阅读说明：本技术 用压制工具制造生坯的方法、压制工具、生坯和烧结件 (Method for producing a green body with a pressing tool, green body and sintered part ) 是由 S.蒂勒 R.施密特 N.博尔内曼 于 2018-03-14 设计创作，主要内容包括：本发明涉及一种用压制工具(2)来制造生坯(1)的方法、一种压制工具(2)、一种生坯(1)以及一种烧结件(30)。所述压制工具(2)包括模具(3)并且此外包括能够沿着轴向方向(4)移动的第一冲头(10)以及能够沿着径向方向(11)通过所述模具(3)中的通道(12)并且朝接收部(9)移动的并且在此填充所述接收部(9)的开口(8)的第二冲头(13)。所述方法包括以下步骤：a)提供所述模具(3)和所述第二冲头(13),其中所述第二冲头(13)在步骤b)之前或期间相对于内周面(7)沿着径向方向(11)向外偏移地布置；b)将粉末状的材料(14)填入到所述接收部(9)中；c)至少移动所述第一冲头(10)和所述第二冲头(13)并且对所述接收部(9)中的材料(14)进行压制,其中使所述第二冲头(13)沿着径向方向(11)朝所述接收部(9)仅仅如此移动,使得其以与所述内周面(7)齐平地终结的方式来布置。(The invention relates to a method for producing a green body (1) using a pressing tool (2), to a green body (1) and to a sintered part (30). The pressing tool (2) comprises a die (3) and furthermore a first punch (10) which is movable in the axial direction (4) and a second punch (13) which is movable in the radial direction (11) through a passage (12) in the die (3) and towards the receptacle (9) and fills the opening (8) of the receptacle (9) there. The method comprises the following steps: a) providing the die (3) and the second punch (13), wherein the second punch (13) is arranged offset outwardly in a radial direction (11) with respect to the inner circumferential surface (7) before or during step b); b) filling the receiving part (9) with a powdery material (14); c) moving at least the first punch (10) and the second punch (13) and pressing the material (14) in the receptacle (9), wherein the second punch (13) is moved in the radial direction (11) only in the direction of the receptacle (9) such that it ends flush with the inner circumferential surface (7).)

1. Method for producing at least one green body (1) with a pressing tool (2), wherein the pressing tool (2): comprising at least one die (3) which extends in the axial direction (4) between a first end face (5) and a second end face (6) and which forms an inner circumferential face (7) with an opening (8) between the end faces (5, 6), wherein the inner circumferential face (7) forms a receptacle (9) for the green body (1); and furthermore comprises at least one first punch (10) which is movable in the axial direction (4) into the receptacle (9) by means of one of the end faces (5, 6) of the die (3), and at least one second punch (13) which is movable in the radial direction (11) through a passage (12) in the die (3) and towards the receptacle (9); wherein the method comprises at least the following steps:

a) -providing the die (3) and the second punch (13), wherein the second punch (13) is arranged offset outwardly in the radial direction (11) with respect to the inner circumferential surface (7) before or during step b);

b) filling the receiving part (9) with a powdery material (14);

c) -moving at least the first punch (10) and the second punch (13) and pressing the material (14) in the receptacle (9), wherein the second punch (13) is moved in a radial direction (11) only towards the receptacle (9) such that it is arranged at least flush with an area (36) of the inner circumferential surface (7) arranged in the axial direction (4) between one of the end faces (5, 6) and the opening (8), or in a radial direction (11) towards the inside of the receptacle (9) protruding at most 0.1mm at least relative to this area (36) of the inner circumferential surface (7), wherein the first punch (10) is moved into the receptacle (9) by means of the one of the end faces (5, 6).

2. Method according to claim 1, wherein the second punch (13) is arranged offset in relation to the inner circumferential surface (7) in a radial direction (11) in step a) or during step b) in such a way that the material (14) filled in step b) is also arranged in the channel (12).

3. Method according to claim 2, wherein in step c) the material (14) arranged in the channel (12) is transferred via the opening (8) into the receptacle (9) by movement of the second punch (13).

4. Method according to any one of the preceding claims, wherein the second punch (13) comprises at least one first sub-punch (16) and a second sub-punch (17), the sub-punches being movable independently of each other.

