DE102012018229A1 - Making cam for shaft e.g. drive in internal combustion engine of motor vehicle by forming cam blank of hardenable steel material by punching and/or cutting process, subjecting blank to heat treatment, and machining surface portion of blank - Google Patents

Abstract

The process comprises forming a cam blank of a hardenable steel material by punching and/or cutting process (302), subjecting the cam blank to a heat treatment, machining (312) a surface portion of the blank, partially hardening (310) the blank by an inductive surface hardening, annealing the blank by inductive rapid annealing, and finishing the cam blank by a vapor deposition process and/or a physical vapor deposition method and/or phosphating a functional layer. A set of cam is formed on a cam shaft main body without further machining processing steps on the cam. The process comprises forming a cam blank of a hardenable steel material by punching and/or cutting process (302), subjecting the cam blank to a heat treatment, machining (312) a surface portion of the blank, partially hardening (310) the blank by an inductive surface hardening, annealing the blank by inductive rapid annealing, and finishing the cam blank by a vapor deposition process and/or a physical vapor deposition method and/or phosphating a functional layer. A set of cam is formed on a cam shaft main body without further machining processing steps on the cam, and is formed by internal high-pressure forming and/or thermal and/or mechanical joining and/or bonding cam blanks with a shaft.

Description

The invention relates to a method for producing a cam made of a hardenable steel material for use for a built camshaft in an internal combustion engine of a motor vehicle according to the preamble of patent claim 1.

Internal combustion engines for motor vehicles often use so-called built-up camshafts. Such a built camshaft consists of a hollow or solid carrier shaft to which several attachments, such as cams, thrust washer, drive wheel, pulse wheels and the like., Are joined.

Built camshafts have the advantage that the materials of the individual components can be very precisely adapted to the functional requirements of these components, so that compared to a conventional one-piece camshaft both weight and material and / or manufacturing costs can be saved. Furthermore, the design of the individual components leaves more room for maneuver for a cost-optimized design of the production process chain and its individual sections.

The production of individual cams is usually carried out in a three-stage process, in which initially a cam blank is forged or thermoformed from a suitable steel material, then machined and finally annealed and / or cured in a heat treatment. Such methods are for example from DE 19 716 554 C1 , of the DE 100 48 234 A1 , of the DE 101 13 952 A1 and the DE 10 2007 023 087 A1 known.

To cope with the high loads during operation of the camshaft, these cams are often made of the bearing material 100Cr6 and then hardened and tempered. The choice of this material is, however, associated with high costs, since the bearing steel 100Cr6 must be treated to improve the structure and the machinability usually with special care. For example, additional heat treatment (eg GKZ annealing) and, in some cases, high expenses in process management are necessary in order to obtain defect-free parts.

From the DE 10 2007 023 087 A1 For the production of cams for a built camshaft is known that the choice of a material with a carbon content of 0.3 to 0.8% with high load capacity of the cam more cost effective and quality robust cam production compared to the representation of 100Cr6 cams is possible.

For the sake of weight reduction and thus the lightweight construction in automobiles, designers are increasingly seeking to provide lighter and thus narrower cams for camshafts. For very narrow cams (for example, narrower than about 10 mm) forming technical steps, such as hot extrusion for producing cam blanks for technical and / or economic reasons can no longer be used effectively.

It is therefore an object of the present invention to provide a method for producing a cam according to the preamble of claim 1, which provide a cost-effective and process-reliable production, in particular of narrow cams.

This object is achieved by a method having the features of patent claim 1.

In a method according to the invention is preferably selected as the starting material for the production of a cam sheet material from which a cam blank is machined by punching and / or cutting. Accompanying the punching or cutting process also deburring and / or minimal forming (calibrating) process steps are possible. The stamping or cutting process or the accompanying process steps mentioned can be cold, warm or warm. In the case of an increased process temperature, a controlled cooling of the cam blank for the defined setting of a suitable microstructure state can follow.

