Method for manufacturing a sliding sleeve

Abstract

Method for manufacturing a sliding sleeve for a transmission synchronization unit from a metal powder, comprising the steps: - Providing a tool mold (26) with two rigid mold halves (28, 30) that can be moved relative to each other and define sections of an outer contour of a sliding sleeve pressing (10), - Introducing at least one structural element (134a-134c) into the space (32) defined by the closed mold halves (28, 30), which defines at least one undercut with respect to the direction of travel (V) of the mold halves (28, 30) in the sliding sleeve pressing (10), wherein the structural element(s) (134a-134c) are formed by one or more inserts which are movably fixed to the mold halves (28, 30) in the direction of travel (V) relative to the mold halves (28, 30) before the metal powder is introduced into the tool mold (26), - Introducing metal powder into the tool mold (26), - Pressing the metal powder into the tool mold (26) to produce the sliding sleeve pressing (10), - Moving apart the mold halves (28, 30) of the tool mold (26), - Removal of the sliding sleeve pressing (10) from the tool mold (26), wherein, as the mold halves are pulled apart, the insert parts detach from the tool mold (26), wherein, as the mold halves (28, 30) are pulled apart, the insert part(s) initially remain attached to the sliding sleeve pressing (10) and are demolded together with it, and - Sintering of the sliding sleeve pressing (10).

Description

[0001] The invention relates to a method for manufacturing a sliding sleeve from a metal powder using a sintering process.

[0002] In a synchronizer unit, a sliding sleeve is used to create a rotationally fixed connection between a synchronizer body and a gear to be shifted. The sliding sleeve is an annular component with internal teeth that can engage with external teeth on both the synchronizer body and the gear simultaneously, and with an external engagement geometry where a shift fork engages to move the sliding sleeve axially towards the gear and away from it when the gear is engaged.

[0003] Traditionally, sliding sleeves are manufactured from pipe sections using rolling, crimping, and machining processes. It is also possible to produce a forged blank and then machine it to the final finish.

[0004] It is also known to manufacture a sliding sleeve using a sintering process. In a sintering process, metal powder is first filled into a mold and solidified under pressure to form a compact (green compact). This is then sintered, during which the metal particles permanently bond together and the strength increases. Using a sintering process offers advantages over conventional machining of a pre-formed part in terms of processing effort, as part of the shaping can already be achieved by producing the compact in the mold. However, not all geometric structures of a sliding sleeve can be formed in a simple pressing operation. Structures with undercuts relative to the demolding direction are particularly problematic; these structures can only be created by a radially outward tool movement.Such problematic structures include, in the case of a sliding sleeve, backings and detent grooves on an internal toothing, as well as an outer circumferential engagement groove for a shift fork.

[0005] DE 102 50 432 A1 proposes pre-sintering the pressed part after pressing, but not yet completing the final sintering process, and then machining the internal gear teeth. However, a disadvantage of this method is that even the pre-sintered component already has a relatively high hardness, making the machining required to introduce the necessary geometric structures time-consuming and expensive.

[0006] AT 505 947 A1 describes a method for manufacturing a blank for a sintered sliding sleeve using a pressing process in a tool mold with several movable mold parts. Slides are provided that are radially adjustable to allow undercuts to be incorporated into the blank.

[0007] DE 37 26 259 C1 shows the production of a sintered component in a lost mold.

[0008] The object of the invention is to improve a method for manufacturing a sliding sleeve and, in particular, to shorten the processing time.

[0009] According to the invention, this is achieved with a method for manufacturing a sliding sleeve for a transmission synchronization unit from a metal powder having the features of claim 1.

[0010] According to the invention, the undercuts contained in the geometry of the sliding sleeve are generated by using one or more structural elements that are detachably or slidably arranged in the mold. In this way, structures can be created in the pressed part without significant manufacturing effort, structures that would otherwise prevent the mold halves from separating in the direction of travel. In principle, it is possible to generate all geometric structures of the sliding sleeve directly during pressing by using suitable structural elements, thus significantly reducing machining time.

[0011] Structural elements are used which are formed by one or more inserts that are fixed to the mold halves before the metal powder is introduced into the tool mold.

