METHOD FOR PRODUCING A PISTON

Abstract

The present invention relates to a method for producing a piston (1) for an internal combustion engine from a piston upper part (2) and a piston lower part (3).

The method has the following method steps: producing a piston upper part (2) having a piston top (6), at least parts of a ring section (12) and at least part (7) of a cooling channel (8), by forging or casting for example, producing the piston lower part (3) and closing the part (7) of the cooling channel (8) which is arranged in the piston upper part (2) by means of an additive method, finish-machining the piston (1), including the production of at least one annular groove (4) in the ring support (5) for receiving a piston ring.

In this way, it is possible to provide a piston (1) that has a greater strength in its piston upper part (2), which is subjected to high thermal and mechanical loads, than in its piston lower part (3), which is subjected to lower thermal and mechanical loads, and that permits greater freedom of manufacture in respect of the shape of the piston lower part (3).

Claims

1. A method for producing a piston for an internal combustion engine, the method comprising: producing a piston upper part including a piston top, at least part of a ring section, and at least part of a cooling channel; producing a piston lower part and closing the part of the cooling channel arranged in the piston upper part via an additive method; finish-machining the piston; and wherein finish-machining the piston includes producing at least one annular groove in a ring support for receiving a piston ring.

2. The method according to claim 1, wherein producing the upper piston part includes at least one of forging and casting the ring support into the piston upper part, and wherein the ring support forms the annular groove.

3. The method according to claim 1, further comprising, prior to producing the piston lower part via the additive method, facing the piston upper part at least on a side facing the piston lower part.

4. The method according to claim 1, wherein producing the piston lower part via the additive method includes forming a second part of the cooling channel in a region of the piston lower part, the second part of the cooling channel having a rougher surface than the part of the cooling channel arranged in the piston upper part, wherein the rougher surface of the second part of the cooling channel is produced via the additive method.

5. The method according to claim 1, wherein the cooling channel has a non-rotationally symmetrical shape with respect to at least one of a piston vertical axis and a piston transverse axis.

6. The method according to claim 1, wherein producing the piston lower part via the additive method includes producing, via the additive method, a second part of the cooling channel in a region of the piston lower part, the second part of the cooling channel including at least one of an oil-guiding structure, a jet splitter, a ramp, a cooling fin, and a constriction.

7. The method according to claim 1, wherein the piston upper part is produced from at least one of a steel alloy and an aluminum alloy.

8. The method according to claim 1, further comprising subjecting the piston to a heat treatment prior to finish-machining the piston.

9. The method according to claim 1, wherein the piston lower part is produced via a laser melting additive method.

10. The method according to claim 1, further comprising alfinizing the ring support in an aluminum melt prior to producing the piston upper part, and wherein producing the piston upper part includes casting the piston upper part.

11. The method according to claim 1, wherein producing the piston lower part via the additive method includes producing at least part of the ring section and producing at least one of (i) at least part of a piston pin boss and (ii) at least part of a piston skirt.

12. A piston for an internal combustion engine, produced via the method according to claim 1.

13. The method according to claim 1, wherein producing the piston upper part includes introducing the part of the cooling channel into the piston upper part via at least one of a forging method, a casting core method, and a chip-removing method.

14. The method according to claim 1, wherein the cooling channel includes a plurality of branches.

15. The method according to claim 1, wherein the piston includes a plurality of cooling channels including the cooling channel.

16. The method according to claim 1, wherein the cooling channel has a kidney-shaped cross-sectional profile.

17. The method according to claim 1, wherein producing the piston lower part via the additive method includes forming at least one cavity in at least one region of the piston lower part that is subject to lower mechanical loading relative to other regions of the piston lower part.

18. The method according to claim 1, wherein producing the piston lower part via the additive method includes forming at least one heat dissipation cavity in the piston lower part that is structured and arranged to guide an outflow of heat from the piston lower part.

