Method for producing a green compact using a pressing tool, a pressing tool, a green compact, and a sintered part

Abstract

A method for producing a green compact uses a pressing tool including a die, a first punch to be displaced in an axial direction, a second punch to be displaced in a radial direction through a channel in the die and a receptacle having a filling opening. The method includes locating the second punch before or during filling of a powdery material into the receptacle so as to be outwardly offset in the radial direction relative to an inner peripheral surface, filling the powdery material into the receptacle, and moving at least the first punch and the second punch and compressing the material in the receptacle, with the second punch being moved in the radial direction toward the receptacle only so far that it is disposed flush with a region of the inner peripheral surface. A pressing tool, a green compact and a sintered part are also provided.

Claims

1. A green compact produced by compression of a powdery material, the green compact comprising: a first end and a second end defining an axial direction therebetween; a longitudinal axis extending along said axial direction; a wall region extending parallel to said longitudinal axis and along said axial direction from said first end to said second end; said wall region including a subregion spaced apart from said first end and said second end; said wall region having a compressed first surface texture outside said subregion; and said subregion having a second surface texture being different from said first surface texture; wherein said subregion has no undercuts to said wall region and ends flush with said wall region or is offset into the green compact by no more than 0.1 mm relative to said wall region in a radial direction.

2. The green compact according to claim 1, which further comprises first and second parting lines disposed between said subregion and said wall region, said subregion extending along said axial direction between said first and second parting lines, and said first and second parting lines forming a transition from said first surface texture to said second surface texture.

3. The green compact according to claim 2, wherein at least one of said parting lines has a curved shape.

4. The green compact according to claim 1, which further comprises a portion tapering along said axial direction, said portion having a largest cross section and a smallest cross section transverse to said axial direction, said portion having a ratio between said largest cross section and said smallest cross section of at least 2:1, and said subregion being disposed on said portion.

5. A sintered part, comprising: a heat-treated green compact according to claim 1; said heat-treated green compact having a third surface texture disposed in a region of said first surface texture; and said heat-treated green compact having a fourth surface texture in a region of said second surface texture.

6. A method for producing the green compact according to claim 1, the method comprising the following steps: providing a pressing tool including at least one die extending along the axial direction between a first end face and a second end face of the at least one die and forming an inner peripheral surface of the at least one die with an opening between the end faces, the inner peripheral surface forming a receptacle for the green compact, at least one first punch being movable along the axial direction from one of the end faces of the die into the receptacle, and at least one second punch being movable along a radial direction through a channel in the die toward the receptacle, the inner peripheral surface having a region disposed along the axial direction between the one end face, from which the first punch is movable, and the opening; a) placing the second punch outwardly offset in the radial direction relative to the inner peripheral surface before or during step b); b) filling a powdery material into the receptacle; and c) moving at least the first punch and the second punch and compressing the material in the receptacle, the second punch being moved in the radial direction toward the receptacle only far enough to be disposed flush with or to protrude into the receptacle by no more than 0.1 mm at least relative to the region of the inner peripheral surface in the radial direction.

7. The method according to claim 6, which further comprises placing the second punch offset in step a) or during step b) so far in the radial direction relative to the inner peripheral surface that the material filled in step b) is also disposed in the channel.

8. The method according to claim 7, which further comprises displacing the material disposed in the channel through the opening into the receptacle as a result of the movement of the second punch in step c).

9. The method according to claim 6, which further comprises providing the second punch with at least one first punch part and at least one second punch part being movable independently of one another.

10. The method according to claim 9, which further comprises placing the punch parts next to one another along the axial direction.

11. The method according to claim 6, which further comprises using the second punch to compact said subregion of said wall region of the green compact extending along the axial direction from said first end to said second end of the wall region in step c), the subregion being spaced apart at least from the first end or from the second end.

12. The method according to claim 6, which further comprises placing the second punch on a portion of the green compact that tapers along the axial direction, and providing a ratio of at least 2:1 between a largest cross section and a smallest cross section of the portion transverse to the axial direction.

