oberflächenverdichten insbesondere durch Wälzen, Oberflächenhärten, insbesondere Einsatzhärten, und eventuelles anschließendes partielles Schleifen auf eine Endkontur. Das Verfahren kann ganz oder teilweise in einer Fertigungstrasse ablaufen.
   Eine weitere Ausgestaltung sieht vor, dass beim Oberflächenhärten ein Vakuum-Einsatzhärten ausgeführt wird, an den sich ein Honschritt für partielle Bereiche der Verzahnung anschließen.
3. 3. Insbesondere für die Produktion von Rotoren und Ölpumpenräder wird eine Vorform aus einem aluminiumhaltigen Material im Bereich der Zahnflanken und/oder der Zahnfüße oberflächenverdichtet. Beim Oberflächenverdichten wird insbesondere eine Endform der Verzahnung erzielt. Die Kerndichte des Werkstücks beträgt vorzugsweise zwischen 2, 6 g/cm³ und 2,8 g/cm³.
   Das Sintermaterial wird beispielsweise warmgepresst, beispielsweise bei einer Temperatur zwischen 40°C und 65°C, anschließend entwachst, beispielsweise bei einer Temperatur von mehr als 400°C, insbesondere in einem Temperaturbereich zwischen 420°C und 440°C dann gesintert, beispielsweise in einem Temperaturbereich oberhalb von 550°, insbesondere in einem Temperaturbereich zwischen 600°C und 630°C, dann homogenisiert und gekühlt, beispielsweise auf eine Temperatur zwischen 480°C und 535°C, wobei anschließend ein Oberflächenverdichten insbesondere durch Walzen erfolgt. Anschließend kann eine Aushärtung erfolgen, beispielsweise in einem Temperaturbereich zwischen 120°C und 185°C für einen Zeitraum zwischen 6 h und 24 h.
4. 4. Die Vorform wird vorzugsweise entlang der Zahnflanke und des Zahnfußes verdichtet, wobei insbesondere zwei Walzwerkzeuge eingesetzt werden, in deren Mitte die Vorform drehbar angeordnet wird. Eine Kerndichte des Werkstücks beträgt je nach Material vorzugsweise zwischen 7,2 g/cm³ und 7,5 g/cm³, eine Oberflächendichte ist materialabhängig zumindest abschnittsweise größer als 7,8 g/cm³. Eine maximale Dichte ist insbesondere bis zu einer Tiefe von 1 mm vorliegend, eventuell auch darüber hinaus.
   Von den Herstellungsschritten wird gemäß einer Ausgestaltung vorgeschlagen, vorlegiertes Material kalt zu verpressen, anschließend zu sintern, insbesondere in einem Temperaturbereich zwischen 1100C° und 1150°C, eine Oberflächenverdichtung durchzuführen, eine Härtung auszuführen und die Oberfläche partiell eventuell zu schleifen.
   Eine weitere Ausgestaltung sieht vor, ein partiell legiertes Sintermaterial warm zu verpressen, insbesondere in einem Temperaturbereich zwischen 50°C und 90°C, ein Hochtemperatursintern auszuführen, insbesondere in einem Temperaturbereich zwischen 1240°C und 1290°C, eine Oberflächenverdichtung durchzuführen, eine Vakuum-Einsatzhärtung vorzunehmen und eventuell anschließend zu honen.
   Eine andere Ausgestaltung sieht vor, eine Hybridlegierung heiß zu verpressen, wobei das Pulver und das Presswerkzeug vorzugsweise in einem Temperaturbereich zwischen 120°C und 160°C aufgewärmt sind. Nach einem Sinterschritt erfolgt eine Oberflächenverdichtung, an die sich eine Härtung, vorzugsweise eine Induktionshärtung anschließt.
5. 5. Weiterhin besteht die Möglichkeit, das einem Vorsintern ein Oberflächenverdichten nachfolgt und dann wiederum ein Nachsintern als Verfahrensschritt bei der Herstellung eines Werkstückes mit Verzahnung vorgesehen ist. Das Vorsintern kann beispielsweise in einem Temperaturbereich zwischen 650°C bis 950°C erfolgen. Das Nachsintern kann beispielsweise bei einer für das Material üblichen Sintertemperatur erfolgen, zum Beispiel zwischen 1050°C und 1180°C. Auch besteht die Möglichkeit der Hochtemperatursinterung, zum Beispiel im Bereich zwischen 1250°C und 1280°C. Hiernach kann sich optional ein Härten und/oder eine Nachbearbeitung anschließen, zum Beispiel ein Honen oder auch ein Schleifen.
   Das vorhergehende Verpressen kann kalt, warm oder heiß erfolgen, wobei bei letzterem vorzugsweise das Presswerkzeug und das Pulver aufgeheizt sind. Beispielsweise erfolgt das Heizpressen in einem Temperaturbereich zwischen 120°C und 160°C.
6. 6. Eine Weiterbildung sieht vor, dass einem Nachsinterschritt ein Sinterhärten nachfolgt. Optional kann sich daran ein Schleifen oder Honen anschließen.
7. 7. Ein weiteres Herstellungsverfahren sieht vor, die Vorform bei einer Temperatur zu verdichten, die oberhalb von 150°C liegt, insbesondere über 500°C. Beispielsweise kann die Vorform direkt von einem Sinterofen in eine Maschine zur Oberflächenverdichtung geführt werden. Dabei kann die Vorform eine Temperatur aufweisen, die beispielsweise oberhalb von 600°C liegt, insbesondere auch über 800°C beträgt. Vorzugsweise werden das oder die Werkzeuge zur Oberflächenverdichtung beheizt, zum Beispiel auf eine Temperatur von etwa 150°C. Gemäß einer anderen Ausgestaltung ist das Werkzeug zur Oberflächenverdichtung gekühlt, vorzugsweise durch eine im Inneren des Werkzeugs verlaufende Kühlung.
8. 8. Ein weiteres Herstellungsverfahren sieht vor, dass eine Oberflächenverdichtung erfolgt, während die Vorform zumindest partiell beheizt wird. Insbesondere erfolgt die Beheizung auf eine Temperatur, die das Oberflächenverdichten vereinfacht. Vorzugsweise wird hierfür eine Induktionsbeheizung eingesetzt. Anschließend erfolgt ein rasches Kühlen, um eine martensitische Struktur zu schaffen. Auf diese Weise kann beispielsweise ein Ausform-Prozess mit einer Oberflächenverdichtung kombiniert werden.

