They, whoever “they” are, say that form follows function. In other words, design to make your project work, and worry about appearance later. It’s logical, but not always very helpful, especially when it comes to selecting sheet metal.

For example, imagine you’re designing a structure for use outdoors. Stainless steel looks good and doesn’t need protecting, but is expensive. Cold-rolled low carbon steel is cheaper but needs protecting against the elements. Aluminum can look good too, and is lightweight, which may be an advantage, but it lacks strength. Or you could even go with copper.

The point is, there are lots of options when it comes to picking the sheet metal for your next project. Unless you weigh up the options carefully there’s a risk of compromising both function and form. With that in mind, here’s what we suggest are the most important sheet metal selection criteria.

1. Is strength required?

If the sheet metal is going to be purely decorative and/or protective, (like cladding on a building,) It need not be strong. However, strength becomes more important if you need it to bear some loads. A polished sheet of aluminum can look terrific but it doesn’t offer much in the way of tensile strength. That is, unless you form it into a profile, which gives it more rigidity.

2. Corrosion resistance

Stainless, aluminum and copper don’t corrode, although they do develop oxide films. Cold-rolled steel on the other hand rusts quickly if unprotected. Another factor here is what’s called galvanic corrosion. This is when you put two dissimilar metals in contact and the difference in electrical potential makes one corrode

3. Appearance

If you’ll be applying a plated, painted or powder finish perhaps it doesn’t matter too much what the sheet metal looks like. In some applications though you may want a bare metal look.

4. Weight

This applies to both mobile and fixed fabrications. If something is going to be moved it helps if it’s lighter. Trailer components are a great example. Towing the trailer consumes fuel, so less weight equals less fuel, but in addition, less weight means more payload. Keeping weight down also enables slimming-down of the supporting structure, perhaps reducing the amount of metal needed elsewhere. It’s also important to consider strength along with weight. While stronger metals are generally denser and therefore heavier, aluminum is surprisingly strong for its weight.

5. Formability

Some types of sheet metal are easier to bend than others. Most grades of aluminum for example are very ductile. Stainless on the other hand is very prone to cracking. And low carbon steels fall somewhere between the two. The advantage of a sheet material that’s easily formed is that you may be able to combine separate pieces. In effect, you replace welding or screwing with bending. It reduces piece count and simplifies assembly.

6. Joining processes

If welding is your preferred process, be careful. Some sheet metal materials are easier to weld than others. Our familiar cold-rolled steel welds without too much trouble but stainless gets more difficult. Aluminum can be welded, but it’s not easy, and as for copper, we’ll just say “No.”

What about cost?

We’re going to be a little provocative here and argue that material cost should not be one of your main sheet metal selection criteria. The reason is that a low cost material may need expensive processing while a more costly material lowers overall project expense.

High strength steels for instance cost more than the regular cold-rolled stuff, but because they’re stronger you may not need as much. Or maybe you can buy a thinner gauge. In the same way, aluminum costs more than cold-rolled but may not need painting, and stainless is both strong and durable.

Function comes first

Always select your sheet metal with a view to what the product or assembly needs. After all, if it’s cheap and good looking, but doesn’t work you’ll have wasted your money. Our six criteria should help you work through the selection issues and narrow down the options. And if you need advice we’re always happy to talk.