There are a wide range of alloys and metals which come in sheet form and that are used in manufacturing and fabrication. Which material is used depends on a number of factors such as weldability, formability, strength, weight, cost and the corrosion resistance of the material.
The more common sheet metals used in fabrication are:
- Stainless steel
- Hot rolled steel
- Cold rolled steel
Stainless steel comes in a variety of grades, which make up five families. These families are:
- Precipitation Hardening Steels
We discuss these families in more detail in our article What are the Five Types of Stainless Steel.
Common applications include surgical tools and medical equipment, automotive applications, conveyor systems and machinery parts within the food industry; typically, stainless steel is a popular choice in clean environments.
Hot Rolled Steel
Between hot and cold rolled steel, hot rolled steel is the easier to make, shape and form. Hot rolling is a mill process where steel is rolled at a high temperature, typically over 900 degrees Celsius as this is above the materials recrystallisation temperature.
When steel reaches temperatures above recrystallisation, this makes the material easier to form and to work with.
To begin the process, manufacturers of sheet metal start with a large rectangular length of metal called a billet. This is heated before being flattened into a large roll where, while being kept at a high temperature, it is run through a number of rollers until it has achieved the desired finish. For sheet metal the rolled steel is then spun into coils before being left to cool at room temperature – this is known as normalising, which means freeing it from internal stresses which may come about from work-hardening or quenching processes.
As hot rolled steel cools it shrinks slightly which results in less control over the size and shape of its final form.
Hot rolled steel is a common choice when tight tolerances are not critically important and where price is of higher priority than precision. It is commonly used in structural applications within construction, pipes and tubes, railroad tracks and chassis components in the automotive industry.
Cold Rolled Steel
Cold rolled steel starts out with a similar set of processes to Hot Rolled Steel, being heated to extremely high temperatures before being left to cool at room temperature – however with cold rolled steel, it is processed further in cold reduction mills by being rolled again, below its recrystallisation temperature.
Cold rolled steels are typically harder than hot rolled steels. Due to being shaped at lower temperatures, cold rolled steels hardness and resistance against tension breaking and deformation are all increased by work hardening – also known as strain hardening and cold working, which means the strengthening of a metal by plastic deformation (the permanent distortion which occurs as a result of a material being subjected to bending, compressive, tensile or torsion/twisting stresses which surpasses the yield strength of the material, causing it to compress, elongate or twist etc.).
Common applications of cold rolled steel include aerospace structures, home appliances, metal furniture and structural components where a higher tensile strength is required.
“however with cold rolled steel, it is processed further in cold reduction mills by being rolled again, below its recrystallisation temperature”
Aluminium production is broken down into three stages:
- Extraction of bauxites which contain aluminium from the ground
- These bauxites are then processed into alumina or aluminium oxide
- Electrolytic reduction (where aluminium oxide is broken down using electric currents) is used to create pure aluminium
Once the pure aluminium is created, the liquid metal is cast into ingots. To form aluminium sheets, these ingots are then heated to around 525°C before being fed into a breakdown mill (typically a single-stand four-high reversing hot rolling mill). The main function of the mill is to “break down” the ingot in order to reduce it to the required dimensions. In some instances, the aluminium is further hot or cold milled to reduce the thickness more and/or to improve the surface finishing.
Benefits of aluminium include very good strength to weight ratio, natural corrosion resistance, exceptional workability and high thermal/electrical conductivity. It is also infinitely recyclable without losing any of its quality in the process.
Common uses of aluminium include window frames, household and industrial appliances, aircraft and spacecraft components, and power lines.
Although not as common as steel or aluminium, brass is still one of the more widely used materials in sheet metal fabrication.
Brass is an alloy which is made up of copper and zinc, with the proportions of each varying dependent on the mechanical and/or electrical properties which are to be achieved. It is a popular material due to its easy formability, and because it retains high levels of strength after being formed.
Common uses are bathroom fixtures and fittings, and medical applications as it is not a great breeding ground for bacteria; ammunition components (as brass is used in applications which require low friction) and musical instruments such as trumpets, horns and trombones.
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Similar to Brass, Copper is not as common as steel or aluminium but is still one of the more widely used materials in sheet metal fabrication.
Copper minerals are found within the earth’s crust and is removed from the ground via open pit or underground mines, in the form of “ores” – typically these ores are chalcopyrite (this accounting for around 50 percent of copper production) or bornite, with these containing both copper and iron sulphites. The ore is crushed and ground into a powder, before being enriched using a process called froth flotation where unwanted material (called gangue) is removed. Once the powder has been enriched, it is heated between 500°C and 700°C to dry the ore and remove a portion of the sulphur which creates a solid called Calcine. Fluxes (a flux being a substance which is added to the ore as this makes the melting process easier) is then added and the calcine is heated to 1200°C in order to melt it. Air is then blown into the liquid matte which is formed as a result of the calcine being melted, to form what is known as blister copper due to the gas bubbles which become trapped causing “blisters” on the surface before being cast into anodes to begin electrolysis, at which point the copper is purified.
Copper is popular due to its malleability, ductility, corrosion resistance, its thermal and electrical conductivity, and its natural antimicrobial property. Common uses of copper include copper alloy “touch surfaces” which are said to destroy a range of microorganisms which come into contact with it, electrical equipment, jewellery (often being added to precious metals to improve their elasticity, flexibility and hardness etc.) and in construction as part of heating and cooling systems, pipes and tubing, and within roofing systems.
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