Casting tool and method for producing a piston for an internal combustion engine

Abstract

A casting tool for a piston may include a casting mold for forming a piston part from a casting melt and a casting head including a feeder for feeding the casting melt into the casting mold. The casting head may include a ring-shaped groove, and the groove may include an inner groove flank for forming the casting melt into a circumferential, ring-shaped sealing rib such that an inner rib flank of the sealing rib rests with a sealing effect against the inner groove flank when the casting melt solidifies in the groove. Additionally or alternatively, the casting head may include a ring-shaped collar, and the collar may include an outer collar flank for forming the casting melt to provide a circumferential, ring-shaped sealing groove such that an outer groove flank of the sealing groove rests with a sealing effect against the outer collar flank when the casting melt solidifies.

Claims

1. A method for producing a piston, comprising: introducing a casting melt into a casting head of a casting tool via an inlet; casting the casting melt, wherein casting the casting melt includes at least one of: forming the casting melt into a ring-shaped sealing rib via a ring-shaped groove of the casting tool that extends around a feeder of a thermally insulating material in the casting head at a radial distance therefrom, such that upon solidification of the casting melt an inner rib flank of the sealing rib rests with a sealing effect against an inner groove flank of the groove, wherein forming the casting melt into the ring-shaped sealing rib includes contacting the casting melt with the inner groove flank having a slope angle of 10° to 15° relative to a perpendicular to a surface of the casting head to facilitate sealing the casting melt along the inner rib flank; and forming the casting melt to provide a ring-shaped sealing groove via a ring-shaped collar of the casting tool that extends around the feeder in the casting head at a radial distance therefrom, such that upon solidification of the casting melt an outer groove flank of the sealing groove rests with a sealing effect against an outer collar flank of the collar, wherein forming the casting melt into the ring-shaped sealing groove includes contacting the casting melt with the outer collar flank having a slope angle of 10° to 15° relative to a perpendicular to a surface of the casting head to facilitate sealing the casting melt along the outer groove flank; inserting at least one porous insert into a casting mold of the casting tool, and infiltrating the at least one porous insert with the casting melt via exerting a pressure on the casting melt, wherein infiltrating the at least one porous insert includes providing a negative pressure via suction lines leading to the at least one porous insert to facilitate infiltration with the casting melt; and guiding the feeder in the casting head via a sleeve coupled to the casting head, the sleeve extending through the casting head from an interior of the casting mold outwards beyond the casting head, and wherein a pressurized gas line is coupled to the sleeve in a pressure tight manner for pressurizing the casting melt.

2. The method as claimed in claim 1, further comprising cooling at least one of the groove and the collar by circulating a cooling medium through at least one passage arranged in the casting head in a region of the at least one of the groove and the collar.

3. The method as claimed in claim 1, further comprising compressing the casting melt within the casting head.

4. The method as claimed in claim 3, wherein compressing the casting melt includes providing a casting pressure of between 0.35 bar and 20 bar after filling the casting mold with the casting melt and after partial solidification of the casting melt.

5. The method as claimed in claim 3, wherein compressing the casting melt includes pressurizing the casting mold via the pressurized gas line that opens into the feeder to exert the pressure on the casting melt for infiltrating the at least one insert with the casting melt while providing the negative pressure via the suction lines to facilitate infiltration.

6. The method as claimed in claim 1, wherein the casting melt includes molten aluminum containing 10% to 14% by weight of silicon and at least one of up to 6% by weight of copper, up to 3% by weight of nickel and up to 1% by weight of magnesium.

7. The method as claimed in claim 6, wherein a percentage of impurities present in the casting melt, defined by one or more low-melting elements with a melting point <490° C., is in each case less than 0.01%.

8. The method as claimed in claim 1, wherein casting the casting melt includes one of gravity diecasting and low-pressure diecasting.

9. The method as claimed in claim 1, wherein the casting melt includes molten aluminum containing 10% to 14% by weight of silicon.

