Spot Welding Electrode Geometry for Symmetrical Nugget Formation
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Solution Overview
Problem
Single-sided double-spot welding in resistance spot welding often results in asymmetrical nugget morphologies, leading to mechanical performance issues and reduced welding quality due to uneven heat input.
Innovation Solution
A device and method for resistance spot welding that employs a pair of electrodes with special-shaped contact surfaces, symmetrically arranged around a symmetry axis, to alter the current density distribution, ensuring symmetrical and uniform nugget morphology.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If single-sided double-spot welding is used to improve production efficiency, then two welding spots can be simultaneously welded, but the nugget morphology becomes asymmetrical with the distal end having smaller thickness
Solution Approach 1:
The patent applies asymmetry principle by deliberately designing electrodes with different shapes - one electrode has a spherical end face while the other has a flat end face. This asymmetric electrode configuration compensates for the inherent asymmetry in single-sided double-spot welding, ensuring that both nuggets achieve symmetrical and uniform morphology despite being welded from one side only.
2Strength
If more welding heat input is applied to increase distal end thickness, then mechanical performance conditions are met, but the proximal end thickness becomes greatly beyond demand and welding spatter occurs
Solution Approach 1:
The patent applies local quality principle by using electrodes with different end face geometries (spherical vs. flat) to create localized differences in heat input distribution. The spherical electrode concentrates heat at the distal end where thickness is insufficient, while the flat electrode provides more uniform heat distribution at the proximal end, preventing both spatter and insufficient penetration simultaneously.
3Productivity
If single-sided double-spot welding is used for tailor rolled blanks, then welding efficiency is improved, but nugget shift and insufficient penetration rate occur at the thin thickness side
Solution Approach 1:
The patent applies asymmetry principle by configuring electrodes with different shapes (spherical and flat end faces) to compensate for the thickness differential in tailor rolled blanks. This asymmetric electrode design ensures that the thinner workpiece receives concentrated heat from the spherical electrode, preventing nugget shift and insufficient penetration while maintaining high welding efficiency.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution enhances the heat input at the distal end of the nugget while reducing it at the proximal end, achieving symmetrical and uniform nugget morphologies that meet mechanical performance requirements, thereby improving welding quality.
Implementation Method 1
the pair of electrodes are energized and the periphery of the metallic cap 22 is subjected to spot welding
Data Source
Figure 1~2
Figure 3~4
Figure 5~6
AI summary
An electric resistance spot welding device, comprising a pair of electrodes located on the same welding surface of an assembly to be welded. The assembly to be welded is provided with an axis of symmetry (6); the pair of electrodes are symmetrically disposed on two sides of the axis of symmetry; one end of each electrode has a special-shaped contact surface (20); the special-shaped contact surfaces are respectively offset in directions away from the axis of symmetry relative to the electrode axis, wherein the special-shaped contact surfaces are used for offsetting a current density centerline (21) formed by the electrodes in a direction away from the axis of symmetry relative to the electrode axis (11), and/or used for deflecting the tendency of the current density of each electrode away from a welding face within the assembly to be welded. The device can achieve a symmetrical and uniform shape of distal and proximal ends of a nugget with respect to the axis of symmetry, such that both the shape and stress state of the nugget can meet requirements for mechanical properties under load, thus improving the welding quality. The present application also relates to an electric resistance spot welding method.