Further possible process steps or process sequences as well as further details on workpieces are given below by way of example. However, the process steps can also be carried out with other materials and density values achieved. The sintered materials that can be used are generally usable as follows within the scope of the invention, examples of usable materials being given:

• mixed powder (admixed powders): For example iron powder is mixed with other preferably elementary powders. For example:
  • Ancorsteel 1000 + 1.5-3.5 w / o Cu + 0.6-1.1 w / o graphite + 0.5-1.2 w / o lubricant
  • Ancorsteel 1000B + 1.5-2.2 w / o Ni + 0.4-0.9 w / o graphite + 0.6-1.1 w / o lubricant
• Partially alloyed, diffusion alloyed powders: A powder in which the alloy component (s) are metallurgically combined with elemental powder or pre-alloyed powder. For example: Distaloy AB, Distaloy 4600A, Distaloy AE, Distaloy 4800A
• Pre-alloyed powders: Powder consisting of two or more elements that are alloyed during powder production, with the powder particles being evenly distributed. For example: Ancorsteel 4600V, Ancorsteel 2000, Ancorsteel 86, Ancorsteel 150HP
• Hybrid alloy: pre-alloyed or partially alloyed powder with elemental or iron-alloyed additions, which are mixed to obtain the desired material composition. For example:
  • Ancorsteel 85P + 1.5-2.5 w / o Ni + 0.4-0.8 w / o graphite + 0.55-1.1 w / o lubricant
  • Distaloy AE + 1.5-2.5 w / o Ni + 0.4-0.8 w / o graphite + 0.55-0.95 lubricant
  • Ancorsteel 85HP + 1.1-1.6 w / o FeMn + 0.35-0.65 w / o graphite + 0.6-0.95 lubricant

1. 1. The workpiece has a core density between 6.5 and 7.5 g / cm ³ . The surface density is more than 7.5 g / cm ³ . A maximum density is created to a depth of 0.1 mm.
   Starting materials for the preform are sintered metal powders, in particular pre-alloyed materials, partially alloyed materials or hybrid alloys.
   A pre-alloyed material is used for cold pressing, sintering in a temperature range between 1100 ° C and 1150 ° C, surface compression, case hardening and subsequent grinding in order to achieve a final shape of a workpiece with teeth.
   With a partially alloyed metallic sintered material, hot pressing at a press temperature in a range between 50 ° C and 80 ° C, high temperature sintering in a range preferably between 1250 ° C and 1280 ° C, surface compression, subsequent vacuum case hardening and honing carried out to achieve a final shape of a workpiece with teeth.
   With a sintered material comprising a hybrid alloy, hot pressing is carried out, in which the powder and the tool are preferably heated. These are preferably heated in a range between 120 ° C and 150 °. This was followed by a sintering step, for example as high-temperature sintering, surface compaction and then induction hardening. Post-treatment can be omitted, for example.
2. 2. The preform is powder forged. This preform is at least partially surface compacted in the area of the tooth flanks and / or the tooth base. A core density of the workpiece is between 5.7 g / cm ³ and 7.7 g / cm ³ . A surface density in the range of is more than 7.8 g / cm ³ , all remaining preferably in this range Pores on the surface are closed. However, a maximum density down to a depth of 1.5 mm can also be generated.
   A manufacturing process can proceed as follows: selection of the powder material, cold pressing of the powder material, sintering preferably at a temperature around 1120 ° C., then forging, preferably at a temperature around 1000 ° C., possible removal of an oxidation layer, surface compaction, in particular by rolling, Surface hardening, in particular case hardening, and possibly subsequent partial grinding to an end contour. The method can run entirely or partially in a production line.
   A further embodiment provides that a vacuum case hardening is carried out during surface hardening, which is followed by a honing step for partial areas of the toothing.
3. 3. In particular for the production of rotors and oil pump wheels, a preform made of an aluminum-containing material is surface-compacted in the area of the tooth flanks and / or the tooth feet. A final shape of the toothing is achieved in particular during surface compaction. The core density of the workpiece is preferably between 2.6 g / cm ³ and 2.8 g / cm ³ .
   The sintered material is, for example, hot pressed, for example at a temperature between 40 ° C. and 65 ° C., then dewaxed, for example at a temperature of more than 400 ° C., in particular in a temperature range between 420 ° C. and 440 ° C., then sintered, for example in a temperature range above 550 ° C, in particular in a temperature range between 600 ° C and 630 ° C, then homogenized and cooled, for example to a temperature between 480 ° C and 535 ° C, followed by surface compaction, in particular by rolling. Curing can then take place, for example in a temperature range between 120 ° C. and 185 ° C. for a period between 6 h and 24 h.
4. 4. The preform is preferably compacted along the tooth flank and the tooth base, two rolling tools in particular being used, in the middle of which the preform is rotatably arranged. Depending on the material, a core density of the workpiece is preferably between 7.2 g / cm ³ and 7.5 g / cm ³ , and a surface density is dependent on the material at least in sections greater than 7.8 g / cm ³ . A maximum density is present in particular up to a depth of 1 mm, possibly also beyond.
   According to one embodiment, the manufacturing steps propose to cold-press pre-alloyed material, then to sinter, in particular in a temperature range between 1100 ° C. and 1150 ° C., to carry out a surface compaction, to carry out a hardening and possibly to partially grind the surface.
   A further embodiment provides for a partially alloyed sintered material to be hot-pressed, in particular in a temperature range between 50 ° C. and 90 ° C., for high-temperature sintering, in particular in a temperature range between 1240 ° C. and 1290 ° C., for surface compaction, a vacuum - Case hardening and possibly honing afterwards.
   Another embodiment provides for hot pressing a hybrid alloy, the powder and the pressing tool preferably being warmed up in a temperature range between 120 ° C. and 160 ° C. After a sintering step, the surface is compacted, followed by hardening, preferably induction hardening.
5. 5. There is also the possibility that a pre-sintering is followed by a surface compaction and then a re-sintering is again provided as a process step in the production of a workpiece with teeth. The pre-sintering can take place, for example, in a temperature range between 650 ° C to 950 ° C. The re-sintering can take place, for example, at a sintering temperature that is customary for the material, for example between 1050 ° C. and 1180 ° C. There is also the possibility of high-temperature sintering, for example in the range between 1250 ° C and 1280 ° C. After this, hardening and / or post-processing can optionally follow, for example honing or grinding.
   The previous pressing can take place cold, warm or hot, the latter preferably heating the pressing tool and the powder. For example, the hot pressing takes place in a temperature range between 120 ° C and 160 ° C.
6. 6. Further training provides that a post-sintering step is followed by sinter hardening. This can optionally be followed by grinding or honing.
7. 7. Another manufacturing process provides for the preform to be compacted at a temperature which is above 150 ° C., in particular above 500 ° C. For example, the preform can be fed directly from a sintering furnace into a surface compaction machine. The preform can have a temperature which is, for example, above 600 ° C., in particular also above 800 ° C. The tool or tools for surface compaction are preferably heated, for example to a temperature of approximately 150 ° C. According to another embodiment, the tool for surface compaction is cooled, preferably by cooling running inside the tool.
8. 8. Another manufacturing process provides that surface densification takes place while the preform is at least partially heated. In particular, the heating takes place to a temperature that simplifies surface compaction. Induction heating is preferably used for this. This is followed by rapid cooling to create a martensitic structure. In this way, for example, a molding process can be combined with a surface compaction.

A further embodiment of the invention provides that surface compaction can be carried out using a wide variety of methods. One embodiment in particular provides that the surface compaction is carried out with a different method in a first area than in a second, different area. Shot blasting, shot peening, compaction by means of a ball, by means of a roller or by means of another rotatable body, by means of tooth-shaped tools, in particular rolling tools and the like, can be used as methods. These methods are also suitable, each separately, to allow the necessary surface compaction.

