MX2008002432A - Method, production line, and piston blank used for the production of a monolithic piston for combustion engines, and piston for combustion engines - Google Patents

Abstract

Disclosed are a method and a production line that make it possible to produce near net-shaped piston blanks (R) which have to be cut only slightly during the final machining process. In order to be able to do so, the piston shaft (KS) of the piston blank (R) is made using reverse extrusion while a groove (H) is created already on the piston blank (R) by means of a shaping process. For this purpose, a special forging tool is provided which acts upon the piston blank (R) once the piston shaft (KS) has been made in such a way that said groove (H) is formed no later than during the subsequent shaping of the piston head (B). The invention allows the weight of a piston to be reduced significantly compared to conventionally produced forged pistons.

Description

METHOD, PRODUCTION LINE AND ROUGH PISTON TO PRODUCE A MONOLITHIC CONFIGURATION PISTON FOR COMBUSTION ENGINES INTERNAL, AND PISTON FOR INTERNAL COMBUSTION ENGINES FIELD OF THE INVENTION The invention relates to a method for producing by means of forging and final finishing machining a piston of monolithic configuration for internal combustion engines comprising a piston shaft, a piston base supported by the piston shaft as well as at least one throat formed laterally on a peripheral surface of the piston. The invention furthermore relates to a production line for carrying out this method, to a crude piston produced in monolithic form by forging for the production of a piston for internal combustion engines, and to a finished processing piston configured accordingly . BACKGROUND OF THE INVENTION Pistons for internal combustion engines are usually produced by casting and forging processes.

