This article takes an in depth look at sheet metal fabrication.
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Sheet metal fabrication is a process that is used to shape and form thin, flat metal sheets by cutting, bending, punching, and welding them into various shapes. Different metals, such as brass, steel, copper, tin, titanium, and aluminum, are formed and configured using sheet metal fabrication. Platinum, gold, and silver are useful for decorative purposes. Sheet metal is used to construct numerous objects with varying thicknesses from extremely thin sheets, also known as foil or leaf, to thicker sheets > 6 mm, also known as plate. Metal sheet thickness is referred to as gauge and ranges from 30 gauge to 8 gauge with the metal gauge being inversely proportional to the thickness of the metal.
In essence, sheet metal fabrication entails turning or processing sheet metal into functional parts by cutting, bending, or stretching. The process can create holes and 2D geometric cut out shapes while other deformation processes bend sheets into different angles or yield complex contours from stretching.
The raw material used by fabricators for sheet metal fabrication 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’ in 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 fabricators use a set of complex processes to shape and form metal sheets. Fabricator processes include cutting, forming, stamping, and bending.
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.
Fabricator shear cutting includes basic cutting, shearing, and blanking. Cuts from these processes are used for non-industrial end products due to their low 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.
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 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.
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.
Punch Press uses shearing force to punch holes and cutouts in a workpiece of different sizes and shapes. The metal sheet is placed between the punch and the die. The punch presses is driven downward at great force and high speed to cut the holes and shapes.
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.
Panel Bending is used for large metal sheet fabrication. It is a simple automated process where the metal sheet is held in place by a counter blade and blank holder. A panel bender has upper and lower bending blades that produce lateral bending force. With the introduction of the Savagnini panel bending machine in 1977, the bending process has been further automated and become less labor intensive.
Stamping uses a mechanical or hydraulic stamping press with a tool and a die. The process is similar to punching, but in stamping, the material does not necessarily have to be removed from the sheet metal. Stamping is useful in tasks such as drawing, curling, flanging, hemming, and embossing.
Stretching uses a stretcher, English wheel, or hammer and dolly to pull metal apart. The sheet metal is stretched and bent over a die simultaneously. Large contours on the sheet metal are thus possible. The process uses a stretch press with the sheet metal gripped along the edges by gripping jaws that are attached to a carriage pulled by a hydraulic or pneumatic force. This applied force stretches the sheet. As a tool for this process, a stretch form block, also known as a form die, is used. It is a solid, contoured material against which the sheet metal is pressed. Various stretch presses exist, with the most common ones being oriented vertically; a hydraulic ram is used to raise the forming die and press it into the sheet metal resting on a press table. In contrast, horizontal stretch presses use a stationary press table to mount the form die sideways while the sheet is pulled horizontally around the die by gripping jaws.
Spinning uses a lathe machine to rotate the sheet metal while it is pressed against a tool. It is a unique metal forming technique that is like CNC turning and is used to create round metal parts such as cylinders and cones. Metal spinning is a shaping process used to produce axially symmetric parts that are shaped over a rapidly rotating mandrel using a round roller tool to fabricate and shape a metal sheet.
Some processes overlap between cutting and forming. These include processes like sheet metal expanding, where multiple slits are cut into the sheet metal, then stretched open.
Assembly may not always be regarded as a fabrication process, however, its use is critical in the overall manufacturing process. Sheet metal disparate components are assembled using fasteners like bolts, rivets, and screws. Processes like punching can be used to make holes for rivets, pins, and other fasteners in the overall sheet metal fabrication process. Critical processes in assembly are welding, riveting, brazing, and adhesive use.
Welding uses heat to melt a section of the metal where it will intersect with another component while adding a filler. The melted components fuse together. Different types of welding, arc, MIG, TIG, etc., offer different weldability for different metals. Welding has several applications, including joining metals, joining plastics, and joining wood.
