The hottest stud welder and its welding technology

2022-09-19
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Analysis of stud welding machine and its welding process in daily life

welding equipment manufactured by different manufacturers is used, and its welding process parameters are also different. Therefore, multiple trial welding should be carried out, and the appearance and formation of the weld, the height and mechanical properties of the stud after welding should be tested. The so-called stud welding machine refers to the arc generated between the end face of metal or similar metal parts and the surface of another metal workpiece, and the pressure should be applied quickly when the joint surface melts, A method of completing welding. Stud welding method originated in 1918. Because this new welding technology has a series of advantages, such as fast, reliable, simplified process, reduced cost and so on, it has attracted widespread attention of countries around the world, such as rueva, who prepared PHA series microspheres as drug transportation carriers. After continuous improvement and improvement, it has developed rapidly, especially after the Second World War, and has been widely used in bridges, highways, housing construction, shipbuilding, automobiles Power station, electric control cabinet and other industries. It can weld low carbon steel, stainless steel, low alloy steel, copper, aluminum and their alloy studs, welding nails, pins, studs, etc. It is reported that 1) the annual welding volume of round stud (stud) in Japan is 60million, and the annual welding volume of special-shaped rod stud is 3million. It can be seen that the application scale of stud welding in steel structure buildings in Japan. In recent years, China's economic construction has developed rapidly, and the field of stud welding has become more and more extensive. Therefore, it is necessary to conduct in-depth research on stud welding technology and welding process, so as to improve the quality of 10 point wide joint used in the automotive industry and popularize this welding technology

stud welding technology has become a basic hot processing method in western developed countries. More than 80% of stud (stud) welding is completed by stud welding machine. The first stud welding machine was successfully developed in Chengdu in 1986. As for the application of stud welding technology, it was only gradually launched in the 1990s, and now it has only a history of more than 20 years. Therefore, stud welding is still a newly emerging industry in our country, and there are many gaps between welding equipment and welding technology and foreign countries. It is the sacred mission of China's stud welding industry to analyze this gap and gradually shorten it until it catches up with and surpasses the world level

1. Classification of stud welding machines

stud welding machines are divided into arc stud welding machines and capacitor discharge stud welding machines. The former uses arc welding rectifier as the power source for welding, and the latter uses the energy stored in capacitors for instantaneous discharge for welding. See Table 1 for the characteristics and application of the two welding methods

Table 1 Characteristics of arc stud welding and capacitive discharge stud welding welding welding mode welding time twms weldable stud diameter DMM welding current ia protection mode minimum plate thickness arc stud welding ceramic ring protection> 1003 ~ 25300 ~ 3000 ceramic ring 1/4d but not less than 1mm gas protection> 1003 ~ 16300 ~ 3000 gas 1/8d but not less than 1mm short cycle welding ≤ 1003 ~ 12 ≤ 1500 unprotected or gas protection 1/8d but not less than 0.6mm arc capacitive discharge stud welding <1 03 ~ 10 ≤ 3000 (peak) does not protect 1/10d but cannot be less than 0.5mm note: the minimum plate thickness refers to the thickness to avoid burning through

1.1 arc stud welder

arc stud welder is composed of welding power supply, controller, welding gun, ground wire pliers, welding cable, etc. However, the welding power supply of most welding equipment is combined with the controller, which is called the host. The more advanced control method is to use a microprocessor to accurately set and timely control the welding current, welding time and other parameters in the welding process. The welding power supply is generally thyristor controlled or inverter type arc welding whole electronic universal testing machine, which is a frequently used testing machine product type streamer. Inverter type arc welding rectifier is undoubtedly the first choice of welding machine because of its small volume, light weight and good dynamic characteristics. However, due to the limitation of high-power devices, at present, the arc welding rectifier controlled by thyristor is still the main type of high-capacity welding machine. However, no matter what kind of welding power supply structure, its safety requirements should comply with the provisions of GB15579. The DC welding power supply for stud welding shall have the following characteristics:

