Welding involves melting metals to join them, and it is widely applied in various fields, including mechanical components, and automobiles. It is frequently used in rapid metal prototyping and low-volume manufacturing in the sheet metal processing industry. This article provides a comprehensive overview of sheet metal welding.
What Is Sheet Metal Welding?
Sheet metal Welding is the process that joins two pieces of metal sheet with similar melting points and compositions using fusion. Heating the junction or applying high pressure to the joint of metals, melting the metal, and then cooling it to harden, thus achieving the union. It differs from using adhesives or screw fastening in that it involves melting a portion of the material to fuse it with another material.
Advantages of Sheet Metal Welding
High Air Tightness
Because the materials melt and fuse at the joint, welding results in a high level of airtightness (sealing performance). Therefore, welding is widely used in applications such as shipbuilding and aerospace.
Reduced Number of Components
By eliminating the need for adhesives or screws, welding can reduce the number of components, leading to cost savings. Additionally, even complex shapes can sometimes be assembled at a lower cost using welded sheet metal compared to cutting and stamping processes.
Simplified Operations and Equipment
While the specifics of welding methods can vary, many welding techniques do not require large mechanical equipment. This allows for flexibility in outdoor operations, such as construction sites, and small-batch, high-variety production scenarios.
Disadvantages of sheet metal welding
- Heat-induced deformations or residual stresses may occur due to material heating.
- Unlike screws, welded joints cannot be easily disassembled without damage.
- The quality of manual welding can vary depending on the skill of the operator.
Particularly, to mitigate variances arising from operator skill, rigorous management of welding processes is crucial. Sometimes, non-destructive testing methods, such as inspections, are required to ensure correct welds.
6 Methods for Sheet Metal Welding
1. MIG Welding
MIG welding, named Metal Inert Gas welding, is a welding process that uses an electric arc to melt filler material, effectively joining two or more pieces of metal together. This method is commonly employed for welding thin materials, such as sheet metal and tubing.
The process involves shielding gas, typically a mixture of argon and carbon dioxide, and a consumable wire feeder to supply the filler material. As the filler material melts, it forms a bead at the joint, creating a strong bond.
2. TIG Welding
TIG welding, named Tungsten Inert Gas welding, relies on tungsten, a synthetic element with a high melting point and low vapor pressure. This welding method is prevalent in various industries, including electronics, optics, and metallurgy.
In TIG welding, argon and helium are commonly used gases. Instead of an oxyacetylene flame, an electric torch is employed. The filler material may be added for reinforcement or building up seams, with the welder’s hands feeding the filler rod into the molten puddle. This technique is versatile, allowing the welding of sheet metal and various metals.
3. Gas Welding
Gas welding is an excellent choice for joining thin sheets of various materials like steel, aluminum, copper, brass, stainless steel, and more. This method is economical and doesn’t require electricity. It is also suitable for joining small components like nuts, bolts, screws, washers, and springs, although it demands skill and experience.
4. Stick Welding
Arc welding is a process that uses an electric current to melt metal wire or rod, fusing it together. This method is commonly used in shipbuilding, construction, and steel fabrication industries. It requires two electrodes, a consumable electrode or filler material (positive electrode), and a base material (negative electrode). A ground or shield plate provides a path for the electrical current.
5. Plasma Arc Welding
Plasma Arc Welding is a process that melts metal wire using an electric current. A gas is blown through the molten pool to form plasma, generating a strong arc that heats and melts the base material, creating a weld. It is frequently used in industries such as shipbuilding and aircraft manufacturing due to its ability to produce high-quality welds at lower power and higher speeds compared to TIG welding.
6. Electron Beam and Laser Welding
Electron beam welding (EBW) employs a focused stream of electrons to melt filler metal and join materials. Laser welding uses a laser beam for the same purpose. Both methods are used in various industrial applications.
MIG Welding Vs TIG Welding
MIG uses a solid wire that is machine-fed to the weld area while TIG uses a non-consumable electrode and a hand-held filler rod to form the weld. MIG welding is affordability, speedy welds, and ease of learning, it is accessible for less experienced welders to create high-quality welds. On the other hand, TIG welding is a more challenging skill to master, comes with a higher cost, and typically has a slower pace.
However, TIG welding offers unparalleled precision and aesthetic excellence that surpasses what MIG welding can achieve. While MIG welding apply with thicker materials, TIG welding shines when working with thinner materials or handling delicate projects.
Materials Used in Sheet Metal Welding
Carbon steels are typically not welded using the TIG method due to their preference for speed in MIG welding. However, there are cases where TIG welding becomes necessary, particularly when working in tight spaces where the MIG gun’s size limits access to the weld.