10. The method as claimed in claim 1, wherein casting the casting melt includes forming the casting melt into the ring-shaped sealing rib via the ring-shaped groove, and further including compressing the casting melt via a pressurized gas within the casting head.

11. The method as claimed in claim 1, wherein casting the casting melt includes forming the casting melt to provide the ring-shaped sealing groove via the ring-shaped collar, and further including compressing the casting melt via a pressurized gas within the casting head.

12. The method as claimed in claim 5, wherein introducing the casting melt into the casting head includes communicating a free space within the feeder with an external environment via the pressurized gas line for pressure equalization.

13. The method as claimed in claim 1, wherein casting the casting melt includes both of forming the casting melt into the ring-shaped sealing rib via the ring-shaped groove and forming the casting melt to provide the ring-shaped sealing groove via the ring-shaped collar.

14. The method as claimed in claim 13, wherein the ring-shaped collar is disposed on the casting head radially inwards of the ring-shaped groove, and wherein the ring- shaped collar is arranged separately from the feeder.

15. A method for producing a piston, comprising: introducing a casting melt into a casting head of a casting tool via an inlet; casting the casting melt, wherein casting the casting melt includes at least one of: forming the casting melt into a ring-shaped sealing rib via a ring-shaped groove of the casting tool that extends around a feeder in the casting head at a radial distance therefrom, wherein forming the casting melt into the ring-shaped sealing rib via the ring-shaped groove includes contacting the casting melt with an inner groove flank of the ring-shaped groove having a slope angle of between 3° and 20° relative to a perpendicular to a surface of the casting head to facilitate sealing along the inner groove flank and an inner rib flank of the sealing rib upon solidification of the casting melt; and forming the casting melt to provide a ring-shaped sealing groove via a ring-shaped collar of the casting tool that extends around the feeder in the casting head at a radial distance therefrom, wherein forming the casting melt to provide the ring-shaped sealing groove via the ring-shaped collar includes contacting the casting melt with an outer collar flank of the ring-shaped collar having a slope angle of between 3° and 20° relative to a perpendicular to a surface of the casting head to facilitate sealing along the outer collar flank and an outer groove flank of the sealing groove upon solidification of the casting melt; and guiding the feeder in the casting head via a sleeve coupled to the casting head, the sleeve extending through the casting head from an interior of the casting mold outwards beyond the casting head.

16. The method as claimed in claim 15, wherein casting the casting melt includes both of forming the casting melt into the ring-shaped sealing rib via the ring-shaped groove and forming the casting melt to provide the ring-shaped sealing groove via the ring-shaped collar, and wherein the ring-shaped collar is arranged separately from the feeder.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Of the figures, which are each schematic:

(2) FIG. 1 shows a section through a casting tool according to the invention in accordance with a first embodiment, having a groove situated radially on the outside in the casting head of the piston casting tool,

(3) FIG. 2 shows a section through a casting tool according to the invention in accordance with a second embodiment, having a groove situated radially on the inside in the casting head of the piston casting tool,

(4) FIG. 3 shows a section through a casting tool according to the invention in accordance with a third embodiment, having an annular collar situated radially on the outside in the casting head of the piston casting tool, wherein the annular collar can also be formed on the inside, similarly to FIG. 2,

(5) FIG. 4A shows a detail A from FIGS. 1 and 2,

(6) FIG. 4B shows a detail B from FIG. 3,

(7) FIG. 5 shows an illustration like that in FIG. 1 but with a porous insert,

(8) FIG. 6 shows an illustration like that in FIG. 2 but with a porous insert,

(9) FIG. 7 shows an illustration like that in FIG. 3 but with a porous insert,

(10) FIG. 8 shows an illustration similar to that in FIG. 3 with an annular collar in the casting head, in which a recess shape precast by means of the annular collar is depicted.

