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Metal Fabrication: Material Types – Steel, Aluminum, AR Steel

Fabrication is the art of taking raw-materials and producing an end-product with them. The finished product could be a variety of items within the metal fabricating industry; it may be a truck body, an enclosure for a computer, kitchen equipment, or a small component which combines with other pieces to assemble a completed product.

Commonly seen materials in metal fabrication are steel, aluminum, and nowadays AR steel. Within these materials there are subsets and categories made of different alloys. All these variable sheet-metal elements are the base on which fabricators create today’s world needs. Let’s take a look at some of these alloys and how their unique mechanical properties affect our daily work.

Steel:

Steel is an alloy made using Iron and other elements; the most important element being Carbon. Carbon has the ability to increase the alloy’s strength (the ability to resist deformation) and hardness (resistance to penetration). Carbon accounts for approximately 0.05% to 2.4% of the weight of the alloy. Even though this seems like a small amount, its ability to increase resistance reaches an exponential level.

Most steel alloys have less than 0.45% of Carbon, and those that have a greater amount will increase the hardness and most importantly the brittleness of the material. This is because Carbon reduces the ductility on the steel, and ductility is essential for fabrication.

** Ductility Definition**

Ductility is the ability of a material to be drawn or plastically deformed without fracture. It is therefore an indication of how 'soft' or malleable the material is. The ductility of steels varies depending on the types and levels of alloying elements present. (https://www.sciencedirect.com/topics/chemistry/ductility)

Various other elements are melted together in furnaces in order to create different steel alloys. Some of the most common elements used are Chromium, Silicon, and Nickel. Each one of these provides different mechanical and chemical properties to the finished alloy produced. The steel alloy material properties can directly be influenced by the heat temperature and the amount of oxygen introduced into the furnace during production.

Stainless Steel:

Stainless is an alloy that contains at least 11% chromium. Chromium creates a film on the steel, which prevents the Iron from rusting when in contact with oxygen. Corrosion resistance is increased further by adding to the alloy some Nickel and Molybdenum. These elements also increase resistance on the new material.

What we get at the end of the day is a variety of SS alloys depending on their percentage of carbon, nickel, molybdenum, chromium and other less important elements.

All SS alloys resist rusting and have a higher resistance than normal mild steel. We notice this when we need more tons per foot to bend SS than what we normally use on MS with the same thickness.

Aluminum:

Aluminum as an element occurs naturally in the Earth’s crust, but when looking at Aluminum within metal fabrication; we need to understand it as an alloy. This is because Aluminum that we fabricate with is mixed with Zinc, Silicon, and copper, among other elements.

Aluminum is a non-ferrous metal; meaning that it does not contain any iron. Without having iron within its’ composition; it allows it not to rust or corrode. Typically Alluminum is not as resistant as steel. There are, of course, special aluminums made for aerospace that can be really tough to bend, but they are not common on the marketplace. Being less resistant and more ductile makes it softer to bend and easier to work with. Although, we must make sure to use the correct radius on our upper tool (typically 1x thickness) when we bend it; since a sharp punch tip might result in cracks on the material (due to force concentration and surface area contact).

Abrassive Resistant Steels

Mining, transportation, trucking, agricultural and many other “tough” industries have experienced the benefits from using AR steels in the present day. Such alloys are specifically designed to provide a material that lasts longer and resists better to wearing. But also a material that’s stronger and much more resistant. This last aspect is of great help on many fabricated parts that work with loads. Typically a truck bucket that can resist a higher load with a lighter structure (because it’s made on a thinner gauge material using AR steel).

AR steels contain manganese to increase their resistance, but they also use nickel, silicon and molibdenum in different percentages to create different varieties of AR steels.

Some AR steels are not ductile enough to be bent, but some are; and so they are used on parts for the above industries. Even if they are good for fabrication, it’s important to know the rules of how to work with them. Typically, a large radius upper tool and a large V opening are required, but it’s not that simple. We also need to account for a huge amount of springback.

The complexity of this fabricating makes most AR steel suppliers provide a chart with empirical tests and recommendations; so fabricators can choose the correct tooling and press brake for each material.

Getting to know the material we fabricate with often, is a basic step on the learning curve of every fabricator. We might not need to learn by heart the chemical composition of every sheet-metal we use, but knowing the basic mechanical properties would be a good starting point.

To improve our approach on the matter, next time we will discuss the meanings and implications of concepts like: UTS (ultimate tensile strength), resistance, ductility, elongation, hardness and brittleness. Specifically, how to use this knowledge to our advantage and better understand what is going on physically while we fabricate our parts.

Stay tuned for more sheet-metal fabrication papers from Rolleri USA….