Evaluation of injection pressure as a process fingerprint for Injection and Injection Compression Molding of micro structured optical components

Injection pressure is one of the most significate factor governing the effectiveness of Molding based manufacturing processes. Being the monitoring of injection pressure easy to implement, the opportunity to address quality control on injection pressure as manufacturing fingerprint opens up to the possibility of implementing online process control solutions for Industry 4.0 approaches; examples are machine learning, deep learning and artificial intelligence. For the purpose, the calibration of process fingerprints with a quality feature of the final part is required. In this study, the injection pressure is assessed in different Injection Molding and Injection Compression Molding process conditions when replicating a polymer microstructured optical part [1]. The study case presents a high clarity polymer Fresnel lens showing a square aperture with varying low aspect ratio features. Grooves step height size ranges from 17.3 μm to 346.6 μm for peak-to-valley (PV) while the pitch has a constant value of 748.1 μm. Absolute dimensions of the grooves, as long as global part mass, are investigated in varying compression gap and holding pressure levels. Defining relationship between the geometrical dimensions of the micro structures, global mass and process fingerprint is the main outcome of this research work.