Before getting into the details of material selection, product teams must first take stock of their project requirements. Start by considering these four questions:

How will the part be used?

Engineers need to think about the end use of their part and where it will be used, as these factors have a significant impact on material selection. For example, both stainless steel and carbon steel are suitable for CNC machining, but only stainless steel is inherently corrosion resistant. Choosing the wrong type of steel would compromise the longevity of a part. You should also keep FDA, FAA and other industry-specific regulations in mind.

Does weight matter?

If a part needs to be lightweight – a common requirement when manufacturing parts for the automotive and aerospace industries – there are a variety of low-density metal options. Manufacturers may also consider using a plastic such as ABS to reduce weight if they are willing to sacrifice strength.

Does the part need to have high strength or heat resistance?

Strength can be measured in a variety of ways (tensile strength, wear resistance, etc.), so engineers need to determine what strength and how much strength is needed for their part. These parameters will affect the size of the material available. Similarly, temperature requirements will rule out certain materials from the start. Almost all materials expand or contract in response to temperature changes, so engineers also need to consider whether the part will be exposed to temperature fluctuations.

What is the budget for the project?

The cost of materials will almost always affect the choice of materials. The goal of most product teams is to select materials that maximize the desired material properties and performance while minimizing expenditures. when it comes to CNC machining, material costs are especially important because this process generates a relatively large amount of waste material. Some materials, such as specialty metals, are very expensive and can have a significant impact on the overall cost-effectiveness of a project when waste material emissions are taken into account. Engineers need to carefully evaluate their budgets before making any final decisions.

Aluminum

Aluminum alloys are easy to machine in large quantities, have an excellent strength-to-weight ratio, and have high thermal and electrical conductivity. It is also inherently resistant to corrosion. Aluminum 6061 is an all-purpose aluminum alloy often used for CNC machining. It is often used in automotive parts, bicycle parts, sporting goods, and other recreational products. This material is highly machinable, but is more expensive than other metals and does not hold up well in salt water or in the presence of certain chemicals. Aluminum 7075 is a material that is a step above 6061. It is ideal for aerospace frames and high-performance recreational equipment, and is the strongest aluminum alloy on the market.

Stainless steel

Resistant to distortion, abrasion, and corrosion, with high strength. 303 stainless steel contains sulfur to improve machinability, but there are some limitations to this material that engineers must keep in mind.

303 cannot be cold-formed, heat-treated, or welded, and in CNC machining, special attention must be paid to speed, feed, and cutting tool sharpness. Nevertheless, 303 is capable of making excellent nuts, bolts, non-marine grade fittings, shafts, and gears.

304 stainless steel is a non-magnetic all-purpose steel for CNC machining, known for its toughness. It is readily machined and corrosion resistant like 303, but it can be welded. 304 is well suited for a wide range of consumer and industrial applications, kitchen accessories, tanks and pipes, architecture, etc. 316 stainless steel, with the addition of molybdenum, can be made even more corrosion resistant than 304 and 303. It is even more corrosion resistant than 304 and 303. It is strong, weldable, and one of the few marine-grade stainless steels.

Since stainless steels are indistinguishable by appearance alone, engineers should always inspect the raw materials to verify the properties of the steel used.