Application of the hottest stud welding technology

2022-09-23
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Application of stud welding technology

stud welding technology has the advantages of fast, reliable, simple operation and low cost. It can replace riveting, drilling, manual arc welding and brazing, and can weld carbon steel, stainless steel, aluminum, copper and its alloys. Now it has been widely used in automotive, shipbuilding and other fields. The history of applying stud welding technology in China is not long, but with the rapid development of China's economy and the continuous improvement of manufacturing level, stud welding technology is being adopted by more and more domestic enterprises

stud welding technology and principle

the method of welding studs or metal studs and other fasteners with similar characteristics such as wide measurement range, high accuracy and fast response to the workpiece is called stud welding. There are many ways to realize stud welding: resistance welding, friction welding, explosion welding and arc welding. At present, the most widely used method is arc stud welding. According to the different welding power sources, it can be divided into energy storage (capacitive discharge) stud welding and arc stud welding

1. energy storage stud welding

the energy required for welding is provided by charging capacitor discharge. When the capacitor discharge, a short-time arc appears between the stud and the workpiece. Zhang Jianfeng, chairman and general manager of CGNPC, said that the arc will melt a small amount of metal on the surface of the workpiece and the top of the stud. Then the stud is immersed in the molten pool, and the molten metal will be cooled quickly to form a welded joint. The welding time of energy storage stud welding is very short, usually within 5ms, without shielding gas; The molten pool is shallow, about 0.1mm, and the back of the workpiece is free of deformation and indentation, which is suitable for thin plate welding; It can be used to weld carbon steel, stainless steel, aluminum, copper and its alloys; The ratio of plate thickness to stud diameter can reach 1 ∶ 10

energy storage stud welding equipment can be divided into contact type and gap type according to the configuration of welding gun

contact stud welding relies on the built-in spring of the welding gun to compress the stud. The distance between the workpiece and the stud is guaranteed by the small boss on the top of the stud. When the capacitor discharges, the small boss vaporizes rapidly, and an arc appears between the stud and the workpiece. The heat generated by the arc makes the top of the stud form a melting layer, and the surface of the workpiece forms a very shallow molten pool. Under the pressure of the built-in spring of the welding gun, the stud sinks rapidly. Within 3 ~ 4ms, the stud immerses in the molten pool, the arc disappears, and the molten pool cools to form a welded joint quickly (see Figure 1)

Figure 1 contact stud welding process

the gap stud welding process is roughly the same as the contact stud welding, but different from the contact spring compression stud contacting the workpiece, the gap type lifts the stud from the workpiece surface to a certain distance by electric or pneumatic means, and then the stud sinks. At the same time, the capacitance discharges, and an arc is generated between the stud and the workpiece. Compared with contact welding, this welding method has shorter welding time

(1) welding process parameters. The technological parameters of energy storage stud welding mainly include: stud diameter, welding voltage, welding time and stud extension length. Energy storage stud welding has only one remarkable feature: the capacitor discharge process is not controllable, and the welding time is not adjustable. The stud extension length can be determined according to experience, usually between 1.0 ~ 1.5mm

the welding energy of energy storage stud welding is determined by the capacitance and charging voltage of the capacitor bank of the stud welding machine: w = Cu2, where W is the rated stored energy of the welding equipment, C is the total electrical capacity of the capacitor bank, and u is the charging voltage

the peak value of the instantaneous welding current of the energy storage stud welding equipment is about 1000 ~ 10000a, which depends on the equipment capacitance, charging voltage, welding circuit resistance and inductance. Generally speaking, the charging voltage is usually within 200V in consideration of the safety of the operator and the equipment itself. Since the capacitance of the equipment has been fixed when it leaves the factory, the charging voltage can only be adjusted during actual work, and the appropriate voltage value can be determined according to the diameter of the stud and the thickness of the workpiece plate

(2) equipment composition and characteristics. The energy storage stud welding equipment is composed of welding power supply, welding gun, ground wire pliers and hybrid cable. Add automatic feeder and other auxiliary equipment, which can be configured as semi-automatic or automatic stud welding equipment. According to the different welding power supply and stud specifications, the manual welding efficiency can reach about 15/min, and the automatic welding efficiency can reach about 50/min. The energy storage stud welding equipment is simple to operate and light. It is suitable for stud welding with diameter ≤ 10mm and low requirements for connection strength

2. Arc stud welding

arc stud welding is different from the capacitor discharge of energy storage welding. It is welded by DC power supply or inverter welding power supply controlled by thyristor. In the arc stud welding process, the metal melting amount of the stud and workpiece is more than that of the energy storage stud welding, and the penetration is deeper. The parameters that affect the welding quality are more complex, and the strength that the stud can withstand is also greater

arc stud welding can be divided into long-cycle stud welding and short-cycle stud welding according to the length of welding time. The working process of pull arc stud welding is (see Figure 2): the stud contacts the workpiece, and the stud is lifted by the stud clamping mechanism after being powered on. At this time, a stable combustion arc appears between the stud and the workpiece, and the arc heats up the top of the stud and the surface of the workpiece. Then the stud clamping mechanism presses the stud to sink to the workpiece molten pool, and forms a welding joint after being powered off. The difference between short-term stud welding and long-term stud welding is that the welding time is only one tenth to one tens of times that of long-term stud welding. In addition, short cycle stud welding has a guiding arc before the welding arc, which is used to remove the oil, grease or coating on the top surface of the workpiece or stud

