Press tool and method for forming cutting insert green body having through hole - Patents.com

Abstract

The present invention relates to a press tool and a method for compressing powder to form a cutting insert green body (5) having a through hole (6) of length (L). The press tool includes a cavity (4) operable to define a compression space, and a first core rod (7) and a second core rod (8) for forming the through hole (6) together, the first core rod (7) and the second core rod (8), each having a contact surface (9) at a front end. Both core rods (7, 8) are arranged to be movable in both directions along a core axis (10). When both core rods (7, 8) are in their respective press positions, their respective contact surfaces (9) contact each other within the compression space, and when both the first core rod (7) and the second core rod (8) are in their respective release positions, their respective contact surfaces (9) are spaced apart by a distance greater than the length (L). The first core rod (7) comprises a base (11) with a forward-facing abutment surface (17) and a piston (12) having a front portion in the form of a shaft (13) and a head (14). The contact surface (9) of the first core rod (7) is the front end surface of the head (14). The head (14) comprises a rearward-facing abutment surface (17). The piston (12) is movable between a plurality of extended and retracted positions, in which the abutment surface (17) of the head (14) abuts against the abutment surface (17) of the base (11). When both the first core rod (7) and the second core rod (8) are in their respective pressing positions, the piston (12) is in the retracted position.

Description

[Technical field]

[0001] The present invention relates to a press tool for compressing powder to form a cutting insert green body having a through hole of length (L). The present invention further relates to a method of forming a cutting insert green body having a through hole of length (L) using the press tool. [Background technology]

[0002] WO 2004 / 0414463 discloses a uniaxial press for forming green parts from compressed metallurgical powder, in which an opening is imparted to the green part by placing the metallurgical powder around an oblong core rod. The core rod includes a first segment and a second segment, each having complementary ends. The segments are arranged on opposite sides of the press and are movable along their longitudinal axes. In operation, the segments are pressed together such that their ends meet, forming a continuous core rod. Powder is then filled into the die cavity to form the green part. Finally, the segments are retracted and the finished green part is ejected. A problem with this known press is that the segments leave a ring of burrs in the opening of the green part where the ends of the segments touch each other. In the finished cutting insert, such a remaining ring of burrs can form a sharp edge that can damage the fastening screw. Summary of the Invention

[0003] The object of the present invention is to at least partially avoid the above-mentioned problems. This object is achieved according to the present invention by a press tool according to claim 1 and a method for forming a cutting insert green body according to claim 14.

[0004] The press tool of the present invention for compressing powder to form a cutting insert green body having a through hole of length (L) comprises: a cavity operable to define a compression space corresponding to the dimensions of the green body; a first core rod and a second core rod for forming together a through hole, each having a longitudinal extension from a front end to a rear end and a contact surface at the front end; Equipped with - both the first core rod and the second core rod are longitudinally disposed along the core axis with their respective front ends facing each other; - both the first core rod and the second core rod are arranged to be movable in both directions of the core axis, both the first core rod and the second core rod being movable to a respective pressing position and a respective releasing position; When both the first core rod and the second core rod are in their respective pressing positions, their respective contact surfaces contact each other in the compression space; when both the first core rod and the second core rod are in their respective release positions, their respective contact surfaces are spaced apart by a distance greater than a length (L); a first core rod comprising a longitudinally extending rear portion in the form of a base body with a forwardly facing abutment surface at its front end, and a piston having a rear part in the form of a longitudinally extending shaft (13) and a front part in the form of a radially projecting head, The contact surface is the front end surface of the head, the head is provided at its rear end with a rearwardly facing abutment surface, the shaft (13) is longitudinally movably disposed within the base along the core axis such that the piston is movable between a plurality of extended positions and a retracted position in which an abutment surface of the head abuts against an abutment surface of the base; When both the first core rod and the second core rod are in their respective pressed positions, the piston is in a retracted position.

[0005] A method of the present invention for forming a cutting insert green body having a through hole of length (L) using a press tool, the press tool comprising: - a cavity; a first core rod and a second core rod, each having a longitudinal extension from a front end to a rear end and a contact surface at the front end; The first core rod is a longitudinally extending rear portion in the form of a base body with a forwardly facing abutment surface at its front end; a piston having a rear part in the form of a longitudinally extending shaft and a front part in the form of a radially projecting head, the contact surface being a front end surface of the head, the head being provided at its rear end with a rearwardly facing abutment surface; Equipped with - positioning both the first and second core rods longitudinally along the core axis with their respective front ends facing each other; - positioning the piston with its shaft longitudinally along the core axis of the base; - filling the cavity with a predetermined amount of powder; - moving the piston along the core axis to a retracted position, where the abutment surface of the head abuts against the abutment surface of the base; - moving the first core rod and the second core rod along the core axis to respective pressing positions, in which their contact surfaces are in contact with each other in a cavity in the compression space corresponding to the dimensions of the green body; - operating the cavity to compress the powder in the compression space to form a cutting insert green body; - moving the second contact rod rearwardly and the piston forwardly along the core axis to a first extended position; - moving the first and second core rods along the core axis to respective release positions, wherein the respective contact surfaces are separated by a distance greater than a length (L); - operating the cavity to reduce the pressure in the compression space; - removing the cutting insert green body; A method comprising:

[0006] During the formation of the cutting insert green body, both the first core and the second core rod are placed in their respective pressing positions, the contact surfaces contacting each other and the abutment surfaces contacting each other. At the first interface of the contact surfaces and the second interface of the abutment surfaces, respectively, annular burr rings can be formed in the through hole of the cutting insert green body. Thanks to the first core rod with a piston movable in an extended position, these burr rings can be removed or at least significantly reduced before the cutting insert green body is removed from the press tool. This can be achieved, for example, by first retracting the second core rod a certain distance backwards from its pressing position. Thereafter, or at the same time, the piston is moved forward past the burr rings at the interface between the contact surfaces. Then, both the first core rod and the second core rod are moved to their respective release positions, and the piston moves a second time over the interface between the contact surfaces and over the interface between the abutment surfaces. As the piston moves over the burr rings, they are at least partially scraped off from the inner surface of the through hole.

