Split die press tool

Abstract

A split die press tool for forming a green body (8) for a double-sided double positive cutting insert for cutting metal by compressing a powder, comprising a die having at least two die sections (1, 2) forming a punch tunnel (18) extending along a vertical pressing axis (6) between them, an upper punch unit (3) and a lower punch unit (4), wherein when the lower punch unit (4) is in a distal position in the form of a reduced pressure position, a front end periphery (20) of the lower punch unit (4) is at a first expansion level (24) corresponding to a maximum downward vertical reduced pressure expansion of the green body (8) to be formed. The punch tunnel (18) includes a first side portion (22) located on at least one of the die sections (1), the first side portion (22) having a downward vertical extension from a first pressing level (23) to a first expansion level (24) and inclined downwardly away from the pressing axis (6) by an angle β that is equal to or greater than the angle α of the adjacent inclined lower surface (13) of the green body (8). The punch tunnel (18) includes a second side portion (25) located on at least one of the die sections (1), the second side portion (25) being vertically aligned with the first side portion (22) and having a downward vertical extension from the first expansion level (24) to a first restraining level (27), where the horizontal distance to the adjacent front end periphery of the lower punch unit (4) is smaller than at the first expansion level (24).

Description

[Technical field]

[0001] The present invention relates to a split-die press tool for compacting powder to form a green body for a double-sided positive cutting insert. [Background technology]

[0002] A conventional cutting insert typically comprises a body having a top surface, a bottom surface, and circumferential side surfaces. A midplane exists between the top and bottom surfaces. A type of cutting insert commonly referred to as a conventional "double-sided cutting insert" has a top cutting edge at the intersection between the top and side surfaces and a bottom cutting edge at the intersection between the bottom and side surfaces. Moreover, such cutting inserts are indexable to present one of the cutting edges at a time for the cutting operation.

[0003] A group of such double-sided cutting inserts are arranged to have as chip surfaces a portion of the top surface adjacent the top cutting edge and a portion of the bottom surface adjacent a portion of the bottom cutting edge. The portion of the side surface adjacent the top cutting edge and the portion of the side surface adjacent the bottom cutting edge form respective flanks. The flanks have a negative nominal clearance angle if they are inclined 90° to the mid-plane and a positive nominal clearance angle if they are inclined inwardly from the associated cutting edge toward the mid-plane toward the center of the cutting insert. A double-sided cutting insert is called double positive if both of its second flanks have a positive nominal clearance angle. In such double positive cutting inserts, the side surfaces typically have a waist at the mid-plane.

[0004] A conventional method for making cutting inserts for metal cutting is to form a green body by compressing a powder in a press tool. The process of forming the green body in the press tool typically includes filling a press tunnel in the press tool with powder, compressing the powder to form a green body in a compressed state, and decompressing the compressed green body, which causes the green body to expand. The expanded and relaxed green body is then removed from the press tool and then typically undergoes additional process steps such as sintering, grinding, and / or coating to form the final cutting insert.

[0005] When compressing the powder to form a green body for a double-sided and double positive cutting insert, a split die press tool having horizontally movable and separable die sections may be used. The press tool further includes upper and lower punches that are vertically movable. The side surfaces of the green body for forming the double-sided and double positive cutting insert typically have a shape similar to that of the side surfaces of the finished cutting insert, including sloping inwardly toward the center of the green body. When the powder is compressed to form the green body in its compressed state, the lower punch is in the uppermost position inside the press tunnel in the press tool. The press tunnel surface of the die section adjacent to the green body when the green body is in the compressed state has an extension equal to the side surface of the green body. Thus, in the case of a green body for a double-sided and double positive cutting insert, the press tunnel surface is configured to follow the slope of the side surface of the green body. Furthermore, the sloped surface of the press tunnel extends a vertical distance below the front end surface of the lower punch when the lower punch is in the uppermost position. Thus, the green body can expand downwardly upon depressurization without risk of damaging the bottom edge at the lower end of the sloping side surfaces.

[0006] A problem associated with split die press tools of the type described above is that when the press tool is being filled with powder for a green body, an unwanted amount of powder tends to leak out between the lower punch and the side surface of the die section, which can affect the health of the operator, cause damage to the press tool, or cause shape deviations near the edges of the green body due to localized loss of material. Summary of the Invention

[0007] The object of the present invention is to alleviate the drawbacks of the prior art and to provide a split die press tool which allows for reduced powder leakage. This object is achieved according to the present invention by means of a split die press tool as claimed in claim 1.

[0008] The present invention relates to a split die press tool for forming a green body for a double sided double positive cutting insert for metal cutting by compacting a powder, the green body having a top edge, a bottom edge and a side surface connecting the top edge and the bottom edge, the top edge being associated with an adjacent sloping upper surface at the side surface and the bottom edge being associated with an adjacent sloping lower surface at the side surface, both respective sloping surfaces having a positive nominal angle α, the split die press tool comprising: - a die comprising at least two die sections, - each dissection is movably disposed along a horizontal axis to a respective proximal pressing position and to a number of respective distal positions; when each die section is in its respective pressing position, the die sections form a punch tunnel therebetween extending along a vertical pressing axis, Die and an upper punch unit and a lower punch unit, - both having a forward end including a circumferential forward end perimeter and both being disposed within the punch tunnel with their forward ends facing each other; - both are disposed within the punch tunnel movably along a pressing axis to a respective proximal pressing position and to a number of respective distal positions; an upper punch unit and a lower punch unit; Equipped with - when the die section, the lower punch unit and the upper punch unit are in their respective pressing positions, the front end periphery of the lower punch unit is located at a first pressing level, and a compression space corresponding to the compressed state of the green body to be formed is formed in the punch tunnel; - when the lower punch unit is in a distal position in the form of a decompression position, a front end periphery of the lower punch unit is located at a first expansion level corresponding to a maximum downward vertical decompression expansion of the green body to be formed; - the punch tunnel comprises a first side surface portion located in at least one of the die sections, the first side surface portion having a vertical extent from a first pressing level downwardly to a first expansion level; - the first side surface portion is inclined downwards and away from the pressing axis by at least an angle β of the angle α of the adjacent inclined lower surface of the green body to be formed, when viewed in a vertical cross-section of the punch tunnel, - the punch tunnel comprises a second side surface portion located in at least one of the die sections, the second side surface portion being vertically aligned with the first side surface portion and having a vertical extent from the first expansion level downward to a first containment level, the horizontal distance at the first containment level to an adjacent forward end perimeter of the lower punch unit being less than the horizontal distance at the first expansion level; Regarding split die press tooling.

