METHOD OF MAKING ENDMILLS

Abstract: The present invention relates to an endmill provided with cutting edges of cBN or PCD and consisting of a shank part and a part containing the cBN or PCD brazed to the shank. The latter part is in the form of a disc in which the superhard material is present in a groove in the envelope surface and extends from one end surface to the other. After brazing the disc to the shank, the body obtained is ground to an endmill with cutting edges formed of superhard material. In a preferred embodiment, the shank is provided with a tenon against which the part containing the superhard material is brazed. This minimises the risk of braze joint failure and provides an endmill with several cutting edges which can be achieved at a low cost.

Description: Method of making endmills This invention relates to an endmill with cBN (cubic boron nitride) or PCD (polycrystalline diamond) in the cutting edges and a method of making the same. The purpose of the method is to decrease the cost compared to existing methods. An endmill is used for machining of grooves, pockets and slots and consists of a cylindrical holder with cutting means at the end. It can be made of high speed steel, or solid cemented carbide, but it can also consist of a steel holder with cemented carbide inserts as cutting means . For certain applications metal cutting inserts having cutting edges formed of a superhard material, such as PCD, are usually used for the machining of non-ferrous alloys such as brass, magnesium and aluminium, and the like, whereas inserts with cutting edges formed of a superhard abrasive, such as cBN are usually used for the machining of cast iron and hardened steel and the like. There are several types of PCD or cBN endmills on the market today. Essentially there are two different methods to manufacture them. One method includes sintering cBN or diamond powder under elevated pressure and temperature into a solid cylindrical body which is then brazed onto a shank and finished into an endmill . The other method includes bonding a layer of cBN or diamond under elevated pressure and temperature to a substrate, usually a cemented carbide disc, from which smaller pieces, "chips", are cut out. These chips are then brazed onto a cemented carbide rod and ground to the finished shape. Tools produced that way are normally quite expensive due to the many steps the product must undergo before it is finished. CONFIRMATION COPY The object of the present invention is therefore to provide a method, where an endmill with several cutting edges can be achieved but at a substantially lower cost. Fig 1 shows the principle of the method where 1 is the element that will form the cutting part, 2 is the shank 3 is the braze joint and 4 is a tenon 5 is a top view of the element 1 after shaping to expose the cutting edges. According to the method of the present invention the starting point is a cemented carbide disc preferably with a binder phase content of >10 wt-% provided with superhard bodies according to the teachings of US 5,676,496. The cemented carbide disc is made from a cemented carbide rod with a circular, square, triangular or other suitable cross section preferably with a center hole. Into this rod one or more grooves are ground throughout its whole length and parallel to its axis. The groove can be straight but it can also be helical. The number of grooves and their location depend on the type of disc that is to be produced. The shape of the grooves can be made in different ways. It is important, however, that they have a rounded or plane shape. Their size shall be such that the cutting work essentially is performed by the superhard material . After HP/HT sintering the rod is cut into discs of desired thickness . Alternatively, in one or more cemented carbide discs at least one groove is ground and filled with a powder mixture containing cBN and/or diamond after which the discs are treated at a temperature and pressure where cBN and/or diamond is stable. During this treatment the discs are separated from each other in such a way that they do not sinter together. The shank 2 is preferably made in cemented carbide preferably with a binder phase content of >10 wt-%. The diameter of the shank is somewhat smaller than the diameter of the disc with superhard materials . The other end of the shank is provided with clamping means . The PCD/cBN disc is then brazed together with the shank . In a preferred embodiment the end of the shank where the PCD/cBN disc is brazed is ground down to form a tenon, 4. The shape of the tenon is generally cylindrical but it may alternatively be tapered, square, triangular, elliptical or other non-round shape. The diameter (or equivalent) of the tenon is about 15 - 40 % of the diameter of the shank and is designed to fit within the center hole of the disc 1 although the tenon does not have to extend through the entire length of that center hole. The PCD/cBN disc is then brazed together with the shank using the tenon as guide and braze joint, 3. It is according to the invention essential that brazing is made only at the tenon. This will minimise the risk of braze joint failure. After brazing the tool obtained is ground in such a way that cutting edges are formed from the superhard bodies as shown in the top view 5 of Fig 1.

Claims: Claims 1. Endmill provided with cutting edges of cBN or PCD and consisting of a shank part and a part containing the cBN or PCD brazed to the shank c h a r a c t e r i s e d in that said shank is provided with a tenon against which the part containing the superhard material is brazed. 2. Endmill according to the preceding claim c h a r a c t e r i s e d in that said tenon is round. 3. Endmill according to claim 1 c h a r a c t e r i s e d in that said tenon is tapered. 4. Endmill according to claim 1 c h a r a c t e r i s e d in that said tenon is of non- round shape . 5. Endmill according to claim 1 c h a r a c t e r i s e d in that said tenon extends at least part way into the part containing the superhard material . 6. Method of making an endmill provided with at least one cutting edge of cBN or PCD and consisting of a shank part and a part containing the cBN or PCD c h a r a c t e r i s e d in comprising the steps providing a cemented carbide disc preferably with a cylindrical cross section provided with at least one body of a superhard material in a groove in the envelope surface and extending from one end surface to the other brazing said cemented carbide disc to a shank grinding the obtained body to form an endmill with cutting edges formed from the superhard material . 7. Method according to claim 6 c h a r a c t e r i s e d in that said cemented carbide disc is made using the following steps providing a cemented carbide bar grinding at least one groove in said bar filling said groove with a powder mixture containing cBN and/or diamond heat treating said cemented carbide bar at a temperature and pressure where cBN and/or diamond is stable and cutting said bar into discs. 8. Method according to claim 6 c h a r a c t e r i s e d in said cemented carbide disc is made using the following steps providing one or more cemented carbide discs grinding at least one groove in said discs filling said groove in said discs with a powder mixture containing cBN and/or diamond heat treating said cemented carbide discs at a temperature and pressure where cBN and/or diamond is stable whereby the discs are separated from each other in such a way that they do not sinter together. 9. Method according to any of claims 6 - 8 c h a r a c t e r i s e d in the step of brazing said shank part to the part containing the superhard material with the aid of a tenon formed in the end of said shank part and a hole extending at least partway through said part containing the superhard material . 10. The product according to any of claims 6 - 8.

Inventors: LITTECKE PETER, LITTECKE, PETER
Applicants: SANDVIK AB
Application year: 1998
Main classification: B23C5
IPC codes: B23B27, B23C5, B23P15