Punching tool of a sintering press and method therefor

Abstract

The present invention relates to a punching tool of a sintering press, comprising at least one lower punch and an upper punch, a first punch of the upper punch and/or lower punch having a top piece that is asymmetric with respect to an axial axis of the punch press. The first punch has a geometry which widens from the top piece towards a base and is also asymmetric with respect to the axial axis of the punch press. The invention further relates to a method for pressing at least one powdery material to a green body in a sintering press.

Claims

1. A punch tool of a sintering press, the punch tool comprising at least one lower punch and one upper punch, wherein a first punch of the at least one upper punch and/or at least one lower punch has a head piece that is a portion of the first punch that is receivable into a die cavity to form a surface of a powder metal part therein and in which the head piece is asymmetrical with respect to a central axis along a pressing direction of the sintering press so that, within the first punch, an axial force acting during pressing acts spaced apart from the central axis along the pressing direction of the sintering press initiates a bending moment in the first punch, wherein the first punch has a geometry which conically widens from the head piece to a foot piece and which is also asymmetrical with respect to the central axis along the pressing direction of the sintering press and which asymmetrical widening is utilizable to compensate a lateral offset of the first punch with respect to the central axis along the pressing direction of the sintering press during pressing wherein the geometry of the first punch includes a conical section having a conical ring shape providing the asymmetrical widening and further includes a straight section having a cylindrical ring shape.

2. The punch tool as claimed in claim 1, wherein the asymmetrical geometry between the head piece and the foot piece stiffens the first punch, which, in a manner adapted to the asymmetry of the head piece, serves for accommodating a tilting moment on the first punch.

3. The punch tool as claimed in claim 1, wherein the first punch has, between the head piece and the foot piece, a widening hollow structure which has a varying material thickness at a constant height along a cross section perpendicular to the central axis along the pressing direction of the sintering press.

4. The punch tool as claimed in claim 1, wherein the first punch is an assembled punch with the head piece, a middle part, a lower part and the foot piece.

5. The punch tool as claimed in claim 1, wherein the first punch is rotationally movable for play compensation purposes.

6. The punch tool as claimed in claim 1, wherein the first punch and a second punch are movable one inside the other, wherein the first punch and the second punch each have a respective head piece which are asymmetrical with respect to the central axis along the pressing direction of the sintering press, wherein the first punch and the second punch each have a geometry which widens from the respective head piece to the respective foot piece, which geometries are also asymmetrical with respect to the central axis along the pressing direction of the sintering press.

7. A punch of a punch tool as claimed in claim 1 in which the punch is one of the at least one lower punch or one upper punch, wherein the punch serves for use in a sintering press, wherein the punch has, from the head piece toward the foot piece, a widening which is asymmetrical with respect to a longitudinal axis of the punch, in which the head piece is the portion of the punch that is receivable into a die cavity to form a surface of a powder metal part therein, wherein the geometry of the punch includes a conical section having a conical ring shape providing the asymmetrical widening and further includes a straight section having a cylindrical ring shape.

8. The punch tool of claim 1, wherein the first punch includes an oblique transition between the conical section and the straight section.

9. The punch tool of claim 2, wherein a green product is producible in the punch tool by compressing a powder material therewith and wherein the head piece of the first punch is configured to act on a face surface of the green product by providing the axial force.

10. The punch tool of claim 8, wherein the oblique transition between the conical section and the straight section has a narrowing oviform or non-circular elliptical ring shape.

11. The punch tool of claim 8, wherein the oblique transition from the conical section and the straight section runs along a circumference obliquely situated in relation to the central axis along the pressing direction of the sintering press.

12. A method for compressing at least one powder material in a sintering press to form a green product by a movement of upper punches and lower punches in a die, the method comprising filling of the die with the powder material, and compressing the powder material to form the green product, the green product having a geometry asymmetrical with respect to a central axis along a pressing direction of the sintering press imparted to it by a punch tool, wherein an asymmetrical conical widening from a head piece toward a foot piece of a punch of the punch tool is utilized to compensate a lateral offset of the punch with respect to the central axis along the pressing direction of the sintering press during the compressing the powder material, in which the head piece is the portion of the punch that is receivable into a die cavity to form a surface of a powder metal part therein wherein a geometry of the punch includes a conical section having a conical ring shape providing the asymmetrical conical widening and further includes a straight section having a cylindrical ring shape.

