In this section, you will learn the various common metal materials that are valuable for CNC machining. We’ve listed these materials below.

Aluminum 6061

This is the most common general purpose aluminum used for CNC machining. The main alloying elements are magnesium, silicon, and iron. Like all aluminum alloys it has a good strength-to-weight ratio and is naturally resistant to atmospheric corrosion. Other advantages of this material are that it has good workability and CNC machinability, can be welded and anodized, and its wide availability means that it’s economical.

When heat-treated to a T6 temper, 6061 has a considerably higher yield strength than annealed 6061, although the price is slightly higher. One of the drawbacks to 6061 is poor corrosion resistance when exposed to salt water or other chemicals. It’s also not as strong as other aluminum alloys for more demanding applications.

6061 is a material that’s typically used for auto parts, bicycle frames, sporting goods, some aircraft components, and frames for RC vehicles.

Aluminum 7075

7075 is a higher grade of aluminum, alloyed mainly with zinc. It’s one of the strongest aluminum alloys used in machining, with excellent strength-to-weight characteristics.

Because of the strength of this material it has average workability which means it tends to spring back to its original shape when being cold-formed. 7075 is also machinable and can be anodized.

7075 is often hardened to T6. However, it’s a poor choice for welding and this should be avoided in most cases. We routinely use 7075 T6 for making plastic injection mold tools. It’s also used for high-strength recreational equipment for mountain climbing, as well as for automotive and aerospace frames, and other stressed parts.

Brass

Brass is an alloy of copper and zinc. It’s a very soft metal, and can often be machined without lubrication. It’s a material that’s also highly workable at room temperature, so it often finds applications that doesn’t require great strength. There are many kinds of brass, largely depending on the percentage of zinc. As this percentage increases, corrosion resistance decreases.

Brass takes a high polish that looks much like gold. This is the reason it’s often found in cosmetic applications. Brass is electrically conductive but non-magnetic, and can be easily recycled.

Brass can be welded but is most often joined with low-temperature processes like brazing or soldering. Another feature of brass is that it doesn’t spark when struck with another metal, so it finds use for tools in potentially explosive environments. Interestingly, brass has natural anti-bacterial and anti-microbial properties, and its use in this regard is still being studied.

Brass is common in plumbing fittings, home decorative hardware, zippers, naval hardware, and musical instruments.

Stainless Steel 303

There are many varieties of stainless steel, so called because of the addition of chromium that helps to deter oxidation (rust). Because all stainless steels look alike, great care must be taken to test incoming raw material with modern metrology equipment like OES detectors to confirm the characteristics of the steel you’re using for machining.

In the case of 303, sulfur is also added. This sulfur helps to make 303 the most readily machined stainless steel, but it also tends to reduce its corrosion protection somewhat.

303 isn’t a good choice for cold forming (bending), nor can it be heat treated. The presence of sulfur also means it’s not a good candidate for welding. It does have excellent machining properties but care must be taken with speeds/feeds and the sharpness of cutting tools.

303 is often used for stainless nuts and bolts, fitting, shafts, and gears. It should not, however, be used for marine grade fittings.

Conclusion

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