Assessment of polymeric flow in micromouldings coated with nanocrystalline diamond

Abstract

With the increased production of microcomponents, it is necessary to overcome various technological challenges existing in the micro-injection moulding process: the wear of the microfeatured moulding tool; the perfect filling of high aspect ratio paths; the rheology and heat transfer mechanism in such conditions; among other factors. To address some of these challenges, appropriate moulding surface coatings, displaying high hardness, high thermal conductivity, high thermal shock capacity and low friction coefficient may be of great importance. In this work, a moulding insert was coated with nanocrystalline diamond films. This insert, especially designed to evaluate the flow front of two pathways, was then used for the production of polypropylene microparts with the scope of analysing the relative position of the welding line, and therefore, evaluate the polymeric melt flow in the microimpressions. The morphology, quality and stress developed in the obtained diamond film was analysed, showing an average grain size of about 100 nm, in which their crystals are homogeneous, forming a coalescent film. The coatings present a typical Raman spectrum. Through the moulding path with the diamond coating, it was found that the melt temperature is the variable that has the greatest influence on the advance of the front flow. The front flow appears to benefit from the coating, leading to a more controlled filling process, replicating the findings presented formerly. It is suggested that the diamond coating can act as a heat buffer, weakening the heat transfer mechanism in the polymer/ mould interface at the flow stage, reducing the importance of the design of the temperature control system.