1st ICAI 2020

International Conference on Automotive Industry 2020

Mladá Boleslav, Czech Republic

1.1 Bio-based plastics Bio-plastics refer either to the bio-based origin of the plastic (derived from biomass) or its biodegradable nature (broken down by microorganisms) or both. In general, the bio-plastic properties are quite similar to their synthetic counterpart. However, the use of various grades of bio-plastics needs to be evaluated for certain application fields. (Frost & Sullivan, 2020) Bio-plastic represent about one percent of the more than 359 million tons of plastic produced annually. But the demand is rising: Besides materials already launched into the market like PLA or PET, new and innovative bio-polymers, such as bio-PP and PHA (polyhydroxyalkanoates) show the highest relative grow rates. In 2019 the global production capacities of PLA was one of the largest with nearly 13.9 %. This shows the importance of research studies for an increased world-wide use, especially for packaging applications. (European Bioplastics, 2020) Polylactic-acid (PLA) represents the bio-based polyesters. The monomer is typically produced from fermented plant starch such as corn, cassava, sugarcane or sugar beet pulp. Compared to Bio-PP, which has comparable properties like petro-chemical PP, PLA has no synthetic twin. Precisely for this reason the industrial acceptance is difficult, due to lack of experience in production and processing. This is where the junior research project “bioESens”, launched at the HTW Dresden, Germany comes in: in addition to enhancements of the basic materials and special applications in electronics, dissimilar joining with metals is investigated and compared to conventional petro- chemical thermoplastics (HTW, 2017). 1.2 Joining techniques for metal-plastic connections The generation of hybrid parts made from plastics and metal elements are preferably done by over-molding the metal structures during an injection molding process. Here the delta- α problem, caused by the different thermal expansion coefficients, results in limited joint properties. Thus, to connect much more complex metal parts to plastics often mechanical joining techniques using screws or rivets are applied. Disadvantages are the local damage on the plastic part (hole) and the need of additional material (screw, rivet). Besides mechanical joining adhesive bonding processes are frequently used in the industry. It is known that adhesive bonding is sensitive to any surface contamination; it is slow because of long curing times and achieves only limited joint strengths. Especially the adhesion behavior of thermoplastic parts is very limited due their low-energetic surface properties. Only strong efforts in surface pre-treatment can guarantee good and reproducible joint strength. (Meschut and Bergau, 2014; Kleffel and Drummer, 2017; Kreling, 2015; Köckritz, 2013) Within the last years research projects were working on different process solutions, especially thermal based solutions like ultrasonic and thermal direct joining (Wand, 2016; Hopmann et al, 2016; Amenda et al, 2013; Flock, 2011; Rösner, 2014; Klotzbach et al 2017). During ultrasonic welding an oscillating ram presses the joining partner together. Based on the high frequencies heat will be generated at the interface. The thermoplastic melts and wets the metallic surface. After cooling the plastic solidifies and the connection is generated. During thermal direct joining, also called “HPCi ® technology” (HeatPressCool integrative), the metallic joining partner is heated up

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