How to determine the material suitable for CNC machining?

The raw metal or plastic material used for the part is as important as the processing method of the part; choosing the wrong one may unnecessarily increase the cost of the part. For example, titanium, the darling of superalloys and aerospace, is difficult to machine, and parts made of it are almost certainly more expensive than parts made of aluminum or stainless steel. What's the point? If it is not really needed, choose a cheaper metal.

Polyether ether ketone (PEEK) is the superman among polymers. It is strong enough to replace metals in certain applications, but it must be prepared for price shocks, because the price of PEEK is usually about five times that of other high-performance thermoplastics. . Other technical considerations that help select materials suitable for part applications include specific measurements such as tensile strength, thermal deformation, and overall hardness.

Here are some of the more common materials used for machined parts and their key characteristics:

Aluminum: Like all metals, there are many types of aluminum alloys, but the most common are 6061-T6 (considered a general-purpose alloy) or 7075-T6 (a favorite in the aerospace industry). Both materials are easy to process, corrosion resistant, and have a high strength-to-weight ratio. Aluminum is suitable for aircraft parts, computer parts, cooking utensils, construction parts, etc. (if you want to know, T-6 refers to the tempering of aluminum, or the way it is processed in the factory).

Cobalt Chrome: Do I Need Knee or Hip Replacement? It is likely to be made of cobalt-chromium alloy (CoCr), which is a tough and wear-resistant alloy. This biocompatible metal is also known for its brand name stellite, 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 a workability of around 15% (compared to 100% workability for 1212 mild steel and 400% workability for aluminum).

Inconel: Another heat-resistant super alloy (HRSA), Inconel is the best choice for extreme temperatures or corrosive environments. In addition to being used in jet engines, Inconel 625 and its harder and stronger brother Inconel 718 are also used in nuclear power plants, oil and gas drilling platforms, chemical processing facilities, and more. Both are quite weldable, but they are expensive and even harder to process than CoCr, so they should be avoided unless needed.

Stainless steel: By adding a minimum of 10.5% chromium, reducing the carbon content to a maximum of 1.2%, and adding alloy elements such as nickel and molybdenum, metallurgists convert ordinary rusty steel into stainless steel. Stainless steel is the anti-corrosion switch killer of the manufacturing industry. . However, since there are dozens of levels and categories to choose from, it may be difficult to determine which one is best for a given application. For example, the crystal structure of austenitic stainless steels 304 and 316L makes them non-magnetic, non-hardenable, ductile and quite tough. On the other hand, martensitic stainless steel (grade 420 is the first grade) is magnetic and hardenable, and is an ideal choice for surgical instruments and various wear-resistant parts. There are also ferritic stainless steels (mostly 400 series), duplex steels (think oil and gas), and precipitation hardening stainless steels 15-5 PH and 17-4 PH, all of which are favored for their excellent mechanical properties . Machinability ranges from fairly good (416 stainless steel) to moderately poor (347 stainless steel).



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

1. The cost of steel is usually lower than that of stainless steel turned parts and superalloys
2. In the presence of air and moisture, all steel will corrode
3. Except for some tool steels, most steels have good machinability
4. The lower the carbon content, the lower the hardness of the steel (represented by the first two digits of the alloy, such as the three common choices of 1018, 4340 or 8620). In other words, so far, steel and its close relative iron are the most commonly used of all metals, followed by aluminum.

This list does not mention the red metal copper, brass and bronze, and another super important superalloy-titanium. There is also no mention of some polymers, such as ABS, which is the material of Lego bricks and drain pipes, which can be molded and processed, and has excellent toughness and impact resistance.

Engineering grade plastic-acetal is a notable example, suitable for everything from gears to sporting goods. The combination of the strength and flexibility of nylon replaced silk as the material of choice 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 process it. Sujia provides more than 40 different grades of plastic and metal materials.