The invention relates to a press with contra-rotating jaws and forming cavity closure members for cold pressure-forming of particulate, tungsten carbide into helically-shaped blanks for fitting to a cutting tool bit as inserts; a separate sinter piece has components of similar configuration and function to those of the press and has means built in for continually maintaining correct angular and radial dimensions of the pressed insert blank to compensate for shrinkage and prevent distortion during sintering.

Sintered tungsten carbide cutting tool bit insert blanks used as cutting edges fixed to high-speed cutting tools such as augers with helical cutting edges are made by pressing tungsten carbide, sometimes mixed with cobalt, under pressure into slabs or ingots from which special shapes are then cut or pressed directly into blanks of desired shape or size. Blanks are then semi-sintered in a non-oxidizing atmosphere at temp-0 eratures below 1472 F and further formed by machining. Final sintering is then carried out but the sintered carbide so obtained is so hard that the sintered shape can only be corrected by diamond cutter grinding. Uncontrolled shrinkage of the carbide blanks occurs with distortion of shape in existing methods in which carbide powder is brushed onto a spiral or helical cutting tool edge and the carbide is partially sintered on the tool. This requires reheating and bending the tool. Again a strip of pre-sintered or partially sintered carbide is placed along or beside the spiral cutting contour of the cutting tool and fused onto the tool by sintering at a higher temperature than the first-stage temperature. Uncontrolled shrinkage and distortion of the pressed blank occurs during existing sintering processes.

This causes irregularities in the sintered insert and loss of edge and shoulder sharpness or definition.

The invention as claimed is intended to remedy the above problem of shrinkage distortion of a sintered blank by controlling or confining those surfaces and edges which are critically affected during shrinkage caused by sintering and namely the whole diameter or radial height and the angular thickness or the thickness of the insert blank in the pitch circle direction of the insert when it is in mounted position on a spiral cutting bit. The whole diameter of the insert is that distance between the root diameter or base of the insert on the cutter bit face and the radial distance from the base to the top of the insert or the.outer diameter of the cutter.

The advantages of the invention are mainly that the correct configuration of a spiral insert blank is obtained by press forming and then maintained during sintering and shrinking of the blank by a sinter piece having distortion-correcting design features built in which continually correct or maintain correct configuration of an insert blank of tungsten carbide during sintering.

One way of carrying out the invention is described in detail below with reference to drawings which illustrate several specific embodiments, in which:-

• Figure 1 is a perspective view of a forming press in accordance with the invention with a top pressure member removed, and side cavity sealing plate loosened.
• Figure 2 is a plan view of the press with side cavity- sealing plate closed up.
• Figure io a vertical section taken alomg line A-A of figure 2_;
• Figure 4 is a partially exploded view of the shrinkage-compensating, sintering fixture for pressed and formed cutter bit insert blanks for cutting tools.

The figures 1 to 3 show a cold-forming press for making pre- sinter blanks of tungsten carbide for tool cutter bit inserts or tips for milling machine cutters, augers and other such devices and which comprises a bowl shaped body 1 with a recessed base 2, a side wall 3 and a central column 4 supporting a centre forming pin 5. The column 4 is bolted to the base of the body by a socket screw 6 the head of which clamps a securing collar 7 into the recess 8 under the body. There is mounted around the centre pin a compression jaw 9 the base of which is fixed on a compression plate 10 by socket screws 11. An ejection jaw 12 is similarly fixed to the ejection plate 13 beneath the compression plate, both plates being designed for limited, angular reciprocating movement about the column and centre pin. The plates are retained within the body by the plate-retaining collar 14. The jaws are formed as matching cylindrically curved sleeves split into two segments along a blank shaped in this example, helical or spiral separation cut or cuts forming a helical or spiral forming cavity on one side of the centre pin and an identical jaw-separation ejection travel slot on the opposite side of the pin. The complementary, helically-shaped mating surfaces 15 and 16 of the split-shell segments close towards each other to compress a particulate charge of carbide in an angular movement about the centre pin and move away from the pressed blank and each other when the ejection jaw is actuated. The two helical surfaces opposite the pin from the surfaces 15 and 16 close towards each other about the pin when 15 and 16 open up and vice versa. The opening and closing movements of the compression jaw 9 and compression plate 10 are actuated by the reciprocating angular movement of the compression lever 17 which is powered by suitable means such as a pneumatic ram 18 to compress a charge by applying sufficient pressure of the order.of 100 pounds. The movement of the ejection jaws 12 and ejection plate 13 is effected by the ejection lever 19 actuated by a pneumatic ram. The extent of angular travel of the compression lever, plate and jaw is limited by the limit stop screw 20 mounted on the threaded post 21 and the screw is adapted to bear against the stop block 22. The extent of the angular travel of the ejection lever, plate and jaw is limited by the confining edges of the angular slot 23. The forming cavity is sealed against loss of particulate carbide charge material by,means of the separate top cavity sealing collar 24 sealed under pressure by vertically reciprocating means 25, the separate cavity side sealing plate 26 clamped in place by upper threaded press bolt 27 mounted on the post 28 and the lower threaded press bolt 29 mounted through the plate-retaining ring 14.

Referring to figure 4, there is shown a sintering fixture for sintering press-formed, helically-shaped, tungsten carbide cutting tool bit inserts which although is a separate assembly from the press assembly nevertheless has components of the same shape and function and comprises four components of graphite in the form of a spool-shaped body on a centre pin and which is longitudihally split into two sleeve-like segments along helical separation cuts 15 and 16 in the press or 32 and 33 in the fixture which divide the segments 30 and 31. The segments 30 and 31 have flanged partially circular ends 34 and 35 and a longitudinal or axial bore 36 which is adapted to receive a removeable, rod-like pin 37The round surface of the pin is, when the pin is inserted into the bore, adapted to maintain contact with the bottom surfaceof a pressed blank and the helical edge walls defining the two sleeve segments are adapted to maintain contact of the sides of a pressed blank. A cover piece 38 of complementary curvature to the spool or sleeve segments is adapted to bear against the top edge of a pressed blank and the flanged ends each have a flattened portion 39 and 40, respectively which, when the assembled fixture containing a pressed blank is placed upon the flat surface in a sinter furnace, the flattened rim portions 39 and 40 which are each off-set with respect to each other in an angular direction about the longit- udihal axis of the sintering fixture produce a torque or twisting action of each segment of the shell towards each other so that the edge surfaces 32 and 33 close up or bear against a helical blank to counteract angular shrinkage distortion in the direction of the pitch circle of the sintered blank insert installed on or against the cutting edge profile 0 of a cutting tool bit when the blank is sintered at 1500 to 1600 C, depending on the composition of the sinter mix.