Sheet metal fabrication is the process of bending, cutting, punching, assembling sheet metal to form into the desired form. Special tools, such as band saws and chops saws, can also be used in the sheet metal fabrication process. These ensure even cutting throughout the process. Parts are fabricated from a single piece of sheet metal so designs should have a uniform thickness.
1.Introduction
Metal Fabrication is the construction of items from different parts using at least one of a range of the below processes. Due to its versatility and cost, mild steel is the most common fabrication material.
Stainless steel fabrication would be necessary for high corrosive environments whereas aluminium fabrication is primarily considered when weight of the product is a major concern.
2.Metal Cutting
Each fabrication process typically starts with sheet metal cutting. For every metal cut and discarded, you’ll see the product taking shape little by little. There are several ways to cut metal depending on the thickness and project specification.
2.1.Laser Cutting
Laser cutting is a thermal cutting process that uses a computer-directed high-powered laser together with an active gain mechanism (either gas or optical fiber) to concentrate the laser. Fiber laser cutting is typically the premier choice for metal fabrication applications.
Although laser cutting was developed in 1960s, industrial laser cutting become the metal fabrication norm in the late 1990s by professional metal fabricators.
There are currently two methods of laser cutting machines — CO2 laser cutters and fiber laser cutters. Both use a laser to create a beam used to cut metal, but fiber laser us optical fiber to concentrate the beam whereas the CO2 lasers use gas.
Each type of laser does have its strengths and distinct use cases, CO2 is an older technology and fiber lasers are gaining market fast as the technology advances. With the speed benefits, almost half of the operating costs and three to four times greater throughput than CO2 lasers, fiber lasers offer greater opportunities in terms of financial gain.
Check our article about Fiber vs Co2 Laser Cutting
Laser Cutting provides designers with the ability to let their imagination run wild without worrying about the upfront costs of custom punch and stamp tools. Laser Cutting is a cost effective metal cutting process that can be used in rapid prototyping through to mass production of mild Steel, stainless steel, aluminium, copper and brass.
2.2.Plasma Cutting
Plasma Cutting is a sheet metal cutting technique which can cut through any conductive metal. This includes metals like steel, aluminium, brass, titanium and copper – either thick or thin.
Plasma cutting works by passing a hot plasma through conductive metals to cut through it. To make the plasma, an electric arc is passed through a gas such as nitrogen or oxygen. This creates a fourth state of matter called plasma. The plasma can then be forced through a small opening like a nozzle, which can then cut through conductive metal.
Plasma Cutter cut performance is quoted for mild steel. Stainless Steel and Aluminium require more power, so generally, cut performance will be less for these materials.
Although plasma cutting offers low investment and operating costs, the cutting quality is not as precise as laser cutting machines. Therefore plasma cutting is a more preferable means of cutting for thick sheet metals and high tolerance applications.
Check our article about Laser cutting vs plasma cutting
2.3.Shearing
Shearing is a metal fabrication process that’s used to trim and remove unwanted material from sheet metal. It involves the use of a machine or tool, such as a bench shear, to slice through sheet metal with extreme precision. Shearing doesn’t require the use of heat — sheet metal is typically sheared while cold or at room temperature — nor does it produce waste in the form of chips, making it an attractive choice for manufacturers. Shearing is a fast cutting method, performed in seconds and offers smooth edges. It is cost-effective for high-volume manufacturing applications. However, the shear length is limited to the capacity of the shear machine. Also shearing does not allow non-linear cutting.
3.Punching
Sheet metal punching is a cutting process in which material is removed from a piece of sheet metal by applying a shearing force. CNC Punching can be used to produce holes and special cut-outs of various dimension and shapes. The most common punched holes are frequently used geometric shapes such as circle, square, rectangle, etc.
The die, located underneath the sheet, has a cut-out in the shape of the desired feature. Punches and dies of standard shapes are typically used, but custom tooling can be made for punching complex shapes. The punch press drives the punch downward at high speed through the sheet and into the die below. There is a small clearance between the edge of the punch and the die, causing the material to quickly bend and fracture.
