Sheet Metal Welding Techniques for Custom Sheet Metal Parts
Do you know which sheet metal welding technique is best for your industrial applications out of the various available techniques?
This article offers a thorough overview of the many sheet metal welding techniques, along with an analysis of their benefits and uses. Additionally, it offers crucial advice on how to get the best results when welding thin metal sheets.
Methods for Sheet Metal Welding
Let’s delve into an in-depth exploration of various methods employed for sheet metal welding:
MIG Welding
Metal Inert Gas welding (MIG), or Gas Metal Arc Welding, utilizes a continuous solid wire electrode fed into the weld puddle with a welding gun. The molten wire in the pool facilitates the joining of metal pieces, while shielding gas prevents atmospheric contamination. This technique is renowned for producing high-quality welds and is well-suited for a range of sheet metals, including aluminum, steel, and stainless steel. Widely embraced in the automotive and home improvement industry, MIG welding stands out as a cost-effective sheet metal welding method that doesn’t necessitate sophisticated machinery.
TIG Welding
Tungsten Inert Gas (TIG) welding involves using a non-consumable tungsten electrode under DC or AC to produce its weld. Similar to MIG welding, TIG welding employs inert shielding gases such as argon or helium to prevent atmospheric contaminants and oxidation. This method excels in welding non-ferrous metals like aluminum, titanium, copper, nickel, magnesium, and chromium. Valuable in the aviation, aerospace, and fabrication industries, TIG welding offers precise control for creating neat and robust welds. However, this sheet metal welding method may be time-consuming and demands a high level of expertise from the welder.
Stick Welding
Shielded Metal Arc Welding, commonly known as stick welding, is a manual arc welding process utilizing a flux-covered stick as an electrode. An electric current from the welding power supply creates an arc between the metals being joined and the electrode. This sheet metal welding method is particularly well-suited for robust metals such as iron and steel.
Unlike some welding processes, stick welding does not rely on shielding gas. Instead, the heat generated disintegrates the flux covering the electrode, forming a slag that shields the weld pool from contamination. This sheet metal welding technique is highly convenient due to its compact and portable equipment, making it a prevalent choice in construction, shipbuilding, and steel fabrication industries.
Plasma Arc Welding
Similar to TIG welding with the use of a tungsten electrode, plasma arc welding employs a small arc and allows placing the electrode on the welding torch body. Pressurized gas forms a hot plasma, effectively melting the metals together to create solid welds.
Known for its low power requirement and high-speed operation, plasma arc welding produces precise welds, earning widespread acceptance in the aviation and marine industries. Similar to TIG welding, this sheet metal welding process does not necessitate filler materials and yields high-quality welds with minimal need for finishing.
Electron Beam and Laser Welding
As the names imply, both laser and electron beam welding employ lasers and electron beams as heat sources to meld and unite metal pieces. Distinct from many other methods, this welding technique necessitates sophisticated machinery or automated robots.
Notable for its high precision, this technique is well-suited for operations involving intricate details, with laser beams capable of focusing on minuscule substances for extremely accurate welding. It is particularly effective for welding robust metals like carbon steel, titanium, stainless steel, and aluminum, as well as thermoplastics. The sheet metal welding method produces aesthetically appealing products, minimizing post-production requirements.
Gas Welding
Gas welding, a traditional form of heat welding, utilizes heat generated from burning fuel (gasoline), oxygen, or oxyacetylene to join metal pieces. The combustion of these fuels produces intensely hot flames that melt metal surfaces during the joining process.
Remaining widely employed in industries, gas welding has a broad application scope, suitable for both ferrous and non-ferrous metals. It proves effective and efficient for welding pipes, tubes, and for repairs in ventilation and air conditioning systems. Notably, it does not rely on electricity, offering portability, cost-effectiveness, and independence from specialist services.
If you’re uncertain about whether to join your sheet metal parts through welding or riveting, feel free to reach out to us for valuable advice on making the choice between sheet metal welding and riveting.
Considering Surface in Sheet Metal Welding Methods
When choosing sheet metal welding methods, it’s essential to take into account the specific characteristics of the surfaces involved. Here’s a breakdown of surfaces commonly encountered during sheet metal welding and the recommended methods for each:
Flat Surface
Welding on a flat surface is known as flat welding. The welder approaches this surface from the upper side of the joint, leveraging gravity to assist in the molten flow. To achieve a high-quality weld on a flat surface, the welder should position the tip angle at 45 degrees to the metal surface, directing the flame carefully towards the point of joining. MIG and TIG welding methods are well-suited for flat surfaces, with the wire feed and gas flows performing excellently in this configuration.
Horizontal Surface
In a horizontal configuration, metal sheets are positioned horizontally relative to the welder. This can take two forms:
Fillet Weld: The welding occurs on the upper end of a horizontal surface against a vertical surface, creating a joint area resembling the junction of two perpendicular pieces of metal in an ‘L’ shape.
Groove Weld: The welding surface lies in a vertical plane, with both metal pieces to be joined on the same plane.
Stick welding is particularly well-suited for working on a horizontal surface, especially in situations where achieving the perfect balance between TIG and MIG welding might be challenging.
Vertical Surface
When welding on a vertical surface, the welding shaft is positioned upright, facing the welder. Molten metal tends to flow downward and accumulate during welding, requiring the welder to carefully control the metal flow. This involves pointing the welding gun at a 45-degree angle to the plate and positioning the electrode between the flame and weld pool.
Stick welding is the preferred method for vertical surfaces. Welders often adjust the weld axis to appear flat or horizontal for enhanced convenience.
Overhead Surface
Welding materials on overhead surfaces presents the most challenging scenario, involving welding a workpiece placed above the welder’s head. The molten metal tends to drop off as welding is attempted.
