G. L. Chen

Monitoring and intelligent control of electrode wear based on a measured electrode displacement curve in resistance spot welding

Advanced high strength steels are being increasingly used in the automotive industry to reduce weight and improve fuel economy. However, due to increased physical properties and chemistry of high strength steels, it is difficult to directly substitute these materials into production processes currently designed for mild steels. New process parameters and process-related issues must be developed and understood for high strength steels. Among all issues, endurance of the electrode cap is the most important. In this paper, electrode wear characteristics of hot-dipped galvanized dual-phase (DP600) steels and the effect on weld quality are firstly analysed. An electrode displacement curve which can monitor electrode wear was measured by a developing experimental system using a servo gun. A neuro-fuzzy inference system based on the electrode displacement curve is developed for minimizing the effect of a worn electrode on weld quality by adaptively adjusting input variables based on the measured electrode displacement curve when electrode wear occurs. A modified current curve is implemented to reduce the effects of electrode wear on weld quality using a developed neuro-fuzzy system.

On-Line Estimation of Electrode Face Diameter Based on Servo Gun Driven by Robot in Resistance Spot Welding

Enlargement of electrode face diameter in resistance spot welding was the main factor that led to undersize nugget diameter. A mathematics model was established to estimate electrode face diameter by applying the characteristic that servo gun can detect axial wear online but not equip additional measurement apparatuses. Firstly the precision of servo gun was compensated to assure it can meet the requirement of axial wear measurement online. Then the model was established to estimate electrode face diameter online by a minimum amount of experiment data to determine the numerical constant in the model. To verify the model, electrode life tests for welding different galvanized steels were carried out. It was shown that estimation results of the model agreed well with the experiment results and spot welding the steels with higher electrode wear rate would result in a shorter electrode life