EP2066468A2

EP2066468A2 - Method of compacting the surface of a sintered part

Info

Publication number: EP2066468A2
Application number: EP07800161A
Authority: EP
Inventors: Herbert Schmid; Karl Dickinger; Wolfgang Siessl
Original assignee: Miba Sinter Austria GmbH
Current assignee: Miba Sinter Austria GmbH
Priority date: 2006-09-04
Filing date: 2007-08-31
Publication date: 2009-06-10
Anticipated expiration: 2027-08-31
Also published as: US8474295B2; CN101557894A; AT504081B1; EP2066468B1; WO2008028207A9; US20110132057A1; WO2008028207A2; JP2010502834A; WO2008028207A3; AT504081A1; CN101557894B; EP2066468B2; CA2662392A1

Abstract

The invention describes a method of compacting the surface of a sintered part (2), in which a sintered part (2) is moved in a die tool (1) along an axis (3) in a pressing direction (20) through a number of die portions (7, 8, 9) from a first die portion (7) at a first die opening (6) to a last die portion (9), wherein a wall area (16) of each die portion (7, 8, 9) forms at least one pressing area (18), against which a contact area (17) that is formed by an outer area (12) of the sintered part (2) is pressed, and an inner contour (25) that lies in a cross section with respect to the axis (3) and is defined by the pressing area (13) corresponds at least approximately to an outer contour (26) that is defined by the contact area (17). During the movement of the sintered part (2), the compacting of the surface takes place from the first die opening (6) to the last die portion (9) through die portions (7, 8, 9) that steadily merge one into the other and through monotonously decreasing inside diameters (19) of the die portions (7, 8, 9), measured between interacting pressing areas (18).

Description

Method for surface compacting a sintered part

The invention relates to a method for surface densification of sintered parts with the features of claim 1, as well as a die tool with the features of claims 15 and a die with the features of claim 37 for carrying out the method.

Sintered parts, ie workpieces made of pressed and sintered metal powder have long been an alternative to cast or from the fully machined workpieces. However, due to the manufacturing process, each more or less pronounced porosity of the sintered parts has a negative impact on the flexural strength and the wear resistance of, for example, which restricts the use of powder-metallurgically produced gears in high-load gearboxes.

In order to reduce the adverse effects of the porosity of sintered parts, it is known to effect surface densification on sintered blanks by re-pressing. A method using a die tool is known from US 6,168,754 Bl. In this method, a sintered blank, that is pressed from powder metal and then sintered part is compacted on its outer surface by this is pressed by a multi-stage die tool. The die tool comprises a plurality of axially spaced die plates with die openings, which substantially correspond to the shape of the sintered blank, but whose inner diameter decreases gradually and is smaller than the outer diameter of the sintered blank. In this pushing from the largest to the smallest die opening the outer periphery of the sintered part is plastically and elastically deformed, whereby the surface is compacted and the sintered part receives its final dimension. The distances between the die plates allow the sintered part to expand by expanding a portion of the elastic deformations after each die plate. As a result of this sequence of die plates and intermediate spaces, the sintered part undergoes intermediate relief after each die plate, as a result of which a compressive residual stress remaining after deformation in the sintered part is built up stepwise.

These compressive residual stresses increase the bending strength in tensile stressed zones and at the same time improve the wear resistance of the surface thus compacted. adversely However, in the case of the method or die tool described in the US-B1, the die tool has a lower stability and wear resistance owing to the interspaces between the individual die plates, whereby the forming forces which can be borne by the die tool are clearly limited and the achievable surface compacting for some Applications is still insufficient.

The object of the invention is to provide a method for surface compacting a sintered part, which offers the possibility of a high compression of a sintered part surface while at the same time a simple tool design.

This object is achieved by a method for surface densification of sintered parts with the features of the independent claim 1 and by a die tool or a punch with the features of claim 15 and 37, respectively. Characterized in that the die sections continuously merge into each other and a measured between cooperating Pressflächen- measured inner diameter on the inner contour monotonically decreases from the first die section to the last die section, each die section is supported by the following and deformations in the movement of a sintered part in the pressing direction to the last die section of the die tool largely prevented. Due to this robust design of the die tool, the overall reduction of the inner diameters can be made stronger, which significantly improves the surface densification of the sintered part. A surprising effect of this design is that, even without the intermediate relief between successive die sections known from the prior art, the surfaces of the sintered parts have no negative effects of the high forming forces, e.g. Eating disorders, can be compacted.

The compaction of the surface does not have to take place on the entire outer circumference of a sintered part, but can be limited to subsections of the outer surface. For carrying out the method, it is merely necessary for the pressing surfaces acting on the contact surfaces on the sintered part to be arranged approximately opposite one another in order to be able to compensate for the radially acting forces. The term inner diameter in this application is not limited to the diameter of a cylinder, but is generally understood to mean the distance between facing press surfaces as measured between cooperating pressing surfaces. In a die tool in which the last die section ends inside the tool body, the sintered part must be removed from the die tool after reversing the movement through the first die opening, but the method can be advantageously supplemented by the second sintered part being opposite one of the first die opening Die opening is moved out of the die tool.

The relative movement between the sintered part and the die tool can advantageously be rectilinear or in a screwing motion. Sintered parts, whose contact surfaces are rotationally symmetrical with respect to the axis, can be pressed both rectilinearly and with a screwing motion or a combination thereof through the die tool. Sintered parts whose contact surfaces are formed by screw surfaces must be pressed in a screwing motion by the die tool. In the case of a rotationally symmetrical sintered part, in addition to the axially acting sliding friction forces on the pressing faces of the die sections, additional tangential stress components can be introduced into the surface of the sintered part by means of a rotating movement, which can favorably influence the compacting process.

