Selecting the Right Material for Your CNC Machined Part

Learn how choosing the right CNC material can save you time and money on your next job.

By Scott Kaplan · October 31, 2016

CNC machining can create high precision, end-use parts for nearly any application. It allows for amazingly tight tolerances on part dimensions and complex designs. But like any manufacturing process, the material selected is a critical component in determining the overall functionality and cost of your part: the designer defines the important material characteristics to the design — hardness, rigidity, chemical resistance, heat treatability and thermal stability just to name a few.

Xometry machines a wide variety of metals and plastic materials as well as other custom materials available on request. Read on to learn more about the advantages and trade-offs of manufacturing metals and plastics.

Metals

As a general rule, softer metals, like aluminum and brass, as well as plastics machine easily and will take less time to remove material from the part blank which in turn reduces machine time and cost of machining. Harder materials, like stainless steel and carbon steel, must be machined with slower spindle RPMs and machine feed rates which would increase the cycle times versus the softer materials. As a general rule, aluminum will machine about 4 times faster than carbon steel, and stainless steel will machine half as fast as carbon steel.

The type of metal is a critical driver in determining the overall cost of the part. For example, 6061 aluminum bar stock is approximately half the price per pound of aluminum plate, and 7075 aluminum bar stock can be 2 to 3 times the cost of 6061 bar stock. 304 stainless steel costs about 2 to 3 times what 6061 aluminum costs and is about twice as much as 1018 carbon steel. Depending on the size and geometry of the part, the material cost can be a significant portion of the overall price of the part. If the design does not warrant the properties of a carbon or stainless steel, consider using 6061 aluminum to minimize the material cost.

Plastics

Plastic material can be a less expensive alternative to metals if the design does not require the rigidity of metal. Polyethylene is easy to machine, and it is about 1/3 the cost of 6061 aluminum. In general terms, ABS is about 1 ½ times the cost of Acetal, Nylon and Polycarbonate are approximately 3 times the cost of Acetal. Although plastics could be a cost effective material alternative, keep in mind that, depending on the geometry, tight tolerances can be harder to hold with plastics, and the parts could warp after machining because of the stress created when material is removed.

Posted in Machining Manufacturability Tips

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