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Guide for welding and backing of aluminium
Author： From： Time：2017/11/23 Hits：6216
Guide for welding and backing of aluminium
Base metal preparation: to weld aluminum, welders must carefully clean the base metal, and use oil or solvent to eliminate any oxide and hydrocarbon pollution on the surface of aluminum. The oxide on the surface of the aluminum melts at 3700 degrees Fahrenheit, while the aluminum base metal below melts at 1200 degrees Fahrenheit. Therefore, any residual oxide on the surface of the aluminum base metal will restrict the penetration of the filler metal to the machined parts.
To eliminate the oxide on the surface of aluminum, stainless steel wire brush or solvent corrosion can be used. When using stainless steel brush, it can only be brushed in a fixed direction. Be careful not to use too much force and carelessness: rough action will form oxide embedded in aluminum base metal. Together, only use stainless steel brush on the surface of aluminum, not on stainless steel or carbon steel. When using the method of chemical solvent, make sure that the solvent is removed before welding.
In order to minimize the adverse effects of hydrocarbons by using oil agents or solvents, oil removers should also be used. Together, make sure that the degreaser does not contain any hydrocarbons.
Preheat: preheat aluminum parts to help avoid welding cracks. The preheating temperature should not exceed 230 degrees Fahrenheit. Use a thermometer to monitor the temperature to avoid overheating. In addition, continuous welding at the beginning and end of the welding area can help to strengthen the preheating effect. The welder shall also preheat a thick piece of aluminum when welding the thin material.
Disposal speed: the process of aluminum welding requires "high temperature and high speed" disposal. Unlike steel, aluminum's higher thermal conductivity requires higher current and voltage settings at higher temperatures and higher welding speeds. If the welding speed is too slow, there will be too much welding penetration, especially when welding thin materials.
Maintenance Gas: argon is the most commonly used aluminum welding maintenance gas because of its excellent cleaning function. When welding 5xxx series aluminum alloy, the maintenance gas used is a mixture of argon and helium. At most 75% helium can reduce the effect of MgO.
Welding wire: select aluminum filler wire near the melting point of base metal. The more welders can constrain the ablation scale of metal, the simpler the alloy is to be welded. Use a 3 / 64 - or 1 / 16 inch diameter filler wire. The larger the diameter of the filler wire, the simpler the wire feeding. To weld thin profile data, use 0.035 inch diameter welding wire plus pulse welding processing, low-speed wire feeding (about 100 to 300 inches per minute), the effect will be ideal.
Concave data welding: in aluminum welding, spark splashing will cause welding failure. Cracks are the result of shortening from high-speed thermal expansion of aluminum to a lot of cooling. The risk of welding crack is greatest when welding concave data, because the small pit on the data surface will be shortened, and the data will be torn when it is cooled. Therefore, the welder should make a pit with convex shape, which will compensate for the shortening of welding.
Selection of power supply: when selecting the voltage of gas metal arc welding machine for welding aluminum, the first consideration is the question of droplet transfer splash or pulse.
Stable current and voltage welding machine can be used to spray arc welding. The eruption arc is to erupt a very small molten metal drop on the electrode to the base metal through the arc. In the application of welding thick aluminum, the welding current is required to exceed 350 a, which can achieve the best effect.
Pulse transition is usually carried out with the support of inverter. The new power supply includes a built-in pulse program. In the gas metal arc welding pulse time, each current pulse has a drop of filler metal from the electrode to the workpiece, in this process, there will be a positive droplet transfer, to less spatter and higher welding speed. When using the pulse gas metal arc welding technology to weld aluminum, the control of heat input is also very good, and it can easily carry out the dislocation welding, so that the welder can carry out the welding of thin materials with low wire feeding speed and low current.
Wire feeder: the preferred way to send soft aluminum wire in long distance is push-pull wire feeding. In this way, the closed wire feeding organization is used to maintain the welding wire from environmental impact. The stable torque in the wire feeding organization and the variable speed motor act as the wire feeding power to guide the welding wire through the welding gun together to reach a stable output and speed. The high torque motor of the welding gun pulls the welding wire to ensure the coordination of wire feeding speed and welding arc.
Some welders use the same wire feeder to transport steel wire and aluminum wire. In this case, the use of plastic or nylon liner can help achieve smooth and coordinated wire (aluminum) feeding. During detailed welding, try to keep the welding gun cable vertical to reduce wire feeding resistance. Carefully check the coaxiality between the automatic roll and the guide tube to avoid aluminum scraping.
Use of automatic rollers planned for aluminum. Set the automatic roll tighter to reach the constant wire feeding speed. Too tight setting will lead to deformation of welding wire and unstable wire feeding; too loose setting will lead to unstable wire feeding. Both conditions will directly lead to the instability of welding arc and welding porosity.
Welding gun: use different welding gun liners to weld aluminum. To avoid the wire being disturbed, try to tighten both ends of the pad together to eliminate the gap between the pad and the gas diffuser.
