Not all sheet metal parts are created equal, and the most important factor in the success of a sheet metal part is the material it’s made from.
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The type of metal a sheet metal part is made from must be chosen carefully to ensure that the part meets fabrication requirements during manufacture and performance requirements in its final application. Picking the wrong material can cause part or whole product failure, low yields, high costs, poor performance or a number of safety issues.
Imagine a safety critical structural part failing due to improper material selection, and you have an idea of one potential concern. If you imagine products having to be recalled, at a high cost, due to in-use failure you have an idea of another potential concern.
The process of selecting the material for a sheet metal part can be complex because of the sheer number of factors involved. The issue is something that requires careful consideration.
The most important questions to answer when selecting a material for sheet metal parts are:
Fig. 1: Sheet Metal Parts at Komacut
In this guide, we'll look at the most common sheet metal materials used and go over the factors that need to be considered when choosing the right material.
There are many types of sheet metal, and each type has its benefits and drawbacks that must be considered when selecting a material for a project. The different properties different materials have make them suitable for different applications.
We will explore the types of sheet metal materials used at Komaspec and give examples of real-life uses for each of them.
Mild or Low Carbon Steel
Mild steel is by far the most commonly used material for sheet metal fabrication. The relative strength it has, combined with the ease of fabrication and relatively low cost compared to stainless steel or aluminum, means that it’s suitable in plenty of applications. These steels can be used to create a wide variety of custom steel parts. Automotive body panels, furniture and structural parts are common examples of mild steel in application.
Mild Steel Pros
Mild Steel Cons
Stainless Steel
Stainless steel is an alloy containing chromium, which provides good corrosion resistance and improved strength. Stainless steel is great in outdoor applications or other applications in which parts might be exposed to rust or corrosive chemicals. It’s also useful in applications that need more hardness than mild steel. As well as this, it is non-magnetic and non-sparking, making it ideal for medical instruments.
Fig. 2: Mill Finish – Stainless Steel
Stainless Steel Pros
Stainless Steel Cons
Galvanized Steel
When steel is galvanized, a layer of zinc is bonded to its surface. This method serves as a cost-effective way to build a high level of corrosion resistance into the material. In turn, this reduces the potential for rusting prior to fabrication and the need for additional surface finishing. Galvanized steel is perfect for things like fencing and other outdoor frameworks that are exposed to the weather.
Fig. 3: Cold Galvanized Steel
Galvanized Steel Pros
Galvanized Steel Cons
Aluminum
Aluminum has many wonderful qualities. Its primary qualities are its high level of resistance to rust and its reduced weight, being one-third of the weight of steel. It is less strong than other materials, but this can sometimes be overcome through design. In some applications, aluminum can also be designed to be equally as strong as steel.
Because of its lack of strength, aluminum may often not be able to handle the same stresses as steel. As such, you might want to contact our representatives at Komaspec to help you decide if aluminum is suitable for your intended use or not.
Fig. 4: Aluminum RAL
Aluminum Pros
Aluminum Cons
Spring Steel
Spring steel is a very resilient material containing manganese and high concentrations of carbon. It is designed to bend or flex under load and to return to its original shape when the load is removed. This makes it an excellent choice for making latching mechanisms, drive belts and, of course, springs.
Spring Steel Pros
Spring Steel Cons
For more info about each of the sheet metal materials Komaspec offers, including specific physical properties and surface finishing options, you can refer to the sheet metal material selection on our website.
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The costs that come with sheet metal parts fabrication begin with the cost of the raw material. Costlier materials, such as aluminum, stainless steel, and copper, can provide superior performance compared to cheaper materials, such as mild steel and galvanized steel. Still, they obviously come with a higher price tag.
In some cases, a cheaper metal will be suitable for a job and will provide adequate performance at a lower cost. For example, if aluminum is too expensive for a part that requires light weight and corrosion resistance, galvanized steel might be a better choice.
Ultimately, choosing the right material will mean weighing up performance requirements and the cost constraints of a project.