13. The method as claimed in claim 12, wherein the punch tool includes more than one punch and a coordinated release of stress from the punches of the punch tool in an inter-coordinated manner without open-loop equalization control or closed-loop equalization control being used on the sintering press for the equalization of differences between individual stress release processes during a movement of the punches away from the green product.

14. The method as claimed in claim 12, wherein before the compressing the powder material, at least the punch of the punch tool which extends asymmetrically with respect to the central axis along the pressing direction of the sintering press is assembled from multiple individual pieces and installed into the sintering press.

15. The method of claim 12, wherein the punch includes an oblique transition between the conical section and the straight section in which the oblique transition between the conical section and the straight section has a narrowing oviform or non-circular elliptical ring shape and runs along a circumference obliquely situated in relation to the central axis along the pressing direction of the sintering press.

16. A punch tool of a sintering press, the punch tool comprising at least one lower punch and one upper punch, wherein a first punch of the at least one upper punch and/or at least one lower punch has a head piece that is a portion of the first punch that is receivable into a die cavity to form a surface of a powder metal part therein and in which the head piece is asymmetrical with respect to a central axis along a pressing direction of the sintering press so that, within the first punch, an axial force acting during pressing acts spaced apart from the central axis along the pressing direction of the sintering press initiates a bending moment in the first punch, wherein the first punch has a geometry which conically widens from the head piece to a foot piece and which is also asymmetrical with respect to the central axis along the pressing direction of the sintering press and which asymmetrical widening is utilizable to compensate a lateral offset of the first punch with respect to the central axis along the pressing direction of the sintering press during pressing wherein the asymmetrical shape between the head piece and the foot piece is realized by material openings extending through a wall of the first punch.

17. A punch tool of a sintering press, the punch tool comprising at least one lower punch and one upper punch, wherein a first punch of the at least one upper punch and/or at least one lower punch has a head piece that is a portion of the first punch that is receivable into a die cavity to form a surface of a powder metal part therein and in which the head piece is asymmetrical with respect to a central axis along a pressing direction of the sintering press so that, within the first punch, an axial force acting during pressing acts spaced apart from the central axis along the pressing direction of the sintering press initiates a bending moment in the first punch, wherein the first punch has a geometry which conically widens from the head piece to a foot piece and which is also asymmetrical with respect to the central axis along the pressing direction of the sintering press and which asymmetrical widening is utilizable to compensate a lateral offset of the first punch with respect to the central axis along the pressing direction of the sintering press during pressing wherein the foot piece of the first punch is symmetrical about the central axis along the pressing direction of the sintering press, but the head piece is asymmetrical about the central axis along the pressing direction of the sintering press.

18. A method for compressing at least one powder material in a sintering press to form a green product by a movement of upper punches and lower punches in a die, the method comprising filling of the die with the powder material, and compressing the powder material to form a green product, the green product having a geometry asymmetrical with respect to a central axis along a pressing direction of the sintering press imparted to it by a punch tool, wherein an asymmetrical conical widening from a head piece toward a foot piece of a punch of the punch tool is utilized to compensate a lateral offset of the punch with respect to the central axis along the pressing direction of the sintering press during the compressing the powder material, in which the head piece is the portion of the punch that is receivable into a die cavity to form a surface of a powder metal part therein wherein the foot piece of the first punch is symmetrical about the central axis along the pressing direction of the sintering press, but the head piece is asymmetrical about the central axis along the pressing direction of the sintering press.

Description

(1) Further advantageous embodiments and refinements will emerge from the following figures, which may be combined with other features of the invention from the description also. Individual features from individual figures are not restricted thereto. Rather, one or more features from one or more figures and also from the description may together form further embodiments. In particular, the figures are to be interpreted not as being restrictive but as being exemplary. In the figures:

(2) FIG. 1 shows an oblique view of a detail of a sintering press having a punch tool with two punches, the asymmetrical head pieces of which are movable in a die,

(3) FIG. 2 shows a cross section through the sintering press from FIG. 1,

(4) FIGS. 3 to 6 shows the sintering press from FIGS. 1 and 2 comparatively in different illustrations,

(5) FIG. 7 shows an oblique view of a detail of a further embodiment of a sintering press having a punch tool with two punches, in the case of which bending moments can be compensated by means of the design of the punches,

(6) FIG. 8 shows an oblique view of the two punches from FIG. 7, and

(7) FIG. 9 shows an oblique view of one of the two punches from FIG. 7 and FIG. 8.