In joining metals, welding uses high heat to melt the base metal with the typical addition of the filler material. The high-temperature heat causes a pool of molten weld, which then cools to form a joint. The joint can be stronger than the parent material. In some instances, pressure can be used in forming the weld; this is accomplished by the pressure itself or in conjunction with the heat. Shielding gas can also be used to protect the melted and filler metals from being oxidized or becoming contaminated.
In joining plastics, heat is also used and involves three stages. Firstly, the surfaces are prepped before application of pressure and heat, then heat and pressure are applied; finally, the materials cool to create a fusion. The joining methods for plastics can be categorized as internal or external heating methods.
In joining wood, heat is generated from friction and is used to join the materials. The materials are first exposed to extensive pressure before linear friction movement is applied to create the heat to bond the pieces together. This approach allows the wood to be joined without the use of nails or adhesive and is a fast process.
Riveting makes use of small metal parts that embed through metal sheets to join them. The rivets are either drilled in, punched, or placed into the hole. The rivet tails are then deformed to hold the rivet in position. The rivet can be deformed by smashing or pounding the tail, which flattens the material and expands the tail size by about 150% of the stem‘s original diameter. Riveting creates either butt or lap joints using a wide variety of rivet configurations such as single, double, or zig-zag configurations. Eight common rivet types include:
Brazing is akin to welding but melts the filler metal without melting the sheets. The molten filler metal, which is a braze alloy, solidifies in the joint. The filler metal melting point is usually above 450°C and should be below that of the parts to be joined. This differentiates it from welding since in welding the high temperatures melt the base metals. In brazing, the filler metal is protected by a flux. The joint is created when the molten filler metal solidifies as it cools to make the joint between similar or dissimilar metals. The brazing process can be undertaken in various atmospheres including nitrogen, ammonia, hydrogen, inorganic vapours, noble gases, and vacuum. A variety of heating sources can be used such as furnaces or torches. A good brazed joint is formed when both the filler and the parent metals have metallurgical compatibility. There should be a gap in the joint design into which the molten filler can be drawn by capillary action. The joint gap is reliant on factors such as the braze alloy and base metal composition and the brazing atmosphere. Brazing is ideal for joining dissimilar metals and is used in numerous industries because of its versatility and the integrity of the joints. Therefore, it is reliable in critical applications.
Adhesives can be used to hold metal sheets either on their own or in conjunction with other methods. Structural adhesives can be used on their own to make the joints while machinery adhesives are used with other joining methods. Contemporary adhesive technologies permit metal fabrication without the use of welding or mechanical fasteners while increasing the strength of the joints and the structural integrity. Innovation in adhesives is cost-effectively increasing the durability and strength of products. Unlike spot welding and fasteners that create points of stress, adhesives spread the stress across the whole bond joint. This prevents corrosion while increasing fatigue resistance. Flexible adhesives have the capability of absorbing stresses caused by flexing, impact, and vibration. This reduces fatigue even further. Types of adhesives used in sheet metal fabrication include:
Acrylics: They are high strength and fast setting.
Epoxies: They have high-temperature resistance and high strength with good gap-filling capabilities.
MS polymers and modified epoxies: They have good shock-absorbing capabilities and are flexible adhesives with minimal shrinkage.
Typical applications of adhesives include office furniture and cabinets, foodservice equipment and appliances, and machinery enclosures and shielding.
Robotic sheet metal fabricators are a growing aspect of the industry. They are a complicated and complex form of technology that make it possible to complete several fabrication processes in a single pass over the metal sheet. Fabricator robotic metal fabrication reduces human error and makes it possible for one worker to complete several fabricating tasks. There are a multitude of complex and simple functions that can be completed using robotics such as configuring a line, loading metal sheets, and unloading completed workpieces.
Robots are capable of using vision snapshot sensor seeing to determine the location and orientation of a part to be fabricated in a matter of seconds. The camera in a robot examines the workpiece, finds its features, and measures the workpiece's position. The vision system of a robot can be programmed for multi-pass functions and prevention of errors by proofing the workpiece during processing or detecting errors before a process is performed.
