JP7478545B2 - Press tool and method for manufacturing press tool - Google Patents

Description

The present disclosure relates to a press tool for producing a cutting insert raw body.

Cutting inserts are metal cutting tools for machining metals by milling, drilling, or turning, or similar chip forming processes. Cutting inserts are manufactured by powder metallurgy from metal composite powders, such as cemented carbide powders, or from ceramic powders, such as mixtures containing aluminum oxide and silicon nitride. Cemented carbides are metal composites having metal carbides, e.g., tungsten carbide, titanium carbide, or tantalum carbide, in a metal binder, e.g., cobalt, nickel, or iron.

The cutting insert can also be manufactured from a cermet, such as a mixture containing titanium carbide and nickel, or from other materials, such as a cBN material. The powder can be compressed into a cutting insert green by opposing first and second punches in a die cavity. After compression, the cutting insert green is removed from the die cavity and sintered into a solid cutting insert blank.

The mould used to contain the powder for compaction can be a so-called split mould press tool, comprising first and second mould halves movable relative to one another in order to be able to remove geometrically complex green bodies from the mould after their compaction. Depending on the shape of the green body to be formed, the mould halves can be of different shapes. According to one design principle, each mould half comprises a body having a U-shaped recess at its end. The two sides of the U-shaped recess can be considered to be defined by two rectangular parallelepiped-shaped legs extending from the remainder of the body of the mould half.

According to another design principle, each mold half has a body with a V-shaped recess at its end. The two sides of the V-shaped recess can be considered to be defined by two wedge-shaped legs that extend from the remainder of the mold half's body.

During compression, the two die halves are positioned with their V-shaped recesses facing each other, whereby the opposing recesses define a die cavity. A lower punch or die element is placed at the bottom of the die cavity, powder is introduced into the die cavity, and an upper punch introduced into said die cavity from above is used to compress the powder in combination with the corresponding introduction of the lower punch into the die cavity from below. During such compression, the powder exerts outward pressure on the legs of each die half, tending to bend the legs outward.

The applicant has recognized that die halves made of a grade of cemented carbide having the wear resistance required for the intended application may develop cracks in the corner regions of the die members where the two die surfaces contact each other after repeated compression sequences due to the outward bending of the legs during each compression sequence. In other words, cracks form in the corner regions before the inner surfaces of the legs are worn down to an unacceptable standard due to wear caused by the powder. Thus, crack initiation and propagation in the corner regions of each die half becomes a critical factor for the functioning of the press tool.

To the best of the applicant's knowledge, the problems identified have not previously been addressed in the prior art for this type of mold.

The objective of this disclosure is therefore to provide a solution to the problems identified above.

The object of the present disclosure is achieved by a press tool for producing a cutting insert blank, the press tool comprising:
at least one mould member having a first leg defined by a first mould surface and a second leg defined by a second mould surface, each leg having a base connecting to the remainder of the mould member and a free end at each of the ends of the first and second mould surfaces;
- the first and second mold surfaces define a mold cavity within which the cutting insert green body is formed upon compaction of powder;
- in the region of the base of the first and second legs (4, 6), the mould cavity (3) presents a corner region having a corner between two contacting surfaces, and - the mould members consist of cemented carbide, the press tool being characterised in that in the corner region there are parts of the mould members in which the cemented carbide has a higher toughness than the cemented carbide of the mould members which are further away from the corner region.

The diverse mould material properties can be achieved by sintering together different parts made of sintered cemented carbide of different microstructure and/or composition into a single body, followed by forming recesses by electro-discharge machining, so that a mould is formed with the above-defined geometry and cavity. The less tough cemented carbide has a higher wear resistance than the more tough parts. Apart from the corner regions, the first and second surfaces of the first and second legs are formed by a less tough and more wear-resistant cemented carbide.

According to one embodiment, the corner has an angle α of less than 100°.

According to one embodiment, the corner has an angle α of less than 70°.

According to one embodiment, the corners of the corner region have a corner curvature corresponding to a radius of less than 1.65 mm, preferably less than 1.1 mm.

According to one embodiment, at least one of the two contacting surfaces is one of the first and second mold surfaces.

