How Does Sheet Metal Fabrication Work?

illustration of sheet metal process
During the sheet metal fabrication process, thin sheet metal stock is placed on a flat bed where a laser cutter (1) draws programmed part patterns. Depending on the part geometry, a sheet metal punch (2) can form additional features. Once the parts are deburred, they move to the press brake (3) where they are formed into the final geometries.
Sheet metal fabrication is metal that has been formed into thin and flat sheets which is then cut and bent into various shapes. Different metals, brass, steel, copper, tin, titanium, Aluminium etc., can be made into sheet metal. Platinum, gold, and silver are useful for decorative purposes among other uses. Sheet metal is used to construct numerous objects with varying thicknesses, from extremely thin sheets, also known as foil or leaf, to thicker sheets i.e. >6mm, also known as plate. The metal sheet thickness is referred to as gauge and generally ranges from 30 gauge to 8 gauge. The sheet metal gauge is inversely proportional to the metal thickness.
In essence, sheet metal fabrication entails turning or processing sheet metal into functional parts by cutting, bending, or stretching into almost any shape. The processing of the metal sheets can create holes and 2D geometric cut-out shapes while deformation processes bend sheets into different angles or yield complex contours from stretching.
The raw material for sheet metal fabrication processes comes from rolling processes where sheet metal is sold as standardized flat and rectangular sheets. In instances where these sheets are thin and long, they come in the form of rolls. Thus, the first step in sheet metal fabrication is to cut out a ‘blank,‘ which is the desired shape and size of a sheet from the larger sheet.
Parts formed from sheet metal fabrication can be used in a wide range of industries, namely construction, automotive, aircraft, consumer products, furniture, and HVAC.
Sheet metal fabrication techniques can be categorized into cutting, forming, and assembly.
This technique makes use of manual and power tools or handheld plasma torches from Computer Numerical Control (CNC) cutters, e.g. lasers to saw, shear, or chisel. In the context of cutting, sheet metal fabrication can be viewed as a subtractive manufacturing process due to the functional parts‘ creation through the removal of sections of the metal. Various pieces of machinery can be used to cut the sheet metal, with some being unique to sheet metal fabrication.
In essence, there are two categories of cutting: without shear and with shear.
Cutting with Shear
Shear cutting includes different processes, which can be distinguished as basic cutting, shearing, and blanking where the cuts from these processes are mostly used for non-industrial end products due to their lower precision compared to processes without shears.
Basic cutting uses a blade to cut through the metal to split it into smaller sections. This can be the first stage of many other fabrication processes which follow or it can be the only process used. Shearing uses upper and lower blades to cut in straight lines, similarly to scissors. However, in the case of shearing, both blades do not move as with scissors; instead, one blade lowers while the other remains stationary. Its advantages include the clean cuts and smooth edges it creates, its ability to be used on a wide variety of gauges, the fact that it does not create chips in the metal, (hence the low waste), cost-effectiveness in mass production, and ability to be used at room temperature, which removes any need to preheat the sheet metal.
Shearing process
In blanking, the most powerful of the three processes, a hole punch is used to cut out holes in the sheet. This process of punching, also known as piercing, uses a punch and a die to create more precise holes in the sheet metal. This is accomplished by placing the sheet metal between the die and the punch, where the punch will be forced through the sheet metal to reach the die. After punching, the punched circular pieces of material that are removed can be used as new workpieces or they become scrap.
Cutting without Shear
Cutting without shears is more accurate and more useful in the creation of precision industrial products such as those in aviation. The processes used in fabrication include laser beam cutting, waterjet cutting, plasma cutting, and machining.
Laser-beam Cutting uses a focused beam of light intensified by a lens or mirror to cut through or engrave sheet metal. Precision and energy efficiency are advantages of laser cutting. However, laser cutting is better suited for thin or medium sheet metal gauges as it may struggle to penetrate the harder metals.
Waterjet Cutting uses a high-pressure jet of water shot at high speed to cut through sheet metal. The water is mixed with an abrasive substance to facilitate eroding of the material during cutting. Waterjet cutting is particularly useful in cutting metals with a lower melting point. This is because it does not generate heat, which could potentially deform the material.
Waterjet cutting process
Plasma Cutting uses heated compressed gases that eject from a nozzle at high speeds, thereby becoming ionized and capable of conducting electricity. Examples of heat-compressed gases include nitrogen and hydrogen. The electrical canal of ionized gas forms a hot plasma jet that penetrates even the thicker metal gauges. Plasma cutters are less accurate than waterjet and laser cutters, but they are powerful and fast with lower setup costs.
Machining cuts off pieces of material using tools such as drill bits or lathe blades. This extends to processes such as spinning and milling.
Sheet Metal Fabrication: Forming
In contrast to cutting, which subtracts material from the sheet metal, forming reshapes and reconfigures the material to the desired outlines. Forming processes include bending, stamping, roll forming, stretching, and spinning.
Bending uses machines such as press brakes to bend sheet metal into U-shapes, V-shapes, and channels. The angles can be from 0 to 120 degrees. Thicker sheet metal gauges are more difficult to bend. Conversely, horizontal bends on sheet metal can be removed from strip-shaped pieces in a process called decambering.