For carrying out the method, it can also be advantageous if the movement is carried out by the sintered part and / or the die tool. In the simplest case, with a fixed die tool, the sintered part is moved from the first die section to the last die section, but it can be advantageous for structural reasons or for procedural reasons to let the movement be performed by the die tool or to drive both the sintered part and the die tool. In this case, the same drive concepts but also different drive concepts for the two components can be used, e.g. in that the sintered part or the die tool executes a smooth, slow movement, and the die tool or die performs an intermittent fast movement, resulting in a pulsating relative velocity, which may be advantageous when a relative movement stop is undesirable and the movement from one Matrizenabschnitt to the subsequent section with higher speed to be performed.

During the movement through the die tool, the sintered part can be pressed and pulled both in the axial direction, and the introduction of correspondingly high tensile forces should be avoided in the axial direction of small dimensions of the sintered part due to the risk of breakage and should remain limited to sintered parts with axially larger dimensions.

Optimum introduction of the required forces into the sintered part is achieved when the sintered part is placed between two pressure elements, e.g. two stamping associated with drive means, is largely pressurized over the entire surface axially. As a result, the movement through the die tool can also be carried out with a reversal of the direction without the risk of the sintered part being damaged by the occurrence of higher tensile stresses. For this purpose, the sintered part can be clamped between two pressure punches, the shape of which essentially corresponds to the matrix shape.

For carrying out the method, it may be favorable to change the direction of movement of the sintered part at least once before reaching the second die opening, for example to enable intermediate relief in a more sensitive sintered material before moving into or through the last die section.

An advantageous variant of the method can also be that the sintered part is removed from the mold after reaching the last die section through the first die opening, i. the direction of movement is reversed after reaching the last die section. The fact that the part removal is carried out on the die tool at the same position as the parts feed before the Verfahrensdurchfülirung, this variant may be advantageous for the part flow.

Since the last die section has an influence on the finished size of the sintered part achieved after the process, it is advantageous if the sintered part in the last die section is compressed to an inner diameter which reduces a nominal dimension of a sintered part by the value of the elastic deformation of the sintered part caused by the pressing forces Sintered parts corresponds to this inner diameter. Since the plastic deformation takes place essentially on the outer surface of the sintered part, the elastic part of the deformation can be estimated relatively well by calculation methods, which is why it is possible to form the last die section such that the sintered part after removal of the last Matrizenabschnitts essentially has its nominal size. The dimensional accuracy achieved thereby can subsequent processing steps for further approximation the finished measure to a nominal size, eg make a grinding process unnecessary.

In order to facilitate the introduction of the sintered part into the die tool, it is favorable if the sintered part is introduced into an insertion section arranged in front of the first die opening, which has an insertion diameter which is greater than a rough measurement of the sintered part on its outer surface. This insertion section may e.g. be formed by an additional insertion plate, which is arranged in the pressing direction before the first die portion, and has an opening which is larger by a small functional clearance, as the Rohabmessungen the sintered part on its outer surface. This results in reliable positioning and guidance of the sintered part before and during the pressing into the first die section.

It is also advantageous if the sintered part is moved after the last die section into a subsequent calibration section which has a calibration diameter which corresponds to a nominal diameter of the sintered part on its outer surface. In this case, the calibration section can connect directly to the last die section, or it can also be provided with a gap between the last die section and the dimensional calibration section, whereby an intermediate relief of the sintered part is possible before the calibration.

A possible embodiment of the method consists in that a sequence of sintered parts with or without pressure-resistant spacer elements each arranged between two sintered parts is moved by the die tool.

While in the simplest case, the method is carried out at about room temperature, it may be advantageous if the sintered part has a temperature in the process implementation, the temperature below the melting temperature, in particular in a range of 100 ° C or 200 ⁰ C below the melting temperature, lies. Due to the increased temperature compared to the room temperature in the process execution of the process of surface compaction and thereby occurring change of the structure can be facilitated, which on the one hand, the surface properties of the finished sintered part can be favorably influenced and the forces required for the process performance can be reduced. The application of the method is particularly advantageous if the sintered part is designed as a bearing bush, as a bearing shell, as a gear wheel, as a sprocket, as a toothed belt wheel or as a cam element. The surface densification and flexural strength achievable with the method proves to be particularly advantageous in these applications of a sintered part.

It may be advantageous for the use of the die tool if a second die opening opposite the first die opening adjoins the last die section, i. the sintered part can be moved through the entire die tool, in particular pressed.

An advantageous development of the die tool according to the invention is that the inner diameter within a die section is constant, i. that the die section does not taper. In the case of a rotationally symmetrical contact surface on the sintered part, the pressing surface of the die section acting on it is a circular-cylindrical surface with generatrix parallel to the axis. Since a circular cylindrical die portion is relatively easy to manufacture, a die tool for circular cylindrical sintered parts can be produced by simple means, when all die sections each have constant inner diameters.

For carrying out the method, however, it may also be advantageous if the inner diameter decreases linearly within a die section in the direction of the second die opening. This can e.g. be effected by a conical or pyramidal design of the pressing surfaces, wherein the taper is oriented in the direction of the second Matrizenöff- opening. Further possibilities for influencing the compression process are when the inner diameter decreases progressively or degressively within a die section in the direction of the second die opening.

For carrying out the method, it may also prove advantageous if an axial die section length is greater than an axial contact face length. This ensures that a sintered part or its contact surface is completely introduced into a die section before a leading edge of the sintered part or the contact surface already experiences the deformation by the subsequent die section. The for the movement of the Sintered parts required force is thus occasionally largely constant, whereby a phase-wise, constant movement speed relatively easy, for example via a pressure control of a Fluidzy Linders, which acts on the sintered part, can be achieved.