19. The method according to claim 9, wherein producing the piston lower part via the laser remelting additive method includes: applying a layer of metal powder on the piston upper part; locally melting the layer of metal powder via laser radiation; and allowing the layer of melted metal powder to solidify and form a solid material layer.

20. The method according to claim 19, wherein producing the piston lower part via the laser remelting additive method further includes producing a plurality of additional solid material layers on the solid material layer to form the piston lower part.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The following figures are each schematic, wherein

[0026] FIG. 1 shows a sectional view through a piston produced by a method according to the invention,

[0027] FIG. 2 shows a first method step of the method according to the invention for producing a piston upper part,

[0028] FIG. 3 shows an illustration like that in FIG. 2, but with an additional cooling channel,

[0029] FIG. 4 shows an additive method according to the invention for producing a piston lower part on the cast or forged piston upper part.

DETAILED DESCRIPTION

[0030] In accordance with FIG. 1, a piston 1 according to the invention produced by a method according to the invention (compare FIGS. 2 to 4) for an internal combustion engine (not shown) has an piston upper part 2 and a piston lower part 3. At least one annular groove 4, which is formed or reinforced by means of a ring support 5, for example, is provided in the piston upper part 2. Moreover, the piston upper part 2 has a piston top 6 facing a combustion chamber (not shown) and a part 7 of a cooling channel 8. For the sake of simplicity, the top 6 is drawn straight according to FIG. 1, but can of course alternatively also have a combustion chamber recess.

[0031] The piston lower part 3 usually has at least a part of a piston skirt 9, which serves to guide the piston 1 in a cylinder, as well as a piston pin boss (not described specifically) for receiving a piston pin via which the piston 1 is connected to a connecting rod of the internal combustion engine. Likewise, at least parts 10 of the cooling channel 8 can be arranged in the piston lower part 3. According to FIG. 1, one part 7 of the cooling channel 8 lies above a parting plane 11 in the piston upper part 2, while the other part 10 is arranged below the parting plane 11 in the piston lower part 3.

[0032] Here, the piston upper part 2 is produced in a conventional manner, more specifically by means of a forging method or a casting method for example, while the piston lower part 3 is, according to the invention, produced by means of an additive method, e.g. a laser melting method. This offers the great advantage that the region, in this case namely the piston upper part 2, which is subjected to high mechanical and thermal loads during operation, can be formed from a comparatively solid material, while the piston lower part 3, which is subjected to lower thermal and mechanical loads, can be produced by means of the additive method.

[0033] In general, the piston 1 according to the invention is produced as follows:

[0034] First of all, the piston upper part 2 is produced, being forged or cast for example, wherein a ring support 5 can be forged or cast into the material 13 of the piston upper part 2. The piston upper part 2 has the piston top 6 and at least parts of a ring section 12 and at least part 7 of the cooling channel 8 (cf. FIG. 2).

[0035] In this case, the part 7 of the cooling channel 8 which is situated above the parting plane 11, i.e. in the piston upper part 2, can be produced by means of a corresponding punch during forging or by means of a corresponding casting core during casting of the piston upper part 2. As an alternative, it is of course also conceivable for the part 7 of the cooling channel 8 which is situated in the piston upper part 2 to be introduced into the material 13 of the piston upper part 2 by means of a chip-removing method or of milling or grinding after the production, in particular the casting or forging, of the piston upper part 2. This might be illustrated, for example, in the method step shown in FIG. 3, while FIG. 2 shows the casting or forging of the piston upper part 2 without the presence therein of part 7 of the cooling channel 8.

[0036] The piston upper part 2 is then turned over, whereupon the piston lower part 3 (cf. FIG. 4) is produced by means of an additive method and, at the same time, the cooling channel 8 can be closed in the process. In the additive production method, it is of course possible for the cooling channel 8 to be closed directly and in a level manner along the subsequent parting plane 11, or part 10 of the cooling channel 8 is provided in the piston lower part 3.

