Mechanical Engineering Research Team Led by Professor Kim Sang-yup Publishes Paper in the Prestigious International Journal “Composites Part B: Engineering”
▲ (From left) Professor Kim Sang-yup and Master’s student Kang Hyung-woo of the Department of Mechanical Engineering
A research team led by Professor Kim Sang-yup of the Department of Mechanical Engineering (first author: Master’s student Kang Hyung-woo) developed a “removable susceptor” technology—which functions as a heating element during welding but melts and is removed once the process is complete. This innovation resolves the long-standing issue of permanent residue from metal heating elements in conventional induction welding and presents a new approach to joining thermoplastic composites for aerospace and automotive applications.
Thermoplastic composites are lightweight, impact-resistant, and recyclable, making them a promising next-generation structural material for the aerospace, automotive, and future mobility sectors. In particular, while induction welding is considered a promising joining technology because it can selectively heat only the joint surfaces without contact, it has the limitation that a metal heating element (susceptor) must be inserted into the joint to convert electromagnetic energy into heat. These metal susceptors remain inside the joint after welding, causing unnecessary weight gain and potentially leading to fatigue cracks and moisture penetration due to interfacial discontinuities.
The research team utilized Field’s Metal (In-Bi-Sn), a low-melting-point alloy with a melting point of approximately 62 °C, as a temporary heating element. Field’s Metal acts as a current-carrying pathway during the induction heating process and then transforms into a liquid state during the pressing and compaction process, being expelled from the joint surface. Through this method, the team succeeded in reducing the amount of metal residue within the joint to 2.5 wt% or less, unlike conventional metal susceptors.
Additionally, they identified that the increase in electrical resistance during the alloy’s phase transition leads to enhanced heat generation efficiency. Their findings showed that heat generation can increase by up to 35.1% during the phase transformation, enabling rapid heating rates exceeding 20 °C per second and achieving heating uniformity that is up to eight times greater than that of conventional approaches.
The team applied this technology to polyetherimide (PEI) welding, reducing the time to reach the target temperature by more than 60% compared to the conventional mesh method and achieving a 17% improvement in joint strength. They also developed machine learning-based design techniques (U-Net and CMA-ES) to predict the diffusion behavior of molten metal, demonstrating that the technology can be uniformly applied even to joints with complex geometries. Furthermore, by applying the technology to unidirectional PEKK carbon fiber-reinforced thermoplastic composites (UD CFRTP)—which were difficult to heat using conventional induction welding—the team achieved a joint strength of 15.7 MPa without the need for an additional resin layer.
This research was conducted with support from the Korea Institute of Materials Science, the National Research Foundation of Korea (RS-2024-00448445), and the Hyundai Motor Chung Mong-koo Foundation. The findings were published in Composites Part B: Engineering (IF 14.2, top 0.5% in the JCR Engineering category), a world-renowned journal in the field of composite materials.
Mr. Kang stated, “High-efficiency, high-reliability thermoplastic composite joining technology is essential for realizing sustainable next-generation mobility,” adding, “This study is significant in that it presents a new concept of utilizing a metal susceptor not as a permanent structural material but as a temporary heating medium.” He continued, “We expect this technology to be widely utilized in industries where lightweighting is critical, such as aerospace, automotive, and Urban Air Mobility (UAM).”
▶Paper Title: Removable Metallic Susceptor for Induction Welding of Thermoplastic Composites
[SEO keyword]
induction welding, thermoplastic composites, removable susceptor
A research team led by Professor Kim Sang-yup of the Department of Mechanical Engineering (first author: Master’s student Kang Hyung-woo) developed a “removable susceptor” technology—which functions as a heating element during welding but melts and is removed once the process is complete. This innovation resolves the long-standing issue of permanent residue from metal heating elements in conventional induction welding and presents a new approach to joining thermoplastic composites for aerospace and automotive applications.
Thermoplastic composites are lightweight, impact-resistant, and recyclable, making them a promising next-generation structural material for the aerospace, automotive, and future mobility sectors. In particular, while induction welding is considered a promising joining technology because it can selectively heat only the joint surfaces without contact, it has the limitation that a metal heating element (susceptor) must be inserted into the joint to convert electromagnetic energy into heat. These metal susceptors remain inside the joint after welding, causing unnecessary weight gain and potentially leading to fatigue cracks and moisture penetration due to interfacial discontinuities.
The research team utilized Field’s Metal (In-Bi-Sn), a low-melting-point alloy with a melting point of approximately 62 °C, as a temporary heating element. Field’s Metal acts as a current-carrying pathway during the induction heating process and then transforms into a liquid state during the pressing and compaction process, being expelled from the joint surface. Through this method, the team succeeded in reducing the amount of metal residue within the joint to 2.5 wt% or less, unlike conventional metal susceptors.
Additionally, they identified that the increase in electrical resistance during the alloy’s phase transition leads to enhanced heat generation efficiency. Their findings showed that heat generation can increase by up to 35.1% during the phase transformation, enabling rapid heating rates exceeding 20 °C per second and achieving heating uniformity that is up to eight times greater than that of conventional approaches.
The team applied this technology to polyetherimide (PEI) welding, reducing the time to reach the target temperature by more than 60% compared to the conventional mesh method and achieving a 17% improvement in joint strength. They also developed machine learning-based design techniques (U-Net and CMA-ES) to predict the diffusion behavior of molten metal, demonstrating that the technology can be uniformly applied even to joints with complex geometries. Furthermore, by applying the technology to unidirectional PEKK carbon fiber-reinforced thermoplastic composites (UD CFRTP)—which were difficult to heat using conventional induction welding—the team achieved a joint strength of 15.7 MPa without the need for an additional resin layer.
This research was conducted with support from the Korea Institute of Materials Science, the National Research Foundation of Korea (RS-2024-00448445), and the Hyundai Motor Chung Mong-koo Foundation. The findings were published in Composites Part B: Engineering (IF 14.2, top 0.5% in the JCR Engineering category), a world-renowned journal in the field of composite materials.
Mr. Kang stated, “High-efficiency, high-reliability thermoplastic composite joining technology is essential for realizing sustainable next-generation mobility,” adding, “This study is significant in that it presents a new concept of utilizing a metal susceptor not as a permanent structural material but as a temporary heating medium.” He continued, “We expect this technology to be widely utilized in industries where lightweighting is critical, such as aerospace, automotive, and Urban Air Mobility (UAM).”
▶Paper Title: Removable Metallic Susceptor for Induction Welding of Thermoplastic Composites
[SEO keyword]
induction welding, thermoplastic composites, removable susceptor