The quality of the weld of the electronic pulse spot welding machine directly affects the mechanical properties, conductivity and appearance integrity of the welded parts, and this process is comprehensively regulated by multiple factors. From equipment parameter settings to workpiece pretreatment, from electrode performance to environmental conditions, subtle differences in each link may lead to fluctuations in weld quality. The following is an in-depth analysis of the core factors affecting weld quality from the perspective of technical principles and practical applications.
The peak value, width and frequency of the pulse current are the key parameters that determine the quality of the weld. The current peak directly affects the welding heat input - a high peak value can easily cause metal splashing and burn through the parent material; a low peak value may cause a cold weld due to insufficient energy. For example, when welding a 0.5mm thick stainless steel plate, the peak current needs to be controlled within the range of 8-12kA. A high peak current will cause the molten core to expand rapidly and break through the surface of the plate, forming pits or perforations; a low peak current will not be able to completely melt the parent material, resulting in insufficient weld strength.
The pulse width (i.e., the power-on time) is closely related to the heat accumulation effect. Shorter pulse widths are suitable for thin parts or heat-sensitive materials (such as electronic component pins) to reduce thermal deformation; longer pulse widths are used for thick parts welding, but overheating should be prevented to cause coarse grains. In terms of frequency, high-frequency pulses (such as above 100Hz) can achieve more precise energy control and are suitable for precision welding, while low-frequency pulses (such as below 50Hz) may cause local overheating due to concentrated heat input.
Electrode pressure affects the welding process by changing the contact area and contact resistance between the workpieces. When the pressure is insufficient, the contact resistance is too large, which is prone to local overheating, spattering, and even adhesion between the electrode and the workpiece; excessive pressure will squeeze the base material, resulting in a reduction in the size of the molten core and a decrease in the strength of the weld. For example, when welding aluminum alloys, the electrode pressure needs to be maintained at 2-3kN, which can not only press the surface oxide film to reduce the contact resistance, but also avoid excessive flattening of the workpiece.
Electrode wear is a hidden influencing factor in long-term use. After frequent welding, the end face of the copper alloy electrode will wear due to high-temperature oxidation and plastic deformation, resulting in an increase in the contact area, a decrease in the current density, and a decrease in the weld core. When the electrode end face diameter is worn from the initial 5mm to 8mm, the welding current needs to be increased by 20%-30% to maintain the same nugget size, otherwise unfused defects are prone to occur.
The physical properties of the workpiece (such as electrical conductivity, thermal conductivity, and melting point) directly determine the difficulty of welding. Highly conductive materials (such as copper and aluminum) require a larger welding current to overcome rapid heat dissipation, while alloys such as stainless steel can use a smaller current due to their high resistivity. For example, when welding pure copper, the peak current required is more than 15kA, while welding 304 stainless steel of the same thickness only requires about 10kA.
The influence of surface condition is also significant. Oil stains, oxide films, and rust layers will increase contact resistance, resulting in local energy concentration or poor conductivity. If the oxide film (Al₂O₃, melting point 2050℃) on the surface of aluminum alloy is not removed, it may hinder the passage of current and cause a cold weld; the zinc layer on the surface of galvanized steel plate evaporates at high temperatures, which may cause violent spatter and needs to be pre-treated by pre-degreasing, mechanical grinding or chemical cleaning.
The welding time (i.e. pulse duration) and cooling rate jointly determine the growth and solidification process of the molten core. Under constant current, if the welding time is too short, the molten core will not be fully formed and the bonding surface strength will be insufficient; if it is too long, the molten core will be too large and the parent material will be burned through. For a 0.8mm thick low-carbon steel plate, the ideal welding time is usually 20-30 cycles (400-600ms at an industrial frequency of 50Hz), at which time the diameter of the molten core can reach 4-5mm, and the tensile shear strength meets the industrial standard.
The cooling rate affects the microstructure of the weld. Rapid cooling (such as direct heat conduction of copper electrodes) can form fine-grained structure and improve the toughness of the weld; slow cooling may cause coarse columnar crystals and reduce crack resistance. When welding high-strength steel, the cooling time is often increased by water-cooling the electrode or optimizing the pulse interval to avoid welding cracks caused by martensitic transformation.
The control system accuracy of the electronic pulse spot welding machine directly affects the parameter stability. The thyristor trigger circuit of old equipment may cause pulse waveform distortion due to component aging, while new digital control systems (such as DSP or FPGA) can control the current error within ±2% to ensure consistent welding energy each time. For example, in the welding of precision electronic components, current fluctuations exceeding 5% may cause the pad to fall off or the chip to overheat and damage.
The rigidity of the mechanical system should not be ignored. The elastic deformation of the electrode arm will cause pressure fluctuations during welding. Especially in high-current welding, the displacement between the arms may cause the actual pressure to deviate from the set value by more than 10%, affecting the consistency of the weld core. High-end equipment usually uses servo motors to drive electrodes, combined with real-time feedback from stress sensors to achieve closed-loop pressure control.
The indirect impact of environmental conditions on the welding process is often overlooked. In a low-temperature environment, the heat conduction of the workpiece is accelerated, and the welding energy may need to be increased by 10%-15% to compensate for heat loss; a high-humidity environment may cause the oxidation of the electrode surface to increase and the contact resistance to increase. Especially when welding active metals such as magnesium alloys, the hydrogen produced by the decomposition of water vapor may penetrate into the weld core and form pore defects. For example, when welding aluminum alloy in an environment with a humidity of more than 80%, the porosity of the weld can rise from 5% under normal conditions to more than 15%.
The operator's understanding and adjustment ability of equipment parameters directly affects the quality of welds. For example, when welding different batches of workpieces of the same material, the current or pressure parameters need to be fine-tuned due to differences in the surface treatment of the plate; novices often rely too much on default parameters, resulting in fluctuations in the quality of welds in different batches of products. In addition, details such as the frequency of electrode cleaning (such as sandpaper polishing the end face after every 500 welds) and the accuracy of workpiece clamping (such as whether the overlap meets the process requirements) also need to be controlled through standardized operating procedures.
The quality of the weld of the electronic pulse spot welding machine is the result of the coupling of multiple physical fields of electricity, heat, and force. It is necessary to establish a full-process control system from the dimensions of parameter setting, equipment maintenance, material adaptation, environmental control, and personnel training. Through the digital control system to achieve accurate energy output, combined with electrode wear monitoring and automatic compensation technology, and with the standardized surface pretreatment and process parameter database, the consistency and reliability of the weld can be maximized. In the field of precision manufacturing, the introduction of online detection technology (such as laser visual flaw detection) to monitor the solder joint morphology in real time can achieve closed-loop control of welding quality and ensure that the product meets high reliability requirements.
