Discussion on the development of precision spot welding technology for metal container parts
Text / Xin Qiaojuan
In the manufacture of metal container products, a large number of electric resistance welding is involved. The electric resistance welding for the metal container is mainly the seam welding of the can body (barrel), the spot welding of the barrel body, the spot welding of the lifting ear and the sealer, etc., and some parts are small in size or complex in shape, so that Welding is difficult and requires a dedicated point (convex) welder. At present, the welding technology of metal container cans (barrels) in China is equivalent to the level of developed countries, but the welding quality of metal container parts is still quite a lot. For example, common problems include falling ear, barrel plug buckle, and barrel hoop welding. These technical problems mainly include unstable welding quality, easy damage to the container, difficulty in forming normal fusion, and low welding pass rate. The parts are even difficult to weld with general resistance spot welding.
The reason why the resistance welding of metal container parts often has problems, the main reason is that the equipment and technology of resistance welding of metal container parts are not precise enough. We have used a lot of energy to solve the improvement of seam welding technology, and the parts of metal container parts. Resistance welding technology has not made much effort. Therefore, our metal container parts resistance welding technology needs to develop in a more precise direction. The precision of resistance welding includes fine adjustment of power supply, precise control of parameters and precision stabilization of pressurizing mechanism. Multi-technology integration constitutes a precision resistance welding system.
Resistance welding power supply provides resistance heating energy for resistance welding. Its overall development process has emerged as single-phase power frequency AC spot welding power supply, DC pulse spot welding power supply, three-phase low-frequency spot welding power supply, secondary rectification spot welding power supply and capacitor. Energy storage spot welding power supply, in recent years, there has been an inverter spot welding power supply. Power supplies for part welding mainly include single-phase AC power, capacitor energy storage, and inverter power. The adjustability of the inverter resistance spot welding power supply is significantly improved, which is a better power supply, but there is a certain difference between the inverter resistance spot welding power source itself. In order to achieve precision welding of miniature parts, the inverter resistance spot welding power supply technology needs to be further developed.
First, metal container parts commonly used spot welding power supply output adjustment principle and characteristics
1. Single-phase power frequency AC spot welding power supply
The equivalent circuit and current waveform of the single-phase thyristor spot welding power supply are relatively simple. As long as the control angle of the thyristor is changed, the primary current of the welding transformer can be adjusted to control the welding current of the secondary welding circuit.
2, capacitor storage resistance spot welding power supply
Capacitor storage spot welders also have other disadvantages. Capacitor energy storage welding machine energy conversion efficiency is lower than other types of welding machine, storage capacitors and welding transformers are bulky, power circuit parts are complex, welding machine costs are high, the capacity is higher and higher; storage capacitors are often in the process of rapid charge and discharge , medium loss, short life and so on.
3, inverter DC resistance spot welding power supply
Compared with general single-phase power frequency AC resistance spot welding power supply and capacitor storage spot welding power supply, inverter DC resistance spot welding power supply has the following advantages: small and lightweight welding transformer; high-speed precision control, good dynamic response; low output pulsation rate DC welding current; three-phase balanced load, high power factor, good energy saving economy, etc.
Although the inverter DC spot welding power supply has so many advantages, its manufacturing cost is relatively high and the circuit is relatively complicated. For the spot welding of metal container parts, due to its controllability, it is an ideal power source, the development of power electronic devices and the maturity of inverter technology, such power supplies have gradually gained application. Considering the need to precisely adjust the output energy and fast response speed of spot welding of metal container parts, the resistance welding inverter power supply technology needs further development.
Second, the development direction of inverter welding spot welding technology for metal container parts
Some metal container parts are difficult to spot weld. In order to improve the spot welding yield and spot welding quality, and to expand the application of resistance spot welding technology in the manufacture of metal container parts, it is necessary to further develop the resistance spot welding technology of metal container parts.
1. Improve power supply output adjustment resolution and response speed.
Due to the large resistance spot welding current, the inverter frequency of the resistance spot welding inverter power supply is much lower than that of arc welding or other power supply, usually about 1 kHz, which adjusts the resolution and control response speed. Correspondingly lower. In recent years, there have been 2 kHz, 4kz and 5kHz products on the market, and there are reports of 25kHz technology. For precision spot welding, increasing the inverter frequency is an inevitable trend. The improvement of the inverter frequency requires efforts in the design of the transformer and the reduction of the loop loss, which directly affect the quality of the product. For the welding of small parts, the capacity of the welding power source is small, and it is easier to increase the inverter frequency, and it is more difficult for a high-power power source. Precision spot welding of micro-components can also use analog transistor power supplies, which have large energy losses, and improvements in inverter power supplies are expected to replace such power supplies.
2. Improve the welding current waveform and improve the process adaptability of welding parameters.
The common power supply is designed for single heating and two heating. The complicated power supply has three heating or current ramping control. Due to the complex structure and materials involved in precision spot welding, these waveforms do not meet the optimal welding requirements. For some material spot welding, the removal of the oxide film and the adjustment of the initial welding conditions can improve the consistency of the welding. For precision spot welding, the waveform is carefully designed, and even the waveform is adjusted to match the heating and cooling process of the material.
3. Develop real-time quality control technology for precision spot welding.
The real-time control of the spot welding process is an important means to eliminate various disturbances in the process and improve the production yield. Control methods include stable control of process parameters and feedback control of quality. The real-time control of spot welding quality is an important but long-term unsolved problem. The research of multi-parameter intelligent control has a good prospect.
4. Develop precision pressurization system.
Welding pressure is very important for spot welding. Welding of metal container parts requires precise pressurization guarantee, including small pressure stability, follow-up of mechanical system (fast response suitable for welding deformation), positional adaptability and accuracy. Position control, etc. Conventional pneumatic pressurization is difficult to adapt to the requirements of precision spot welding, and it is difficult to accurately control the pressure by using the amount of spring compression to trigger the welding energization. Other pressurization methods, including pressure sensor feedback control, require further investigation.
5. Improve the level of computer application.
The use of computer simulation technology, database technology to establish an auxiliary system for precision spot welding, will be a good help for the precision spot welding application of quite complex metal container parts. The collection and recording of welding data ensures the traceability of the product and is very important for the welding of important parts such as medical equipment. The development of a precision spot welder with networking technology facilitates the recording and updating of data, making it easy to remotely monitor and control.
Third, metal container parts resistance welding technology development recommendations
1. Compared with power frequency communication and capacitor energy storage welding power source, the precision inverter spot welding power source has good controllability, and has good process adaptability for spot welding of micro parts.
2. The inverter frequency of the precision inverter spot welding power source is improved, which is beneficial to improve the control resolution, the dynamic response of the power supply and the current stability. For precision spot welding power supplies for micro-components, it is necessary to further increase the inverter frequency and improve the power supply design.
3. Three-phase precision inverter spot welding power supply is more stable than single phase, and the grid load is balanced.
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