Microinjection Molding of Enhanced Thermoplastics

Abstract

Injection molding is, nowadays, a well known and wildly used manufacturing process to produce both thermoplastic and thermosetting polymeric material components, in a large scale, with accuracy and at low prices. Even though the electronics industry provides an economy of scale for the silicon industry, polymer devices can be produced in huge volumes maintaining the requested features and quality, with a great variety of material characteristics, a fact that has considerably open the market to injection molding of micro- components. A simple miniaturization/rescale of the conventional injection molding process is not valid due to problems related with the rheology of the polymer flow in the micro cavity/channel and requires that all the process layout, as well as adjacent technologies, should be reconsidered, enhanced and properly adapted. The dimensional reduction of the components requires a higher control of the overall accuracy of the devices. The molding blocks of this type of objects are bounded to an amplified wear due to the fact that the surface roughness is dimensionally very close to the dimensions being controlled. The wear of the molding surfaces and the adhesion forces involved in the part extraction stage are greatly influenced by the nature of the material being injected and are enlarged when the molded object shrinks in the core or in the pins of the molding blocks. This is even more critical due to the flow behavior of enhanced polymer materials, developed for highly demanding applications in what concerns material mechanical or chemical properties. Tailored special polymers are of fundamental importance in the supplement of micro- components. Complex polymeric materials engineered to detain both the mechanical properties and the memory shape suitable for applications such as active control, impose enormous challenges in what concerns both the process and the molding tools. In conventional injection molding tools, surface engineering is used to improve the molding block performance to obtain parts with superior mechanical quality. In micromolding, surface engineering has a more important role due to the above-sited requisites, in order to reduce the deterioration of the molding impressions, increase its durability and reduce the need for corrective intervention on the tool. Different thin film coatings may be used, but diamond films seem to assume an extreme importance in these types of applications due to its superior properties. The …