Resistance Spot Weld Quality Detection During Cooling Phase
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Solution Overview
Problem
Existing resistance welding technologies face challenges in efficiently and cost-effectively detecting weld quality due to the hidden nature of the joining area, leading to issues like insufficient weld joints and spatter, with current methods being costly, inefficient, and lacking automation.
Innovation Solution
A method and device for weld quality detection that applies a detection voltage during the cooling phase after the welding current is cut off, measuring resistance variations using Ohm's law, and comparing these with pre-defined resistance curves to determine weld defects, allowing for real-time, automated quality assessment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If destructive inspection methods (manual chisel, metallographic analysis) are used, then weld quality can be detected, but cost increases, efficiency decreases, and online implementation becomes difficult
Solution Approach 1:
The patent replaces mechanical destructive inspection methods with an electrical measurement system. By applying detection voltage during the cooling phase and measuring resistance changes, the system achieves weld quality detection without physical destruction of the workpiece, thereby maintaining high detection accuracy while dramatically improving efficiency and enabling online implementation.
Solution Approach 2:
The patent utilizes parameter changes during the cooling phase - specifically, the resistance of the weld nugget changes as it cools from molten state to solidified state. By monitoring these resistance parameter variations, the system can detect weld quality (nugget size, completeness) without destruction, resolving the contradiction between accurate measurement and production efficiency.
2Reliability
If non-destructive inspection methods (ultrasonic testing, infrared testing) are used, then workpieces remain intact, but cost increases, efficiency decreases, and specialized operators are required reducing automation
Solution Approach 1:
The patent makes the welding device itself perform the detection function by utilizing its existing electrodes and power supply system. The detection voltage is applied through the same electrodes used for welding, and the control system uses the existing microprocessor unit. This self-service approach maintains workpiece integrity while reducing device complexity and eliminating the need for separate specialized inspection equipment.
Solution Approach 2:
The welding device is designed to perform both welding and detection functions using the same hardware components. The electrodes serve dual purposes: delivering welding current and applying detection voltage. The power supply and control system are universally used for both operations, thereby maintaining workpiece integrity while reducing overall system complexity and enabling full automation.
3Loss of time
If detection is performed during welding phase, then real-time monitoring is achieved, but the high temperature and current interfere with accurate measurement
Solution Approach 1:
The patent employs periodic action by switching between welding mode and detection mode. During the cooling phase (after welding current is cut off but before the workpiece completely cools), the system periodically applies detection voltage to measure resistance. This timing strategy avoids the interference of high welding current and temperature while still achieving real-time monitoring within the production cycle.
Solution Approach 2:
The patent dynamically adjusts the detection timing based on the thermal state of the weld nugget. By detecting during the cooling phase when temperature is decreasing but still above ambient, the system captures resistance changes that reflect nugget formation quality. This dynamic timing approach balances real-time monitoring requirements with measurement accuracy, avoiding both the interference of active welding and the complete cooling state.
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
Enables quick, efficient, and cost-effective detection of weld quality without additional sensors, supporting a wide range of materials and environments, and ensuring full coverage on production lines with minimal human intervention.
Implementation Method 1
calculating a resistance of the weld continuously varying during the cooling phase based on the detection voltage and the detection current
Implementation Method 2
calculating a resistance of the weld continuously varying during the cooling phase... based on the trend of the variation of the resistance
Data Source
AI summary
The present application provides a method for weld quality detection comprising: applying a detection voltage to a weld during a cooling phase after the cut-off of the metal material welding current; detecting a detection current corresponding to the detection voltage applied to the weld; calculating continuous values of resistance of the weld during the cooling phase based on the detection voltage and the detection current; and determining whether a welding defect exists at the weld based on an initial value, an intermediate value, and an end value of the resistance. By measuring and analyzing the resistance variation in the melting core cooling phase and using the relationship between the resistivity of metal material and temperature to indirectly characterize the heat stored in weld nugget, the detection and evaluation of the quality of resistance spot welding can be realized.