The axial die section length of the last die section may be less than 30% of the contact surface length of the sintered part. Such a relatively short executed Last Matrizenabschnitt causes a limited to a small proportion of the contact surface kneading effect, which can increase the effectiveness of surface compaction in addition. In this case, this Matrizenabschnitt be conical, whereby the kneading effect is enhanced. In particular, this is advantageous if the sintered part is removed again from the die tool through the first die opening.

Particularly in the case of long-length sintered parts, it is advantageous if the total axial length of all die sections is smaller in total than the axial contact surface length of the sintered part. As a result, the surface compaction takes place only on a small part of the contact surface and the influences of the axial sliding friction are thereby lower compared to a longer tool.

For the execution of the method, it has proved to be favorable to provide a total of between three and seven, in particular five, die sections each having a constant inner diameter. Since the increasing compaction of the surface layer also causes solidification, which, like a solid shell, offers increasing resistance to further deformations, the possible reduction in diameter is limited, the division into the mentioned numbers of die sections being advantageous, since the production costs for the die tool are increase the number of die sections.

A further advantageous embodiment of the die tool is when a sequence of successive die sections alternately has a constant inner diameter and a decreasing inner diameter. The die sections with a decreasing inner diameter can act as a kind of continuous transition between the die sections with a constant inner diameter, whereby pronounced steps between successive die sections can be avoided. It is also advantageous to form the transition from a die section to a subsequent die section by a chamfer or at least a rounding. A sharp-edged design of a stepped transition and a correspondingly higher wear on the die tool can be largely avoided.

In order to approximate an actual diameter of the sintered part achievable by the die tool to a target diameter, it is advantageous if the inner diameter in the last die section has a value which reduces a nominal dimension of the sintered part by the value of the elastic deformation of the sintered part due to the pressing forces this inner diameter corresponds. As already explained above, the elastic deformation of the sintered part can be estimated for this purpose with sufficiently good accuracy, whereby the sintered part after passing through the last die section has at least approximately its nominal dimension.

For the surface compaction of circular cylindrical sintered parts, such as e.g. Bushings, it is advantageous if the inner contour is rotationally symmetrical with respect to the axis. Thereby, the surface of a circular cylindrical sintered part can be compacted with a single process implementation over its entire circumference, while in only partially executed as a circular cylinder pressing surfaces a two or more times performing the pressing process with intermediate lying rotation of the sintered part would be required.

It is also advantageous if the inner contour is rotationally symmetrical with respect to the axis, whereby the die tool, in particular for the surface compression of sintered gears, Zahnπemenrädem or sprockets is applicable. However, the method is also applicable to irregularly shaped sintered parts, if the pressing surface of a

Matrizenabschnitts is formed as a general cylindrical surface. The application is therefore not limited to rotational or rotationally symmetrical sintered parts.

The pressing surface of a die portion can also be formed by a screw surface, whereby the surfaces of a helical gear can be compressed when the movement is performed by the die tool with a screwing movement. For compacting the surface of a straight-toothed spur gear or a spur gear segment, the pressing surfaces of the die sections are each formed at least in sections by internal straight toothing. The tooth flanks extend in the axial direction.

If the pressing surfaces of the die sections are each formed, at least in sections, by internal helical gearing, helical spur gears or spur gear segments can also be surface-compacted.

The die tool can be composed of several die parts both in the axial and in the radial direction, but an extremely robust design is achieved if the die tool is made in one piece.

The introduction of a sintered part into the die tool is substantially facilitated if, in the direction of the second die opening, before the first die section, an insertion section whose inner diameter is larger than a raw diameter of the sintered part is arranged. The insertion section corresponds to a die section, but with a clearance fit instead of a press fit to the sintered part.

To increase the dimensional accuracy can further be provided that in the pressing direction after the last die section followed by a Kalibrierabschnitt having a Kalibrierdurchmesser which is smaller than the nominal diameter of the sintered part. In this case, the calibrating section can connect directly to the last die section or a gap can be provided therebetween which effects an intermediate relief of the sintered part, which thereby at least partially degrades its elastic deformation by expansion before the actual calibration section.

The invention will be explained in more detail below with reference to the exemplary embodiments illustrated in the drawings.

Each shows in a simplified schematic representation:

1 shows a longitudinal section along the line II in Figure 2 through an inventive die tool with a sintered part to be machined. 2 shows a cross section through a further Ausfülirungsform a Matrizenwerkzeugs with a processed sintered part according to the lines II-II in Fig. 1.

3 shows a section of a longitudinal section of a further embodiment of a die tool;

4 shows a section from a longitudinal section of a further embodiment of the die tool;

5 shows a section of a longitudinal section of a further embodiment of the die tool;

Fig. 6 shows a detail of a longitudinal section of a further embodiment of the

Die tooling;

Fig. 7 is an axial plan view of another embodiment of the die tool;

Fig. 8 is a plan view of another embodiment of the die tool;

Fig. 9 is a plan view of another embodiment of the die tool;

10 is a plan view of two further Ausfülirungsformen the Matrizenwerkzeugs with a straight and angled inner teeth.

11 shows a longitudinal section through a further embodiment of the die tool;

12 shows a longitudinal section through a further embodiment of the die tool;

13 shows the implementation of the method with simultaneous pressing of two sintered parts by the die tool;

14 shows the method with passing through the sintered part by the die tool; Fig. 15 the Verfalirensdurchführung with both sides druckbeaufschlagbarem sintered part;

Fig. 16 shows another embodiment of a die tool with an additional

Import section and an additional calibration section.

By way of introduction, it should be noted that in the differently described embodiments, identical parts are provided with the same reference numerals or identical component names, wherein the disclosures contained in the entire description can be mutatis mutandis to identical parts with the same reference numerals and component names. Also, the location information chosen in the description, such as top, bottom, side, etc. related to the immediately described and illustrated figure and are to be transferred to the new situation mutatis mutandis when a change in position. Furthermore, individual features or combinations of features from the different exemplary embodiments shown and described can also represent independent, inventive or inventive solutions.

