Definition of resistance welding and laser welding
Resistance welding is a manufacturing process and technology of joining metal or other thermoplastic materials such as plastics by heating.
It is a method of welding by applying pressure through the electrode after the workpiece is combined and using the resistance heat generated by the current passing through the contact surface and adjacent area of the joint.
Laser welding is a high-efficiency, precise, non-contact, pollution-free and radiation-free welding method using high-energy density laser beam as heat source.
Welding Equipment classification
Classification of resistance welding equipment
According to welding process, it is divided into:
Spot welding machine, projection welding machine, seam welding machine and butt welding machine.
According to the energy supply mode, it is divided into:
Single phase power frequency welder, secondary rectifier welder, three-phase low-frequency welder, energy storage welder and inverter welder.
Classification of laser welding equipment
According to the welding method, it is divided into:
Spot welding, continuous welding, butt welding, overlap welding
According to the light output mode, it can be divided into:
Pure fiber laser welding, hard optical path fiber transmission laser welding, YAG laser welding, semiconductor laser welding.
Classification of resistance welding
Resistance welding methods mainly include spot welding, seam welding, projection welding and butt welding (resistance butt welding and flash butt welding)
1. Spot welding
Spot welding is a resistance welding method in which the weldment is assembled into a lap joint, pressed between two cylindrical electrodes, and the base metal is melted by resistance heat to form a welding spot.
Spot welding is mainly used for sheet welding.
Process of spot welding
① Prepress to ensure good contact with the workpiece.
② Power on to form nugget and plastic ring at the welding joint.
③ Power off forging to make the nugget cool and crystallize under the continuous action of pressure to form a solder joint with dense structure and no shrinkage cavity and crack.
2. Seam welding
The process of seam welding is similar to that of spot welding, except that the rotating disc-shaped roller electrode is used to replace the cylindrical electrode, the weldment is assembled into a lap or butt joint and placed between the two roller electrodes, the roller pressurizes the weldment and rotates, and continuously or intermittently sends power to form a continuous weld.
Seam welding is mainly used for welding structures with regular welds and sealing requirements, and the plate thickness is generally less than 3mm.
3. Projection welding
Projection welding is a variant of spot welding;
There are prefabricated bumps on a workpiece. During projection welding, one or more nuggets can be formed at the joint at one time.
4. Resistance butt welding
Resistance butt welding is a method to assemble weldments into butt joints, make their end faces in close contact, heat them to the plastic state by resistance heat, then cut off power and quickly apply upsetting force to complete welding.
Resistance butt welding is mainly used for weldments with simple section, diameter or side length less than 20mm and low strength requirements.
5. Flash butt welding
Flash butt welding is a method to assemble the weldment into a butt joint, connect the power supply, gradually move the end face closer to local contact, heat these contact points with resistance heat, generate flash under the action of large current, melt the end metal, and then cut off the power and quickly apply upsetting force to complete the welding when the end reaches the preset temperature within a certain depth range.
The joint quality of flash welding is better than that of resistance welding, the mechanical properties of the weld are equivalent to that of the base metal, and there is no need to clean the pre-welded surface of the joint before welding.
Flash butt welding is often used for welding important weldments.
It can weld the same metal or different metal;
It can weld 0.01mm metal wire or 20000mm metal bar and profile.
Disadvantages of resistance welding:
- At present, there is still a lack of reliable nondestructive testing methods, and the welding quality can only be checked by the destructive tests of process samples and workpieces, as well as by various monitoring technologies.
- The lap joint of spot and seam welding not only increases the weight of the component but also forms an included angle around the weld nugget of the two plates, resulting in low tensile strength and fatigue strength of the joint.
- The equipment has high power, high mechanization and automation, which makes the equipment cost high and maintenance difficult, and the commonly used high-power single-phase AC welding machine is not conducive to the balanced operation of the power grid.
Advantages of laser welding:
- The heat input can be reduced to the minimum required amount, the metallographic change range of the heat-affected zone is small, and the deformation caused by heat conduction is also the lowest.
- The workpiece can be placed in a closed space (vacuumized or under the control of internal gas environment).
- It is easy to carry out high-speed welding by automation, and can also be controlled by digital or computer.
- If perforated welding is used, the depth to width ratio of weld bead can reach 10:1.
- It is not affected by magnetic field (arc welding and electron beam welding are easy) and can accurately align weldments.
- There are a wide range of weldable materials, and various heterogeneous materials can also be joined to each other.
- There is no need to use electrodes, and there is no concern of electrode contamination or damage. Because it is not a contact welding process, the loss and deformation of machines and tools can be minimized.
- No vacuum or X-ray protection is required.
- The switching device can transfer the laser beam to multiple workstations.
- When welding thin materials or fine diameter wires, it will not be easy to have the trouble of remelting like arc welding.
- The welding process parameters of 32mm thick single pass welding have been verified to be qualified, which can reduce the time required for thick plate welding and even save the use of filler metal.
- The laser beam can be focused on a small area and can weld small and closely spaced parts.\
- The laser beam is easy to focus, align and guided by optical instruments, can be placed at an appropriate distance from the workpiece, and can be guided between machines and tools or obstacles around the workpiece. Other welding rules cannot be played due to the above space constraints.
- It can weld more than two metals with different physical properties (such as different resistances).
It can be seen that laser welding is far better than traditional resistance welding in terms of welding advantages, welding quality, welding cost and welding benefits.
It also has a wide range of applications. It is a necessary configuration for welding processing in the future.
Its only disadvantage is that the purchase cost will be relatively high. However, its application, production efficiency and benefit are unmatched by any other equipment.