a. the welding power supply shall have reduced static and external characteristics. Only in this way can the stability of the arc be maintained and the welding quality be guaranteed

b. The welding power supply should have arc striking current (40 ~ 50a) and high no-load voltage (70 ~ 100V). To ensure 100% success rate of arc striking, the no-load voltage of stud welding with large diameter even exceeds 100V. Only in this way can we meet the needs when the lifting height is large

c, higher load voltage is required. According to the definition of the falling characteristics of arc welding power source, when the welding current is ≥ 600A, its load voltage should remain 44V unchanged. The welding cables of the welding machines used at the construction site are long, some of which are as long as 50m, and the voltage drop is very large. If the load voltage is not increased to compensate, its welding ability will be reduced. If the cross-sectional area of the welding cable is not prepared according to iso14555, the situation will be more serious and even unable to weld. This is one of the main reasons why the maximum diameter of welding studs of welding machines with the same current level manufactured by different manufacturers is quite different

d, the welding current should have a sharp rise front. The biggest feature of stud welding is the instantaneous high current, so it is required that the welding current should reach its peak within 32ms after the welding power supply is connected. For short cycle stud welding, when the welding current rises, the European standard for headlights has been modified recently. The time should be shorter, otherwise the welding time may have arrived, but the welding current has not reached its peak. If the set welding current is not proportional to the energy obtained by stud welding, it is difficult to ensure the welding quality

the only way to increase the rising speed of welding current is to reduce the inductance of reactor. The reason why the ordinary arc welding rectifier needs to increase the reactor is to limit the rise speed of short-circuit current and the peak value of short-circuit current in addition to filtering, so as to reduce the impact current during arc striking, reduce spatter and arc crater, and avoid burning through the workpiece. Stud welding is different. It is carried out according to the set logic sequence of arc striking, stud lifting, and connecting the main power supply. In other words, the main welding power supply is connected only when there is a certain gap between the stud and the workpiece, so the spatter during arc striking is avoided. In fact, the biggest "splash" of stud welding is the splash that occurs instantly when the stud is pressed into the molten pool

it has been proved by tests that three-phase full wave silicon rectifier power supply (ripple coefficient γ= 0.042), even if there is no filter reactor, stud welding can still be carried out. The reactor of welding power supply controlled by thyristor for stud welding is only filtering, so it can be greatly reduced. As for how much reduction? It depends on the main circuit structure of the power supply and the current regulation range

e. the power supply should have a small internal impedance. The electrical insulation of the main circuit of the welding power supply adopts class H heat-resistant grade. Compared with class B, it has the advantages of small volume and light weight, and is highly respected by people. But after in-depth analysis, it is not perfect. Gb11021 stipulates that the maximum temperature of class H and class B heat-resistant grades are 180 ℃ and 130 ℃ respectively, and the temperature of class H is about 40% higher than the allowable temperature of class B. In other words, when designing the main circuit, the current density of the coil can be greatly increased to reduce the cross-sectional area of the conductor. This is followed by an increase in the resistance of the conductor, that is, the impedance of the circuit. This is a fatal disadvantage for stud welding machine with high current welding. If the insulation of the main circuit of the welding power supply is changed from level B to level H, the reduction of the cross-sectional area of all wires in the secondary circuit will lead to the increase of the total resistance, even if it is only 0.006 Ω. Based on the welding current of 2500A, the increased power consumption is 37.5kw, plus the increased power consumption of the primary of the main transformer, which is quite considerable. The increase of the power consumption of the main circuit of the welding power supply is bound to reduce the output welding power and reduce the welding capacity, which is the price of the reduction of volume and weight. In other words, when welding studs with the same diameter, class H welding machine requires higher power than class B insulated welding machine to achieve the same effect, and the efficiency is significantly reduced. Domestic RSN arc stud welding machine, with class B insulation, can weld studs with d=30mm, which is impossible for the same class of class H insulation arc stud welding machine

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