PRESS TOOL AND METHOD FOR FORMING A CUTTING INSERT GREEN BODY HAVING A THROUGH HOLE

Abstract

A press tool and a method for forming a cutting insert green body. The press tool includes a first and a second core rod. Both core rods are movably arranged along an axis. When both core rods are in a press position, their respective contact surfaces contact each other and when both the first and second core rods are in a release position, their respective contact surfaces are separated. The first core rod includes a base body having a forwardly facing abutment surface and a piston having a shaft and a head. The piston is movable to a plurality of extended positions and to a retracted position, in which the abutment surface of the head abuts against the abutment surface of the base body. When both the first core rod and the second core rod are in their respective press positions, the piston is in the retracted position.

Claims

1. A press tool for forming, by compressing a powder, a cutting insert green body having a through hole of length, the press tool comprising a cavity operable arranged to define a compression space corresponding to dimensions of the cutting insert green body; and a first core rod and a second core rod together forming the through hole, each first and second core rod having a longitudinal extension from a front end to a rear end, and a contact surface at the front end, wherein the first core rod and the second core rod both are longitudinally arranged along a core axis with their respective front ends facing each other, the first core rod and the second core rod both being movably arranged in both directions of the core axis, wherein the first core rod and the second core rod both are movable to a respective press position and to a respective release position, wherein when both the first core rod and the second core rod are in their respective press positions, their respective contact surfaces contact each other inside the compression space, and wherein, when both the first core rod and the second core rod are in their respective release positions, their respective contact surfaces are separated by a distance that is larger than the through hole length, wherein the first core rod includes a longitudinally extending rearward portion in form of a base body, which, at a front end, includes a forwardly facing abutment surface, and a piston having a rear portion in a form of a longitudinally extending shaft, and a front portion in form of a radially protruding head, wherein the contact surface is a front end surface of the head, the head including, at a rear end, a rearwardly facing abutment surface, and wherein the shaft is longitudinally movably arranged in the base body along the core axis, such that the piston is movable to a plurality of extended positions and to a retracted position, in which retracted position the abutment surface of the head abuts against the abutment surface of the base body, and wherein, when both the first core rod and the second core rod are in their respective press positions, the piston is in the retracted position.

2. The press tool according to claim 1, wherein the first core rod is movable to a scraping position, wherein the forwardly facing abutment surface of the base body is at most so far forward as when the first core rod is in the press position, wherein the piston is in a first of the plurality of extended positions, and wherein the contact surface in a form of the front end surface of the head is further forward than in the press position.

3. The press tool according to claim 1, wherein the second core rod includes a segment that tapers toward the front end, the base body comprises a segment that tapers toward the front end, the head has a constant cross section, and wherein, in the press position, the length includes at least a portion of the tapering segment of the second core rod, the head, and at least a portion of the tapering segment of the base body.

4. The press tool according to claim 1, wherein the piston is biased toward the first extended position.

5. The press tool according to claim 4, wherein the piston is biased by means of a resilient element, which, in a rear end, abuts a forwardly facing surface of the base body, and, in a front end, a rearwardly facing surface at the shaft.

6. The press tool according to claim 1, wherein the first core rod includes a stop mechanism defining a maximal extended position of the plurality of extended positions of the piston.

7. The press tool according to claim 6, wherein the stop mechanism includes a base body stop surface, and a shaft stop surface, wherein the base body stop surface and the shaft stop surface are arranged opposite and facing each other as seen along the core axis, and wherein when the piston is in the maximal extended position, the base body stop surface and the shaft stop surface contact each other.

8. The press tool according to claim 1, wherein the front end of one of the first core rod and the second core rod includes a rearward extending recess, and the front end of the other one of the first core rod and the second core rod includes a mating forward extending projection, wherein, when both the first core rod and the second core rod are in their respective press positions, the projection is received in the recess for aligning the first core rod and the second core rod.

9. The press tool according to claims 1, wherein the base body has a bore that extends rearward from an opening in the front end of the base body, wherein a rear end of the shaft extends through the opening and into the bore, and wherein the forwardly facing abutment surface of the base body is a front end surface surrounding the opening.

