Perfect appearance Kurz and Arburg make the finishing of plastic parts more productive
07/19/2021Editor: Alexander Stark
Germany – Leonhard Kurz is a film specialist, Arburg is an expert in injection molding of plastics. In this article, the partners explain what a combination of know-how makes possible.
Arburg and Leonhard Kurz achieve careful handling of surface-refined washing machine panels. Handling is carried out by a Multilift V 40 linear robot system from Arburg.
The injection molding of decorative films with plastics is used to produce high-quality and / or functionalized surfaces, such as those required for control panels in the automotive and household appliance sectors. The process is also called in-mold decoration (IMD) and is in increasing demand. Arburg and Leonhard Kurz were the first to demonstrate how the film back injection molding of a washing machine cover works. An electric Allrounder 820 A injection molding machine from Arburg and a film feed unit with control cabinet from Leonhard Kurz are used.
Incidentally, the IMD not only transfers endless designs and color motifs onto the surface of an injection-molded part. In addition, the back injection of the film saves time-consuming and costly post-processing. The companies emphasize that design variants and changes can also be implemented in no time at all.
Nothing beats automated processes
The injection molding machine used for this achieves a clamping force of around 4,000 kilonewtons and produces the plates 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 mold has a cavity. The short film feed 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 over the film transport unit above the clamping unit. In this example, this is done using an oilcloth that keeps dust away. The film rolls through the open tool, which is equipped with a clamping frame. When back-molding with plastic, only the wafer-thin layers of paint are transferred. As a result, the component is easily recyclable at the end of its life cycle, emphasize Arburg and Kurz. After being rolled up, the carrier material can also be recycled as it is pure PET.
As part of the joint project, an electric Allrounder 820 A (4,000 kilonewtons clamping force) injects the washing machine panels. With the help of the special IMD (In-Mold-Decoration) technology from Leonhard Kurz, these are decorated to a high quality, according to the company.
Everything runs through precise timing of the surface decoration
A simple exchange of signals between the injection molding machine and the film feed unit is sufficient for precise timing. Before each cycle, the clamping frame on the movable ejector side of the tool is also raised. The exact positioning of the carrier film in the shape provided with registration marks on the edges is ensured by optical sensors. Then the clamping frame with the sealing lip moves back to its starting position, while the film is fixed in the cavity by vacuum and back-injected with the plastic, they explain.
Due to the mixed effect of pressure and temperature, the decorative element – in this case black high-gloss lacquer – detaches from the PET carrier roll during the injection molding process and adheres firmly to the plate surface. The finished part, which weighs around 145 grams, is ejected via a hydraulic core puller on the nozzle side of the tool. A linear Multilift V 40 robot system with vacuum suction cups gently picks up the part and places it on a conveyor belt. If necessary, the lacquer layer of the finished part can also be fed directly onto the conveyor belt by a UV curing system and removed ready for assembly. No further process steps are required.
When the washing machine panels are back-molded, an endless film is drawn through the injection molding tool from a short feed unit. A clamping frame fixes the whole thing in place before the plastic is injected.
More than just surface decoration
There is increasing demand for visually enhanced products, say Kurz and Arburg. The spectrum of what is feasible ranges from trim strips, various panels and center consoles for the automobile interior to control panels for household appliances, laptop lids, mobile phone cases and cosmetic caps. In addition to pure surface decoration, as can be seen in the example of the opaque design front of the washing machine panel, surfaces that are appealing to the touch and functionalized are also possible. With the additional integration of touch sensors, for example, interactive displays and touch control panels can also be produced economically.