[0012] The separate inserts can be fixed in any suitable way. In particular, grooves and projections can be provided in the inner walls of the mold halves and / or on the inserts themselves, allowing the inserts to move along the direction of travel relative to the inner wall of the mold halves. The fastening must, of course, be designed so that the inserts do not shift during the pressing process and the applied pressure forces. The inserts should also be dimensionally stable enough that they do not deform, or only deform minimally, during pressing.

[0013] The insert(s) are removed from the sliding sleeve pressing, for example, after the mold halves have been separated, in a direction different from the direction of travel of the mold halves. When the mold halves are separated to demold the pressing, the insert(s) detach from the mold and initially adhere to the sliding sleeve pressing, from which they are then removed, for example, radially.

[0014] Multiple inserts can be used to create a single undercut feature, or a single structural element can be used per undercut, for example, in the case of indexing grooves. The circumferential groove, for instance, is defined by several composite inserts.

[0015] The structural elements can, in particular, form a circumferential groove on the radial outside, for example for the engagement of a shift fork, detent grooves on the radial inside for contact with pressure pieces of a synchronizer body and / or backings on an internal toothing for engagement with a gear toothing.

[0016] To achieve homogeneous compression of the metal powder, all usual powder pressing measures can of course be carried out, such as the use of powder columns and the provision of several lower and upper punches.

[0017] The inserts can be designed to be reusable, which saves on material costs. In this case, the inserts are removed from the sliding sleeve pressing without damage and reinserted into the mold halves for the next pressing process.

[0018] It is also conceivable to leave the inserts attached to the pressed part during sintering and remove them only afterward. In this case, the inserts must have sufficient temperature resistance. For example, inserts made of a suitable ceramic could be used.

[0019] According to a third preferred embodiment, the insert(s) are designed as a expendable mold and initially remain attached to the sliding sleeve die after pressing, preferably only being destroyed during sintering by the high temperatures present. Such expendable molds can consist of wax, plastic, epoxy resin-impregnated sand, or similar materials, whereby the selected material must be dimensionally stable under the pressure generated during pressing, but should detach from the sliding sleeve die during sintering without damaging the resulting structures. The insert(s) can melt, disintegrate, or chemically decompose during sintering.

[0020] When using lost molds, new inserts are required for each sliding sleeve pressing.

[0021] It is possible to form all structural elements of the sliding sleeve directly in the pressed part, so that the sliding sleeve does not require any mechanical post-processing after sintering. In this case, any shaping post-processing can be completely omitted. Post-processing, for example of the circumferential groove, can also be performed only on the contact surfaces for a shift fork.

[0022] The different structural elements described can also be combined in any way desired, with certain structures being realized via sliders and others via inserts.

[0023] Of course, it is also possible not to create all the undercuts on the sliding sleeve directly during pressing and to produce the remaining structures through mechanical, shaping post-processing using known methods, for example, by milling. Conversely, however, it is quite possible to actually produce all undercuts during sintering, i.e., without any mechanical post-processing.

[0024] The invention is described in more detail below with reference to several exemplary embodiments and the accompanying drawings. The drawings show: - Fig. 1 a schematic perspective view of a sliding sleeve, manufactured according to a method according to the invention; - Fig. 2 a schematic sectional view of a tool shape for the inventive method using slides; and - Fig. 3 a schematic sectional view of a tool shape for the inventive method according to inventive embodiments.

[0025] Fig. Figure 1 shows a sliding sleeve pressing 10, from which a finished sliding sleeve is produced in a sintering process with essentially no change to its outer contour. Since the finished sliding sleeve is identical in appearance to the sliding sleeve pressing 10, it is not shown separately here.

[0026] On a ring-shaped base body 12 of the sliding sleeve pressing 10, a circumferentially closed circumferential groove 16 for the engagement of a (not shown) switching fork is formed on an outer circumferential surface between two webs 14 located at the axial edges.

[0027] An internal toothing 18 with axially pointed teeth 20 is provided on a radial inner surface. At least some of the teeth 20 have backings 22 which extend inwards in the axial direction towards the interior of the annular base body 12 with respect to the tooth flanks. In addition, further geometric structures necessary for the function of the sliding sleeve are formed in the area of ​​the internal toothing 18, for example several detent grooves 24 distributed around the circumference.

[0028] The manufacturing process for the sliding sleeve is described below.

[0029] The sliding sleeve pressing 10 is manufactured in a tool mold 26 using a pressing process.

