The following points highlight the six main factors affecting metal cutting in the Industries. The factors are: 1. Velocity 2. Size of Cut 3. Tool Geometry 4. Tool Material 5. Ductile Materials 6. Forces Involved in Metal Cutting.
Factor # 1. Velocity:
It directly affects the temperature at tool point. If velocity is so low that the temperature at tool point is below the re-crystallization temperature of the material, then work hardening in the chip will be retained and the built-up edge will be formed. On ductile materials, high velocity can lead to formation of less distorted and longer chips, and the use of artificial chip breaker is must. It has been found that direction of chip flow is not affected by velocity.
Factor # 2. Size of Cut:
Increasing of depth of cut has not that much effect on chip as the feed. Increasing of feed widens the area of contact and changes the force per unit length, resulting in great distortion of chip. In case of ductile materials, it is possible to form segmented chips by increasing feed and depth of cut, but increasing them too much may lead to chatter, poor surface quality if the machine is not rigid enough.
Deep turning cuts on small diameters have a greater percentage change in velocity along the length of cutting edge and this may lead to erratic built up edge behaviour with poorer surface quality. It is noted that direction of chip flow changes with change in size of cut.
Factor # 3. Tool Geometry:
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This changes the shear angle and ultimately the chip thickness. The smaller the rake angle, lesser the shear angle and greater the chip distortion and more the resistance to chip flow. At low rake angles, the built up edge is bigger in size and produces rough and more work- hardened surfaces, but the chip being highly distorted breaks up into short lengths.
The side rake angle is found to have much more effect than the back rake angle. Increasing of side cutting edge and nose radius reduces the chip thickness, thereby reducing the chip contact width to thin out the built- up edge. Too much nose radius, however, may lead to chatter in non-rigid setups.
Factor # 4. Tool Material:
It should be able to sustain high cutting velocities and the coefficient of friction between chip and tool material must not change.
Factor # 5. Ductile Materials:
They produce continuous chips (normally with built-up edge) whereas brittle materials produce segmented or discontinuous chips. In latter case the cutting forces are also lower. Low friction, high cutting velocities and materials of low work-hardening capacity are desirable features for getting less distorted chip. Additions of lead, sulphur and phosphorous to low carbon steels help to break up chips, reduce built-up edge and improve surface quality.
Factor # 6. Forces Involved in Metal Cutting:
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Inspite of large theories put forward, it is still not possible to predict precisely the forces involved in metal cutting, because of the extreme complexity and the lack of geometrical constraint which is the characteristic of metal cutting.