CNC: Insert coatings and your shoe’s sole – what’s the connection ?
A shoe must be comfortable on the feet, made of material that is soft and that moulds itself to the shape of the foot. Leather has this quality, so we make shoes out of leather. But this same quality of softness causes results in the sole wearing out fast. We want the body of the shoe to be soft, but the sole to be hard. So, to get a hard sole that withstands wear and tear and has a long life, we stick a sheet of hard rubber on the sole. We are combining the comfort of the leather with the long life of the hard rubber.
We have a similar problem with inserts, and a similar solution is used. We want a cutting edge to be hard so it can cut faster and have a longer life. Unfortunately, the harder a cutting tool material is, the more brittle it is and the easier it breaks. We need two opposite qualities, toughness and hardness. We want the body of the insert to be tough, but the cutting edge surface to be hard, with high wear resistance. To improve the wear resistance and life of an insert, we just coat it with hard but brittle materials like Aluminium Oxide, Titanium Nitride, or Titanium Carbonitride.
This picture shows a plain Tungsten Carbide insert, the grey one on top, and a coated insert, the gold one at the bottom. An insert may have multiple coatings, of different materials. The cross section in this picture shows 3 different coatings, each between 2 microns and 10 microns thick. Since inserts are typically multiple materials sandwiched together, tool manufacturers use the word ‘Grade’ to instead of ‘material’. This document shows you how to select the correct insert grade, chip breaker and cutting parameters for turning.
Action point
When we buy footwear we take great care to look at their soles and check if they suit our application – formal shoes, shoes for shop floor use, for jogging, etc. Just ensure that you take as much care in selecting the coating on an insert as the sole on your shoe.
Pics. and text source: CADEM NCyclopedia multimedia CNC training software.