The cam material used is primarily a hardenable steel material having a carbon content of between 0.4% by weight and 1.1% by weight, preferably between 0.4 and 0.8% by weight, preferably a steel of the type C55E or C56E2 , if necessary, with respect to the DIN EN 10083 respectively. DIN EN ISO 683-17 modified chemical composition to achieve improved cuttability, machinability and / or hardenability. Furthermore, it is possible to use case-hardenable or carbonitrisable steels. Furthermore, the bearing steel 100Cr6 can be used.

Subsequent to the stamping or cutting process, the cam blank may be subjected to a cold or hot calibration process to achieve an even more accurate cam shape or contour. Depending on the achievable accuracy in the punching or cutting process, this calibration process may be necessary in order to achieve the lowest possible machining allowance on a cam track and thus to achieve the required in a later process step To minimize machining costs, and / or to minimize or avoid any machining operations such as milling / turning / grinding of faces or bore.

In order to reduce the subsequent grinding allowance on the cam track, as an alternative or in addition to a calibration process after stamping or cutting, the cam blank may also be subjected to targeted machining. In this way, even in the soft state of the cam, the allowance to be abraded later (i.e., after hardening, for example) is reduced to a minimum. This saves cycle time during subsequent contour grinding (ie, for example, during finishing of the camshaft) and thus machine capacity and ultimately investment costs. A machining pre-machining (eg milling) of the cam blanks after punching or cutting also has the advantage that thereby the variety of variants of the punching or cutting tools is reduced.

The machining can be done on the bore and / or on the track and / or on one or both side surfaces. The machining is preferably carried out in single clamping. The machining of the cam blanks can alternatively be done in a package clamping on a common mandrel. Several cam blanks are taken on a common mandrel and the outer contour removed circumferentially to a remaining Schleifaufmaß (about 0.4 mm) by cutting.

It may also be advantageous to deburr and / or clean the cam blanks before and / or after the machining operation. In particular, the cam blanks can be shot blasted or sandblasted.

In the state after punching or cutting, but before the raceways are hardened, the cam may be subjected to a heat treatment process, such as annealing, normalizing, or quenching, to accommodate the cam for later process steps and / or later operational requirements optimize.

Subsequent to the stamping or cutting process, the optionally calibrated and / or machined and / or heat-treated cam blanks are subjected to a heat treatment for the purpose of hardening the cam track. Preferably, the cam blanks are inductively edge layer or through hardened.

In inductive surface hardening, the cam blank is at least locally austenitized, quenched and then optionally tempered. The parameters of this hardening process are chosen such that the hardening depth of the cams in the ready-to-install state on the cam track is at least 0.3 mm. The joining tolerances and the grinding allowance must be taken into account, so that a correspondingly lower hardening of the cam blanks may be required during surface hardening. As an alternative to inductive surface hardening, it is also conceivable that hardening takes place on the cam blank at least locally or over the entire circumference.

Due to the residual stress distribution in the cam between the hard layer produced in the case of inductive surface hardening in the area of the cam track and the unchanged soft core results in the possibility of increased rolling resistance and wear resistance. Such an inherent stress characteristic of surface-hardened cams is significantly more advantageous in terms of operating stress than the through-hardened cams.

The starting of the cam blanks can advantageously be carried out by inductive short-term starting. It is also conceivable to carry out conventional furnace tempering (typically about 2 hours at about 160 ° C.) or tempering from the residual heat of the previous process step. Optionally, the starting at z. B. C55E and C56E2 cams completely eliminated.

Instead of the inductive surface hardening for curing the cam track, the cam blank can also be hardened or tempered by austenitizing in a hardening furnace under a defined atmosphere and subsequent quenching in a salt or oil bath. Furthermore, with a suitable choice of material, the cam blanks can be case hardened or carbonitrided and then tempered in the furnace.

For cost reasons, the heat treatment process for hardening the cam track preferably comprises only those process steps that are necessary to achieve the requirements imposed on the cam (hardness, permanently sustainable surface pressure, etc.).

After the heat treatment for the purpose of race hardening, the hardened cam blank can be machined. Since no further thermally induced distortions take place in the further process steps up to the joining of the cams to the shaft, in particular a cost-effective internal machining of the cam bore can take place with sufficient final contour. Thereby, an increase in accuracy of the single cam can be achieved, which has a higher accuracy of joining the camshaft blanks result and thus a reduction allows the grinding allowance, provided that the cams are finished only in the joined state.

