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Small sensor - great technology Gabriele Hopf, Wittmann Battenfeld GmbH Multi-functional housing components for sensors in automobiles are the automotive segment in which the Austrian family-owned company Promotech, based in Schalchen near Mattighofen, specializes. One example is a combined rain, light and moisture sensor for motor cars (Fig. 1). The top part of its housing with a diameter of just 33 mm incorporates seven infrared rain detectors and two lenses to measure the ambient light level. A connection plug with insertion-molded metal contacts is an additional component integrated in the housing. A vertical 3-component injection molding machine from Wittmann Battenfeld with an ultra-compact configuration of the injection aggregates is used to produce this part. ![]() Abb. 1: Einbaubeispiel eines Kombinationssensors zur Fahrlicht- und Scheibenwischersteuerung in einem PKW an der Windschutzscheibe als Teil der Innenspiegelhalterung. ![]() Abb. 2: Der Regen-/Licht-/Feuchte-Sensor ist ein 4-Komponenten-Formteil: Zwei Linsen aus PC-glasklar, zusätzlich sieben Linsen aus PC-violett, und der Gehäusekörper aus PC-schwarz. Die vierte Komponente sind drei Metallkontakte, die in das Spritzgießwerkzeug eingelegt und umspritzt werden. Combination of micro and standard shot weights A comparison of the weights of the three polycarbonate components clearly shows that the production of this 3-component part requires a combination of micro with standard injection molding. Every molded part contains 0.1 g of crystal-clear PC, 0.2 g of purple PC and 4.2 g of black PC for the housing. With the required 4-cavity production, the total shot weights of 0.4, 0.8 and 16.8 grams still remain at the lower limit of standard injection molding technology, especially at the first two injection stations. Production without sprue where possible and consequently without the necessity for recycling was also aimed at. Accordingly, the choice of the ideal injection molding technology was a real challenge for the Promotech project team, especially since insertion and insert-molding of 3 contact pins for every part had to be integrated into the injection molding process as well. Christoph Feichtenschlager, project leader at Promotech, comments: “Our many years of experience in the production of metal/plastic hybrid parts prompted us to choose a vertical machine concept. We also wanted to inject all 3 material components directly, that is, via a hot runner system in each case. In spite of the shot volumes, some of which were extremely small, we wanted to minimize as much as possible the dwell times in the hot-runner distributors. So only the most compact injection molding system with the shortest possible melt paths and minimal melt volumes could suit our purpose. This concept provided the basis for our bidding procedure. Following comparison of several systems, we finally found that the concept proposed by the injection molding manufacturer Wittmann Battenfeld suited us best.” Ultra-compact vertical injection molding machine ![]() Abb. 3: Das aus 3 unterschiedlichen PC-Typen und Metall-Einlegeteilen bestehende Regen/Licht-Sensorgehäuse wird auf einer Wittmann Battenfeld Vertikalmaschine vom Typ VM 100/210/60/60 R 752 hergestellt. Sie besteht aus einer 100 Tonnen 4-Holm Vertikal-Schließeinheit mit einem 752 mm Rundtisch und drei vertikalen Spritzaggregaten für kleine Schussgewichte (Foto: MKE). Wolfgang Glawatsch, project coordinator at Battenfeld, comments: “Although we have used modules from our standard range as far as possible, the design of this system was anything but a standard task. As already mentioned above, minimization of the material paths and material quantities in the hot runner system was the top priority in the configuration, in order to keep the dwell time of the polycarbonate and consequently potential damage to the material below the critical level.” ![]() Abb. 4: Die drei Spritzaggregate (A = Baugröße 210 mit 30 mm Schnecke, B und C = Baugröße 60 mit 14 mm Schnecke) wurden in Abstimmung mit den, auf minimale Schmelzevolumina ausgelegten Heißkanälen und dem 752 mm 3-Stationen-Rundtisch engst möglich positioniert. Small-quantity injection molding packed extremely tight Integration of the two micro injections in one of the three rotary table stations makes it possible to use just one hot runner system for guiding both materials simultaneously on two levels via needle shut-off nozzles, each to the five injection points per cavity. Accordingly, the designers of the machine have placed the two smallest aggregates (designated as B and C in Fig.4) as close as possible to each other on the fixed platen of the machine. But in spite of all these machine and mold technology features, an additional process technology trick had to be used to ensure a safe material dwell time in the hot runners, i.e. by producing a small-volume material disk together with each part, and then transferring it to the reclaim process by the parts removal handling system at the end of each cycle. During the next production step, the standard aggregate (A) insertion-molds the housing around the individual optical parts. At the third rotary table station, a handling device simultaneously removes the finished parts. This is immediately followed by placing the metal contact pins into the cavities, which is accomplished by a high-precision robot arm during the cooling period, all within the 21-second production cycle. Vertical injection molding system as part of a production cell ![]() Abb. 5: Wittmann Battenfeld-Projektkoordinator Wolfgang Glawatsch (links) und der geschäftsführende Gesellschafter der Promotech GmbH, Ing. Günter Benninger (rechts) ziehen nach einer zweijährigen Projektzusammenarbeit sichtlich eine positive Bilanz. About WITTMANN BATTENFELD WITTMANN BATTENFELD is a member company of the WITTMANN group and a leading manufacturer of injection molding machines for the plastics industry with its headquarters and production plant in Kottingbrunn / Lower Austria and sales and service companies as well as sales agencies in 60 countries worldwide. Its production program includes the complete range of injection molding machinery from micro injection molding machines up to large machines with 1,100 tons clamping force, as well as vertical machines and machines for multi-component injection molding. The range is rounded off by comprehensive application technology packages, which are complemented by the robotics and peripheral equipment range from Wittmann. www.wittmann-group.com About PROMOTECH Promotech was established in 1995 and is a middle-sized, family-owned company with 180 associates. Its range of products and services includes punching technology, tooling and mold-making, injection molding technology (specialty: insert molding) and automatic assembly technology. Its core competence lies in the field of mechatronical hybrid parts made of metal and plastics. The main product lines are parts for the automotive industry, primarily sensor and plug-and-socket connection assemblies in all conceivable sizes and variants. In parking sensors, Promotech covers about 60 per cent of the total global production with appox. 30 million units per annum. In addition to automotive components, the company also produces medical technology parts. www.promotech.at Wittmann Battenfeld GmbH Wiener Neustädter Straße 81 Phone: +43 2252 404-0 Internet: www.wittmann-group.com |
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