The production by casting techniques has the advantage that it allows the production of pistons of complex shape with little weight. However, for this purpose it is necessary to accept a considerable manufacturing cost. This is particularly true if, as a material, a steel material must be used to produce pistons that are suitable for particularly high stresses. REF .: 190215 Forged steel pistons can be configured in one piece as well as consisting of two or more parts, depending on their size and their purpose of application. In the case of multi-part pistons that are composed of two or more parts, the individual parts are usually joined to each other by positive and non-positive joining processes so as to withstand the forces acting on them in the practical application. For this purpose, for example, welding or conventional screwing of the individual parts of the piston are suitable. An example of a multi-part piston for an internal combustion engine is known from DE 102 44 513 A1. On the one hand this piston has a steel-forged upper piston part in which a combustion concavity is formed, ring wall and a cooling channel configured in the manner of a throat. On the other hand, the piston has a lower piston part that constitutes the piston shaft that supports the upper piston part, and in which cubes are configured to receive a piston pin that connects the piston with a connecting rod. To produce this piston, the upper piston part and the lower piston part are preformed by forging in separate processing steps, and then machining is finished by chip removal. The finishing machining of the upper piston part also comprises the machining with chip removal of the wall sections that limit the cooling channel by means of which a positive connection with the lower piston part is then produced by welding or brazing. It is true that a structure of several parts of this type can give a complex shape to a piston. However, apart from the problems that result from the multiplicity of parts in relation to the capacity of effort, also the production expense that it represents is considerable. In the production by means of the forging technique of monolithic pistons constituted in one piece for internal combustion engines, usually a raw piston is produced first, which is finished processing by machining with chip removal. Usually all the concavities to be formed on the peripheral surface of the piston, such as for saving in weight, for improving the deformation behavior or the grooves that serve as cooling channels, are only produced in the machining step with chip removal. An example of a production of this type of a monolithic piston is given in DE 100 13 395 Al. According to the method described herein, a rough piston is first forged by casting in a forged billet in the shape of pin, called billet, from one of its front faces, a cavity whose outer wall constitutes the piston axis of the raw piston. A recess is then drilled in the wall of the piston shaft. For this purpose a milling machine or lathe blade is applied from the outside in a lateral direction to the peripheral surface of the raw piston. Despite the advantages obtained by the monolithic formation compared to a multi-part embodiment, the monolithic pistons produced in the known manner have the disadvantage that they are generally heavier than the comparative pistons produced by casting technique. Additionally, the technical production expense is high in machining with chip removal, since in the areas of the fire fence configured on the peripheral edge of the base of the piston and the piston shaft it is necessary to eliminate a large amount of material through chip removal to produce the required finished form. This high manufacturing expense causes high production costs. BRIEF DESCRIPTION OF THE INVENTION From the state of the art summarized in the foregoing, the object of the invention was to create a method and a production line that allow an economical production of monolithic pistons using forging processes. In addition, a one-piece forged rough piston that can be produced economically and a piston finished processing that can also be produced economically. In relation to the method for, by means of forging and final finishing machining, producing a piston of monolithic configuration for internal combustion engines comprising a piston shaft, a piston base supported by the piston shaft and at least one throat formed laterally in a piston. peripheral surface of the piston, the problem is solved because, according to the invention, the forge comprises the following stages of work: By means of a die and using the principle of regressive extrusion, in a forge billet is formed from one of its front faces a cavity whose outer wall formed by a flow of material against the direction of action of the die constitutes the axis of the piston. Next, a forging tool forming the throat acts on the peripheral surface of the forging billet on which the throat must be provided. - Starting from the other front face of the forging billet, the base of the piston is formed by an upsetting operation, keeping the action of the forging tool that configures the throat in place. Analogously, the problem mentioned above in relation to a production line for producing a piston of monolithic configuration for internal combustion engines comprising a piston shaft, a piston base supported by the piston shaft as well as at least one throat formed laterally on a peripheral surface of the piston is solved by the fact that of According to the invention, such a production line comprises a forging device provided to form a cavity in the front face of a forging billet, which device includes a die having a centrally disposed die part surrounded by a slit. annular, which in a forging run enters the forge billet, so that with a forging stroke the material of the forging billet enters