[0037] The great advantage of a piston 1 produced in this way is that the region of the piston 1 which is subject to the highest thermal and mechanical loads, namely the piston upper part 2, can be cast or forged from a comparatively strong material, e.g. an aluminum alloy or a steel alloy, while the piston lower part 3, which is exposed to lower thermal and mechanical loads, is produced by means of the additive method. Here, the additive method offers the great advantage that it is thereby also possible, for example, to produce cavities (not shown), particularly at points subject to low mechanical loading, it being possible, by means of these cavities in the piston lower part 3, to achieve not only a weight saving but also targeted heat dissipation since such cavities act as a heat conduction obstacle.

[0038] Before the additive production of the piston lower part 3, the piston upper part 2 can be faced, in particular face turned, at least on a side facing the piston lower part 3.

[0039] The part 10 of the cooling channel 8 which is situated in the region of the piston lower part 3 can have a rougher surface than the part 7 of the cooling channel 8 which is situated in the piston upper part 2, which surface is produced by means of the abovementioned additive method. A rougher surface of this kind can be produced only at very great expense, if at all, by means of casting cores or in a casting process, for example. By means of a rough surface of this kind, it is possible to achieve a larger surface area and hence improved heat exchange and improved cooling of the piston 1.

[0040] Moreover, it is conceivable that the part 10 of the cooling channel 8 which is situated in the region of the piston lower part 3 has at least one of the following components (not depicted), which are likewise produced by means of additive methods: an oil-guiding structure, such as a jet splitter, a ramp, a cooling fin or a constriction. By means of such constrictions, it is possible, in particular, to create a plurality of cooling channels 8, in particular mutually separate cooling channels 8, which can be produced only with difficulty, if at all, by means of conventional production methods, e.g. casting. This also concerns special cross-sectional shapes, for example, such as a kidney-shaped cross section of the cooling channel 8, which is possible only with very great difficulty, if at all, when casting by means of casting cores, e.g. salt cores, owing to the fragility of salt cores. By means of the additive method according to the invention, however, it is possible to produce the abovementioned components without problems, offering a further major advantage over conventional production of such a piston.

[0041] The piston upper part 2 can be cast, for example, in particular by means of gravity chill casting, wherein the ring support 5 is alfinized beforehand in an aluminum melt, e.g. in an aluminum-silicon melt, in order to be able to achieve a reliable bond with the material 13 of the piston upper part 2.

[0042] In this case, the parting plane 11 depicted in FIG. 1 can of course also be situated further up or further down, and therefore the piston lower part 3 can also include parts of the ring section 12, for example.

[0043] After the production of the piston lower part 3 and the closure of the part 7 of the cooling channel 8 which is arranged in the piston upper part 2 by means of an additive method, the piston 1 is finished, e.g. by turning, grinding and/or lapping, wherein the annular groove 4 is introduced into the ring support 5.

[0044] According to FIG. 2, the subsequent contour of the piston upper part 2 or of the piston 1 is illustrated by means of a broken line, as it is in FIG. 4 too. In the finish-machining of the piston 1, the material outside this broken line is thus removed, and the piston 1 is reduced to the outer contour thereof indicated by the broken line. In this step, it is of course also possible for machining, e.g. grinding or turning, of the piston lower part 3 to take place.

[0045] By means of the combination according to the invention of a conventional production method, in particular casting or forging, of the piston upper part 2 with additive buildup of the piston lower part 3, it is possible to create a combined piston 1 according to the invention which has considerable degrees of freedom, especially in the construction of the piston lower part 3. Moreover, of particular advantage here is the fact that the piston lower part 3 produced by means of the additive method can be thinned out in regions which it was not possible to make thinner in a legacy casting or forging process, for example, owing to the production method. These are, for example, regions of attachment between the piston pin boss and the piston top (currently solid) or between the skirt and the ring section (see monotherm). In principle, significant degrees of freedom in respect of configuration (shape, location, position) of the cooling channel are also obtained.