Ultrasonic mixing head for resin transfer molding

The mixing heads which are currently used to activate resin systems in Resin Transfer Molding (RTM) processes are incapable of ensuring an environmentally friendly and cost-effective production. Low pressure mixing heads are based on friction at shear elements. High pressure mixing heads are based on impingement. Whereas the first requires an expensive, environmentally harmful solvent flushing, the latter requires a high pressure resistance, which is material and cost intensive. The aim of this thesis is to investigate how acoustic cavitation caused by sonication can be utilized to activate resin systems in RTM. The laboratory investigations show that higher amplitudes come along with a higher expansion of the cavitation zone, a faster increase of the viscosity and a higher glass transition temperature of an epoxy resin system. The results of the laboratory investiga-tion are the foundation of the Ultrasonic Mixing Head design. Altschuller’s Theory of Inventive Problem Solving is used to analyze a low pressure Static Mixing Head and to develop the Ultrasonic Mixing Head. The single functions mixing, heating and cleaning of the resin system are cumulatively attributed to the sonication effect. Further, the ultrasonic parameters amplitude and power are utilized for the online quality control of the mixing process. The process characteristics of the Ultrasonic Mixing Head are screened by a Design of Experiment procedure. Hereby, the amplitude, the volume flow and the injection pres-sure are identified as the dominating process factors. The RTM characteristic is determined by the production of fiber reinforced plates and of neat resin plates. By processing a slow and a fast curing epoxy resin system, a UMH process window is derived. It is limited by a lower amplitude threshold. If this threshold is undercut, no sufficient mixing occurs. An upper threshold of the power is detected. By exceeding this threshold, a curing of the resin system occurs before the cavity is com-pletely filled. Tensile tests and in plane shear tests of samples produced within these thresholds show a similar mechanical performance to samples produced with a low pressure Static Mixing Head. The technology transfer of acoustic cavitation to the injection technique is completed by integrating the UMH in a fully automated RTM injection process to build a generic part. For the first time, the use of sonication enables a solvent free production at low injection pressures.