Introduction to friction welding and its advantages and disadvantages
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1. Friction welding concept
FWR refers to a method of welding by using the heat generated by friction on the contact surface of the workpiece as a heat source to cause plastic deformation of the workpiece under pressure.
Under the action of pressure, under the action of constant or increasing pressure and torque, the relative motion between the welding contact end surfaces is used to generate friction heat and plastic deformation heat on the friction surface and its nearby areas, causing the temperature of the friction surface and its nearby areas to rise to In the temperature range close to but generally lower than the melting point, the deformation resistance of the material decreases, the plasticity increases, and the oxide film at the interface is broken. Under the action of the upsetting pressure, the material undergoes plastic deformation and flow, and occurs through molecular diffusion and recrystallization at the interface. Solid state welding method to achieve welding.
2. The essence of friction welding
It is very common for the metal surfaces of mechanical parts to bond and weld due to friction. In the process of metal cutting and high-speed rotation of machines, it is often found that the surfaces of two metal parts are welded together due to friction and heat. For example: during turning processing, built-up edge occurs on the turning tool; during drilling processing, the drill bit and the workpiece are often bonded together; the sliding bearing is stuck due to shaft burning, etc. Of course, these situations are always the kind of accidents people try to avoid. Analyzed as a welding phenomenon, their process is not perfect and the welding quality is not ideal. However, our analysis of these bonding and welding phenomena will help us understand the essence of Friction Weld Process.
Friction destroys the oxide film on the metal surface. Frictional heating reduces the strength of a metal but increases its plasticity. The metal on the friction surface produces plastic deformation and flow, which prevents oxidation of the metal, promotes the mutual diffusion of welding metal atoms, and forms a strong welding joint. This is the essence of Friction Weld Process.
3. Friction welding process
Friction welding usually consists of the following four steps: (1) conversion of mechanical energy into thermal energy; (2) plastic deformation of the material; (3) forging force under thermoplasticity; (4) intermolecular diffusion and recrystallization.
The biggest difference between Friction Weld Process and traditional fusion welding is that during the entire welding process, the temperature at which the metal to be welded gains energy and rises does not reach its melting point, that is, the metal is a forged-like solid phase connection in a thermoplastic state.
Compared with traditional fusion welding, Friction Weld Process has high quality welding joints, can achieve the same strength as the weld seam strength and the strength of the base material, has high welding efficiency, stable quality, good consistency, and can realize welding of dissimilar materials, etc.
4. Characteristics of friction welding
The reason why FWR develops very rapidly and is widely used is because it has a series of advantages. These advantages include the following aspects:
(1) The welding quality of the joint is good and stable. The scrap rate of aluminum-copper transition joints produced by low-temperature Friction Weld Process in my country is less than 0.01%; boiler plants use Friction Weld Process instead of flash welding to produce economizer serpentine tubes, and the welding scrap rate is reduced from the original 10% to 0.001%. West Germany used Friction Weld Process instead of flash welding to produce automobile exhaust valves, and the welding scrap rate dropped from the original 1.4% to 0.04~0.01%. As can be seen from the above examples, the scrap rate of Friction Weld Process is very low, about 1% of that of general welding methods.
(2) Suitable for welding dissimilar steels and dissimilar metals. Friction Weld Process can not only weld ordinary dissimilar steels, but also weld dissimilar steels and dissimilar metals with widely different mechanical and physical properties at room temperature and high temperature, such as carbon structural steel-high-speed tool steel; copper-stainless steel, etc. In addition, it can also weld dissimilar metals that produce brittle alloys well, such as aluminum-copper, aluminum-steel, etc.
(3) The dimensional accuracy of the weldment is high. The maximum error in the total length of the diesel engine pre-combustion chamber produced by Friction Weld Process is ±0.1 mm. Some special Friction Weld Process machines can ensure that the length tolerance of the weldment is ±0.2 mm and the eccentricity is less than 0.2 mm. Therefore, Friction Weld Process is not only used to weld blanks, but also to weld assembled finished products.
(4) The welding machine has low power and saves energy. Compared with friction welding and FWR, the energy saving is about 80~90%.
(5) The working place of FWR is hygienic, without sparks, arc light and harmful gases, which is conducive to environmental protection and is suitable for use in automatic production lines together with other advanced metal processing methods.
5. Advantages of friction welding
FWR is a method of welding materials through the heat generated by thermal friction. Compared with traditional welding methods, it has several obvious advantages:
(1) No heating equipment required: FWR does not require external heating equipment, but uses the heat generated by rotating friction to weld. This allows Friction Weld Process to be performed under simpler and faster conditions.
(2) Low energy consumption: Since no external heating equipment is required, FWR usually consumes less energy than traditional welding methods, so it has more advantages in energy utilization.
(3) Fast welding speed: FWR is usually faster than traditional welding methods because there is no need to wait for the heating equipment to heat up during the welding process, but can start welding immediately.
(4) Wide range of applications: FWR can be used for welding various materials, including metals, plastics, etc., so it has a wide range of application prospects.
(5) High quality of welded joints: Since the heat generated during FWR is relatively uniform, welded joints usually have higher quality, with better weld strength and sealing.
6. Friction welding defects
(1) High equipment cost:
The equipment required for FWR is often complex, including specialized machines that need to control parameters such as friction, pressure and rotational speed. The cost of these equipment is usually higher, which may put some pressure on corporate investment.
(2) Material selection is limited:
Although FWR can be applied to weld a variety of materials, not all materials are suitable for this welding method. For example, some high-temperature, fusible materials may not be suitable for Friction Weld Process because material damage or deformation may occur during the welding process.
(3) Restrictions on the shape and size of workpieces:
Because Friction Weld Process usually requires the workpiece to rotate or vibrate during the welding process, there may be certain restrictions on the shape and size of the workpiece. Especially for workpieces with complex shapes or larger sizes, special fixtures or equipment may need to be designed to achieve FWR.
(4) High demand for welded joints:
Compared with other welding methods, FWR has higher requirements on joint quality and geometry. If the surface quality of the welded joint is poor or the geometry is inappropriate, it may affect the welding quality and the strength of the joint.
(5) High technical requirements:
FWR requires precise control of welding parameters, including friction, pressure, rotation speed, etc., so it requires operators to have certain professional knowledge and skills. This may require additional training and learning costs.
(6) Smoke and odor may be produced during the welding process:
Some smoke and odor may be produced during FWR, especially when the materials being welded contain certain harmful substances. This may require appropriate safety measures to protect the health of the operator.
7. FWR category
After years of development, FWR technology has developed many classifications of Friction Weld Process: friction stud welding, FWR, third body friction welding, embedded FWR, inertial Friction Weld Process, friction stir welding, and radial friction welding. , linear FWR and friction stack welding, etc.
The definition of traditional Friction Weld Process: a pressure welding method that uses the heat generated by the friction between the surfaces of the weldment to bring the end face to a thermoplastic state, and then quickly forges to complete the welding.