The table below shows a rough outline of how much each material costs. We can see that, while aluminum is twice as expensive as steel per kg, stainless steel is nearly five times more costly. Titanium is much more expensive again and is used sparingly in products such as jet engines, where the extra strength it provides is crucial.
Fig. 5: Material Cost Per Kg (USD)
The Difficulty in Comparing Material Costs
When considering which sheet metal material to buy for a project based on cost, there’s more to consider than just the price of a material per kg. You have to weigh material cost per kg against the design and performance goals of the project. Not all sheet metal is created equal in strength, weight, and appearance.
Stainless steel is stronger by weight than aluminum, for example, meaning that designs can be adapted. Thinner stainless steel can be used for a tank or vessel than it can for an aluminum one, for example.
Cost Increase of Custom Steel Parts
Custom design requirements often impact the price of steel sheet metal parts. This is because custom designs often require more intricate processes and skills to manufacture, increasing the cost of labor and materials.
Custom metal parts fabrication often also requires additional processes, such as welding, cutting, and bending, which can also increase the cost of the parts. They may require the use of specialized tools and equipment to construct correctly as well.
Understanding the mechanical properties different sheet metals have and the effect these properties have in application is critical to selecting the right material. There are many physical qualities inherent in different metals, and each one can be used to serve a different purpose.
Some of the most essential mechanical factors to consider in the material selection process include:
Strength of Sheet Metal Parts
Material strength is often the most widely used metric in determining material suitability. It is measured according to how much load a material can withstand before it bends out of its original shape. This bending is also known as plastic deformation.
There are two ways of looking at the strength of a material when it comes to choosing one for manufacture. Considering each separately may give a different outcome in decision making.
Strength By Cost
This simply considers how strong a material is in respect to how much it costs. Titanium is an example of a material with a high cost to strength ratio, and mild steel is an example of the opposite.
For metal enclosures or tanks that require large amounts of high strength material at low cost, for example, low-carbon (mild) steel would generally be considered the ideal material.
Strength By Weight
This considers how strong a material is in relation to its mass (or weight). Gaining high strength with lightweight materials is important in certain applications. In airplanes, for example, reducing weight is essential, and aluminum is often a good choice.
Strength to weight properties are also assessed by looking at specific strength.
Interestingly, in a comparison of aluminum, carbon steel, and stainless steel, the aluminum alloy has the highest specific strength (ASM Material Data Sheet), despite having the lowest tensile strength.
Fig. 6: Tensile Strength vs. Specific Strength
Also referred to as formability, this is the ability of a material to be stretched without cracking or breaking. If a material is highly ductile, it will withstand a large amount of stretching. Stretching commonly occurs in manufacture when a tight radius is formed during a metal stamping or folding process.
Fig. 7: Sheet Metal Materials at Komaspec
A simple way to visualize ductility is to imagine a material acting as a spring - the greater the elasticity of a material, the better its ductility. One thing to note is that this flexibility can be increased using a metal-forming process called annealing.
Corrosion Resistance
Corrosion occurs when a metal deteriorates as a result of the action of air, moisture or a chemical. The most common form is rust, which happens when iron in a material reacts with the oxygen and moisture in its surroundings. Good corrosion resistance (Metals - Corrosion Resistance to Aggressive Fluids) is a crucial factor in sheet metal selection because corrosion can weaken steel in a surprisingly short period of time if the conditions are right.
Fig. 8: Corrosion From Aggressive Fluids
The two main factors that help reduce corrosion are:
What is the Best Material for Corrosion Resistance?
Stainless Steel
Stainless steel contains chromium, which forms a thin film of chromium oxide on its surface, protecting it from corrosion. Stainless steel can become discolored, or it can rust if there is long term exposure to the elements. It is particularly vulnerable to corrosion where there are high salt concentrations. However, the resistance is greatly superior to mild steels.
Bimetal corrosion is a risk with stainless steel and must be considered when mating with other parts or fasteners.
Aluminum
A lightweight alternative to steel, aluminum is a naturally non-reactive metal that will not corrode in the presence of air or water.
Aluminum can be somewhat vulnerable to corrosion when in contact with concrete, however, and there’s also a risk of bimetal corrosion. Both of these problems can be overcome through anodizing or painting.
