The Sheet Metal Welding Process

The sheet metal welding process helps us choose the best method for your specific needs, saving you both money and time. Just like with any sheet metal work, planning and making decisions early will make sure the welding part of your project goes well. This blog will explain how to do that.

Welding is a way to join two or more pieces together using heat, pressure, or both. As the pieces cool down, they stick together. Welding is mostly used for metals and plastics but can also work with wood.

The pieces being joined are called the ‘parent’ material. A ‘filler’ material is added to help make the join. Fillers can be plates, pipes, wires, or electrodes and are usually similar to the parent material, creating a uniform weld. However, sometimes, like with brittle cast irons, a different filler is needed. These are called heterogeneous welds.

The major welding methods

Choosing the right welding method depends on the materials you are working with and the specific situation.

The TIG method

TIG welding, also called Gas Tungsten Arc Welding (GTAW), uses heat from an electric arc to melt a tungsten electrode, which acts as the filler material. A protective gas shield keeps the weld pool clean from contaminants.

This type of welding is often used for jobs where appearance matters, like stainless steel handrails. The wire is fed slowly (7 to 15 inches per minute), allowing for more precise and neat welding. After welding, the pieces just need to be cleaned, ground, and polished.

The MIG method

MIG welding, also known as Gas Metal Arc Welding (GMAW), uses a continuous wire that is automatically fed through a welding gun. The tip of the gun is charged with electricity, which generates enough heat to melt the wire and form a pool of molten metal for welding. A shielding gas protects this molten pool from contamination.

MIG welding is often used for heavy-duty projects that need strong welds, like making metal gates or sturdy railings. The thicker welds produced by MIG welding are both strong and visually suitable for such structures.

Laser welding

Laser welding is a quick and precise process, ideal for making a large number of parts (like 500 or more). For smaller quantities, TIG or MIG welding is usually cheaper.

Laser welding is very consistent and works at speeds between 50 to 80 inches per minute. The laser beam provides focused heat to melt the materials and join them together. However, the gap between the parts should not be more than .005 inches.

There are two types of laser welds: cosmetic (or conduction) and keyhole. In cosmetic welding, the laser is made less sharp to create a smooth and wide weld. In keyhole welding, used for thicker steel, the laser burns through the top layer of the material into the second layer. When the molten material cools, it forms a solid weld joint.

Laser welding has several advantages, such as fast operation, thin and small weld seams, and low heat distortion. Unlike TIG or MIG welding, no filler wire is needed, so there is very little extra weld material. This makes it suitable for welding very small parts.

Types of metals you can weld

Welding can be used on many different materials. The most common ones in sheet metal work are mild steel, stainless steel, aluminum, and copper.

Carbon steels (coated and uncoated)
MIG welding is often chosen over TIG welding for carbon steel because it’s faster. MIG welding is also better for situations where the parts being joined don’t fit together perfectly, like an outside corner weld.

Laser welding, both cosmetic and keyhole, works well for carbon steel using machines with either short or long wavelengths. This method adds very little extra material, so the welded steel parts can go straight to painting with minimal cleaning needed afterward.

However, welding coated steels (like galvanized or galvannealed) with lasers, especially keyhole welding, is challenging. The different melting points of the coating and the steel can cause the weld to be incomplete. When the coating melts and turns into gas, it creates ‘spatter’ that disrupts the welding process.

Stainless steel sheet metal

Pulse MIG welding is used for stainless steel to reduce spatter. In this process, the electrode doesn’t touch the weld pool. Instead, the electrical current pulses from high to low, causing drops of molten metal to form from the electrode.

When a clean, attractive appearance is important, TIG welding is usually preferred for stainless steel. This method requires careful control of heat and speed because stainless steel can warp from uneven heating. TIG welding typically doesn’t need much clean-up afterward unless a specific texture, like brushing, is needed.

Laser welding is also good for stainless steel, whether for a cosmetic look or deep, strong welds. The main advantage is the high speed of laser welding, which keeps the heat-affected area small. Depending on what the final product will be used for, you might need to remove heat discoloration after welding. However, because the weld seams are so small, there is usually no need for re-graining or blending.

Aluminium sheet metal

We use a pulse MIG machine to weld aluminum with a special gas to help the process. Since aluminum can get spatter and dust during welding, it’s important to clean the surface before starting.

For laser welding aluminum, which can be used for neat, cosmetic welds or deeper, keyhole welds, a short wavelength laser is best. This type of laser focuses more energy on the welding area. Many modern lasers let you adjust the beam shape, so you can get a smooth and clean weld that looks similar to a TIG weld.

Copper and iron

Welding copper or iron can be tricky because of their different types. For copper, laser welding works well by adjusting power and speed. TIG and MIG welding are also common for copper due to its high heat conductivity.

Cast iron comes in various grades like grey iron, white iron, ductile (nodular) iron, and malleable iron, each with different welding challenges. Cast iron has about ten times more carbon than most steels. When you weld it, the carbon moves into the weld or the heated area, making it brittle and hard. This can cause cracks after welding.

Tips for welding sheet metals

Choose the Right Welding Process and Filler Metal:
Select the welding method and filler metal that match the material you’re using and how it will be used. For instance, if it’s for indoor use and appearance matters, or for tough outdoor structures where durability is key, your choices will differ.

Good Fit-Up and Joint Design:

Fit-up refers to how closely parts fit together before welding. When working with thin metal, it’s crucial to have a tight fit-up. Avoid creating holes that could lead to burning through or gaps that can’t handle the heat. This ensures a stronger weld and prevents flaws in the finished product.

Alroys welding skills and experience

At Alroys, we have the expertise and experience to ensure that sheet metal welding is made easy and straightforward for all our customers. Our skilled team has mastered the techniques over many years, so you can rely on us to deliver top-quality welding services tailored to your needs.