[0007] The press tool according to the invention is suitable for compacting powders such as cermets, cemented carbide powders or metallurgical powders to form cutting insert green bodies. After the finished cutting insert green body is formed and removed from the press tool, it can be subjected to other processes such as sintering, grinding, edge treatment and / or coating. Cutting inserts can be obtained from the cutting insert green body and can be used for machining, for example metal cutting. Examples of such cutting inserts are milling cutting inserts, turning cutting inserts and drilling cutting inserts.

[0008] The press tool according to the invention can be of any suitable type. Preferably, the press tool comprises a die and two punches, which are movable towards and away from each other along the punch axis. For example, the press tool is a so-called single-axis press tool with a die and two punches, a so-called split-die press tool with a die having at least two moving parts and two moving punches, or a so-called cross-hole press tool, whose core axis is perpendicular to the punch axis. The space defined by the die and punches in their closest positions constitutes a compression space corresponding to the shape and dimensions of the cutting insert green body.

[0009] Both the first and second core rods are longitudinally disposed along a core axis with their respective front ends facing each other. The core axis may have any suitable extension within the press tool, for example horizontally or vertically. In a press tool with a movable punch, the core axis may be the same as the punch axis or perpendicular to the punch axis. In a press tool with a split die with halves movable toward and away from each other along the die axis, the core axis may be coincident with the die axis or perpendicular to one or both of the die axis and the punch axis.

[0010] Preferably, the longitudinal axis of the first core rod and the longitudinal axis of the second core rod are aligned and coincident with the core axis, however, the axes may be slightly offset and parallel.

[0011] The advance of a core rod is towards the other core rod, and the retreat is away from the other core rod. Advancement can therefore be towards the centre of the compression space, but also through the centre.

[0012] Optionally, the first core rod and the second core are self-contained components, or one or both are integral and one piece with other parts of the press tool. For example, the core rod may be part of a punch or die half and only movable together with the punch or die half. However, it is preferred that the core rod is a separate component that is movably guided within the press tool, for example within the die or punch.

[0013] According to at least one embodiment, the first and second core rods are arranged to be independently movable. This advantageously allows the first core rod to be moved to any of its positions independent of the position of the second core rod, and vice versa. In another embodiment, the first and second core rods are arranged to be synchronously movable. This advantageously makes the movement of the first and second core rods towards and away from each other easier to drive and control. Optionally, the piston is at least partially movable independently of the movement of the first and second core rods. One or more drive units, such as, for example, electric motors, pneumatic or hydraulic drive units, can be used to drive the movement of the core rods and the piston. The operation of the drive units can be controlled by a control unit, such as a PLC (Programmable Logic Controller).

[0014] Preferably, the first core rod is movable to a scraping position, and the forward facing abutment surface of the base is at most forward when the first core rod is in the press position. The piston is in a first extended position of the plurality of extended positions, and the contact surface in the form of the front end surface of the head is further forward than in the press position, such that the base of the first core rod does not have to move further forward to move the head of the piston forward.

[0015] According to at least one embodiment, the second core rod comprises a tapered segment toward the front end, the base comprises a tapered segment toward the front end, the head has a constant cross section, and in the press position, the length (L) includes at least a portion of the tapered segment of the second core rod, the head, and at least a portion of the tapered segment of the base. This is advantageous in that a cutting insert green body having a through hole with countersunk holes at both ends can be formed in the press tool. Optionally, the tapered segment can extend all the way to the front end, or the segment can include a portion having the same cross section as the head closest to the front end.

[0016] Preferably, the first core rod and the second core rod together form a continuous core rod when both are in their respective pressing positions. In particular, the cross-sectional shape at the contact surface of the second core rod is the same as the cross-sectional shape at the contact surface of the head, and / or the cross-sectional shape at the abutment surface of the head is the same as the cross-sectional shape at the abutment surface of the base. For example, the cross-sectional shape of the head and the core rod over the length (L) is elliptical or cylindrical. The cross-sectional dimensions of the base and the second core rod can increase from the head toward the rear. At least along the length (L), the continuous core rod can be mirror symmetric across a cross-sectional plane located at the center of the length (L). The longitudinal center of the length (L) can correspond to the longitudinal center of the head.

[0017] Optionally, when both core rods are in their respective pressing positions, both contact surfaces are in a central position along the length (L) or in a position lateral to the central position. Thus, during operation, the length (L) may be occupied by portions of the core rods having equal lengths, or the first core rod may occupy a longer length than the second core rod, or vice versa.

[0018] Preferably, the longitudinal length of the head is at least 1 mm shorter than the length (L). Preferably, the longitudinal length of the head is greater than 0.5 mm, more preferably greater than 1.3 mm. According to at least one embodiment, the longitudinal length of the head is 1 / 3 of the length (L).

