Fürth/Germany, 9 October 2013: Having successfully produced a chrome coated radiator grille with a diamond lattice look, the company Leonhard Kurz has demonstrated that the hot stamping process can be used to decorate complex geometries. The requirement from the auto industry was to apply a partial metallic finish to a radiator grille. The plastic part consisted of a lattice structure with 288 individual pins protruding from the nodes on the external face. These pins, which form the visible face of the radiator, were required to be given a brilliant and high-quality chrome finish. The particular difficulty with this application was that the pins all had domed heads and varying shapes so as to produce a non-uniform refraction, and consequently a diamond-like sparkle, after the metallic coating has been applied. Full-surface galvanic chroming of the plastic part would have adversely affected the appearance of the individual pins. To individually galvanize the pins and then mount them would have required enormous effort. It was therefore decided to use the environmentally friendly and significantly more economical hot stamping process. In this dry transfer process, the chrome layer, together with top lacquer and adhesive layers, are released from a carrier foil by means of a heated silicone die and permanently bonded to the plastic part.
Besides the pin geometry, a further challenging aspect is the size of the radiator grille because an injection molded part of this size is required to meet part tolerances within 2 millimeters. The particular challenge was to ensure that the silicone die, into which the curvature of each individual pin had been incorporated, would contact each pin precisely and transfer the chrome coating accurately and with clean edges. Baier, a company specializing in the construction of technically sophisticated vertical stamping machines and a member of the Kurz Group, developed a custom hot stamping machine especially for this application: a four-head hot stamping machine with four indexed part fixtures that divide the radiator grille into four segments that are coated consecutively. This division of the part enabled the tolerances to be reduced and the individual pins to be decorated with high contour accuracy. Precise adjustment of the stamping time, stamping temperature and stamping pressure ensured reliable transfer onto the curved pins. To meet the complex specifications provided by the client, the formulation of the hot stamping foil was tailored to this specific project, thus enabling the permanency of the coating.
The decorated radiator grille will be on display at K 2013 at the Kurz booth A19 in Hall 5.