For example, the tooth base is not compressed at all or only slightly with a tool that also compresses the tooth flank. It is possible to compress the surface in one section to such an extent that only the pores on the surface are closed. The tooth base can then be processed with another tool or surface compaction method. In particular, a different surface compaction along the tooth flank can be achieved compared to the tooth base. For example, different surface qualities can be set in this way, for example with regard to the roughness. The maximum surface recess may also be different due to the different techniques. Farther there is the possibility that the entire workpiece with the toothing receives a surface compaction, for example during surface blasting. In this way, in particular, aluminum-containing sintered materials or other oxide-forming sintered materials can also be processed, since the surface compaction can also make it possible to remove an oxide layer.

Furthermore, a preform is used for a method for producing an at least partially surface-hardened metal toothing element, which has a compressed sintered material, a first and a second flank of a tooth each having asymmetrical dimensions that differ from one another. Furthermore, it is also provided that a first and a second foot region of a tooth have deviating, in particular asymmetrical oversizes.

A toothing element with a metallic sintered material can have a locally varied compression at least in the region of at least one flank of a tooth of the toothing element. This preferably enables elasticity of the powder metallurgical material, which is expedient for many applications, in conjunction with surface hardening. With gearwheels, for example, noise reduction during power transmission is particularly preferably made possible and, at the same time, good wear resistance is provided.

The toothing element can be a straight toothed gear.

In particular for improved power transmission as well as for noise reduction between gear wheels, it can be provided that the toothing element is a helically toothed gear wheel. Furthermore, a bevel gear can also be provided. According to the description given above, it is expedient if opposing flanks of teeth of a toothing element have an asymmetrical compression.
Furthermore, it is expedient if there is asymmetrical compression in a foot area. This compression is particularly adapted to the forces that occur during use. To avoid stress cracks, it is provided in particular that the depth of the locally compacted edge layer is only so high that sufficient tooth elasticity or rigidity is still ensured. The depth of the compacted edge layer in the foot region is particularly preferably less than on a tooth flank.

As a special form of the toothing element it can be provided that the toothing element is a cam. The above statements are to be applied accordingly, for example flanks of the cam replacing the flanks of teeth.

Different compositions can be provided for a material of a gear element. In a first variant, an iron material is selected as the main component of the sintered material and at least one alloy component from the group consisting of carbon, molybdenum, nickel, copper, manganese, chromium and vanadium. An iron alloy is, for example, Fe -1.0 Cr -0.3 V +0.2 based on a reference 15CrNiMo6. Another iron alloy is, for example, Fe-1.5 Mo + 0.2C based on 20MnCr5. Furthermore, Fe -3.5 Mo based on 16MnCr5 is provided as an iron-containing alloy. Likewise, for example, the alloy C 0.2% Cr 0.5% Mn 0.5% Mo 0.5%, the rest including iron and impurities, can be used. In addition, other compositions can be provided.

To reduce the weight of a toothing element, it is preferably provided that aluminum or magnesium is selected as the main constituent of the sintered material. A surface-compressed toothing made of sintered material can have at least 80% aluminum and at least copper and magnesium as further sintered materials. A first embodiment provides that silicon is additionally used as the sintered material. For example, silicon can range from about 0.45% to about 0.8%, preferably between 0.6% and 0.75%. However, silicon can also be present in a higher range, for example between 13% and 17%, in particular between 14.5% and 15.5%. If the silicon content is higher, the copper content of the sintered material is reduced. For example, a first mixture can contain copper with a 4% to 5% content, silicon with 0.45% to about 0.8% content, magnesium with about 0.35% to 0.7% content and the rest at least mainly aluminum. In addition, a pressing aid is preferably added. This can have a share between 0.8 and 1.8%. For example, a wax, especially amide wax, can be used for this. A second mixture can have, for example, copper with a 2.2% to 3% share, silicon with 13% to about 17% share, magnesium with about 0.4% to 0.9% share and the rest at least mainly aluminum. Likewise, a pressing aid can be used, as exemplified above. After surface compaction, at least one area of the toothing has a density of, for example, more than 2.5 g / cm ³ preferably up to the maximum density. A workpiece produced in this way with a toothing preferably has a tensile strength of at least 240 N / mm ² and a hardness of at least 90HB. If the silicon is higher, the density can in particular also be more than 2.6 g / cm ³ .

A second embodiment provides that, in addition, at least zinc is used as a sintered material in addition to copper and magnesium as additives and aluminum. Copper preferably has a proportion in a range between 1.2% and 2.1%, in particular between 1.5% and 1.65%, magnesium between 1.9% and 3.1%, preferably between 2.45% and 2.65%, zinc between 4.7% and 6.1%, in particular between 2.3% and 5.55%. The rest is at least mostly aluminum. In addition, a pressing aid as described above can also be used here. A workpiece made from this mixture with a toothing preferably has at least one area of the toothing after the surface compaction, in which a density of at least 2.58 g / cm ^{3 runs} up to the maximum density. A workpiece produced in this way with a toothing preferably has a tensile strength of at least 280 N / mm ² and a hardness of at least 120HB.

It is particularly expedient if a toothing element is sintered with a further functional component, in particular a shaft or a further gearwheel. In particular, this makes it easier to maintain a precise working distance between a plurality of toothing elements, for example in a transmission.

The gear element can be part of a pump. For example, it is an involute gear, which is brought into engagement with another involute gear.

A device for producing an at least partially surface-compressed toothing element and for carrying out a method described above with a tool control adapted to a different allowance is explained below. The device comprises in particular at least one rolling tool, which can preferably act on the preform in an adapted engagement with the aid of the adapted tool control, preferably under an adapted pressure and / or controlled path. In particular, the device comprises a rolling tool with a toothed surface which can be brought into engagement with the toothing of the toothing element and can be rolled thereon.

A device for producing an at least partially surface-hardened toothing element from a preform consisting at least in one surface area of a sintered material can comprise a tool which has a compensation of different dimensions on a first and a second flank of a tooth of the preform to be compressed by means of rolling motion. The rolling tool can have a contour necessary for shaping, for example an involute toothing, only on one flank or on both flanks of a tooth. In another variant, however, it is also provided that there are different dimensions on each of a first and a second flank of a tooth of the toothing of the rolling tool. This can be a different involute toothing, for example.

Furthermore, a method for designing an oversize to achieve a surface compression of a sintered metal gear element during a rolling process is explained, the oversize being determined iteratively. In a first step, for example, a geometry and in particular a torque and / or a pressure distribution are specified. In a further step, for example, a design of a rolling tool is defined. Furthermore, a preform with a locally defined oversize is determined. A selection can be made, for example, using data libraries. Such a data library contains, for example, experimental density profiles determined using various parameters. Furthermore, the compression or rolling process can be simulated. For this purpose, for example, the kinematics of the rolling process is simulated in conjunction with a simulation of elastic and plastic properties of the preform and, if appropriate, of the rolling tool. For the simulation of the elastic or plastic properties of the preform, for example, models of continuum mechanics are used in connection with a discrete solution using, for example, finite element or finite volume methods.

It can be provided that a geometry of a rolling tool is determined iteratively taking into account the oversize. For example, an oversize of an involute toothing of the rolling tool can be determined. A measurement for a toothing other than involute can be determined accordingly.