Figure 2 short cycle stud welding process

(1) welding process parameters. The welding process parameters of arc pulling studs mainly include: welding current, welding time, arc striking current, arc striking time, lifting height, stud extension length and nail feeding time

welding current - mainly selected according to the flange diameter at the top of the stud. For ordinary low-carbon steel, the relationship between welding current and stud diameter is: short cycle stud welding, I = (95 ~ 110) d, d = 3 ~ 15mm; Long cycle stud welding, I = (50 ~ 100) d,

d = 16 ~ 30mm. For galvanized studs or studs welded to galvanized workpieces, the welding current needs to be increased by 20%. Of course, in practice, the welding time can be adjusted according to the thickness of the workpiece

welding time - short cycle stud welding, TW = (4 ~ 5) d, d = 3 ~ 15mm; Long cycle stud welding, TW = (10 ~ 100) d, D ≥ 16mm. For short cycle stud welding, the welding time is usually between 20 ~ 100ms; Long cycle stud welding usually requires high welding strength, deep weld pool and welding time of 200 ~ 2000ms. Whether short-term stud welding or long-term stud welding, the welding time and welding current together constitute the welding input heat, which can be coordinated and flexibly adjusted

arc striking current and arc striking time - these two process parameters only appear in short cycle arc stud welding, in order to remove oil, grease or coating on the surface of the workpiece and the flange on the top of the stud. The arc starting current is generally 30 ~ 50a, and the adjustable range is relatively small; The arc striking time is usually 20 ~ 40ms. At present, the arc striking current and arc striking time of many brands of welding machines have been set to fixed values at the factory and cannot be adjusted

lifting height - the lifting height of the stud is an important parameter that determines the welding quality. It is proportional to the diameter of the stud. The lifting height can effectively prevent arc instability and poor welding formation caused by short circuit during droplet transfer. However, too high lifting height also has disadvantages: first, due to the growth of arc, magnetic bias blowing is easy to occur, which affects the welding quality; The second is to increase the number of weld pores. This is a sensitive factor affecting welding quality. For short cycle stud welding, the lifting height of the welding gun that uses electromagnetic induction to lift the stud is usually 1.2mm, and the lifting height of the welding gun that uses servo motor to lift the stud is usually 1.5mm

stud extension length - for long-cycle stud welding, the stud extension length is the sum of the stud melting length and the workpiece molten pool depth, which is proportional to the stud diameter, and the empirical value is 1.5 ~ 6mm; For short cycle stud welding, the stud extension length of electromagnetic welding gun is the length of stud melting, and the penetration of machined parts is usually 1.2mm; The stud of servo motor welding gun extends out of the end face of the gun nozzle for a certain length, which is only convenient for the stud to contact with the workpiece and form a stable circuit short circuit, usually 2.2 ~ 3mm. The melting length of the stud of the servo motor welding gun and the depth of the molten pool of the workpiece are independent parameter values, which have no direct relationship with the extension length of the stud

welding current, welding time, stud lifting height and stud extension length are four important parameters of arc stud welding process. In practice, the market prospect is promising, and it should be set according to the stud diameter, workpiece thickness and material. Carry out multiple trial welding and adjust the appropriate process parameters according to the welding effect

(2) equipment composition and characteristics. The arc stud welding equipment is mainly composed of welding power supply, control system, welding gun and grounding pliers. According to requirements, it can also be equipped with automatic nail feeding equipment. Generally, the welding power supply is combined with the control system, which is called the welding host. At present, advanced welding machines use microprocessors and liquid crystal displays, which can intuitively and accurately set, record and store welding parameters, and can monitor and display in real time during the welding process. Most welding machines use thyristor controlled arc welding rectifier; The advanced welding machine power supply adopts inverter DC power supply. In order to obtain a stable arc, the stud welding power supply is a DC power supply with steep external characteristics and high no-load voltage. The biggest feature of arc stud welding is the instantaneous high current, so it is required that the welding current of the welding power supply reaches the set value in a very short time, and the current rise time of the short cycle stud welding machine is shorter. If the capacity of the power supply is insufficient, the voltage of the welding power supply will be unstable, resulting in poor welding quality. At present, as far as welding guns are concerned, long-term stud welding is dominated by electromagnetic induction welding guns with manual nail feeding; The servo motor welding gun with automatic nail feeding is mainly used for short cycle stud welding at the position with high production rate. Of course, the manual welding gun can be used for short cycle stud welding at the position with low production rate

application of stud welding technology in the automotive industry

stud welding has the advantages of fast, reliable, simple operation and hole free connection. It is replacing the riveting, tapping and drilling connection processes in automotive manufacturing. At present, the role of studs in the car compartment is to fix wire harnesses, interior trims and carpets; The function outside the carriage is to fix the harness, oil pipe, brake oil pipe, heat shield, deflector and other chassis accessories. Now, the use of studs in car manufacturing is increasing. Take the models of DPCA as an example, the studs of Elysee ◎ sample preparation instrument: more than 5 standard samples are obtained by injection molding machine or the amount of machine added samples is more than 50, the amount of studs used in Peugeot 307 is 106, and the amount of studs used in Citroen C5 is 187. The types of studs commonly used in car manufacturing are shown in Figure 3

Figure 3 types of studs commonly used in car manufacturing

energy storage stud welding. The welding time and welding current are not adjustable, and the penetration is very shallow, so it is rarely used in the automotive industry. At present, the stud welding process used in the automotive industry is short cycle arc stud welding, mainly using inverter type

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