Modified Mild Steel
Using galvanized mild steel could be a great alternative if cost is a factor. The Zinc coating gives a layer of protection at lower cost. Be aware, however, that when galvanized mild steel sheets are cut, the edges are exposed and will be vulnerable to rust.
Mild Steels
Mild carbon steels without secondary finishing will rust rapidly in the presence of moisture or salt. In fact, unprotected steel sheets can begin to rust even before fabrication, which often leads to the need for deburring or chemical treatment to remove rust before surface finishing.
Rust can be so severe, in some cases, that it impacts the final part appearance even after painting. Parts can appear “mottled” or like they have a blotched surface when this happens.
Sheet metal part fabrication processes involve procedures such as cutting, bending, and joining sheets of metal. These procedures create different configurations of sheet metal to create custom steel parts. Each material has its own specific advantages and disadvantages in the fabrication process that need to be considered.
Laser Cutting
Laser cutting is a precise and reliable method for cutting all different types of metal. This method is a great option in many different situations. However, it’s particularly useful where speed and precision are important, such as in the automotive industry. Lasers are also useful for cutting thicker materials, for making complex cut-outs and for making very clean cuts.
Shiny metals, such as aluminum and copper, are more difficult to cut, although it is still possible to cut these materials with a laser. The minimum / maximum thickness which can be cut, however, varies depending on the material type, which in the case of very thick or very thin material, may limit potential choices.
Bending
There are two factors that have an impact on bendability:
Some materials can be bended more easily than others and with more success in application. It’s worth noting, however, that even within the same material, there can be differences in bendability between different grades. If ductility is important, for example, the series aluminum is best avoided as the hardness of the material can result in micro-cracks and part failure duing bending.
Generally speaking, aluminum is commonly considered a good choice where sheet metal bending is required.
Designs with tight bend radii and low tolerances will mean that a more bendable material is required. For more about bend design, read our article on sheet metal design guidelines. Very stiff materials (i.e. medium carbon or stainless steels) may require larger reliefs are larger bend radii vs mild steels and aluminum parts.
Fig. 9: Metal Bending at Komacut
Weldability
Welding is one of the most common methods for joining and manufacturing metal components. This process uses a high-powered and highly controlled electric arc to heat base metals to the point where they melt. They are then joined and solidify as almost one piece.
The weldability of sheet metal will depend on the type of filler metal used, the process used and the material makeup of the sheet.
Mild carbon steels are highly weldable with a variety of processes, are generally finished with secondary processes which help to resolve discoloration of the base material. Aluminum requires TIG welding, which can be more time and cost intensive than MIG, and the material is more vulnerable to deformation and discoloration due to heating during the welding process. Stainless is also weldable, but requires TIG or special robotic welding equipment and may need passivation or secondary processes to hide discoloration from the welding process.
Fig. 10: Robotic Welding at Komacut
Different materials have different properties when it comes to surface finishing. Not all materials are compatible with all surface finishing options, such as anodization being largely specific to aluminum, or the difficulty of electropolishing mild steel parts.
For which options are available for various sheet metal materials, please see the table below or explore in greater detail in our surface finishing article.
Finish Corrosion Resistance Coating Thickness Abrasion ResistanceTable 1: Surface Finishing: Corrosion, Thickness, Abrasion
Finish Carbon Steel Stainless steel Aluminium Application Visual Requirements Thickness Corrosion resistance Mill Finish Internal Parts or Parts with Subsequent Processing Low-Visual - - Antirust Oiling Parts with Subsequent Processing Low-Visual - 24 Hours NSS Brushed Indoor Med-Visual - - Anodized Indoor / Outdoor High-Visual - - Mircro-Polishing Indoor / Outdoor High-Visual - - Passivation Indoor / Outdoor Med-Visual 0.5 to 15μm - Zinc Plating Indoor / Outdoor Low-Visual 5 to 25μm 48 to 94 Hours NSS E-Coating Indoor / Outdoor Low-Visual 5 to 25μm 96 Hours NSS Powder Coating Indoor / Outdoor High-Visual 70 to 150μm 480- HoursTable 2: Metal Finishing Guide
The application of the part often determines the finishing requirements. Some reasons for wanting an enhanced surface finish include:
Because these aspects are critical to quality for many applications, it’s important to think about these requirements when selecting a material.