[0009] Thus, the first side surface portion in the punch tunnel is inclined downwards and away from the pressing axis by an angle β, which is at least the angle α of the adjacent lower inclined surface of the green body to be formed in the split die tool. Furthermore, the first side surface portion has a vertical extent from a first pressing level, where the front end periphery of the lower punch unit is located when the lower punch unit is in the pressing position, to a first expansion level, a short distance below the first pressing level, corresponding to the maximum downward vertical expansion of the green body during decompression. Such an inclination and vertical extent of the first side surface portion allows the green body, after being compressed to a compact state in the tool, to expand during decompression without damaging the bottom edge or its associated inclined lower surface through deleterious contact with the side surface in the punch tunnel.

[0010] The second side surface portion is vertically aligned with the first side surface portion and extends downward from the first expansion level to the first suppression level. Thanks to the horizontal distance between the second side surface portion at the first suppression level and the adjacent front end periphery of the lower punch unit being less than the horizontal distance at the first expansion level, the horizontal gap through which powder may leak during filling is narrowed from the first expansion level to the first suppression level. Thus, at least a part of the powder leaking beyond the first expansion level can be stopped at the first suppression level. Thus, the inventive second side surface portion can prevent unwanted leakage of powder through the horizontal gap formed between the lower end of the first side surface portion at the first expansion level and the punch unit during filling of the tool.

[0011] The split die press tool according to the invention is suitable for forming green bodies by compressing powders such as cermets, cemented carbide powders or metallurgical powders. During the formation of the green body in the split die press tool, the powder is compressed to form a green body, which takes on a compressed state after the intended maximum pressure is applied. In the compressed state, the green body has a minimum dimension. When the pressure is removed, the green body expands. When the decompression is complete, the green body is no longer in a compressed state and has experienced a maximum decompression expansion. After the green body is formed and removed from the press tool, it can undergo other processes such as sintering, grinding, edge treatment and / or coating. Cutting inserts are obtained from the green body and can be used for machining, for example metal cutting. Examples of such cutting inserts are cutting inserts for milling, cutting inserts for turning and cutting inserts for drilling.

[0012] The split die press tool according to the invention is suitable for forming green bodies for double-sided double positive cutting inserts for metal cutting. The green body typically comprises a top edge, a bottom edge and a side surface connecting the top edge and the bottom edge. In the finished cutting insert, these edges may constitute cutting edges. The top edge is associated with an adjacent inclined upper surface at the side surface and the bottom edge is associated with an adjacent inclined lower surface at the side surface. In the finished cutting insert, these inclined surfaces may constitute a second clearance surface. Both respective inclined surfaces have a positive nominal angle α, for example between 2 and 35°. In the finished cutting insert, the positive nominal angle α corresponds to a positive nominal clearance angle.

[0013] When viewed in a vertical cross-section through the top edge, the angled upper surface extends downwardly and inwardly towards the center of the cutting insert. When viewed in a vertical cross-section through the bottom edge, the angled lower surface extends upwardly and inwardly towards the center of the cutting insert. The cross-sections define vertical planes parallel to a central vertical plane through the edges. Optionally, the side surfaces have a waist, and the angled surfaces project outwardly from the waist to terminate at the respective edges.

[0014] In some cases, the green body has a circular shape or a polygonal shape, such as a square, rectangular, pentagonal, or hexagonal shape, when viewed in a top view. The green body may have sloping upper and lower surfaces along the entire side surface or a portion thereof, for example, on only a small portion of the side, such as along two sides of a green body having a square or rectangular shape. In some cases, only a portion of the side surface of one or some sides of the green body has both an upper sloping surface and a lower sloping surface.

[0015] The split die press tool includes a die having at least two movable die sections and two movable punch units, the die sections being movable in a direction perpendicular to the punch units.

[0016] When the split die press tool is positioned for operation, the die sections are arranged to be movable in both directions along a horizontal axis, and the punch units are arranged to be movable in both directions along a vertical axis. In this application, terms such as vertical and horizontal, or "up", "down", "inward" and "outward" are used in relation to the operating positions of the split die press tool. A level of the split die press tool corresponds to a vertical position in a vertical cross-section of the split die press tool.

[0017] The split die press tool can include any suitable number of die sections, for example, two or four. The die sections are preferably circumferentially organized around a center, where they can be moved inward toward the center and outward away from the center. Thus, the space in the center of the punch tunnel configuration can be operated to become smaller or larger. Optionally, each die section can be moved individually or synchronized with some or all of the die sections, for example with the die section opposite the center. When a die section moves inward to a position where the punch tunnel has a size for pressing, that die section is in a proximal pressing position. In operation, the proximal pressing position is the innermost position for each die section. Any position of the die section outward from the proximal pressing position is a distal position.

[0018] The punch units are movable along a vertical pressing axis. Possibly, each punch unit comprises a single punch or each punch unit is divided vertically into several part punches. The part punches of a punch unit are arranged, for example, concentrically, forming vertical sections arranged around a center or next to each other as slices. Possibly, each punch unit is movable individually or synchronously with the other punch units. In case of a punch unit comprising several part punches, each part punch can be movable individually or synchronously with some or all of the part punches. The punch units are arranged in a punch tunnel formed in the center of the die section, the upper punch unit enters from above and the lower punch unit enters from below. Their respective front ends therefore face each other. The punch units are in the proximal pressing position when they are moved inwards to a position for applying the intended maximum pressure on the green body to be formed. In operation, this is the innermost position for both punch units. Any upward position of the upper punch unit and any downward position of the lower punch unit are distal positions.