5. Method according to claim 4, wherein the sub-punches (16, 17) are arranged side by side along the axial direction (4).

6. Method according to one of the preceding claims, wherein in step c) a partial region (18) of the green body (1) of a wall region (21) extending in the axial direction (4) from a first end (19) to a second end (20) is compacted by the second punch (13), wherein the partial region (18) is arranged at least spaced apart from the first end (19) or the second end (20).

7. Method according to any one of the preceding claims, wherein the second punch (13) is arranged on a section (24) of the green body (1) tapering along the axial direction (4), wherein the ratio between a maximum cross section (25) and a minimum cross section (26) of the section (24) transverse to the axial direction (4) is at least 2: 1.

8. Pressing tool (2) for producing at least one green body (1), wherein the pressing tool (2): comprising at least one die (3) which extends in the axial direction (4) between a first end face (5) and a second end face (6) and which forms an inner circumferential face (7) with an opening (8) between the end faces (5, 6), wherein the inner circumferential face (7) forms a receptacle (9) for the green body (1); and furthermore comprises at least one first punch (10) which is movable in the axial direction (4) via one of the end faces (5, 6) of the die (3) into the receiving portion (9), and at least one second punch (13) which is movable in the radial direction (11) through a passage (12) in the die (3) and towards the receiving portion (9); wherein the second punch (13) can be moved in the radial direction (11) only toward the receptacle (9) in such a way that it ends flush at least with a region (36) of the inner circumferential surface (7) arranged in the axial direction (4) between one of the end faces (5, 6) and the opening (8), or in such a way that it protrudes in the radial direction (11) toward the inside of the receptacle (9) by at most 0.1mm at least with respect to this region (36) of the inner circumferential surface (7), wherein the first punch (10) is moved into the receptacle (9) by means of the one of the end faces (5, 6).

9. A green body (1) produced by pressing a powdery material (14), wherein the green body (1) has a longitudinal axis (27) extending along an axial direction (4) and a wall region (21) running parallel to the longitudinal axis (27) and extending along the axial direction (4) from a first end (19) to a second end (20), wherein the wall region (21) comprises a partial region (18) which is arranged at a distance from the first end (19) and the second end (20), wherein a first surface structure (28) of the wall region (21) which occurs outside the partial region (18) by pressing differs from a second surface structure (29) of the partial region (18).

10. The green body (1) according to claim 9, wherein the partial region (18) extends along an axial direction (4) between a first parting line (22) with respect to the wall region (21) and a second parting line (23) with respect to the wall region (21), wherein the parting lines (22, 23) form a transition from the first surface structure (28) to the second surface structure (29).

11. The green body (1) according to claim 10, wherein at least one of the separation lines (22, 23) has a curved course.

12. The green body (1) according to any one of the preceding claims 9 to 11, wherein the partial region (18) is embodied without undercuts with respect to the wall region (21) and terminates flush with the wall region (21) or is arranged offset by at most 0.1mm with respect to the wall region (21) in a radial direction (11) towards the inside of the green body (1).

13. The green body (1) according to any one of the preceding claims, wherein the partial region (18) is arranged on a section (24) of the green body (1) tapering along the axial direction (4), wherein the ratio between a maximum cross section (25) and a minimum cross section (26) of the section (24) transverse to the axial direction (4) is at least 2: 1.

14. Sintered part (30) produced by heat treatment of a green body (1) according to any one of the preceding claims 9 to 13, wherein the sintered part (30) has a third surface structure (31) in the region of the first surface structure (28) of the green body (1) and a fourth surface structure (32) in the region of the second surface structure (29) of the green body (1).

Technical Field

The present invention relates to a method for producing a green body with a pressing tool, to a green body and to a sintered part (or a component produced by heat treatment of a green body, also referred to below as a sintered part). In particular, sinterable green bodies or any green bodies to be further processed (for example by heat treatment), i.e. green bodies which can be sintered, for example, after the pressing process, are produced with the pressing tool. In particular, metallic and/or ceramic powders can be pressed into green bodies in a mold. In particular, the method can be used for operating a pressing tool and for producing green or sintered parts. In particular, the pressing tool can be used for producing green bodies.