DETAILED DESCRIPTION

(11) As shown in FIGS. 1 to 3 and 5 to 8, a casting tool 1 according to the invention for a piston 2 has a casting mold 3 for forming the piston 2 from a casting melt 4 (cf. FIG. 2). The casting mold 3 has a casting head 5 having a preferably centrally arranged feeder 6 for feeding the casting melt 4 into the casting mold 3, and a pressurized gas line 7 opening into the feeder 6 for the purpose of compressing the casting melt 4 within the casting mold 3 (cf. FIG. 2). The feeder can be formed from ceramic material, for example. According to the invention, a groove 8 arranged in the casting head 5, running in a ring shape around the feeder 6 and at a radial distance therefrom is provided, having an inner groove flank 9 (cf. FIG. 4a) for forming the casting melt 4 into a circumferential ring-shaped sealing rib 10 in such a way that an inner rib flank 11 of the sealing rib 10 rests with a sealing effect against the inner groove flank 9 when the casting melt 4 solidifies in the groove 8. As an alternative (or in addition) thereto, it is also possible to provide an annular collar 12 arranged in the casting head 5, running in a ring shape around the feeder 6 and at a radial distance therefrom (cf. FIGS. 3, 7 and 8), having an outer collar flank 13 for forming the casting melt 4 into a ring-shaped sealing groove 14 in such a way that an outer groove flank 15 of the sealing groove 14 rests with a sealing effect against the outer collar flank 13 when the casting melt 4 solidifies and shrinks. This has the major advantage that the feeder 6 is not subjected to a load by shrinkage of the casting melt 4 as the casting melt 4 solidifies. At the same time, premature separation of the piston 2 is prevented. After the removal of the piston 2 from the mold, the sealing rib 10 and the sealing surfaces of the sealing groove 14 are removed by turning during the production of the final shape of the piston head.

(12) According to FIG. 1 and FIG. 5, the groove 9 or the collar 12 is arranged radially on the outside, whereas, according to FIGS. 2 and 6, it is arranged radially on the inside, i.e. is at a shorter radial distance from the feeder 6 than the groove 9 shown in FIGS. 1 and 5. As an alternative, it is, of course, also possible to provide an annular collar 12 instead of the groove 9, as illustrated in FIGS. 3 and 7. Here too, it is conceivable for the annular collar 12 to be arranged further out or further in, although there is always a spacing with respect to the feeder 6.

(13) In this case, the groove flank 9 or the collar flank 13 can have a slope angle α of between 3° and 20°, preferably from 10° to 15°, relative to a perpendicular 16 to a surface of the casting head 5. On the one hand, the slope angle α selected should be small enough, with regard to the friction coefficients, to ensure reliable retention of the shrunk-on casting on the sealing surface. On the other hand, the slope angle α should still be sufficiently large to allow easy removal of the fully cast piston 2. This geometrical configuration furthermore ensures that, for its part, the sealing rib 10 or sealing groove 14 formed after the hardening of the casting melt 4 defines an inner rib flank 11 or outer groove flank 15 which rests flat against said inner groove flank 9 or outer collar flank 13 and thus seals off the casting head 5 or head die against premature and unwanted escape of the casting pressure and hence allows correct infiltration of the porous inserts.

(14) By means of the casting tool 1, a piston 2 can be produced as follows: first of all, the casting melt 4 is fed via the inlet 21 into the casting head 5 and, via the latter, into the casting mold 3 of the casting tool 1, wherein the casting melt 4 is subjected to pressure within the casting head 5 by means of the pressurized gas line 7 opening into the feeder 6 in order to avoid the formation of shrinkage cavities and in order to infiltrate porous cast-in parts. As the casting melt 4 is poured into the casting mold 3, it also enters the groove 8 running in a ring shape around the feeder 6 in the casting head 5 and at a radial distance therefrom and solidifies to form a ring-shaped sealing rib 10, wherein the respective inner rib flank 11 of the sealing rib 10 rests leaktightly against the inner groove flank 9 of the groove 8 (cf. FIGS. 1, 2, 4a, 5 and 6). As an alternative, the casting melt 4 can also solidify in such a way at the annular collar 12 running in a ring shape around the feeder 6 in the casting head 5 and at a radial distance therefrom, forming a ring-shaped annular sealing groove 14, that an outer groove flank 15 of the sealing groove 14 rests with a sealing effect against the outer collar flank 13 of the annular collar 12.

