The technique of scoring is used to produce the weakening lines needed in the decorative skins of instrument panels in automobiles to facilitate airbag deployment. With this technique, the wall thickness is reduced by a very specific amount in order to create a defined location for splinter-free breaking of the part’s surface in the event that deployment of the airbag is triggered. Two opposing objectives must be satisfied while producing these weakening lines. On the one hand, the wall thickness must be reduced to a point where deployment is assured once the airbag is activated. On the other, the weakening line should remain hidden and unseen on the appearance surface after years of intense use.
With the scoring systems used to date, the cutting precision, and thus the remaining wall thickness, depend on numerous factors, including among others positioning of the robot, the dynamics of the robot’s axes, the tool tolerances and the ambient temperature. For this reason, KraussMaffei has developed a new rugged and inexpensive system for creating weakening lines in parts. The backing surface that serves as part support is a precision-mounted ball that can rotate freely and is connected via a C-shaped bracket to the knife. The distance between the tip of the knife and the surface of the ball can be set with the aid of a servo-driven high-precision spindle arrangement that features position measuring system. As long as the skin remains in contact with ball during the entire scoring operation, all of the previous sources of defects associated with imprecise guidance are eliminated completely.
The new scoring system is characterized by its simple yet reliable principle of operation, which achieves greater accuracy than other robot-guided systems used to date. At the same time, the quality of process monitoring is enhanced considerably by taking the forces needed for cutting into consideration.