According to one embodiment, the two contacting surfaces are the first and second mold surfaces.

According to one embodiment, the portion extends at least 0.1 mm, preferably at least 0.25 mm, most preferably at least 1 mm, measured along the first and second mould surfaces in a direction from the apex of the corner towards the free ends of the first and second legs. The portion thus defines a portion of the first and second surfaces that extends at least 0.1 mm, preferably at least 0.25 mm, most preferably at least 1 mm from the apex of the corner. The minimum extension depends, for example, on the method of manufacture of the portion and the stress conditions in the corner region.

According to one embodiment, the portion extends less than half the length of the mold surface, measured along the first and second mold surfaces in a direction from the apex of the corner toward the free ends of the first and second legs. Thus, the portion defines a portion of the first and second surfaces that extends less than half the length of the first and second mold surfaces in a direction from the apex of the corner. At such a distance from the corner, wear resistance may be prioritized over toughness.

According to one embodiment, the part has a thickness of at least 0.1 mm, preferably at least 1 mm, in the direction normal to the mould surface of the part that bounds the mould cavity. The part thus has a thickness as seen in the extension of the corner apex, whereby a predetermined minimum technical effect of the part is achieved.

According to one embodiment, the portion extends from the apex of the corner of the mold member to the opposite end in a first direction pointing away from the first and second legs towards the opposite end. Such an embodiment facilitates accurate and rapid positioning of the first and second parts that are sintered together to form the mold member. Provided that the mold member has a longitudinal direction parallel to the first direction and that the cross-section of the portion and the mold member is constant along the length of the mold member, viewed transversely or perpendicularly to the longitudinal direction of the mold member, the V-shaped recess of the mold member defining the leg, and therefore the mold cavity, can be formed deeper and deeper into the original mold member as the latter mold cavity-defining surface wears.

According to one embodiment, the portion extends along the corner from a first end to an opposite second end of the mold member. Alternatively, the portion is concentrated in an area of the mold member where the green body of the cutting insert will ultimately be formed during compression by at least one punch moving into the mold cavity.

According to one embodiment, the portion has a rectangular cross section when viewed in a plane perpendicular to a first direction from the apex of the corner to the opposite end of the mold member. The first direction may be the longitudinal direction as described above.

According to one embodiment, the portion has an elliptical or circular cross section when viewed in a plane perpendicular to a first direction from the apex of the corner to the opposite end of the mold member. The first direction may be the longitudinal direction as described above.

According to one embodiment, the portion has the same cross section along its entire length from the corner apex to the opposite end of the mold member in a first direction parallel to the longitudinal direction described above, as viewed in a plane perpendicular to the first direction from the corner apex to the opposite end of the mold member. Thus, the V-shaped recess of the mold member defining the leg, and thereby the mold cavity, can be formed deeper and deeper in the longitudinal direction into the original mold member as the latter mold cavity-defining surface wears away. Also, the cross section of the portion in the corner region remains the same.

According to one embodiment,
the first leg has an outer surface on an opposite side of the first leg with respect to said first surface;
- the second leg has an outer surface opposite the second leg with respect to said second mould surface, and - said outer surface of the first leg is parallel to said outer surface of the second leg.

According to one embodiment,
- from the first leg towards the opposite end of the mould member, in the extension of the outer surface of the first leg, the remainder of the mould member has an outer surface aligned with the outer surface of the first leg, and - from the second leg towards the opposite end of the mould member, in the extension of the outer surface of the second leg, the remainder of the mould member has an outer surface aligned with the outer surface of the second leg.

According to one embodiment, the first leg has a wedge-shaped configuration and the second leg has a wedge-shaped configuration, each having a base connecting to the remainder of the die member and a respective free end at the end of the first and second surfaces opposite said corner. The first and second legs have a wedge-shaped configuration when viewed in a direction perpendicular to the longitudinal direction of the die member defined above and in the direction of movement of the punch into the die cavity in connection with the compression of the powder therein.

Further embodiments include alternative embodiments in which the legs may have shapes other than wedge shapes, such as rectangular prisms, and there may be multiple corners and therefore multiple corner regions.

