Metal Fabrication Resources by Blackstone Advanced Technologies

Spot Welding Design: 3 Key Considerations

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Spot welding is ideal for stamping, assemblies, and sheet metal fabrications. There is no shortage of spot welding design considerations to keep in mind to ensure reliable, economical, and high-quality work.


Chief among these crucial considerations are:

  • The amount of stress placed on spot weld locations
  • The number of spot welds per foot of joined material
  • The strength of the materials being joined


Spot Welding Design Considerations

1. Weld Strength and Size

The size of a weld is typically slightly smaller than the diameter of the electrode impression. The strength of your base metal and the strength of your spot welds are directly related. In applications where weld space is limited, specifying a single, larger weld is generally preferable and will produce stronger bonds than using two or more smaller welds.


Diameters of spot welds typically range from ⅛” to ½”. The thicker the materials you are working with, the larger your spot welds should be.

2. Placement

Experienced sheet metal fabricators don’t like receiving rigid guidelines from customers when determining weld size, number, and location. Once the strength requirements of the piece have been evaluated, it is usually best to use the minimum number of welds that can be equally spaced.


While spot welding is very economical, in cases where two or more joining methods are called for, it may be more cost-effective to redesign the project so only one joining method is used.

3. Material Strength

Different types of metal have different characteristics that should be considered when spot welding.


A. Low-Carbon Steel

Low carbon steel is the most commonly used material in sheet metal fabrication and is the easiest to weld. It is very versatile and generally preferred for most sheet metal fabrication projects.


B. High Carbon Steel

Higher carbon steel will form harder welds, which can degrade the weld performance and make sheet metal fabrications overly rigid. A general guideline to remember: The higher the carbon content, the more brittle the weld.


Higher-strength steel may also require tempering after welding. The spot weldability of high-strength low-alloy (HSLA) steel has a direct relation to the type and composition of the microalloying elements.


C. Stainless Steel

Stainless steel can be spot welded, some grades better than others. Austenitic grades in the 300 series and ferritic steel are the most commonly used stainless steels for welding applications. Martensitic stainless steels are less common in welding due to their brittleness.


Stainless steel requires special methods and careful adjustment to achieve optimum welds.


D. Conductive Metals

Conductive metals require higher power for quality spot welds to form. Aluminum is an exception since it is a soft metal.

All Welds Need Proper Care

Congrats! You’re on your way to specifying a smarter spot weld. There’s a lot more you can learn about weld issues to make things run smoother next time you work with a vendor. Click here to learn about common weld defects and how you may be responsible for them.


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