13. A green compact produced by compression of a powdery material, the green compact comprising: a first end and a second end defining an axial direction therebetween; a longitudinal axis extending along said axial direction; a wall region extending parallel to said longitudinal axis and along said axial direction from said first end to said second end; said wall region including a subregion spaced apart from said first end and said second end; said wall region having a compressed first surface texture outside said subregion; said subregion having a second surface texture being different from said first surface texture; and first and second parting lines disposed between said subregion and said wall region, said subregion extending along said axial direction between said first and second parting lines, and said first and second parting lines forming a transition from said first surface texture to said second surface texture; wherein at least one of said parting lines has a curved shape.

14. A sintered part, comprising: a heat-treated green compact according to claim 13; said heat-treated green compact having a third surface texture disposed in a region of said first surface texture; and said heat-treated green compact having a fourth surface texture in a region of said second surface texture.

15. A green compact produced by compression of a powdery material, the green compact comprising: a first end and a second end defining an axial direction therebetween; a longitudinal axis extending along said axial direction; a wall region extending parallel to said longitudinal axis and along said axial direction from said first end to said second end; said wall region including a subregion spaced apart from said first end and said second end; said wall region having a compressed first surface texture outside said subregion; and said subregion having a second surface texture being different from said first surface texture; a portion tapering along said axial direction, said portion having a largest cross section and a smallest cross section transverse to said axial direction, said portion having a ratio between said largest cross section and said smallest cross section of at least 2:1, and said subregion being disposed on said portion.

16. A sintered part, comprising: a heat-treated green compact according to claim 15; said heat-treated green compact having a third surface texture disposed in a region of said first surface texture; and said heat-treated green compact having a fourth surface texture in a region of said second surface texture.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

(1) FIG. 1 shows a green compact in a first perspective view;

(2) FIG. 2 shows the green compact according to FIG. 1 in a second perspective view;

(3) FIG. 3 shows the green compact according to FIGS. 1 and 2 in a side view;

(4) FIG. 4 shows a sintered part in a side view;

(5) FIG. 5 shows the sintered part according to FIG. 4 in a perspective view;

(6) FIG. 6 shows a first pressing tool during step b) of the method in a cutaway perspective view;

(7) FIG. 7 shows the first pressing tool according to FIG. 6 during step c) in a partially cutaway perspective view;

(8) FIG. 8 shows a second pressing tool before step b) of the method in a cutaway perspective view; and

(9) FIG. 9 shows another sintered part in a perspective view.

DESCRIPTION OF THE INVENTION

(10) FIG. 1 shows a green compact 1 in a first perspective view. FIG. 2 shows the green compact 1 according to FIG. 1 in a second perspective view. FIG. 3 shows the green compact 1 according to FIGS. 1 and 2 in a side view. FIGS. 1 to 3 are described together below.

(11) The green compacts 1 produced in dies 3 can have a variety of geometries. It has hitherto proven difficult to produce green compacts 1 that taper at least in portions 24 of the green compact 1 along the axial direction 4. Particularly in portions 24 of the green compact 1 having side surfaces that are inclined relative to the axial direction 4—i.e., that taper conically—, inhomogeneities can occur in the density distribution of the green compact 1. Therefore, these parts either cannot be produced or do not have the desired strength or the desired properties particularly in these portions 24, even as sintered parts 30.

(12) The green compact 1 shown here was produced by compressing a powdered material 14. The green compact 1 has a longitudinal axis 27 that extends along an axial direction 4 and a wall region 21 that extends parallel to the longitudinal axis 27 and along the axial direction 4 from a first end 19 to a second end 20, the wall region 21 having a subregion 18 that is arranged so as to be spaced apart from the first end 19 and from the second end 20. A first surface texture 28 of the wall region 21 outside the subregion 18 created through compression is different from a second surface texture 29 of the subregion 18. The subregion 18 of the wall region 21 is formed as a result of the compression with the second punch 13 along the radial direction 11.

(13) It can be seen that the subregion 18 is free of undercuts relative to the wall region 21 and flush with the wall region 21. The term “undercut” denotes any shape of the green compact 1 that is minimally undersized (along the radial direction 11) relative to every surface of the green compact 1 between the subregion 18 of the green compact 1 that is formed by the end face 15 of the second punch 13 and the first end 19 and/or the second end 20 of the wall region 21 or of the green compact 1 along the axial direction 4.

