This application claims priority to German Patent Application No. 10 2013 220 256.3, filed Oct. 8, 2013, and International Patent Application No. PCT/EP2014/070166, filed Sep. 23, 2014, both of which are hereby incorporated by reference in their entirety.
The present invention relates to a casting mold for casting a piston for an internal combustion engine. The invention also relates to a piston cast in such a casting mold.
When casting internal combustion engine pistons, sufficient removal of air during the casting process must always be ensured, in order in particular to avoid undesirable cavities. In this context, a surface texture referred to as a waffle pattern has proven advantageous in the prior art, which surface texture makes it possible to improve not only the flowability of the casting material but also the removal of air. However, the known waffle pattern has the drawback that it must be introduced in the pull direction of the casting mold, since demolding of the cast piston which lies outside the waffle pattern drafts produces an undercut and can thus result in damage to the cast piston. Nonetheless, such surface textures are thoroughly desirable, and not only for improved removal of air but also for identifying the origin of the piston produced with this casting mold.
The present invention thus addresses the problem of specifying a casting mold which in particular has markedly increased flexibility with respect to a demolding direction.
This problem is achieved, according to the invention, with the subject matter of the independent claim(s). Advantageous embodiments form the subject matter of the dependent claims.
The present invention is based on the general concept of now providing, in a casting mold which is known per se for casting a piston for an internal combustion engine, in the region of a subsequent internal surface of a piston skirt, a surface texture which is formed by grooves and which permits demolding of the casting blank up to approximately 90° with respect to the surface texture, that is to say parallel to the surface texture. To that end, the grooves forming the surface texture have according to the invention a depth of 0.2 mm<t<0.5 mm, a width of 0.02 mm<b<0.05 mm and groove walls which are inclined outward at 0°<α<10°. The cross section of such a groove is thus trapezoidal. The grooves according to the invention are smaller and also steeper than previous grooves forming a surface texture and contribute to optimum de-airing of the casting mold during the casting process being possible, but the casting metal does not penetrate into the grooves where it would get caught in the manner of an undercut. Generally, the surface texture according to the invention is freely configurable, although it is important to ensure that the individual grooves can be de-aired. In that context, the surface texture can be used with or without shield gas, and with or without release agent or with or without a permanent coating, and also with a combination of a permanent coating and release agent. A particular advantage of the surface texture according to the invention having the above-described grooves is that this generates a surface texture with an appearance which is difficult to imitate, and which can serve as proof of origin.
In one further advantageous embodiment of the solution according to the invention, the grooves form a quadrilateral structure. Such a quadrilateral structure can for example be a rectangular structure or a rhombus structure, which can in particular also be termed a waffle pattern, and which permit demolding of the casting blank from the casting mold in almost all directions, that is to say up to approximately parallel to the surface.
In one advantageous development of the solution according to the invention, the grooves are created by means of a laser. The creation of such grooves and, also indirectly thereby, such surface textures by means of a laser represents a cost-effective and simultaneously high-quality production method.
Advantageously, a coating, in particular a release agent, is applied to the surface texture. Such a coating can at least partially narrow the entrance of the groove and thus make it more difficult for the casting material to penetrate therein. At the same time, the coating does not close the individual grooves, such that the removal of air can be ensured even with a coating, in particular a permanent coating or release agent. In order to increase the service life of the tools, suitable options include metallic or ceramic coatings or combinations thereof.
Further important features and advantages of the invention can be found in the subclaims, the drawings and the associated description of the figures with reference to the drawings.
Of course, the features mentioned above and those still to be explained below can be used not only in the combination indicated in each case, but also in other combinations or alone, without departing from the scope of the present invention.
Preferred exemplary embodiments of the invention are presented in the drawings and are described in greater detail in the following description, wherein identical reference signs relate to identical or similar or functionally identical components.
In the drawings, in each case schematically:
As shown in
The casting mold according to the invention no longer has this drawback since, in the case of this casting mold, the surface texture 5 is configured such that the casting material cannot penetrate into the surface texture 5, i.e. in particular not into the grooves 4, and thus permits a large degree of freedom with respect to the demolding direction, since no undercuts are produced. Nonetheless, the grooves 4 according to the invention, or the surface texture 5 produced thereby, also permit an improvement in the flowability and in the removal of air during the process of casting the piston 2.
Thus, with the casting mold 1 according to the invention, substantial advantages can be achieved, namely:
Number | Date | Country | Kind |
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10 2013 220 256 | Oct 2013 | DE | national |
Filing Document | Filing Date | Country | Kind |
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PCT/EP2014/070166 | 9/23/2014 | WO | 00 |
Publishing Document | Publishing Date | Country | Kind |
---|---|---|---|
WO2015/051991 | 4/16/2015 | WO | A |
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Number | Date | Country | |
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20160236273 A1 | Aug 2016 | US |