It can further be provided that, in a first step, an allowance that is locally varied, at least pointwise, at least in a region of a flank of a tooth a preform of the toothing element is automatically generated on the basis of at least one design specification, in a second step a geometry of a rolling tool is automatically generated, in a third step a rolling process and a local course of compression of at least one edge layer of the toothing element generated in this way are simulated and in a fourth step an automatic evaluation of the generated course of the compression is compared with a specification and, if necessary, the process is repeated from the first step using at least one variation for optimization until an abort criterion is met. The variation takes place, for example, with the help of an optimization process. A termination criterion is, for example, a tolerance between the desired density profile and the density profile achieved in the simulation. Furthermore, an abort criterion can also be a predefined number of iterations being exceeded.

It is particularly useful if the design specification is selected from the group of material density, geometry, torque and pressure distribution. The torque is to be understood here as the torque occurring in the intended use of a gear element.

In particular, in order to avoid material cracks, it is expedient if a material stress is simulated at least in the area of the compression and is used in particular for the evaluation. This preferably avoids that a surface is sufficiently hardened, but is brittle due to tension and tends to crack.

Furthermore, it is advantageous if data stored in a database library are used for variation. In particular, methods for optimization and data analysis can be used, for example by means of neural networks. Features stored in the database are also used, for example, for optimization using a genetic algorithm.

At least one of the steps can be replaced by a specification. A rolling tool geometry is preferably predetermined. This takes into account, for example, the fact that a rolling tool is much more difficult to modify than, for example, a preform. Another embodiment provides a reverse procedure. Starting from a final shape, a preform is preferred or the rolling tool for producing the final shape as well as the press tool for producing the preform.

A computer program product is proposed with program code means which are stored on a computer-readable medium in order to carry out at least one of the methods described above when the program is executed on a computer. A computer-readable medium is, for example, a magnetic, a magneto-optical or an optical storage medium. A memory chip is also used, for example. In addition, a computer-readable medium can also be realized by means of a remote memory, for example by means of a computer network.

The computer program can, for example, be stored in a machine for surface compaction. A calculation can also be carried out separately from the machine for surface compaction. However, the machine has a control system, in particular a path-controlled and / or force-controlled control system, in which the coordinates and movement sequences can be entered in order to compress the preform.

A pressing tool mold is provided with which a preform made of sintered material can be pressed, which is subsequently surface-compacted onto a final mold. This mold shape is calculated iteratively. Preferably, data of an end contour of the workpiece with its toothing are also used as the starting point.

A roller test stand can also be provided, which offers the possibility of being able to carry out test rolling for a wide variety of surface densifications. In particular, data can also be determined in this way, which can be evaluated and included in the calculation methods. For example, suitable characteristic values can be formed from a large number of measurements. Starting values for the iterative calculation of preform, tool or pressing tool can be made using this. The roller test stand can also have an automated measurement of surface-compacted workpieces that have teeth.
In the following, further ideas are proposed which are combined with the previously proposed aspects but can also be carried out independently of them.

Furthermore, a method for producing a toothing from compressed sintered material is provided, wherein a pre-compressed tooth preform at least in one area by means of iteratively determined data has at least 0.05 mm on its surface on its final shape is compressed, and a quality of the final shape is achieved at least in a range of at least f _Hα = 4, F _α = 7 and F _fα = 7. Here, f _{Hα means} the deviation in terms of the toothing, F _α the total deviation and f _fα the profile shape deviation of the flanks. The specified values correspond to the DIN classes with regard to the deviation.

According to a development, it is provided that an iteration takes into account parameters which relate to a material behavior when the tooth shape is surface-compacted. One embodiment provides that an iteration to determine a preform is based on input data that are taken from a specification of the final shape. At least one rolling tool is preferably used, which has the same quality as the final shape created later. The iterative determination and therefore extremely precise processing during surface compaction enables the quality of the tool to be transferred to the preform. In particular, the extremely precise surface compaction enables the toothing to have this quality of the final shape after the surface compaction without a further material-removing finishing step. For example, a workpiece with the toothing is produced with a core density of at least 7.4 g / cm ³ with a surface density that is at a maximum in at least one area of a tooth flank, the maximum surface density in the area extending at least 0.02 μm in depth .

Furthermore, a method for producing a toothing from compressed sintered material is provided, wherein a pre-compressed tooth preform is compressed to its final shape at least in one area by means of iteratively determined data, and a roughness in the area is improved by at least 400% compared to the preform, with a surface hardness of at least 130 HB. Preferably, a core density of the final shape is set which has at least a density of 7.3 g / cm ³ , and a surface hardness is impressed which has a convex shape from the surface to a center of the final shape.

The teeth made of pre-compressed material have a roughness in a first surface-compressed area that is at least 400% smaller than a roughness in a second area that is less or not surface-compressed at all. The roughness R _z is, for example, less than 1 μm in the first region. Another embodiment provides that there is a surface hardness of at least 700 HV [0.3] on the surface of the final shape, while at a depth of 0.4 mm from the surface there is at least a hardness of 500 HV [0.3] . Another embodiment has a surface hardness of at least 700 HV [0.3] on the surface of a tooth flank and in a tooth base, a hardness of at least 500 HV [0.3] at a depth of 0.6 mm from the surface in the tooth base and a hardness of at least 500 HV [0.3] at a depth of 0.8 mm from the surface on the tooth flank. The production of surface compaction makes it possible to set precise compaction as well as hardening according to the desired specifications.

A calculation method for the design of a preform of a toothing made of sintered material is now explained, wherein data are included in the calculation method, which are determined from a predetermined final shape of the toothing, depending on at least one condition of use of the final shape, one or more load parameters of the toothing are determined local allowance of the preform is calculated, which correlates with an expected compression of the preform on the surface, a load on the sintered material below the surface being included in the calculation.

Preferably, the calculation is additionally based on penetration of the tool into the workpiece to be produced during the calculation, the behavior of the sintered material during penetration and after penetration being taken into account in particular. For example, the calculation method provides that elastic deformation of the sintered material to be compressed is taken into account. The calculation method can also provide that elastic-plastic deformation of the sintered material to be compacted on the surface is taken into account. A depth of a maximum load below the surface is preferably included in the calculation method when the workpiece is used as a force-transmitting gear. The calculation method can further include shrinkage of the sintered material in the calculation during sintering. Empirically determined data can also be included in the calculation.

A calculation method for designing a tool for the surface compression of a preform of a toothing made of, in particular, compacted sintered material for creating a predetermined tooth geometry can include that determined data from the predetermined tooth geometry to be produced for the calculation of machine tool kinematics, taking into account associated machine tools of a workpiece, from which the workpiece to be produced Tool is formed, and at least one tool former, whose coupled system coordinates and their movement to one another, are iteratively included. So now there is the possibility, instead of repeated Attempts to finally find measurement results and adaptations of the workpiece former to a final form, to carry this out using an iterative calculation. This is much more time-saving and enables a wide range of influencing parameters to be taken into account. In particular, a simulation of the design is also made possible, so that, for example, an operation of the tool to be manufactured on a designed preform can be checked in the simulation.

The calculation method can include contact conditions between the workpiece to be manufactured and the tool form maker between a tip and a foot of the toothing. Preferably, a maximum tension on the surface is also included in the calculation in the region of a base of the toothing. Furthermore, there is the possibility that a maximum tension below the surface is included in the calculation in the area of a flank of the toothing. This method is particularly suitable for sintered materials, but also for steel workpieces or workpieces made of other materials.

