Induction Heating System Applied to Injection Moulding of Micro and Nano Structures

The present Ph.D. thesis contains a study concerning induction heating system applied to injection moulding of micro and nano structures. The overall process chain was considered and investigated during the project including part design, simulation, conventional and non-conventional tooling, moulding, final verification of the mould part.
The main object of the project was to develop a system for fast heating of the cavity of an injection moulding mould. The technology adopted was an embedded induction heating system. This system was developed to increase the replication quality of the mould part. In fact one of the main problems in micro injection moulding is the premature freezing of the polymer flow inside the cavity and often is not possible to obtain a full replica of the nano/micro structures embed on the surfaces. Some other defects that can be avoided with the use of an additional source of heat in the cavity are; flow marks, sink marks, welding lines, is possible to release stresses and obtain a glossy surfaces.
Different tooling chains for creating the heating system were investigated. A series of experimental investigations were carried out for testing the induction system and for understanding the influence of the main process parameters on the quality of the parts.
The experiments were conducted on a manual injection machine for the first campaign and in a second phase on two different completely automatic injection moulding machines.
Metrology was performed to characterize the moulded parts. The polymer parts were mainly measured with atomic force microscopy (AFM) and an optical coordinate measurement machine (CMM). The results show that the main influencing factor on the replica quality is the mould temperature.
Another part of the project consisted in benchmarking of the developed embedded induction heating system with other heating systems suitable for injection moulding already available on the market. The two selected systems were a variothermal system based on the convective/conductive heating principle and one based on infrared light.
During the project simulation software for injection moulding (Moldflow) was used to predict the flow length of the polymer inside the cavity when the induction heating system was running. The simulations were running under different conditions and different optimization strategy.