Friction Welding: Characteristics and Practical Applications

Features of Friction Welding

Friction welding offers many advantages and has been highly valued in the welding industry at home and abroad in recent years, leading to rapid development in the research and industrial application of new friction welding technologies. The main features of friction welding are as follows.

(1) Good and Stable Welding Quality

The material being welded does not melt during the welding process, which eliminates welding defects and brittleness in the joint area related to melting and solidifying. The metal in the welded area has a forged structure. The welding time is short, the heat-affected zone is narrow, and it’s easy to produce a good-quality weld joint.

(2) Wide Range of Suitable Materials

Most similar and dissimilar metals can be friction welded. Materials that are difficult to weld using conventional fusion welding methods, such as aluminum-steel, aluminum-copper, titanium-copper, intermetallic compound-steel, can also be welded. Friction welding is also capable of welding composite materials, functional materials, and refractory alloys.

(3) Short Welding Time, High Productivity

Generally, the productivity of friction welding is 1 to 100 times higher than other welding methods, making it suitable for mass production. For instance, the productivity of the engine exhaust valve double-head automatic friction welding machine can reach 800 to 1200 pieces/h.

For the welding of the petroleum drill rod with an outer diameter of Φ127mm and an inner diameter of Φ95mm with the end head, continuous-drive friction welding can complete the job in just a few seconds.

(4) High Precision and Low Cost

The welding deformation caused by the welding heat cycle is small, so the size accuracy after welding is high, and there is no need for post-welding reshaping and stress relief. The full-length error of the pre-combustion chamber of the diesel engine produced by friction welding is ±0.1mm. The specialized welding machine can ensure a length tolerance of ±0.2mm and eccentricity of 0.2mm after welding.

As friction welding saves electricity, the joint does not need special treatment before welding, and no filler material or protective gas is required during welding, significantly reducing manufacturing costs. For instance, replacing CO2 gas shielded welding with friction welding for the propulsion shaft of heavy trucks reduces the cost by about 30%.

(5) High Degree of Mechanization and Automation

Once the welding conditions are given, friction welding operations are straightforward, requiring low technical competence from the welder.

(6) Small Power Consumption, Energy Saving, and No Pollution

Compared to flash welding, friction welding can save 5 to 10 times more electric power and energy. The welding process does not produce smoke, arc light, or harmful gases, thus not polluting the environment.

Like other welding methods, friction welding also has its drawbacks and limitations: the required equipment is complex, and the one-time investment in a friction welding machine is substantial. Only with mass production can the production cost be reduced. Sometimes, the flash of the friction weld joint is redundant and may cause certain hazards, necessitating an additional cleaning process.

It’s difficult to weld non-circular cross-sections, disc-shaped thin parts, and thin-walled pipe fittings due to difficulties in clamping. Also, due to the power and pressure limitations of the friction welding machine’s main shaft motor, the maximum cross-sectional area of the friction weld does not exceed 200cm².

Applicability of Friction Welding

As friction welding technology continues to evolve, materials that are difficult to weld using conventional methods can now be firmly welded together using a transition metal layer through friction welding, thereby continuously improving the weldability of metal materials.

Friction welding is also widely used in the production of dissimilar metal parts to manufacture products with composite properties, save precious metals and steel, and even weld plastics and other non-metal products. Table 4-1 lists the weldability of friction welding for similar and dissimilar material combinations. The adaptability of metal materials to friction welding can be divided into the following scenarios:

Table 4-1 Weldability of Friction Welding for Similar and Dissimilar Material Combinations

Material TypePure Iron and Carbon SteelHigh-Strength SteelStainless SteelHeat-Resistant SteelHigh-Temperature AlloyRust-Proof AluminumHard AluminumForged AluminumMagnesium and its AlloysStructural CeramicsFiber Reinforced AlloysHard AlloysPowder Metallurgy High-Temperature Alloys
Pure Iron and Carbon SteelAAAAAAABAA
High-Strength SteelAAAAAAA
Stainless SteelAAAAABAA
Heat-Resistant SteelAAAAA
High-Temperature AlloysAAAAAA
Rust-Proof AluminumABAAA
Hard AluminumAA
Forged AluminumAAAAA
Magnesium and Its AlloysA
Structural CeramicsBAC
Fiber-Reinforced AlloysA
Hard AlloysAAA
Powder High-Temperature AlloysAAAAA

Note:

  • A – Exhibits good friction welding characteristics, capable of achieving joints of equal strength or joints with the same strength as the low-strength parent material;
  • B – Has mediocre friction welding characteristics, able to form joints, but unable to achieve equal-strength performance;
  • C – Exhibits poor friction welding characteristics, unable to form joints;
  • Blank – Friction welding characteristics have not yet been studied.

1) At high temperatures, both metals of the same type with good plasticity and dissimilar metals capable of mutual solubility and diffusion have good weldability. They can achieve high-strength, ductile weld joints.

2) When welding can produce brittle alloys of dissimilar metals, such as aluminum-copper, aluminum-steel, titanium-steel, etc., it is difficult to ensure the strength and plasticity of the joint if no measures are taken to prevent the brittle alloy layer from thickening.

3) Materials with high-temperature strength, low plasticity, and good thermal conductivity are not easy to weld. The greater the difference in high-temperature mechanical and physical properties between the two metals, the more difficult it is to weld, such as stainless steel-copper, hard alloy-steel, etc.

4) Reactive metals like titanium and zirconium, steel materials with good hardenability, those with surfaces that are not easily broken or have coatings, infiltration layers, etc., as well as cast iron, brass and other metals with too small friction coefficients are difficult to friction weld.

Friction welding has been widely used in various industrial sectors. Table 4-2 lists some fields and application examples where friction welding is widely used. Figure 4-11 shows a typical product manufactured using friction welding technology.

Table 4-2 Fields and Application Examples of Friction Welding Technology

Application FieldsApplication Examples
AerospaceTurbine rotor components, engine parts, fan shafts, landing gear components, bi-metallic rivets, aluminum heat pipes, etc.
Weapons ManufacturingHigh-energy bombs, front sections of bombs, mid-section shell components, bulletproof windshields, linings inside machine gun barrels, chase gun propellant hole plugs, torsion tubes of amphibious troop carriers, etc.
Tool ManufacturingWelding of workpieces such as drills, vertical milling cutters, taps, reamers, pull cutters, etc., usually welding between the cutting edge (high-speed tool steel) and the handle (carbon steel).
Machinery ManufacturingShaft parts, tubes, screws, push rods, pull rods, forks, main spindles of machine tools and circular knives, milling machine knife rods, geological drill rods, hydraulic jacks, shafts and flanges, etc.
Vehicle ManufacturingHalf shafts, gear shafts, rear axle heads of cars, turbochargers, dissimilar material gas valves, piston rods, bi-metallic bearing shells, etc.
Petrochemical IndustryOil drill rods, valve bodies of high-pressure valves, pipelines, serpentine tubes, etc.
Light Industry, Textile MachinerySmall shafts, rolls, tubular parts, etc.
Power IndustryCopper-aluminum terminal connectors.
Figure 4-11 Typical Product Examples of Friction Welding
  • a) Engine Exhaust Valve
  • b) Engine Fan Shaft
  • c) Turbocharger
  • d) Rear Axle of a Car
  • e) Steering Shaft
  • f) Structural Steel

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