Welding processes

Circular friction welding is suitable for components in dimensions up to approx. 100 x 100mm² as well as for non-symmetrical components. The generated motion is a harmonic circular movement similar to that of an excenter grinder. The advantage here is the significantly lower acceleration loads. The tool and thus the upper joining partner perform a continuous movement without being regularly accelerated in opposite directions. This results in a weld seam with an identical appearance all around. Sensors and actuators can be implemented in the upper tool and components can also be processed when having an undercut in the welding area.
Circular friction welding is an useful welding process wherever ultrasonic welding cannot be used due to the high-frequency excitation and laser welding cannot be used sensibly due to economic or accessibility reasons. Due to the comparatively high frequencies of up to ~300 Hz and the bidirectional motion sequence, very fine weld seams are produced with short welding times of usually ~2s. Circular friction welding is thus optimal when quality and economy are to be brought into harmony.

Infrared welding is a well established welding technique for polymers. The method offers clearly multiple advantages over a contact based heat mechanism. Both, systems based on metal foil and based on glass emitters suffers from systematic limitations. Surprisingly the technologies has not changed for a decade, this was reason enough for us, to develop a modern alternative. The process is always attractive whenever large-format three-dimensional components are to be joined. The fields of application include applications in the automotive area of the interior, exterior and drive train

Our work leads into a setup based on ceramic emitters produced in an 3D printing process. The result is: flexible in design, high emitter performance, superb lifetime. The operating temperature is well above the usual 800°C and ensures a significant increase in performance compared to a metal foil emitter. In theory, doubling the temperature means 16 times the optical power output. This power reserve may be used to reduce the cycle time. However, it also enables a heating process with significantly increased distances between the component surface and the emitter. This distance in turn helps to ensure a constant temperature even when processing components with tolerances.

Hot plate welding is one of the oldest welding processes for plastics and still offers a multitude of advantages. Hot plate welding is a two-step process in which a heating element is placed between the component half-shells. The components are brought into contact with the heating element and rest there as lightly as possible. During the dwell time, the plastic geometry adjusts to the heating element through melting and a melt layer is created through thermal conduction. After a sufficiently strong melt has formed, it has to be done quickly - in the so-called changeover phase, the half-shells are lifted off the heating element. The heating element moves back and the components are brought into contact. The material cools down during this phase, so the changeover time has a disproportionate impact on the overall cycle and on the weld quality.

Hot plate welding is ideal when the components are subject to a relatively high tolerance. This process can also be used to work on large-format components such as double-shell fuel tanks or plastic pallets.

During ultrasonic welding, a high-frequent mechanical movement (between 15 and 40 kHz) is exerted on the component. The process is based on the generation of heat within the plastic component. This is caused by the elastic deformation of the component in the area of the weld seam - the so-called energy director. Ultrasonic welding is a one-step process and is characterized by extremely short cycle times. The process is particularly suitable for small-format and two-dimensional components.

In addition to classic ultrasonic welding, the technology is also used in ultrasonic riveting. Here, a plastic dome is plasticized and reshaped using ultrasound. This technology also enables non-weldable materials to be connected by form closure. Another application is ultrasonic punching. This is used, for example, when processing bumpers.

In spin welding, the heat for fusion is generated by friction. The half-shells are brought into contact with a defined force and start rotating. Heat is generated at the contact surface and the thermoplastic melts. When it reaches the desired state, the rotary movement is stopped at the correct angle.

Spin friction welding is an economically attractive solution when rotationally symmetrical components need to be joined together.

The riveting of thermoplastics is an interesting option for connecting non-weldable materials. Analogous to ultrasonic riveting, a plastic dome is formed in order to create a permanent connection by means of a form closure. In contrast to the ultrasound process, thermal riveting uses a heating stamp that introduces the melting energy. This reduces the mechanical load on the component, so the method can also be used for processing electronic assemblies. This method is used, for example, for the gap-free installation of printed circuit boards.