10. The press tool according to claim 9, wherein the opening of the bore in the base body includes a countersink.

11. The press tool according to claim 10, wherein the piston further includes a neck, which extends along the core axis from the rear end of the head to a front end of the shaft, and mates with the countersink, wherein the rearwardly facing abutment surface of the head is a rear end surface bordering the neck, and, when the piston is in the retracted position, the neck is received in the countersink for aligning the piston and the base body.

12. The press tool according to claim 1, wherein the core axis is horizontal, and the shaft has side surfaces that converge upward forming a ridge.

13. The press tool according to claim 1, wherein the head has a length in an axial direction of the core axis, wherein an axial length of the head, in the press position, is reduceable by 5-40 μm.

14. A method for forming a cutting insert green body having a through hole of a length with a press tool, the press tool comprising: a cavity ; a first core rod and second core rod, which each have a longitudinal extension from a front end to a rear end, and a contact surface at the front end, wherein the first core rod includes a longitudinally extending rearward portion in form of a base body, which, at a front end, includes a forwardly facing abutment surface; a piston having a rear portion in form of a longitudinally extending shaft, and a front portion in form of a radially protruding head, wherein the contact surface is a front end surface of the head, and the head includes, at a rear end, a rearwardly facing abutment surface; the method comprising the steps of arranging both the first core rod and the second core rod longitudinally along a core axis with their respective front ends facing each other; arranging the piston with the shaft thereof longitudinally along the core axis in the base body; moving the piston along the core axis to a retracted position, wherein the abutment surface of the head abuts against the abutment surface of the base body; moving the first core rod and the second core rod along the core axis to a respective press position, wherein their respective contact surfaces contact each other inside the cavity in a compression space, which corresponds to the dimensions of the cutting insert green body; filling the cavity with a predetermined amount of powder; operating the cavity to compress the powder in the compression space to form the cutting insert green body; moving, along the core axis the second core rod rearward and the piston forward to a first extended position; moving the first core rod and the second core rod along the core axis to a respective release position, wherein their respective contact surfaces are separated by a distance that is larger than the length of the through hole; operating the cavity to decompress the compression space; and removing the cutting insert green body.

15. The method according to claim 14, wherein, after the steps of moving the first core rod and the second core rod to the respective press position, and moving the piston along the core axis to the retracted position, further comprising the step of reducing the axial length of the head in the direction of the core axis by 5-40 μm, by moving the contact surface of the first core rod and the contact surface of the second core rod against each other.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0074] In the following, example embodiments will be described in greater detail and with reference to the accompanying drawings, in which:

[0075] FIG. 1 is an exploded view with partly cutaway portions of the general design of the press tool according to an embodiment of the present invention as realized in a cross hole press tool;

[0076] FIG. 2 shows a longitudinal section of a first core rod and a second core rod according to the first embodiment;

[0077] FIG. 3 is a top view of the press tool according to the first embodiment;

[0078] FIGS. 3a-3f are longitudinal sections, as indicated in FIG. 3, of the press tool in a sequence according to the first embodiment of the inventive method;

[0079] FIGS. 4-6 show longitudinal sections of the first core rod and the second core rod according to further embodiments;

[0080] FIGS. 7a-7c are cross sectional views through the base body of additional embodiments;

[0081] FIG. 8 shows a longitudinal section of the first core rod and the second core rod according to another embodiment;

[0082] FIGS. 9-11 shows longitudinal sections of the first core rod according to further embodiments.

[0083] All the figures are schematic, not necessarily to scale, and generally only show parts which are necessary in order to elucidate the respective embodiments, whereas other parts may be omitted or merely suggested. Unless otherwise indicated, like reference numerals refer to like or corresponding parts in different figures.

DETAILED DESCRIPTION

[0084] In FIG. 1 the general design of an embodiment of the press tool according to the present 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 broken apart in the middle in order to show the interior thereof. The press tool further comprises an upper punch 2 and a lower punch 3. The punches 2, 3 are movable toward and away from each other along a 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 toward each other along a vertical punch axis. The compression space corresponds to the space and dimensions of a cutting insert green body 5 that is to be 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), c.f. FIG. 3f.

[0085] The press tool further comprises a first core rod 7 and a second core 8. They each have a longitudinal extension from a front end to a rear end and a contact surface 9 at the front end. The first and the second core rods 7, 8 are longitudinally arranged along a horizontal core axis 10, wherein their respective central longitudinal axis coincide with the core axis 10 and their respective contact surfaces 9 face each other. The first core rod 7 and the second core rod 8 are both movably arranged in both directions of the core axis 10. A forward movement of a core rod is in a direction toward the other core rod, and a rearward movement is away from the other core rod.

