This article takes an in depth look at sheet metal fabrication.
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Sheet metal fabricating 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 manufacturing. 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 fabricating 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 manufacturing 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. Fabricating processes include cutting, forming, stamping, and bending.
This technique involves the use of both manual and powered tools, including handheld plasma torches and Computer Numerical Control (CNC) cutters like lasers, for processes such as sawing, shearing, or chiseling. In sheet metal fabrication, cutting can be considered a subtractive manufacturing process, as it involves creating functional parts by removing sections of metal. Various types of machinery, some specifically designed for sheet metal work, can be employed for cutting.
Cutting methods in sheet metal fabrication are generally categorized into two types: shear cutting and non-shear cutting.
Shear cutting in sheet metal fabrication includes methods such as basic cutting, shearing, and blanking. These processes are typically used for non-industrial applications due to their lower precision compared to non-shear cutting methods.
Basic cutting involves using a blade to divide the metal into smaller sections. This can serve as an initial step in various fabrication processes or as a standalone operation.
Shearing employs upper and lower blades to make straight cuts, similar to scissors. Unlike scissors, only one blade moves while the other remains stationary. The advantages of shearing include producing clean cuts and smooth edges, versatility across various gauges, minimal waste as no chips are generated, cost-effectiveness for mass production, and the ability to operate at room temperature, eliminating the need to preheat the metal.
Blanking, the most forceful of the three shear cutting processes, involves using a hole punch to cut out holes in the sheet metal. This punching process, also known as piercing, employs a punch and die to create precise holes. The sheet metal is placed between the die and the punch, which forces through the material to form the desired holes. The circular pieces removed during this process can either be repurposed as new workpieces or become scrap material.
Cutting methods without shears offer higher accuracy and are ideal for producing precision industrial components, such as those used in the aerospace industry. Fabrication processes in this category include laser beam cutting, waterjet cutting, plasma cutting, and machining.
Laser Beam Cutting employs a concentrated beam of light, enhanced by a lens or mirror, to cut or engrave sheet metal. The advantages of laser cutting include high precision and energy efficiency. However, it is most effective on thin to medium gauges of sheet metal, as it may have difficulty penetrating harder metals.
Waterjet Cutting uses a high-pressure stream of water, often mixed with an abrasive substance, to cut through sheet metal. This method is particularly effective for materials with lower melting points because it generates no heat, reducing the risk of material deformation.
Plasma Cutting utilizes ionized, heated gases ejected at high speeds from a nozzle to cut through sheet metal. Gases such as nitrogen and hydrogen are commonly used. The ionized gas creates a hot plasma jet that can penetrate thicker metal gauges. While plasma cutting is less precise compared to waterjet and laser cutting, it is known for its speed, power, and lower setup costs.
Machining involves removing material using tools like drill bits or lathe blades. This category includes various processes such as spinning and milling.
Punch Press applies shearing force to create holes and cutouts of various sizes and shapes in a workpiece. The metal sheet is positioned between a punch and a die, with the punch press applying high-speed, high-force pressure to produce the desired holes and shapes.
Unlike cutting, which removes material from the sheet metal, forming reshapes and reconfigures the material to achieve the desired contours. Forming processes include bending, stamping, roll forming, stretching, and spinning.
Bending involves using machines like press brakes to create bends in sheet metal, forming shapes such as U, V, and channels. Angles can range from 0 to 120 degrees. Bending thicker sheet metal gauges can be more challenging. Additionally, horizontal bends in strip-shaped pieces can be corrected through a process known as decambering.
Panel Bending is employed for fabricating large metal sheets. This automated process involves securing the metal sheet with a counter blade and a blank holder. Panel bending machines feature upper and lower bending blades that apply lateral force to shape the metal. The introduction of the Savagnini panel bending machine in 1977 significantly advanced this process, making it more automated and reducing the need for manual labor.