1 shows a longitudinal section through a die tool 1 according to the invention for surface compacting a sintered part 2 by moving it along an axis 3 through the die tool 1. This comprises a tool base 4 which has a first die opening 6 on a tool surface 5, along which the axis 3 multiple die sections 7, 8 and 9 lead into the interior of the tool base 4. In this case, a first die section 7 adjoins the first die opening 6, a last die section 9 extends in the illustrated embodiment as far as an opposing second tool surface 10 and thereby forms a second die opening 11. In contrast to the illustrated embodiment, the last die section 9 also end in the interior of the tool base 4, whereby no second die opening 11 is formed. In this case, the sintered part 2 must in any case be removed again from the die tool 1 through the first die opening 6.

The sintered part 2 consists of pressed and subsequently sintered powder metal, the methods and materials for producing such a sintered blank from the prior art are sufficiently known and therefore not further explained. The sintered part 2 is designed disc-shaped in the illustrated embodiment and has on an outer surface 12 has a diameter 13, which corresponds to a raw diameter 14 before the surface compression and after the surface compression corresponds to a smaller final diameter 15.

The surface compacting of the sintered part 2 is carried out by being introduced through the first die opening 6 in the first die section 7 and subsequently in all other die sections 8 and also to the last die section 9, wherein in each die section 7, 8, 9, the outer surface 12 of the sintered part 2 at least on sections of the outer surface 12 against wall surfaces 16 of the die sections 7, 8, 9 is pressed. In this case, one or more contact surfaces 17 on the outer surface 12 of the sintered part 2 in pressure contact with one or more pressing surfaces 18 on the wall surfaces 16 of the die sections 7, 8, 9. The contact surface 17 may thus by a part of the outer surface 12 or through the entire outer surface 12 may be formed; the pressing surface 18 can be formed by a partial section of the wall surface 16 or even by the entire wall surface 16, whereby the partial section can refer to the axial extension and / or also to the extension in the circumferential direction.

The pressing effect is achieved in that an inner diameter 19, by the clear width between opposite or cooperating portions of the pressing surface

18 is a die portion 7, 8, 9 is defined, each smaller than the raw diameter 14 of the sintered part 2. The term inner diameter 19 is not limited to circular cross-sections to understand, but also as a clear width between co-operating press surface parts, not necessarily by the Axis 3 of the die tool 1 go. Similarly, the diameter 13 on the sintered part 2 is not limited to radial directions.

The successive die sections 7, 8, 9 along the axis 3 merge into one another continuously and have monotonically decreasing inner diameters 19 from the first die section 7 to the last die section 9, i. consecutive inner diameter

19 can be the same size or decrease, but can not get bigger. As a result, the pressing action on the contact surface 17 of the sintered part 2 increases from the first die section 7 to the last die section 9, whereby a pressing direction 20 is defined, which is defined by the first ting die section 7 to the last die section 9 has. In the simplest case, the movement of the sintered part 2 in the die tool 1 takes place in a straight line in the pressing direction 20 from the first die opening 6 to the last die section 9, followed by the removal of the sintered part 2 from the die tool 1 via the second die opening 11 or after reversing the direction of movement against the pressing direction 20 through the first die opening 6.

The rectilinear movement in the direction of the axis 3 can also be a rotational movement, e.g. in a rotational direction 21, be superimposed, whereby the sintered part 2 performs a screwing in the die 1. As a result of this form of movement, sintered parts 2 can also be compacted on their surface with the die workpiece 1, the outer surface 12 of which also includes sealing surfaces. The movement of the sintered part 2 in this case takes place about a screw axis 22 which coincides or is parallel to the axis 3, for example if the screw surface to be compacted on the outer surface 12 of the sintered part 2 is not disposed on the entire circumference of the sintered part 2 and this does not have a rotationally symmetrical basic body.

The direction of movement of the sintered part 2 in the die tool 1 can, as well as the speed of movement for optimizing the surface compaction, have an arbitrary course and, for example, also include a reversal of the direction of movement, a stoppage of movement, very slow but also very fast movements. Due to the interference fit, which is effective between the contact surfaces 17 and the pressing surfaces 18, Drackspannun- gene arise, which are oriented substantially perpendicular to the contact surfaces 17, by the movement of the sintered part experiences the contact surface 17 additionally also a Gleitreibungsspan- voltage in the axial direction in a straight line movement or in both the axial and tangential direction in a screwing movement. These stresses acting on the contact surfaces 17 in the sintered part 2 cause both an elastic and a plastic deformation of the sintered part 2, the plastic part causing the permanent surface compression. In this surface compaction, the powder metal particles joined together by pressing and subsequent sintering on so-called bridges are strongly pressed against each other and plastically deformed. The existing between the powder metal particles after sintering pore-like voids are thereby reduced in volume and increases the material density in this area. The effect of surface compaction is greatest due to the additional sliding friction stresses directly on the contact surface 17 and decreases in the direction of the interior of the sintered part 2. With the aid of the method, it is typically possible to compact edge layers of sintered parts 2 having a thickness of a few hundredths of a millimeter up to several tenths of a millimeter and above. After this surface compaction remain in the sintered part 2 in its boundary layers compressive stresses that cause a beneficial increase in flexural strength and an increase in wear resistance.

The axial length of the sintered part 2 or the length of its contact surfaces 17 and the axial lengths of the die sections 7, 8, 9 are further influenced by the method. In FIG. 1, all the die sections 7, 8, 9 have approximately equal die section lengths 23, Deviating from this, individual or multiple die portion lengths 23, in particular the die portion length 23 of the last die portion 9, may be shorter than the contact face length 24 of the sintered part 2. It is even possible that the contact face length 24 is greater as the sum of all template sections 7, 8, 9.