According to one embodiment, the cemented carbide forming the portion has a larger average carbide grain size than the cemented carbide forming the first leg and the second leg.

According to one embodiment, the cemented carbide comprises particles of tungsten carbide in a matrix of cobalt binder.

According to one embodiment, the cemented carbide comprises particles of tungsten carbide in a matrix of cobalt binder, and the cemented carbide forming the portion has a higher cobalt content than the cemented carbide forming the first leg and the second leg.

According to one embodiment, the press tool comprises a first die member and a corresponding second die member according to the invention described above or below, the first and second die members being arranged with the free ends of their respective first and second legs facing each other, thereby defining a die cavity, and at least one punch arranged to be introduced into the die cavity defined by the first and second die members for the purpose of compressing powder introduced into the die cavity.

The objects of the present invention are also achieved by a method for manufacturing a press tool as defined above or below, comprising the following steps:
- forming a first green body configured to form a first part of a mould member;
- forming a second green body configured to form a second part of the mould member;
- sintering the first green body into a first part of a mould member;
- sintering the second green body into a second part of the mold member, which second part forms said portion of the mold member when attached to the first part, and - attaching the first part to the second part by sintering, wherein the binder of the first part and the binder of the second part melt during the sintering at the interface between the first and second parts.

According to one embodiment, the method includes the further step of electrochemical machining the sintered die parts into a final shape, the final shape being characterized in that the press tool has portions of the die in which, in the corner regions, the cemented carbide has a higher toughness than the cemented carbide of the first and second legs that are further away from the corner regions in a direction towards the respective opposing free ends of the respective legs.

Further features and advantages of the press tools and methods disclosed herein are presented in the detailed description of the embodiments below.

Embodiments of the present invention will now be described in more detail, by way of example, with reference to the accompanying drawings, in which:

FIG. 1 is a top view of two die members in the ejection or open position. FIG. 2 corresponds to FIG. 1 and shows the die members in a pressing or closed position. FIG. 2 is an end view according to II-II of FIG. 1 showing a first embodiment of a mold member; FIG. 2 is an end view according to II-II of FIG. 1 showing a second embodiment of a mold member; 1 is a top-down close-up view of a mold member according to the present disclosure; FIG. 1 illustrates steps of an embodiment of a method according to the present disclosure. FIG. 1 illustrates steps of an embodiment of a method according to the present disclosure. FIG. 1 illustrates steps of an embodiment of a method according to the present disclosure. FIG. 1 illustrates steps of an embodiment of a method according to the present disclosure. FIG. 1 shows a press tool according to the invention FIG. 1 shows a press tool according to the present invention including a fixture.

Figures 1, 10 and 11 show parts of a press tool according to the present disclosure. The press tool is a press tool for producing cutting insert green bodies and, in the embodiment shown, comprises two die members 1, 2, each of which is configured to define a part of a die cavity 3. The press tool also comprises two punches 24, 25 (seen in Figures 10 and 11) configured to be introduced into the die cavity 3 from above and below in order to compress the powder introduced into said die cavity into a cutting insert green body. Also shown in Figure 11 is a fixture 26 in which the die members 1, 2 can be positioned during the compression of the powder therein.

Although only one of the mold members 1 and 2 is disclosed below, it should be understood that the second mold member may have the same features as the one disclosed.

The mould member 1 comprises a solid body having a first leg 4 defining a first mould surface 5 and a second leg 6 defining a second mould surface 7. The first mould surface 5 and the second mould surface 7 bound a mould cavity 3 in which the cutting insert body is formed upon compression of the powder. The first mould surface 5 and the second mould surface 7 extend at an angle α of less than or equal to 96° relative to each other at a corner 8 in a corner region of the mould member 1 where the first and second surfaces 5, 7 contact each other. The corner 8 in the corner region has a corner curvature corresponding to a radius of less than 1.65 mm.

The first leg 4 has a wedge-shaped configuration and the second leg 6 has a wedge-shaped configuration, each having a base connected to the remainder of the mould member 1 and a respective free end 10, 11 at the end of the first and second surfaces opposite the corner 8 where the first and second surfaces 5, 7 contact each other.

