| Micro-resistance spot welding is one of the most commonly used connection methods in micro-connection technology.Due to the small size of the miniature parts,the low heat evolution and the thermal inertia effect,the connection area of the workpiece is easily affected by the instantaneous value of the current,and the welding quality is unstable and the workpiece is easy to burn.In the welding process,the electrode is an important part of transmitting welding pressure and heat conduction.The burning loss and life of the electrode are often the key factors that restrict the welding efficiency,affect the welding quality and production cost.Therefore,in view of the above problems,in order to improve the control accuracy of the power supply,improve the welding quality and reduce the production cost,the high-performance micro-spot welding power supply equipment and electrode burning process are studied in depth.Based on the high-frequency inverter + H-bridge dual-phase chopper technology,the main circuit topology of the micro-spot welding power supply is designed.A digital power control system based on high-performance STM32 dual-core controller is developed.The capacitor variable pulse width-constant current fast charging method is proposed to complete the power prototype assembly and output characteristic test.The power inverter and chopper frequency are both 100 k Hz,the rated current is 4 k A,and the control accuracy is 1 A.It has two output modes and four control modes,and the polarity switching time can be as low as0.1 ms.A synchronous data acquisition system for micro-spot welding process is designed to realize real-time acquisition of electrode temperature,current and voltage data,and an electrode burning test platform is built.The mathematical model of electrode burning loss dynamic resistance in micro-spot welding process was established.The electrode behavior under different heating modes was quantitatively analyzed by using the macroscopic physical quantity change of electrode burning loss in micro-spot welding process.The influence of power output mode on electrode service life and burning loss law was compared and analyzed.The microstructure of electrode failure morphology was observed by metallographic microscope to clarify the electrode failure mechanism.The results show that the bipolar heating mode of power supply can effectively prolong the electrode life and improve the uniformity of electrode burning loss.Electrode erosion and fatigue cracking are the main failure modes of electrode in micro-spot welding process.Aiming at the advantages of bipolar heating mode of power supply,the relationship between electrode heat accumulation effect and heat generation behavior under different control modes of power supply is analyzed by establishing the characteristic relationship between electrode dynamic resistance and electrode heat generation and temperature,so as to clarify the mechanism of power supply control mode on electrode burning loss.The effect of electrode burning loss on the quality of solder joints was investigated by carrying out micro-dot test of micro-aluminum wire and copper foil.The morphology and tensile strength of solder joints were used as the evaluation indexes of welding quality.The results show that the constant voltage control method is less affected by electrode burning loss,and the minimum tensile force of solder joints is 28.4 g.It is superior to the other two control methods in ensuring the reliability and consistency of solder joint morphology and welding quality,which will provide an effective reference for practical welding applications. |
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