Alternatively, after the heat treatment for the purpose of career hardening, the finishing of the cam, in particular of the raceway, can also be carried out prior to joining to the shaft main body. This represents a more favorable compared to the completion of the complete camshaft process variant, provided that the required geometry specifications can be met.

It is particularly advantageous if the cam should be coated in the final state. Therefore, prior to joining the cam to the shaft body, the cam can be finished and coated. Such a functional layer is applied, for example, using a CVD and / or PVD method. In particular, a diamond-like functional layer may be present in this case.

If it is necessary for cleaning the cam surface, for setting defined roughness ratios and / or for the defined introduction of internal compressive stresses, the cam is shot blasted or sandblasted in the course of the process, primarily after hardening of the raceway area. If it is necessary for the production of fit ratios between the inner bore of the cam and the outer diameter of the carrier shaft, the cams are machined inside. If the cams are to be joined to the shaft by means of hydroforming, for example, it is advantageous to radiate the inner bores of the cams. If, on the other hand, the cams are to be fastened to the shaft by means of thermal joining, the inner bores should be treated with priority.

Finally, the cams are tested in a suitable test for geometry, material properties and freedom from cracks.

The narrow cam produced in this way is then joined to a camshaft on a hollow or solid shaft to represent. If the cam to be mounted on a hollow shaft, this joining step is preferably carried out using the hydroforming of the hollow shaft. Alternatively, however, the cam can also be fastened by thermal or mechanical joining methods and by gluing or by a combination of said methods on the shaft main body.

The cam may have the classic blank shape, be nearly annular or have more elevations. Furthermore, the method is suitable for the production of cams for z. B. high pressure pumps, so-called pump cam.

Overall, the inventive use of punching or cutting technology thus allows the provision of a narrow cam blank with a typical thickness of 3 mm to 10 mm, which cured at least in the raceway area and made of a hardenable steel material preferably having a carbon content of substantially 0.4 wt. -% to 0.8 wt .-% carbon. Such cams are technically and / or economically not representable with conventional forming processes such as forging. With the help of such narrow cams therefore particularly lightweight built camshafts can be displayed.

In the following the invention and its embodiments will be explained in more detail with reference to the drawing. Show it:

1 a perspective view of a built camshaft ( 1 a) and a cam ( 1 b);

2 a schematic representation of the process steps of a method for producing a forged cam of 100Cr6 according to the prior art;

3 a schematic representation of the process steps of a method for producing a forged cam of Cf53, C55E or C56E2 according to the prior art;

4 a schematic representation of the process steps of an embodiment of a method according to the invention for producing a cam by punching or cutting a blank.

1a shows a built camshaft 1 with cams 2 , using a joining method (eg hydroforming, thermal joining) along with other attachments (thrust washer, drive wheel, pulse wheels and the like.) On a shaft 3 are attached. 1b shows a detailed view of a cam 2 ,

Conventionally, the cams 2 produced from a thermoforming process; 2 shows a typical procedure 100 for the production of cams of rolling bearing steel according to the prior art:
Starting from a cam piece, a cam blank is first produced by hot forming, in particular by forging (step 102 ), which essentially already has the in 1b has shown shape. Subsequently, the cam is blasted for surface cleaning and descaled (step 104 ).

To improve the structure or to achieve better machinability, the cam blank is subsequently isothermally annealed (step 106 ). Subsequently, the cam blank is machined in the soft state (step 108 ). To increase wear resistance, the cam blank is then hardened and tempered (step 110 ). Should the cam 2 later by hydroforming (hydroforming) on the shaft 3 be joined, so will the cam 2 blasted in the area of the inner holes (step 112 ). Finally, a quality assurance of the cam 2 performed (step 114 ). For the production of the camshaft is the cam 2 finally with hydroforming (hydroforming) on the shaft 3 joined (step 116 ). Finally, a fine machining (grinding) of the camshaft 1 to give the cam the required shape (step 118 ).

