In order to study plastication in injection molding, we designed an industry-sized metallic barrel, featuring 3 optical glass windows; each window possessing 3 plane faces to allow for visualisation and record by synchronised cameras and lighting by lasers. The images recorded can be further analysed by digital image processing. The mechanical behaviour of this assembly was analysed by numerical simulation under different thermal stresses, pressures and constraints. The heterogeneity of the structural materials (steel and glass) showed potential leakage problems that have been addressed in the design. Results confirm Tadmor's plastication theory and show a compacted solid bed located on the trailing flight and a melt pool side by side. The total plastication length is a direct function of screw rotation frequency as it is obvious from results on the melt pool width, which increases when the screw rotation frequency decreases. However, evidence of solid bed breakage has been recorded, whereby the solid bed does not diminish continuously along the screw but is fractured in the compression zone. Solid bed velocity has been measured using digital image processing, showing that it is accelerating when it reaches the compression zone. Moreover, when the screw is idle, which is specific to injection moulding, evidence has been found of a transient growing melt film lying the flight side and the solid bed.