Considerations when selecting sheet metal materials

There are dozens of types of metal that could be used to create sheet metal parts and these all vary in use, physical properties, cost, and availability. The following pages will give you an idea of which might be best for your project.

This section is not an exhaustive list of materials; rather, it is just an overview of some of the most common ones that you are likely to encounter. Within these materials, there are also many specific grades (sub-types) of metal, each with slightly different properties. If in doubt, discuss your needs and budget with your sheet metal manufacturer and your material supplier to find the most suitable choice for your needs.

Steel and aluminum

The vast majority of sheet metal parts around us are made from either steel or aluminum, and of those, steel is probably the most common material.

Advantages and disadvantages of steel

Steel is an excellent all-round material, and if you're unsure which material to use, then steel is usually a solid choice. Steel is so popular and widely used for a number of reasons. It is very strong, easy to weld, and ductile, which means it is easy to bend and form compared to more exotic metals. Steel is also fairly inexpensive—it can be up to three times cheaper than aluminum for the same weight—and is widely available.

Material choice is always about compromise, so every material will have disadvantages. One of the main downsides of steel is that it is quite heavy—around two and a half times denser than aluminum, depending on the exact grades used. This means that if you have two pieces that are the exact same size and shape, then the steel part will be significantly heavier than the aluminum part.

Steel also has poor corrosion protection, meaning that it often goes rusty. You will have seen rusty steel items such as car bodywork. This rust is corrosion that is caused by a reaction between the metal and elements in the environment such as water and oxygen. The rust weakens and eventually destroys the metal. Steel can be treated to prevent or slow corrosion, but this will add to the material cost, and some other metals have much more natural resistance to corrosion.

Pros and cons of aluminum

Aluminum is the second-most common material used in sheet metal and is used in a wide range of items including bike frames, aircraft parts, and drinking cans.

One of the reasons why aluminum is so popular in the aerospace industry is that it is much lighter than steel. It also has excellent natural resistance to corrosion and so doesn't need extra surface treatments to stop it from going rusty. Another great property of aluminum is how malleable it is, meaning that it is very easy to bend. Consider how flexible aluminum foil is, or how easy it is to crush a drinks can.

Unfortunately, these positive properties also come with downsides, and aluminum is a lot more expensive than steel. However, because it is less dense, parts can be made lighter, which somewhat offsets this cost. Another factor is that although aluminum is lighter than steel, it is also weaker, meaning that parts that bear the same load will have to be made thicker in aluminum. However, due to the lower density of aluminum, these can actually be lighter than the equivalent steel parts. So overall, depending on exactly which grades of metal are used, aluminum generally has a better strength-to-weight ratio (SWR) than steel.

Other common metals

Steel and aluminum make up the vast majority of sheet metal parts but some other materials are reasonably common, such as the following:

• Copper: Copper is often used for parts such as electronics or heat-exchanging components because it has good electrical and thermal conductivity.

It is also easy to bend and form and has good corrosion resistance, and so is often used in plumbing, to make pipes and fixtures. Copper is more expensive than steel and aluminum, and some areas have issues with copper theft due to the higher price of the metal.

• Brass: This metal is an alloy (a mixture) of copper and zinc that looks similar to copper but has a brighter, shinier look. For this reason, it is often used for decorative items such as door knockers, fixtures, and trinkets.

It is extremely malleable and so is commonly used to make musical instruments in the brass section, such as trumpets. Brass has exceptional corrosion resistance and so is often seen in extreme environments, like door handles on ships. As with copper, it is quite an expensive metal and so is usually used sparingly.

• Stainless steel: Steel can be alloyed with other metals such as chromium to create different grades of stainless steel. This is steel that has a much greater resistance to corrosion than standard steel, while still retaining much of the strength and other benefits. For this reason, it is often used to make cutlery or surgical instruments.

Stainless steel sheet metal parts include things like large items of kitchen equipment—for example, sinks and countertops. However, this improved corrosion resistance makes stainless steel much more expensive than standard steel.

This overview is not intended to be a complete list of metals, and other niche materials might include tin, gold, and titanium. Each of these will have specific properties that suit different applications and budgets. As mentioned earlier, it is wise to discuss your specific needs with your sheet metal supplier and manufacturer to get the best fit for your project.

A summary of sheet metal material properties can be seen in the following table:

Sheet metal thicknesses and sheet sizes

Depending on where you live in the world, sheet metal is usually sold either by gauge number or the actual thickness of the sheet. As previously mentioned, gauge numbers are a way of measuring sheet metal thickness based on the weight of the material, and generally, a higher gauge number means a thinner sheet.

Gauge numbers are specific for each material, so 16 gauge steel will be a different thickness than 16 gauge aluminum. Therefore, it is highly recommended that sheet thickness is also specified in actual thickness, to avoid any confusion.

Metal sheets are also available in a wide range of sheet sizes, both metric and imperial. Some common sizes are shown in Figure 1.26 and include 48x120 " or 2x1 meters (m):

Figure 1.25: Common metal sheet sizes

When creating very big parts, or even large numbers of small parts, it is worth checking which sheet sizes are available to you and designing with this in mind. If making lots of small parts, it is even possible to use third-party "nesting" software to arrange the parts on the sheet in the most efficient way and avoid wasted material.

Material selection recap

Even when designing parts virtually in SolidWorks, it is important to consider how those parts will be created in the real world, and a vital aspect of this is the material choice. Most sheet metal parts are made from steel or aluminum, but other common metals include copper, brass, and stainless steel, and each of these materials has unique properties that suit different needs.

Sheet thicknesses are generally defined by actual thickness or using a gauge number. This is based on the material's weight, meaning that the same gauge number gives different thicknesses for different materials. Sheets come in a variety of common sizes that may have an impact on the design of your parts.