Are there any general recommendations on the dimensions and use of annular projections in resistance welding?

Frequently Asked Questions

1. Machined annular projections

Typically, an annular 'V' projection is machined in a solid component to achieve, just prior to welding, line contact with the component to which it is to be welded. In the early stages of welding, the projection concentrates force and current into a small contact area. Uniformity of projection shape and height is essential for achieving consistent weld quality.

 

General rules for machined annular projections:

• projection included angle should normally be 90°
• avoid positioning the projection on the component's edge
• a recess adjacent to the projection is sometimes used as a spit trap
• projection height is typically 1 to 2mm depending on sheet thickness and weld strength required
• if less heat is needed in the joint, or when welding to thinner sheet, the projection angle can be reduced, e.g. 60°
• for larger welds, it may be necessary to increase the projection angle to 120°
• tubular components (including threaded bosses), into which projections are machined, should have sufficient wall thickness to prevent overheating (and damage to threads)
• location pins must be insulated

Welding Conditions

Electrode force: Weld time: Welding current:

typically 18 to 24kg per mm of projection length (circumference) 7 to 10 cycles normally between 470 and 630A per mm of projection length

2. Stud to plate

60° included angle cone

Suitable where sheet is thick enough to support electrode force and prevent stud protruding through lower surface. This design gives stronger welds than a shallow cone.

150° included angle cone

Achievable weld area is only up to about 90% of the stud cross-section.

Further information

Some items are only available to Industrial Members of TWI.

FAQ: What projection profile suits projection welding?

Best practice guide: Resistance welding of sheet metals. Please note that the guide does not cover projection welding in detail, but basic information to supplement this FAQ is available at the end of section 3.