The relative movement between the sintered part 2 and the die tool 1 required for carrying out the method can be achieved by moving the sintered part 2 and / or by moving the die tool 1, with the sintered part 2 and the die tool 1 each having a suitable drive or a fixed frame are connected.

After completion of the method for densifying the surface, the sintered part 2 leaves the last die section 9 either through the second die opening 11 or after reversal of the direction of movement against the pressing direction 20 through the first die opening 6. The elastic deformations of the sintered part 2 which occur during the pressing in may thereby at least partially degrade and the diameter 13 of the sintered part 2 rises from the inner diameter 19 of the last Matrizenabschnitts 9 by the elastic spring back slightly on the larger end diameter 15, which corresponds as possible to the nominal diameter of the sintered part 2. In Fig. 1, this is shown with a sintered part 2 shown in dashed lines, which is located in the pressing direction 20 after the last die section 9 and the end diameter 15 is slightly larger than the inner diameter 19 of the last die section. 9 Fig. 2 shows a cross section according to the lines II-II in Fig. 1 by the erfϊndungsgemäße die 1 with a pressed therein sintered part 2. This is not rotationally symmetrical with respect to the axis 3 in the illustrated embodiment, further extends its contact surface 17, at which the surface compression takes place, not over its entire outer circumference, ie that only part of its outer surface 12 is compressed. The stencil tool 1 does not involve the entire wall surface 16 at the compression, but only the pressing surfaces 18, which contact the corresponding contact surfaces 17 of the sintered part 2. It can be seen that in the most general case the compaction of the surface takes place only where an inner contour 25 of a die section 7, 8, 9 defined by the wall surface 16 cooperates with an outer contour 26 defined by the outer surface 12 of the sintered part 2. A contact surface 17 on the sintered part 2 can be compressed in all die sections 7, 8, 9 by a corresponding pressing surface 18, but it is also possible that in individual or multiple die sections 7, 8 and or 9 only individual contact surfaces 7 or parts be compacted by the pressing surfaces 18 in single or more die sections 7, 8, 9 are made smaller.

As can be seen in Fig. 2, not only diameter 13 are considered in the context of the invention, which also extend through the axis 3, but also diameter 13, which correspond to a tooth thickness 27 on an outer toothing of the sintered part 2. Also in this case, the opposite contact surfaces 17 of the sintered part 2 between opposite

Pressing surfaces 18 of a die section 7, 8, 9 pressed by monotonically decreasing inner diameter 19 and compressed.

FIG. 3 shows a section from a longitudinal section through a further embodiment of the die tool 1 according to the invention with four die sections 7, 8, 9 whose inner diameters 19 are gradually reduced in the pressing direction 20. The transition from a die section 7, 8 to the adjoining die section 8, 9 can be designed as a chamfer 28, or be provided with a rounding 29, wherein in the pressing direction 20 can connect to a concave curve convex rounding. As a result, a smooth transition of the sintered part 2 from one die section 7, 8 to the subsequent die section 8, 9 can take place without an unintentional material removal at the sintered part 2 being effected by a sheep-edged step, or the edges breaking off at the transitions of the die tool 1. 4 shows a detail from a longitudinal section through a further embodiment of the inventive die tool 1, which in this embodiment variant is not in one piece, but is composed of several die plates 30. Notwithstanding the embodiment according to FIG. 3, in which the inner diameters 19 within the die sections 7, 8, 9 are each constant, ie are formed by a circular cylinder surface 31, the die tool 1 according to FIG. 4 has between two die sections 7 and 8, 8 and 8, or 8 and 9 with circular cylindrical surfaces 31 also have a die section 8, which has a cross-sectional taper 32 in the pressing direction 20. By such a sequence of circular cylindrical surfaces 31 and cross-sectional tapers 32, which is formed for example by a conical surface 33, a pyramid surface 34 or other tapered surface 35, by the, based on the axial length, slow decrease of the inner diameter 19, the structure of the compressive stresses on the Contact surfaces 17 of the sintered part 2 slower and gentler.

5 shows a section of a longitudinal section through a further embodiment of the die tool 1. In this case, a die section 8, which is arranged between two further die sections 7 and 8, or 8 and 8, or 8 and 9 with circular cylinder surfaces 31, has a tapering surface 35, which has a progressive course in the pressing direction 20, ie the decrease of the inside diameter 19 within the die portion 8 in the pressing direction 20 becomes stronger. The decrease in the inner diameter 19 is progressive in the region of the taper surface 35.

6 shows a section from a longitudinal section through a further embodiment of the die tool 1, in which between two die sections 7 and 8, or 8 and 8, or 8 and 9 with a circular cylindrical surface 31 as a wall surface 16, a die section 8 with a tapering surface 35 as Wall surface 16 is arranged, in which the decrease in the inner diameter 19 in the pressing direction is lower, that has a degressive course.

FIG. 7 shows a plan view of a further embodiment of the die tool 1 according to the invention, in which the inner contour 25 of the wall surface 16 is rotationally symmetrical with respect to the axis 3.

8 shows a plan view of a further embodiment of the die tool 1 according to the invention, in which the inner contour 25 of the wall surface 16 of the die sections 7, 8, 9 is executed rectangular. The inner contour 25 is therefore only rotationally symmetrical with respect to the axis 3 and suitable for compacting sintered parts with a rectangular cross-section.

Fig. 9 is a plan view of another embodiment of the die tool 1 with an inner contour 25 of the wall surfaces 16 of the die sections 7, 8, 9 which is composed of a circular section, a straight and a toothing. The method for compacting the surface of sintered parts 2 is thus not applicable to rotationally symmetrical or rotationally symmetrical outer contours 26 of sintered parts 2, but also for arbitrarily shaped outer contours 26.