[0086] With reference to FIG. 2, the first core 7 comprises a longitudinally rearward portion in form of a base body 11, and a piston 12. In a longitudinally forward portion, the base body comprises a segment 16 that tapers toward the front end. A bore 15 extends rearward from an opening in the tapering segment 16 at the front end of the base body 11. A forwardly facing abutment surface 17 is a front end surface surrounding the opening, which front end surface is normal to the core axis 10.

[0087] The piston 12 comprises a rear portion in form of a longitudinally extending shaft 13 and, at a front end of the shaft, a head 14 that is radially protruding from the shaft 13. The shaft 13 is longitudinally movably arranged in the bore 15 of the base body 11. A longitudinal axis of the shaft and a longitudinal axis of the bore both coincide with the core axis 10. The contact surface 9 of the first core rod is a front end surface of the head 14, which front end surface is normal to the core axis 10. The head 14 has a rearwardly facing abutment surface 17, which is a rear end surface bordering the shaft 13 and normal to the core axis 10.

[0088] The second core rod 8, the base body and the piston 12 are all arranged independently movable. Thus, each can individually be brought into positions independent of the positions of the others. The individual movements are driven by electric motors that are controlled by a control unit in form of a PLC (not shown).

[0089] In a longitudinally forward portion, the second core rod 8 comprises a segment 18 that tapers toward the front end. The contact surface 9 of the second core 8 is a front end surface that is normal to the core axis 10.

[0090] Typical lengths (L) of the through hole of cutting insert green body 5 that can be formed in the inventive press tool is 6-10 mm. In a cutting insert green body 5 having a through hole 6 with a countersink at both sides, a typical length of a cylindrical central part of the through hole 6 is 1-5 mm. In the example embodiment, the head has a longitudinal length of 1.3 mm, a portion of 1 mm of the total length (L) is formed by the tapering segment of the second core rod 8, and a portion of 0.7 mm of the total length (L) is formed by the tapering segment 16 of the first core rod 7. The cross section of the head 14 and the core rods over the length (L) is elliptical. The head 14 has a constant cross section. Typical dimensions for the long axis of the elliptical cross section of the head is 3-10 mm, and in the example embodiment 5.4 mm.

[0091] The die, the punches, the second core rod 8, the base body 11 and the shaft 13 of the piston 12 are made of cemented carbide. The head 14 of the piston 12 is made of steel having a Young's modulus (E) of 200 GPa.

[0092] With reference to schematic FIGS. 3-3f, in the following an embodiment of the method of forming a cutting insert green body with the above described first embodiment of the inventive press tool.

[0093] In FIG. 3a, both the first core 7 and the second core rod 8 are arranged longitudinally along the core axis 10 with their respective contact surfaces 9 at their respective front ends facing each other. The shaft 13 of the piston 12 is arranged in the bore 15 of the base body 11, wherein the longitudinal axis of the shaft 13 coincides with the core axis 10. The piston 12 is moved along the core axis 10 to a retracted position, wherein the abutment surface 17 of the head 14 abuts against the abutment surface 17 of base body 11.

[0094] The first core rod 7 and the second core 8 are moved along the core axis to their respective press position. Therein, 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 press position as shown in FIG. 3b, their respective contact surfaces 9 contact each other inside the cavity 4 in the compression space. The piston 12 is still in the retracted position wherein the abutment surfaces 17 abut against 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 around and past the core rods 7, 8 and fills a portion of the cavity from below and upwards. Eventually, the core rods 7, 8 are surrounded by the powder 19.

[0095] In FIG. 3c, the cavity is operated to compress the powder 19 by moving the punches 2, 3 towards each other and thereby compressing the powder 19 in a compression space. The compression space is a reduced space in the cavity 4 and has the same shape and dimensions as the cutting insert green body 5 that is to be formed. At the beginning of the compression, the punches are moved faster than at the end. During compression, the core rods 7, 8 remain in their respective press positions. As can be seen, the through hole 6 having length (L) is formed by the first core rod 7 and the second core rod 8, wherein the first core rod 7 and the second core rod 8 together form a continuous core rod. Therein, a portion of length (L) is occupied by the tapering segment 18 of the second core rod 8, a portion of length (L) is occupied by the head 14, and a portion of length (L) is occupied by the tapering 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 symmetrical over a cross sectional plane through the longitudinal centre of the head 14. The continuous core rod with the tapering segments forms a through hole 6 with a countersink at both sides.