[0019] When all die sections and both punch units are in their respective proximal pressing positions, the space in the center of the punch tunnel forms a compression space corresponding to the dimensions of the green body to be formed in the compressed state.

[0020] Each punch unit has a front end. In embodiments where the punch unit is composed of several partial punches, the front end is generally formed by the front ends of all the partial punches. Each punch unit preferably has a front end surface located at the front end. The front end surface has a topography / geometry that corresponds to the desired topography / geometry of the green body to be formed. The front end has a periphery, which should be understood as the edge of the front end that is furthest away from the center of the punch tunnel, in other words the edge that is closest to the die section. The periphery is preferably also the outer edge of the front end surface and also the outer edge of the entire punch unit.

[0021] Optionally, each punch unit has a circumferential side surface extending downwardly from the end surface. The circumferential side surfaces of the punch units are preferably vertical so that the punch units are guided to slide in the vertically straight portion of the punch tunnel, further reducing the risk of escaping powder hitting and being caught by the circumferential side surfaces.

[0022] The punch tunnel is formed around a space in the center of the die section and is limited radially outward by inwardly facing side surfaces of the die section. These side surfaces comprise several side surface portions that may vary in location, extent, and / or inclination. In some cases, a side surface portion is located on a single die section or extends across several die sections. A side surface portion that extends across several die sections may be a non-continuous surface that is divided by a gap between the die sections when the die sections are in their distal positions.

[0023] During operation, the first and second side surface portions are circumferentially and vertically aligned with the side surface of the green body, and specifically with adjacent sloped lower surfaces of the side surface of the green body, and the first side surface portion faces the adjacent sloped lower side surface of the green body so as to contribute to the formation of the adjacent side surface of the green body during decompression.

[0024] The first and second side surface portions are vertically aligned, with the first side surface portion being vertically above the second side surface portion and connected to the second side surface portion at its lower end.

[0025] The horizontal distance from any one of the side surface portions of the punch tunnel located in at least one die section to the adjacent front end perimeter of the punch unit is, for example, a distance measured horizontally in a vertical cross section. The distance is also measured horizontally when the perimeters are located at different levels. The horizontal distance at the first suppression level is less than the horizontal distance at the first expansion level. According to an embodiment, the horizontal distance at the first suppression level is less than 50%, preferably less than 25%, of the distance at the first expansion level. The horizontal distance at the first suppression level is preferably at most 20 μm, preferably at most 10 μm. It is thus advantageously ensured that a significant amount of powder leakage is prevented.

[0026] According to one embodiment, the horizontal distance at the first restraint level is at least 0.1 μm, preferably at least 2 μm, so that the punch unit can slide in the punch tunnel without excessive friction.

[0027] The vertical distance between the two levels is, for example, the distance measured vertically in a vertical cross section. According to one embodiment, the vertical distance from the first expansion level to the first containment level is at most 1 mm, preferably at most 0.5 mm. Thus, the space between the lower punch unit and the second side surface portion is kept small. Since the leakage of powder is suppressed at the first containment level, the amount of powder that can leak beyond the first expansion level corresponds to the amount of powder that fits within this space located above the first containment level. Such a limited vertical extent therefore advantageously contributes to limiting the leakage of powder.

[0028] During the powder filling step in operation, the lower punch unit is lowered and the space above the lower punch unit in the punch tunnel is filled with powder. When the lower punch unit is operated to move upwards in the subsequent compression step, the front end of the lower punch carries the powder into the compression space. The excess powder fills the space between the second side surface portion and the lower punch. According to one embodiment, the vertical distance from the first expansion level to the first containment level is at least 0.05 mm, preferably at least 0.2 mm. It is thus ensured that there is sufficient space to accommodate such excess powder.

[0029] The maximum vertical downward decompression expansion of the green body to be formed can be 0.5-3% of the total vertical extent (height) of the green body in the compressed state. According to one embodiment, the vertical distance from the first pressing level to the first expansion level is at least 0.05 mm, preferably at least 0.1 mm. This accommodates the most common green body expansion for double-sided double positive cutting inserts.

[0030] The first side surface portion, when viewed in a vertical cross-section of the punch tunnel, is inclined downwards and away from the pressing axis by at least the angle β of the angle α of the adjacent inclined lower surface of the green body to be formed. Thus, in the vertical cross-section, the angles α and β are measured between the respective inclined surfaces and a vertical plane perpendicular to the plane of the vertical cross-section. The same result is obtained when measured in the vertical cross-section between the surfaces in question and the projection of the vertical pressing axis. According to an embodiment, the angle β is between 2 and 35°, preferably between 5 and 20°. This accommodates the most common desired nominal clearance angles for double-sided double positive cutting inserts to be made.

[0031] In some cases, angle β is greater than angle α, and the first side surface portion may extend linearly or concavely when viewed in a vertical cross-section. In embodiments including a curved first side surface portion, angle β should be measured as a tangent to the first side surface portion. Thus, a safety margin is created so that the bottom edge of the green body to be formed is further protected from being damaged by contact with the first side surface portion during expansion.

[0032] According to one embodiment, the angle β is equal to the angle α. Advantageously, the green body to be formed is thus supported during the decompression expansion.

[0033] According to one embodiment, the second side surface portion comprises an upper portion extending downward from the first expansion level to the first relaxation level. Optionally, the upper portion extends in the same direction as the first side surface portion and has a larger inclination angle ε or a slightly concave shape. Thus, the bottom edge of the green body to be formed is further protected from being damaged by contact with the upper portion of the second side surface portion during expansion.

[0034] Optionally, the vertical distance from the first expanded level to the first relaxed level is between 0 and 0.5 mm, preferably between 0.05 mm and 0.2 mm.