Background

The die extends in the axial direction between a first end face and a second end face and forms an inner circumferential surface between the end faces, which inner circumferential surface forms a receptacle for the powdery material or for a green body produced from the material by pressing. At least one punch of the pressing tool is provided, which is movable in the axial direction through the (first) end face towards the inside of the die and presses the material arranged in the receptacle into a green body. Of course, it is also known to use further punches which can be moved in the axial direction and which are pushed into the die via further (second) end faces.

In order to produce a geometric undercut in the green body, an opening can be provided in the inner circumferential surface, through which opening at least one second punch, which can be moved in the radial direction through a passage in the die and toward the receptacle and fills the opening in the process, can be moved into the receptacle.

On the one hand, the inner circumferential surface of the mold forms a receptacle for the powder or green body to be produced. The at least one upper punch of the pressing tool can be moved in particular in the axial direction into the die via the first end face of the die which is open at the top. At least one upper punch slides along the inner circumferential surface of the die and presses the powder to an increased extent. In particular, at least one lower punch can additionally be provided, which is moved into the die by the second, downwardly open end face of the die in the axial direction or between an upper position and a lower position in the die, wherein the die can also be moved relative to the optionally unmoved lower punch. This makes it possible to compact the powder into a green body between at least one upper punch and at least one lower punch, wherein the inner peripheral surface of the die defines in particular the lateral contour of the green body.

The green body produced in the mold may have a variety of geometries. However, it has hitherto proved difficult to produce green bodies which taper in the axial direction, at least in sections of the green body. In particular in sections of the green body having a side surface inclined relative to the axial direction, i.e. a conical taper, inhomogeneities may occur in the density distribution of the green body. As a result, these components either cannot be produced or do not have the desired strength or the desired properties even if they are just in these sections as sintered parts. No compaction methods are known to date with which such geometries can be produced with reasonable expenditure or with optimum component properties.

Disclosure of Invention

Starting from this, the object of the invention is to solve the problems described with reference to the prior art at least in part. In particular, the highly required geometries of the green body to be produced should also be able to be produced by a method and/or by a pressing tool, wherein in particular density inhomogeneities in the green body can be reduced or prevented.

To solve this object, the invention proposes a method according to the features of claim 1, a pressing tool according to the features of claim 8, a green body according to the features of claim 9 and a sintered part according to the features of claim 14. Advantageous developments are the subject matter of the dependent claims. The features listed individually in the claims can be combined with one another in a technically meaningful manner and can be supplemented by explanatory facts from the description and by details from the drawing, in which further embodiment variants of the invention are illustrated.

A contribution is made to a method for producing at least one green body with a pressing tool. The pressing tool comprises at least one die, a first punch and a second punch. The mold extends between a first end face and a second end face in an axial direction and constitutes an inner peripheral face having an opening between the end faces. The inner peripheral surface forms a receiving portion for the green compact. The at least one first punch can be moved in the axial direction into the receptacle by one of the end faces of the die. At least one second punch is movable in a radial direction through a passage in the die and towards the receiving portion, wherein the second punch here (when it has been moved all the way to the receiving portion) preferably fills the opening, the method comprising at least the following steps:

a) providing a die and a second punch, wherein the second punch is arranged offset outwardly in a radial direction with respect to the inner circumferential surface (and the opening) before or during step b);

b) filling a powdered material into the receiving portion;

c) moving at least the first punch (at least one) and the second punch (at least one) and pressing the material in the receptacle, wherein the second punch (at least one) is moved in the radial direction only toward the receptacle in such a way that the second punch is located at least in a region of the inner circumferential surface in the axial direction between one of the end faces (through which the first punch (at least one) is moved into the receptacle) and the opening

Flush termination, or

At least with respect to this region of the inner circumferential surface, projects in the radial direction into the receptacle by at most 0.1mm [ mm ], in particular by at most 0.05mm

Are arranged.

The second punch, which can be moved in the radial direction, is not used in particular for producing undercuts here. In order to produce the undercut, the second punch is moved beyond the opening into the receiving region, wherein the second punch must be moved out of the receiving region before the green body is removed from the receiving region, so that the form-locking produced between the second punch and the green body in the axial direction is eliminated. Such a "resetting movement" of the second punch is not necessary for removing the green body from the receptacle, but in particular also enables the green body to be removed when the second punch is in the "flush" or "slightly protruding" end position described above. In particular for removing the green body, the second punch is moved back in the radial direction only by at most 0.1mm relative to the end position (i.e. the position in which the second punch is moved the furthest distance in the radial direction towards the receiving portion during step c).