[0019] According to at least one embodiment, the head has a length in the axial direction of the core axis, and the axial length of the head in the press position can be reduced by 5 to 40 μm, preferably 20 to 30 μm. This allows the press tool to be designed to provide additional compression in the direction of the core axis, which is advantageous when forming cutting insert green bodies with countersinks. For example, the head comprises a material having a Young's modulus (E) of less than 400 GPa, such as steel, or the head comprises a piezoelectric disk that can be operated to vary its thickness.

[0020] According to at least one embodiment, the piston is arranged to be biased towards the first extended position, such that when the second core rod is moved rearward, the piston automatically moves to the extended position, e.g., a further forward position, such as a scraping position. For example, a resilient element, such as a spring, can be arranged to push the piston forward towards the extended position. Alternatively, the first core rod can be configured to provide a bias to the piston by a pressurized fluid, such as air or oil.

[0021] Preferably, the first core rod includes a stop mechanism that defines a maximum extension position of the multiple extension positions of the piston, such that when the piston is in this maximum extension position and the base is moved rearward, the piston moves rearward with the base, and the stop mechanism also prevents the piston from disengaging from the base.

[0022] According to at least one embodiment, the base has a bore extending rearward from an opening at the front end of the base, and the rear end of the shaft extends through the opening into the bore. The forward facing abutment surface of the base is the front end surface surrounding the opening. This is a convenient design of the first core rod that allows the shaft to be guided inside the base in the bore. In embodiments with a biasing element and / or a stop mechanism, these can be located inside the bore.

[0023] According to at least one embodiment, the front end of one of the first and second core rods includes a rearwardly extending recess, and the front end of the other of the first and second core rods includes a mating forwardly extending protrusion that is received within the recess to align the first and second core rods when both are in their respective press positions. For example, the head includes a male protrusion that protrudes forward from the front end, and the second core rod includes a mating female recess that extends rearward from the front end. Good alignment of the first and second core rods allows good tolerance of the through hole of the cutting insert green body to be achieved.

[0024] Optionally, the contact surface is a forward-facing front end surface. The contact surface may be, for example, a front end surface perpendicular to the core axis. In embodiments having mating protrusions / recesses, the contact surface may be a surface of the protrusion / recess. In such embodiments, the contact surface may also be, or include a portion of, the forward-facing, longitudinally extending circumferential surface of the protrusion / recess.

[0025] Optionally, the opening of the bore in the base comprises a countersink.

[0026] According to at least one embodiment, the piston further comprises a neck extending along the core axis from the rear end of the head to the front end of the shaft and mating with a countersink in the base bore. When the piston is in a retracted position, the neck is received within the countersink to align the piston with the base. Good alignment of the piston with the base allows good tolerance of the through hole of the cutting insert green body to be achieved.

[0027] Preferably, both the front and rear ends of the head include protrusions that mate with corresponding recesses in the second core rod and base body, respectively, to provide better alignment of the through holes of the cutting insert green body, and thereby further improved tolerances. The protrusions / recesses may include cooperating conical guide surfaces.

[0028] According to at least one embodiment, the countersink in the base does not cooperate with a corresponding neck in the head. Instead, the countersink is configured to receive debris from a scraped burr ring so that debris is removed from the surface of the shaft. This can reduce wear caused by debris sliding on the surface of the shaft and the inner surface of the through hole. Additionally or alternatively, the head can be provided with an annular groove on a rearward facing abutment surface adjacent the shaft.

[0029] To improve the wear resistance of the head, the head may contain a hard metal, or the head may be provided with a wear-resistant coating, preferably deposited by PVD or CVD techniques.

[0030] Preferably, the piston is removably received in the base so that the piston can be replaced when the head becomes worn, for example at its periphery due to chipping off of a burr ring.

[0031] According to at least one embodiment, the forwardly facing abutment surface of the base is a front end surface adjacent the opening in the base, and the rearwardly facing abutment surface of the head is a rear end surface adjacent the neck. Optionally, the abutment surface is perpendicular to the core axis. In embodiments having a mating neck / countersink, the abutment surface may also be, or include a portion of, the longitudinally extending circumferential surface of the neck / countersink.

[0032] According to at least one embodiment, the shaft and the bore of the base body have the same cross-sectional shape, at least along the portion closest to the opening. The inner dimensions of the bore are adapted to the outer dimensions of the shaft so that the shaft fits into sliding contact in the bore. The cross-sectional shapes of the shaft and the bore can be circular. Optionally, the cross-section has a shape that prevents relative rotation. For example, the cross-sectional shape is polygonal or has a circular portion with straight sides. Alternatively, the shaft is provided with a radially protruding pin that is received in a slot in the bore.

[0033] According to at least one embodiment in which the core axis is horizontal, the shaft has upwardly converging sides forming a ridge. This allows any debris from the chipped burr ring that falls onto the shaft to be guided downwards and away from the shaft. This reduces the risk of debris getting stuck in the opening and causing clogging or wear of the shaft in the bore. For example, the shaft can have a triangular cross section.

[0034] According to at least one embodiment of the present invention method for forming a cutting insert green body having a through hole of length (L) using a press tool includes using a press tool according to the present invention and any embodiment thereof. The steps of the present invention method may be performed in any order suitable for the process in question.

[0035] Preferably, the steps of manufacturing the press tool and placing the first core rod, the second core, and the piston therein are performed initially and before starting the first press cycle. In the following press cycles, these steps can be omitted.