the annular gap according to the principle of the regressive extrusion in the opposite direction to that of the stroke of the die, and an additional forging device including a housing for the forging billet formed in the first forging device, a Forging tool that configures the throat, an adjusting device for applying the forging tool that configures the throat to the peripheral surface of the forging billet held in the housing, as well as a die to form the base of the piston by upsetting the billet of Forge from its front face opposite the cavity. The method according to the invention and the line of production equipped in accordance with the invention allow the production of crude pistons having dimensions close to the final ones, which in the course of the final finishing machining need only be processed to a lesser extent with chip removal. This is achieved on the one hand by the fact that the piston axis of the raw piston is produced by regressive extrusion. In this deformation method the material of the forging billet flows into a slit of suitable configuration against the direction of travel of the forging die used for the deformation, so that a particularly large shape fidelity is obtained. On the other hand, in accordance with the invention a throat is already produced in the raw piston part by a deformation operation. For this purpose a special forging tool is provided which after the production of the piston shaft acts on the raw piston so that it forms this throat at the latest during the next formation of the piston base. The formation of the throat according to the invention that already takes place in the course of the forging allows a remarkable reduction in the weight of a piston that is produced according to the invention in comparison with the forging pistons that are produced in conventional manner , since the forging billet in each available case no longer needs to include the existing volume in the throat area. In addition the expense is reduced to a minimum for the production of the throat, since in the course of finishing machining with chip removal in any case it is only necessary to eliminate minimum amounts of material in the area of the throat. During the execution of the method according to the invention, the forging tool forming the groove can be applied so as to shape the groove in the forging billet by active material displacement. For this purpose, the corresponding forging tool can mold the throat directly on the peripheral surface of the forging billet by a corresponding deformation operation before the piston base is produced. During the formation of the piston base the tool producing the throat remains in its molding position so that the shape of the throat also lasts during the deformation operation which is carried out to produce the piston base. A particularly favorable development in the technical aspect of production of the method according to the invention, which additionally allows to forge rough pistons whose dimensions only differ minimally from the final finished shape of the piston to be produced is characterized by that after the production of the piston shaft and prior to the action of the forging tool that molds the throat, the forge billet has a larger diameter in the area of the piston axis that in its section so far has not yet deformed, so that the forging tool that molds the throat can be applied in the transition area between the piston shaft and the section so far not yet deformation of the forge billet without having to apply greater deformation forces to the forging billet. In the subsequent upsetting which is carried out to produce the base of the piston, the upset material of the forging billet is fitted to the forging tool which is held in the position that it previously adopted, so that in the rough finished forging piston it is molds a throat that corresponds particularly closely to the dimensions of the tool. If in the formation of the piston axis greater degrees of deformation must be overcome, then it was found convenient to form the cavity of the piston shaft in at least two stages. For this purpose, for example, the cavity can be preformed in a previous step and then finished forming with the formation of the piston shaft by the use of regressive extrusion. Similarly, it may be advantageous if, in a production line according to the invention, the forging device for forming the cavity in the forging billet is preceded by a forging device for preforming the cavity. A rough forged piston and configuration monolithic according to the invention for producing a piston for internal combustion engines which is provided with a piston shaft, a piston base supported by the piston shaft and at least one throat molded laterally on a peripheral surface of the crude piston is characterized because the throat differs by a machining supplement of maximum 4 mm of the corresponding finished dimension of the piston that must be produced from the raw piston. In a raw piston formed in this way the expense for finishing machining with chip removal is reduced to a minimum. Depending on the finishing accuracies required in each case, it is possible that even in the area of the throat, the subsequent machining with chip removal can be completely dispensed with. Preferably the proximity to the final dimensions of the raw piston which are obtained according to the invention is not only limited to the region of the throat. Rather, it is favorable that its diameter in the region of the piston axis should also differ only by a maximum of 3 mm machining of the corresponding final dimension of the piston to be produced from the raw piston. It is also favorable that in the raw piston according to the invention the piston base differs by a maximum of 4 mm machining of the corresponding final dimension of the piston to be produced from the raw piston.