Furthermore, a compression molding tool with a press geometry for producing a preform of a toothing made of sintered material is described, the press geometry having a course adapted to a surface compression of the toothing with at least one elevation, which at least in the area of the toothing of the preform produces a depression which is made with sintered material during the Surface compaction is refillable.

The elevation on an end face of the preform preferably causes a depression in the region of a head of a tooth of the toothing. For example, the height of the elevation or depth of the depression as well as further dimensions thereof can be determined by iterative calculation. Another embodiment provides, instead of a one-sided elevation, that a bilateral elevation is provided in order to bring about a depression on both end faces of the tooth. According to a further development, the elevation is arranged in a region of the geometry which causes a depression on a tooth tip of the preform, the elevation being such that the shaped depression at least partially causes the tooth tip to grow due to the processing of the preform into the final shape by surface compaction at least diminished. In this way, for example, a preform with at least one recess on an end face of a toothing to compensate for a material throw-up when a running surface of the toothing is compacted can be calculated and in particular manufactured. A preform with at least one recess on one can also be made in this way Calculate and, in particular, manufacture a tooth head of a toothing for at least reducing the tooth head from growing in height with a surface compaction of at least the flanks of the toothing. The calculation method for determining a geometry of a preform or a compression molding tool preferably provides that the geometry is determined on the basis of data of a final shape of the preform and at least one depression or elevation is calculated, which at least partially compensates for a material shift during surface compaction.

Furthermore, a method for the surface compression of a toothing is proposed, wherein a number of a repetitive compression movement of a molding tool for surface compression of a surface on the preform is calculated iteratively. Rollover is preferably calculated iteratively until a predetermined surface density is reached. A further development provides that a feed of the molding tool is calculated iteratively. According to one embodiment, the preform is rolled over less than 20 times in order to achieve the predetermined geometry of a final shape of the surface compaction. Rolling is preferably carried out less than 10 times. In particular, the preform is rolled over less than 6 times until a predetermined geometry of a final shape of the surface compaction is achieved. It must be taken into account here that the surface compaction does not end when it is reached. Rather, the tool is then moved over the surface several times, in particular less than 25 times, preferably less than 15 times. This ensures an accuracy of the surface shape.

Furthermore, a method is proposed in which a reversing rolling is carried out on a toothing made of sintered material in order to compress the preform to the final shape of a surface compaction. Before the direction is reversed, the preform is preferably relieved briefly by the molding tool. It has been found that by reversing, that is, by reversing the movement, a uniform compression can be created. In addition, manufacturing problems were further minimized by reducing the pressure of the tool on the workpiece before the movement reversal started. The tool can remain in contact with the workpiece. But it can also detach itself from the surface for a short time.

Furthermore, a surface compaction of a workpiece with at least one toothing made of sintered material is proposed, with a first surface of the workpiece with another method is compacted than a second surface of the workpiece. A first toothing of the workpiece preferably has a different compression than a second toothing of the workpiece. A further development provides that an internal toothing of the workpiece undergoes a different surface compression than an external toothing of the workpiece. There is also the possibility that an external toothing is surface-compressed by means of a rolling method, while a second surface is a bore which is surface-compressed by another method. After a surface compaction, a hole in the workpiece is preferably given a hardened surface and is subsequently brought to a final shape. This allows the bore to be used for a shaft or an axis. An improvement in the accuracy can be achieved by surface densification after hardening of the toothing.

A shaft with at least a first and with a second toothing can be designed such that the first toothing is rolled out of sintered material and is surface-compressed. Features regarding the shaft and the toothing are given below. In this case, the further disclosure relating to the toothing, the materials, the manufacturing steps, etc. can be used in particular for further configurations.

According to one embodiment, the shaft has a second toothing, which is produced by a different method than the first toothing. This enables a multitude of combinations, which provide different material solutions for each stress situation. According to a further embodiment, the second toothing forms a workpiece with the first toothing. For example, both teeth can be produced together in one press. The first and the second toothing are preferably calculated iteratively and produced accordingly. According to one embodiment, production can take place in succession, but according to another embodiment it can also take place simultaneously. In particular, this also applies to further processing steps such as surface compaction.

A further development provides that the second toothing has a hardened surface without surface compaction. For some load cases, the density achieved by sintering or the inherent strength of the material used is sufficient. This applies, for example, to pump applications.

Furthermore, it has proven to be advantageous if at least the first toothing has different flank slopes at the same height of the tooth at least on one tooth. This is advantageous in applications in which a main direction of rotation and in particular only one direction of rotation of the shaft is specified. The different flank slopes can thus be designed to reduce wear and reduce noise.

Another embodiment provides that the second toothing is forged. It can also be surface-compacted. This toothing can take up, for example, a greater power transmission than the first toothing.

The second toothing is preferably made of a different material than the first toothing. For example, the second toothing is made of steel. However, the second toothing can also consist of a different sintered material than the first toothing. In addition, the shaft can also be made of sintered material. For example, it can have the same material as the first toothing. The shaft can also be formed at least together with the first toothing, i.e. be pressed from powder material, preferably in a common mold.

An exemplary method for producing the shaft described above can also provide that at least the first toothing is surface-compressed and a bore for receiving the shaft is surface-compressed, hardened and then honed before the shaft and the first toothing are connected to one another. For this purpose, an iterative calculation of a preform of the first toothing is preferably carried out starting from a final shape of the shaft with the first toothing.

Preferred applications for such a shaft arise in automotive engineering as well as in gear construction and in household appliances.

Furthermore, a method for producing a surface compaction on a toothing is proposed, wherein at least two preforms receive surface compaction in one device at the same time.

According to one embodiment, the preforms are arranged on shafts arranged in parallel and at the same time come into engagement with at least one tool for surface compaction.

According to a second embodiment, at least two preforms are arranged on a common shaft and are brought together into engagement with at least one tool for surface compaction.

With a device for producing a surface compaction on a toothing, it can be achieved that at least two preforms for surface compaction are durable in the device and can be machined at the same time.

For example, it is provided that a movement of at least one shaft is provided, in which both preforms come into engagement with a tool for surface compaction. A further development provides that at least three shafts for at least two preforms and at least one tool are arranged parallel to one another and form a triangle, wherein at least one of the shafts can be moved towards the other two shafts. A further embodiment provides that at least two preforms can be attached to a common shaft, the tool having a greater length than an added length of at least both preforms. The preforms can preferably lie against one another with their end faces. Another embodiment provides that a distance is arranged between the preforms, the tool protruding along the shaft over both outer end faces of the preforms.

A component with a surface-compressed toothing made of sintered material can, viewed over a cross section, have a gradient with respect to the sintered materials used.

The component preferably has a gradient that has a step function. The sintered materials are provided with a transition limit at least in this area. According to one embodiment, this transition boundary is present along the entire area between the first and second sintered material. Another embodiment provides that there is no fixed boundary in one area but a gradual transition. In particular, it can be provided that the component has different sintered materials that extend into one another without having a pronounced mixing zone with increasing or decreasing gradient.

According to a first variant of the component, the sintered material of the toothing can have a lower core density than the sintered material of an adjoining the toothing Area of the component. A second variant of the component provides that the sintered material of the toothing has a higher core density than the sintered material of an area of the component adjoining the toothing.

Another variant has a component that has a first toothing with a first sintered material and a second toothing with a second sintered material.

A toothing preferably has different flank angles on a tooth at the same height.

