| As an important welding method,resistance spot welding is widely used in aerospace,automotive,hardware,electronics,medical equipment and other fields.In recent years,with the miniaturization of devices and equipment,the application of resistance spot welding of micro parts has been increasing.In the welding of miniature parts,the thermal inertia of the weldment is small,and the temperature tends to fluctuate with the instantaneous value of the current;the size of the weldment is small,the temperature difference between the bonding surface and the outer surface is small,and it is difficult to form a concentrated heating effect on the bonding surface;The welding quality is easily affected by the surface condition of the weldment,such as the coating,oxide layer,surface roughness,etc.Therefore,welding of micro parts requires precise control of welding current,welding time,electrode shape,electrode pressure and other factors.Therefore,it is of great significance to improve the quality of solder joint of micro parts by studying the resistance spot welding power source with precise adjustment of welding parameters,fast dynamic response speed and diversified control modes.In this subject,a 4k A unipolar transistor resistance spot welding power supply is designed for the characteristics of resistance spot welding of miniature parts.The power supply includes constant current,constant voltage,constant power,and multiple control modes combined in stages.At the same time,three-stage discharge waveforms are designed to meet the needs of different welding processes.In addition,based on the 4k A unipolar power supply,a 2k A variable polarity transistor-type power supply is further designed to avoid the unevenness of positive and negative solder joints caused by the polarity effect in single-sided double spot welding,further improving the process adaptability of the power supply.The main circuit of 4k A unipolar power supply adopts Buck step-down chopper circuit,and the main circuit of 2k A variable polarity power supply adopts H-bridge inverter circuit.The control system takes Microchip’s PIC32MK1024MCF064 chip as the core to design the relevant control circuit hardware,and designs the control software of the power supply based on C language programming.Based on the design of power supply’s main circuit,control circuit and control software,the main circuit and control circuit hardware PCB boards were made,the prototype assembly and the construction of the test platform were completed,and the control effect of the power supply was tested.The test results show that the power supply can achieve stable constant current,constant voltage,constant power and two kinds of composited control.The developed 4k A unipolar transistor resistance spot welding power supply has a fast current rising rate,small ripple,and accurate parameter control.It can realize high-quality welding of small parts.The actual welding test shows that the designed constant voltage and current composited control mode can automatically adapt to the surface condition of the weldment,automatically adjust the output power according to the condition of the weldment,reduce the impact of the change of contact resistance on the spot welding quality of the miniature parts,and avoid welding spatter,improve the quality of spot welding;the constant pulse width and constant current composited control mode provides a method of breaking through the dense coating on the surface of miniature parts to achieve reliable welding of high-density plated weldments.In addition,the developed 2k A variable polarity power supply has a pulse width control mode,its current rising speed is fast,the ripple is small,and the welding parameter setting is flexible and precise,which further improves the process adaptability of the power supply for single-sided double spot welding. |
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