The convenience of robots makes it possible to continually monitor the manufacturing process regardless of the fabrication function or operation. With their use, it is possible to track inventory, have serial number traceability, and perform troubleshooting. More and more, modern metal fabrication is relying on robotic automation to enhance their business productivity. As of the moment, this is especially true for cutting and welding functions, which are just the beginning of robotic functions used in sheet metal fabrication.
There is a wide variety of sheet metals used for fabrication. The common metals used in fabrication include:
There are basic equipment that are necessary for various sheet metal fabrication projects:
Various tools are employed in the cutting, forming, and assembly processes as the metal is fabricated into the desired shape. The most common among the tools are the CNC machines. These are programmed to execute specific tasks to achieve exact manufacturing specifications. Their major advantages are precision manufacturing and labor costs reduction as they make use of computer-loaded CAD files to perform bending, turning, and welding processes.
Processes such as joining or assembly can make use of welding where the sheet metal parts are formed, assembled, and tack welded in position. In order to avoid visual defects such as warping, techniques like welding in a staggered manner, stout fixtures, covering the sheet metal as it cools, and various specialized straightening processes are utilized. Other tools such as rivet guns and brazing equipment are also important in the joining process.
Hydraulic brakes, rolling machines, and oxy-acetylene torches are very useful in sheet metal fabrication. Hydraulic brakes, in particular, simplify sheet metal fabrication in creating predetermined bends at specific angles.
Rolling machines are useful in forming steel into rolls, thereby creating a more finished product. Oxy-acetylene torches are also used in straightening warped steel in sheet metal fabrication by applying the heat slowly and linearly.
In executing cutting processes, bands, chop saws, miters, and cutting torches are used to accomplish sheet metal fabrication. Cutting torches make use of a flame and an oxygen stream to cut large pieces of metal while band saws use specialized hardened blades with a feed to facilitate even cutting. Chop and miter saws have specific abrasive disks dedicated to cutting sheet metal. Chop saws accomplish this by moving up and down, whereas miter saws cut at an angle.
Sheet metal fabrication is flexible enough to be used in industries like aerospace, automotive, construction, robotics, consumer goods, and HVAC. This is not an exhaustive list as sheet metal applications go far and wide. The popularity in use comes from affordability and ease of manufacture unlike processes like additive manufacturing or casting.
The various sheet metal applications can be grouped as follows:
These are formed in a heated state and cost-effectively facilitate easier forming. Due to the ease of forming, thicker sheets and plates are available as hot rolled. However, hot rolled steel does not have accurate dimensions because the metal cools down and shrinks after rolling. This yields intermittent stress concentrations that can warp the material, and this changes the configuration of the steel.
These are less expensive and are rolled at room temperature. The process works well in smooth-finish applications and results in a maximum thickness of 3mm. Cold rolled steel can be used in home appliances such as furniture and cabinets as well as in larger structures such as garages.
They are more expensive, but they are more corrosion resistant, lighter, and stronger. They are mostly used in industries where material weight reduction is critical such as in transportation or for consumer goods like phones where durable and light casings are used.
They are good for strength and useful in corrosive environments. They are used in the manufacturing of storage tanks, pipes, and valves, or for surgical instruments and kitchen accessories.
Sheet metal fabrication has advantages such as:
However, sheet metal fabrication also pose disadvantages such as:
Sheet metal fabrication is versatile and can be used for a wide variety of industries. Fabricators for sheet metal fabrication produce products and parts that are used in numerous industries such as construction, automotive, aircraft, consumer products, furniture, HVAC, etc. Fabricator methods and approaches vary according to the types of metals being fabricated and the types of fabricators.
When dealing with sheet metal fabrication it is important to be cognizant of the sheet metal fabrication techniques (Cutting, Forming, and Assembly), types of sheet metal fabrication metals, equipment to facilitate sheet metal fabrication, sheet metal fabrication tools, and sheet metal applications; sheet metal fabrication advantages and disadvantages.
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