For example, a first sintered material can be arranged in an outer region of the component and form the toothing, and a second sintered material is arranged in an inner region of the component and forms a bore.

Furthermore, a method for producing a surface-compressed toothing on a component is proposed, wherein a first sintered material is let into a mold before a second sintered material is added, then compression and sintering is carried out and only one of the two sintered materials is compressed by means of surface compression of the toothing. while the other sintered material does not change.

A further development provides that a second surface compaction is carried out, which only affects the sinter material that has not yet been surface-compacted. It is preferably provided that the first sintered material forms at least one surface of the tooth flanks and the second material forms a relining of the toothing.

Another proposed method for producing a surface-compressed toothing on a component provides for a first sintered material to be let into a mold before a second sintered material is added, then for pressing and sintering and for compressing the first and the second sintered material by means of surface compression of the toothing .

For the implementation of the method, it has proven to be advantageous that a movement sequence for surface compaction is iteratively determined taking into account a material behavior of at least one of the two sintered materials.

A development for both methods provides that a relative rotation acts between the mold, in particular a press mold, and a sintered material to be filled in, so that the sintered material collects in an outer region of the mold as a function of a speed of the relative rotation.

In addition, it can also be provided that the first and at least the second sintered material are added to the mold at least over a period of time.

Furthermore, the US 5,903,815 referred. Various sintered materials, conditions for sintered materials, shapes, principles relating to the processing of two or more sintered materials, applications and process steps are derived from this. In this regard, reference is made within the scope of the disclosure to the content of this publication, which belongs to the disclosure content of this invention.

It is further proposed that, in particular in the case of a forged gear, sprocket or ring gear, in addition to the surface compression step of the toothing, the production method is also provided for grinding or honing the compressed tooth flanks and or tooth feet. The forging preferably achieves a density of at least 7.6 g / cm ³ as the core density. Surface compaction can therefore bring about full compaction and / or precision in the shape of the toothing. A further development provides that for a material-removing processing step after the surface compaction, an allowance for this step is in a range of 4 μm to 8 μm material above the final dimension. If, instead of forging, pressing, sintering and hardening, in particular case hardening, is carried out, for honing it is preferably 30 μm to 50 μm and for grinding 50 μm to 0.3 mm, preferably 0.1 mm to 0.2 mm, according to the allowance Surface compaction provided. The iterative calculation makes it possible to determine the areas and dimensions in advance and to be able to implement them later in the process. For a hole in the gear, sprocket or ring gear, a surface compaction is preferably also provided, followed by hardening and then preferably honing. The bore can also have an allowance between 30 µm and 50 µm after the surface compaction.

Another advantage has arisen when lubrication occurs during surface compaction. In addition to the use of emulsions, oils can also be used for lubrication. This is preferred for hot rolling, for example at temperatures of over 220 ° C. In addition, it is proposed to carry out the hot rolling at a temperature between 500 ° C. and 600 ° C., oil cooling preferably being used to lubricate on the one hand and to cool the tool on the other hand.

The invention is explained in detail below by way of example with reference to the drawing. However, these illustrated embodiments are not to be interpreted as limiting the scope and details of the invention. Rather, the features emerging from the figures are not limited to the individual configurations. Rather, these features can be combined with other features specified in the drawing and / or in the description, including the description of the figures, to form further developments, which are not shown in any more detail.

Fig. 1

eine Wälzanordnung,

Fig. 2

einen ersten Zahn,

Fig. 3

einen zweiten Zahn,

Fig. 4

einen dritten Zahn,

Fig. 5 bis 7

verschiedene Aufmaßverläufe verschiedener Verzahnungselemente,

Fig. 8

ein erstes Verfahrensschema,

Fig. 9

ein zweites Verfahrensschema,

Fig. 10

einen Aufmaßverlauf eines Verzahnungselementes eines Wälzwerkzeuges,

Fig. 11

eine schematische Ansicht einer berechneten Vertiefung an einer Stirnseite,

Fig. 12

eine schematische Ansicht berechneter Extremfälle von Werkzeugen,

Fig. 13

eine schematische Ansicht eines Vorgehens bei der iterativen Berechnung und Verknüpfungen bei einer Simulation,

Fig. 14,

eine Ansicht von Dichteverläufen in Abhängigkeit von verschiedenen Ausgangsdichten der verwendeten Vorformen,

Fig. 15

einen Überblick über die ermittelten Fehler, die bei unterschiedlichen Oberflächenverdichtungsschritten auftreten und das Materialverhalten mitcharakterisieren,

Fig. 16

einen Härteverlauf in HV auf einer Flanke einer Verzahnung bei verschiedenen Oberflächenverd ichtungsschritten,

Fig. 17

einen Härteverlauf in HV in einem Fußbereich einer Verzahnung bei verschiednen Oberflächenverdichtungsschritten,

Fig. 18

eine schematische Ansicht von verschiedenen berechneten Aufmassverläufen für verschiedene Dichten,

Fig. 19

eine schematische Darstellung von Parametern, die in die iterative Berechnung eingehen können.

Show it:

Fig. 1

a rolling arrangement,

Fig. 2

a first tooth,

Fig. 3

a second tooth,

Fig. 4

a third tooth,

5 to 7

different dimensions of different gearing elements,

Fig. 8

a first procedural scheme,

Fig. 9

a second process scheme,

Fig. 10

an oversize curve of a gear element of a rolling tool,

Fig. 11

1 shows a schematic view of a calculated depression on one end face,

Fig. 12

a schematic view of calculated extreme cases of tools,

Fig. 13

1 shows a schematic view of a procedure in the iterative calculation and links in a simulation,

Fig. 14

a view of density curves depending on different initial densities of the preforms used,

Fig. 15

an overview of the determined errors that occur with different surface compaction steps and characterize the material behavior,

Fig. 16

a hardness curve in HV on a flank of a toothing with different surface compaction steps,

Fig. 17

a hardness curve in HV in the base area of a toothing in various surface compaction steps,

Fig. 18

1 shows a schematic view of different calculated measurement curves for different densities,

Fig. 19

a schematic representation of parameters that can be included in the iterative calculation.

Fig. 1 shows an exemplary rolling arrangement in a schematic view. A first rolling tool 101 with a first toothing 102 is rotatably mounted about a first axis 103 in a direction of rotation 104. The first toothing 102 is in engagement with a second toothing 105 of a preform 106. The preform 106 is rotatably mounted about a second axis 107. A second direction of rotation 108 results accordingly. Furthermore, the second toothing 105 is in engagement with a third toothing 109 of a second rolling tool 110. This second rolling tool 110 is rotatably mounted about a third axis 111 in a third direction of rotation 112. For example, the first axis 103 or the second axis 107 can be fixed axes, while the other two axes can execute an infeed movement. For example, the third axis 111 can be displaced in a displacement direction 113 along a connecting line 114 of the first 103, the second 107 and the third axis 111. For example, a dimension rolling process can be carried out. Here, tooth flanks in particular are only slightly compressed and in particular the tooth bases are not compressed. This results in surface compaction in a desired area. In the case of surface compaction, on the other hand, the tooth base can also be surface-compacted only or additionally. For example, a progressive shift takes place in the direction of the shift direction 113 during a rolling process. In particular, a region of the tooth feet of the preform 106 is also compacted by means of the first and second rolling tools 101, 110. To adjust the first and / or the second rolling tool 110 and to impress a pressure necessary for a rolling process, an adjusting device, not shown, is preferably provided with a gear. Very high pressures can also be applied in particular.

