tailieunhanh - Volume 16 - Machining Part 8

Tham khảo tài liệu 'volume 16 - machining part 8', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Fig. 15 Three types of carbide inserts. a Brazed inserts. b Square indexable throwaway inserts. c Round button-type indexable inserts on a half-round broach Carbide insert StìủlrữnaP teeth Round button-type indexable carbide inserts are also used for broaching castings. They offer the same advantages as square or rectangular inserts with the additional benefit in some applications of longer tool life. A tool life of 85 000 workpieces per insert index has been reported. Less cutting force is required with round inserts because they have a reduced depth-of-cut capability which may require lengthening the broaching stroke. On a unit-load basis a round insert requires greater force than a square one. A half-round broach with double-sided button inserts retained by center screws is shown in Fig. 15 c . Inserts can be overlapped and mounted at a shear angle along the length of the broach to produce the required size progression and to balance the cutting load. Provided the holder is manufactured to close tolerances particularly in those sections that determine the height of the cutting edge gaging is not required when cutters are changed to present a new cutting edge. Disposable carbide cutters can be inserted in any position without removing the broach from the machine. To provide the required clearance behind the cutting edges inserts must have a negative rake. Inserts for contour cutting can be sharpened on the top and face and shimmed to the correct position. A considerable savings in tool cost is made possible by changing from brazed carbide tools to disposable carbide inserts for the same broaching operation. Internal and External Broach Configurations. A number of typical broaches and the operations for which they are intended are shown in Fig. 16. Fig. 16 Typical broaches and the configurations they generate. See text for discussion A square broach Fig. 16a produces a round-cornered square hole. Prior to broaching square holes it is common to drill a round hole .