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When machining  carbon and alloy steels, Crater Wear is the normal tool failure mode.  Overheating is an unpredictable failure mode.  It can be one of two failure modes, Thermal Checking ( or Cracking- my first boss called it “Crazing” ) or Deformation. Usually, when an irate customer ran into overheating issues, the tool they sent back to me had deformed to the point that it looked like it had been made out of lava.
craterwear
The lack of predictability of failure by overheating  creates issues for the shop beyond the obvious. Parts produced immediately prior to failure are suspect and must be validated prior to release, to avoid sending rejectable product to customers. Overheating can thus be a “delivery problem” in your customer’s eyes.
Here are 5 tips to get out of Overheating  Tool Failure Mode and back to normal predictable Crater Wear Tool Failure Mode when machining steel:

  1. Improve lubrication coolant delivery or formulation. Sometimes adding an extra coolant line to the position will eliminate the problem. Confirming your coolant is up to spec should be done before electing to buy a new “super duper formulation.” First things first!
  2. Use  a harder grade of carbide with more Ti (Titanium)
  3. Increase the Feed Rate (IPR) inches per rev
  4. Reduce the Speed (SFM)
  5. Consider Ceramic or Cermet Tooling. Note- these are not  really appropriate for low carbon (less than 0.20% C) steels. Low carbon steels  become gummy and stringy at speeds typically used  for ceramic tools.

These tips will address your  overheating problem by reducing the friction, surface adhesion, and  improving removal of heat, (improved coolant, delivery); improving the tool’s ability to withstand cutting conditions, and reducing the heat inputs by decreasing speed and increasing feed.
For more great information on this subject look at this lesson from Fox Valley Technical College.

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