3 shows an alternative, known process flow 200 for the production of cams, also using hot forming: From a bar stock in shelled or unpeeled state after heating the rod first a slug is cut from the produced by a hot forming step, in particular by forging or by hot extrusion at about 1100 ° C, a cam blank becomes (step 202 ), which essentially already has the in 1 b has shown shape. The cam blank is advantageously cooled directly after the hot forming in a targeted manner to a suitable structure as a basis for subsequent steps ie for a spin out and, if necessary, facing (step 206 ), a contour processing in the soft state (step 208 ) and inductive hardening (step 210 ).

The in the 2 and 3 Processes shown have the disadvantage that hereby cams smaller width (narrower than typically about 10 mm) technically and / or economically can no longer be meaningfully displayed.

In the context of an embodiment of the method according to the invention, the cam blank is produced by a stamping or cutting process. 4 shows an exemplary procedure for this purpose 300 ,

The cam blank is punched or cut, for example, from a sheet material of a hardenable steel material in the cold, semi-warm or warm state (step 302 ). The punching or cutting process can be a calibration and / or deburring and / or a cleaning process (step 304 ) connect. In a stamping or cutting process at a higher temperature, starting from the process temperature, a controlled cooling of the cam blank can take place for targeted microstructure adjustment.

During the course of the process chain for producing the cam blank, at least one heat treatment process such as, for example, annealing, normalization or tempering can take place in order to optimize the cam with regard to later process steps and / or later operational requirements. This heat treatment step ( 306 ) or the heat treatment steps can be carried out before and / or after punching or cutting, also between the above-mentioned optional process steps calibration and / or deburring and / or cleaning.

Depending on the accuracy achieved by the punching or cutting process with optionally subsequent process steps calibration and / or deburring and the accuracy required by subsequent processes, an optional machining process (step 308 ) connect. In this case, either the cam bore and / or the cam track and / or one or both side surfaces can be processed. These processing steps can be done on a single cam or in package voltage.

Subsequently, the raceway of the cam is at least partially cured and optionally tempered (step 310 ). Advantageously, the curing of the track by induction hardening, particularly preferably followed by inductive annealing. In induction hardening, both surface hardening and full hardening can be produced. As an alternative to induction hardening, curing can also be carried out by conventional oven curing with optionally subsequent tempering.

After the race has hardened, optional machining of the cam can take place (step 312 ). These processing steps may be required to prepare the cam for the subsequent joining process to the fundamental. By machining but can also be done in addition or only a finishing of the cam. These processing steps can be done on a single cam or in package voltage.

Following this, the cam can optionally be coated at least in sections (step 314 ). Such a functional layer for later motor operation can be applied using a CVD and / or PVD method. In particular, a diamond-like functional layer may be present on the hardened cam track. Additionally or alternatively, the cam bore, for example, for advantageous joining of the cam on the shaft 3 be coated. Such a coating may, for example, be a phosphating.

In step 316 will be joining the cam to the shaft 3 carried out. Joining takes place with the help of hydroforming or thermal joining or mechanical joining or gluing or a combination of said joining methods.

If not yet done in previous process steps, the camshaft on the cam tracks in step 318 finished.

In the course of the process shown 300 Quality assurance tests and measurements are carried out on the cam 2 in appropriate test severity.