[0036] Preferably, - moving the piston along the core axis to a retracted position, where the abutment surface of the head abuts against the abutment surface of the base; - moving the first core rod and the second core rod along the core axis to respective pressing positions, in which their contact surfaces are in contact with each other in a cavity in the compression space corresponding to the dimensions of the green body; - filling the cavity with a predetermined amount of powder; can be performed in any order.

[0037] According to one embodiment using a cross-hole press tool, the first of these steps is to move the piston, the second step is to move the first and second core rods, and the third step is to fill the cavity. Both the first and second core rods are moved forward into the cavity to reach their respective press positions.

[0038] According to one embodiment using a single axis press tool, the first of these steps is to fill the cavity, the second step is to move the piston, and the third step is to move the first and second core rods. To reach the respective pressing positions, the second core rod is moved backwards from a filling position in the cavity and the first core rod is moved forwards.

[0039] Preferably, the step of operating the cavity to compress the compression space is performed after the above three steps. Preferably, the step of operating the cavity to compress the compression space includes a step of moving the punches towards each other according to a predetermined scheme. For example, the movement of the punches can follow a curve that has a steeper slope, for example, at the beginning of the compression step than at the end. In an embodiment in which a press tool with a split die is used, the movement of the die parts also follows a predetermined scheme. The movement of the die parts can follow a curve that has a steeper slope, for example, at the beginning of the compression step than at the end. Optionally, the movement of each punch and, if applicable, each die is controlled individually or moves all or partly in unison.

[0040] When the cavity reaches the desired compression, a compression space is defined between the die and punch that corresponds to the shape and dimensions of the cutting insert green body.

[0041] According to an embodiment, the method includes an unloading step after the compacting step, in which the punch is retracted a small distance, for example 0.05-0.1 mm, to relax the green body to facilitate the subsequent movement of the core rod.

[0042] Optionally, the step of moving the second core rod backwards includes moving the second core rod completely outward or at least at least 0.1 mm from the through hole of the green body. This gives the head enough space to move forward and scrape off any burr rings that may form in the step of compressing the powder. In that, the head reaches a first extended position that is further forward than the pressing position. In the first extended position, the contact surface of the head is further forward than the burr ring that formed at the interface between the contact surfaces during the compression step. In an embodiment of the method in which a biased piston is used, the head moves forward together with the second core rod moving backwards.

[0043] Preferably the advancement of the head to the first extended position is at least the thickness of the burr ring, which is typically less than 0.1 mm.Preferably the head moves forward a distance equal to the longitudinal length of the head.

[0044] Preferably, the following step includes moving the first core rod and the second core rod to their respective release positions. Optionally, both core rods are positioned with their contact surface outside the through hole, or only one of the first and second core rods is positioned with its contact surface outside the through hole. Preferably, when both the first and second core rods are moved to their respective release positions, the distance between the contact surfaces is at least 1 mm, preferably at least 5 mm, greater than the length (L) of the through hole.

[0045] Preferably, the step of operating the cavity to depressurize the compression space comprises a step of moving the punch, and, where applicable, the die part, away from each other according to a predetermined scheme, in which the punch and any movable die part may follow a curve that may be less steep at the start of the depressurization step than at the end of the depressurization step.

[0046] Finally, the cutting insert green body is removed from the press tool. In an embodiment where one of the core rods has a release position inside the through hole, the cutting insert green body is lifted off from the core rod and only then is it separated from the press tool. Optionally, the contact surface of one of the first and second core rods has the same position in the compression space in both the press position and the release position. In an embodiment where the distance between the contact surfaces in the release position is only a smaller distance than the length (L), the cutting insert green body is removed from the cavity perpendicular to the core axis.

[0047] Exemplary embodiments will now be described in more detail with reference to the accompanying drawings. [Brief description of the drawings]

[0048] [Figure 1] FIG. 2 is a cutaway exploded view of the general design of a press tool according to one embodiment of the present invention as implemented in a cross-hole press tool. [Diagram 2] FIG. 2 shows a longitudinal cross-sectional view of a first core rod and a second core rod according to a first embodiment. [Diagram 3] FIG. 2 is a top view of the press tool according to the first embodiment. [Figure 3a] FIG. 4 is a longitudinal section of a series of press tools according to a first embodiment of the method of the invention, as shown in FIG. [Figure 3b] FIG. 4 is another longitudinal section of the series of press tools according to the first embodiment of the method of the invention as shown in FIG. 3. [Figure 3c] FIG. 4 is yet another longitudinal section of the series of press tools according to the first embodiment of the method of the present invention, as shown in FIG. 3. [Figure 3d] FIG. 4 is yet another longitudinal section of the series of press tools according to the first embodiment of the method of the present invention, as shown in FIG. 3. [Figure 3e] FIG. 4 is yet another longitudinal section of the series of press tools according to the first embodiment of the method of the present invention, as shown in FIG. 3. [Figure 3f] FIG. 4 is yet another longitudinal section of the series of press tools according to the first embodiment of the method of the present invention, as shown in FIG. 3. [Figure 4] 13 shows a longitudinal cross-sectional view of a first core rod and a second core rod according to a further embodiment. [Diagram 5] 13 shows a longitudinal cross-sectional view of a first core rod and a second core rod according to a further embodiment. [Figure 6] 13 shows a longitudinal cross-sectional view of a first core rod and a second core rod according to a further embodiment. [Figure 7a] FIG. 2 is a cross-sectional view of a substrate according to an additional embodiment. [Figure 7b] 1 is another cross-sectional view of an additional embodiment of a substrate. [Figure 7c] 13 is yet another cross-sectional view of an additional embodiment of a substrate. [Figure 8] 1 shows a longitudinal cross-sectional view of a first core rod and a second core rod according to another embodiment. [Figure 9] 13 shows a longitudinal cross-section of a first core rod according to a further embodiment. [Figure 10] 13 shows a longitudinal cross-section of a first core rod according to a further embodiment. [Figure 11] 13 shows a longitudinal cross-section of a first core rod according to a further embodiment.