[0096] In order to compact the powder at the countersinks an extra amount, the core rods are pushed together to force the head 14 to elastically reduce the length thereof about 20-30 μm.

[0097] After the punches have reached their closest position and the powder 19 has been compressed a predetermined amount, the press tool is unloaded by moving the punches 2, 3 a small distance of 0.07 mm apart. This allows the compressed body to relax and prevent the core rods 7, 8 from jamming inside the through hole 6.

[0098] During compression, annular burr rings 20 are formed in the wall of the through hole 6 the contact surfaces and where the abutment surfaces meet, i.e. at both sides of the head 14. In order to remove these, the second core rod 8 is moved rearward along the core axes 10 so that the contact surface 9 thereof is outside the through hole 6 and the compression space. Thereafter, as can be seen in FIG. 3d, the piston 12 is moved forward along the core axis 10 to a first extended position, while the base body 11 remains still. When the base body 11 and the piston 12 are such arranged, the first core rod 7 is in a scraping position. Due to the head 14 having a constant cross section that is equal to smallest cross section of the tapering segment 18 of the second core rod 8, the head can move forward without damaging the countersink provided by the tapering segment 18 of the second core rod 8. Furthermore, the forwardly facing abutment surface of the base body 11 is longitudinally in the same position in the through hole 6 as when the first core rod 7 is in the press position. Thereby, the countersink provided by the tapering segment 16 of the base body remains unaffected when the piston 12 is moved forward. During the forward movement to the first extended position of the piston 12, the head travels over the burr ring 20 formed in the thorough hole wall at the location of the interface between the contact surfaces 9. Thereby, the outer surface of the head 14, especially the circumferential front edge, scrapes off the burr ring 20 from the wall.

[0099] With reference to FIG. 3e, the base body 11 is moved rearward along the core axes 10 so that the abutment surface 17 thereof is outside the through hole 6 and the compression space. Then, the piston 12 is moved rearward along the core axis 10. Therein, the head 14 travels over the burr ring 20 formed in the thorough hole wall at the location of the interface between the contact surfaces a second time. Then, as it is moved further rearward, the head 14 travels over the burr ring 20 that was formed at the location of the interface between the abutment surfaces 17. Thereby, the outer surface of the head 14, especially the circumferential rear edge, scrapes off the burr ring 20 from the wall. Due to the head 14 having a constant cross section that is equal to smallest cross section of the tapering segment 16 of the base body 11, the head can move rearward without damaging the countersink provided by the tapering segment 16.

[0100] Eventually, the piston 12 is so far rearward that the contact surface 9 is located outside the through hole 6 and the compression space. The contact surfaces 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 larger than the length (L) of the through hole 6. In FIG. 3f, the cavity is operated to decompress the compression space by moving the punches 2, 3 away from each other. At the beginning of the decompression, the punches are moved more slowly than at the end. Finally, a 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 a countersink at both ends.

[0101] In FIGS. 4-11 alternative embodiments of the present invention are shown. These embodiments differ from the first embodiment described above mainly by the construction of the first core rod 7, why the FIGS. 4-11 and the description is limited to the description of these components.

[0102] FIG. 4 shows a second core 8 and a base body 11 that both lack a tapering segment. Instead, the front portion of the second core rod 8, the head 14 and the front portion of the base body 11 all have the same, constant cross section. When both the first and the second core rods 7, 8 are in their respective press positions, a continuous core rod with constant cross section is formed. This continuous core rod forms a through hole 6 with a constant cross section without countersinks.