[0035] According to one embodiment, the second side surface portion comprises a lower portion, which extends downward from the first relief level to the first restraint level and is inclined downward and towards the pressing axis by an angle γ of at least 5° and at most 45° when viewed in a vertical cross-section of the punch tunnel. It is thus ensured that excess powder that is initially caught between the lower second side surface portion and the adjacent side of the lower punch unit does not get stuck. After the decompression step during operation, the lower punch is retracted, the section is moved to a distal position and the excess powder is released and can slide down on the lower surface portion.

[0036] The lower portion of the second side surface portion is preferably shaped, when viewed in vertical cross section, to allow excess powder to fall off more easily, for example in a straight or curved shape, where a convex shape may be beneficial.

[0037] According to one preferred embodiment, all locations of the first side surface portion and the second side surface portion below the expansion level have a horizontal distance to the adjacent forward end periphery of the lower punch unit that is greater than the horizontal distance at the suppression level.

[0038] According to one embodiment, when the lower punch unit is in the distal retracted position in the form of the filling position, the front end periphery of the lower punch unit is located at the filling level, which is below the first suppression level. It is advantageous to design a split die press tool with such a low filling position, since it allows enough room to initially fill the powder at a low density and still achieves strong compaction when moving the lower and upper punch units to their respective proximal pressing positions. It is also advantageous that all available space for leaked powder, which is the space above the first suppression level, is located above the level of the filling position.

[0039] According to one embodiment, the punch tunnel comprises a bottom side surface portion located in at least one of the die sections, which is vertically aligned with the second side surface portion and has a vertical extent from a first suppression level downward to a filling level. At each level between the first suppression level and the filling level, the horizontal distance from the bottom side surface portion to the adjacent front end periphery of the lower punch unit is the same. Thus, the lower punch unit is properly guided in the punch tunnel and all available space for leaked excess powder is located above the first suppression level.

[0040] Both the bottom side surface portion and the adjacent portion of the circumferential side surface of the punch unit are preferably straight and vertical when viewed in a vertical cross-section.

[0041] According to one embodiment, the side surface portion corresponding to the first and second side surface portions is arranged adjacent to the upper punch unit, which is advantageous to prevent the powder from leaking upwards during the compaction of the powder in the pressing step. According to one exemplary embodiment, when the upper punch unit is in the pressing position, a front end periphery of the upper punch unit is located at a second pressing level; when the upper punch unit is in a distal position in the form of a decompression position, a forward end periphery of the lower punch unit is located at a second expansion level corresponding to a maximum upward vertical decompression expansion of the green body; - the punch tunnel comprises a third side surface portion located in at least one of the die sections, the third side surface portion being vertically aligned with the first and second side surface portions and having a vertical extent from the second pressing level upwardly to a second expansion level; the third side surface portion is inclined upwards and away from the pressing axis by at least an angle β of the angle α of the adjacent upper inclined surface of the green body to be formed, when viewed in a vertical cross-section of the punch tunnel; - the punch tunnel comprises a fourth side surface portion located in at least one of the die sections, the fourth side surface portion being vertically aligned with the third side portion and having a vertical extent from the second expansion level upwardly to a second suppression level, wherein at the second suppression level a horizontal distance to an adjacent forward end perimeter of the upper punch unit is less than the horizontal distance at the second expansion level.

[0042] Other embodiments have first and second side surface portions and differently shaped surfaces on at least one die section in the upper punch unit.

[0043] It is preferred that the third side surface portion is symmetrical to the first side surface portion and the fourth side surface portion is symmetrical to the second side surface portion across the horizontal axis between the first and second pressing levels. The symmetry can be mirror symmetry or rational symmetry. Double-sided cutting inserts to be made from the green bodies to be formed in the press tool usually have rotational symmetry. This embodiment is therefore advantageously suitable for forming green bodies for such common cutting inserts.

[0044] According to another aspect of the invention, the split die press tool described above comprises a powder pressable into a green body in a compressed state and decompressible to form a green body. The split die press tool thus also includes a powder and a green body to be formed from the powder. The formed green body has a top edge, a bottom edge, and side surfaces connecting the top and bottom edges, the top edge associated with an adjacent sloping upper surface at the side surfaces and the bottom edge associated with an adjacent sloping lower surface at the side surfaces, both respective sloping surfaces having a positive nominal angle α.

[0045] Exemplary embodiments will now be described in more detail with reference to the accompanying drawings. [Brief description of the drawings]

[0046] [Figure 1] FIG. 1 is a schematic diagram of a first embodiment of a split die press tool with two die sections, an upper punch, and a lower punch in a pressing position. [Diagram 2] FIG. 1 is a schematic exploded view of a first embodiment of a split die press tool. [Diagram 3] FIG. 2 is a perspective view of a green body formed in a split die press tool according to a first embodiment. [Figure 4] FIG. 4 is a view of a vertical cross-section through the green body of FIG. 3, the plane of the vertical cross-section being the mid-vertical plane. [Diagram 5] FIG. 2 is an enlarged cross-sectional view of a split die press tool according to a first embodiment when the split die press tool is set to compress powder to form a green body in a compressed state. [Figure 6] 6 is an enlarged cross-sectional view corresponding to FIG. 5 of a split die press tool according to the first embodiment when the split die press tool is set to allow the green body to expand downward to its maximum extent during depressurization. [Figure 7] FIG. 7 is a view corresponding to the view of FIG. 6 of a second embodiment of a split die press tool. [Figure 8a] FIG. 2 is a cross-sectional view of a split die press tool illustrating the positions of the die sections and punch units during the press cycle. [Figure 8b] FIG. 2 is a cross-sectional view of a split die press tool illustrating the positions of the die sections and punch units during the press cycle. [Figure 8c] FIG. 2 is a cross-sectional view of a split die press tool illustrating the positions of the die sections and punch units during the press cycle. [Figure 8d] FIG. 2 is a cross-sectional view of a split die press tool illustrating the positions of the die sections and punch units during the press cycle. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0047] The figures are all schematic, not necessarily to scale, and generally show only those parts necessary to clarify the respective embodiment, while other parts may be omitted or merely suggested. Unless otherwise indicated, like reference numerals refer to like or corresponding parts in the various figures.

