Suitable projections for projection welding can be formed in steel sheet by embossing, and standard designs are set out in BS EN 28167 (ISO 8167). Elongated projections based on these designs are used particularly when welding curved surfaces to ensure proper set down of the projection and adequate weld formation. For welding thin sheet an annular profile may be preferred as it has greater stability against collapse under the electrode force.
When solid parts are to be projection welded, a rounded or V section projection can be forged or machined. The main design criteria are sufficient mass to heat a spot on the opposing surface to welding temperature before collapsing, and stability against buckling to withstand the initial electrode force. Studs and nuts can have standard projection profiles, e.g. BS 7670. Annular projections can be machined on components such as threaded bosses to provide a continuous leak tight seal with the sheet to which they are welded. These are typically V section with a 90° included angle.
Guidance on projection welding procedures when using embossed projections is available in BS EN ISO 16432.
FAQ: Are there any general recommendations on the dimensions and use of annular projections in resistance welding?