(14) The subregion 18 is disposed on a portion 24 of the green compact 1 that tapers along the axial direction 4, with a ratio between a largest cross section 25 transverse to the axial direction 4 of the portion 24 and a smallest cross section 26 being at least 2:1.

(15) In the green compact 1 that is shown, the tapering of the portion 24 occurs continuously over side surfaces of the portion 24 that are arranged so as to be inclined relative to the axial direction 4; here, only the side surface of the green compact 1 having the subregion 18 extends parallel to the longitudinal axis 27.

(16) FIG. 4 shows a sintered part 30 in a side view. FIG. 5 shows the sintered part 30 according to FIG. 4 in a perspective view. FIGS. 4 and 5 are described together below. The sintered part 30 is produced by sintering a green compact 1. The sintered part 30 has a longitudinal axis 27 that extends along an axial direction 4 and a wall region 21 that extends parallel to the longitudinal axis 27 and along the axial direction 4 from a first end 19 to a second end 20, the wall region 21 having a subregion 18 that is arranged so as to be spaced apart from the first end 19 and from the second end 20.

(17) The subregion 18 is disposed on a portion 24 of the sintered part 30 that tapers along the axial direction 4, with a ratio between a largest cross section 25 transverse to the axial direction 4 of the sintered part 30 and a smallest cross section 26 being at least 2:1. In the sintered part 30 that is shown, the taper occurs continuously over side surfaces of the sintered part that are arranged so as to be inclined relative to the axial direction 4. The side surface of the sintered part 30 having the subregion 18, extends parallel to the longitudinal axis 27.

(18) FIG. 6 shows a first pressing tool 2 during step b) of the method in a cutaway perspective view. The pressing tool 2 comprises at least one die 3, one first punch 10, and one second punch 13. The die 3 extends along an axial direction 4 between a first end face 5 and a second end face 6 and forms an inner peripheral surface 7 with an opening 8 between the end faces 5, 6. The inner peripheral surface 7 forms a receptacle 9 for the green compact 1. The first punch 10 can be moved along an axial direction 4. The second punch 13 can be moved along a radial direction 11 through a channel 12 in the die and toward the receptacle 9 while filling the opening 8 (once it has been moved to the receptacle 9; see position of the second punch 13 in FIG. 7). The first punch 10 can be moved over the first end face 5 of the die 3 into the receptacle 9 along the axial direction 4. The die 3 and the second punch 13 are provided in step a) of the method, the second punch 13 being offset from the inner peripheral surface 7 (and opposite the opening 8) outward in the radial direction 11 and thereby arranged in the channel 12. The filling of a powdery material 14 into the receptacle 9 takes place in step b) of the method.

(19) As can be seen, the second punch 13, which can be moved in the radial direction 11, is not used to produce an undercut. In order to produce an undercut, the second punch 13 would be moved beyond the opening 8 into the receptacle 9 and would have to be moved out of the receptacle 9 before the removal of the green compact 1 from the receptacle 9, so that the form lock produced in the axial direction 4 between second punch 13 and green compact 1 is eliminated.

(20) Therefore, no undercut is produced here, but rather a compaction of the powdery material 14 through a compression in the radial direction 11. For this purpose, it is permitted that the powdery material 14 enter the channel 14 via the opening 8. It is only in this way that an additional amount of material 14 can be transported into this region of the eventual green compact 1, this additional amount being supplied through the second punch 13 via the of the receptacle 9 and thus fed to the green compact 1 via the opening 8. A transporting of the powdery material 14 along the axial direction 4 by the first punch 10 during compression is thus replaced and/or supplemented here through the transporting of the powdery material 14 along the radial direction 11.

(21) Particularly in the case of tapered components—with conically tapering side walls, for example—the powdery material 14 cannot be moved into this portion 24 of the eventual green compact 1, or only with great difficulty. The use of a second punch 13 that can be moved in the radial direction 11 now enables the required amount of material 14 to be moved toward this portion 24 in a targeted and precise manner.