[0048] 1 and 2 the general design of one embodiment of a split die press tool according to the invention is shown. The split die press tool comprises two die sections 1, 2, an upper punch unit in the form of a single upper punch 3 and a lower punch unit in the form of a single lower punch 4.

[0049] Both die sections 1, 2 are movably disposed along a horizontal axis 5, each movable to a respective proximal pressing position and to a number of respective distal positions. Specifically, die sections 1, 2 are movable inwardly towards a center 7 and outwardly away from the center 7.

[0050] Both punches 3, 4 are movably arranged along a vertical pressing axis 6, each movable to a respective proximal pressing position and to a number of respective distal positions. In particular, punches 3, 4 are movable towards each other and towards a centre 7, and outwardly movable away from each other and from the centre 7.

[0051] In the exemplary embodiment, both die sections 1, 2 and both punches 3, 4 are individually moveable independent of the other die section and punch.

[0052] The split die press tool is operable to form a green body by compressing a powder, which in this exemplary embodiment is a cemented carbide powder. During operation, the powder is compressed to form a green body in a compressed state, which is then decompressed to expand the green body to a final shape. In FIG. 2, the green body 8 formed in the tool is shown, the green body having a final shape. The green body 8 is to be used later in a process for making cutting inserts for metal cutting.

[0053] 3 and 4, the green body 8 includes a top surface 14, a bottom surface 15, and a circumferential side surface 11 connecting the top surface 14 and the bottom surface 15. At the intersection between the side surface 11 and the top surface 14, a top edge 9 is defined. At the intersection between the side surface 11 and the bottom surface 15, a bottom edge 10 is defined. The top edge 9 is associated with an adjacent inclined upper surface 12 at the side surface 11, and the bottom edge 10 is associated with an adjacent inclined lower surface 13 at the side surface. In FIG. 4, a vertical cross section is shown through the top edge 9 and the bottom edge 10, which is a central vertical plane 21. The top surface 12 extends downwardly and inwardly by an angle α, and the bottom surface 13 extends upwardly and inwardly by an angle α. Both angles α constitute positive nominal angles that will form a positive nominal clearance angle in the finished cutting insert. The finished cutting insert made from the green body 8 will be double positive on both sides. In the green body 8, the nominal angle α is the angle between the vertical planes 16 perpendicular to the plane of the vertical cross section according to the diagram in FIG. 4. In a first embodiment, the angle α is 15°. Due to the inclined upper and lower surfaces 12, 13, the green body has a waist in a central horizontal plane 17.

[0054] When die sections 1, 2 are in their respective pressing positions, they form a punch tunnel 18 therebetween, with center 7 located at the center of punch tunnel 18. In FIG. 1, both die sections 1, 2 and both punches 3, 4 are in their respective proximal pressing positions, with a compression space formed therebetween that corresponds to the shape of green body 8 in a compressed state. By operating die sections 1, 2 and / or punches 3, 4 to move to their respective distal positions, the space between components 1, 2, 3, 4 becomes larger to allow green body 8 to expand and to allow green body 8 to be removed from the split die press tool.

[0055] The upper punch 3 and lower punch 4 each have a forward end surface 19 that corresponds to the desired topography of the top surface 14, bottom surface 15, respectively, of the green body. Each forward end surface 19 has a circumferential perimeter 20. Depending on the location of the lower and upper punches 3, 4 in the punch tunnel, the respective perimeters are located at corresponding different heights, or levels, within the punch tunnel 18.

[0056] When the lower punch 4 is in the proximal pressing position, as shown in FIG. 5, its front end perimeter 20 is located at the first pressing level 23. The green body is in a compressed state. When the lower punch 4 is in the distal decompression position, as shown in FIG. 6, its front end perimeter 20 is located at the first expansion level 24. The vertical distance 38 between the first pressing level 23 and the first expansion level 24 corresponds to the maximum downward vertical decompression expansion of the green body 8 after it is released from the compressed state. According to the first embodiment, the vertical distance 38 is 0.1 mm. The first expansion level 24 is therefore located below the first pressing level 23.

[0057] During operation, when the split die press tool is filled with powder, the upper punch 3 is moved aside to expose the punch tunnel 18 and the lower punch 4 is in a distal filling position, see FIG. 8a. When the lower punch 4 is in the filling position, the front end perimeter 20 is at the filling level 35.

[0058] The upper and lower punches 3, 4 each have a circumferential side surface 36 extending rearwardly from the periphery 20 of the respective forward end surface 19. According to a first embodiment, the circumferential side surfaces 36 are each vertical and, when viewed in the transverse plane of Figures 5 and 6, parallel to the pressing axis 6.

[0059] The punch tunnel 18 comprises a first side surface portion 22 located on the first die section 1, see Figs. 5 and 6. As can be derived from Figs. 1 and 2, in the first embodiment described, the second die section 2 also comprises a corresponding first side surface portion 22. The first side surface portion 22 is located in circumferential alignment with the adjacent inclined lower surface 13 of the green body 8 and has a vertical extent from a first pressing level 23 downwards to a first expansion level 24. The first side surface portion 22 is inclined downwards and outwards away from the pressing axis 6 from the first pressing level 23 by an angle β, see Fig. 6. The angle β can also be measured as the angle between the first side surface portion 22 and the vertical plane 16 perpendicular to the plane of the vertical cross section according to the view of Fig. 6. In the first embodiment shown, the angle β is 15° and is therefore equal to the angle α. In other embodiments, the angle β is greater than the angle α.