The second punch thus effects a compaction of the powdery material by pressing in the radial direction. For this purpose, the powdery material is allowed to pass through the opening into the channel. Thus, an additional quantity of material can be conveyed into this region of the later green body, wherein this additional quantity is conveyed by the second punch via the opening to the receiving portion and thus to the green body. The transport of the powdery material in the axial direction by the first punch during pressing is therefore (partially) replaced and/or supplemented here by the transport of the powdery material in the radial direction.

In the case of, for example, tapered components with tapering side walls, the powdered material cannot be removed with sufficient precision and/or only with a high risk of inhomogeneities occurring in this section of the green body later on. The use of a second punch, which can be moved in the radial direction, now makes it possible to transfer the required amount of material to this section in a targeted and precisely metered manner.

It is thus possible to produce green bodies having a very high and/or very uniform density throughout their cross-section.

In particular, the second punch has an end face which forms a receptacle together with the inner circumferential surface in the illustrated end position, wherein the end face extends parallel to the axial direction. Preferably, the inner circumferential surface also extends parallel to the axial direction, in particular in the region between the first end face of the die and the opening. There should also be a "parallel" orientation, as long as this can generally be set with the manufacturing tolerances of the components described here, so that deviations from the axial direction of, for example, at most two (2) angles, preferably at most one (1) angle, particularly preferably at most 0.3 angle, should be included.

In particular, the (at least one) second punch is arranged offset in the radial direction with respect to the inner circumferential surface in step a) or during step b) in such a way that the material introduced in step b) is also arranged in the channel (before step c)).

The filling of the material and the movement of the second punch are preferably performed at least partially in parallel with each other. In particular, the second punch is arranged substantially flush with the inner circumferential surface before the material is filled, wherein the second punch is moved back in the radial direction during the filling of the material. The movement of the second punch acts like a vacuum pump and pulls material into the channel.

In particular, in step c) the material arranged in the channel is transferred into the receptacle via the opening by the movement of the (at least one) second punch.

Preferably, the (at least one) second punch comprises at least one first sub-punch and a second sub-punch, which are movable independently of each other. Two second punches can likewise be provided. This enables the method to be adapted more precisely to the respective conditions present. For example, it is possible to gradually fill and compact a partial volume of the green body afterwards.

In particular, all the punches (and ejectors) provided in the method can be coupled to one another or can be moved and adjusted completely independently of one another.

In particular, the sub-punches are arranged side by side in the axial direction. However, other arrangements of the sub-punches are also contemplated. The sub-punches can also be arranged coaxially with one another or side by side in the circumferential direction.

In particular, in step c), a partial region of the green body of the wall region extending in the axial direction from the first end to the second end is compacted by means of a (at least one) second punch, wherein the partial region is arranged at a distance from the first end and/or the second end. The wall region between the first end and the partial region is pressed in particular by a first punch. In this region, the powdery material is first transferred along the inner circumferential surface in the axial direction. The wall region extends from a first end to a second end of the wall region or the green body, wherein the end does not necessarily have to represent the maximum extension of the green body in the axial direction. In step c), a partial region of the wall region is compacted by means of a second punch. The partial region here is the region of the green body which is arranged in the radial direction in front of the end face of the second punch.

In particular, the partial region extends between a first separation line and a second separation line on or relative to the wall region in the axial direction, wherein at least one separation line has a curved, in particular meandering course. On the one hand, these separation lines can be produced as a result of a minimal offset in the radial direction of the partial region relative to the wall region which is not compacted in the radial direction and can therefore be well identified. In a further aspect, a further surface pattern and/or a further second surface structure is formed in the partial region, which may be visually different from the first surface structure of the wall region outside the partial region.

Preferably, the (at least one) second punch is arranged on a section of the green body tapering in the axial direction, wherein the ratio between the largest cross section and the smallest cross section of the section transverse to the axial direction is at least 2:1, preferably at least 3: 1. The maximum cross section of the tapered section is arranged in particular between the first and second dividing lines. Preferably, the smallest cross section is also arranged between the first and second parting line.

