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Innovating in the union of metals and polymers results in better products and less damage to the environment

13 November 2020

Article by Nuno Felício, responsible for business development in the field of Optics and Experimental Mechanics at INEGI

The weight optimization of components and equipment, as well as the reduced use of resources, are among the biggest transversal challenges in the industry, creating, in turn, challenges in terms of the union of materials. In this context, an innovative technique has emerged, the potential of which remains yet to be tapped: linear friction welding.

This technique (also known by the acronym SFL) emerged as a bonding method capable of welding high-strength metal alloys, hitherto difficult or impossible to weld with conventional fusion welding techniques. Since then, it has been refined for application in the aerospace, naval, nuclear, railway and automobile industries.

The advantages speak for themselves, but this technique still needs greater industrial dissemination, namely in Portugal, having only been applied in the welding of different aluminum alloys.

Gives superior mechanical properties and is more environmentally friendly

One of the greatest advantages is that linear friction welding results in joints with superior mechanical properties (identical to the base material) in the welded joints, and creates less intense residual stress fields. Two common and recurring problems when using other techniques, which are usual catalysts for reliability failures.

It is also necessary to highlight the ecological character of the process, since it does not result in the emission of smoke, not even, for the vast majority of applications, the use of gases. It also does not require the addition of bonding material and minimizes material waste, which is why it is harmless to operators and efficient in the use of resources, thus contributing to environmental sustainability.

Another advantage, resulting from these characteristics, is the reduction of production costs. In addition to not requiring an external or internal auxiliary source of heat, vibrations or ultrasound, it does not create expenses in terms of the elimination of smoke and slag from the material, nor does it require as much investment in the protection of workers.

In addition to these incentives, since it is a solid state welding process, the benefits also include the fact that they result in joints that are free of porosity or hot cracking, and with a low thermal delivery of the process when compared to techniques that involve generation of energy for the melting of materials.

INEGI is developing applications in polymer and hybrid materials

INEGI team's experience with linear friction welding ranges from its application to structural design and characterization of structures produced by SFL, to the development of process monitoring tools and systems, and has focused particularly on the aeronautical industry.

As Shayan Eslami, engineer in the Experimental Mechanics area at INEGI, and responsible for the development of this technology, says, "the Institute, always seeking to anticipate trends and new technologies that add value to the industry, in addition to dominating the process, has remained at the forefront state of the art and is a pioneer in adapting this welding technique for the connection of dissimilar materials such as polymers and hybrids (polymer-metal)”.

In particular, one highlights the recent development of a tool that implements a variant of this technique for the bonding of polymers with different thicknesses and different joint configurations, as well as for bonding thermoplastics with aluminum. As a result of this development, a patent was submitted for the polymer welding tool. The results, similar to the equivalent process for metal, speak for themselves: resource efficiency, improved mechanical properties, watertight joints, and less occurrence of operator errors.