307 Каталог INGERSOLL 2011 Режущий инструмент и инструментальная оснастка Стр.309

Каталог INGERSOLL 2011 Инструмент и оснастка Стр. 309 0307 Lab2u

BETTER SURFACE FINISHES geometries and provide extremely free cutting action. Excellent chip evacuation leaves the finish-milled surface free of scratches and scoring. Lead angle also affects cutting forces. Increasing the lead angle from 0 lessens radial force slightly and increases axial force significantly. Generally chip evacuation is easier with a higher lead angle. Insert design. One common insert design has a wiping flat on the face of the insert. The width of this flat must be greater than the advance per revolution to allow the cutting edges to overlap. Spindle tilt is critical when using wipers. Due to the sharp ends on the insert excessive spindle tilt can cause dig-in (Fig. 3). The MICRO MILL insert has four radiused cutting edges which project a very shallow ellipse in the plane of the cut. The large elliptical radius aligns to the surface regardless of spindle tilt. This ensures that the ends of the cutting edge do not dig-in the surface as can occur when inserts with conventional flats are used. The cutting edge is ground with a hook as well as a radius so that the axial rake is positive. This creates a shearing action which eases entry into the cut and directs chips up and away so they do not cause scratches. With this type of insert however if the advance per revolution is too great the elliptical cutting edges will not overlap enough to form a smooth surface finish. Other recommendations. Climb milling is generally best for finish milling because the cutter takes the thick part of the chip when it enters the cut. In conventional milling the chip thickness starts at zero causing rubbing or burnishing before the chip can reach its full thickness. Pressure and heat build up at the finished surface. The thin section will then weld to the cutting edge and be carried around to scratch the surface. Avoid cutting with the full diameter of the tool. This also results in zero chip thickness at the point of cutting edge entry just as in conventional milling. Two-thirds of the tool diameter is best when finish milling. It is also important to cut in the same direction when consecutive passes are required. Finish milling depths are usually light (.003-.010). Greater Advance Per Tooth (APT) can be used sometimes as high as .125. Finish milling cutters should be less dense than rough or semi-finish cutters although high-density cutters may be required for some high production cast iron applications. Fig. 3 Wiping Flat Geometry MICRO MILL Geometry Avoid too much spindle tilt otherwise scrat- If advance per tooth is too great the elliptical ches may be created on the workpiece surface. cutting edges will not overlap enough to form a smooth surface finish. 309