The tapering is particularly continuous on the inner circumferential surface or on a side of the receptacle which is arranged at an angle to the axial direction.

Furthermore, a pressing tool for producing at least one green body is proposed. The pressing tool can be used in particular in the proposed method for producing a green body. The compaction tool comprises at least one die, at least one first punch and at least one second punch. The mold extends along the axial direction between a first end face and a second end face and constitutes an inner peripheral face having an opening between the end faces. The inner peripheral surface forms a receiving portion for a green body. The at least one first punch is movable in an axial direction. The at least one second punch can be moved in the radial direction through the passage in the die and towards the receptacle, wherein it preferably fills the opening there (when it has moved all the way to the receptacle). The first punch can be moved in the axial direction into the receptacle by one of the end faces of the die. The pressing tool is now set up such that the second punch is moved in the radial direction only toward the receptacle such that it can be arranged at least flush with the region of the inner circumferential surface which is arranged in the axial direction between one of the end faces (through which the first punch is moved into the receptacle) and the opening, or at least projects in the radial direction at most 0.1mm, in particular at most 0.05mm, toward the inside of the receptacle relative to this region of the inner circumferential surface.

In particular, the second punch has no contour on its end face facing the receptacle for forming an undercut in the green body. In this case, undercut preferably means a shoulder in the outer surface of the green body which, with respect to each (other) face of the green body, has a dimensional deficiency in the axial direction between the face of the green body formed by the end face of the second punch and the wall region or the first end and/or the second end of the green body of more than 2 or 1mm, or even more than only 0.1mm [ mm ], in particular more than 0.05 mm.

In particular, the first end and the second end are each arranged directly adjacent to the wall region.

In particular, the (at least one) second punch has an end face which forms a receptacle together with the inner circumferential surface, wherein the end face extends parallel to the axial direction.

Preferably, the inner circumferential surface also extends parallel to the axial direction, in particular in the region between the first end face of the die and the opening.

The explanations with respect to the aforementioned method apply equally to the pressing tool and vice versa.

A green body produced by pressing a powdery material is proposed, wherein the green body has a longitudinal axis extending in an axial direction and a wall region extending parallel to the longitudinal axis and extending in the axial direction from a first end to a second end. The wall region includes a sub-region disposed spaced apart from the first end and the second end. The first surface structure of the wall region outside the partial region, which surface structure occurs by pressing, differs from the second surface structure of the partial region.

In particular, the first surface structure outside the partial region is produced during the compacting by shearing, i.e. by the particles moving along the inner circumferential surface in the axial direction, wherein a glossy surface with squashed particles is produced.

In particular, the partial region extends in the axial direction between a first separation line with respect to the wall region and a second separation line with respect to the wall region, wherein the separation lines form a transition from the first surface structure to the second surface structure.

The partial region of the wall region is formed by pressing in the radial direction with a second punch. Due to the radial pressing, a second surface structure is present in the partial region, which already may be visually different from the first surface structure (outside the partial region).

The second surface structure of the partial region is in particular not formed exactly by shearing. Here, the particles are compacted in the radial direction. A matt surface with flattened particles is produced here.

According to a preferred embodiment, at least one of the separation lines (in particular two separation lines) has a curved, in particular meandering course. Here, there is a "curved" course of the parting line, if the course does not run straight, i.e. the parting line has at least one radius of curvature. If the course has a plurality of segments with different radii of curvature, in particular different (opposite) orientations with respect to the course of the separation line, a meandering or meandering course can be attributed to the presence. The curved or meandering course prevents the formation of a predetermined breaking point, which is more likely to be expected for a linearly running separation line. Such a predetermined breaking point of the green body is caused in particular by: in the region of the parting line, there is a transition between the partial region compacted by the second punch and the wall region formed by the axial compaction. These smallest edge and/or structural differences that may be present there may form predetermined breaking points. This transition in the green body, which is a possible density difference between the partial region and the wall region, is "vanished" by the curved parting line.