(15) In this case, the casting melt 4 should be subjected to pressure after the filling of the casting mold 3 and before the complete solidification of the casting melt, at the earliest after the filling of the casting mold 3 and after the partial solidification of an edge shell of the piston and partial areas of the inlet 21. In order to be able to reinforce regions subject to particularly high loads, e.g. a recess edge 17 or a ring support region of the piston, provision can be made to insert a porous insert 18 at that point (cf. FIGS. 5 to 8). Moreover, the piston can contain further inserts that do not require infiltration, e.g. ring supports or salt cores for the formation of cooling passages.

(16) The insert 18, in particular a ring support or a recess edge protector, can, for example, be porous and infiltrated by means of pressure exerted on the casting melt 4. At the same time, infiltration can be assisted by the production of a vacuum by means of suction lines 20. A near-eutectic aluminum alloy containing 10% to 14% by weight of silicon and/or furthermore up to 6% by weight of copper, up to 3% by weight of nickel and/or up to 1% by weight of magnesium is particularly suitable for the casting melt 4. Moreover, it is possible, for the purpose of increasing hot strength, to add further elements, e.g. V and Zr (in each case <0.2%), and, for grain refinement, Ti (<0.2%) and P (<0.01%), for example. A near-eutectic or even hypoeutectic configuration of the AlSi alloys has proven advantageous in terms of suitability for infiltrating porous inserts. Moreover, there is a preference for a casting melt which is largely free from impurities due to low-melting elements with a melting point <490° C., e.g. Pb, Bi, Sn, Zn, wherein the concentrations of these elements individually are each below 0.01%.

(17) Casting of the pistons 2 is performed by the gravity diecasting or low-pressure casting method, and solidification of the casting melt in the casting mold takes place, in particular, under a pressure of between 0.3 bar and 20 bar.

(18) In a manner known per se, the casting melt 4 described is introduced into the casting tool 1 via the inlet 21, with the result that the free regions of the casting mold 3 around a core 19, which subsequently forms the small end bearing eye of the piston 2, fill up all around with casting melt 4. The specific embodiment of the casting head 5 and the feeder 6 allows the formation of the sealing rib 10 or sealing groove 14 holding the feeder contents in position when, to achieve short cycle times, the casting tool is opened in accordance with the method at a time at which the contents of the feeder 6 may still be partially liquid internally. In this case, the stabilizing effect of the sealing rib 10 or sealing groove 14 is assisted by the groove 8 essential to the invention surrounding the feeder 6 in the casting head 5 or, in the complementary embodiment, by the annular collar 12, within which the casting melt 4 solidifies to form the ring-shaped sealing rib 10 or sealing groove 14.

(19) For this purpose, the casting melt 4 can rise to a desired extent within the feeder 6, giving rise to a free space within the feeder 6 above the introduced casting melt 4 after feeding of casting melt 4 has ended, via which free space the casting melt 4 can be subjected to a gas pressure of between 0.3 bar and 20 bar. It has proven advantageous to configure the casting head 5 of the piston casting tool 1 in such a way that the feeder 6 is guided at the outside diameter in the casting head 5 by a sleeve 22, to which the pressure line 7 is flanged in a pressure tight manner. The gas for pressurization is fed to the feeder 6 via the pressurized gas line 7, which is open to the environment during the process of introducing the casting melt 4, thus allowing pressure equalization to take place (cf. FIG. 2). For the sake of simplicity, the pressurized gas line 7 is depicted only in FIG. 2, and the inlet 21 and the sleeve 22 are depicted only in FIG. 8, while it is clear that they can also be present in other embodiments. As shown in FIG. 8, the casting head 5 may have cooling passages 23 arranged to carry a cooling medium in a region of the groove 8 and/or the collar 12 for cooling the groove 8 and/or the collar 12.