The pistons according to the invention for internal combustion engines that are produced from a crude piston that is produced monolithic by forging and that comprises a piston shaft, a piston base supported by the piston shaft and at least one throat that is molded laterally on a peripheral surface of the piston are characterized in that the extension of the fibers of the texture on the surface of the throat corresponds to the extension of the fibers that the forging billet has before the finishing machining at a distance of at most 3 mm from the surface of your throat. By virtue of the close proximity of the dimensions of a raw piston obtained and produced according to the invention to the final dimensions of the piston that must be produced with it, in the finishing machining it is only necessary to eliminate a small amount of material , particularly in the throat region. Correspondingly, the texture of the piston in this zone has an extension of fibers in which in any case the fibers that are adjacent to the surface of the crude piston are cut or interrupted. BRIEF DESCRIPTION OF THE FIGURES Below, the invention is explained in more detail by means of figures that represent an embodiment. They show in each case in schematic form in a longitudinal section: FIGURES la, Ib a forging device for preforming a forging billet in two operating positions; Figures 2a-2d a forging device for forming the piston shaft in four operating positions; Figure 3 a forging billet in an intermediate stage of production; Figures 4a-4b a forging device for forming the throat and the base of the piston; Figure 5 a rough piston finished forging. DETAILED DESCRIPTION OF THE INVENTION The forging device VI shown in FIGS. 1a, 1b, for preforming a cavity A in a cylindrical forging billet S consisting of forging steel comprises a matrix 1 in which an open housing 2 is formed for the Forge S billet. The housing 2 has in its lower region a section 2a in which the diameter of the housing 2 corresponds to the diameter of the forging billet S. The section 2a is followed upward by an enlarged section 2b in the form of a cup, so that the opening diameter of the housing 2 is greater than the diameter of the forging billet S. The forging device VI also comprises a die 3 that for a forging stroke moves in the direction of the die 1 from a rest position disposed above the die 1. On its face facing the die 1 the die 3 has a 4 punching stamp with bulging convex that is arranged concentric to the housing 2 of the matrix 1. At the bottom of the matrix 1 is the head of a dumper with which the forging billet S is ejected from the housing 2 of the matrix 1 after the cavity A has been preformed To preform the cavity A, the billet S of cylindrical forging obtained by dividing a bar material not shown, heated to the forging temperature, is placed in the housing 2 of the matrix 1 (figure 1). The die 3 then carries out a forging stroke in which the stamp punch 4 penetrates the front face of the forging billet S associated with the die 3. The section of the forging slab S arranged in the section is thus enlarged. 2b enlarged top of the die 2, so that its peripheral surface comes in contact with the inner surface of the section 2b and by the die punch is formed in the billet S of forging a preform Av of the cavity A (figure Ib) . The forging device V2 shown in FIGS. 2a-2d to finish the forging of the cavity A also comprises a die 5 having a housing 6a formed in a holder 6 for the forging billet S formed in the device VI. The height and diameter of the housing 6a correspond to the height and diameter of the section without deformation of the billet S of forging. Additionally, the forging device V2 is equipped with a die 7 which, on its face dedicated to the matrix 5, has a convex and, in the rest, cylindrical convex punch 8 which is arranged concentric with respect to the opening of the housing 6a. The external shape of the tip of the stamp punch 8 corresponds to the internal shape of the cavity A that must be manufactured in the forging billet S. The stamp punch 8 is surrounded by a concentric alignment ring 9 with respect to the stamp punch 8 which likewise is held in the die 7, whose opening diameter is greater than the external diameter of the cylindrical section of the stamp punch 8. Simultaneously, the opening diameter of the ring 9 and the external diameter of the cylindrical section of the stamp punch 8 are larger than the diameter of the undistorted section of the forging billet S seated in the housing 6a. In this way, an annular gap 10 open towards the die 5 is formed between the ring and the punch 8, the diameter of which is also greater than the diameter of the undistorted section of the forging billet S. In its section protruding from the annular slit 10 towards the die 6 a rest 11 is formed in the ring 9, so that the opening diameter of the ring 9 it expands once more in this area compared to its opening diameter in the area of the annular gap. The opening diameter of the enlarged ring 9 in the resting area 11 is adapted to the external diameter of the fastener 6 which has a cylindrical shape, so that with its wider diameter zone the ring 9 laterally surrounds the fastener 6 when the die reaches the final position of the forging race. The height of the annular gap 10 is greater than the forging stroke H carried out by the die 7. Simultaneously the forging stroke and the rest position 11 of the ring 9 are provided so that when the die 7 is in the The final position of the forging stroke is a distance between the resting surface of the ring 9 opposite the front face of the fastener 6. In this way, when the die 7 is in the final position of the forging stroke it is formed in the rest area 11 a surrounding annular space 12, open towards the annular gap 10 and towards the forging bilge S seated in the housing 6 a of the fastener 6. The space 12 serves, during the deformation of the forging billet S, to receive the material surplus that exists in the preformed zone of the forging billet S that can not be accommodated by the volume of the annular slit 10, while guaranteeing a safe filling of the annular slit 10. In those piston shapes in which, when the forging slab S is formed, the annular gap 10 is surely filled with material without the existence of excess material, it is possible to do without the formation of the space 12, and therefore of the formation of the Walloon K in the billet S of forge. To finish forming the cavity A, the forging billet S preformed in the device VI is placed with its non-deformed part in the housing 6a of the fastener 6, so that the section of the expanded forging billet S during the preform protrudes free of the bra 6 (figure 2a). The die 7 then executes a forging stroke in which the tip of the stamp punch 8 enters the preform Av of the cavity A and first laterally displaces the material from the preformed section of the forging billet S until it meets the inner surface of ring 9 (figure 2b). By virtue of which the material of the forging billet S can no longer be deflected laterally, it flows according to the principle of the backward extrusion against the direction X of the stroke of the die 7 into the annular gap 10 until it is filled completely. The material of the forging billet S simultaneously fills the space 12 (Figure 2c). In this way, at the end of forming the cavity A in the forging slab S, in addition to the cavity A, a cylindrical piston axis KS formed by the material that penetrated into the annular gap 10 and which surrounds the cavity is formed as an external wall. TO.