Fig. 2 shows a first tooth 201 of an associated toothing element, not shown. This gear element is a gear. A geometry of the toothing element or of the first tooth 201 is characterized by a first root circle 202, a first root useful circle 203, a first pitch circle 204 and a first tip circle 205. On a first flank 206, the first tooth 201 has a first oversize curve 207 before a rolling process. After an ended Rolling results in a first gauge block course 208, correspondingly resulting in a first compacted edge layer 209. This is shown schematically by a first compression boundary line 210. This line delimits the area of the first tooth 201 within which the full density is reached. The full density is preferably based on a density of a comparable powder-forged tooth.

Fig. 3 shows a second tooth 301 of a toothing element, not shown. This gear element is also a gear. The second tooth 301 and the gearwheel are characterized by a second tip circle 302, a second pitch circle 303, a second root useful circle 304 and a second root circle 305. A second oversize profile 308 and a third oversize profile 309 are provided to achieve an identical compression profile on a second flank 306 and a third flank 307. After a rolling process, a second gauge block curve 310 results on the second flank 306 and a third gauge block curve 311 on the third flank 307. Furthermore, a second compression limit line 312 and a third compression limit line 313 result. Due to the different forces on the second due to the rolling movement in one direction of rotation Flank 306 and third flank 307, the second oversize profile 308 and the third oversize profile 309 are configured differently. The different effects of forces on the tooth flanks 306, 307 during a rolling process are illustrated by the sliding speed directions shown. A first 314 and a second sliding speed direction 315 result on the second flank 306. Starting from the second pitch circle 303, these are directed in the direction of the second tip circle 302 and in the direction of the second root circle 305. On the third flank 307, however, results in a third sliding speed direction 316 and a fourth sliding speed direction 317, which are directed towards each other.

Fig. 4 shows a third tooth 401 of a toothing element, not shown. This gear element is also a gear. Gearwheel and third tooth 401 are in turn characterized by a third tip circle 402, a tip usage circle 403, a third pitch circle 404, a third root usage circle 405 and a third root circle 406. The third tooth 401 shown is a toothing with a head relief, preferably in the form of a rounded head. However, other geometries are also possible in this area. A tooth profile is withdrawn in a tooth tip region 401.1 between the third tip circle 402 and the tip usable circle 403. As a result, the tooth does not engage with an involute counter-toothing in this area. In this case there is an active one Tooth area only in the area between the head circle 403 and the foot circle 405 or between the head circle 403 and the third circle 406. A fourth measurement curve 407 results after a rolling process in a fourth compression limit line 408. Furthermore, a fourth gauge block curve 410 is formed on the fourth flank 409 achieved.

Fig. 5 shows an oversize curve between two adjacent teeth of a toothing element, not shown. This gear element is in turn a gear wheel. Gear and teeth are characterized by a fourth root circle 502, a fourth useful circle 503 of the preform, a fifth useful circle 504 of the preform after a grinding process, a fourth circle 505 after a milling process and a fifth circle 506 after a finishing process. After a rolling process, a fifth gauge block curve 507 results. A lateral dimension in millimeters is plotted on the abscissa axis. On the ordinate axis, the corresponding lateral dimension, which is oriented perpendicular thereto, is also plotted in millimeters. The gearing runs completely in the drawing plane.

Fig. 6 shows a compilation of further measurement courses. On the axis of the abscissa, the nominal floor length is shown along a flank line of a gear element. This curve line relates to a course from a tooth head of a first tooth to a tooth head of an adjacent tooth. The absolute arc length of the corresponding flank line is shown in millimeters on the upper axis of the abscissa. The left ordinate axis indicates an oversize in millimeters. The right ordinate axis describes the corresponding radius of the associated toothing. A sixth oversize curve 601, a seventh oversize curve 602 and an eighth oversize curve 603 are shown. Furthermore, an associated radius 604 of the corresponding toothing is shown. The sixth oversize curve 601 and the eighth oversize curve 603 are designed symmetrically to a tooth base symmetry line 605. In contrast, the seventh measurement curve 607 is designed asymmetrically. In the vicinity of the tooth symmetry base line 605, that is to say in the area of the tooth base, the measurements each have a local minimum. This promotes a reduction in the risk of stress cracking.

Fig. 7 shows another measurement course. A ninth measurement curve is shown, which runs asymmetrically from a left tooth head 702 to a right tooth head 703. As already in Fig. 6 An oversize in the area of a tooth base 704 is also shown here less than in the area of the fifth 705 and the sixth flank 706. This serves in particular to avoid stress cracks.

Fig. 8 shows a first process scheme. Starting from a target 801, which includes the geometry, a torque of a gear to be transmitted and a pressure distribution, a geometry of a rolling tool is generated with a first geometry generation module 802. In addition, a geometry of a preform is generated in a second geometry generation module 803 both on the basis of the target 801 and on the basis of the geometry of the rolling tool. A rolling process is simulated in a first simulation module 804. Both a kinematics of the rolling process and the compression process that is caused during the rolling process are simulated. In particular, a redistribution of material, such as that in Fig. 3 is outlined. The plastic deformation is simulated here, for example, using a finite element method. This can be coupled with a CAD program. A second simulation module 805 can optionally be taken into account for simulating a bracing. This module includes both the target 801 and the geometry of the preform. On the other hand, the second simulation module 805 also enables the determined geometry of the preform to be corrected. In particular, the first geometry generation module 802, the second geometry generation module 803, the first simulation module 804 and optionally the second simulation module 805 can be repeatedly executed in an optimization loop.

Fig. 9 shows a second process scheme. In a first step 901, a ninth measurement curve 902 of a tooth profile 903 is generated. A second tooth profile 905 of a third rolling tool 906 is then generated in a second step 904. Subsequently, a rolling process is simulated in a third step 907. The rolling process of the first tooth profile 903 on the second tooth profile of the rolling tool 905 and the resulting compression are simulated. The first, second and third steps 901, 904, 907 are then optionally repeated in a variation 908.

Fig. 10 shows an oversize curve of a gear element of a rolling tool. A tenth dimension curve 1001 of a fifth tooth 1002 of a rolling tool, not shown, is shown. A different allowance is provided on a seventh flank 1003 and an eighth flank 1004 of the fifth tooth 1002. On the seventh Flank 1003 a material addition is provided, which is indicated by a first arrow 1005. In contrast, a tooth relief is provided on the eighth flank 1004, which is indicated by the second arrow 1006. In this example, the measurement is based on a regular profile of an involute toothing. The asymmetrical configurations of the two tooth flanks 1003, 1004 take into account in particular an asymmetrical material load on a toothing element to be compressed therewith. With respect to the final shape of the workpiece, a symmetrical profile of both flanks of a tooth can be achieved by means of this rolling tool, for which compensations in the range of preferably less than 0.1 μm are carried out.

Fig. 11 shows a schematic view of a calculated depression on an end face of a toothing. The depression serves to at least minimize, if not even compensate, for a growth of the displacement of sintered material achieved by the surface compaction and the associated growth of the tooth in height and / or width. The shape of the recess depends on the oversize and the dimensions of the tooth. The shape can be iteratively optimized using the calculation method. A simulation enables the actual behavior of the preform to be estimated later.

