Application of Friction Welding Technology in Engine Valves

Engine valves need to endure extreme high temperatures, high pressures, and frequent mechanical impacts during the operation of an internal combustion engine. The exhaust valve, in particular, operates in harsh conditions as it directly contacts high-temperature exhaust gases. To meet the specific performance requirements of different parts of the valve, traditional single-material manufacturing methods are no longer sufficient. As a result, manufacturers worldwide have widely adopted friction welding technology to join two different metal materials, thereby enhancing the overall performance of the valve.

Application of Different Material Combinations

The head of the exhaust valve requires high wear resistance, corrosion resistance, and strength at elevated temperatures, while the valve stem must have good thermal conductivity and wear resistance. A common combination is using austenitic heat-resistant steel for the valve head because of its excellent high-temperature strength and oxidation resistance, ensuring a long service life under harsh conditions. The valve stem is usually made from martensitic structural steel, known for its high hardness, good thermal conductivity, and wear resistance, ensuring the valve stem operates stably over long periods. Additionally, the valve tip often undergoes hardening treatment, such as quenching, to further enhance its wear resistance.

Introduction to Friction Welding Technology

Friction welding technology joins two metal materials by rotating or vibrating them together, causing their contact surfaces to generate plastic deformation under high temperature. By applying pressure, the materials are tightly bonded. This process does not require filler materials, avoiding potential welding defects commonly seen in traditional methods. Moreover, it ensures a strong bond between different materials at high temperatures, allowing the materials to fully leverage their respective properties and thus extending the valve's service life.

Differences in Welding Methods

In valve production, two common friction welding methods are used: stem-to-stem friction welding and head-to-stem friction welding.

The internal quality of the welded products from both methods is generally consistent, and both meet the long-term operational requirements of valves in internal combustion engines. However, head-to-stem friction welding offers superior dimensional accuracy in the welding size. The complex shape of the valve head requires precise dimensions after welding. As a result, the dimensions of head-to-stem welding are more accurate. In contrast, stem-to-stem welding, after the welding process, requires upsetting (electric upsetting), which may introduce some deviation in the L1 dimension, leading to slightly lower precision in the final weld dimensions.

Advantages of Friction Welding

Friction welding offers significant advantages over other welding methods. First, it is a solid-state bonding process, meaning no metal melting occurs during welding, which reduces the risk of welding defects. Second, the heat-affected zone during welding is small, and the mechanical properties of the weld joint are close to or even better than the base material. Additionally, friction welding is a fast and efficient process, making it ideal for mass production. Therefore, it is widely used in modern manufacturing.

Conclusion

By using friction welding to combine different materials in a valve, not only can the overall performance of the valve be significantly improved, but the service life is also extended. Furthermore, the rational selection of materials can reduce production costs. The application of this process ensures that internal combustion engine valves can maintain stable performance in complex working environments, thereby guaranteeing the overall efficiency of the engine.