With around 120 employees, A. & J. Stöckli AG (Netstal, Switzerland) manufactures premium quality injection-molded components for household items, logistics units, as well as technical parts and visible parts. The IMD technology is to be used for the first time within the framework of a customer project for the realization of "design panels for an oven". One thing was clear for Stöckli: In order to be able to meet the tight deadline and ensure the high component quality, the new technology had to be implemented correctly.
In the automotive sector everyone immediately thinks of the orange juice test or sun cream test when it comes to the topic of durability of plastic parts. It is easy to fail to see that the requirements in the kitchen are significantly higher. Chemical resistance, in particular, deserves a special mention here.
Dough quickly spreads from fingers to the front of an oven - and then proteins and fats act on its surface. Cleaning agents are also stronger and used more frequently.
Stöckli has already been relying on KraussMaffei machines for years and operates 20 such machines with clamping forces from 500 to 10,000 kN at its production site in Switzerland. For the realization of the machine and system concept, Stöckli therefore also chose its long-term partner, who together with the film manufacturer Leonhard Kurz planned the entire configuration of the new system. A GX 400 with articulated-arm robot (IR 300 R2430 F/K) was used as the basis; the latter was delivered as a package by the KraussMaffei Automation division, who also played a significant role in the project.
Decoration and scratch-resistant coating in one
The IMD process fulfills two tasks for the component: it provides a decorative feature and a scratch-resistant coating. For this, a film passes through the mold and with every shot transfers its lacquer package to the part. So that this part looks perfect afterward, the manufacture must take place free of particles where possible. A FlowBox is therefore fitted on the GX. It causes a laminar air flow so that particles are kept away from the mold area. The robot protective housing is also closed at the top.
When the mold is opened, the robot integrated in the MC6 machine control takes the cover, separates the sprue, and feeds the product to the UV tunnel unit where the scratch-resistant coating obtains its final strength.
During the conceptual design of the system it was necessary to optimally coordinate the interfaces of all components in order to offer Stöckli maximum operating comfort with the new technology. For instance, there were mechanical and electrical interfaces for the feeder from Kurz, and also the FlowBox, UV tunnel, and other elements had to be connected.
Thanks to its design, the two-platen GX machine is perfect for integrating process steps such as IMD in a confined space, because there is sufficient space in the zone of the ejector and the moving platen for the equipment for providing and pulling through the films. The GX also impresses with high precision on the clamping side. This is necessary because the finisher must be manufactured in an accurate and repeatable manner within a narrow tolerance range in order to be able to be installed properly later. The combination of a robust guide shoe GuideX and fast locking device GearX guarantees secure positive locking.
"The system concept is optimally designed for our requirements and customer needs."
APC plus for enhanced process stability
For the injection molding itself, the APC plus machine function ensures that all components are filled with exceptional consistency so that they have perfect installation suitability. Using the melt viscosity and preset material parameters, the machine controls the switchover point from filling phase to holding pressure from shot to shot. This is particularly useful in the case of batch fluctuations and changing ambient conditions, or during production downtimes – for example, when the IMD production is started up again following a production interruption.
In order to design the machine flexibly for various shot weights and residence times, different injection units were used by adaptation. A mold changeover system with magnetic mold fixing platens allows rapid set-up processes. With the sophisticated protection device, production can be effected either with UV tunnel, conveyor belt, or both together.
For Stöckli, the cooperative venture with KraussMaffei as a machine builder and system integrator had a dual benefit.
Andreas Pittermann, Head of the "Plastic Parts" business segment, highlights: "We were able to realize the entire system technology with virtually one contact partner. This was an important factor in order to implement the sophisticated project within a very tight timeframe with perfect results. The system concept is optimally designed for our requirements and customer needs."