[0103] FIG. 5 shows a first core 7 wherein the piston 12 is biased toward the first extended position. The bore 15 in the base body 11 comprises a longitudinally front portion with a smaller cross section for guiding the shaft 13 and a longitudinally rear portion with a larger cross section. The shaft 13 extends into the rear portion. The rear end of the shaft comprises a thread onto which a stop nut 22 is threaded. The stop nut is slidable in the larger rear portion of the bore 15. At a rear end of rear portion of the bore 15, a support block 23 is fixed to bore wall. A resilient element in form of coil spring 24 is at a rear end attached to the support block 23 and at a front end to the stop nut 22. Due to the force exerted by the coil spring 24 acting between the fixed support block 23 and the movable stop nut 22, the piston 12 is biased toward extended positions. The force can be adjusted by fixing the support block 23 in other longitudinal positions in the rear portion of the bore 15.

[0104] The maximal extend position of the piston 12 is defined by the stop nut 22 abutting against the front wall of the rear portion of the bore 15. Thus, the stop nut 22 and the front wall of the rear portion of the bore 15 together form a stop mechanism. In this example, the stop mechanism comprises the rearwardly facing front wall of the bore 15 and the forwardly facing front surface of the stop nut 22, which are arranged opposite and facing each other along the core axis 10. When the piston 12 is in this maximal extended position and the base body 11 is moved rearward, the piston 12 will move rearward together with the base body 11. The piston 12 is also prevented from disengaging from the base body 11.

[0105] 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. The coil spring 24 is at a rear end attached to the bottom of the bore 15 and at a 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 radially protruding into the bore 15 and the slot 25. The maximal extend position of the piston 12 is defined by the pin 26 abutting against a rear wall of the slot 25. In this example, the stop mechanism comprises the forwardly facing rear wall of the slot 25 and the rearwardly facing surface of the pin 26, which are arranged opposite and facing each other along/in parallel with the core axis 10. This embodiment is advantageous in that a prior art core rod can be retrofitted with a biased piston 12 and a stop mechanism without needing access to the rear end of the first core rod 7.

[0106] 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.

[0107] In an alternative embodiment, the biasing force is provided by conducting pressurized fluid, such as air or oil, into the bore 15.

[0108] FIGS. 7a-7c show cross sections of the first core rod 7 through the shaft 13 in the bore 15 of the base body 11 according to different embodiments wherein relative rotation of the shaft 13 and the base body 11 is prevented. In FIG. 7a, the shaft 13 and the bore 15 each have a planar surface 27. In FIG. 7b, the shaft is provided with a ridge 28 that is arranged in a slot 29 in the wall of the bore 15 in the base body 11. In FIG. 7c, the shaft 13 is polygonal and in this case triangular. When used in a press tool with horizontal core axis 10 such as the cross hole press tool described above, debris from the scraped off burr rings 20 that falls onto the shaft 13 will slide down over the diverging side surfaces and is therefore less likely to get stuck between the shaft 13 and the bore 15.

[0109] In FIG. 8, an embodiment is shown wherein the front end of one of the second core rod 8 comprises a rearward extending recess 30, and the front end of the head 14 comprises a mating forward extending projection 31. The contact surface 9 of the second core 8 is a bottom surface of the recess 30, and the contact surface 9 is front end surface of the projection 31. The circumferential side surfaces of the recess 30 and the projection 31 are conical. When the first core rod 7 and the second core rod 8 are moved to their respective press positions, these conical side surfaces guide the first core rod 7 and the second core rod 8 into alignment when the contact surfaces 9 are brought into contact.

[0110] In FIG. 9, an embodiment is shown wherein the opening of the bore 15 is provided with a countersink 32. The piston 12 comprises a neck 33, which extends along the core axis from the rear end of the head to a front end of the shaft, and mates with the countersink 32 in the base body bore 15. The circumferential side surfaces of the countersink 32 and the neck 33 are conical. When the piston 12 is retracted in the base body 11, these conical side surfaces guide the head 14. Thereby the piston 12 and the base body 11 are brought into alignment when their respective abutment surfaces abut against each other.

[0111] FIGS. 10 and 11 show one example embodiment each of grooves 34 arranged in the abutment surface/abutment surfaces 17. In the embodiment of FIG. 11, an annual groove 34 is provided in the abutment surface 17 surrounding the opening of the bore 15. The groove 34 has a square cross section. In FIG. 11, in addition, 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 semi-circular cross sections. When used in a press tool such as the cross hole press tool described above, debris from the scraped off burr rings 20 can be collected in these grooves 34 and is therefore less likely to get stuck between the shaft 13 and the bore 15.