[0049] All figures are schematic, not necessarily to scale, and generally show only parts necessary to clarify the respective embodiment, while other parts may be omitted or merely suggested. Unless otherwise indicated, like reference numbers refer to like or corresponding parts in the different figures. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0050] In FIG. 1 the general design of one embodiment of the press tool according to the invention is shown in an exploded view. The press tool is a cross-hole press tool with a die 1. In the figure, the die is shown exploded in the middle to show its interior. The press tool further comprises an upper punch 2 and a lower punch 3. The punches 2, 3 are movable towards and away from each other along the punch axis. The die 1, the upper punch 2 and the lower punch 3 define a cavity 4 between them. The cavity (4) is operable to define a compression space by moving the punches towards each other along the vertical punch axis. The compression space corresponds to the space and dimensions of the cutting insert green body 5 formed by the press tool. In FIG. 1 the compression space is occupied by the cutting insert green body 5, which has a through hole 6 of length (L) (see FIG. 3f).

[0051] The press tool further comprises a first core rod 7 and a second core 8, each of which has a longitudinal extension from a front end to a rear end and a contact surface 9 at the front end. The first and second core rods 7, 8 are arranged longitudinally along a horizontal core axis 10, with their respective central longitudinal axes coinciding with the core axis 10 and their respective contact surfaces 9 facing each other. Both the first core rod 7 and the second core rod 8 are arranged to be movable in both directions of the core axis 10. Advancement of a core rod is towards the other core rod, and retreat is away from the other core rod.

[0052] 2, the first core 7 comprises a longitudinal rear portion in the form of a base body 11 and a piston 12. In the longitudinal front portion, the base body comprises a segment 16 tapering towards its front end. A bore 15 extends rearwardly from an opening in the tapering segment 16 at the front end of the base body 11. A forward facing abutment surface 17 is a front end surface surrounding the opening, the front end surface being perpendicular to the core axis 10.

[0053] The piston 12 has a rear portion in the form of a longitudinally extending shaft 13 and a head 14 at the front end of the shaft and projecting radially from the shaft 13. The shaft 13 is longitudinally movably disposed within a bore 15 in the base body 11. The longitudinal axis of the shaft and the longitudinal axis of the bore both coincide with the core axis 10. The first core rod contact surface 9 is the front end face of the head 14, which is perpendicular to the core axis 10. The head 14 has a rearwardly facing abutment surface 17, which is adjacent the shaft 13 and is perpendicular to the core axis 10.

[0054] The second core rod 8, the base and the piston 12 are all arranged to be independently movable, so that each can be individually moved to a position independent of the others. The individual movements are driven by electric motors controlled by a control unit in the form of a PLC (not shown).

[0055] In its longitudinal front part, the second core rod 8 comprises a segment 18 tapering towards its front end. The contact surface 9 of the second core 8 is its front end surface perpendicular to the core axis 10.

[0056] A typical length (L) of the through hole of the cutting insert green body 5 that can be formed in the press tool of the present invention is 6-10 mm. In a cutting insert green body 5 having a through hole 6 with countersinks on both sides, a typical length of the cylindrical center of the through hole 6 is 1-5 mm. In an exemplary embodiment, the head has a longitudinal length of 1.3 mm, a 1 mm portion of the total length (L) is formed by the tapered segment of the second core rod 8 and a 0.7 mm portion of the total length (L) is formed by the tapered segment 16 of the first core rod 7. The cross section of the head 14 and the core rod over the length (L) is elliptical. The head 14 has a constant cross section. A typical dimension of the major axis of the elliptical cross section of the head is 3-10 mm, and in an exemplary embodiment is 5.4 mm.

[0057] The die, punch, second core rod 8, substrate 11 and shaft 13 of piston 12 are made of cemented carbide. The head 14 of piston 12 is made of steel with a Young's modulus (E) of 200 GPa.

[0058] With reference to schematic figures 3 to 3f, in the following there is described one embodiment of a method for forming a cutting insert green body using the above-mentioned first embodiment of the press tool of the present invention.

[0059] In Figure 3a, both the first core 7 and the second core rod 8 are disposed longitudinally along the core axis 10 with the respective contact surfaces 9 at their respective front ends facing each other. The shaft 13 of the piston 12 is disposed within a bore 15 of the base body 11 with the longitudinal axis of the shaft 13 coinciding with the core axis 10. The piston 12 is moved along the core axis 10 to a retracted position where the abutment surface 17 of the head 14 abuts against the abutment surface 17 of the base body 11.

[0060] The first core rod 7 and the second core 8 are moved to their respective pressing positions along the core axis. In it, both the first core rod 7 and the second core 8 are moved forward toward a central position in the cavity 4. When both the first core rod 7 and the second core rod are in their respective pressing positions as shown in FIG. 3b, their respective contact surfaces 9 contact each other in the cavity 4 in the compression space. The piston 12 is still in the retracted position where the abutment surfaces 17 abut each other. The lower punch 3 is raised to form a bottom in the cavity 4, and the cavity 4 is filled with a predetermined amount of metallurgical powder 19. The powder 19 flows through around the core rods 7, 8 and fills a part of the cavity from below and above. Finally, the core rods 7, 8 are surrounded by the powder 19.

