Investigations on the Production of Hybrid Structures Using the Two-Stage GITBlow Process

The special injection molding process GITBlow was developed by the Kunststofftechnik Paderborn and combines the processes of gas assisted injection molding ("GIT") and blow molding ("Blow"). The parts feature large, thin-walled hollow spaces and additional functional elements. This is realized by using two consecutive gas injections and a mold with two cavities of different sizes. The first gas injection creates a hollow space within the part. In a second larger cavity the hollow space is inflated further by a second gas injection. The aim of the current research project is to manufacture hybrid structures consisting of GITBlow structures and continuous fiber-reinforced thermoplastic sheets. The new approach is to join the parts with the molten sheet material during the final phase of inflation in order to strengthen the parts locally. The parts produced with this process are characterized by their low weight, large volume and high compressive strength. To achieve the highest possible bond strength between the two components, it is necessary to maximize the temperature of the GITBlow part within the joining area. In a case study with Polycarbonate (Covesto Makolon OD 2015) and Styrene-Butadiene copolymer (Styrolution Styrolux 656C) the influence of the melt temperature and various process times on these factors can be shown. For PC a maximum temperature in the joining area of 165 degrees C can be achieved while still maintaining optimal part quality (SBC: 120 degrees C). Further investigations show that heat transfer within the part is of major importance for the final temperature distribution. With this knowledge an optimization of the process concerning the production of hybrid structures can be achieved.