Material Selection

When you're designing and fabricating a part, perhaps the most important step is choosing the right material. This page contains information about some of the materials you're most likely to see in the shop. Even if you know a lot about materials, this set of guides will give you a lot of valuable information about the specifics of selecting the right stock for your part. If you haven't worked with a material before and you don't know EXACTLY how to machine it, speak to a proctor or Drew before trying to work. DO NOT wait until you've broken a machine or hurt yourself.

Please note: Glass is NOT allowed in the shop. Carbon fiber and other fibrous materials may be allowed, but speak with Drew first.

Below is a set of brief descriptions, as well as more detailed material selection data for each of the listed materials. For material selection charts and material properties, we recommend CES EduPack (available in the ECF).

Safety Data Sheets (SDS) (previously MSDS)

Aluminum

Aluminum is a soft, silvery-white to dull gray metal. If you pick up some metal and it's lighter than it looks, it's probably aluminum. It can usually be found as aluminum alloys (containing manganese, zinc, silicon, magnesium, etc.).

Pros

  • Low density / weight

  • Easy to machine

  • Does not corrode (forms surface oxide)

  • Relatively cheap and easy to find

  • Good conductor (heat and electricity)

  • Ductile

Cons

  • Less durable

  • Not suitable for high stress / heavy duty applications

  • Relatively low melting point

  • Parts can be bent out of shape / marked easily, even while fixturing

Aluminum Selection.pdf

Stainless Steel

Stainless steel is a group of silvery iron-based alloys that contain chromium, which prevents the iron from rusting. It is a popular material for its durability and resistance to corrosion. It's good for heavy-duty applications, tooling, and high-stress or high-heat applications. It is magnetic, and can conduct heat and electricity, albeit with some resistance.

Pros

  • Does not corrode (forms surface oxide)

  • Durable, withstands high stress and heavy loads

  • Somewhat good conductor (heat and electricity)

  • Ductile

  • Can be heat treated

Cons

  • High density / weight

  • Harder/slower to machine

stainless_steel_comparator.pdf

Steel and Heat Treating

Steel is an alloy of iron, typically containing carbon to improve strength and toughness. See document below for types and uses of steels.

Steel (including most stainless steels) can be heat treated to change its structure and therefore its properties. This process involves putting the part (often once it is completed) in an oven and heating it to a specified temperature. It is then kept in the oven long enough to change its grain structure, then removed and allowed to cool (or moved to another oven). Different heating and cooling processes and temperatures result in different forms of steel, such as austentite, martensite, bainite, etc.

  • Tempering

    • Increase toughness for durability

  • Annealing

    • Decrease hardness

  • Case-hardening

    • Increasing the hardness/brittleness of the surface only, leaving the inside able to absorb stresses while the outside is wear resistant

Pros

  • Does not corrode (forms surface oxide)

  • Durable, withstands high stress and heavy loads

  • Somewhat good conductor (heat and electricity)

  • Ductile

  • Can be heat treated

Cons

  • High density / weight

  • Harder/slower to machine

  • Can change color /oxidize after heat treating

  • Heat treatment can yield unexpected results

Steel Selection & Heat Treating.pdf

Copper, Brass, and Bronze

Copper is a soft, malleable metal known for its thermal and electrical conductivity, as well its distinctive pink-orange color. It is used primarily for electrical applications, although it is sometimes used decoratively. It forms a distinctive green patina on its surface after extended periods outdoors or in high humidity.

Brass is a bright gold copper-zinc alloy that is harder and tougher than copper, but less so than steel. It is relatively easy to form, and conducts heat and electricity well, while being more corrosion-resistant than copper. It is often used decoratively, and in applications where it is important that sparks are not struck.

Bronze is a copper-tin alloy that has a color between that of copper and brass. It is often alloyed with different metals to form specialized bronzes with varying properties. They are typically ductile and tough. It is often denser than steel. It has a low friction against dissimilar metals, and it is often used where chips cannot be struck. Marine bronze is often used in water-based applications.

Pros

  • Excellent conductor

  • Visual appeal

  • Heavy

  • Brass and Bronze are corrosion resistant

  • Will not spark when struck

  • High ductility and malleability

Cons

  • Can form patina / discoloration

  • Some can be very soft and easy to deform

Copper_Brass and Bronze Selection.pdf

Plastics and Laminates

Plastics encompass a wide range of fully or partially synthetic compounds that possess a range of properties, appearances, and uses. Common plastics used in the shop are PVC, nylon, ABS, acrylic, polycarbonate, Delrin, PET, and PMMA.

Laminates are a class of composite materials formed by permanently adhering multiple layers using heat, pressure, welding, or gluing. The resulting material has increased strength, toughness, and various other properties. Common laminates are plywood, plastic laminates, fiberglass, and carbon fiber sheets.

Pros

  • Low density/weight

  • Easy to machine

  • Can be 3D printed / laser cut

  • Does not corrode

  • Generally cheap and easy to find

  • Can be clear / colored / transparent

  • Nonconductive

  • Elastic recovery

Cons

  • Less durable

  • Not suitable for high stress/heavy duty applications

  • Low melting point

  • Parts can be bent out of shape/marked easily, even while fixturing

Plastics & Laminates Selection.pdf