[0061] In FIG. 3c, the cavity is operated to compress the powder 19 by moving the punches 2, 3 towards each other, thereby compressing the powder 19 in the compression space. The compression space is a reduced space in the cavity 4, which has the same shape and dimensions as the cutting insert green body 5 to be formed. At the beginning of the compression, the punches are moved faster than at the end. During the compression, the core rods 7, 8 remain in their respective pressing positions. As can be seen from the figure, a through hole 6 having a length (L) is formed by the first core rod 7 and the second core rod 8, which together form a continuous core rod. In it, part of the length (L) is occupied by the tapered segment 18 of the second core rod 8, part of the length (L) is occupied by the head 14, and part of the length (L) is occupied by the tapered segment 16 of the base body 11. The continuous core rod formed by the first core rod 7 and the second core rod 8 is mirror symmetric across a cross-sectional plane passing through the longitudinal center of the head 14. The continuous core rod with tapering segments forms a through hole 6 with countersunk holes on both sides.

[0062] To compress the powder by an extra amount in the countersink, the core rods are pressed together, elastically reducing the length of the head 14 by about 20-30 μm.

[0063] After the punches have reached their closest position and the powder 19 has been compressed by a predetermined amount, the press tool is unloaded by moving the punches 2, 3 apart by a small distance of 0.07 mm. This allows the compact to relax and prevents the core rods 7, 8 from getting stuck in the through holes 6.

[0064] During compression, annular burr rings 20 are formed where the wall of the through hole 6, the contact surface and the abutment surface meet, i.e. on both sides of the head 14. To remove them, the second core rod 8 is moved backwards along the core axis 10 so that its contact surface 9 is outside the through hole 6 and the compression space. Then, as can be seen in FIG. 3d, the piston 12 is moved forwards along the core axis 10 to the first extended position, while the base 11 remains stationary. When the base 11 and the piston 12 are so positioned, the first core rod 7 is in the scraping position. The head 14, which has a constant cross section equal to the minimum cross section of the tapering segment 18 of the second core rod 8, allows it to be moved forwards without damaging the countersink provided by the tapering segment 18 of the second core rod 8. Moreover, the forward-facing abutment surface of the base 11 is in the same position in the longitudinal direction in the through hole 6 as when the first core rod 7 is in the pressing position. This ensures that the countersink provided by the tapered segment 16 of the base remains unaffected as the piston 12 is moved forward. During advancement of the piston 12 to the first extended position, the head moves over a burr ring 20 formed on the through-hole wall at the interface between the contact surfaces 9. This causes the outer surface of the head 14, and in particular the peripheral leading edge, to scrape the burr ring 20 from the wall.

[0065] With reference to FIG. 3e, the base 11 is moved rearward along the core axis 10 so that its abutment surface 17 is outside the through hole 6 and the compression space. The piston 12 is then moved rearward along the core axis 10. In the process, the head 14 moves a second time over the burr ring 20 formed on the through hole wall at the interface between the abutment surfaces. Then, as the head is moved further rearward, the head 14 moves over the burr ring 20 formed at the interface between the abutment surfaces 17. This causes the outer surface of the head 14, particularly the circumferential trailing edge, to scrape the burr ring 20 from the wall. The head 14 having a constant cross section equal to the minimum cross section of the tapering segment 16 of the base 11, allows the head to move rearward without damaging the countersink provided by the tapering segment 16.

[0066] Finally, the piston 12 is so far back that the contact surface 9 is located outside the through hole 6 and the compression space. The contact surface 9 of the first core rod 7 and the contact surface 9 of the second core rod 8 are then separated by a distance (21) that is greater than the length (L) of the through hole 6. In FIG. 3f, the cavity is operated to depressurize the compression space by moving the punches 2, 3 away from each other. At the beginning of the depressurization, the punches are moved more slowly than at the end. Finally, the cutting insert green body 5 formed by compressing the metallurgical powder 19 in the press tool is removed. The cutting insert green body 5 has a through hole 6 with countersunk holes at both ends.

[0067] Alternative embodiments of the present invention are shown in Figures 4 to 11. These embodiments differ from the first embodiment described above primarily by the structure of the first core rod 7, and therefore Figures 4 to 11 and the discussion are limited to a discussion of these components.

[0068] FIG. 4 shows the second core 8 and base 11, both of which lack tapering segments. Instead, the front of the second core rod 8, the head 14 and the front of the base 11 all have the same constant cross section. When both the first and second core rods 7, 8 are in their respective pressing positions, a continuous core rod with a constant cross section is formed. This continuous core rod forms the through hole 6 with a constant cross section without a countersink.

[0069] FIG. 5 shows the first core 7 with the piston 12 biased towards the first extended position. The bore 15 of the base body 11 comprises a longitudinal front part with a smaller cross section for guiding the shaft 13 and a longitudinal rear part with a larger cross section. The shaft 13 extends in the rear part. The rear end of the shaft comprises a thread on which a stop nut 22 is screwed. The stop nut is slidable in the larger rear part of the bore 15. At the rear end of the rear part of the bore 15 a support block 23 is fixed to the bore wall. An elastic element in the form of a coil spring 24 is attached to the support block 23 at its rear end and to the stop nut 22 at its front end. The piston 12 is biased towards the extended position by the force exerted by the coil spring 24 acting between the fixed support block 23 and the movable stop nut 22. The force can be adjusted by fixing the support block 23 to another longitudinal position at the rear of the bore 15.

