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Free Machining

CASE STUDIES
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Unfortunately "free machining" isn't an offer for free precision parts, but a term often used to describe "machine friendly material".

However, the exact definition of free machining is subjective. The www.businessdirectory.com describes free machining as:

“Characteristic of a metal alloy that, when subjected to machining operations, consumes lower power, gives better surface finish, produces small metal chips, and results in longer tool life. Alloy M25 (beryllium alloy of copper), for example, is a free machining type of copper.”

www.About.com adds that the addition of sulfur or lead to steel or brass, lead and bismuth to aluminum and sulfur or selenium to stainless steel makes material easier to machine.

As new markets develop and a concern for the environment grows, certain chemicals and elements such as lead are being reduced or eliminated from many materials. Because of this, in part, today’s machinist is challenged to find ways to machine high precision components from materials that do not meet the free machining description. All our raw materials are RoHS compliant.

Our material page on www.gompc.net lists the various materials we machine. Most material machinability charts compare alloys from within the same material group such as all stainless steels or all copper alloys. Our chart provides a general guideline that covers all material types and their relative machinability to brass. All rankings are based on how a specific material compares to the top free machining brass alloys.

The chart is not based on scientific data, but rather our machining experience based on the group of high precision machines we utilise. The following factors are considered in our ranking, all of which ultimately affect cost.

  1. Straight machine/part speed (parts per minute)
  2. Tool sharpening (parts per day)
  3. Tool replacement such as thread dies or special cutters (down time / parts per week)
  4. Ability to cut, drill or turn material cleanly with little or no residual burr
  5. Size of chips created (removable from parts and cutting tools easily and consistently)
  6. Raw material consistency (some materials can vary greatly from one lot to another based on the chemical composition “tolerance”)
  7. Part design (add a deep hole drilling requirement and material machinability becomes critical to speed)

These items come into play for any company machining metals, but will vary based on the type of parts, machines used and experience. The majority of our machines are high precision CNCs and the traditional high precision automatic lathes often referred to Swiss automatics. While our high precision machines can produce precision parts with extraordinarily tight tolerances, they are not always strong enough for “hogging” through the more difficult, gummy materials.

With our new group of high precision CNCs, the additional strength has made the transition to non free machining materials smoother. Still, certain machine models are better suited for certain materials. Matching the right machine with the right part and material is critical to creating a high quality process with the lowest cost.

Many of our customers use our experience with materials to help design components that can optimise machine speed, quality and price while giving them the part characteristics they need. If you have any questions about raw material selection, please feel free to contact us. We can offer pricing for multiple materials for engineers and buyers starting a new project.

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