In particular, the partial regions are embodied without undercuts with respect to the wall regions and terminate flush with the wall regions or are arranged offset in the radial direction with respect to the wall regions by at most 0.1mm [ mm ], in particular at most 0.05mmr, toward the inside of the green body. The undercut preferably means in this case each of the shapes of the green body which, relative to each face of the green body, have a dimensional deficiency in the axial direction (in the radial direction) of more than 0.1mm, in particular at most 0.05mm, between the partial region of the green body formed by the end face of the second punch and the wall region or the first end and/or the second end of the green body.

In particular, the partial region is arranged on a section of the green body tapering in the axial direction, wherein the ratio between the largest cross section and the smallest cross section of the section transverse to the axial direction is at least 2:1, in particular at least 3: 1.

The maximum cross section of the tapered section is arranged in particular between the first and second dividing lines. Preferably, the smallest cross section is also arranged between the first and second parting line.

The tapering is particularly continuous on a side face of the section of the green body which is arranged obliquely to the axial direction, wherein at least the side face of the green body having the partial region extends parallel to the longitudinal axis at least in the partial region.

The green body can in particular be produced by the method and/or by the use of the pressing tool. The explanations with respect to the method and the pressing tool apply in the same way to the green body and vice versa.

Furthermore, a sintered part or heat-treated component (hereinafter referred to as "sintered part") is proposed which is produced by sintering or heat treatment of the green body described above, wherein the sintered part forms a third surface structure in the region of the green body in which the first surface structure was previously present and has a fourth (different from the third surface structure) surface structure in the region of the green body in which the second surface structure was previously present.

The third and fourth surface structures relate to the surface structure, starting from the surface structure of the green body, as a result of a change caused by sintering or heat treatment. Differences in the surface structure between the partial regions and the wall regions can also be detected on the sintered part.

The explanations with respect to the green body also apply to the sintered part and vice versa.

It should be noted that the terms "first", "second", "etc.", as used herein, are used primarily (merely) to distinguish a plurality of similar objects or parameters, and therefore the relevance and/or order of these objects or parameters to one another is not mandatory in particular. If dependencies and/or sequences are required, this is explicitly stated here or is obvious to the person skilled in the art when studying the specifically described design.

Drawings

The invention and the technical environment are explained in detail below with the aid of the drawings. It should be noted that the invention should not be limited by the illustrated embodiments. In particular, if no further statements are explicitly made, it is also possible to extract some aspects of the facts explained in the figures and to combine them with other components and knowledge from the description and/or the figures. It should be noted in particular that the drawings and in particular the dimensional ratios shown are purely schematic. The same reference numerals denote the same objects, and thus explanations from other drawings can be used supplementarily as necessary. In the drawings:

fig. 1 shows a green body in a first perspective view;

fig. 2 shows a green body according to fig. 1 in a second perspective view;

fig. 3 shows a green body according to fig. 1 and 2 in a side view;

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

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

fig. 6 shows a first pressing tool during step b) of the method in a sectional perspective view;

fig. 7 shows the first press tool according to fig. 6 during step c) in a partially cut perspective view;

fig. 8 shows a second press tool before step b) of the method in a sectional perspective view; and is

Fig. 9 shows a further sintered part in a perspective view.

Detailed Description

Fig. 1 shows a green body 1 in a first perspective view. Fig. 2 shows the green body 1 according to fig. 1 in a second perspective view. Fig. 3 shows a green body 1 according to fig. 1 and 2 in a side view. Fig. 1 to 3 are described together below.

The green body 1 produced in the mould 3 can have a variety of geometries. It has hitherto been shown to be difficult to produce a green body 1 which tapers in the axial direction 4 at least in a section 24 of the green body 1. In particular in the section 24 of the green body 1 with a side surface inclined relative to the axial direction 4, i.e. tapering conically, inhomogeneities may occur in the density distribution of the green body 1. As a result, these components either cannot be produced or do not have the desired strength or the desired properties even if they are just in the sections 24 as sintered parts 30.

The green body 1 shown here is produced by pressing a powdery material 14. The green body 1 has a longitudinal axis 27 extending along the axial direction 4 and a wall region 21 extending parallel to the longitudinal axis 27 and extending along the axial direction 4 from the first end 19 to the second end 20, wherein the wall region 21 has a partial region 18 which is arranged at a distance from the first end 19 and the second end 20. The first surface structure 28 of the wall region 21 outside the partial region 18, which surface structure is produced by pressing, differs from the second surface structure 29 of the partial region 18. The partial region 18 of the wall region 21 is formed by pressing in the radial direction 11 with the second punch 13.