10 shows a plan view of a further embodiment of the die tool 1, in which the inner contour 25 of the wall surfaces 16 of the die sections 7, 8, 9 form an internal toothing 36 with which the outer surfaces 12 of a gearwheel can be compressed.

The inner contour 25 can thereby run straight in the direction of the axis 3, whereby the

Matrizenwerkzeug 1 is suitable for surface compaction of straight-toothed gears, the inner contour 25 is in the tool interior but not straight, but continues with an additional screwing in the direction of rotation 21, can be surface-hardened with the die tool 1 gears with helical teeth. Likewise, for example, the wall surfaces 16 in inner contours 25 of the wall surfaces 16, according to the embodiments Figs. 8 and Fig. 9, follow a screwing, and formed as a screw surfaces wall surfaces 16 of the die tool 1 in accordance with as cooperating screw surfaces shaped contact surfaces 17 a axially twisted helical sintered compact 2.

FIG. 11 shows a longitudinal section through a further embodiment of the die tool 1, which has only a first die opening 6 and a sintered part 2 is therefore removed again from the die tool 1 through the first die opening 6 after reaching the last die section 9. The pressing surfaces 18 of the individual die sections 7 go in this embodiment with linear decreasing inner diameter 19 steplessly into one another. As a result, the individual die sections 7 merge into a single large die cut. This embodiment of the die tool 1 can also be used to influence the final diameter 15 of the sintered part 2, by the sintered part 2 is used with different depth of immersion 37 in the die tool 1. In particular, sintered parts 2 can be surface-compacted with this embodiment of the die tool 1, in which it is not the maintenance of a specific final diameter 15 that is the focus, but the degree of surface compression. If, for example, a constant maximum force is always expended for the movement of the sintered part 2 in the pressing direction 20, in each case approximately the same surface compaction is achieved even when the raw diameters 14 of the sintered parts 2 fluctuate.

FIG. 12 shows a longitudinal section through a further embodiment of the die tool 1, in which the individual die sections 7, 8, 9 are likewise fused into a single die section. Whose wall surface 16 and the pressing surface 18 is formed by a general tapered surface 35, the inner diameter 19 decreases in the direction of compression 20 degressive and expires with a circular cylindrical surface 31 in the region of the second die opening 11.

Fig. 13 shows the implementation of the method according to the invention, in which two sintered parts 2 by means of a pressing against an end face 38 of a sintered part 2 pressing member 39, e.g. of a ram in the pressing direction 20 are pressed by the die tool 1. Between the two sintered parts 2, a pressure-resistant spacer element 56 is arranged. The pressure element 39 is for this purpose connected to a suitable drive device 40, for example with a hydraulic press, a pneumatic press, a mechanical press, etc.

FIG. 14 shows the implementation of the method in which a sintered part 2 is pulled in the pressing direction 20 through the die tool 1. For this purpose, in the sintered part 2 a tensioning element 41 is fastened with a suitable anchoring 42, e.g. by screwing in the tension element 41, which in turn is connected to a suitable drive device 40.

The implementation of the method with pushing through the sintered part 2 by the die 1 is particularly recommended for sintered parts 2, the axial length, in particular the contact surface length 24, is small, compared to the diameter 13, while the process variant with the pulling of the sintered part 2 by the die tool 1 can be used for sintered parts 2, whose axial length is greater than the diameter 13 of its cross section. 15 shows a further variant of the method for surface compaction, in which the sintered part 2 is acted upon by pressure forces 43-indicated by small arrows-at its two opposite end faces 38 between two pressure elements 39 during the entire compaction process. Both in a movement in the pressing direction 20, as well as in a movement in an opposite direction 44 - indicated by a dashed arrow. In this variant of the method, a reversal of the direction of movement can also be carried out in the case of disc-shaped sintered parts 2 with a small axial length, for example in order to enable intermediate relief and a reduction of elastic deformation.

16 shows a die tool 45, which comprises a die tool 1 according to the invention, an additional insertion section 46, which is arranged in front of the first die opening 6 of the die tool 1, viewed in the pressing direction 20, and an additional calibrating section 47, viewed in the pressing direction 20, after the second die opening 11 of the die tool 1 is arranged.

The insertion section 46 is formed by an insertion plate 48, which is directly adjacent to the first tool surface 5 of the die tool 1. An insertion opening 49 arranged coaxially with the die tool is formed in the insertion plate 48, the wall surface 16 of which has the same inner contour 25 as the die sections 7, 8, 9 but has an import diameter 50 which is greater than the raw diameter 14 of the sintered part 2. The insertion section 46 thus facilitates the accurate and positionally correct feeding of the sintered part 2 into the first die section 7 of the die tool 1.

The calibration section 47 comprises a calibration plate 51 abutting the second, opposite tool surface 10, which has a calibration opening 52 coaxial with the die tool 1, the wall surface 16 of which has the same inner contour 25 as the matrix tool 1, but has a calibration diameter 53 corresponding to the nominal diameter of the sintered part 2 corresponds or is smaller. After the last die section, whose diameter 19 is smaller than the nominal diameter of the finished sintered part 2, this can extend in the calibration section 47 up to the calibration diameter 53, ie the nominal diameter, whereby the final diameter 15 at least approximately corresponds to the nominal diameter. In addition, a relief section 54 can be connected directly to the second die opening 11, which has a relief diameter 55 which is greater than the nominal diameter or The end diameter 15 of the sintered part 2. This can thereby reduce its elastic deformation in the relief section 54 for the most part, whereby the accuracy of the subsequent calibration process is increased. Due to a small calibration diameter, an additional kneading effect is achieved. Calibration makes it possible to compensate for axial conicities that may arise due to the compaction process.

