No abstract

To allow cost effective mass production of reinforced thermoplastics for visible parts, in-situ a surface quality with "Class-A" standard must be achieved. Furthermore, after the application of varnish, an appearance (gloss, waviness, color) similar to that of the traditional metal component is required. Porosity and fiber readout are the common surface defects. Fiber readout results from the significantly higher volume shrinkage of the thermoplastic resin (higher CLTE) in comparison to that of the reinforcement during the cooling process in production combined with the uneven distribution of resin and fibers. While glass mat reinforced thermoplastic (GMT) parts show a disorderly readout influenced (among other factors) by fiber length. processing and fiber content of the semi-finished material, the fabric reinforced thermoplastics (organic sheets) suffer from a regular print-through-a display of the textile reinforcement. Modem tools of measurement enable one to quant @ gloss, roughness, and waviness of the surfaces. Thus parameters significantly influencing the surface characteristics can be identified. This leads to the development of procedures for improving the surface quality.

Endless fiber reinforced thermoplastic sheets (organic sheets) offer a range of mechanical properties (stiffness, strength, energy absorption) that make them interesting for many high-duty applications. However they often fail to come into operation due to cost and surface problems. Cost problems can occur in consequence of either expensive raw materials or of the investment outlay required for the impregnation and consolidation steps when only small quantities are produced. The surface problem on the other hand is caused mainly by the print-through of the reinforcing fibers and it affects especially those applications in the field of automotive exterior panels. The following article describes the work needed to analyze the material and the process parameters that influence the surface appearance. A finite element model has been created, that represents a semi-finished sheet with four layers of a 2/2 twill textile reinforcement. Based on that geometry various matrix characteristics as well as the vertical orientation of the reinforcing layers have been analyzed. Finally the influence of pressure and cooling rate during the consolidation process was investigated. The simulations helped to identify primary influence parameters and clarified the possibilities and also certain limitations concerning the surface quality of this material class.