It can be seen that the partial region 18 is embodied without undercuts with respect to the wall region 21 and terminates flush with the wall region 21. Here, "undercut" means each shape of the green body 1 which, with respect to each face of the green body 1, has a specific minimum dimensional deficiency (in the radial direction 11) in the axial direction 4 between the partial region 18 of the green body 1 formed by the end face 15 of the second punch 13 and the wall region 21 or the first end 19 and/or the second end 20 of the green body 1.

The subregion 1 is arranged on a section 24 of the green body 1 which tapers in the axial direction 4, wherein the ratio between the largest cross section 25 and the smallest cross section 26 of the section 24 transverse to the axial direction 4 is at least 2: 1.

In the case of the illustrated green body 1, the tapering of the section 24 is effected continuously on the side of the section 24 which is arranged obliquely to the axial direction 4, wherein only the side of the green body 1 having the subregion 18 extends parallel to the longitudinal axis 27.

Fig. 4 shows the sintered part 30 in a side view. Fig. 5 shows the sintered part 30 according to fig. 4 in a perspective view. Fig. 4 and 5 are described together below. The sintered part 30 is produced by sintering the green body 1. The sintered part 30 has a longitudinal axis 27 extending along the axial direction 4 and a wall region 21 running parallel to the longitudinal axis 27 and extending along the axial direction 4 from the first end 19 to the second end 20, wherein the wall region 21 comprises a partial region 18 arranged at a distance from the first end 19 and the second end 20.

The subregion 18 is arranged on a section 24 of the sintered part 30 tapering along the axial direction 4, wherein the ratio between the maximum cross section 25 and the minimum cross section 26 of the sintered part 30 transverse to the axial direction 4 is at least 2: 1. In the case of the illustrated sintered part 30, the tapering takes place continuously on the side of the sintered part which is arranged obliquely to the axial direction 4. The side of the sintered part 30 with the partial region 18 extends parallel to the longitudinal axis 27.

Fig. 6 shows the first pressing tool 2 in a sectional perspective view during step b) of the method. The pressing tool 2 comprises a die 3, a first punch 10 and a second punch 13. The die 3 extends in the axial direction 4 between a first end face 5 and a second end face 6 and constitutes between the end faces 5, 6 an inner circumferential face 7 with an opening 8. The inner circumferential surface 7 forms a receiving portion 9 for the green body 1. The first punch 10 is movable along the axial direction 4. A second punch 13 can be moved in the radial direction 11 through a passage 12 in the die 3 and towards the receptacle 9, wherein it fills the opening 8 here (when it is moved all the way to the receptacle 9) (see the position of the second punch 13 in fig. 7). The first punch 10 can be moved in the axial direction 4 into the receptacle 9 by the first end face 5 of the die 3. In step a) of the method, the die 3 and the second punch 13 are provided, wherein the second punch 13 is offset in the radial direction 11 outwardly with respect to the inner circumferential surface 7 (and with respect to the opening 8) and is arranged in the channel 12. The filling of the receptacle 9 with the powdery material 14 is completed in step b) of the method.

Here, the second punch 13, which is movable in the radial direction 11, is clearly not used for producing undercuts. In order to produce the undercut, the second punch 13 is moved beyond the opening 8 into the receptacle 9, wherein the second punch 13 must be moved out of the receptacle 9 before the green body 1 is removed from the receptacle 9, so that the form-locking produced between the second punch 13 and the green body 1 in the axial direction 4 is eliminated.

Therefore, the material 14 in powder form is compacted by pressing in the radial direction 11, without undercutting occurring in this case. For this purpose, the powdered material 14 is allowed to enter the channel 12 via the opening 8. Only then is it possible to transfer an additional quantity of material 14 into this region of the subsequent green body 1, which additional quantity is conveyed by the second punch 13 to the receiving portion 9 and thus in turn to the green body 1 through the opening 8. Thus, the transport of the powdery material 14 in the axial direction 4 by the first punch 10 is supplemented here by the transport of the powdery material 14 in the radial direction 11 during pressing.

