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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, specialises. One example is a combined rain, light and moisture sensor for motor cars. The top part of its housing with a diameter of just 33mm incorporates seven infrared rain detectors and two lenses to measure the ambient light level. A connection plug with insertion-moulded metal contacts is an additional component integrated in the housing. A vertical three-component injection moulding machine from WittmannBattenfeld with an ultra-compact configuration of the injection aggregates is used to produce this part.
Every modern car is equipped with an abundance of electronic systems to enhance both safety and comfort. Sensors are vital components of such systems. One such sensor is the rain/light/moisture sensor. Its housing consists of three different types of polycarbonate. Material number one is crystal-clear PC for the two lenses which measure the ambient light (to activate vehicle lighting) and the headlamp light of oncoming traffic (to control automatic dimming). Material number two is purplePC used to form six lenses positioned on the corners of a hexagon, as well as an additional central lens. These lenses support the emission and reception of infrared light rays.
The rays are emitted by an LED lamp on one side and reflected by the boundary surface of the windshield to the receiver photodiode positioned on the other side. The infrared light ray, however, is only completely reflected as long as the windshield is dry. As soon as there are rain drops on the windshield, the reflection is disrupted, and only part of the light reaches the receiver diode. The difference in intensity compared to the degree of light reflection when the windshield is dry controls the function of the windshield wiper.The lenses are embedded in a housing made of black polycarbonate.
Another integral part of the housing (with a total weight of less than 5grams) is a connector with three insert-moulded male contacts. The housings are also connected by means of a “flexband” to a moisture sensor, which detects moisture on the inside of the windshield and activates the blowers accordingly.
Comparison of weights
A comparison of the weights of the three polycarbonate components clearly shows that the production of this three-component part requires a combination of micro with standard injection moulding. Every moulded 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 requiredfour-cavity production, the total shot weights of 0.4, 0.8 and 16.8 grams still remain at the lower limit of standard injection moulding 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 moulding technology was a real challenge for the Promotech project team, especially since insertion and insert-moulding of three contact pins for every part had to be integrated into the injection moulding process as well.
ChristophFeichtenschlager, 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 three 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 minimise as much as possible the dwell times in the hot-runner distributors.