(22) The second punch 13 has an end face 15 that forms the receptacle 9 together with the inner peripheral surface 7, with the end face 15 extending parallel to the axial direction 4. The inner peripheral surface 7 also extends parallel to the axial direction 4 in the region between the opening 8 and the first end face 5 of the die 3.

(23) In step a), the second punch 13 is offset so far in the radial direction 11 relative to the inner peripheral surface 7 that the material 14 filled in step b) is also disposed in the channel, as shown here. The material 14 arranged in the channel 12 is displaced via the opening 8 into the receptacle 9 as a result of the movement of the second punch 13 in step c).

(24) FIG. 6 also shows a third punch 33, an ejector 34, and another (fourth) punch 35. The third punch 33 and, if applicable, the additional punch 35 are likewise used to compact the powdery material 14. Due to the tapered portion 24, the ejector 34 cannot be used for the compacting of the material 14 (or only to a small extent). This would cause shear stresses in the green compact 1, which can result in the failure of the green compact 1. The ejector 34 is used here exclusively for the purpose of removing the green compact 1 from the die 3 (together with the third punch 33 and the additional punch 35).

(25) FIG. 7 shows the first pressing tool 2 according to FIG. 6 during step c) in a partially cutaway perspective view. Reference is made to the remarks in relation to FIG. 6.

(26) In step c) of the method, the first punch 10 and the second punch 13 are moved in the receptacle 9 in order to compress the material 14, the second punch 13 being moved in the radial direction 11 toward the receptacle 9 only so far that it is arranged at least with a region 36 of the inner peripheral surface 7 that moves along the axial direction 4 between the first end face 5 and the opening 8 so as to be flush or so as to protrude into the receptacle 9 by no more than 0.1 mm relative to this region 36 of the inner peripheral surface 7 in the radial direction 11.

(27) A subregion 18 of a wall region 21 of the green compact 1 extending along the axial direction 4 from a first end 19 to a second end 20 is compacted in step c) by the second punch 13, the subregion 18 being arranged so as to be spaced apart from the first end 19 and from the second end 20.

(28) FIG. 8 shows a second pressing tool 2 before step b) of the method in a cutaway perspective view. Reference is made to the remarks in relation to FIGS. 6 and 7.

(29) In contrast to the first pressing tool according to FIGS. 6 and 7, the second punch 13 comprises a first punch part 16 and a second punch part 17 that can be moved independently of one another. This enables the method to be adapted more closely to the prevailing conditions. For example, partial volumes of the later green compact 1 can be successively filled and compacted. As can be seen, the punch parts 16, 17 are arranged next to one another along the axial direction 4.

(30) FIG. 9 shows another sintered part 30 in a perspective view. Reference is made to the remarks in relation to FIGS. 1 to 3. The sintered part 30 was produced by sintering the green compact 1 according to FIGS. 1 to 3.

(31) The subregion 18 of the green compact 1 or of the sintered part extends between a first parting line 22 to the wall region 21 and a second parting line 23 to the wall region 21 along the axial direction 4, with the first parting line 22 having a meandering shape. For one thing, these parting lines 22, 23 are visible due to the minimal offset of the subregion 18 in the radial direction 11 relative to the wall regions 21 that are not compressed in the radial direction 11. For another, a different surface pattern or another fourth surface texture 32 is formed in the subregion 18 that is visually distinguishable from the third surface texture 31 of the wall region 21.

(32) It can be seen here that the largest cross section 25 of the tapered portion 24 is arranged between the first parting line 22 and the second parting line 23. The smallest cross section 26 of the tapered portion 24 is also arranged between the first parting line 22 and the second parting line 23.

LIST OF REFERENCE SYMBOLS

(33) 1 green compact 2 pressing tool 3 die 4 axial direction 5 first end face 6 second end face 7 inner peripheral surface 8 opening 9 receptacle 10 first punch 11 radial direction 12 channel 13 second punch 14 material 15 end face 16 first punch part 17 second punch part 18 subregion 19 first end 20 second end 21 wall region 22 first parting line 23 second parting line 24 portion 25 largest cross section 26 smallest cross section 27 longitudinal axis 28 first surface texture 29 second surface texture 30 sintered part 31 third surface texture 32 fourth surface texture 33 third punch 34 ejector 35 additional punch 36 region