The mold member 1 is made of cemented carbide, and in the corner region there is a portion 9 of the mold member 1 in which the cemented carbide has a higher toughness than the cemented carbide of the mold member further away from the corner region in the direction towards the opposing free ends 10, 11 of the first leg 4 and the second leg 6, respectively. A material with lower toughness is more wear resistant than a material with higher toughness. Thus, the first and second surfaces 5, 7 have a higher wear resistance in the other parts than in the corner region in which the portion 9 with higher toughness is located.

The difference in toughness between the portion 9 and the other parts of the die member is due to differences in the composition or microstructure of the cemented carbide between the portion 9 and the other parts of the die member 1. For example, the portion 9 may have a higher binder content and/or a larger average carbide grain size than the other parts of the die member 1.

The tough portion 9 extends in a direction y from the apex 23 of the corner toward the opposing free ends 10, 11 of the first leg 4 and the second leg 6. The portion 9 extends in a direction y from the apex 23 of the corner 8 toward the free ends 10, 11 of the first leg 4 and the second leg 6 by at least 0.1 mm of the length of the first and second mould surfaces 5, 7. The portion 9 extends in a direction y from the apex 23 of the corner 8 toward the free ends 10, 11 of the first leg 4 and the second leg 6 by no more than half the length of the first and second mould surfaces 5, 7. The tough portion 9 has a thickness in a direction normal to the first and second mould surfaces of at least 0.1 mm, preferably at least 1 mm.

In the embodiment shown, the tough portion 9 extends in a first direction x from the apex 23 of the corner 8 of the mould member 1 to the opposite end 13, from the first and second legs towards the opposite end. The direction x is parallel to the longitudinal direction of the mould member 1. However, the tough portion 9 may have a length in the direction x that is significantly shorter than the length of the mould member.

In the embodiment shown, the tough portion 9 has the same cross section along its entire length from the apex of the corner of the mold member 1 to said opposite end 13. Such a design is not required, but it facilitates the manufacture of the mold member and also allows for further incremental machining of the V-shaped recesses defining the first and second legs 4, 6 as the first and second surfaces wear away, while still maintaining the cross section of the tough portion 9 in the corner region.

Figure 3 shows an embodiment in which the tough portion has a rectangular cross section as viewed in a plane perpendicular to the longitudinal direction x, the tough portion 9 extending in this case from a first end 14 all the way to a second end 15 in a direction perpendicular to said longitudinal direction x and in the direction in which the punch moves into the die cavity in connection with the compaction of the powder therein. The tough portion 9 extends in a first direction from a corner 8 of the die member 1 all the way to the opposite end 13.

Figure 4 shows an alternative embodiment in which the stiffening portion 9' has a circular cross section when viewed in a plane perpendicular to the longitudinal direction x.

The tough portions 9, 9' are located at the corners 8 of the mold cavity 3 where the cutting insert green body is finally compressed, i.e., the tough portions are located in those parts of the mold cavity 3 where the stresses caused by the compressive pressure on the first and second surfaces 6, 7 reach very high values.

The first leg 4 has an outer surface 16 opposite the first leg 4 with respect to the first surface 5, and the second leg 6 has an outer surface 17 opposite the second leg 6 with respect to the second surface 7. The outer surface 16 of the first leg 4 is parallel to the outer surface 17 of the second leg 6.

In the extension of the outer surface 16 of the first leg 4 in said longitudinal direction x from the first leg 4 towards the opposite end 13 of the die member 1, the remaining part of the die member 1 has an outer surface 18 aligned with the outer surface 16 of the first leg 4. In the extension of the outer surface 17 of the second leg 6 in said longitudinal direction x from the second leg 6 towards the opposite end 13 of the die member 1, the remaining part of the die member 1 has an outer surface 19 aligned with the outer surface 17 of the second leg 6. This design makes it possible to machine a V-shaped recess in the end of a rectangular parallelepiped having such parallel outer surfaces and to use said recess as a die cavity. When an inner surface such as such a recess wears away due to the abrasive effects of the repeated compression of the powder therein, it can be simply displaced further into a rectangular parallelepiped by suitable machining, while the important geometrical measures of the part of the die member 1 defining the recess remain the same, and thus the die cavity remains the same.

