In this article we will discuss about the influence of various angles on cutting edges in milling of steels.
1. Radial Rake Angle:
It is obvious from Fig. 16.33 that radial rake angle is the angle between the blade (flute) face and a radial reference plane drawn from the cutter axis to the cutting edge. Its value depends upon the material of work- piece and the tool. Positive radial rake angle presents the weakest point first and cutting edge is likely to break. Negative rake strengthens the cutting edge, of course, it produces higher force and requires more power.
2. Axial Rake Angle:
It represents the inclination of the cutting edge with respect to the axis of the cutter and decides the direction of chip flow. Positive axial rake helps the chips to come out of cut and negative axial rake forces the chips towards the work.
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With positive axial rake nose of cutter first contacts the work-piece which is not desirable. Negative axial rake strengthens the cutting edge and is used in carbide cutters.
3. Approach Angle:
It is the angle between a plane perpendicular to the cutter axial and a plane tangent to the surface of revolution of the cutting edges. Its value is 90° in case of end mills and shoulder mills, and 45°, 60° or 75° in case of face milling. Approach angle of 45° reduces chipping of cast iron work material and is also used for fine finishing applications and for milling of stainless steel.
Approach angle of 60° is employed with positive axial and negative radial geometry. Approach angle of 75° is used for throwaway tipped cutters for roughing and interrupted cuts in general milling of steels. The chip thickness for a given feed increases with increase in approach angle.
The length of the cutting edge over which cutting force acts increases with decrease in approach angle thereby decreasing thermal stress and slightly improved tool life. Increased approach angle permits use of higher feeds resulting in higher productivity.
4. Side Clearance Angle:
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It is the angle between the cut surface and the clearance flank on the cutter. While higher clearance results in less wear but it weakens the cutting edge. It is sometime necessary (in end mills) to provide primary and secondary clearances. Value of clearance angle also depends on the diameter of end mill; this being larger for smaller diameter end mills.