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 microstructures 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 the description of the background of the present invention that follows reference is made to certain structures and methods, however, such references should not necessarily be construed as an admission that these structures and methods qualify as prior art under the applicable statutory provisions. Applicants reserve the right to demonstrate that any of the referenced subject matter does not constitute prior art with regard to the present invention.

#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 resistance) and the inner part (toughness) as discussed in U.S. Pat. No. 5,541,006, in which is emphasized 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 ability 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, U.S. Pat. No. 4,743,515. Tools as wear parts, rolling rings and slitter/trimming knifes can be manufactured with a method described in U.S. Pat. No. 5,543,235, including removing a partitioning means.

#The objects and advantages of the invention will become apparent from the following detailed description of preferred embodiments thereof in connection with the accompanying drawings in which like numerals designate like elements and in which:

#FIG. 1 shows a compound insert according to prior art.

#FIGS. 2a-e illustrates the method of the present invention.

#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 in FIGS. 2a-e. In FIG. 2apowder P1 is filled from a filling shoe, F, into the main cavity, 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 P1 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 P1 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 11/12 in FIG. 2e shall not exceed ½.

#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.