This process can be performed on a manual punch press, but today CNC Punch presses are most common for quick and automated production.
4.Bending
Metal bending is a process by which metal can be deformed when applying force to the subject, which causes it to bend at an angle and form the anticipated shape.
4.1.Press Braking
A press brake is a tool used in order to bend sheet metal and uses a punch and die to do this. Although press braking may seem straight forward, it can be quite difficult to remain accurate throughout the process. There are several types of press brakes which deliver different levels of force applied, such as mechanical, pneumatic, hydraulic and CNC to name a few examples.
Sheet metal bending techniques are similar in that their purpose to transform sheet metal structures to the desired forms. However, their operation would be different. Factors such as material thickness, bending size, and bending radius are the main parameters to determine the optimum bending method.
4.1.1.Air bending
The sheet metal is placed along the die and a punch tip is then forced into the V-shape, bending the sheet metal in the process. This method involves a limited amount of contact with the die in comparison to other processes, as the sheet metal only contacts with the edge of the punch and the edges of the V-die.
4.1.2.Coining
The coining involves the sheet metal being bottomed onto the die. This technique of bending leads to limited spring back, meaning that it is likely to stay in its intended shape.
4.1.3.Bottom bending
Bottom bending is similar to other methods above, but it is the safest technique of all three as it provides the least spring back. For bottom bending, the punch bottoms the sheet metal into the die before the radius of the punch is forced into the metal. Finally, the punch is released and the metal springs back to meet the die.
4.2.Plate Rolling
Plate rolling or curving, designates the manufacture of sheet-metal parts that are rolled or curved into shapes that have a smooth radius associated with them. Although sheets of various sizes and thicknesses may be used, curving is the primary manufacturing process for metal bending large pieces of plate.
Roll bending uses either three or four rolls to feed and bend the plate to the desired shape.The positioning of the rolls determines the exact bend of the work.Different curves are obtained by controlling the distance and angle between the rolls.Moveable rolls provide the ability to control the degree of the curve.
5.Machining
Machining is a process in which a metal is cut to a desired final shape and size by a controlled material-removal process. Three principal machining processes are categorized as turning, drilling and milling. Other operations classified under miscellaneous categories are shaping, planing, boring, broaching and sawing.
6.Welding
Welding is a fabrication process whereby two or more metal parts are fused together by means of heat forming a join as the parts cool. The most common welding method is MIG welding which uses a thin wire as an electrode. The wire heats up as it is fed through the welding instrument and towards the welding site. Shielding gas must be used to protect the weld from contaminants in the air.
Typically, this comes in the form of carbon dioxide, oxygen, argon or helium. MIG/MAG welding processes are very versatile and can be used in a range of sectors, including the metalworking industry, shipbuilding, steel and container construction, and the automotive industry. MIG/MAG processes can be used with components of different thicknesses and geometries, and which are made from different materials. MIG welding is particularly suited to the non-ferrous metals; aluminium, magnesium, copper, and titanium. MAG welding is usually used to weld unalloyed, low-alloy, and high-alloy steels.
7.Painting
Painting plays an important role in finishing metal parts, products, and components. Painting custom metal fabrication is done for many reasons, such as providing colour or identifying a brand. However, painting also supplies a protective finish to fabricated metal surfaces.
Metal coating processes are applied to prevent specific environmental degradation and ensure metal parts and products last. The primary role is to protect custom metal fabrication from the corrosive of the natural elements such as rain, fog, or salt spray that could result in oxidation or contact with harmful chemicals.
Metal surface painting forms a solid barrier to remove contact between chemical compounds or corrosive materials. Metal paints may come in a liquid, paste, or powder and are applied through various methods. Wet paint is applied through spray or pump, whereas powder is applied through an electrostatic plating process. In every type of application, once the paint hardens, it creates a protective skin on the custom metal fabrication that adheres to the metal and protects it against corrosion.