To alleviate the difficulties of overhead welding, it is advisable to minimize the weld puddle and ensure sufficient use of filler material for a robust weld.
Stick welding is the most suitable method for overhead welding configurations. It’s worth noting that welding overhead surfaces is relatively uncommon in custom sheet metal fabrication facilities.
Tips for Sheet Metal Welding
The sheet metal welding goal is to ensure that the welded parts maintain sufficient mechanical properties for the intended application. Here are tips to keep in mind during the sheet metal welding process:
Select the Right Filler Metals
Choose a filler metal that aligns with the mechanical characteristics of your fabrication. The filler should be thinner than the sheet metal being welded. For instance, when welding a thin metal of 1 mm, a 0.6 mm filler is the optimal choice. Thinner wires require less heat to melt, reducing the risk of excessive heat buildup and increasing the likelihood of achieving optimal welding outcomes. The right filler metal selection also minimizes the risks of rusting, cracking, and other potential defects.
Utilize the Skip Welding Technique
Employ the skip welding technique, which involves using a series of short welds or stitches at crucial points to secure the thin sheet metal in place. After allowing it to cool for a few minutes, the welder can proceed to weld the areas previously skipped. Skip welding helps prevent metal distortion and warping, often caused by uneven heat distribution. Additionally, avoid weaving the welding torch during welding, as this may lead to excessive heat. Instead, move the torch quickly along a straight path.
Employ the Tack Welding Technique
Tack welding serves as an effective method to mitigate the risk of excessive heat build-up and burn-through. Tacks, which are small and temporary welds, are utilized to hold metal parts together until the final welding is performed. To prevent burning holes, keep the metal pieces closely butted together with a 1 mm space between them. Proceed to create small tack welds until the joint is fully covered.
Opt for Small Wire Diameter
When using a solid wire electrode, such as in MIG welding, opt for wires with the smallest diameter available. Smaller wires offer the welder better control and a higher likelihood of correcting mistakes since they produce fewer deposits. Additionally, smaller-diameter wires require less heat for melting, reducing the likelihood of excessive heat issues. In general, when working with light gauge sheet metal, it is recommended to use 0.023 or 0.024-inch wires. However, a 0.030-inch wire may be suitable when welding 18-gauge or thicker metals.
Opt for a Small Electrode
Choose a rod that is thinner than your metal, opting for electrodes smaller than ⅛ inch. A smaller electrode performs exceptionally well at lower heat and currents, reducing the risk of burn-through. Additionally, it allows you to grind your electrode to a smaller area for running a tight arc.
Secure a Backing Bar with Clamps
Clamping a backing bar to the work metal facilitates quicker heat dissipation compared to simply waiting for it to cool. The backing bar efficiently draws heat away from the metal, minimizing the risk of warping or burn-through. Typically made of copper or aluminum for optimal heat conductivity, ensure the backing bar is securely clamped to the workpiece for effective heat transfer.
Utilize High-Argon-Based Shielding Gas
When welding, opt for shielding gas with a high percentage of argon, such as the common combination of 75% argon and 25% carbon dioxide. A shielding gas with a high argon content is preferred because argon emits less heat. For TIG or MIG welding of aluminum, pure argon is often recommended as the shielding gas.
Fit-up and Joint Design
Welding thin sheet metals requires precise fit-up and joint design due to minimal margins for error. It’s crucial to ensure a tight and firm fit-up, minimizing spaces between the joining metals to prevent burn-through, as any holes may absorb heat.
As a general rule, welders should adhere to the principle of measuring twice and cutting once. In certain cases, joint redesign may be necessary to enhance heat resistance.
Butt Joint
A butt joint involves placing two pieces of metals side by side for welding. The faying surface, where melting occurs during welding, requires edge preparation to enhance weld strength. Bending one side may be necessary to ensure a strong fit. Butt welds are relatively easy to prepare and exhibit better stress resistance, making them a common choice in structural fabrication.
Lap Joint
Lap joints are a modification of butt joints and are ideal for varying thickness sheet metal welding. In a lap joint, two pieces of metal overlap, with one placed over the other. However, the junction of the two metals in a lap joint is susceptible to rust.
T-Joint
A T-joint occurs when two pieces of metal intersect perpendicularly, forming a right angle in a ‘T’ shape. Common in structures with piping and tubing systems, T-joints are considered a form of fillet weld. Adequate penetration into the weld root is essential, and a stopper may be added to reduce joint restrictions at the connection point.
Corner Joint
Corner joints are similar to T-joints but involve joining metals in different orientations, creating a single right angle in an ‘L’ shape at the corner. These joints are standard in parts fabrication, particularly frames and boxes.
Edge Joint
In edge joints, sheet metals are placed side by side and welded on the same edge, often occurring in workpieces with flanging edges. Bending the edge of either metal piece may be necessary to ensure a proper fit for a firm weld.
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FAQs about Sheet Metal Welding
What type of sheet metal welding is best for thin metals?
The best method for welding thin metal sheets together is TIG welding. The TIG welding process is extremely accurate, staying true to its intended welding focus. As a result, the welded parts have a delicate and smooth finish.
Can I MIG weld aluminum using AC or DC power?
Aluminum can be welded using MIG welding with both alternating and direct current. The common type of MIG welding, direct current welding, is much faster because it doesn’t need equipment with AC and DC specifications.
Which sheet metal thickness is the thinnest that can be welded?
Experts who can precisely control the heat applied to the metal are needed to weld extremely thin metals. With MIG welding, sheet metal as thin as 0.8 mm can be welded with proper heat control. Furthermore, TIG enables you to weld at thicknesses of up to 0.6 mm.
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