The calibration stage can be longer in the direction of the axis 3 than the overall height of the sintered part in this direction. Furthermore, the calibration stage can aufeisen a larger diameter than the last die section 9, whereby in the ejection of the sintered part 2 on the first die opening 6 in turn a kneading effect is achieved.

Of course, the invention is also useful for surface compaction of breakthroughs, e.g. Holes, suitable in sintered parts 2. Instead of the die tool 1, a punch is used which, like the die tool 1, also has sections with different diameters, in which case, however, the diameter of the sections merging into one another increases monotonously. All other comments on the die tool apply mutatis mutandis to the stamp, the information "inside" and "outside" are to be changed accordingly.

All statements on ranges of values in the description of the present invention should be understood to include any and all sub-ranges thereof, e.g. is the statement 1 to 10 to be understood that all sub-areas, starting from the lower limit 1 and the upper limit 10 are included, ie. all subregions begin with a lower limit of 1 or greater and end at an upper limit of 10 or less, e.g. 1 to 1.7, or 3.2 to 8.1 or 5.5 to 10.

The Ausfülirungsbeispiele show possible embodiments of the method or die tool according to the invention, which should be noted at this point that the invention is not limited to the specific embodiments thereof, but also various combinations of the individual embodiments are mutually possible and this variation possibility due to the teaching technical action by objective invention in the skill of working in this technical field expert. So there are also all conceivable variants that can be combinations of individual details of the embodiment variant shown and described are possible, encompassed by the scope of protection.

For the sake of order, it should finally be pointed out that, for a better understanding of the structure of the die tool, this or its components have been shown partially unevenly and / or enlarged and / or reduced in size.

The problem underlying the independent inventive solutions can be taken from the description.

Above all, the individual in Figs. 1, 2; 3; 4; 5; 6; 7; 8th; 9; 10; 11; 12; 13; 14; 15; 16 embodiments form the subject of independent solutions according to the invention. The relevant objects and solutions according to the invention can be found in the detailed descriptions of these figures.

S u b e c u s e c tio n a tio n s

1 die tool 36 internal toothing

2 sintered part 37 offset

3 axis 38 face

4 Tool body 39 Pressure element

5 Tool surface 40 Drive device

6 die opening 41 pulling element

7 Matrix section 42 Anchoring

8 die section 43 compressive force

9 die section 44 opposite direction

10 Tool surface 45 Die tool

11 die section 46 insertion section

12 outer surface 47 Calibration section

13 diameter 48 insertion plate

14 raw diameter 49 insertion opening

15 final diameter 50 insertion diameter

16 Wall surface 51 Calibration plate

17 contact surface 52 calibration opening

18 pressing surface 53 Calibration diameter

19 Inner diameter 54 Relief section

20 pressing direction 55 unloading diameter

21 Direction of rotation 56 Distance element

22 screw axis

23 die section

24 contact surface length

25 inner contour

26 outer contour

27 tooth thickness

28 chamfer

29 rounding

30 die plate

31 circular cylindrical surface

32 cross-sectional rejuvenation

33 conical surface

34 pyramid surface

35 rejuvenation area

Claims

Patent claims

A method for surface densification of a sintered part (2), comprising a sintered part (2) in a die tool (1) along an axis (3) in a pressing direction (20) through a plurality of die sections (7, 8, 9) from a first die section (7) is moved at a first die opening (6) into a last die section (9), wherein a wall surface (16) of each die section (7, 8, 9) forms at least one pressing surface (18) against which one of Outside surface (12) of the sintered part (2) formed contact surface (17) is pressed, and one, in a cross-section with respect to the axis (3) lying, of the pressing surface (18) defined inner contour (25) at least approximately one of the contact surface (17 ) defined outer contour (26), characterized in that during the movement of the sintered part (2) from the first die opening (6) in the last die section (9), the surface compression by continuously merging into each other Matrizenabschnitt e (7, 8, 9) and monotonically decreasing, between cooperating pressing surfaces (18) measured inner diameter (19) of the die sections (7, 8, 9) takes place.

2. The method according to claim 1, characterized in that the sintered part (2) by one of the first die opening (6) opposite the second die opening (11) from the die tool (1) is moved.

3. The method according to claim 1 or 2, characterized in that the movement is rectilinear or in a screwing movement.

4. The method according to any one of claims 1 to 3, characterized in that the movement of the sintered part (2) and / or the die tool (1) is performed.

5. The method according to any one of claims 1 to 4, characterized in that the sintered part (2) is pressed or pulled on one or both end faces (38) by the die tool (1).

6. Verfairen according to one of claims 2 to 5, characterized in that the sintered part (2) during the movement through the die tool (1) between two pressure elements (39) is largely fully pressurized axially over the entire surface.

7. The method according to any one of claims 1 to 6, characterized in that the direction of movement of the sintered part (2) before reaching the last Matrizenabschnitts (9) is changed at least once.

8. The method according to any one of claims 1 or 3 to 7, characterized in that the sintered part (2) after reaching the last die portion (9) through the first die opening (6) from the die tool (1) is moved.

9. The method according to any one of claims 1 to 8, characterized in that the sintered terteil (2) in the last die section (9) is compressed to an inner diameter (19) which reduces a nominal dimension of the sintered part (2) by the value of due to the pressing forces caused elastic deformation of the sintered part (2) at this inner diameter (19).

10. The method according to any one of claims 1 to 9, characterized in that the sintered part (2) in a front of the first die opening (6) arranged insertion section (46) is introduced with an insertion diameter (50) which is greater than a raw diameter (14) of the sintered part (2) on its outer surface (12).

11. The method according to any one of claims 2 to 10, characterized in that the

Sinter part (2) after the second die opening (11) in a subsequent calibration (47) is moved, which has a calibration diameter (53) corresponding to a desired dimension of the sintered part (2) on its outer surface (12).

