Complex Mechanical Slide Mold for Blinker Levers

Injection Molding with Almost No Tolerance

The injection mold for blinker levers operates with multiple mechanical slides at various angles (figures: Braunform)

To meet the ultra-strict standards that consumers make for a premium class car, quality assurance must start with toolmaking at the latest. Braunform GmbH, Bahlingen, Germany, on behalf of a well-known automotive supplier, developed a highly complex mechanical slide mold for blinker levers that had to meet extreme precision requirements with tolerances of ±2 µm. The specification also require an accurate fit of the subsystem into the vehicle architecture and a precise orientation of the integrated guides of the multifunction lever, which is also used for gear shifting or volume control.

The three-plate injection mold operates with several mechanical slides at various angles to free up the complicated contour, with boreholes and many undercuts, for demolding as the mold opens. As hydraulic movements are eliminated, setup can be handled more easily. There is no risk of damaging the mold, e.g. due to incorrectly connected core pullers, faulty programming or improper operation. This meets the customer’s demand to allow the mold to be operated easily at several sites in Europe.

According to the specification, the part is required to have high lateral stiffness and strength; ultimately, the gear selector must withstand operating forces of up to 250 N in four directions. The customer has therefore specified a polyamide containing 65 % glass fibers. For injection molding, the temperature control, at the necessary mold wall temperature of over 100°C, must be designed so as to ensure a uniform temperature profile, and the gating point must be located at a concealed position in such a way as to ensure uniform glass-fiber orientation in the flow direction. To counteract wear of the mold inserts due to the high glass fiber content Braunform uses specially coated chromium steels.

In crash tests, the automotive manufacturers test the lever’s durability in normal use and the predetermined rupture point at the guide ball intended to avoid injury to the driver in accidents. Thanks to the extremely narrow tolerances, the snap functions required by the manufacturer are ensured. In addition to the different functions, however, the surface design, e.g. the fine EDM-machined structure in the handle region and the smooth transitions in the parting area also give the plastic articles its high-quality appearance. Since the start of the project, Braunform has now produced and delivered 16 lever molds with one or two cavities.

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