A Guide to Different Methods of Welding Sheet Metal Fabricated Parts (Updated for 2026)

Last updated on February 9th, 2026 at 09:05 am

At Approved Sheet Metal, we find that welding sheet metal is one of the most misunderstood processes in precision sheet metal fabrication. To help our customers choose the most appropriate welding method, we clearly outline the benefits and limitations of the custom welding techniques used in our shop.

Below, we explore the sheet metal welding methods we use and explain what to expect from each one in terms of strength, appearance, cost, and manufacturability.

Spot Welding

Also known as resistance welding, spot welding involves compressing two pieces of sheet metal and applying heat and pressure through copper electrodes. This creates a small weld nugget that permanently joins the parts.

Spot welding is often confused with tack welding, which uses small welds for temporary positioning. Unlike tack welding, spot welding produces a permanent structural connection.

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 grinding
• Can be just as strong as seam weldments when properly designed
• Ideal for creating hat channels
• The fastest and most cost-effective option for high-volume projects
• Requires strategic placement to ensure proper part function

Tack Welding

Tack welding is a low-heat, typically temporary process used to hold sheet metal components in alignment until permanent welding is completed.

Considerations for tack welding

• An inexpensive method for temporarily fastening parts
• Not suitable for structural applications
• Welds are not watertight

Fuse Welding

Fuse welding, also known as fusion welding, joins two surfaces by heating them until the base material melts together. This method may be performed with or without filler metal.

Considerations for fuse welding

• Typically used on steel or stainless steel parts
• Can create watertight welds
• Can be performed finely with little to no cleanup

Stitch Welding

Stitch welding, also called intermittent or step welding, applies short, spaced sections of weld along a joint. Individual welds are typically one to two inches long, and filler metal is commonly used.

Considerations for stitch welding

• Used when a continuous seam is not required
• Welds are not watertight due to gaps between stitches
• Lower risk of deformation due to reduced heat input
• Less expensive than welding an entire seam

Plug Welding

Plug welding fills a round hole or slot with weld material to join overlapping parts. While effective in limited cases, it is generally not preferred for precision sheet metal fabrication.

Considerations for plug welding

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

Seam/Fillet Welding

Seam welding, or fillet welding, is one of the most common methods used at Approved Sheet Metal. This arc welding process uses filler metal to create a continuous weld along the entire joint.

Considerations for seam/fillet welding

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

MIG Welding

Metal inert gas (MIG) welding is an arc welding process typically used on larger parts made from thicker materials, such as structural steel. A continuous wire electrode is fed through a welding gun into the weld pool to join components.

Considerations for MIG welding

• Faster than other arc welding methods, such as TIG welding
• Can create watertight welds
• Produces less clean welds than TIG, making it less suitable for precision parts

TIG Welding

Tungsten inert gas (TIG) welding is frequently used at ASM for precision applications. This arc welding technique uses a non-consumable tungsten electrode and allows filler metal to be added by hand for maximum control.

Considerations for TIG welding

• Produces high-quality, strong, clean welds
• Slower and more expensive than other methods
• One of the most commonly used methods for precision parts

Weld Strength and Durability

Weld strength and durability play a major role in determining which welding method is appropriate for a given application, especially in high-stress or structural environments.

• Spot Welding: Structurally sound but best suited for non-structural or lightly loaded connections.
• Tack Welding: Temporary only and not intended for long-term strength.
• Fuse Welding: Can produce strong, watertight joints when properly controlled.
• Stitch Welding: Balances strength and cost but is weaker than continuous seams.
• Plug Welding: Limited strength and higher distortion risk.
• Seam/Fillet Welding: One of the strongest and most durable options available.
• MIG and TIG Welding: Both provide strong welds, with TIG offering greater precision and consistency for thin materials.

Heat Affected Zone (HAZ)

The Heat Affected Zone (HAZ) is the area of base material altered by heat during welding. The size and impact of the HAZ depend on the welding method and heat input.

• Spot Welding: Small, localized HAZ with minimal impact when controlled.
• Tack Welding: Minimal HAZ due to low heat input.
• Fuse Welding: Larger HAZ if heat is not carefully managed.
• Stitch Welding: Generally minimal HAZ due to intermittent welds.
• Plug Welding: Larger localized HAZ with higher distortion risk.
• Seam/Fillet Welding: Moderate to large HAZ along long seams.
• MIG and TIG Welding: Moderate HAZ, with TIG typically producing a smaller affected zone.

Applications and Best Use Cases

• Spot Welding: High-volume production and non-load-bearing sheet metal joints.
• Tack Welding: Temporary alignment during fabrication.
• Fuse Welding: Watertight joints in steel and stainless steel components.
• Stitch Welding: Cost-sensitive applications where continuous welds are unnecessary.
• Plug Welding: Limited applications where direct access is restricted.
• Seam/Fillet Welding: Pressure vessels, tanks, and enclosures requiring strength and sealing.
• MIG Welding: Thick materials and large structural components.
• TIG Welding: Precision parts, thin materials, and cosmetic weld requirements.

At Approved Sheet Metal, providing reliable welding services is part of being a fabrication partner you can trust. Request a quote to discuss the best welding approach for your project.

Sheet Metal Part Design for Manufacturing Tip

CORNERS AND WELDING

Proper technique on corners that need to be welded is necessary to reduce cost and increase the overall strength of the corners. Approved Sheet Metal will always reprogram corners that need to be welded to ensure customers receive the best possible welds.

Get more DFM Tips

Sheet Metal Fabrication Welding FAQ

What are the key welding methods used by fabricators?

Fab shops typically employ several welding methods, including spot welding, tack welding, fuse welding, stitch welding, plug welding, seam/fillet welding, MIG welding, and TIG welding, each with unique applications and characteristics.

What is the difference between spot welding and tack welding?

Spot welding creates a permanent weld by compressing two pieces of sheet metal with copper electrodes, while tack welding is a low-heat, temporary method used to temporarily hold metal pieces in alignment before permanent welding. Spot welding is structurally sound and ideal for high-volume projects, while tack welding is cost-effective but not suitable for structural applications.

When should fuse welding be used, and what materials are best suited for it?

Fuse welding is primarily used on steel or stainless steel parts to create watertight welds. It involves heating two surfaces until they melt together, and it can be done finely with minimal cleanup, making it suitable for specific applications.

What is the purpose of stitch welding, and in what scenarios is it ideal?

Stitch welding is employed when a fully welded seam or connection point is not required. It involves applying short, spaced sections of weld along a connection point, and while it’s not watertight, it minimizes the risk of part deformation due to minimal heat generated. It’s also a cost-effective alternative to welding entire seams.

When is MIG welding preferred over other welding methods, and what should be considered when choosing MIG welding?

MIG welding is typically used on large parts made of thick material, such as structural steel parts. It’s faster than other arc welding methods and can create watertight seals. However, it may not be the best choice for precision parts due to its cleanliness. Consider the specific application and material when choosing MIG welding.