Impressive Approach Enables Multi-Function Car Sensor

An amazing amount of injection molding technology goes into a combined rain, light and moisture sensor integrated into the rear view mirror bracket on the windshield of a car. The top part of the polycarbonate housing for the sensor has a diameter of just 33 mm and incorporates seven infrared rain detectors and two lenses to measure the ambient light level.

The housing comprises 0.1 g of clear PC, 0.2 g of purple PC and 4.2 g of black PC. OK, so that’s three barrels, two of which are micro capable. A fourth mold cavity is required for a connector (under five grams) that has three insert-molded male contacts

“Our many years of experience in the production of metal/plastic hybrid parts prompted us to choose a vertical machine concept,” says Christoph Feichtenschlager, project leader at Promotech (Schalchen, Austria), producer of the part, comments: “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 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.”

Here is the system lineup that Promotech is using:

  • A vertical, fully hydraulic, 4-tie-bar, 100-ton injection molding machine from Wittmann Battenfeld equipped with a clamping unit and a 3-station rotary table with a diameter of 752 mm and three injection units, which are also vertical, in sizes 60 (twice) and 210. The first two injection units are fitted with 14 mm screws are the third has a 30 mm screw. The top priority in the configuration is the minimization of the material paths and material quantities in the hot runner system.
  • Mold Masters supplied the hot runner systems
  • KTW, the 3 x 4-cavity mold system, and
  • MKE, the automation equipment.

The production cycle? Just 21 seconds. The metal contact pins for the connection plug are punched, bent and prepared for transfer by the handling system in the same production cell.


Clear PC houses two lenses that measure the ambient light to activate vehicle lighting and the headlamp light of oncoming traffic to control automatic dimming. Purple PC is 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. (Photo and text: Wittmann Battnefeld)


Sensor is made in a vertical machine. (Wittmann Battenfeld)


About Doug Smock

Former Chief Editor at Plastics World and Senior Technical Editor Design News

Automotive, Design, Europe, Hot runner systems, Indexing, Injection Molding, Injection Molding, Micro Molding, Polycarbonate, Three-Shot , ,

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