Welding of bio-based plastics for applications in the field of injection moulding

Abstract

Abstract. Due to intensive research in the field of material development considerable progress in terms of processing and performance characteristics could be achieved during the last years. Therefore, bio-based plastics are increasingly being used for the production of durable injection moulded components. Several applications can be found in the automotive sector, in the field of consumer electronics or the sports industry. For an economic production, joining technology often plays a key role to realise modular designed components. Detachable connections, which are frequently used in plastics processing (e. g. snap hooks or screw connections), often reach their limits with respect to reliability and tightness of the joint. In order to meet the increasing requirements on the joint, plastics joining processes can allow suitable component assembly. Bio-based plastics may differ from conventional plastics regarding their processing properties, such as the melting and solidification behaviour. For these reasons, investigations were carried out to gain extensive process knowledge about the welding of bio-based plastics. To perform a scientific examination of the influence of the moulding process on the mechanical weld seam quality, cellulose and lactic acid based plastics were selected and injection moulded with varying parameters like melt temperature, mould temperature and injection flow rate. In subsequent welding experiments using ultrasonic welding, materially bonded connections have been produced and analysed with regard to mechanical and morphological properties. The investigations show that all of the selected bio-based plastics can be welded. Depending on the material and the welding method the choice of the moulding parameters can have different influences on the weld seam strength. For example, a higher mould temperature during injection moulding can lead to higher weld seam strengths for ultrasonic welded test specimens of lactic acid-based plastics.

The use of variotherm systems for microinjection molding

“…This work showed that moldings in a range of 100 nm to 300 µm with an aspect ratio from 1 to 10 were possible by laser molding and this new process was flexible in using different mold inserts and molding materials and sizes. Hopmann and Schongart employed an external high power diode laser scanner to the heat mold surface. The laser parameters, heating time, area‐related energy density and the spot diameter, influenced the temperature profile during the heating period.…”