Metal fabrication is much more than just welding, although the two terms often get confused. Metal fabrication involves the entire creation of a product made from metal. Fabrication involves all the steps in making a product including: cutting, bending and assembling structures.
Normally a fabrication shop will win jobs by studying engineering drawings, and bidding on the job. If the fabrication shop and employer can come to an agreement the fabrication shop will often utilize several different tools and specialists to create the product. In order to build the finished metal product both human labour and automation will most likely be used.
A fabricated product is referred to as a fabrication, and the places that specialize in creating metal structures are often called fab shops. The end products of other common types of metalworking such as machining, metal stamping, forging, and casting, may be similar in design and purpose, but while those individual processes may overlap with fabrication the terms are not interchangeable.
- Variations of Cutting include: sawing, shearing, or chiselling with manual and powered labour
- Torching with handheld torches (such as oxy-fuel torches or plasma torches); and via numerical control computer operated (CNC) cutters using a laser, mill bits, torch, or water jet.
- Variations of Bending include: hammering (manual or powered) or via press brakes, tube benders and similar tools. Today metal fabricators use press brakes to coin or air-bend metal sheets into a form. CNC-controlled backgauges use hard stops to position cut parts to place bend lines in specific positions.
- Variations of Assembling (joining of pieces) include: welding, binding with adhesives, riveting, threaded fasteners, or further bending in the form of crimped seams. Structural steel and sheet metal are the most common materials for fabrication; welding wire, flux and fasteners are often used to join the cut pieces.
Fabrication comprises or overlaps with various metalworking specialities:
- Fabrication shops and machine shops often have overlapping capabilities and processes, but fabrication shops generally concentrate on metal preparation and assembly. Machine shops cut metal, but focus primarily on the machining of parts of machine tools. Some companies offer both fab work and machining.
- Blacksmithing historically has been a part of fabrication.
- Welder-produced products are usually called weldments, and are products of fabrication.
- Boilermakers originally specialized in fabricating boilers, but the term is now used more broadly.
- Millwrights originally specialized in setting up grain mills and sawmills, but now perform a wide range of fabrication.
- Ironworkers, also known as steel erectors, also participate in fabrication. They generally work with prefabricated segments, produced in fab shops, that are delivered to the ironworkers’ site.
Standard metal fabrication materials are:
- Plate metal
- Formed metal
- Expanded metal
- Tube stock
- Welding wire
- Welding rod
- Casting materials
There are a variety of tools that can be used to cut metal, these include: cutting torches, a variety of band saws, chop saws, as well as plasma, laser and water jet cutters. Commonly, metal is cut through a process of burning or melting. This is known as shearing.
Unique band saws for cutting metal have been created with hardened blades and feed mechanisms to ensure straight cutting. Chop saws are similar to mitre saws but have been made with abrasive disks, suitable for cutting steel. Cutting torches use heat to easily cut large sections of metal. Burn tables are a type of computer operated cutting torch that is powered by natural gas.
Plasma cutting is a process of cutting metal using a stream of hot plasma. Laser cutting involves the use of a laser to easily slice through different materials. Water jet cutters are capable of cutting through metal and other materials with a stream of water and abrasive material. To use any of these methods of cutting, the plate steel or other material is placed in the table and the parts are cut out. Higher end tables may use CNC (computer operated) punch technology or even robots to assist in the process.
Forming can include a variety of different processes to re-shape and deform metal. Some of these processes include: rolling, bending, deep drawing, extrusion, drop forging and open die forging. Forming changes the shape of the metal without adding or removing mass. Generally, expensive and heavy machinery and robots are used to automate the process of forming. Forming may also utilize smaller tools, such as punches and dies. Forming is a necessary component in many industries, including jewellery, aerospace, automotive and architectural work. Forming may also combine with other processes (such as welding) to produce large lengths of fabricated metal sheeting.
Machining involves removing part of the material from a piece of metal to reshape the original metal. Machining often involves using metal lathes, mills, drills, and other portable and handheld machining tools. The space where machining is done is called a machine shop, but most fab shops also have machining capability. Small metal parts such as bolts, screws and nuts are machined components.
Welding is generally the main focus in steel fabrication, but the terms welding and fabrication cannot be used interchangeably. The pieces of a product are usually formed, machined and assembled before welding occurs. The parts are assembled and tack-welded (a temporary weld) first, double checked for precision and accuracy, and finally welded based on engineering drawings. If drawings are not available, a welder may use their own experience, knowledge and judgement. If multiple weldments have been ordered, a fixture may be used to hold parts for welding.
Welding can become quite complicated when possible warping of the metal is taken into consideration. Sometimes the product may need to be completely redesigned in order to limit the amount of welding required (limiting the amount of warping). Other options include staggered welding, using a fixture, or covering the weldments in sand as it cools. If the warping is impossible to avoid, the piece may require post-weld straightening. Removing warpage is a difficult and precise job that only a highly skilled welder will be successful at. An oxyacetylene torch will be required if a piece is in need of post-weld straightening. If the welder has a significant amount of expertise, they will be able to remove warpage by using the torch to apply heat to the steel in a slow sweep. This causes the steel to contract in the direction of the sweep as it cools.
Sometimes there are negative residual stresses in the material after the welding process. Annealing the product in a low-temperature oven can relieve these residual stresses.
When the weldment has completely cooled there are still a few more steps before the product is ready to be shipped. Usually, the product will need to be sandblasted, primed and painted. All extra manufacturing will be completed before the final product is finally inspected.