[0060] The punch tunnel 18 further comprises a second side surface portion 25, which is also located on the first die section 1. In the first embodiment, the second die section 2 also comprises a second side surface portion 25. The second side surface portion 25 is vertically aligned with the first side surface portion 22 and is connected to a lower end of the first side surface portion 22 at the first expansion level 24. The second side surface portion 25 has a vertical extent from the first expansion level 24 downward to a first containment level 27. The first containment level 27 is a level in the punch tunnel 18 below the first expansion level 24, and the vertical distance 39 from the first expansion level 24 to the first containment level 27 is 0.19 mm. In the first embodiment, the total distance from the first pressing level 23 to the first suppression level 27 is the sum of the distance 38 and the distance 39, which in the first embodiment amounts to 0.29 mm.

[0061] Each point on the first and second side surface portions 22, 25 has a horizontal distance to the adjacent front end perimeter 20 of the lower punch 4. This horizontal distance is the distance measured in the horizontal direction when viewed in cross-section in Figure 6, and also measured horizontally when the perimeter 20 is located at different levels.

[0062] 5, the horizontal distance 28 between the second side surface portion 25 at the first restraining level 27 and the front end perimeter 20 of the lower punch 4 is less than the water wall distance 29 between the second side surface portion 25 (or the first side surface portion 22) at the first expansion level 24 and the front end perimeter 20 of the lower punch 4. When the first die section 1 is in the proximal pressing position as shown in FIG. 5, the horizontal distance 28 between the second side surface portion 25 at the first restraining level 27 and the front end perimeter 20 of the lower punch 4 is 5 μm, and the horizontal distance 29 between the second side surface portion 25 (or the first side surface portion 22) at the first expansion level 24 and the front end perimeter 20 of the lower punch 4 is determined by the maximum downward vertical decompression expansion and the angle β.

[0063] The second side surface portion 25 comprises an upper portion 30 extending downward from the first expansion level 24 to a first relieving level 31. In the first embodiment described, the upper portion 30 extends in the same direction as the first side surface portion 22. The upper portion 30 is inclined downwards and outwards away from the pressing axis 6 by an angle ε. The angle ε can be measured as the angle between the upper portion 30 and the vertical plane 16 perpendicular to the plane of the vertical cross section according to the view of FIG. 5. In the first embodiment shown, the angle ε is 15° and is therefore equal to the angles α and β.

[0064] The second side surface portion 25 further comprises a lower portion 32 extending downwards from the first relief level 31 to the first restraint level 27. The lower portion 32 extends downwards towards the pressing axis 6 by an angle γ of 30°. The angle γ can be measured as the angle between the lower portion 32 and the vertical plane 16 perpendicular to the plane of the vertical cross section according to the view of FIG.

[0065] According to the first embodiment, both the upper portion 30 and the lower portion 32 have a linear extent when viewed in the cross-section of FIG. 6. In the first embodiment, the vertical distance 33 between the first expansion level 24 and the first relief level 31 is 0.1 mm, and the vertical distance from the first relief level 31 to the first restraint level 27 is 0.09 mm. In the first embodiment, the total vertical distance 39 of the second side surface portion 25 from the first expansion level 24 to the first restraint level 27 is the sum of the distance 33 and the distance 40. When the first die section 1 is in the proximal pressing position as shown in FIG. 5, the horizontal distance 34 from the second side surface portion 25 at the first relief level 31 to the front end perimeter 20 of the lower punch 4 is affected by the angle ε and the distance 33. This is the maximum horizontal distance from the side surface of the punch tunnel 18 to the front end perimeter 20 of the lower punch 4.

[0066] Finally, the punch tunnel 18 comprises a bottom side surface portion 37, which is also located in the first die section 1. In the first embodiment, the second die section 2 also comprises a bottom side surface portion 37. The bottom side surface portion 37 is vertically aligned with the first and second side surface portions 22, 25 and is connected to the lower end of the lower portion 32 of the second side surface portion 25 at the first restraining level 27. The bottom side surface portion 37 has a vertical extent from the first restraining level 27 downwards to the filling level 35, the bottom side surface portion 37 being vertical. The filling level 35 is below the first restraining level 27, and the vertical distance 41 from the first pressing level 23 to the filling level 35 is 50% of the total vertical extent (height) of the green body in the compressed state. At each level between the first restraining level 27 and the filling level 35, the horizontal distance from the bottom side surface portion to the adjacent front end periphery 20 of the lower punch 4 is the same. Thus, the gap between the circumferential side surface 36 and the bottom side surface portion 37 of the lower punch 4 is constant and equal to the horizontal distance 28 at the first restraining level 27. When the first die section 1 is in the proximal pressing position as shown in FIG. 5, the horizontal distance 28 and the gap are 5 μm.

[0067] The first die section of the first embodiment comprises a third side surface portion 42 and a fourth side surface portion 43. These side surface portions 42, 43 have locations and extents relative to the top edge 9 of the green body 8, the upper surface 12 of the green body 8, and the upper punch 3 that correspond to the locations and extents of the first side surface portion 22 and the second side surface portion 25 relative to the bottom edge 10 of the green body 8, the lower surface 13 of the green body 8, and the lower punch 4. Thus, the third side surface 42 and the fourth side surface portion 43 will not be described in detail. In the first embodiment, across a central neutral horizontal plane in the waist of the green body in the compressed state, the third side surface portion 42 is a mirror image of the first side surface portion 22, and the fourth side surface portion 43 is a mirror image of the second side surface portion 25. However, in other embodiments, the third side surface portion 42 and the fourth side surface portion 43 have other symmetries about the horizontal axis in the neutral plane. Still other embodiments have only the first side surface portion 22 and the second side surface portion 25 and have various side surfaces on the upper punch.

[0068] With reference to Figures 8a to 8f, the positions and steps during a pressing cycle when a split die press tool according to a first embodiment is operated will be described.