In the disclosed embodiment, the mold member 1 is formed by a rectangular parallelepiped having adjacent outer surfaces perpendicular to each other, and the V-shaped recess is formed at one end of the rectangular parallelepiped.

Figures 4-6 show the steps of the method for manufacturing the mould member 1 according to the present disclosure. In a first and a second step, not shown, the powder is shaped into two first green bodies which are sintered and are arranged to form the first parts 20, 21 of the mould member 1 when later joined together. In the embodiment shown, the two first parts 20, 21 shown in Figure 6 are rectangular parallelepipeds having the shape of rectangular sheets with respective thicknesses _t1 , _t2 . In this embodiment, _t1 = _t2 . However, the two first parts 20, 21 may differ from each other in terms of shape and/or thickness. This depends on the design of the press tool or on the specific design of the cutting insert green bodies to be compressed and thus of the recesses to be moulded in the mould member 1.

In corresponding first and second steps, a second powder having a different microstructure and/or composition than the powder forming the first green body is formed and sintered to form the second part 22 of the mould member 1 when later joined together with the first parts 20, 21. The second part 22 has a thickness _t3 . The second part 22 is intended to form the tough portion 9 disclosed above, for which purpose its thickness _t3 is in this embodiment substantially smaller than the thicknesses _t1 , _t2 of the first parts 20, 21. The different microstructure may refer for example to a different carbide grain size, and the different composition may refer for example to a different binder content or a different type of carbide.

According to one embodiment, the first parts 20, 21 are made of a cemented carbide with a cobalt content of 3 to 13% by weight, and the second part 22 is made of a cemented carbide with a cobalt content of 6 to 25% by weight.

According to one embodiment, the first parts 20, 21 are made of a cemented carbide containing tungsten carbide particles having an average grain size of 0.2 to 3.0 μm, and the second part 22 is made of a cemented carbide containing tungsten carbide particles having an average grain size of 0.5 to 8.0 μm.

In a subsequent step shown in FIG. 7, a second part 22 is sandwiched between the first parts 20, 21 and attached to the second part by sintering, where at the interface between the first and second parts, the binder of the first part and the binder of the second part are melted during the sintering.

This results in the formation of a rectangular solid. In a further step shown in Figure 8, a V-shaped recess is machined into the end of the body formed by the first and second parts, resulting in the mould member 1 shown in Figure 9, having the shape disclosed above.

Instead of molding the green bodies 20, 21, 22 by compression, at least one of the green bodies can be molded, for example, by one of the following molding methods: extrusion, powder injection molding, or additive manufacturing.

Although the mold surfaces 5, 7 are shown as planar in the drawings and as straight in cross section, it should be understood that the mold surfaces may be non-planar to correspond to the geometry of the green body.

In the disclosed embodiment, the invention is exemplified as being composed of two first bodies 20, 21 having a rectangular parallelepiped shape and one second body having a rectangular parallelepiped shape, but it is to be noted that other numbers and shapes of such bodies are within the claimed scope of the invention in its broadest sense, so long as at least one tough portion 9 is formed in the area of the corner 8 of the formed mold member 1, as shown above and further defined in the appended claims.

Claims (16)