Simultaneously, after finishing forming the cavity A, the forging slab S has, formed in space 12, a surrounding K-flange projecting laterally from the piston axis KS in the region of the transition from the KS axis of the piston to the part so far without deforming the forging slab S. To eject the forging billet from the housing 6a of the fastener, a bolt is again provided, the head of which rests on the base of the housing 6a (FIG. 2d). Forging devices VI and V2 can be together part of a forging press that is not represented mostly in this document. After forming the cavity A the Walloon K is separated from the Forge billet S in a deburring device that is not shown in this document. The free forging billet S of the flange K obtained after this is shown in FIG. 3. The device for separating the flange K from the forging billet S can be part of a second forging press additionally comprising a V3 device. forging that is provided to finish forging the rough piston R that must be formed from the forging billet S. The forging device V3 comprises a clamping mandrel 14 mounted on a base plate 13 whose external shape conforms to the shape of the cavity A formed in the forging billet S. Simultaneously the height of the clamping mandrel 14 is greater than the height of the piston axis KS.

The forging device V3 further comprises two forging tools 15, 16 for forming a throat H in the raw piston R to be produced. These forging tools 15, 16 are in each case formed in the form of a half shell and move from a lateral direction against the clamping mandrel 14 by means of an adjustment drive 17, 18, so that in their working position they enclose the circumference of the chuck 14 and hold the forging billet S on the chuck 14. The forging tools 15, 16 have on their inner surface associated with the holding mandrel 14 a horizontally extending projection 19 extending radially over the entire width or the entire circumference of the respective inner surface. The depth by which the shoulder 19 protrudes in each case from the inner surface of the forging tools 15, 16 corresponds to the depth of the molding Kue which, in preforming the cavity A, is formed in the area of the external side of the billet S of forge in the transition from its non-deformed section to the deformed section. Simultaneously both the shape of the free end of the shoulder 19 and its height on the base plate 13 are provided so that with the forging billet S placed with the cavity A on the chuck 14 and the forging tools 15, 16 in working position, its shoulders 19 adhere to the Kue molding. The cross section shape of the shoulder 19 corresponds to the cross-sectional shape of the throat H to be formed in the crude piston R. By means of a rest 20 projecting in each case at the base of the forging tools 15, 16 in the direction of the clamping mandrel 14, the inner surfaces and the shoulders 19 of the forging tools 15, 16 are kept in the operating position at a distance from the clamping mandrel 14 corresponding to the respective nominal external diameter of the piston axis KS and of the base B of the piston. Simultaneously the height of the rest 20 on the base plate 13 is provided so that the height between the rest 20 and the shoulder 19 corresponds to the nominal height of the piston axis KS. For the upsetting of the forging billet S, the device V3 finally comprises a die 22 supported by a yoke 23 and aligned concentrically with respect to the chuck 14. On its front face associated with the chuck 14 the die 22 has protuberances by means of which the shape of the concavities M of the combustion chamber that must be formed in the base B of the piston is determined. In order to finish forging the rough piston R the forging billet S is placed with its cavity A on the clamping mandrel 14 when the forging tools 15, 16 are located remote from the clamping mandrel 14 and the die is in rest position. 22, so that the undistorted part of the forging billet S points freely in the direction to the die 22. Then the forging tools 15, 16 are moved to their working position in which they are pressed against the forging billet S which is on the clamping mandrel 14, so that the finished piston KS axis of forming is held in a defined position and the shoulders 19 sit flush in the molding Kue in the transition to the undeformed part of the forging billet S (figure 4a). Then the yoke 23 with the die 22 carries out a forging stroke by means of which the unformed part of the forging slab S is stressed in the direction of the clamping mandrel 14, forming the piston base B of the piston R in stupid. The material now stressed from the previously undistorted part of the forging billet S is now fitted to the shoulders 19, so that the throat H is dimensionally dimensioned in the area of the transition from the piston axis KS to the base B piston (figure 4b). After the forging stroke is completed, the die 22 and the forging tools 15, 16 are moved back to their rest position, so that the finished rough piston R (FIG. 5) can be removed from the device V3. The dimensions of the finished rough piston R differ from the final dimensions of the piston not shown here, which must be finished from the crude piston R, by a Zl machining insert. only 3 mm in the region of the throat bottom of the throat H, by a machining insert Z2 of only 2 mm in the region of the transition from the throat H to the adjoining peripheral surfaces of the piston base B and of the shaft KS piston, for a machining fee Z3 equal to only 2 mm in the region of the peripheral surfaces of the piston KS axis, for a machining fee Z3 equal to only 2 mm in the region of the front surface of the base B of piston and for a machining supplement Z3 again only 3 mm in the region of the peripheral surface of the base B of the piston. The final finishing machining with chip removal of the R-piston R is carried out in a manner known per se with conventional machining devices. The devices VI, V2 and V3 as well as the devices that are required for the finishing machining with chip removal are part of a production line that is not represented mostly, in which pistons are produced from the forging billets S finished processing. For this purpose, in addition to the forging devices VI, V2 and V3 presented here and the aforementioned devices for finishing machining with chip removal, the production line can, if necessary, comprise respectively devices for thermal treatment and cleaning. Since during the formation of cavity A in the Forging device VI according to the invention the forging of the forging billet S is carried out in such a way that the molding Kue is formed in the region of the transition between the non-deformed zone at the end of the processing in device VI and the axis KS of piston of the forging billet S, then the throat H can be molded simultaneously with the molding of the piston base B. In addition to the advantages of great closeness to the final dimensions and fidelity of form in comparison with the conventional form of production, in this way it is possible to save at least one process step that until now was necessary to form the throat in the piston in stupid. As a result, the invention thus allows a high productivity by shortening the cycles with little loss of temperature of the forged parts.