Aesthetics
Polishing is a common technique used to create a high-quality look that’s pleasing to the eye. The process involves progressively removing all surface imperfections to give a metal part a shiny finish.
Fig. 11: Surface Finishing
Polishing for Sheet Metal Parts
Stainless steel can be brought to a mirror finish and is very durable; aluminum is less durable and can take longer to reach the same finish. It is not possible to create a durable polished surface on mild steel.
Hygienic Sheet Metal Parts
Sheet metal parts are often used in both the food industry and medical settings. The material chosen must be resistant to the build-up of bacteria and other contaminants.
Stainless steel, for example, is a popular choice for sheet metal products because it is non-porous and resistant to corrosion. This eliminates the need for potentially toxic paints and other coatings.
Additionally, stainless steel can be easily cleaned and sterilized using various chemical and thermal methods. This makes it an ideal choice for food-grade products and medical instrumentation.
Stainless steel 316, for example, is widely used for food service or medical equipment due to its excellent resistance to chemical cleaning agents, acids and other corrosion.
Durability for Sheet Metal Parts
Durability is the main factor that affects a material’s resilience to dents, scratches and bending. Also important in hygienic environments, the durability of a material affects how well it can withstand harsh environments without needing to be repaired or replaced.
Stainless steel is a great option if a part needs to resist scratching and be easy to repair. When scratched, it does not cause possible contamination with aluminum oxide. Aluminum, along with copper, will resist scratches and deformation very poorly.
Mild steel is another durable material, but the paints and coating needed should be considered as they can often lead to the same problems with contamination.
Material finishing requirements will help determine the best material choice for any particular part. For more about different types of finishing, read this guide.
Rather than starting with a block of material, much of which will be machined away, sheet metal lets you buy what you need and use what you need. The remainder of a metal sheet is still usable, while swarf—the shavings removed in machining—must be recycled.
As with many modern fabrication techniques, sheet metal manufacturing can be automated and parts produced directly from CAD models. The technology uses a variety of materials and a range of processes for shaping finished components and products. Perhaps most important, in a world of mass production, sheet metal fabrication is highly scalable. While setup for the first piece can be costly, the price per piece drops quickly as the volume increases. This is, of course, true of many processes, but cost-per-piece for sheet metal generally drops more steeply than for a subtractive process like machining.
Sheet metal is cut, stamped, punched, sheared, formed, bent, welded, rolled, riveted, drilled, tapped, and machined. Hardware can be inserted into sheet metal components. The components can be brushed, plated, anodized, powder coated, spray painted, silk screened, or otherwise marked. And, of course, parts can be riveted, screwed, or welded into complex assemblies.
Like most other technologies today, sheet metal fabrication is evolving. Materials, equipment, and tooling have become more specialized than ever before. To take full advantage of sheet metal, it is critical that you leverage the correct supplier and method of manufacturing for your parts and their application. Along these lines, this white paper explores key components of sheet metal fabrication:
Sheet metal, by definition, starts out flat but can be shaped in many different ways to meet many different requirements. While this paper focuses on the technologies that shape sheet metal by bending it along a single axis, a variety of techniques exist for shaping the material into multi-axis forms that are not made up of flat planes or bent along a single axis. These include hot and cold forming techniques of deep drawing, hydroforming, spinning, and stamping. These are the kind of processes that create the body panels for modern vehicles, complex formed objects like metal sinks, and aluminum beverage cans. In many cases these techniques are iterative, shaping the metal by repeating the process several times to change the shape of the metal in increments.
Cold-forming processes addressed here are:
Cutting
Bending. Most metals can be bent along a straight axis using a variety of presses. The shapes of bends can range from gentle curves, like those along the vertical axis of a steel can, to sharp corners at angles above, below, or right at 90 degrees. Press brakes are used to create these relatively sharp bends. Rolling and forming methods produce open or closed single-axis curves in a continuous bending operation.