Joining Process Monitoring Using ML-Based Joint Quality Estimation
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Solution Overview
Problem
Current quality control methods for automatic joining processes, such as resistance spot welding, are not comprehensive, relying on random sampling and manual inspection, which can lead to inconsistent detection of faulty joints due to high process variance.
Innovation Solution
A method using machine learning to monitor the quality of joints in an automatic joining machine by creating a digital process image from predetermined process parameters and variables, and training a machine learning estimation model to automatically assess the quality of joints, thereby eliminating the need for manual testing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If random sampling inspection is used, then inspection cost and time are reduced, but quality control reliability deteriorates due to high process variance
Solution Approach 1:
The system performs preliminary action by capturing process data (current, voltage, time signals) during the joining process itself, before the actual quality assessment is needed. This preliminary data collection enables subsequent machine learning analysis to predict quality outcomes without requiring separate inspection steps, thus maintaining high reliability while improving efficiency.
Solution Approach 2:
The patent replaces the mechanical/manual ultrasonic inspection system with an automated machine learning-based evaluation system. The machine learning model processes electrical process signals (current, voltage, time) to predict joint quality, substituting the need for physical ultrasonic testing devices and manual inspection operations, thereby achieving both high reliability and improved productivity.
2Reliability
If comprehensive inspection of all joints is performed, then quality control reliability is improved, but inspection time and cost increase
Solution Approach 1:
The patent replaces time-consuming physical inspection methods with automated machine learning analysis of process signals. The system evaluates joint quality by analyzing electrical signals already generated during the joining process, eliminating the need for separate inspection operations and achieving comprehensive quality control without additional time loss.
Solution Approach 2:
The system maintains continuity of useful action by performing quality evaluation continuously during the joining process itself, rather than interrupting production for separate inspection cycles. The machine learning model processes data in real-time as joints are created, enabling continuous quality monitoring that does not halt or slow down the manufacturing process.
3Measurement precision
If machine learning model is trained with extensive simulation data, then model accuracy is improved, but training complexity and data acquisition difficulty increase
Solution Approach 1:
The patent introduces an intermediary approach by using actual process signals from the joining machine as training data, rather than relying solely on complex simulation data. The machine learning model is trained on real electrical signals (current, voltage, time) captured during actual joining operations, with quality labels provided by subsequent ultrasonic inspection, creating a practical training pathway that balances accuracy with reduced complexity.
Solution Approach 2:
The system implements feedback by using the results of ultrasonic inspection to label the quality of joints, which then serves as ground truth for training the machine learning model. This feedback loop allows the model to learn from actual outcomes and continuously improve its predictive accuracy without requiring complex simulation frameworks, as the real inspection results provide direct training signals.
Data Source
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AI summary
The invention relates to a method for monitoring a joining process (12) of workpieces (11) in an assembly machine (10), wherein in a training phase (37) a quality indication (35) is generated on joined precursor workpieces (30) and an estimation model (21) of machine learning is generated by means of a predetermined training method (36), which outputs an estimated quality indication (35) that is trained according to the signaled quality indication (35), and in an operating phase (38) a digital process image (18) of the joining process (12) of the respective workpiece (11) is determined and supplied to the estimation model (21) as input and the estimated quality indication (35) with respect to the respective joined workpiece (11) is generated by means of the estimation model (21) and a rejection measure is carried out for the workpieces (11) joined by the assembly machine (10). (17) is triggered to separate such workpieces (11),where the estimated quality rating (35) meets a predetermined rejection criterion (15).