Fig. 12 shows a schematic view of calculated extreme cases of tools for surface compaction, which can be calculated. The starting point of the calculation is the left end geometry of the toothing. The tool shapes shown in the middle and right of it can be determined iteratively by taking into account rolling conditions, measurement parameters and other influencing factors.

Fig. 13 is a schematic view of a procedure in the iterative calculation and links in a simulation. The machine kinematics can be modeled based on the specified end data of the workpiece and its gearing. Here, for example, the mutually assigned machine axes are assumed. The kinematics and functional links can then be used to optimize the tool to be designed using the existing degrees of freedom. This is again on Fig. 12 referred. The examples shown there have corresponding disadvantages, for example, the foot region is too weak in the middle display or the head design is too pointed in the right display. An iteration towards one for the respective requirement profile can then take place via additional influencing parameters such as, for example, strength considerations and / or stress profiles in the material suitable contour of the tool. For the tool for producing the preform, for example, the end geometry determined with the calculated oversizes is taken as the starting point.

Fig. 14 shows a view of density profiles as a function of different initial densities of the preforms used. If the density of the preform is changed in its core as well as in the course towards the outside, there are influences regarding the course of the surface compression. This goes from the right picture of the Fig. 14 forth. By changing the respective preform, the course of density after surface compaction can also be strongly influenced. Therefore, the initial core density as well as the shape of the preform are important parameters in the iteration and calculation.

Fig. 15 gives an example of an overview of the errors that occur during different surface compaction steps and that characterize the material behavior. The error is specified in error classes according to DIN 3972 or DIN 3970. An important point in determining a suitable surface compaction by rolling is the profile change of the rolling tool. By using the above calculation method for the preform and the rolling tool, it is possible to modify the rolling tool based on the results obtained. This is in Fig. 15 shown on a preform with a core density of 7.3 g / cm ³ , which was in engagement with an unmodified set of rolling tools and was surface compacted. The geometry of the gear wheel changes depending on a feed movement of the rolling tool. The goal is to achieve the desired final contour as specified. From the illustrations of the Fig. 15 different states for different feed movements can be found. The profile angle error is shown as an example on the left, the complete profile shape error in the middle and the shape error on the right. These were measured on the gear manufactured in each case. For example, a tooth thickness reduction of 0.27 mm leads to a profile angle deviation corresponding to class 7 according to DIN. In order to achieve a necessary final form of tooth thickness reduction, a feed of 0.4 mm is necessary. However, this leads to an increase in the respective errors. This means that the finished contour comes to lie in the other values outside the necessary quality classes. It is therefore necessary to change the geometry of the tool. Taking into account the found values as input values, a new tool can then be determined, the tests carried out again and in this way iteratively an optimized geometry for determine the tool. The calculation enables a final contour for the tool to be determined with, for example, two or only one iteration.

Fig. 16 shows a hardness curve in HV on a flank of a toothing plotted over the distance from the surface on the x-axis in [mm]. With different surface compaction steps, the profile profile of the hardness can be influenced by suitable dimensioning as well as feed movement. For example, the course can be at least partially convex or concave. As indicated, the preform labeled AVA7-1 had a larger oversize than the preform labeled AVA4-2. Both have an opposite course of hardness: while in the first part until 550 HVAVA7-1 has a rather convex shape, AVA4-2 has a more concave course. After falling below 550HV, this changes.

Fig. 17 a hardness curve in HV in a foot area of a toothing with different surface compaction steps. Due to the smaller oversize there compared to the flank oversize and due to the geometry, the hardness profile is different. The hardness drops more steeply at the beginning, but then almost changes into a straight course with only a slight incline.

Fig. 18 shows a schematic view of different calculated oversize curves for different densities based on a final tooth thickness. The diameter is plotted on the y-axis. The oversize is indicated on the x-axis. D_a or d_a specifies the tip usable circle diameter or the tip circle diameter, 0 is a specification of an oversize, for example by a value on the pitch circle, d_b is the base circle diameter. A indicates the range of preferred values for the pitch circle range. B represents a critical area, since material failure during rolling can already occur there.

Fig. 19 shows a schematic representation of parameters that can be included in the iterative calculation. In particular, these can be places of maximum stress. As shown in the photo on the left, pitting damage can occur on the flank. A reference stress curve is therefore preferably used, in which the following applies: a maximum stress occurs below the surface, in particular in the region of a negative slip, and therefore preferably below the specified pitch circle diameter d_w1. The right photo shows a tooth break due to excessive bending load. From that follows for the calculation model that a location of the maximum tooth foot stress is determined and taken into account. This can be determined, for example, using the 30 ° tangent according to DIN or using the Lewis parabola according to AGMA. For the comparison voltage, it is preferably assumed that a maximum voltage occurs on the surface.

Fig. 20 shows a schematic view of a further possibility, for example, how at least two preforms can be compressed simultaneously. In addition to the movement of the tool, according to one embodiment, the preforms can also be moved in the direction of the tool. There is also the possibility that two or more preforms are arranged on a preform axis.

The invention can be used, for example, in camshaft gears, in planetary gears, in sun gears, in drive gears, in differential gears, in gear gears, in clutch gears, in pump gears, in straight-toothed gears, in helical gears, in electric motors, in internal combustion engines, in actuators, in variable speed drives or internal gears, for external or internal helical gear units with straight or helical gears, for bevel gear units with straight, helical or curved teeth, for helical gear units or worm gear units as well as for high-helix shaft and high-helix hub connections.

Claims (12)

1. Method for manufacturing a toothing from a sintering material, wherein at least a negative oversize, which is determined by means of iterative calculation, is assigned to a preform (106), the negative oversize is, at least in part, filled by displacement of the sintering material during surface densification of the toothing (105); wherein the negative oversize is arranged at least on a flank of a tooth of the toothing (105).
2. Method according to claim 1, characterized in that an oversize material adjacent the negative oversize is displaced into the negative oversize.
3. Method according to claim 1 or 2, characterized in that the preform (106) is surface-densified to yield the final form, wherein optionally a hardening and/or a surface finishing machining is conducted.
4. Method according to one of the preceding claims, wherein the negative oversize extends asymmetrically along the flank.
5. Method according to one of the preceding claims, wherein a negative oversize is arranged on each flank of at least one tooth.
6. Method according to one of the preceding claims, wherein a tooth has on the same level a first negative oversize on a first flank and a second negative oversize on a second flank, wherein the first and the second flank extend asymmetrically in relation to each other.
7. Method according to one of the preceding claims, wherein the negative oversize is arranged between a tip area of a tooth and an oversize on the flank of the tooth.
8. Method according to one of the preceding claims, wherein the negative oversize is additionally arranged in a corner area of the tooth root.
9. Method according to one of the preceding claims, wherein the toothing at least on one tooth has respectively different flank pitches on the same level of the tooth.
10. Method according to one of the preceding claims, wherein the toothing (105) is an internal toothing.
11. Method according to one of the preceding claims, wherein the preform (106) is for a surface-densified gear.
12. Computer program product with program code means, which are stored on a computer-readable medium, for carrying out the method according to at least one of the claims 1 to 11 when the program is run on a computer.

Images