Replication of micro-features on PLA: Effect of viscosity during injection molding with fast evolution of cavity surface temperature

Fast mold temperature evolution allows obtaining injection molded parts with lower filling pressure, better surface finishing and reduced frozen-in orientation. Recently proposed, thin heating devices, with very low thermal inertia, located just below the mold cavity surface, allow obtaining high surface temperature during filling and low surface temperature during cooling stage. The heating stage was limited to a very thin part below the cavity surface, this limits the increase of the processing time. The control of the surface temperature evolution allows controlling replication accuracy of micro-metric features during the injection molded objects. In this paper, the fast evolution of cavity surface temperature was adopted with the aim of obtaining accurate replication of microstructures on molded objects of two grades of poly-lactic acid. The use of two grades of poly-lactic acid allows establishing a correlation between the viscosity of the polymer and its replication ability. As far as the part quality is concerned, a relevant improvement of the replication accuracy of micro-features was attained by increasing cavity surface temperature. The viscosity of the polymer has also a great influence on the replication accuracy, since, the polymer with low viscosity brings to a better replication of the micro-features.