Metal or plastic materials used for the spare parts are just as important as the way the parts are processed; an incorrect selection may substantially increase the cost of the parts. For example, the thermostable alloy and the aerospace darling —— titanium alloy is hard to process, and the parts made from it are almost much more expensive than those made of aluminum alloy or stainless steel. What is the point? Choose a cheaper metal if it’s not really needed.

Polyether ether ketone (PEEK) is the superman of polymers, strong enough to replace metals in some applications, but is also prepared for high prices, because PEEK is usually about five times that of other high-performance thermoplastics. Other technical considerations that can help in the selection of a suitable material for part applications include specific measurements, such as tensile strength, thermal deformation, overall hardness, etc.

cnc machining parts
CNC machining parts

Here are some of the more common materials used for machining parts and their key features:

Aluminum: Like all metals, there are many kinds of aluminum alloy, but the most common is the 6061-T6 (regarded as a general-purpose alloy) or the 7075-T6 (a favorite of the aerospace industry). Both materials are easily processed, corrosion resistant, and have a high strength-to-weight ratio. Aluminum is suitable for aircraft parts, computer parts, cookers, building parts, etc. (if you want to know, the T-6 refers to aluminum tempering, or being processed in a factory).

Cobalt-chromium alloy: Need a knee or hip replacement? It is most likely made of cobalt-chromium alloy (CoCr), a tough, wear-resistant alloy. The biocompatible metal is also well known for its brand name, tungsten, chromium, and cobalt alloy, and it is also widely used in turbine blades and other components that require high strength and heat resistance. Unfortunately, it is difficult to cut and has about 15% processability (compared to 1212 carbon steel and 400% aluminum).

The Inconel: Another heat-resistant superalloy (HRSA), the Inconel is the best option in extreme temperatures or corrosive environments. In addition to jet engines, Inconel 625 and its tougher, stronger brother Inconel 718 are also used in nuclear power plants, oil and gas RIGS, chemical processing facilities, and more. Both are fairly solvable, but are expensive and even harder to process than the CoCr, and therefore should be avoided unless needed.

Stainless steel: By adding a minimum of 10.5% of chromium, reducing the carbon content to up to 1.2%, and adding alloy elements such as nickel and molybdenum, metallurgists convert ordinary rust-prone steel into stainless steel, and stainless steel is the anticorrosion-resistant switch killer of the manufacturing industry. However, with the dozens of grades and categories to choose from, it may be difficult to determine which one is the best fit for a given application. For example, the crystal structures of the austenitic stainless steel 304 and 316L make it non-magnetic, non-enable, ductile, and quite resilient. On the other hand, martensite stainless steel (grade 420) is magnetic and hardening and is ideal for surgical instruments and various wear-resistant components. There are also ferroelastic stainless steel (most of the 400 series), dual-phase steel (think of oil and gas), and precipitated hardened stainless steel of 15-5 PH and 17-4 PH, which are all favored for their excellent mechanical properties. Accessibility ranges from fairly good (416 stainless steel) to moderate (347 stainless steel).

Steel: Like stainless steel, there are too many alloys and properties. But the four important issues to consider are:

  1. Steel usually costs less or lower than stainless steel and superalloys
  2. All steel will corrode in the presence of air and moisture
  3. Except for some tool steel, most steel has good processing ability
  4. The lower the carbon content, the lower the hardness of the steel is (as indicated by the first two digits of the alloy, such as the three common choices in 1018,4340, or 8620). That is, steel and its close relatives are by far the most commonly used of all metals, followed by aluminum.

The list does not mention red metal copper, brass, bronze, and another super important superalloy, —— titanium. No mention of some polymers such as ABS as material for Lego building blocks and drains that are both molded and machined with excellent toughness and impact resistance.

Engineering-grade plastic —— acetal is a notable example for all products from gear to sporting goods. The combination of strength and flexibility of nylon replaced silk as the preferred material for parachutes. There are also polycarbonate, polyvinyl chloride (PVC), high-density, and low-density polyethylene. The key is that the choice of materials is extensive, so, as a part designer, it makes sense to explore what is available, what is good, and how to be processed. Our offers more than 40 different grades of plastic and metal materials.

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