[0069] In FIG. 8a, the first die section 1 and the second die section 2 are in their respective proximal pressing positions and form a punch tunnel 18 between them. The upper punch 3 has been removed from the punch tunnel 18 so that the punch tunnel is accessible from above. The lower punch 4 is in a distal position in the form of a filling position, with the front end perimeter 20 located at a filling level 35. A predetermined amount of cemented carbide powder is filled into the punch tunnel 18. The powder flows downwards in the punch tunnel 18 to fill the space in the punch tunnel 18 upwards from the front end 19 of the lower punch 4. As shown in the figure, the lower portion 32 of the second side surface portion 25 extends downwards towards the pressing axis 6. Thanks to this advantageous design, only a small gap exists between the perimeter 20 of the lower punch 4 and the first die section 1. When the first die section 1 and the second die section 2 are in their respective proximal pressing positions, the horizontal distance 28 of the gap is 5 μm. This narrow gap allows only a small amount of powder to escape past the front end perimeter 20 of the lower punch 4 .

[0070] In FIG. 8b, the split die press tool has been operated to move the lower punch 4 to its proximal pressing position, the periphery 20 of the lower punch 4 being located at the first pressing level 23. Furthermore, the split die press tool has been operated to move the upper punch 3 to its proximal pressing position, the periphery 20 of the upper punch 3 being located at the second pressing level 44. The powder is thus compressed and a green body 8 in a compressed state is formed. Excess powder fills the space between the first and second side surface portions 22, 25 on the one hand and the lower punch 4 on the other hand. Similarly, excess powder fills the space between the third and fourth side surface portions 42, 43 on the one hand and the upper punch 3 on the other hand. Due to the upper portion 48 of the fourth side surface 43 (corresponding to the lower portion 32 of the second side surface portion 25) extending upwards towards the pressing axis 6, only a small gap exists between the periphery 20 of the upper punch 3 and the side surface of the first die section 1. When the first die section 1 and the second die section 2 are in their respective proximal pressing positions, the horizontal distance 28 of the gap is 5 μm. Due to this narrow gap, only a small amount of powder can erupt beyond the front end perimeter 20 of the upper punch 3 as the powder is consolidated.

[0071] The split die press tool according to the first embodiment further comprises a second relaxation level 45 corresponding to the first relaxation level 31 and a second suppression level 46 corresponding to the first suppression level 27 .

[0072] After pressing, the lower punch 4 is operated to move to a distal position in the form of its reduced pressure position, where the periphery 20 is located at the first expansion level 24, see FIG. 8c. At the same time, the upper punch 3 is operated to move to a distal position in the form of its reduced pressure position, where the periphery 20 is located at the second expansion level 47. The first die section 1 and the second die section 2 are still in their respective pressing positions. Thus, the green body 8 experiences a vertical reduced pressure expansion, where the green body 8 expands in a vertical direction. As shown in FIG. 6, the inclination angle β of the first side surface portion 22 and the third side surface portion 42 is equal to the inclination angle α of the lower adjacent surface 13 and the upper adjacent surface 12 of the green body 8, respectively. Thus, advantageously, the bottom edge 10 and the top edge 9 are avoided from being damaged by the side surfaces during the reduced pressure expansion. The first expansion level 24 and the second expansion level 47 correspond to the total maximum vertical decompression expansion of the green body 8. The vertical distance between the second expansion level 47 and the first expansion level 24 corresponds to the vertical distance from the top edge 9 to the bottom surface 10 of the green body 8 in its final shape.

[0073] After decompression, the first die section 1 and the second die section 2 are operated further apart to their respective distal positions to release the finished green body 8. Thus, the green body 8 experiences a horizontal decompression expansion, where the green body 8 expands in a horizontal direction. See FIG. 8d, the excess powder trapped in the punch tunnel 18 can leak downwards and be removed from the split die press tool. This is facilitated by the inclination angle γ of the lower portion 32 of the second side surface portion 25, which is 30°, see FIG. 6. Finally, the upper punch 3 is removed from the punch tunnel 18, and the lower punch 4 is pushed out together with the finished green body 8 resting on the front end surface 19.

[0074] A second embodiment of the split die press tool is shown in FIG. 7. The second embodiment differs from the first embodiment in the design of the first side surface portion 22 and the second side surface portion 25. The first side surface portion 22, the top portion 30, and most of the bottom portion 32 of the second side surface portion 25 are concavely curved. The lowest part of the bottom portion 32 of the second side surface portion 25 is convex in order to smoothly contact the vertical bottom side surface portion 37. This embodiment is advantageous in that the risk of powder getting stuck in sharp corners or pockets is still further reduced. The second embodiment is an example of an embodiment in which the angle β is larger than the angle α.

[0075] The first die section of the second embodiment comprises a third side surface portion 42 and a fourth side surface portion 43. These side surface portions 42, 43 have locations and extents relative to the top edge 9 of the green body 8, the upper surface 12 of the green body 8, and the upper punch 3 which correspond to the locations and extents of the first side surface portion 22 and the second side surface portion 25 relative to the bottom edge of the green body 8, the lower surface 13 of the green body 8, and the lower punch 4. Accordingly, they will not be further described or illustrated in the figures.