[0030] The tool mold 26 has two rigid mold halves 28, 30 that can be moved relative to each other in a traversing direction V. In this example, these halves are essentially mirror images of each other and define a space 32 enclosed by the mold halves 28, 30. The space 32 sectionally determines the outer contour of the sliding sleeve pressing 10 and thus of the later finished sliding sleeve.

[0031] The sliding sleeve has geometric structures that cannot be demolded in a two-part mold if and when it is opened in a traversing direction V. These include the circumferential groove 16, the backings 22, and the locking grooves 24.

[0032] For the production of these structures, structural elements 34 are provided which are placed in the space 32 and which define at least one undercut with respect to the direction of travel V in the sliding sleeve pressing 10.

[0033] In the Fig. In the variant shown in Figure 2, the structural elements 34 are designed as sliders that can be moved in the radial direction r.

[0034] Each of the slides defines a projection 36, with all projections 36 together forming a closed circumferential ring that creates the circumferential groove 16 in the sliding sleeve pressing 10. At least two slides are required for this, which are displaced relative to each other in the radial direction r. If only two slides are used, each of them has a projection 36 extending in a semicircle, with both projections 36 complementing each other to form a closed ring. However, more slides can also be provided, preferably three, extending over a 120° angle.

[0035] In Fig. Figure 2 shows that each mold half 28, 30 is assigned its own set of slides. It is equally possible, of course, to combine the axially adjacent slides of the two mold halves 28, 30 into a single piece, thus reducing the number of slides. The precise design of the slides is left to the expert for the specific application.

[0036] The inner contour 33a of the slides is, for example, matched to an inner contour 33b of the sections of the tool shape 26 adjacent in the axial direction A, such that the curvature of the inner contours 33a, 33b is the same and no edge is formed in the axial direction A when the slides are retracted.

[0037] To produce the sliding sleeve pressing 10, the slides forming the structural elements 34 are first pushed radially r into the chamber 32 until they reach their desired position. Then, a metal powder (for example, an iron alloy) is introduced into the chamber 32, and the mold halves 28, 30 are closed. During this process, the metal powder in the chamber 32 is compressed under high pressure.

[0038] The Fig. 2 and Fig. Figure 3 merely shows a schematic structure of the mold halves 28 and 30. Typically, each mold half consists of several upper and lower punches that can be moved relative to each other, so that the corresponding powder columns can be moved relative to each other and axially to achieve a uniform distribution of the powder in the mold. Filling the chamber 32 can also be achieved, for example, by introducing the powder in several filling steps, between which the punches are moved.

[0039] The powders used should be as brittle as possible to achieve a sufficiently high green body strength.

[0040] The resulting sliding sleeve pressing 10 is removed from the tool mold 26 after the two mold halves 28, 30 have been pulled apart.

[0041] The sliding sleeve pressing 10 is then sintered at high temperatures and brought to its final strength.

[0042] In the Fig. In the embodiment shown in Figure 3, the structural elements 134a, 134b, 134c are not sliders as in the example of Figure 3. Fig. 2 designed as insert parts (see Fig. 3).

[0043] The inserts define the undercuts in the sliding sleeve pressing 10 and are rigid components separate from the mold halves 28, 30, whose dimensional stability is high enough to withstand the pressure during the pressing process without significant deformation.

[0044] The inserts are fixed at the appropriate positions on the inner wall of the mold halves 28, 30 before the metal powder is introduced. This fixing can be achieved, for example, by providing a projection 136 on the insert and a corresponding groove extending in the direction of travel V on the inner side of the respective mold half 28, 30. A stop 138 acting in the direction of travel V ensures that the inserts maintain their position during the closing of the mold halves and the pressing process.

[0045] The groove is open towards the second mold half 30, 28, so that when the tool mold 26 is opened, the inserts remain attached to the sliding sleeve pressing 10 and can be released from the mold halves 28, 30 with little effort along the direction of travel V.

[0046] In Fig. Figure 3 shows a variant in which all undercuts of the sliding sleeve pressing 10 are realized by inserts.

[0047] The circumferential groove 16 is produced by structural elements 134a, which are arranged on the radial outside of the inner wall of the mold halves 28, 30.

