Topic of the month November 2009

Perfectly Connected: Innovative Joining Techniques

Figure 1: Laser welding of acrylonitrile-butadiene-styrene (ABS) material on a chipboard substrate (left) and a polypropylene component (PP) onto a wood-fiber composite material (right). Source: Laser Zentrum Hannover e.V.

Positive, non-positive and adhesive bonded – these are the central keywords for characterizing and differentiating state-of-the-art joining techniques. The field of joining is of major importance in all engineering disciplines utilizing advanced production technologies for the realization of modern products, facilities and processes.

Especially regarding to the top issues of the fairs wire and Tube:
pipes get welded, wires get soldered, steel-plates are riveted and plastic material is glued. The application of novel material systems, the clearly increased demand for sustainable technologies, energy efficiency as well as the fulfillment of challenging property profiles of components are just a few examples, which illustrate the constantly changing demands of the market. This of course influences the currently utilized joining techniques. Obviously conventional methods will not being replaced completely, but they are clearly complemented by new or modified technologies. Presently innovative methods reach marketability – these are to be presented here.

FricRiveting – A new Riveting Method

Friction riveting or FricRiveting is the name of a new joining process developed by materials researcher Dr. Sergio Amancio of the GKSS Research Centre in Geesthacht as part of his doctorate at the Technical University of Hamburg-Harburg. The new process is in particular suitable for joining various plastic materials, different composites and novel material classes, like plastic-metal hybrids. Precisely those material systems which are used in the automotive industry, the transportation industry and in aircraft manufacturing, with the objective of reducing weight and saving energy.

Within FricRiveting, the partners are joined together mechanically as well as thermically. The central function in this process has a metallic bolt – the rivet. This rivet is brought into rotation and is pressed onto the upper surface of the two joining partners. In this period the bolt penetrates the substrate and the produced heat – caused by friction – melts the synthetic component of the material partners. With the duration of the penetration, the friction power increases more and more and the contact pressure is increasing clearly as well. These conditions lead to the result, that high temperatures appear at the tip of the rivet.

The mechanical and thermal system conditions lead to a well-defined deformation of the bolt [Fig. 2]. Thereby the bolt is being fixed into the material and the joining partners are bonded to each other firmly. For this reason FricRiveting combines the advantages of riveting and bonding. The process is secure, realizes weight-savings and lowers production costs because, for example time-consuming preparatory operations like the adjustment of defined surface properties for glued connections, can be saved. Furthermore FricRiveting dispenses the use of environmentally harmful chemicals and health harming weld smoke does not even occur at all.


Figure 2: Schematic diagram of the joining process of two materials with the newly developed
FricRiveting method. Source: GKSS Research Centre in Geesthacht.

Laser Welding – Joining Plastics with Wood

Now scientists and engineers of the Laser Zentrum Hannover e.V. enhanced the laser welding by transfusing the application into a reliable joining method for various combinations of materials. According to the scientists it is possible to connect thermoplastic parts, like for example polypropylene (PP), polyamide (PA) and acrylonitrile-butadiene-styrene (ABS) to technically relevant wood based materials like fibreboard, chipboard or solid wood plates. Depending on the material combination, various joining mechanisms come into operation. The natural thermoplastic polymer lignin – which is a main component of wood – appears to play a dominant key role.

Due to chemical interactions with the molecules of the respective substrate material lignin is responsible for the generation of strong bondings on a molecular basis. Besides the already named advantages of the laser welding, this process particularly allows the abandonment of glue in the joining of wood composites. There are no further costs for gluing materials or for expensive maintenance and cleaning operations, which result from the difficult gluing procedure.

The mechanical property profile of joined components has already been extensively characterized by several tests, like tensile shear tests and impermeability tests. All application-relevant characteristics show the performance of rivaling methods, which are often more complex in their utilization. These facts makes the laser welding a very attractive candidate for challenging joining solutions, that are required for example in the automotive industry, in transport facilities and in the furniture industry.

Dr.-Ing. Christoph Konetschny
Material- und Nanoexperte

www.materialsgate.de


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