Friction welding is a solid-state welding process that generates heat through mechanical friction between the surfaces of two workpieces, then applies axial pressure to forge the heated interfaces into a metallurgical bond. Unlike fusion welding methods, friction welding does not melt the base metals completely; instead, it raises the temperature of the faying surfaces to a plasticized state (below the melting point of the base materials). The combined action of frictional heat and axial forging pressure eliminates surface oxides and contaminants, breaks down the surface asperities, and promotes atomic diffusion and recrystallization at the interface, forming a dense, defect-free weld joint.

 

    2.1 Rotary Friction Welding (RFW)

    RFW is the most widely used friction welding variant, suitable for joining axisymmetric components (e.g., rods, tubes, shafts). One workpiece is clamped in a rotating chuck, while the other is fixed in a stationary fixture. The rotating workpiece spins at a high speed (typically 500–3000 rpm) and is brought into contact with the stationary workpiece under axial pressure. Frictional heat is concentrated at the interface; once the preset temperature or friction time is reached, the rotation stops abruptly, and an upsetting pressure is applied to complete the welding. Key parameters include rotational speed, friction pressure, friction time, and upsetting pressure. RFW features high welding efficiency (cycle time < 60 s per joint) and stable quality, making it ideal for mass production.

 

    2.2 Friction Stir Welding (FSW)

    FSW is a revolutionary solid-state welding technology invented by TWI in 1991, primarily designed for joining low-melting-point non-ferrous metals (aluminum, magnesium, copper alloys). A non-consumable cylindrical tool with a profiled pin and shoulder is inserted into the joint interface of two clamped workpieces. The tool rotates at a constant speed (300–2000 rpm) and moves along the weld seam direction; the shoulder generates frictional heat with the workpiece surface, while the pin stirs the plasticized material, mixing the two base metals and forming a solid-state joint. FSW requires no filler metal or shielding gas, and produces welds with minimal thermal deformation and no porosity or solidification cracks. It is widely used for welding large, thin-walled components (e.g., aircraft fuselages, high-speed train car bodies).

 

    2.3 Linear Friction Welding (LFW)

    LFW is tailored for joining non-axisymmetric components (e.g., aircraft engine blades, gear blanks). One workpiece undergoes reciprocating linear motion (frequency: 50–300 Hz, amplitude: 1–5 mm) relative to the stationary workpiece, generating frictional heat at the interface. After reaching the plasticization temperature, the reciprocating motion stops, and upsetting pressure is applied to form the joint. LFW can join dissimilar materials (e.g., titanium alloy blades to nickel-based superalloy disks) with high joint strength, meeting the strict performance requirements of aerospace components.

 

    2.4 Inertia Friction Welding (IFW)

    IFW is a variant of rotary friction welding that uses the kinetic energy of a rotating flywheel to provide frictional heat. The flywheel is accelerated to a preset speed, then the two workpieces are brought into contact under axial pressure. The flywheel decelerates as kinetic energy is converted into frictional heat; when the flywheel stops rotating, the upsetting pressure is applied to complete welding. IFW is characterized by short cycle times and consistent heat input, making it suitable for joining high-strength alloys in the aerospace and defense industries.

 

    3.1 Superior Joint Quality and Mechanical Performance

    As a solid-state welding process, friction welding avoids the defects associated with fusion welding (porosity, solidification cracks, segregation). The weld joint has a fine-grained recrystallized structure, with tensile strength often exceeding that of the base metal. For dissimilar metal joints (e.g., aluminum-steel, copper-titanium), friction welding prevents the formation of brittle intermetallic compounds compared to fusion welding methods.

 

    3.2 Wide Material Compatibility

    Friction welding can join a broad range of materials, including carbon steel, stainless steel, titanium alloys, nickel-based superalloys, aluminum alloys, and even dissimilar metal combinations that are difficult to weld by fusion methods. It is also applicable to welding heat-sensitive materials that cannot withstand high-temperature fusion welding.

 

    3.3 Environmentally Friendly and Cost-Effective Process

    Most friction welding variants (FSW, RFW) do not require filler metals, shielding gases, or fluxes, reducing material costs and eliminating harmful emissions (spatter, smoke, arc radiation). The process has high energy efficiency, and the minimal thermal deformation reduces post-weld machining requirements, lowering overall production costs.

 

    3.4 High Automation Potential and Production Efficiency

    Friction welding processes are highly compatible with automated production lines. Rotary friction welding and inertia friction welding can achieve cycle times of 10–60 s per joint, while friction stir welding can be integrated with multi-axis robotic systems for welding complex 3D seams. The stable process parameters ensure consistent quality in mass production, with defect rates below 0.1%.

 

    4.1 Aerospace Industry

    LFW is used to weld titanium alloy compressor blades to nickel-based superalloy disks for aircraft engines; FSW is applied to join aluminum alloy fuselage panels and rocket fuel tank structures, reducing weight by 10–15% compared to riveted structures. IFW is used for manufacturing missile guidance system components and satellite structural parts.

 

    4.2 Automotive Manufacturing

    RFW is widely used for welding automotive drive shafts, axle shafts, and gearbox gears, with production lines achieving 1000+ joints per hour. FSW is applied to weld aluminum alloy automotive body panels and battery trays for new energy vehicles, improving structural rigidity and crashworthiness.

 

    4.3 Railway Transportation

    FSW is the standard welding method for high-speed train aluminum alloy car bodies, enabling seamless welding of large panels with minimal deformation. It is also used for welding railway axle components and bogie frames, ensuring long-term fatigue resistance under heavy loads.

 

    4.4 Petroleum and Pipeline Engineering

    RFW is used to weld drill pipe joints and oil pipeline segments, producing welds with high corrosion resistance and pressure-bearing capacity. FSW is applied to weld aluminum alloy pipelines for transporting corrosive media, reducing maintenance costs.