When it comes to welding stainless steel, TIG welding is the first choice, especially when a clean and aesthetic finish is required. Welding stainless steel with TIG demands precise control over heat input and welding speed, as uneven heating can lead to warping, commonly referred to as the heat-affected zone (HAZ). In most cases, there’s no post-weld cleanup required, unless specific applications call for brushing the weld to match the adjacent material seamlessly.
Aluminum welding has traditionally been used by TIG welding. However, advancements in Pulse MIG welding have made it a viable alternative, even for cosmetic applications. TIG welding remains a solid choice for aluminum, especially for thinner materials. For thicker aluminum pieces, a preheat cycle might be necessary to ensure full weld penetration. Keep in mind that TIG welding typically operates at slower speeds due to the need to add filler metal to the weld puddle.
Surface To Consider for Sheet Metal Welding Method
Selecting the appropriate welding method based on the surface type ensures quality welds for your sheet metal projects
- Flat Surface For flat surfaces, it’s essential to angle the torch correctly and move it back and forth along the seam to ensure even melting.
- Horizontal Surface Horizontal surfaces can involve two types of welds:
- Fillet Weld: This weld joins two surfaces at an angle, forming an ‘L’ shape.
- Groove Weld: When two metal pieces meet at an angle, it creates a groove-like seam.
- Stick welding is often the preferred choice for horizontal surfaces.
- Vertical Surface Welding on vertical surfaces requires holding the torch at a 45° angle to the plate. Be careful not to point the torch directly at the molten metal to avoid poor-quality welds.
- Overhead Surface welding is challenging because molten metal tends to drip. To minimize issues, use sufficient filler material, maintain the right heat, and watch out for splatter.
8 Tips for Sheet Metal Welding
Welding sheet metals requires precision to ensure the weld maintains the necessary mechanical properties for your application. Here are some tips to remember when working on your welding projects:
Choose the Right Filler Metals
Select an appropriate filler metal that matches your fabrication’s mechanical requirements. It’s important for the filler to be thinner than the sheet metal. For instance, when welding a 1 mm-thick metal, opt for a 0.6 mm filler.
Choosing the right filler not only reduces the risk of defects but also prevents rusting and cracking.
Focus on Fit-up and Joint Design
Welding thin sheet metals requires precise fit-up with minimal gaps to prevent burn-through. Ensure minimal spacing between joining metals to avoid heat absorption by any holes. Measuring twice and cutting once is a golden rule, and in some cases, you may need to redesign joints for enhanced heat resistance.
Choose Small Electrodes
Select electrodes that are thinner than your metal, preferably smaller than ⅛ inch. Smaller electrodes perform well at lower heat and currents, reducing burn-through and allowing precise arc control.
Use Tack Welding
Tack welding is an effective method to avoid excessive heat build-up and burn-through. Use minor, temporary welds (tacks) to hold metal parts together until the final welding. To prevent burning holes, keep a 1 mm space between tightly butted metal pieces and create small tack welds until the joint is fully covered.
Use Skip Welding
The skip welding technique involves using a series of short welds at key points to secure the thin sheet metal. Allowing the metal to cool for a few minutes helps maintain stability before continuing the welding process.
Skip welding minimizes metal distortion and warping, often caused by uneven heat distribution.
Use High-Argon-Based Shielding Gas
When welding, opt for shielding gas with a higher argon content, such as the common 75% argon and 25% carbon dioxide mixture. High-argon shielding gas emits less heat, making it ideal for TIG or MIG welding of aluminum. For certain applications, pure argon may be necessary.
Use Small Wire Diameter
When working with solid wire electrodes, especially in MIG welding, use the smallest wire diameter available. Smaller wires provide better control, produce fewer deposits, and require less heat for melting. For light gauge sheet metal, 0.023 or 0.024-inch wire is recommended, while 0.030-inch wire may be suitable for thicker metals.
Use a Backing Bar
Clamp a backing bar to the work metal to facilitate quicker heat dissipation. Backing bars made of copper or aluminum, known for their high heat conductivity, draw heat away from the metal, minimizing the risk of warping or burn-through. Ensure the backing bar is securely clamped to the workpiece for effective heat transfer
Welding sheet metal is not a hard job when you know the right techniques to apply. If you need high-quality welding services for custom sheet metal fabrication, including bending, stamping, and sheet metal prototyping. Contact KUSLA, we provide a comprehensive service, from welding to CNC machining and laser cutting, and various related machining solutions