(8) FIG. 1 shows, in an oblique view, a detail of a sintering press 12 (with the sintering press 12 being shown only in part) having a punch tool 36 with two punches (a first punch 1 and a second punch 2), the head pieces (first head piece 3 and second head piece 4) of which are movable in a die 5. By means of this movement of the head pieces 3, 4, a green product 7 can be formed from powder in the die 5. The die 5 has a die outer wall 30, within which the green product 7 can be formed, wherein the respective head piece 3, 4 can act on a face surface 35 of the green product 7. The two head pieces 3, 4 are each individually designed asymmetrically with respect to an axial axis 6 of the sintering press 12 and arranged eccentrically with respect to the axial axis 6. In this embodiment, the first punch 1 constitutes an upper punch 28 and the second punch 2 constitutes a lower punch 29. The first punch 1 is movable along a first movement axis 33, and the second punch 2 is movable along a second movement axis 34.

(9) Also schematically shown is a powder store 31 for the filling of the die 5 of the sintering press 12 with a sinterable powder material 32 from which the green product 7 can be formed. The green product 7, which in the exemplary embodiment shown has a shape which is rotationally non-symmetrical with respect to the axial axis 6, can, after the action of the pressing force by means of the punches 1, 2, be relieved of load such that crack formation in the green product 7 is prevented. Therefore, the respective geometry of the first punch 1 and of the second punch 2 is preferably designed such that not only internal compensation of a bending moment is possible. Rather, both punches 1, 2 are preferably designed such that the elastic behavior thereof during the relief of load of the pressing force is the same. During the relief of load of both punches 1, 2, it is thus possible for the green product 7 to be uniformly relieved of load over the entire face surface 35 of the green product 7. This can prevent the occurrence of non-uniform stresses and thus of possibly non-uniformly distributed shear forces, which can lead to shearing in the material of the green product 7 and thus to crack formation in the green product 7. In this regard, reference is also made to the prior art already cited above, and to the possibilities, described further above, arising from the design of the punches 1, 2.

(10) The first punch 1 is movable in the second punch 2. Both punches 1, 2 have in each case one conical section (first conical section 13 and second conical section 14) at a respective foot piece (first foot piece 17 and second foot piece 18) and a straight section (first straight section 15 and second straight section 16) at the respective head piece 3, 4. The above-described asymmetry is realized through the presence of the conical sections 13, 14 and the straight sections 15, 16. Said asymmetry is formed by a combination of cylindrical ring shape and conical ring shape. Here, the cylindrical ring shape is realized by means of the straight sections 15, 16. The conical ring shape is realized here by means of the conical sections 13, 14. A transition exists between conical sections 13, 14 and straight sections 15, 16. By means of this design, the respective punch 1, 2 narrows from the respective foot piece 17, 18 toward the respective head piece 3, 4. The term “foot piece” 17, 18 is used here synonymously for the further customary expression “punch foot”, and the term “head piece” 3, 4 is used synonymously with the further customary expression “punch head”. By means of this geometry of the punches 1, 2, compensation of a bending moment can be realized. This can be contributed to for example by means of a different wall thickness, wall openings and/or oblique transitions between the respective straight section 15, 16 and the respective conical section 13, 14 of the respective punch 1, 2.

(11) The geometries of the punches 1, 2 differ from one another, in particular both with regard to the respective straight section 15, 16 and with regard to the respective conical section 13, 14. This may be advantageous owing to differently acting forces and owing to different dimensions of the punches 1, 2.

(12) A spread angle 19 (that is to say a cone opening angle) of the respective conical section 13, 14 may also be of different magnitude in the case of the two punches 1, 2. For the sake of clarity, the spread angle 19 is shown only for the second punch 2. In an end position, the respective foot pieces 17, 18 are preferably situated on different planes.

(13) Such punches are preferably used in sintering presses such as emerge from the applicant's application DE 10 2014 201 966 with the title “Pulverpresse mit kegeligem Unterbau” [“Powder press having a cone-shaped substructure”], which has not yet been published, and the entire content of which is hereby incorporated by reference into the disclosure in this regard.

