Young Investigator Group

Techniques & Equipment


Since its introduction in 2009, Friction Spot Joining (FSpJ) has shown high performance in producing polymer-metal hybrid structures. Therefore, this technique is being investigated to join lightweight alloys such as aluminium and magnesium with high performance engineering thermoplastics and composites. For this reason a friction spot welding / joining machine (RPS 100) is employed. Briefly, the metallic partner is plasticized and deformed due to the generated frictional heat and applied force. A metallic nub is created which is inserted into the composite. Simultaneously, a thin layer of polymer matrix is molten, and displaced around the joining area. The joint is formed after consolidation of the polzmeric molten layer. These are the two main phenomena responsible for joining mechanisms.
The term "joining" is used to differentiate spot joints where a sharp interface is present (minimal or absent atomic or molecular diffusion), such as in hybrid polymer-metal joints, while "welding" is used for joints without a discontinuous transition between joining partners (presence of diffusion mechanisms), such as "polymer-polymer" or "metal-metal" spot welds.

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The Friction Spot Welding (FSpW) is a new technology for producing similar and dissimilar overlap joints in thermoplastic and thermoplastic fiber-reinforced composites. As thermoplastic fiber reinforced composites (TPC) are difficult to weld or bond by traditional joining processes, there is an open niche to be filled by the research and development of alternative joining technologies.The main improvement of FSpW over the Friction Stir Spot Welding (patented by The Welding Institute – TWI, England) is the absence of a keyhole in the spot seam; this usually leads to higher joint strengths due to reduction of the geometrical notch effect of the keyhole.

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Friction Riveting (Fricriveting), is an innovative joining technique for polymer-metal hybrid structures, developed and patented by the Helmholtz Zentrum Geesthacht in Germany. In this process, polymeric parts are joined by a metallic rivet; the joining is achieved by mechanical interference and adhesion between the metallic and polymeric joining partners. During the process, a rotating cylindrical metallic rivet is inserted into a polymeric base plate. Due to the local increase of temperature, a molten polymeric layer is formed around the tip of the rotating rivet. The local temperature increases leading to the plasticizing of the tip of the rivet. While the rotation is being decelerated, the axial pressure is increased, the so called forging pressure is applied and the plasticized tip of the rivet is being deformed and anchored in the polymeric plate. The technology is adequate to produce overlap riveted joints between metal-polymer, metal-composite and composite-composite connections.

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Injection Clinching Joining (ICJ) is a new joining process for hybrid structures, composed of one thermoplastic-based partner and a metallic or thermoset partner. The principle of the process is to produce joints through heating and deformation of a thermoplastic element (such as a cylindrical stud) integrated in the polymeric partner, which is previously inserted in a through hole (cavity) of a metallic/thermoset component, therefore creating a rivet from the structure itself. Spot joints created by ICJ process are tight and with good mechanical anchoring due to the cavity profiles on the metallic partner. ICJ is a potential technology for secondary and tertiary structures in automotive and aircraft applications.

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Ultrasonic joining (U-Joining) is a new direct assembly technique developed by Helmholtz-Zentrum Geesthacht (patent EP 3 078 480 A1). U-Joining uses ultrasonic energy to join fiber-reinforced thermoplastics to surface-structured metallic parts, for instance produced by metal injection molding (HZG’s patent EP 2 468 436 B1). Ultrasonic vibration and pressure create frictional heat at the materials interface, which softens the composite matrix and allows the reinforcement (structured on the surface of the metallic part) to penetrate the composite. As a result, a metal-composite hybrid joint with improved out-of-plane strength is achieved.

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The AddJoining concept (German patent application number DE 10016121267.9) uses a new and unique approach to produce complex hybrid parts, by combining the principles of joining and polymer additive layer manufacturing (ALM) to produce layered metal-polymer hybrid structures. This is an important contribution to the state-of-the-art in additive manufacturing. AddJoining has potential to overcome the main limitations of production time of state-of-the-art manual lamination techniques, allowing for the production of future composite-metal layered structures with high-specific strength (Rm/density), tight dimensional and damage tolerances.

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