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 involves using tools like a stretcher, English wheel, or hammer and dolly to elongate metal. During this process, the sheet metal is both stretched and bent over a die, allowing for the creation of large contours. A stretch press, which grips the sheet metal along its edges using gripping jaws attached to a carriage, applies hydraulic or pneumatic force to stretch the material. A stretch form block, also known as a form die, is employed as a solid, contoured surface against which the metal is pressed. Stretch presses can be vertical or horizontal; vertical presses use a hydraulic ram to raise and press the forming die into the metal sheet on a press table, while horizontal presses mount the form die sideways on a stationary table and pull the sheet horizontally around the die with 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.
There are processes that bridge the gap between cutting and forming, such as sheet metal expanding. In this method, multiple slits are first cut into the sheet metal, and then the metal is stretched open to achieve the desired shape.
While assembly may not always be considered a sheet metal fabrication process, it plays a crucial role in the overall manufacturing workflow. The assembly of disparate sheet metal components typically involves the use of fasteners such as bolts, rivets, and screws. Processes like punching are used to create holes for these fasteners during the sheet metal fabrication process. Key assembly techniques include welding, riveting, brazing, and the application of adhesives.
Welding involves applying heat to melt a portion of the metal where it meets another component, along with adding a filler material. The melted metals fuse together to create a strong joint. Various welding methods, such as arc welding, MIG welding, and TIG welding, offer different capabilities for joining different metals. Welding is versatile and can be used for joining metals, plastics, and even wood.
For metal joining, welding uses intense heat to melt the base metal and often includes a filler material. The molten weld pool forms a joint that, once cooled, can be stronger than the original materials. Sometimes, pressure is also applied during welding, either alone or in combination with heat. Shielding gases may be used to prevent oxidation or contamination of the melted metal and filler.
When joining plastics, the process involves three stages: preparing the surfaces, applying heat and pressure, and then allowing the materials to cool and fuse. This can be done using either internal or external heating methods.
For wood, heat generated from friction is used to join the pieces. The process involves applying significant pressure followed by linear friction to produce the heat required for bonding. This method allows wood to be joined without nails or adhesives and is a quick technique.
Welding employs various joint configurations to connect metal parts. A butt joint involves joining two pieces at their edges, forming an angle between 135° and 180°. A T-joint connects the edge or end of one part to the face of another, creating an angle up to 90°. A corner joint connects the edges of two parts at angles ranging from 30° to 135°. An edge joint connects the edges of two parts at an angle between 0° and 30°. A cruciform joint consists of two flat plates or bars welded perpendicularly to a flat plate on the same axis. Lastly, a lap joint connects two overlapping parts, with the weld angle ranging from 0° to 5°.
Riveting involves using small metal fasteners that are inserted through holes in metal sheets to join them together. Rivets can be drilled, punched, or placed into the holes, and then the tails are deformed to secure them in place. This deformation can be achieved by hammering or pounding the rivet's tail, expanding it to about 150% of its original diameter. Riveting can create either butt or lap joints and is performed using various rivet configurations, such as single, double, or zig-zag patterns. Common types of rivets include:
Brazing is similar to welding but differs in that it does not melt the base metals; instead, it melts a filler metal that solidifies to form the joint. The filler metal used in brazing typically has a melting point above 450°C, but below that of the metals being joined. Unlike welding, where the base metals are melted, brazing involves melting the filler metal only. The filler metal is protected by a flux during the process. The joint is created as the molten filler metal solidifies upon cooling, forming a bond between either similar or dissimilar metals. Brazing can be performed in various environments, such as nitrogen, ammonia, hydrogen, inorganic vapors, noble gases, or a vacuum, and utilizes different heating methods including furnaces or torches. A strong brazed joint is achieved when both the filler and base metals are metallurgically compatible and when there is an appropriate gap in the joint design for the filler to flow through by capillary action. The gap depends on the braze alloy, base metal composition, and the brazing atmosphere. Due to its ability to join dissimilar metals and its application versatility, brazing is widely used in many industries and is particularly valued for its reliability 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 sheet 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:
Acrylic Adhesives: Known for their high strength and quick setting times.
