SECTION 2.4
How and Where Heat is Generated

The force or energy that is put into the tool creates movement in a group of metal atoms in the workpiece. This group is a finite number of atoms which are forced to change their positions in relationship to each other. As the atoms in the metal ahead of the tool are disturbed, the friction involved in their sliding over one another is thought to be responsible for 60% or more of the total heat generated. This internal friction, and the heat it generates, can be compared to the friction and heat caused by bending a paper clip back and forth until it breaks.

As the tool continues to push through the work piece, a chip eventually slides up the cutting face of the tool. This sliding creates an external friction which again releases heat. This external friction accounts for about 30% of the total heat generated.

The third area of heat generation is on the land or flank of the tool. This area accounts for about 10% of the heat generated. This is assuming that the tools are sharp and made correctly as far as clearance angles and face angles are concerned. As the tool wears, the above percentages will vary, especially when there is excess wear on the land, or if the clearance angle is insufficient for the material or the part configuration. This contact zone will actually increase as the part continues to close in after the cut resulting in extremely high pressures on the land area of the tool.

Figure 2-1.
The effects of friction upon amount of chip distortion.