MULTIPLE GRADE CEMENTED CARBIDE INSERTS FOR METAL WORKING AND METHOD OF MAKING THE SAME

Abstract: A cemented carbide insert of a first grade has at least one cutting point consisting of a cemented carbide of a second grade and with an uneven transition zone between the cemented carbide grades. A method of making a cemented carbide insert involves filling a die with a first grade powder and placing on top of it, in a corner, a second grade powder, compacting and sintering.

Description: Multiple grade cemented carbide inserts for metal working and method of making the same The present invention relates to multiple grade, composite cemented carbide bodies and a method of making such bodies. The said bodies comprise cemented carbide grades with individually different compositions and/or microstruc- tures and, therefore, correspondingly different properties at different locations in the same body. Such bodies are herein referred to as compound bodies. They are especially aimed at acting as insert in a drill, soldered or by other means attached to a shaft or used as a separate insert in drilling, milling or turning. In tools where the demands on different parts thereof are varying it is proposed to use compound technique. In drill bits for rock drilling the demands differ between the surface (wear re- sistance) and the inner part (toughness) as discussed in US 5,541,006, in which is emphasised on the use of two grades in a rock-drilling bit. The grades are both straight grades with tungsten carbide and Co. Much attention is given the abil- ity to control Co migration, which is in this case preferred to result in an abrupt borderline. This problem is also solved with the technique known as Dual-Phase or DP- technique , US 4,743,515. Tools as wear parts, rolling rings and slitter / trimming knifes can be manufactured with a method described in US 5,543,235, including removing a partitioning means. The use of two active grades in the same insert is presented in US 3,482,295. The wear re- sistant grade formed as a top layer on an insert is just around 0,2 mm thick and seems more like an attempt to solve a problem later on solved by the PVD and CVD techniques. Patents dealing with cemented carbide drills containing cubic carbides are US 6,086,980 and US 4,971,485. The former deals with cylindrical solid tools that are not manufactured by ordinary tool pressing. Also the latter describes a cylindrical tool where the WC-Co grade is used in the shaft to avoid damage due to vibrations in the machine and the shaft is soldered to the cutting part of the tool. Two or more grades in the same insert is also described in AT 269598 where a method is pre- sented with a number of press stages and using frames of rubber or other elastic materials to form the cavities needed for filling the different powders. AT 269598 thus discloses inserts consisting of two or more cemented carbide grades made by (pre ) compacting a blank of one grade provided with groove(s), recess(es) and/or depression (s) . These are filled with cemented carbide powder of the other grade and subsequently compacted to a green body, which is finally sin- tered. DE 19634314 discloses a compound component consisting of at least two constituent parts with different material compositions. At least one of such parts - which are joined into a single com- ponent by a concluding sinter process - consists of a hard alloy or a cermet. The joining surface between its constituent parts is an uneven surface . However, the choice of grades, final compaction pressure and sintering conditions have to be performed with great care in order to avoid cracks developing in the transition region bet- ween the two grades. One reason hereto is that it is generally not possible to obtain the optimum compaction pressure to both grades to obtain the same shrinkage. Generally the one grade shrinks more than the other leading to a distorted body after sintering, see Fig. 1 which shows a cross section of an RNGN insert and the same part of the insert from above. That is why AT 269598 discloses a heat treatment after sintering to decrease the stresses at the boundaries. Even if no cracks develop the body needs excessive grinding in order to be useful as a cutting tool. It is therefore an object of the present invention to provide a method of making cemented carbide inserts containing two different cemented carbide grades, which are less sensitive to developing cracks in the transition zone between the grades . It is a further object of the present invention to provide a cemented carbide insert con- sisting of two different grades which needs less grinding after sintering. Fig. 1 shows a compound insert according to prior art. Figs. 2 a-e illustrates the method of the present invention. Figs . 3 a-d shows cross sections and view from above of RNGN inserts according to the invention . Fig. 4 shows a light optical micrograph at about 1000X of the uneven boundary between the two grades . It has now surprisingly been found that the above mentioned problems can be overcome by using a specially designed press tool for making compound cemented carbide inserts. The method is illustrated i Figs. 2 a-e. In Fig. 2a powder PI is filled from a filling shoe, F, into the main cav- ity, A, of the die and powder P2 into an additional cavity, B. In Fig. 2b the filling shoe has been withdrawn and the lower punch, C, lowered to a position where the powder P2 can be introduced on top of the powder Pi as shown in Figs. 2c and 2d. The resulting insert after compaction and sintering is shown in Figs. 3a and b. Alternatively, the level is chosen somewhat higher so that the powder P2 is pushing powder Pi away during introduction and thereby forming a portion deeper on the rake face. The resulting compacted and sintered insert is shown in Figs. 3c and 3d. The ratio lι/l 2 in Fig. 2e shall not exceed 1/2. The multi axial filling procedure allows the two powders to be compacted simultaneously and a compact with more optimal press density is obtained. The sintered body will need very little grinding . The invention also relates to a cemented carbide insert of a first grade in which at least one cutting point consists of a cemented carbide of a second grade with different composition and/or grain size. Preferably, the first grade is a WC-Co-grade and the second grade a WC-Co-gamma phase grade. The boundary between the first and the second grade after sintering is uneven with no cracks, see Fig. 4. The shape of the bodies of the second grade will always be different within an insert and between inserts .

Claims: Claims 1. Cemented carbide insert of a first grade in which at least one cutting point consists of a cemented carbide of a second grade with different composition and/or grain size c h a r a c t e r i s e d in that the transition zone between the first and second grade is uneven . 2. Cemented carbide according to claim 1 c h a r a c t e r i s e d in that the first grade is a WC-Co-grade and the second grade a WC-Co- gamma phase grade. 3. Method of making a cemented carbide insert of a first grade in which at least one cutting point consists of a cemented carbide of a second grade with different composition and/or grain size c h a r a c t e r i s e d by filling a die with a powder of the first grade and then on top of said powder in a corner placing a powder of the second grade, compacting and sintering.

Inventors: ENGSTROEM LARS-AAKE, OUCHTERLONY HELENE, ENGSTROEM, LARS-AAKE, OUCHTERLONY, HELENE
Applicants: SANDVIK AB
Application year: 2001
Main classification: B22F7
IPC codes: B22F7