Material Selection Cheat Sheet

Designers work in a void.  One of the voids to be filled is selecting appropriate materials.  I have my favorites.  The selection is usually based on performance characteristics such as yield strength and ability to transfer heat.  However, the feel of a material lies beyond conductivity numbers and surface hardness.  Many elements of touch points need to be approached qualitatively.

Material selection is a balance of money, performance and manufacturability. Parts that are not subject to extreme temperatures can usually be made out of plastic, with polyethylene and other commodity plastics at the low end to the ubiquitous ABS on up to high strength, high temperature superstars.  Parts made out of A36 hot rolled steel or gray cast iron are cheap and strong yet we love titanium and gold at the other extreme.

There are natural divisions of material selection based on strength, weight, temperature, thermal and electrical conductivity, production volume and of course cost.  However, at the end of the day you have to pick something so here is a summary of my favorite material types.  This is just a starting point and is largely directed at metals.

Steel

• A36
• 1018
• 1040 (high strength)

Chromium (Stainless) Steel

• 304 (low Chromium)
• 316 (high Chromium, highly corrosion resistant)

Aluminum

• 5052 (good choice for flat work, not machining)
• 2011 (free machining alloy)
• 2024 (high strength, heat treatable)
• 6061 (high strength, structural alloy)

Brass

• C36000, Free Machining (machines like butter)

Polymers

• ABS (common injection moldable polymer)
• Low Friction: Delrin (lots of great surface treatments or impregnations are available with many polymers)
• Epoxies are used in carbon and aramid fiber composites.

Machined Prototype Materials

• Delrin, Nylon 6/6, brass and aluminum. 
• Additive manufacturing has changed prototyping approaches and material selection!

Favorite specialty materials

• Cu-Ni Alloy (Monel, cupro-nickel) and Torlon.