In a press tool for producing a cutting insert blank,
at least one mould part (1) having a first leg (4) defining a first mould surface (5) and a second leg (6) defining a second mould surface (7), each leg (4, 6) having a base connected to the remainder of said mould part (1) and a respective free end (10, 11) at the end of said first and second mould surfaces (5, 7);
It is equipped with
- said first mould surface (5) and second mould surface (7) delimit a mould cavity (3) within which said cutting insert green body is formed upon compaction of the powder;
- in the region of the base of the first and second legs (4, 6), the mould cavity (3) presents a corner region having a corner (8) between two contacting surfaces, and - the mould part (1) consists of a hard metal, the pressing tool being characterised in that in the corner region there is a part (9) of the mould part (1) in which the hard metal has a higher toughness than the hard metal of the mould part (1) which is further away from the corner region.
Press tool. The press tool according to claim 1, characterized in that at least one of the two contacting surfaces is one of the first and second die surfaces (5, 7). The press tool according to claim 1, characterized in that the two contacting surfaces are the first and second die surfaces (5, 7). A press tool according to any one of claims 1 to 3, characterized in that the portion (9) extends at least 0.1 mm, measured along the first and second die surfaces (5, 7), in a direction (y) from the vertex (23) of the corner (8) towards the free ends (10, 11) of the first leg (4) and the second leg (6). A press tool according to any one of claims 1 to 4, characterized in that the portion (9) extends less than half the length of the die surfaces (5, 7) measured along the first and second die surfaces (5, 7) in a direction (y) from the vertex (23) of the corner (8) towards the free ends (10, 11) of the first leg (4) and the second leg (6). A press tool according to any one of claims 1 to 5, characterized in that the part (9) has a thickness of at least 0.1 mm in a direction normal to the mould surface (5, 7) of the part (9) that defines the mould cavity (3). 7. A press tool according to claim 1, characterized in that the portion (9) extends in a first direction (x) pointing away from the first and second legs (4, 6) towards an opposite end (13) of the die part (1) from a vertex (23) of the corner (8) to the opposite end (13). A press tool according to any one of claims 1 to 7, characterized in that the portion (9) extends along the corner (8) from a first end (14) of the die member (1) to an opposite second end (15). A press tool according to any one of claims 1 to 8, characterized in that the portion (9) has a rectangular cross section when viewed in a plane perpendicular to a first direction (x) from the apex (23) of the corner to the opposite end (13) of the die member (1). 8. A press tool according to claim 1, characterized in that, when viewed in a plane perpendicular to a first direction (x) from the apex (23) of the corner towards the opposite end (13) of the die part (1), the portion (9) has an elliptical or circular cross section. 11. A press tool according to claim 1, characterized in that, as viewed in a plane perpendicular to a first direction (x) from the apex (23) of the corner (8) towards the opposite end (13) of the die part (1), the portion (9) has the same cross section along its entire length from the apex (23) of the corner (8) towards the opposite end (13) of the die part (1). A press tool according to any one of claims 1 to 11, characterized in that the first leg (4) has a wedge-shaped shape and the second leg (6) has a wedge-shaped shape, each having a base connected to the remainder of the die member (1) and a respective free end (10, 11) at the end of the first and second die surfaces (5, 7) opposite the corner (8). A press tool according to any one of claims 1 to 12, characterized in that the cemented carbide forming the portion (9) has a larger average carbide grain size than the cemented carbide forming the first leg (4) and the second leg (6). A press tool according to any one of claims 1 to 13, characterized in that the cemented carbide comprises particles of tungsten carbide in a matrix of cobalt binder, and the cemented carbide forming the part (9) has a higher cobalt content than the cemented carbide forming the first leg (4) and the second leg (6). 15. A press tool according to claim 1, characterized in that it comprises a first die part (1) and a corresponding second die part (2) according to any one of claims 1 to 14, the first and second die parts (1, 2) being arranged such that the free ends (10, 11) of their respective first and second legs (4, 6) are arranged towards each other, thereby defining a die cavity (3), and at least one punch (24, 25) arranged to be introduced into the die cavity (3) defined by the first die part (1) and the second die part ( 2 ) for the purpose of compacting a powder introduced into the die cavity (3). 16. A method for producing a press tool according to any one of claims 1 to 15, comprising the steps of:
- forming a first green body adapted to form a first part (20, 21) of a mould member (1);
- forming a second green body adapted to form the second part (22) of the mould member (1);
- sintering said first green body into a first part (20, 21) of said mould member (1),
16. A method for manufacturing a press tool according to any one of claims 1 to 15, comprising the steps of: sintering the second green body into a second part (22) of the die member (1), which when attached to the first part (20, 21) forms the portion (9) of the die member (1); and attaching the first part (20, 21) to the second part (22) by sintering, wherein at the interface between the first and second parts, a binder of the first part and a binder of the second part melt during the sintering.

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