Collets are a particular challenge due to their nature and function. They are very high-precision devices that require high wear, yet to function properly they must be extremely flexile and, often times, even become fragile. A collet should always be well-supported by the interacting parts around it (i.e. drawbolts, arbor bodies and the workpiece itself), and made from the correct material and hardness for each particular application.
When determining the proper material and heat treat choice for a collet, you should first consider one of the fundamental elements of tool design - wear vs. toughness. Though these characteristics may seem to complement each other, from a tooling standpoint they are in stark constrast. For an item to wear, it must be hard, yet when an item is hard it becomes brittle and, therefore, not as tough.
The function of a collet is to expand and contract in order to properly locate the workpiece. The repeated function over a period of many cycles stresses the collet and may eventually lead to its failure. The key to achieving the longest life for a collet is to determine the balance of wear vs. breakage.
We have made significant improvements to many of our customers' collet systems by providing more accurate collets, with longer service life and better sealants to keep out contaminants. If you need assistance with the performance of your collet systems or are curious about ways you might integrate a collet system into your production machining, we would be happy to help you find solutions.