美国机械工程师手册_26663_yg4.pdf

MILLING CUTTERS 771 MILLING CUTTERS Selection of Milling Cutters.— The most suitable type of milling cutter for a particular milling operation depends on such factors as the kind of cut to be made, the material to be cut, the number of parts to be machined, and the type of milling machine available. Solid cutters of small size will usually cost less, initially, than inserted blade types; for long-run production, inserted-blade cutters will probably have a lower overall cost. Depending on either the material to be cut or the amount of production involved, the use of carbide-tipped cutters in preference to high-speed steel or other cutting tool materials may be justified. Rake angles depend on both the cutter material and the work material. Carbide and cast alloy cutting tool materials generally have smaller rake angles than high-speed steel tool materials because of their lower edge strength and greater abrasion resistance. Soft work materials permit higher radial rake angles than hard materials; thin cutters permit zero or practically zero axial rake angles; and wide cutters operate smoother with high axial rake angles. See Rake Angles for Milling Cutters on page 801. Cutting edge relief or clearance angles are usually from 3 to 6 degrees for hard or tough materials, 4 to 7 degrees for average materials, and 6 to 12 degrees for easily machined materials. See Clearance Angles for Milling Cutter Teeth on page 800. The number of teeth in the milling cutter is also a factor that should be given consider- ation, as explained in the next paragraph. Number of Teeth in Milling Cutters.— In determining the number of teeth a milling cut- ter should have for optimum performance, there is no universal rule. There are, however, two factors that should be considered in making a choice: 1) T h e number of teeth should never be so great as to reduce the chip space between the teeth to a point where a free flow of chips is prevented; and 2) The chip space should be smooth a