Free Machining

Definition - What does Free Machining mean?

Free machining is a manufacturing process in which additives are used to improve a metal's machinability. It is a characteristic of a metal alloy, when subjected to machining operations that:

  • Consumes less power
  • Gives better surface finish
  • Produces small metal chips
  • Results in longer tool life

Free machining materials can be cut quickly, easily obtain a good finish and do not wear tooling down as much as other processes.

Corrosionpedia explains Free Machining

Machinability is the ease with which a metal can be machined to an acceptable surface finish. Free machining pertains to the machining characteristics of an alloy to which one or more ingredients have been introduced. Alloy M25 (beryllium alloy of copper), for example, is a free machining type of copper.

Commonly added elements for free machining materials are:

  • Sulfur or lead to steel
  • Lead to brass
  • Lead and bismuth to aluminum
  • Sulfur or selenium to stainless steel

This keeps tools and workpieces clean, improves tool life and permits machining at higher speeds.

Free machining steel is steel that forms small chips when machined. This increases the machinability of the material by breaking the chips into small pieces, thus avoiding entanglement in the machinery. This enables automatic equipment to run without human interaction. Free machining steels have a lower corrosion resistance than the same original steels.

Disadvantages of free machining steel are:

  • Ductility is decreased
  • Impact resistance is reduced
  • Shrink fits are not as strong
  • Copper-based brazed joints suffer from embrittlement with bismuth free machining grades

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