• – Unter Beibehaltung der Leistungsfähigkeit der Nocken sind relativ schmale Nockenbreiten technisch und wirtschaftlich realisierbar.
• – Die Herstellbarkeit schmaler Nocken leistet einen Beitrag zum Leichtbau im Motorbau und somit auch zur Kraftstoff- und CO₂-Einsparung.
• – Bei Verwendung eines Ausgangsmaterials mit mittlerem Kohlenstoffgehalt, beispielsweise bei C55E bzw. C56E2 tritt bei der erfindungsgemäßen Prozesskette 300 im Vergleich zum Prozessablauf 100, der typischerweise beim Wälzlagerstahl 100Cr6 verwendet wird, ein Materialpreisvorteil auf. Ferner ist der C55E bzw. der C56E2 besser stanz- bzw. schneidbar als der weit verbreitete Nockenwerkstoff 100Cr6.
• – Nach der Nockenrohlingsherstellung durch Stanzen oder Schneiden sind in der Regel keine Entzunderungsschritte nötig.
• – Auf Grund der wegfallenden hohen Prozesstemperaturen bei der Nockenrohlingsherstellung durch Schmieden reduziert sich im Fall der Prozesskette die thermische Vorschädigung an der Nockenoberfläche, es kann daher ein geringeres Bearbeitungsaufmaß vorgehalten werden.
• – Der Einsatz eines hochgenauen Stanz- bzw. Schneidprozesses zur Herstellung von Nockenrohlingen ermöglicht grundsätzlich, dass keine weiteren Bearbeitungsschritte außer dem Fertigschleifen der Nockenlaufbahnen erforderlich sind.

Compared with the process flows 100 and 200 For the production of cam blanks by hot forming processes offers the process flow 300 for the production of cam blanks by punching or cutting the following advantages:

• - While maintaining the performance of the cam relatively narrow cam widths are technically and economically feasible.
• - The manufacturability of narrow cams makes a contribution to lightweight construction in engine construction and thus also to fuel and CO ₂ savings.
• - When using a starting material with an average carbon content, for example in C55E or C56E2 occurs in the process chain according to the invention 300 in comparison to the process flow 100 , which is typically used on the bearing steel 100Cr6, has a material price advantage. Furthermore, the C55E or the C56E2 is better punched or cuttable than the widely used cam material 100Cr6.
• - After the cam blank production by punching or cutting usually no Entzunderungsschritte are necessary.
• - Due to the elimination of high process temperatures in the production of cam blanks by forging reduced in the case of the process chain, the thermal pre-damage to the cam surface, it can therefore be maintained a lower machining allowance.
• - The use of a high-precision punching or cutting process for the production of cam blanks basically allows that no further processing steps are required except the finish grinding of the cam tracks.

Basically, for cost reasons of the in process chain 300 shown individual processes used only those that are required to produce the required product quality.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 19716554 C1 [0004]
• DE 10048234 A1 [0004]
• DE 10113952 A1 [0004]
• DE 102007023087 A1 [0004, 0006]

Cited non-patent literature

• DIN EN 10083 [0011]
• DIN EN ISO 683-17 [0011]

Claims (10)

Method for producing a cam ( 2 ) for a camshaft ( 1 ) in an internal combustion engine of a motor vehicle, in which a cam blank made of a hardenable steel material and at least subjected to a heat treatment, characterized in that the production of the cam blank comprises at least one punching and / or cutting process. A method according to claim 1, characterized in that as curable steel material, a steel having a carbon content between 0.4 wt .-% and 1.1 wt .-% carbon, preferably 0.4-0.8 wt .-%, in particular a Steel type C55E or C56E2 is used. Method according to one of claims 1 or 2, characterized in that the cam blank is processed after the punching and / or cutting process on at least one surface section. Method according to one of claims 1 to 3, characterized in that the cam blank is at least partially randschicht- or through hardened in a raceway area. A method according to claim 4, characterized in that the curing takes place in the raceway area by an inductive surface hardening. Method according to one of the preceding claims, characterized in that the cam blank is tempered after curing, particularly preferably by inductive rapid starting. Method according to one of the preceding claims, characterized in that the cam blank is finished after the at least partial hardening of the track and that after the joining of the cam ( 2 ) on the camshaft base body ( 3 ) no further machining operations on the cam ( 2 ) be performed. Method according to one of the preceding claims, characterized in that the cam ( 2 ) is finished after the at least partial hardening of the track and provided by a CVD method and / or a PVD method and / or a phosphating with a functional layer. Method for producing a built-up camshaft ( 1 ), in which at least one cam produced by a method according to one of claims 1 to 8 (US Pat. 2 ) by hydroforming and / or thermal and / or mechanical joining and / or gluing with a shaft ( 3 ) is added. Cams ( 2 ), obtainable by a process according to any one of claims 1 to 8.

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