CNC: Heat removal during CNC machining
In machining, almost all of the energy spent in cutting is transformed into heat. Heat is produced:
1. During deformation of the metal to create chips. Ever felt the heat when you bend a thin steel wire with your hands repeatedly to break it ? Same phenomenon.
2. Friction of the chip sliding across the cutting tool produce heat. Try rubbing your hands together fast – the heat generated is the same phenomenon. One of the key tasks of cutting fluid is in fact lubrication, to reduce the friction and thereby the heat generated because of it.
A surprising fact is that 80 % of the heat generated is carried away by chips. The remaining 20 % is transferred to the workpiece and tool. Coolant only reduces the temperature rise caused by this 20 %.
This is why it makes sense to evacuate chips from the cutting area as fast as possible. If chips stay around the cutting area, it means the heat too stays around the cutting area, reducing tool life, heating up the workpiece and causing thermal distortion and metallurgical changes in it.
Heat evacuation is better with good chip breaking – discontinuous chips carry away the heat more efficiently. Heat evacuation is poor in operations like drilling because chip evacuation is poor, particularly in deeper holes.
Action point
Get those chips out of the way, as fast as possible ! Improves tool life, reduces tool cost, and improves job quality.
Obsess about the coolant, sure, but obsess more about the chip evacuation.
Pic. and text source: Cadem NCyclopedia multimedia CNC training software
