Effects of micro-injection moulding process parameters on accuracy and precision of thermoplastic elastomer micro rings

Significance 

Polymeric materials such as thermoplastic elastomers have a wide range of application in several fields such as medicine, biotechnology, communications and automotive due to their peculiar properties. In response to the high demand of more miniaturized and complex-shaped components, various manufacturing technologies have been developed to address the challenge.

Conventional injection molding has been used to process various polymeric materials such as rigid thermoplastics. However, to keep pace with the advancement in technology which has created a significant need for micro-components, micro-injection molding technology has been designed as an improvement of the conventional one. It is a cost-effective method capable of manufacturing the required micro-components with extremely high accuracy and precision.

Recently, a group of researchers from the Technical University of Denmark, Department of Mechanical Engineering: Ph.D. student Federico Baruffi, Researcher Matteo Calaon and Professor Guido Tosello studied the application of micro-injection technology in the production of thermoplastic elastomer micro rings. They also analyzed the effects of the various parameters of the process on the accuracy and precision of the manufactured micro rings. Their research work was published in the journal Precision Engineering.

To investigate the accuracy and precision required of the process, the authors used a focus variation microscope to measure different dimensions of the parts such as the internal and external diameters of the micro rings. On the other hand, the mold cavities were dimensionally assessed using a 3D optical coordinate measuring machine.

The research team observed that the process parameter indeed had effects on the accuracy of both the internal and external diameters of the thermoplastic elastomer rings. For instance, the variations induced by the process on outer diameters were inversely proportional to those of the inner diameter. The effects of the holding pressure and the temperature of the mold were intense on the outer diameter while the inner diameter was mainly affected by mold and melt temperatures.

This research is the first to investigate micro-injection molding applied to thermoplastic elastomers. The choice of thermoplastic elastomers (TPE) materials was because of their ability to produce soft and flexible micro-polymer parts. The variations of the process parameters investigated in this study produced an antagonistic result to the measured internal and external diameters of the micro rings. This rendered whole process hard to optimize with respect to the achievement of the designed geometrical specifications.

According to the authors, low values of the clamping force were necessary to minimize the size of defects affecting the micro ring quality such as weld lines and air traps. Moreover, by using the average mold diameter as reference, it was shown that the constrained shrinkage on the inner surface of the ring resulted to a high decrease of the inner diameter as compared to the outer diameter. This was caused by the presence of the central pin that did not allow the inner surface to shrink freely as did the outer one.

Effects of micro-injection moulding process parameters on accuracy and precision of thermoplastic elastomer micro rings. Advances in Engineering

About the author

Federico Baruffi: Federico Baruffi’s scientific work focuses on the study and improvement of micro manufacturing processes. He graduated in Mechanical Engineering cum laude at Politecnico di Milano in April 2016, defending a thesis on precision metrology of surface topography developed in collaboration between Technical University of Denmark and LEGO® group. After that, he started a PhD project in May 2016 as early stage researcher (ESR) in the European H2020 project MICROMAN. His PhD project aims at developing and optimizing the micro injection moulding process of an ultra-small three-dimensional micro medical polymeric component. The innovative concept of micro-manufacturing fingerprint is the core of the project: by identifying and linking the most relevant product and process features, the time needed to carry out the quality assurance can be consistently decreased using in-line metrology and process monitoring. Micro injection moulding can be therefore optimized in-line, resulting in a more accurate and productive manufacturing process.

About the author

Matteo Calaon: Matteo is a Researcher at the Technical University of Denmark, Department of Mechanical Engineering, Section of Manufacturing Engineering. The scientific work cover precision manufacturing for final polymer micro and nano structures replication, process chain characterization and calibration for advance manufacturing through surfaces and dimensional metrology, design and product development oriented to industrial production. Micro and nano metrology applied to advance manufacturing to provide traceable measuring methodologies and calibration services into industrial production environment.

About the author

Guido Tosello: Guido Tosello, PhD, is Associate Professor at the Technical University of Denmark, Department of Mechanical Engineering, Section of Manufacturing Engineering. He is senior lecturer, research manager, supervisor of PhD, MSc, and BSc projects, and industrial and management consultant. Guido’s principal research interests are the analysis, characterization, monitoring, control, optimization, and simulation of precision molding processes at micro/nano scales of thermoplastic materials. Technologies supporting precision/micro/nano molding processes are of research interest, for example: advanced process chain for micro/nano tools manufacturing, quantitative validation of injection molding simulation, additive manufacturing, dimensional and surface micro/nano metrology, measurement calibration and uncertainty, statistical process control, design of experiment, polymer materials characterization, design and manufacture of 3D precision/micro components and micro/nano structured surfaces, and multi-material and micro insert molding.

Guido Tosello is the recipient of the “Technical University of Denmark Best PhD Research Work 2008 Prize” for his PhD thesis “Precision Moulding of Polymer Micro Components”; of the 2013 Alan Glanvill Award by The Institute of Materials, Minerals and Mining (IOM3) (UK), given as recognition for research of particular merit in the field of polymeric materials; of the Young Research Award 2014 from the Polymer Processing Society (USA), in recognition of scientific achievements and research excellence in polymer processing within 6 years from PhD graduation; and of the Outstanding Reviewer Award 2016 of the Institute of Physics (UK) for his contribution to the Journal of Microengineering and Micromechanics. Guido Tosello is currently the Project Coordinator of the European Innovative Training Network MICROMAN “Process Fingerprint for Zero-defect Net-shape MICROMANufacturing” funded by the European Commission Horizon 2020 Programme and the Project Leader for ‘3D Printing and New Production Processes’ of MADE Manufacturing Academy of Denmark funded by Innovation Fund Denmark.

Reference

Baruffi, F., Calaon, M., & Tosello, G. (2018). Effects of micro-injection moulding process parameters on accuracy and precision of thermoplastic elastomer micro ringsPrecision Engineering, 51, 353-361.

 

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