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Comeld Advances Composite-to-Metal Joining

07 May 2004

TWI has released Comeld, a new innovative method of metal-composite joining, based upon a metal pre-surface treatment.

The research is still in the early stages, but Comeld claims to represent a step forward in its ability to join a variety of metals with composite parts. The heart of Comeld’s success lies in a metal surface pre-treatment, invented and patented by TWI, and dubbed Surfi-Scult.

The paper presented by Dr Faye Smith, Senior Project Leader at TWI, at the recent Composites Processing Association event in Birmingham focussed on a specific set of materials (GFRP joined to stainless steel for example) that were deemed to be appropriate to the marine industry.

Demonstrations were also made of joins between other materials (CFRP joined to titanium for example) which proved that this technology can be applied to many joints between many different metal and composite combinations. The metals that TWI have used to date in Comeld joints are titanium, aluminium and stainless steel, although the TWI said that many other metals and alloys are suitable for this process and will be used in the future

“The composites that we have used to date are carbon fibre reinforced epoxy and glass fibre reinforced polyester. As with the metals, many other composite materials are suitable and will be investigated as part of on-going research”, said Faye Smith.

To make Comeld joints the pre-treatment (Surfi-Sculpt) that is applied to the metal uses, in the work done so far, an electron beam to move material around the surface of the metal. This produces protrusions (which TWI call 'proggles') and holes in the metal. The proggles and holes can be made to be any shape required and the area seen on joints in the image above took only 8 seconds to treat. Following the pre-treatment the composite is then laid up onto the metal, either with or without an additional adhesive layer, to form a Comeld joint between the two materials.

Judging by the research findings available from the TWI, the Comeld joint fails at a much higher load and absorbs far more energy before failure, than a conventional joint of identical dimensions.

According to Dr Smith, “The preliminary research results have been so encouraging that we are offering the technology to industry at this very early stage. The intention is that, alongside in-house development, a collaborative project (known as a Group Sponsored Project or GSP) is being set-up so that interested companies can collaborate and direct the way future research is performed. In the GSP, Comeld technology will be used in conjunction with joints and materials of interest to participating companies so that they have early access to data that is relevant to their applications”

This project is expected to begin later this year. The potential applications for this technology cross all the industry sectors as composite materials and metals are used and joined in many industries.

A composite component could be manufactured using the same processes as previously (e.g. RTM or vacuum infusion) but using Comeld technology a metallic edge could be applied all the way around the component during the manufacture. This metallic edge would then allow the component to be welded in place to a metallic structure.





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