Epoxy Adhesives: Offer excellent resistance to high temperatures, superior strength, and effective gap-filling properties.
MS Polymers and Modified Epoxies: Provide good shock absorption, flexibility, and minimal shrinkage.
Common uses for these adhesives include applications in office furniture and cabinetry, food service equipment and appliances, as well as 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 makes it possible to complete several fabricating 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 manufacturing.
Selecting the appropriate metal for sheet metal fabrication involves evaluating the specific characteristics needed for the final product, its application, and budget constraints. Below are some frequently utilized metals in the sheet metal fabrication process:
Steel is a popular choice in fabrication because of its robust strength, durability, and adaptability. It is available in multiple grades and is known for its ease of welding and forming.
Magnesium is a low-density metal renowned for its impressive strength-to-weight ratio. It is frequently utilized in the aerospace and automotive sectors, especially for components where minimizing weight is essential.
Aluminum is favored for its light weight and resistance to corrosion, making it ideal for diverse applications, including aerospace and automotive components.
Bronze, an alloy made chiefly of copper and tin, is renowned for its durability, resistance to corrosion, and aesthetic appeal. It is commonly used in the creation of sculptures, bearings, and historical artifacts.
Brass, a copper-zinc alloy, is appreciated for its shiny, gold-like look. It finds applications in decorative pieces, musical instruments, and plumbing components.
Copper is a metal renowned for its excellent electrical conductivity, making it ideal for use in electrical wiring and components. Additionally, it is utilized in certain applications due to its antimicrobial properties.
Galvannealed steel features a coating that merges the rust resistance of zinc with the paintable surface of steel. This type of steel is commonly employed in automotive panels and various appliances.
Essential tools and equipment required for various sheet metal fabrication tasks include:
Fittings are essential for the assembly and connection of sheet metal parts.
Plate metal serves as a foundational or structural element in various sheet metal projects.
Incorporating castings into sheet metal fabrication projects can enhance strength or add particular features.
Formed and expanded metal is ideal for outdoor furniture, allowing moisture to drain effectively.
Flat metal can be incorporated into fabricated designs to add visual appeal and texture, making it suitable for shaping and detailing.
Sectional metals are used for partitioning and come in various shapes such as L-beams, Z-sections, rods, and bars.
For different welding techniques, selecting the correct welding wire or filler metal is essential. Typical options are MIG wire, TIG rods, and electrode wires used in arc welding.
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 versatile and finds applications across numerous industries including aerospace, automotive, construction, robotics, consumer products, and HVAC. This list is not exhaustive, as sheet metal is utilized in a wide range of other fields. Its widespread use is attributed to its cost-effectiveness and ease of production, especially when compared to other manufacturing methods like additive manufacturing or casting.
Sheet metal applications can be categorized into the following groups:
Hot rolled steel is processed while the metal is still heated, which makes it cost-effective and easier to shape. This method allows for the production of thicker sheets and plates. However, the dimensions of hot rolled steel are not as precise because the metal contracts as it cools after rolling. This cooling process can cause stress concentrations and warping, affecting the final shape of the steel.
Cold rolled steel is more affordable and processed at room temperature. This technique is ideal for achieving a smooth finish and typically produces sheets with a maximum thickness of 3mm. Cold rolled steel is commonly utilized in home appliances like furniture and cabinets, as well as in larger constructions such as garages.
Though more costly, these materials offer superior corrosion resistance, reduced weight, and enhanced strength. They are predominantly used in sectors where minimizing material weight is crucial, such as in the transportation industry or for consumer products like smartphones, where lightweight and durable casings are essential.
These materials provide excellent strength and are well-suited for corrosive conditions. They are commonly employed in the production of storage tanks, piping systems, valves, as well as surgical tools and kitchen utensils.
Below are some notable benefits of utilizing a sheet metal fabricator:
Nevertheless, sheet metal fabrication comes with its own set of drawbacks, including:
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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