In the case of a tapered component, for example, with tapered side walls, the powdered material 14 cannot be transferred or only with difficulty into this section 24 of the subsequent green body 1. The use of a second punch 13 which can be moved in the radial direction 11 now makes it possible to transfer the required amount of material 14 to this section 24 in a targeted and precise manner.

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

In step a), the second punch 13 is arranged offset in the radial direction 11 with respect to the inner circumferential surface 7 in such a way that the material 14 filled in step b) is also arranged in the channel 12, as shown here. The material 14 arranged in the channel 12 is moved into the receptacle 9 via the opening 8 as a result of the movement of the second punch 13 in step c).

Fig. 6 also shows a third punch 33, an ejector 34 and a further (fourth) punch 35. The third punch 33 and, if appropriate, a further punch 35 are likewise used for compacting the powdery material 14. Due to the tapered section 24, the ejector 34 cannot (or can only to a small extent) be used to compact the material 14. Shear stresses may thus be generated in the green body 1, which may lead to failure of the green body 1. The ejector 34 is here used only for removing the green body 1 from the die 3 (together with the third punch 33 and the further punch 35).

Fig. 7 shows the first pressing tool 2 according to fig. 6 during step c) in a partially cut perspective view. Reference is made here to the explanation with respect to fig. 6.

In step c) of the method, the first punch 10 and the second punch 13 are transferred for pressing the material 14 in the receptacle 9, wherein the second punch 13 is moved in the radial direction 11 toward the receptacle 9 only in such a way that it ends flush with a region 36 of the inner circumferential surface 7 arranged in the axial direction 4 between the first end face 5 and the opening 8, or in such a way that it protrudes in the radial direction 11 into the receptacle 9 by at most 0.1mm relative to this region 36 of the inner circumferential surface 7.

In step c) of the method, a partial region 18 of the green body 1, which partial region 18 extends in the axial direction 4 from the first end 19 to the wall region 21 of the second end 20, is compacted by the second punch 13, wherein the partial region 18 is arranged at a distance from the first end 19 and the second end 20.

Fig. 8 shows the second pressing tool 2 in a sectional perspective view before step b) of the method. Reference is made here to the explanations with respect to fig. 6 and 7.

In contrast to the first pressing tool according to fig. 6 and 7, the second punch 13 comprises a first sub-punch 16 and a second sub-punch 17 which can be moved independently of one another. The method can therefore be adapted more precisely to the respectively present conditions. For example, part of the volume of the later green body 1 can be gradually filled and compacted. It can be seen that the sub-punches 16, 17 are arranged side by side along the axial direction 4.

Fig. 9 shows a further sintered part 30 in a perspective view. Reference is made to the explanations with respect to fig. 1 to 3. A sintered part 30 is produced by sintering the green body 1 according to fig. 1 to 3.

The partial regions 18 of the green compact 1 or the sintered part extend in the axial direction 4 between a first parting line 22 relative to the wall region 21 and a second parting line 23 relative to the wall region 21, wherein the first parting line 22 has a meandering course. On the one hand, the separation lines 22, 23 can be seen due to the minimal offset of the partial region 18 in the radial direction 11 (relative to the wall region 21 which is not compacted in the radial direction 11). On the other hand, a further surface pattern or a further fourth surface structure 32 appears in the partial region 18, which can be visually different from the third surface structure 31 of the wall region 21.

Here, it can be seen that the maximum cross section 25 of the tapered section 24 is arranged between the first parting line 22 and the second parting line 23. The smallest cross section 26 of the tapering section 24 is also arranged between the first parting line 22 and the second parting line 23.

List of reference numerals:

1 green compact

2 pressing tool

3 mould

4 axial direction

5 first end face

6 second end face

7 inner peripheral surface

8 opening

9 receiving part

10 first punch

11 radial direction

12 channels

13 second punch

14 materials

15 end face

16 first sub-punch

17 second sub-punch

18 partial region

19 first end portion

20 second end portion

21 wall region

22 first separation line

23 second separation line

24 section(s)

25 maximum cross section

26 minimum cross section

27 longitudinal axis

28 first surface structure

29 second surface structure

30 sintered part

31 third surface structure

32 fourth surface structure

33 third punch

34 ejector

35 additional punches

Region 36.