Reference symbols VI Forging device 1 Matrix 2 Housing 2a Housing lower section 2 2b Enlarged shell-shaped section of housing 2 3 Die-cutter 4 Die-cutting punch V2 Forging device Matrix 6 Fastener 6a Fastener housing 6 7 Die 8 Stamp punch 9 Ring 10 Annular ridge 11 Rest 12 Space X Die stroke direction 7 V3 Forging device 13 Base plate 14 Clamping mandrel 15,16 Forging tools 17 , 18 Adjustment drives 19 Highlight 20 Rest 22 Die 23 Yoke A Cavity Av Preform of the cavity AH Throat K Walloon Kue Molding in the transition between the undeformed and deformed part of the forging S billet after produced cavity A KS Piston shaft M Combustion chamber depressions R Raw piston S Forge billet It is noted that in relation to this date, the best method known to the applicant to carry out the aforementioned invention, is that which is clear from the present description of the invention.

Claims (14)

1. CLAIMS Having described the invention as above, the content of the following claims is claimed as property: 1. Method for producing, by forging and subsequent finishing machining, a piston of monolithic configuration for internal combustion engines comprising a piston shaft, a piston base supported by the piston shaft as well as at least one throat that is formed laterally on a peripheral surface of the piston in the transition zone from the piston shaft to the base of the piston, characterized in that the floor comprises the following stages of operation: - by means of a die and using the principle of regressive extrusion, a cavity is formed in a forge billet from one of its front faces whose outer wall formed by a flow of material against the direction of action of the punch constitutes the axis of the piston, - then a forging tool that configures the throat element to ctúa on the peripheral surface of the forge billet on which the throat must be provided, - from the other front face of the forge billet the base of the piston is formed by an upsetting operation, keeping the action of the tool standing of forging that configures the throat.
2. 2. Method of compliance with any of the previous claims, characterized in that the forging tool forming the throat forms the throat in the forging billet by material displacement.
3. Method according to any of the preceding claims, characterized in that after the production of the piston shaft and prior to the action of the forging tool forming the throat _ the forging billet has a larger diameter in the axis region piston in a section that until now is still undeformed.
4. Method according to claim 3, characterized in that the forging tool forming the groove is applied in the region of the transition between the piston axis and the previously undistorted section of the forging billet.
5. Method according to any of the preceding claims, characterized in that the molding of the cavity is carried out in at least two stages.
6. 6. Method according to claim 5, characterized in that the cavity is preformed in a first preliminary stage and then finished molding using regressive extrusion with formation of the piston axis.
7. Method according to any of the preceding claims, characterized in that a Walloon which is formed in the forge billet during the formation of the cavity is separated before finishing the rough piston.
8. 8. Production line for producing a piston of monolithic configuration for internal combustion engines comprising a piston shaft, a piston base supported by the piston shaft as well as at least one throat formed laterally on a peripheral surface of the piston, characterized because - it comprises a forging device provided to form a cavity in the front face of a forge billet, which device includes a die having a centrally arranged die part, surrounded by an annular slit, which in a forging stroke penetrates into the forge billet, so that with a forging stroke the material of the forging billet enters the annular gap according to the principle of the regressive extrusion in the opposite direction to that of the die stroke, and - comprises a forging device additional that includes a housing for the forging billet formed in the first forging device, a forging tool that shapes the gar hook, an adjusting device for applying the forging tool that configures the throat to a peripheral surface of the forging billet held in the housing, as well as a die to form the base of the piston by upsetting the forging billet from its face frontal opposite the cavity.
9. 9. Method according to claim 8, characterized in that the forging device for molding the cavity in the forging billet is preceded by a forging device for preforming the cavity.
10. 10. Method according to claim 8 or 9, characterized in that it comprises a device for separating a flange formed in the forging billet in the first forging device.
11. 11. Forged and monolithically shaped raw piston for the production of a piston for internal combustion engines, with a piston shaft, a piston base supported by the piston shaft and at least one throat formed laterally on a peripheral surface of the piston. rough piston, characterized in that the throat differs from the corresponding finished dimension of the piston that must be produced from the raw piston by a machining fee of 4 mm maximum.
12. 12. Raw piston according to claim 11, characterized in that its diameter in the region of the piston axis differs from the corresponding finished dimension of the piston to be produced from the raw piston by a machining insert of max. 3 mm. .
13. 13. Raw piston according to claim 11 or 12, characterized in that the base of the piston differs from the corresponding finished dimension of the piston to be produced from the raw piston by a machining feeder of 4 mm maximum.
14. 14. Piston for internal combustion engines, produced from a crude piston that is produced monolithic by forging with a piston shaft, a piston base supported by the piston shaft and at least one throat formed laterally on a peripheral surface of the piston, characterized in that the extension of the fibers of the texture on the throat surface is analogous to the extension of the fibers that the forging billet has previously to the finishing processing at a maximum distance of 3 mm from the surface of its throat.