Resistance Spot Welding Sequence to Prevent Expulsion
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Solution Overview
Problem
Existing resistance spot welding methods fail to consistently achieve a stable nugget diameter without expulsion, especially when disturbances such as current shunting or sheet gaps occur, due to variations in electrode wear and unexpected disturbances like nearby existing welds or large sheet gaps.
Innovation Solution
A resistance spot welding method involving three steps: forming a fusion zone with a diameter of at least 2√t mm by constant current control, cooling it to not greater than 80% of the initial diameter, and then performing adaptive control welding to match the target heat generation pattern derived from test welding, ensuring a consistent nugget diameter without expulsion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the same welding current is used throughout electrode life, then the initial welding quality is maintained, but the nugget diameter decreases as electrodes wear
Solution Approach 1:
The welding current is made dynamic rather than static. The control unit adjusts the welding current in real-time based on feedback from voltage detection and heat generation calculations, allowing the system to adapt to electrode wear and maintain consistent nugget diameter throughout the electrode's service life.
Solution Approach 2:
A feedback control mechanism is implemented where the voltage between electrodes is detected during welding, the heat generation amount is calculated based on this voltage and welding current, and the welding current is adjusted accordingly to maintain the heat generation within a target range, ensuring consistent weld quality.
2Manufacturing precision
If a high welding current is set to compensate for current shunting, then the nugget diameter requirement is met, but expulsion occurs more easily
Solution Approach 1:
The system dynamically changes the welding current parameter based on real-time conditions. By calculating the heat generation amount from detected voltage and adjusting the current accordingly, the system achieves the required nugget diameter while preventing excessive current that would cause expulsion, adapting to disturbances like current shunting without using excessively high current settings.
3Manufacturing precision
If the welding current is increased to account for electrode wear, then the nugget diameter is maintained, but the system cannot adapt to unexpected disturbances
Solution Approach 1:
The system uses continuous feedback from voltage detection during welding to calculate heat generation and adjust the welding current in real-time. This allows the system to adapt to both expected conditions (electrode wear) and unexpected disturbances (current shunting, sheet gaps, surface roughness) dynamically, rather than relying on pre-set current increases that cannot respond to actual conditions.
4Manufacturing precision
If a larger sheet gap is present, then the contact diameter decreases facilitating expulsion, but the welding must still achieve required nugget diameter
Solution Approach 1:
The system dynamically adjusts the welding current parameter in response to detected voltage changes caused by sheet gap conditions. By calculating the actual heat generation from voltage detection and adjusting current in real-time, the system compensates for the reduced contact diameter effect of larger sheet gaps, achieving the required nugget diameter while monitoring to prevent expulsion conditions.
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 effectively prevents expulsion and maintains a desired nugget diameter even under significant disturbances, such as large sheet gaps or nearby existing welds, without increasing welding time.
Implementation Method 1
Heat generated from the resistance to the flow of the high welding current is used to obtain a spot weld
Implementation Method 2
a second step of cooling the fusion zone to have a diameter of not greater than 80% of D
Data Source
AI summary
A resistance spot welding method of squeezing parts to be welded, which are a plurality of overlapping metal sheets, by a pair of electrodes and passing a current while applying an electrode force to join the parts to be welded comprises: a first step of passing a current by constant current control to form a fusion zone having a diameter of not less than 2√{square root over (t)}, expressed in mm, between the metal sheets, where t, expressed in mm, is a sheet thickness of a thinnest metal sheet of the metal sheets; a second step of cooling the fusion zone to have a diameter of not greater than 80% of D, where D, expressed in mm, is a diameter of the fusion zone formed in the first step; and a third step of performing adaptive control welding by controlling a current passage amount according to a target that is set.