[0070] The maximum extension position of the piston 12 is defined by the stop nut 22 abutting the rear front wall of the bore 15. The stop nut 22 and the rear front wall of the bore 15 thus together form a stop mechanism. In this example, the stop mechanism comprises the rearward facing front wall of the bore 15 and the forward facing front face of the stop nut 22, arranged opposite and facing each other along the core axis 10. When the piston 12 is in this maximum extension position and the base 11 is moved rearward, the piston 12 moves rearward together with the base 11. The piston 12 is also prevented from coming off the base 11.

[0071] The embodiment shown in FIG. 6 differs from the embodiment described with reference to FIG. 5 in that the bore 15 has a constant cross section. A coil spring 24 is attached at its rear end to the bottom of the bore 15 and at its front end to the rear end of the shaft 13. The first core rod 7 is provided with a stop mechanism comprising a longitudinal slot 25 in the shaft 13 and a pin 26 projecting radially into the bore 15 and the slot 25. The maximum extension position of the piston 12 is defined by the pin 26 abutting the rear wall of the slot 25. In this example, the stop mechanism comprises a rear wall of the slot 25 facing forward and a surface of the pin 26 facing rearward, arranged opposite and facing each other along / parallel to the core axis 10. This embodiment is advantageous in that a prior art core rod can be retrofitted with a biasing piston 12 and a stop mechanism without requiring access to the rear end of the first core rod 7.

[0072] In an alternative embodiment, the shaft 13 is provided with a radially protruding pin 26 that is received in a slot 25 in the bore 15 .

[0073] In an alternative embodiment, the biasing force is provided by directing a pressurized fluid, such as air or oil, into bore 15 .

[0074] 7a-7c show cross-sectional views of the first core rod 7 through the shaft 13 in the bore 15 of the base 11 according to different embodiments in which the relative rotation of the shaft 13 and the base 11 is prevented. In FIG. 7a, the shaft 13 and the bore 15 each have a flat surface 27. In FIG. 7b, the shaft is provided with a ridge 28 arranged in a slot 29 in the wall of the bore 15 of the base 11. In FIG. 7c, the shaft 13 is polygonal, in this case triangular. When used in a press tool with a horizontal core axis 10, such as the cross-hole press tool described above, debris from the chipped burr ring 20 falling on the shaft 13 slides down on the diverging sides and is therefore less likely to get stuck between the shaft 13 and the bore 15.

[0075] 8 shows an embodiment in which one front end of the second core rod 8 includes a rearwardly extending recess 30 and the front end of the head 14 includes a mating forwardly extending protrusion 31. The contact surface 9 of the second core 8 is the bottom surface of the recess 30, and the contact surface 9 is the front end surface of the protrusion 31. The outer peripheral sides of the recess 30 and the protrusion 31 are conical. When the first core rod 7 and the second core rod 8 are moved to their respective pressing positions, these conical sides guide the first core rod 7 and the second core rod 8 into alignment when the contact surfaces 9 come into contact.

[0076] 9 shows an embodiment in which the opening of the bore 15 is provided with a countersink 32. The piston 12 extends along the core axis from the rear end of the head to the front end of the shaft and includes a neck 33 which mates with the countersink 32 in the base bore 15. The countersink 32 and neck 33 have peripheral sides which are conical. These conical sides guide the head 14 as the piston 12 is retracted into the base 11. This ensures that the piston 12 and base 11 are aligned when their respective abutment surfaces abut one another.

[0077] 10 and 11 show an exemplary embodiment of each of the grooves 34 arranged on the abutment surface / abutment surface 17. In the embodiment of FIG. 11, an annular groove 34 is provided in the abutment surface 17 surrounding the opening of the bore 15. The groove 34 has a square cross section. Also in FIG. 11, an annular groove 34 is provided in the abutment surface 17 of the head 14. In the embodiment of FIG. 11, both grooves 34 have a semicircular cross section. When used in a press tool such as the cross-hole press tool described above, debris from the chipped burr ring 20 can be collected in these grooves 34 and is therefore less likely to become lodged between the shaft 13 and the bore 15.

Claims

1. A press tool for compressing powder to form a cutting insert green body (5) having a through hole (6) of length (L), - a cavity (4) operable to define a compression space corresponding to the dimensions of said cutting insert green body (5); a first core rod (7) and a second core rod (8) for forming together said through hole (6), each having a longitudinal extension from a front end to a rear end and a contact surface (9) at said front end; Equipped with - said first core rod (7) and said second core rod (8) are both arranged longitudinally along the core axis (10) with their respective front ends facing each other; - both said first core rod (7) and said second core rod (8) are arranged to be movable in both directions of said core axis (10), both said first core rod (7) and said second core rod (8) being movable into a respective pressing position and into a respective release position; - when both said first core rod (7) and said second core rod (8) are in their respective pressing positions, their respective contact surfaces (9) are in contact with each other in said compression space; - when both said first core rod (7) and said second core rod (8) are in their respective release positions, their respective contact surfaces (9) are spaced apart by a distance greater than said length (L); At Press Tool, The first core rod (7) a longitudinally extending rear part in the form of a base body (11) provided at its front end with a forward facing abutment surface (17); a piston (12) having a rear part in the form of a longitudinally extending shaft (13) and a front part in the form of a radially projecting head (14); Equipped with - said contact surface (9) is the front end surface of said head (14); - said head (14) comprises at its rear end a rearward facing abutment surface (17); - said shaft (13) is arranged to be longitudinally movable within said base body (11) along said core axis (10) such that said piston (12) is movable between a plurality of extended positions and a retracted position in which said abutment surface (17) of said head (14) abuts against said abutment surface (17) of said base body (11); When both the first core rod (7) and the second core rod (8) are in their respective pressing positions, the piston (12) is in the retracted position. A press tool featuring:

2. The first core rod (7) is movable to a scraping position; the forward facing abutment surface (17) of the base body (11) is at its maximum forward position when the first core rod (7) is in the pressing position; the piston (12) is in a first of the extension positions, the contact surface (9) in the form of the front end face of the head (14) being further forward than in the pressing position; 2. The press tool of claim 1.

