Precision Counts

Especially in the field of bodycare products high demands are made of aesthetics. Alongside productivity and safe manufacturing procedures precise production and processing are similarly important. Injection moulding tools and machinery are precision-tailored to specific production processes and are often custom-made.

The production of toothbrushes and mascara wands is extremely demanding. With toothbrushes the parts are largely manufactured in sequence from several plastic components. The necessary tools are generally very large and consist of dozens of single nest units. Precision of the individual nests and their positional tolerance demands great accuracy for smooth processing. In order to avoid the development of burrs when inserts are subsequently replaced the various single nests must not only match with regard to their cavity but also in terms of the 3D curved mould release surface.

Furthermore, in the event of maintenance customers expect individual inserts to be replaced quickly and hassle-free. Here the experience of manufacturers who know the material behaviour of the individual plastics in detail really counts. Because the smallest divergence can have a negative impact on production. Tolerances are extremely fine: for instance, with tool sizes of 0.75 x 10 cm a maximum divergence of 0.02 mm is tolerated. In mould separation, it is under ten microns due to the high injection pressures; in the assembled state as little as just 5 μm. Manufacturers walk a fine line here and look to creating ideal production conditions. Workshops are fully air-conditioned and automatic probes are used to detect the zero points of the components directly in the machine to avoid deviations. Form accuracies are measured by tactile methods and documented on the milling machine. A periodic recalibration using a reference part previously measured externally serves as control. Simulations of the injection moulding process play an essential role in meeting customer demands for aesthetic and haptic concepts in the best possible way.

Precision filling comes care of a development by the German firm ViscoTec. The ViscoTec Hygienic Dispenser VHD promises reliable, high-precision and reproducible dosing for semi and fully automatic filling systems of various viscosities. Even abrasive products are easy to process. Lipstick compounds can be processed and dosed with the system already at 100C° instead of 120°C. This requires less energy to melt the lipstick and it reduces costs. After the heating process the mass can be transferred directly into the lipstick mould. Thanks to the dispenser's retract function, liquid lipstick cannot drip. Clean filling is followed by a short drying time; after which the lipstick can be processed further. The accuracy of the dispenser ensures that the lipstick mass can be dosed with a repeatability of +-1%. This also makes it particularly suitable for small-volume dosing of medium to high-viscosity materials from 0.2 ml and for shear-sensitive products with solids or abrasive components.