Claims

1. 1. A split die press tool for forming a green body (8) for a double sided double positive cutting insert for cutting metal by compacting powder, the green body (8) having a top edge (9), a bottom edge (10) and a side surface (11) connecting the top edge (9) and the bottom edge (10), the top edge (9) being associated with an adjacent inclined upper surface (12) at the side surface (11) and the bottom edge (10) being associated with an adjacent inclined lower surface (13) at the side surface (11), both respective inclined surfaces (12, 13) having a positive nominal angle α, the split die press tool comprising: a die comprising at least two die sections (1, 2), each dissection (1, 2) is arranged to be movable along a horizontal axis to a respective proximal pressing position and to several respective distal positions; when each die section (1, 2) is in its respective pressing position, the die sections (1, 2) form between them a punch tunnel (18) extending along a vertical pressing axis (6); Die and an upper punch unit (3) and a lower punch unit (4), - both have a forward end (19) with a circumferential forward end periphery (20) and both are disposed within the punch tunnel (18) with their forward ends (19) facing each other; both are arranged in a punch tunnel (18) so as to be movable along a pressing axis (6) to a respective proximal pressing position and to several respective distal positions; An upper punch unit (3) and a lower punch unit (4), Including, when the die sections (1, 2), the lower punch unit (4) and the upper punch unit (3) are in their respective pressing positions, the front end periphery (20) of the lower punch unit (3) is located at a first pressing level (23) and a compression space is formed in the punch tunnel (18) which corresponds to the compressed state of the green body (8) to be formed, when the lower punch unit (4) is in a distal position in the form of a reduced pressure position, the front end periphery (20) of the lower punch unit (4) is located at a first expansion level (24) corresponding to a maximum downward vertical reduced pressure expansion of the green body (8) to be formed, the punch tunnel (18) comprises a first side surface portion (22) located in at least one of the die sections (1), the first side surface portion (22) having a vertical extent from a first pressing level (23) downwardly to a first expansion level (24); the first side surface portion (22), when viewed in a vertical cross-section of the punch tunnel (18), is inclined downwards and away from the pressing axis (6) by at least an angle β of the angle α of the adjacent inclined lower surface (13) of the green body (8) to be formed, a split die press tool, wherein the punch tunnel (18) comprises a second side surface portion (25) located in at least one of the die sections (1), the second side surface portion (25) being vertically aligned with the first side surface portion (22) and having a vertical extent from the first expansion level (24) downwardly to a first suppression level (27), characterized in that at the first suppression level (27) the horizontal distance to the adjacent front end periphery of the lower punch unit (4) is less than the horizontal distance at the first expansion level (24).

2. 2. The split die press tool according to claim 1, wherein when at least one die section (1) is in the pressing position, the horizontal distance to the adjacent front end periphery (20) of the lower punch unit (4) at the first restraint level (27) is less than 20 μm.

3. 2. The split die press tool according to claim 1, wherein the vertical distance (39) from the first expansion level (24) to the first containment level (27) is maximum 1 mm.

4. 2. The split die press tool of claim 1, wherein the vertical distance (39) from the first expansion level (24) to the first containment level (27) is at least 0.05 mm.

5. 2. The split die press tool of claim 1, wherein the vertical distance (38) from the first pressing level (23) to the first expansion level (24) is at least 0.1 mm.

6. 2. The split die press tool according to claim 1, wherein the angle β is between 2 and 35°, preferably between 5 and 20°.

7. 2. The split die press tool of claim 1, wherein the angle β of the first side surface portion (22) is equal to the angle α.

8. 2. The split die press tool of claim 1, wherein the second side surface portion (25) includes an upper portion (30) that extends in the same direction as the first side surface portion (22) downwardly from the first expansion level (24) to the first relief level (31).

9. 9. The split die press tool according to claim 8, wherein the second side surface portion (25) comprises a lower portion (32) which extends downwardly from the first relief level (31) to the first restraint level (27) and which is inclined downwardly and towards the pressing axis (6) by an angle γ of at least 5° and at most 45° when viewed in a vertical cross-section of the punch tunnel (18).

10. 2. The split die press tool according to claim 1, wherein when the lower punch unit (4) is in a distal position in the form of a filling position, a front end periphery (20) of the lower punch unit (4) is located at a filling level (35) below the first suppression level (27).

11. the punch tunnel (18) includes a bottom side surface portion (37) located in at least one of the die sections (1), the bottom side surface portion (37) being vertically aligned with the second side surface portion (25) and having a vertical extent from a first containment level (27) downwardly to a fill level (35); A split die press tool according to claim 10, wherein at each level between the first restraining level (27) and the filling level (35), the horizontal distance from the bottom side surface portion (37) to the adjacent front end periphery (20) of the lower punch unit (4) is the same.

12. when the upper punch unit (3) is in the pressing position, the front end periphery (20) of the upper punch unit (3) is located at the second pressing level (44); when the upper punch unit (3) is in a distal position in the form of a reduced pressure position, the front end periphery (20) of the upper punch unit (3) is located at a second expansion level (47) corresponding to a maximum upward vertical reduced pressure expansion of the green body (8); the punch tunnel (18) includes a third side surface portion (42) located in at least one of the die sections (1), the third side surface portion (42) being vertically aligned with the first and second side surface portions (22, 25) and having a vertical extent from a second pressing level (44) upwardly to a second expansion level (47); the third side surface portion (42), when viewed in a vertical cross-section of the punch tunnel (18), is inclined upwards and away from the pressing axis (6) by at least an angle β of the angle α of the adjacent upper inclined surface (12) of the green body (8) to be formed, 2. The split die press tool of claim 1, wherein the punch tunnel (18) comprises a fourth side surface portion (43) located in at least one of the die sections (1), the fourth side surface portion (43) being vertically aligned with the third side portion (42) and having a vertical extent from the second expansion level (47) upwardly to a second suppression level (46), wherein at the second suppression level (46) the horizontal distance to the adjacent front end perimeter (20) of the upper punch unit (3) is less than the horizontal distance at the second expansion level (47).

13. 13. The split die press tool according to claim 12, wherein the third side surface portion (42) is symmetrical to the first side surface portion (22) and the fourth side surface portion (43) is symmetrical to the second side surface portion (25) across a horizontal axis between the first pressing level (23) and the second pressing level (44).

14. a powder, the powder being pressable into a green body (8) in a compressed state, the green body (8) being decompressible to form the green body (8); a green body (8) having a top edge (9), a bottom edge (10) and a side surface (11) connecting the top edge (9) and the bottom edge (10); - the top edge (9) is associated with an adjacent inclined upper surface (12) at the side surface (11) and the bottom edge (10) is associated with an adjacent inclined lower surface (13) at the side surface (11), both respective inclined surfaces (12, 13) having a positive nominal angle α; 2. The split die press tool of claim 1.

Images