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
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
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
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
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