Pulse Spot Welding for Thick-Thin Laminates Without Expulsion
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Solution Overview
Problem
Existing spot welding methods struggle to reliably weld metal sheet laminates with a combination of thin and thick sheets without causing expulsion, as the growth rate of nuggets at thick and thin sheet boundaries is uneven, making it difficult to set appropriate welding conditions.
Innovation Solution
A spot welding method using a pulse current with DC chopping control, where the peak current value and power in the first current application step are higher than in the second step, and the current application stop time is shorter in the first step, allowing for controlled nugget growth and suppression of expulsion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the current application time of the main current application step is set to a predetermined time or more to ensure an appropriate current width of 1 kA or more, then stable joining quality is obtained, but the nugget at the thick sheet-side boundary surface grows too much and expulsion occurs
Solution Approach 1:
The current application process is divided into two distinct stages: a main current application step with higher current to form the nugget, and a post-current application step with lower current to cool and solidify the nugget. This segmentation allows optimization of each stage independently, preventing expulsion during nugget formation while ensuring stable joining quality.
Solution Approach 2:
The welding process uses periodic current application with two distinct phases: a first current application step followed by a second current application step. This periodic action pattern enables controlled nugget growth followed by controlled cooling, resolving the contradiction between achieving stable joining and preventing expulsion.
2Object-generated harmful factors
If the current application time of the first current in the main current application step is set to be shorter than the predetermined time, then expulsion is suppressed, but the nugget at the thin sheet-side boundary surface cannot grow to a sufficient size and the metal sheet laminate is not welded
Solution Approach 1:
The dual-stage current application provides different current conditions tailored to different nugget formation needs: the first stage provides high current for rapid nugget formation, while the second stage provides lower current for controlled cooling. This local quality differentiation ensures proper nugget growth without causing expulsion.
3Ease of manufacture
If the current and the pressing force are simultaneously controlled, then welding is performed, but it is difficult to set an appropriate condition for welding the metal sheet laminate
Solution Approach 1:
The control parameters are segmented into two distinct current application steps with different current levels and durations. This segmentation simplifies the control strategy by breaking down the complex simultaneous control into manageable sequential stages, making it easier to set appropriate welding conditions for metal sheet laminates with varying thicknesses.
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
This method ensures stable joining quality by allowing for controlled nugget growth, preventing expulsion, and improving yield in welding metal sheet laminates with varying thicknesses.
Implementation Method 1
a current is applied between the pair of electrode tips to generate a nugget between the plurality of metal sheets
Data Source
AI summary
Provided is a spot welding method capable of reliably welding a metal sheet laminate while suppressing occurrence of expulsion. In the spot welding method, a pulse current is applied in a first current application step and a second current application step by a DC chopping control method. In the DC chopping control method, a pulse waveform of the pulse current is generated by switching between current application and current application stop to a pair of electrodes 12 and 22 by a current switch 28, a peak current value of the pulse current in the first current application step is set to a value A1 equal to that of the pulse current in the second current application step, and a power of the pulse current in the first current application step is set to a value larger than that of the pulse current in the second current application step.