[0048] The deposits 22 are created here by structural elements 134b on a radial inner wall of the mold halves 28, 30 in the area of ​​the structure provided in the mold halves 28, 30 for generating the internal toothing 18 (shown in the upper part of the figure).

[0049] Furthermore, the indexing grooves 24 are formed by structural elements 134c in the area of ​​the internal toothing 18, which is shown here in the Fig. The lower half of the mold halves 28, 30 is shown.

[0050] The structural elements 134a, 134b and 134c are each shaped and arranged according to the structures they are to produce.

[0051] After the pressing process, the mold halves 28, 30 are pulled apart, and the structural elements 134a-c remain attached to the sliding sleeve pressing 10 and are demolded with it.

[0052] Subsequently, the structural elements 134a-c are also removed radially from the sliding sleeve pressing 10. They can be reused for the next pressing operation.

[0053] In another embodiment, the structural elements 134a-c are also designed as inserts, but as so-called expendable molds. They are formed from a material that is dimensionally stable during the pressing process, but which decomposes, liquefies, or chemically decomposes at the temperatures prevailing during the subsequent sintering step. For this purpose, inserts made of wax, plastic, or similar materials can be used, for example. The molds correspond, for example, to those used in Fig. 3 are shown, so that Fig. 3 represents two embodiments simultaneously.

[0054] As in the embodiment just described, the inserts are fixed in the mold halves 28, 30 before the metal powder is poured in and, after pressing, are demolded from the mold halves 28, 30 together with the sliding sleeve pressing 10.

[0055] However, in this variant, the inserts remain on the sliding sleeve pressing 10 and are subjected to the sintering process together with it, whereby the inserts are destroyed.

[0056] It is of course possible and can also be advantageous for geometric reasons to combine the different described methods and, for example, to use radially displaceable slides for the production of the circumferential groove 16, while reusable or sinterable inserts are used for the undercuts on the internal toothing 18.

[0057] If all undercuts on the sliding sleeve pressing 10 are created during the pressing process, further mechanical post-processing can potentially be almost or even completely dispensed with. If necessary, mechanical post-processing can be limited to the contact surfaces of a shift fork in the area of ​​the circumferential groove 16.

Claims

[1] Method for manufacturing a sliding sleeve for a transmission synchronization unit from a metal powder, comprising the steps: - Providing a tool mold (26) with two rigid mold halves (28, 30) that can be moved relative to each other and define sections of an outer contour of a sliding sleeve pressing (10), - Introducing at least one structural element (134a-134c) into the space (32) defined by the closed mold halves (28, 30), which defines at least one undercut with respect to the direction of travel (V) of the mold halves (28, 30) in the sliding sleeve pressing (10), wherein the structural element(s) (134a-134c) are formed by one or more inserts which are movably fixed to the mold halves (28, 30) in the direction of travel (V) relative to the mold halves (28, 30) before the metal powder is introduced into the tool mold (26), - Introducing metal powder into the tool mold (26), - Pressing the metal powder into the tool mold (26) to produce the sliding sleeve pressing (10), - Moving apart the mold halves (28, 30) of the tool mold (26), - Removal of the sliding sleeve pressing (10) from the tool mold (26), wherein, as the mold halves are pulled apart, the insert parts detach from the tool mold (26), wherein, as the mold halves (28, 30) are pulled apart, the insert part(s) initially remain attached to the sliding sleeve pressing (10) and are demolded together with it, and - Sintering of the sliding sleeve pressing (10). [2] Method according to claim 1, characterized by , that the structural element(s) (134a-c) form a circumferential groove (16) on the radial outer side, locking grooves (24) on the radial inner side and / or backings (22) of an internal toothing (18). [3] Method according to any one of the preceding claims, characterized by, that the insert(s) are removed from the sliding sleeve pressing (10) after the mold halves (28, 30) have been pulled apart in a direction different from the direction of travel (V) of the mold halves (28, 30). [4] Method according to any one of the preceding claims, characterized by that the insert(s) are designed to be reusable. [5] Method according to any one of claims 1 to 3, characterized by that the insert(s) are formed in the form of a lost mold and initially remain on the sliding sleeve pressing (10) after pressing. [6] Method according to claim 5, characterized by that the insert(s) may be destroyed by temperature during sintering. [7] Method according to any one of the preceding claims, characterized by that the sliding sleeve is not mechanically reworked after sintering.

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