METHOD FOR MANUFACTURING INSERTS WITH HOLES FOR CLAMPING

Abstract: The present invention relates to a method wherein a superhard abrasive material is sintered and simultaneously bonded to a sintered cemented carbide body inside a container under elevated pressure and temperature conditions (HP/HT-treatment), whereby said cemented carbide body in contact with at least one other cemented carbide body which after the sintering is removed. At least the cemented carbide surfaces in contact with each other during the HP/HT-treatment is at least one coated with a 1-10 mu m thick layer of a refractory oxide. The method is particularly applicable for making cemented carbide cutting inserts provided a superabrasive material and with a hole for clamping to a tool holder whereby said hole is filled with a cemented carbide plug during the HP/HT-treatment and being removed thereafter. Preferably, both the plug and the insert blank are coated.

Description: Method for manufacturing inserts with holes for clamping The present invention relates to the high pressure/high temperature, HP/HT, process for making polycrystalline diamond or cubic boron nitride cutting inserts. More particularly, the invention relates to certain modifications in the HP/HT process which results in cutting inserts with improved production economy and clamping possibilities. For machining of several non ferrous alloys like brass, magnesium and aluminium, diamond is the best tool material whereas cubic boron nitride (cBN) is very well suited for machining hardened steel, chilled cast iron and cast iron at elevated speeds. The inserts used in such operations are either so called PCD (polycrystalline diamond compact) or PcBN (polycrystalline cubic boron nitride compact) comprising a cemented carbide body with a diamond or cBN layer applied at such high temperature and pressure where diamond or cBN is the stable phase or the inserts are provided with diamond or cBN bodies in at least one corner or along an edge generally fastened by brazing. The method for manufacturing such inserts has been described in e.g. U.S. Patents 3,745,623, 3,743,489, 4,525,179, 5,598,621 and 5,676,496. Many inserts used for machining have holes in the centre to ensure best possible clamping to the tool holder. In case of brazed inserts, this can be achieved by brazing a PCD/cBN tip to a body that already has a hole in it. Otherwise, the hole has to be cut afterwards which is costly since cutting usually involves electro discharge machining (EDM) . US Patent Application 08/601,631 discloses a method of making a cutting insert with a hole for clamping to a tool holder wherein a superhard abrasive material is sintered and simultaneously bonded to a sintered cemented carbide body with a hole inside a container under elevated pressure and temperature conditions. During sintering, the hole is filled with a plug which after sintering is removed. The plug may consist of a refractory metal, cemented carbide or cemented carbide surrounded by a sleeve of a refractory metal. The refractory metal is preferably niobium. The disadvantage with this method is that the refractory metal cannot withstand the high pressure and temperature resulting in cracks in the cemented carbide insert. According to the presently claimed invention making the hole is accomplished by providing a cemented carbide insert blank with a hole. During the HP/HT-treatment the hole is provided with a plug consisting of cemented carbide. The plug and/or cemented carbide blank are provided with a thin coating of a refractory oxide. After the HP/HT-treatment the plug is easily removed by mechanical pressure and the blank is ground to final shape and dimension. Figure 1 is a sectional view of the HP/HT cell as modified by the improvement of the present invention. Techniques for simultaneously applying both high pressure and high temperature in this type of apparatus are well known in the art. Referring now to figure 1 the HP/HT-cell 10 fits within the space in the apparatus subjected to HP/HT-conditions . The assembly consists of a can 11 comprising a cylindrical sleeve 12 and caps 13 of shield metal selected from a group consisting of Zr, Ti, Ta, Nb and Mo. A sintered and coated cemented carbide insert blank 16 with a hole in it is placed in the cup 12. The hole can be cylindrical but it can also have other shapes such as completely or partly tapered or chamfered on one or both sides. The hole is provided with a plug 25 with the same geometry as the hole. In order to avoid undesired sintering between plug and cemented carbide blank, the plug is coated with a thin Al2θ3~layer 20 but a thin l2θ3~layer can also be provided onto the cemented carbide blank in order to avoid undesired surface reactions between cemented carbide and the refractory material of the cell. This thin l2θ3-layer is 1-10, preferably 2-8, most preferably about 5 μm thick. Preferably, both the plug and cemented carbide blank are coated. Preferably, the plug consists of a cemented carbide with essentially the same composition as that of the cemented carbide 16 blank. A mixture containing diamond or cBN powder is filled into the cell e.g. so as to form a top layer, 14, or in grooves as disclosed in US Patents 5,598,621 and 5,676,426 or in any other desirable way. The cell is closed and placed in the HP/HT apparatus. The pressure and temperature is increased to the area where diamond or cBN is stable for a sufficient time for sintering to occur. The charge is then allowed to cool under pressure for a short period of time and after the pressure is relieved, the compact is recovered. The plug can be removed by applying machanical pressure. Finally, the compact is ground to desired final shape, circular, triangular or square, and dimension. The invention has been described with reference to the making of an insert with a hole. It is obvious that the method can be applied also to other cases where the sintering together of two or more cemented carbide part during a HP/HT-treatment or other surface reactions between components in a high pressure cell assembly shall be avoided. Instead of AI2O3 other refractory oxides such as 2O3/ ZrC>2 can be used. Example A cemented carbide cylindrical disc with composition WC + 16 wt-% Co with diameter of about 22 mm, thickness 6 mm and a tapered central hole with a diameter of 4 mm and with four grooves equidistantly located along the peripheral surface of the disc was prepared. The grooves had an essentially semicircular cross section with a diameter of about 4 mm. The cemented carbide disc was placed in a cup of Nb . Into the hole of the disc a plug was squeezed consisting of a 5 mm diameter cemented carbide plug with composition WC + 16 % Co coated with a 5 μm layer of AI2O3. The grooves were filled with a cBN powder mixture with a composition corresponding to Megadiamond commercial grade MN50 and after that the container was sealed and treated at high temperature and high pressure according to the process described in US 5,115,697. After cooling the compact was recovered. The plug was removed by applying a slight mechanical pressure. The disc was then ground to inserts style WNGA 080408 with a central hole that could firmly be clamped to a tool holder.

Claims: Claims 1. A method wherein a superhard abrasive material is sintered and simultaneously bonded to a sintered cemented carbide body inside a container under elevated pressure and temperature conditions (HP/HT-treatment) , whereby said cemented carbide body is in contact with at least one other cemented carbide body which after the sintering is removed c h a r a c t e r i s e d in that at least one of the surfaces in contact with each other during the HP/HT-treatment is coated with a 1-10 μm thick layer of a refractory oxide. 2. A method according to claim 1 c h a r a c t e r i s e d in that said cemented carbide to be provided with a superabrasive material is a cutting insert blank with a hole for clamping to a tool holder and said at least one other cemented carbide body is a cemented carbide plug filling said hole during sintering after which the plug is removed and the blank ground to an insert with final shape and dimension. 3. A method according to claim 2 c h a r a c t e r i s e d in that both insert blank and plug are coated. 4. A method according to claim 2 c h a r a c t e r i s e d in that the cemented carbide of the plug has essentially the same composition as that of the cutting insert blank. 5. A method according to any of the preceding claims c h a r a c t e r i s e d in that said refractory oxide is AI2O3, Y2O3 or Zrθ2-

Inventors: DEN BOER DAVID, LITTECKE PETER, DEN BOER, DAVID, LITTECKE, PETER
Applicants: SANDVIK AB, SANDVIK AB (PUBL)
Application year: 1998
Main classification: B22F3
IPC codes: B22F3, B22F5, B22F7, C22C1