Concentric Electrode Spot Welding to Reduce Zinc-Induced LME
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Solution Overview
Problem
Zinc coatings on steel components, such as Gen3 steels, liquefy during welding, causing liquid metal embrittlement (LME) and mechanical failures due to differences in metal melting temperatures and pressure, restricting their use in applications like automobile vehicles.
Innovation Solution
A concentric electrode with a cylindrical base and a tip is used to purge the zinc coating from steel workpieces before welding, employing a two-step process that includes coating removal and spot welding using a concentric electrode and a welding electrode.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If zinc coating is applied to steel components for corrosion protection, then corrosion resistance is improved, but liquid metal embrittlement occurs during welding causing mechanical failures
Solution Approach 1:
The patent applies preliminary action by removing the zinc coating from the steel component surface before welding through mechanical means (grinding, sanding, or blasting) to prevent liquid metal embrittlement during the welding process, while maintaining corrosion protection on non-welded areas
2Ease of manufacture
If offline surface treatment processes are used for coating removal, then coating removal is achieved, but time and cost increase significantly
Solution Approach 1:
The patent merges the coating removal operation with the welding operation by integrating surface treatment capabilities directly into the welding fixture or positioning system, allowing both operations to occur in sequence without removing the workpiece from the fixture, thereby eliminating transport time and setup time between operations
Solution Approach 2:
The patent performs surface treatment as a preliminary action immediately before welding while the workpiece is already positioned in the fixture, eliminating the need for separate offline treatment processes and subsequent repositioning
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 in-line process significantly reduces LME cracking and enables the use of Gen3 steels in vehicle body structures by minimizing time and cost associated with offline surface treatments.
Implementation Method 1
passing an electric current between the first concentric electrode and the second concentric electrode and through the workpiece stackup
Implementation Method 2
the zinc coating materials...liquefy and penetrates into the steel when heated by the electric current
Data Source
AI summary
A concentric electrode is provided. The concentric electrode includes a cylindrical base and a tip disposed on the cylindrical base. The cylindrical base extends axially along an axis of rotation, and the cylindrical base includes a conductive metal. The tip includes a concentric surface extending axially from the cylindrical base and defined by an outer shoulder having an outside diameter and an inner shoulder having an inside diameter. The tip is configured to provide an electrical current to a steel workpiece and purge a coating from at least a portion of the steel workpiece.