Advantages
The strength of the joint does not deteriorate even when metals are joined. The strength of the joint is equivalent to that of the base metal.
The effect of no deterioration in strength has been proven in friction welding, friction stir welding, and electric resistance welding.
This technology minimizes strength deterioration even when joining metals of different types.
Background & Technology
The Joining and Welding Research Institute (JWRI) at Osaka University is one of the few research institutes in the world that specializes in joining technology. We are pleased to present an innovative and practical joining technology developed by Professor Hidetoshi Fujii, the current director of JWRI.
Professor Fujii and his colleagues have developed a new metal joining technique. The strength of the jointed parts produced by this technique is, surprisingly, equal to or greater than that of the base metal. With conventional fusion welding techniques, it is common knowledge that the strength of the joint deteriorates due to the melting of the metal. In particular, it is known that melt welding is extremely difficult for steels with high carbon content (such as medium carbon steel and high-tensile steel). However, their technology is a solid-phase welding technique that does not heat the temperature more than necessary and joins the materials in a solid-phase state. In addition, by applying the joining conditions at lower temperatures, the phase transformation can be suppressed, the degradation phenomenon of the material called heat-affected zone can be suppressed, and the strength processing (work hardening, precipitation strengthening, grain control, etc.) of the material on the material is less likely to be destroyed. As a result, parts joined with Prof. Fujii’s technology have the same strength as the base metal.
The scientific core of Professor Fujii’s technique is the control of temperature during joining by applying the appropriate pressure. The figure below shows the relationship between the pressure applied during joining (horizontal axis) and the temperature at which plastic deformation occurs at that pressure (vertical axis). This relationship is usually negatively correlated: the higher the pressure applied to the material, the lower the temperature at which plastic deformation occurs. In other words, if a sufficiently high pressure is applied to the materials to be joined, the metals at the interface of the joint will deform at a lower temperature, allowing the metals to deform and join together. And since this temperature is below the A1 transformation point temperature for iron, pearlite (ferrite and cementite) can be joined without transforming to austenite. As a result, it is possible to make a joint material that retains the strength of the base metal without the embrittlement or softening of the heat-affected zone. They call this pressure-controlled solid-phase welding technology, which applies pressure to control the joining temperature.
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pressure-controlled solid-phase welding technology has been applied to three joining techniques in Osaka University research.
Friction Welding
A method of joining two materials to be joined that have a cylindrical shape, such as a round bar, by heating them using frictional heat generated by rotating each of them while pressing them together. In pressure-controlled solid-phase welding technology, low-temperature joining conditions can be achieved by applying sufficient pressure while keeping the rotation speed low (less than 100 rpm). In fact, when Φ10 round bars made of S45C material were joined, it was confirmed that the heat-affected zone was suppressed and the tensile strength was equal to or greater than that of the base metal. The frictional heat generated by sliding motion also joins metallic materials. This method is called linear friction welding (LWF), in which two materials, such as plates or square bars, are joined by rubbing them together in one direction. Pressure-controlled solid-phase welding technology can also be applied to this method to produce parts whose tensile strength is equivalent to that of the base metal.
Friction Stir Welding (FSW)
A method of joining by stirring the metal materials of the butt portions of the joined materials by pressing a cylinder made of hard metal, called a tool, against the joined plate-shaped materials while rotating. In pressure-controlled solid-phase welding technology, the tool is operated at a low rotational speed and sufficient pressure is applied to suppress heat-affected zones and achieve joints with tensile strength equal to or greater than that of the base metal in medium and high carbon steels.
Electrical-resistance solid-phase welding
A method of joining materials such as round bars, square bars, and pipes by arranging them in close proximity to each other and then heating them with Joule heat generated at the butt joints by an electric current applied to the materials. By adjusting the amount of current applied, the temperature rise in the bonded area is controlled, thereby realizing a pressure-controlled solid-phase welding technology. S45C round bars (Φ10) were also joined using this method, and it was confirmed that the tensile strength was equal to or greater than that of the base metal.
Pressure-controlled solid-phase welding technology can also be used to join special metallic materials. For example, it can be applied to steel materials with high carbon content, cast iron, high-tensile steel, and other metallic materials with special compositions and microstructures. In addition to steel, this technology can also be used for nonferrous materials such as titanium, nickel, aluminum, etc., with less strength degradation. Even when combining different materials, this technology can minimize strength degradation.
Expectation
We are looking for a company that is willing to commercialize a joining device employing this technology. The companies should take the initiative in product development. The university will transfer the research results of this technology to such companies through joint research, etc. The university will also license its patents. The university will also license its patents.
Patent & Publication
Osaka University has obtained or applied for numerous patents related to pressure-controlled solid-phase welding technology. We also have rights in the U.S. and Europe.
Project No.DA-01012a