Resistance Spot Welding Multi-Stage Current Control
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Solution Overview
Problem
Resistance spot welding methods struggle to maintain a stable nugget diameter without expulsion in sheet combinations with high sheet thickness ratios, especially when disturbances like sheet gaps or current shunting occur, making it difficult to achieve the required nugget size between thin and thick sheets.
Innovation Solution
A resistance spot welding method that involves dividing the current pattern into two or more steps, with initial constant current control in the first step to prevent expulsion and adaptive control in subsequent steps to ensure the calculated heat generation, and similarly dividing the electrode force into steps to optimize nugget formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If welding current is increased to form a larger nugget, then nugget diameter increases, but expulsion occurs
Solution Approach 1:
The welding current is divided into multiple stages: a first stage with lower current to form an initial nugget without expulsion, and a second stage with higher current to expand the nugget to the required diameter. This segmentation allows the welding process to achieve both sufficient nugget size and prevention of expulsion by controlling heat generation in phases.
Solution Approach 2:
The first current stage performs a preliminary action by forming an initial nugget that establishes a stable molten pool and ensures proper contact between sheets. This preliminary nugget formation creates a foundation that prevents subsequent expulsion when the higher current is applied in the second stage to achieve the final nugget diameter.
2Device complexity
If constant electrode force and welding current are used, then welding process is simple, but nugget diameter becomes unstable with disturbances
Solution Approach 1:
The welding current is made dynamic by implementing multi-stage current control with different current levels in different time periods. The first stage uses a lower current adapted to disturbed conditions (sheet gaps, current shunting), while the second stage uses a higher current to achieve the target nugget diameter. This dynamic current adjustment ensures stable nugget formation despite disturbances, while the electrode force remains constant.
3Temperature
If high welding current is applied to thin and thick sheets, then heat generation increases, but temperature does not increase sufficiently due to cooling by electrode tip
Solution Approach 1:
The welding process uses periodic action with two distinct current stages. The first stage applies a moderate current for a sufficient duration to overcome the cooling effect of the electrode tip and establish thermal conditions favorable for nugget formation. The second stage then applies higher current to rapidly increase temperature and complete nugget formation. This periodic current application ensures that the cooling effect is overcome without requiring excessively high current from the start.
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 approach allows for the formation of a nugget of appropriate diameter without expulsion, even with disturbances, by ensuring controlled heat generation and contact stability between thin and thick sheets, enhancing the reliability of the welding process.
Implementation Method 1
Heat generated from the resistance to the flow of the high welding current is used to obtain a spot weld. The spot weld is called a nugget, and results from the overlapping steel sheets melting and solidifying at their contact portion when the current flows through the steel sheets.
Data Source
AI summary
A resistance spot welding method of squeezing a predetermined sheet combination by a pair of electrodes and passing a current while applying an electrode force to join the sheet combination includes: performing test welding; and performing actual welding after the test welding, wherein in each of the test welding and the actual welding, a current pattern is divided into two or more steps including a first current passage step and a second current passage step subsequent to the first current passage step, and, in the actual welding, a current that causes no expulsion is selected to perform welding by constant current control in the first current passage step, and adaptive control welding is performed from the subsequent second current passage step onward.