Researchers, industry show ways to bond metal and plastics

Düsseldorf, Germany — You may recall the legend of Damocles and the sword that hung over his throne.

Now picture that sword being hung from a bit of plastic glued to metal. Or, as Fraunhofer Institut might prefer, an advanced technology bonding of thermoplastics to metal.

But rather than imagining it, visitors could swing by Aachen, Germany-based Fraunhofer's booth during K 2016 in Düsseldorf in the special Science Campus area at K 2016 and see a new take on it, featuring a 60-kilogram anvil and advanced bonding.

Fraunhofer's ILT institute achieves high bond strength through firstly creating a microstructure on the metal surface by laser, which forms hollow undercuts and a rough surface, so the plastic material, melted by laser penetration welding, can be more firmly anchored.

Alexander Olowinsky, ILT microjoining group leader, said the microstructures are applied “at high speed” in width of 30 to 100 µm.

ILT started working on a project called FlexHyJoin a year ago, aimed at fully automatic PMJoin production.

Carbon-fiber reinforced plastic (CFRP) bonding is the subject of ILT work in the HyBriLight project, which refers photonic tools use for a process chain for cost-effective hybrid lightweight construction with highly productive laser systems.

The anvil is just one approach toward metal/plastic bonding by one group at the trade show.

Plasmatreat GmbH showed its use of plasma treatment for high-strength metal/plastic bonding of a clothes hook in stainless steel, and 30 percent glass-fiber-reinforced nylon 6.

The production cell with Plasmatreat's PT1200 plasma treating system was integrated with an Arburg injection press and a tool from Krallmann Holding und Verwaltungs GmbH.

Akro-Plastic innovation manager Thilo Stier said it took two years for two companies to develop technology used for the metal/plastic demonstrator at K 2016. The result is a process in which an anticorrosive plasma layer is applied to the metal and combined with an appropriately developed nylon 6 compound.

Plasma treatment is applied to the metal in two stages via two “Openair” plasma jets. The first removes contamination and activates the metal surface; the second coats the metal with plasma.

The metal part is placed by one robot on a conveyor belt, where a second robot picks it up after short induction heating and lays the hot metal part in the injection mold.

There was another plastic/metal demonstration at Wittmann Battenfeld GmbH, in which metal cups are formed to final size in an injection mold while being overmolded. The injection molded and back-thermoformed deep-drawn metal process was developed by the IKV institute for plastic processing at RWTH University in Aachen.

An Evonik Industries AG cohesive bonding promoter applied to the metal is key to high metal/plastic bond strength. Evonik has been involved in various metal/plastic hybrid developments with its Vestamelt heat-activated crosslinking copolyamide-based adhesion promoters, now grouped at K 2016 under the “HyLink” brand name.