A Guide to Different Methods of Welding Sheet Metal Fabricated Parts (Updated for 2024)

Last updated on February 1st, 2024 at 11:07 am

At Approved Sheet Metal, we find that welding sheet metal is one of the most misunderstood processes in precision sheet metal fabrication. In an effort to demystify welding and help our customers choose the optimal welding method for a part, we do our best to clearly outline the benefits and limitations of different custom welding techniques. 

Here, we’ll explore the sheet metal welding methods we use in our shop and explain what to expect from each one.

Spot Welding

Also known as resistance welding, spot welding involves compressing two pieces of sheet metal and applying pressure and heat from copper electrodes to create a nugget of weld that connects the pieces. 

Spot welding is often confused with tack welding, which also uses a small amount of weld to attach two pieces. However, unlike tack welding, spot welding creates a permanent weld. 

Considerations for spot welding

• Requires unique tooling and fixturing 
• Welds are structurally sound but not watertight 
• Limited to certain material thicknesses and part geometries 
• Achieves a Class A finish without the need for grinding
• Can be just as strong as seam weldments
• Ideal for creating hat channels
• The fastest and most cost-effective welding option for high-volume projects
• Requires strategic placement to ensure proper part function

Tack Welding

Tack welding is a low-heat, typically temporary welding process that holds sheet metal pieces together in proper alignment until they can be permanently welded. 

Considerations for tack welding 

• An inexpensive method for fastening two parts when a high-quality weld is not required 
• Not a good fit for structural applications
• Welds are not watertight 

Fuse Welding

Fuse welding, also known as fusion welding, is achieved by heating two surfaces to the point where they melt together, with or without a filler rod. 

Considerations for fuse welding

• Typically used on steel or stainless steel parts 
• Can create watertight welds 
• While not a cosmetic weld, it can be done very fine and requires little to no cleanup 

Stitch Welding

Stitch welding, also called intermittent or step welding, involves applying short, spaced sections of weld (1”–2”) along a connection point between two parts, giving the appearance of stitches. We typically use a filler rod with this method.

Considerations for stitch welding 

• Ideal for when a fully welded seam or connection point is not required 
• Welds are not watertight due to gaps between the weld “stitches” 
• Low risk of part deformation due to minimal heat generated 
• Less expensive than welding an entire seam 

Plug Welding

Plug welding is a method in which a round hole or slot is filled with a puddle of weld that is used to mate two parts or surfaces together. Plug welding has many drawbacks and isn’t a popular choice. 

Considerations for plug welding

• Time-consuming and difficult to clean 
• High risk of deformation due to the amount of heat required 
• Welds are not watertight 

Seam/Fillet Welding

Seam welding, or fillet welding, is one of the most common methods we use at Approved Sheet Metal. This arc welding method uses a filler rod to create a continuous weld across the entire seam of the pieces being joined. 

Considerations for seam/fillet welding

• Creates a strong, watertight seal
• Prone to deformation, depending on the material thickness and length of the seam 
• Requires the most cleanup of any welding method

MIG Welding

Metal inert gas (MIG) welding is an arc welding method typically used on large parts made of thick material, such as structural steel parts. With this method, we feed a continuous solid wire electrode through a welding gun into a weld pool to join two pieces together. 

Considerations for MIG welding

• Faster than other arc welding methods, such as TIG welding
• Can create watertight seals 
• Not as clean a weld as TIG welds, so not ideal for precision parts

TIG Welding

We frequently use tungsten inert gas (TIG) welding at ASM because it is an excellent method for precision parts. This arc welding technique uses non-consumable tungsten that can be supplemented with filler metal added by hand. 

Considerations for TIG welding

• Produces high-quality, strong, clean welds 
• Slower and more expensive than other methods
• One of the most common welding methods

At Approved Sheet Metal, we know that providing exceptional welding services is part of being a sheet metal manufacturing partner you can trust. Request a quote to see the ASM difference today!