(14) FIG. 2 shows a cross section through the sintering press 12 (shown only in part) from FIG. 1, in particular through the two punches 1, 2 and the die 5. Here, it is possible to particularly clearly see the design of the transition between the respective conical sections 13, 14 and the respective straight sections 15, 16 of the two punches 1, 2. The conical sections 13, 14 each have a wall thickness 20 of a wall 23 which differs at different locations of the conical sections 13, 14. Furthermore, a wall opening 21 is shown. FIG. 2 shows the asymmetry of the punches 1, 2 with respect to the axial axis 6 more clearly than FIG. 1.

(15) FIGS. 3 to 6 show the sintering press 12 from FIGS. 1 and 2 comparatively in different illustrations (again with the sintering press 12 shown only in part). FIG. 3 shows a perspective view from the outside, FIG. 4 shows a side view from the outside, FIG. 5 shows a cross-sectional view from the same perspective as that illustrated in FIG. 4, and FIG. 6 shows a plan view from the outside. With regard to the reference designations used, reference is made to the above description of FIGS. 1 and 2.

(16) FIG. 7 shows a perspective sectional illustration of a further embodiment of a sintering press 12 (shown only in part) with a punch tool 36 which has two punches (an inner punch 8 and an outer punch 9) which are movable in a die 5. In this embodiment, the outer punch 9 constitutes an upper punch 28 and the inner punch 8 constitutes a lower punch 29. The two head pieces 10, 11 are each individually designed asymmetrically with respect to an axial axis 6 of the sintering press 12 and arranged eccentrically with respect to the axial axis 6.

(17) A green product 7 can be formed from powder in the die 5. The two punches 8, 9 are designed such that a bending moment that can act on the respective punch 8, 9 can be compensated. The inner punch 8 has an inner head piece 11 which is movable within an outer head piece 10 of the outer punch 9. The outer head piece 10 of the outer punch 9 in this case surrounds the inner head piece 11, which is illustrated in the cross-sectional illustration as a surrounding configuration from two sides. In this case, too, the term “head piece” 10, 11 is used synonymously with the further customary expression “punch head”. By means of the arrangement shown, a bending tendency of the two punches 8, 9 can be reduced. Friction between the punches 8, 9 and also with the die 5 can thus be reduced, in particular even eliminated entirely.

(18) FIG. 8 shows a part of the sintering press 12 from FIG. 7 in an oblique view from the outside. It is possible to see the inner punch 8 with the inner head piece 11 and the outer punch 9 with the outer head piece 10. The outer punch 9 has a material cutout 22 which is realized as an aperture through a wall 23 of the outer punch 9. The material cutout 22 constitutes one of the material openings described further above, by means of which the asymmetry of the respective punch 8, 9 can be realized. The material cutout 22 serves in particular (as is likewise described further above) for realizing an asymmetry in the respective punch 8, 9. The material cutout 22 or the asymmetry possibly furthermore serves for realizing a bending compensation means, whereby, for example, bending of the respective head piece 10, 11 or of the respective punch 8, 9 in one direction is counteracted. The material cutout 22 has a longitudinal extent 24 which is greater than a circumferential extent 25.

(19) FIG. 9 shows an oblique view of the outer punch 9 from FIG. 7 and FIG. 8, wherein the inner punch 8 is not shown in this illustration. The outer punch 9 has thickened portions 26 of the wall 23, in particular in the form of reinforcements 27. Furthermore, the outer punch 9 has material cutouts 22 (one of which is shown) in the wall 23. The thickened portions 26 and the material cutouts 22 can contribute to reducing a bending tendency of the outer punch 9.

LIST OF REFERENCE DESIGNATIONS

(20) 1 First punch 2 Second punch 3 First head piece 4 Second head piece 5 Die 6 Axial axis 7 Green product 8 Inner punch 9 Outer punch 10 Outer head piece 11 Inner head piece 12 Sintering press 13 First conical section 14 Second conical section 15 First straight section 16 Second straight section 17 First foot piece 18 Second foot piece 19 Spread angle 20 Wall thickness 21 Wall opening 22 Material cutout 23 Wall 24 Longitudinal extent 25 Circumferential extent 26 Thickened portion 27 Reinforcement 28 Upper punch 29 Lower punch 30 Die outer wall 31 Powder store 32 Powder material 33 First movement axis 34 Second movement axis 35 Face surface 36 Punch tool