3. 3. A press tool according to claim 1 or 2, wherein the second core rod (8) comprises a segment (18) tapering towards the front end, the base body (11) comprises a segment (16) tapering towards the front end, the head (14) has a constant cross section, and in the pressing position, the length (L) comprises at least a part of the tapering segment (18) of the second core rod (8), the head (14) and at least a part of the tapering segment (16) of the base body (11).

4. The press tool of claim 2 , wherein the piston (12) is biased toward the first extended position.

5. 5. A press tool according to claim 4, wherein the piston (12) is arranged biased by a resilient element (24) which at its rear end abuts against a forward facing surface of the base body (11) and at its front end abuts against a rearward facing surface of the shaft (13).

6. A press tool according to any one of the preceding claims, wherein the first core rod (7) is provided with a stop mechanism defining a maximum extension position of the plurality of extension positions of the piston (12).

7. The stopping mechanism is - a substrate stop surface; - Shaft stop surface and Equipped with - said base stop surface and said shaft stop surface are arranged opposite and facing each other along said core axis (10); when the piston (12) is in the maximum extension position, the base stop surface and the shaft stop surface are in contact with each other; 7. A press tool according to claim 6.

8. 8. A press tool according to any one of claims 1 to 7, wherein the front end of one of the first (7) and second (8) core rods comprises a rearwardly extending recess (30) and the front end of the other of the first (7) and second (8) core rods comprises a mating forwardly extending protrusion (31), the protrusion (31) being received within the recess (30) to align the first (7) and second (8) core rods when both are in their respective pressing positions.

9. - said base (11) has a bore (15) extending rearwardly from an opening at said front end of said base (11); - the rear end of said shaft (13) extends through said opening into said bore (15); - the forward facing abutment surface (17) of the base body (11) is a front end surface surrounding the opening; A press tool according to any one of the preceding claims.

10. A press tool according to claim 9, wherein the opening of the bore (15) in the base body (11) is provided with a countersink (32).

11. the piston (12) further comprises a neck (33) extending along the core axis (10) from the rear end of the head (14) to the front end of the shaft (13) and mating with the countersink (32); - said rearwardly facing abutment surface (17) of said head (14) is a rear end surface adjacent said neck (33); when the piston (12) is in the retracted position, the neck is received in the countersink to align the piston (12) with the base (11); 11. A press tool according to claim 10.

12. A press tool according to any one of the preceding claims, wherein the core axis (10) is horizontal and the shaft (13) has sides which converge upwards to form a ridge.

13. A press tool according to any one of the preceding claims, wherein the head (14) has a length in an axial direction of the core axis (10), and wherein the axial length of the head (14) is reducible in the pressing position by 5 to 40 μm.

14. A method for forming a cutting insert green body (5) having a through hole (6) of length (L) using a press tool, the method comprising: - a cavity (4), a first core rod (7) and a second core rod (8) each having a longitudinal extension from a front end to a rear end and a contact surface (9) at said front end; The first core rod (7) comprises: a longitudinally extending rear part in the form of a base body (11) provided at its front end with a forward facing abutment surface (17); a piston (12) having a rear part in the form of a longitudinally extending shaft (13) and a front part in the form of a radially projecting head (14), said contact surface (9) being the front end face of said head (14), said head (14) comprising at its rear end a rearward facing abutment surface (17); A method comprising: - positioning both the first core rod (7) and the second core rod (8) longitudinally along the core axis (10) with their respective front ends facing each other; - positioning said piston (12) with its shaft (13) longitudinally along said core axis (10) of said base body (11); - moving said piston (12) along said core axis (10) to a retracted position, in which said abutment surface (17) of said head (14) abuts against said abutment surface (17) of said base body (11); - moving said first core rod (7) and said second core rod (8) along said core axis (10) to respective pressing positions, in which respective contact surfaces (9) are in contact with each other in said cavity (4) in a compression space corresponding to the dimensions of said cutting insert green body (5); - filling said cavity (4) with a given amount of powder; - operating said cavity (4) to compress said powder in said compression space to form said cutting insert green body (5); - moving said second core rod (8) rearward and said piston (12) forward along said core axis (10) to a first extended position; - moving said first core rod (7) and said second core rod (8) along said core axis (10) to respective release positions, wherein respective contact surfaces (9) are spaced apart by a distance greater than said length (L); - operating said cavity (4) so ​​as to depressurize said compression space; - removing said cutting insert green body (5); The method includes:

15. 15. The method according to claim 14, comprising, after the steps of moving the first core rod (7) and the second core rod (8) to the respective pressing positions and moving the piston (12) along the core axis (10) to the retracted position, reducing an axial length of the head (14) in the direction of the core axis (10) by 5 μm to 40 μm by moving the contact surfaces (9) of the first core rod (7) and the second core rod (8) relative to each other.

Images