What Is Friction Stir Welding?
Friction stir welding is a technique for joining two different materials.
The tool is rotated at high speed, and the materials are joined using frictional heat and plastic flow. It is not suitable for materials with high softening points, but it does not involve complete melting, so the thermal history can be reduced.
Friction stir welding is characterized by less thermal deformation than welding. It is also valued for its ability to join materials together. Although it is a relatively new joining technology, the problems are being solved by optimizing the shape of joining tools and other means.
In recent years, friction stir welding technology has begun to be widely used, and its excellent performance is attracting attention. Further research and development is expected in the future, and this technology will be applied in various industrial fields.
Uses of Friction Stir Welding
Friction stir welding is mainly used for joining aluminum alloys and other metals such as titanium alloys, magnesium alloys, copper, and zinc.
Specific uses of this process include the manufacture of aluminum rolling stock for railroads, automotive frames, aerospace industry, lightweight structures for ships, aircraft gases and engine parts, bridges, and other building structures.
When joining dissimilar metals, care must be taken in waterproofing the joints and selecting the metals to be combined, as there is a risk of electrical corrosion due to the difference in inherent electrical potentials. In recent years, joining techniques for stainless steel and carbon steel with high softening temperatures has been developed, and hybrid methods combined with YAG laser welding have been evolving.
Principle of Friction Stir Welding
In friction stir welding, the tool is cylindrical and has a protrusion called a probe. The outer surface of the probe is threaded. Different materials are butted against each other in the direction of thickness and pressed against the tool, which rotates at high speed. The frictional heat softens both materials, and the probe is pushed in to mix and join the materials.
The tool is made of tool steel because it must have high strength, heat resistance, and wear resistance. It is important to understand the advantages and disadvantages of friction stir welding and to consider its employment carefully.
The advantages of friction stir welding are that there is little strength loss in the welded area, only slight deformation, joining of dissimilar materials is possible, defects are unlikely to occur, no pretreatment is required, and skilled techniques are not necessary. On the other hand, the disadvantages of this method are that it is prone to bonding defects on the back side, requires rigidity to fix the materials to be bonded, and is not suitable for complex bonded shapes.
Other Information About Friction Stir Welding Machines
Dissimilar Metals Welded by Friction Stir Welding Machine
In response to recent global issues of environmental protection and resource conservation, the automotive industry has been contributing to fuel efficiency improvement by reducing vehicle weight. In many cases, weight reduction of car bodies can be solved simply by replacing conventional steel, which has a high specific gravity, with aluminum alloys, which have a low specific gravity.
Therefore, “multi-materials” are widely used as an effective means of creating members with superior overall characteristics by using different materials for the right places, such as steel for parts that require strength as before and aluminum alloys for other parts. Multi-materials are characterized by the large proportion of steel and aluminum alloys combined. Friction stir welding machines are used to join these two dissimilar metals.
There are two major joining methods: welding, in which metals are joined by melting through the application of high thermal energy, and friction stir welding, in which metals are joined by plasticity without melting through the application of high mechanical energy. In the case of welding, it is difficult to control the melting and joining of steel and aluminum alloys, which have very different melting points. Another major challenge is the formation of hard and brittle intermetallic compounds composed of iron and aluminum.
Arc welding, which has a relatively low energy density, is difficult to apply because of the thick intermetallic compound layer that forms. However, laser and electron beam welding, which have high directivity and density, can make the layer thinner, making it possible to apply arc welding, although it is difficult to control. On the other hand, thermal deformation is inevitable.