There are hundreds of metal alloys available for CNC machining. Which one is best for your next project depends on a number of factors, including price, workability, corrosion resistance, strength, weight and aesthetic appearance. To help you choose, here’s a closer look at the ones we use every day and what benefits they may have for your next project.
Aluminum 7075
7075 is a superior grade of aluminum, alloyed primarily with zinc. It is one of the strongest aluminum alloys, with excellent strength that allows it to regain its original shape when cold formed. 7075 is machinable and can be anodized.
7075 often hardens to T6. However, it is a poor choice for welding and should be avoided in most cases. We typically use 7075 T6 to make plastic injection molds. It is also used for high-strength equipment, such as automotive and aircraft frames and other stressed parts.
Brass
Brass is an alloy of copper and zinc. It is a very soft metal and can often be machined without lubrication. It is also highly functional at room temperature, so it is often used in applications that do not require high strength. There are many types of brass, depending largely on the percentage of zinc. As this percentage increases, corrosion resistance decreases.
Brass has a high luster and closely resembles gold, which is why it is often found in cosmetic applications. Brass is electrically conductive but not magnetic, can be soldered and can be easily recycled. Another characteristic of brass is that it does not spark when struck with another metal, which is why it is used in tools in potentially explosive environments. Interestingly, brass has natural antibacterial and antimicrobial properties, and its use in this regard is still under study.
Brass is common in plumbing fixtures, decorative home hardware, zippers, marine hardware and musical instruments.
Magnesium AZ31
AZ31 magnesium is an alloy with aluminum and zinc. It is up to 35% lighter than aluminum, with equivalent strength, but it is also slightly more expensive.
Magnesium is easy to machine, but it is very flammable, especially in powder form, so a liquid lubricant must be used for CNC machining. Magnesium can be anodized to improve its corrosion resistance. It is also highly stable as a structural material and is an excellent choice for die casting.
AZ31 magnesium is often used for aircraft components where light weight and high strength are most desirable, and can also be found in power tool housings, laptop cases and camera bodies.
303 Stainless Steel
There are many varieties of stainless steel, named for the addition of chromium that helps deter oxidation (rust). Because all stainless steels look alike, great care should be taken to test incoming raw material with metrology equipment such as OES detectors to confirm the characteristics of the steel you are using.
To improve its CNC machining, sulfur is added, but it also reduces its corrosion protection.
303 is not a good choice for cold forming (bending), nor can it be heat treated. The presence of sulfur also means it is not a good choice for welding. It has excellent machining properties, but care must be taken with speeds/feeds and sharpness of cutting tools.
303 is often used for stainless steel nuts and bolts, fittings, shafts and gears. However, it should not be used for marine grade fittings.
304 Stainless Steel
This is the most common form of stainless steel, found in a wide variety of consumer and industrial products. Often called 18/8, this refers to the addition of 18% chromium and 8% nickel to the alloy. These two elements also make the material especially tough and non-magnetic.
304 is easy to machine, but unlike 303 it can be welded. It is also more resistant to corrosion in most normal (non-chemical) environments. In machining it must be processed with very sharp cutting tools and not contaminated with other metals.
Stainless steel 304 is an excellent choice for kitchen accessories and cutlery, tanks and pipes used in industry, formula architecture and automotive moldings.
316 Stainless Steel
The addition of molybdenum makes 316 even more resistant to corrosion, so it is often considered a marine-grade stainless steel. It is also tough and easy to weld.
316 is used in architectural and marine fittings, for industrial pipes and tanks, automotive moldings and kitchen cutlery.
1045 carbon steel
This is a common grade of mild steel, i.e. non-stainless. It is usually less expensive than stainless steels, but is considerably stronger and tougher. It is easy to machine and weld, and can be hardened and tempered to obtain different hardnesses.
Steel 1045 (in the European standard, C45) is used in many industrial applications, for nuts and bolts, gears, shafts, connecting rods and other mechanical parts that require a higher degree of toughness and strength than stainless steel. It is also used in architecture, but if exposed to the environment, it is necessary to treat its surface to prevent oxidation.
Titanium
Titanium is known for its high strength, light weight, toughness and corrosion resistance. It can be welded, passivated and anodized to increase protection and improve its appearance. Titanium does not polish particularly well, is a poor conductor of electricity but a good conductor of heat. It is a hard material to machine and special tools must be used.
Titanium is generally biocompatible and has a very high melting point. Although it is more expensive than other metals in commercial form, it is actually very abundant in the earth’s crust but difficult to refine.
Titanium works well for metal 3D printing(sintered). It has applications in aerospace, military, biomedical and industrial fields, where it resists heat and corrosive acids well.
