Perfect appearance Kurz and Arburg make finishing of plastic parts more productive
Germany — Leonhard Kurz is a foil specialist, Arburg an expert in the injection moulding of plastics. In this article, the partners explain what a combination of know-how makes possible.
The back-moulding of decorative foils with plastics is used to create high-quality and/or functionalised surfaces, such as those required for control panels in the automotive and household appliance sectors. The process is also called in-mould decoration (IMD) and is increasingly in demand. Arburg and Leonhard Kurz were the first to demonstrate how the film back injection of a washing machine panel works. An electric Allrounder 820 A injection moulding machine from Arburg and a foil feed unit with control cabinet from Leonhard Kurz are used.
By the way, the IMD not only transfers endless designs and colour motifs onto the surface of an injection-moulded part. Foil back-moulding also saves time-consuming and cost-intensive post-processing. Design variants and changes can also be implemented in no time at all, the companies emphasise.
Nothing beats automated processes
The injection moulding machine used for this purpose achieves a clamping force of around 4,000 kilonewtons and produces the panels in a cycle time of around 60 seconds. The plastic is transparent MABS (a copolymer of the monomers methyl methacrylate, acrylonitrile, butadiene and styrene. Also called Crilo plastic). The mould has one cavity. The short film feeder consists of an unwinder, rewinder and control cabinet. Consequently, the IMD uses a continuous roll-to-roll transfer process. The carrier film with the decorative motif is unrolled via the film transport unit above the clamping unit. In this example, this is done via an oilcloth that keeps dust away. The film rolls through the open mould, which is equipped with a clamping frame. When back-moulding with plastic, only the wafer-thin layers of paint are transferred. This makes the component easily recyclable at the end of its life cycle, emphasise Arburg and Kurz. After rolling up, the carrier material can also be recycled because it is pure PET.
Everything runs by precise clocking of the surface decoration
A simple signal exchange between the injection moulding machine and the film feed unit is sufficient for precise timing. Before each cycle, the clamping frame on the moving ejector side of the mould is also lifted. The exact positioning of the carrier film in the mould, which is provided with fiducial marks on its edges, is ensured by optical sensors. Then the clamping frame, which has a sealing lip, moves back into the starting position while the film is fixed in the cavity by vacuum and back-moulded with the plastic, they explain.
The mixed effects of pressure and temperature result in the decorative element — in this case black high-gloss lacquer — to detach from the PET carrier roll during the injection moulding process and adhere firmly to the surface of the panel. The finished part, which weighs around 145 grams, is ejected via a hydraulic core pull on the nozzle side of the mould. A linear Multilift V 40 robot system with vacuum suction cups gently picks up the part and deposits it on a conveyor belt. If required, the coating layer of the finished part can also be fed directly on the conveyor belt through a UV curing system and discharged ready for assembly. No further process steps are required.
More than mere surface decoration
Products optically upgraded in this way are increasingly in demand, say Kurz and Arburg. The spectrum of what is possible ranges from trims, various panels and centre consoles for automotive interiors to control panels for household appliances, laptop lids, mobile phone trays and cosmetic closures. Beyond pure surface decoration, as can be seen in the example of the opaque design front of the washing machine panel, haptically attractive as well as functionalised surfaces are also possible. The additional integration of touch sensors, also makes it possible to produce for example interactive displays and touch control panels economically.