12. The method according to any one of claims 2 to 11, characterized in that a plurality of sintered parts (2) with or without each between two sintered parts (2) arranged spacer elements (56) simultaneously by the die tool (1) are moved.

13. The method according to any one of claims 1 to 12, characterized in that the sintered part (2) in the process implementation has a temperature which is around 100 ⁰ C, in particular 200 ° C, below the sintering temperature.

14. The method according to any one of claims 1 to 13, characterized in that the Sintered part (2) is designed as a bearing bush, as a bearing shell, as a gear, as a sprocket, as a toothed belt or as a cam member.

15. Die tool (1) for surface compacting a sintered part (2), with several ren along a shaft (3) in a pressing direction (20) successive die sections (7, 8, 9), comprising a first die section (7) a first die opening (6) and a last die section (9), wherein on a wall surface (16) of each die section (7, 8, 9) at least one pressing surface (18) has an inner contour (25) in a cross-section with respect to the axis (3) defined at least approximately one of one, on a

0 outer surface (12) of the sintered part (2) arranged contact surface (17) defined outer contour (26) corresponds, characterized in that the die sections (7, 8, 9) continuously merge into one another and between cooperating portions of pressing surfaces (18) measured inside diameter (19) decreases monotonically on the inner contour (25) from the first die section (7) to the last die section (9).

5

16. die tool (1) according to claim 15, characterized in that on the last die portion (9) to the first die opening (6) opposite second mes- rizenöffnung (11) connects.

17. Die tool (1) according to claim 15 or 16, characterized in that the inner diameter (19) within a die section (7, 8, 9) in the pressing direction (20) is constant.

18. die tool (1) according to one of claims 15 to 17, characterized in that 5 that the inner diameter (19) within a die portion (7, 8, 9) in the pressing direction

(20) decreases linearly.

19. die tool (1) according to one of claims 15 to 18, characterized in that the inner diameter (19) within a die portion (7, 8, 9) in the pressing direction

0 (20) decreases progressively.

20. die tool (1) according to one of claims 15 to 19, characterized in that the inner diameter (19) within a die section (7, 8, 9) decreases in the pressing direction (20) degressive.

21. die tool (1) according to any one of claims 15 to 20, characterized in that an axial Matrizenabschnittslänge (23) of at least one Matrizenabschnitts (7, 8, 9) is greater than an axial contact surface length (24) of the sintered part (2).

22. The matrix tool according to claim 16, characterized in that the axial die section length of the last die section has less than 30% of the axial contact surface length of the sintered part.

23 die tool (1) according to any one of claims 16 to 20 or 22, characterized 0 indicates that the axial length of all die sections (7, 8, 9) in total is smaller than the axial contact surface length (24) of the sintered part ( 2).

24. die tool (1) according to one of claims 15 to 23, characterized in that the die tool (1) between three and seven, in particular five die sections

5 (7, 8, 9) each having a constant, gradually decreasing inner diameter (19).

25. die tool (1) according to one of claims 15 to 24, characterized in that a sequence of successive die sections (7, 8, 9) alternately each have a constant inner diameter (19) and a decreasing inner diameter (19)

10 points.

26. die tool (1) according to any one of claims 15 to 25, characterized in that the transition from a die portion (7, 8, 9) to a subsequent die portion (7, 8, 9) by a chamfer (28) or at least one Rounding (29) is formed.

, 5

27. die tool (1) according to one of claims 15 to 26, characterized in that the inner diameter (19) in the last die section (9) has a value which reduces a nominal dimension of the sintered part (2) by the value caused by the pressing forces elastic deformation of the sintered part (2) at this inner diameter (19) corresponds.

0

28. die tool (1) according to any one of claims 15 to 27, characterized in that the inner contour (25) with respect to the axis (3) is rotationally symmetrical.

29. Die tool (1) according to any one of claims 15 to 27, characterized in that the inner contour (25) with respect to the axis (3) is rotationally symmetrical.

30. die tool (1) according to any one of claims 15 to 29, characterized in that the pressing surface (18) of a die portion (7, 8, 9) is formed as a general cylindrical surface.

31. die tool (1) according to one of claims 15 to 29, characterized in that the pressing surface (18) of a die portion (7, 8, 9) is formed by a screw surface.

32. Matrizenwerkzeug (1) according to any one of claims 15 to 27 or 29, characterized in that the pressing surfaces (18) of the die sections (7, 8, 9) are each formed at least in sections by a Innengeradverzahnung.

33. Die tool (1) according to one of claims 15 to 27 or 29 or 31, characterized in that the pressing surfaces (18) of the die sections (7, 8, 9) are each formed at least in sections by an internal helical toothing.

34. Die tool (1) according to one of claims 15 to 33, characterized in that at least two successive die sections (7, 8, 9), in particular all die sections (7, 8, 9) are integrally connected to each other.

35. die tool (1) according to one of claims 15 to 34, characterized in that in the pressing direction (20) before the first die portion (7) an insertion portion (46) having an insertion diameter (50) which is greater than a raw diameter (14 ) of the sintered part (2) is arranged.

36. die tool (1) according to one of claims 16 to 35, characterized in that in the pressing direction (20) after the last die section (9) is followed by a Kalibrierabschnitt (47) having a Kalibrierdurchmesser (53), the nominal dimension of the sintered part ( 2) corresponds.

37. Stamp for surface compacting of sintered parts (2), with a plurality of stamp sections following one axis in a pressing direction (20), wherein on a wall surface of each stamp section at least one pressing surface defines in a cross section with respect to the axis an outer contour which is at least approximately one of one, on an inner surface of the sintered part (2) arranged contact surface defined inner contour corresponds, characterized in that the stamp sections continuously merge into each other and measured between interacting sections of pressing surfaces outside diameter on the outer contour of the first stamp section to the last stamp section in the pressing direction (20) monotonously increases.