PhD Defence at DTU Mechanical Engineering

PhD Defence 14th September: Modelling Induction Heating in the Surface of Injection Moulding Tools

Wednesday 09 Sep 15

Patrick Guerrier from DTU Mechanical Engineering defends his PhD "Modelling Induction Heating in the Surface of Injection Moulding Tools" Monday 14th Septmeber at 13.00. The defence takes place in Auditorium 38, Building 306.

Injection molding development is moving towards new kind of products with special feature requirements such as micro or nano structures, high length to thickness ratio, special surface and optical requirements, prone to warpage, requires very high pressures to fill or has weaknesses due to weldline. In such cases special care has to be taken to produce such parts successfully. By increasing the mold temperature to close to or above polymers phase transition temperature or its no-flow temperature will alleviate or completely remedy mentioned part defects.

The idea is to combine materials with different magnetic, electrical and thermal properties to concentrate the heating in the cavity surface of the injection molding tools via an mold integrated induction heating system. Since the induction heating is concentrated at the surface, the heat is conducted away quickly after filling and packing with conventional cooling methods, and the overall cycle time should not increase. However, there is still limited insight into the numerical simulation of the combined processes of induction heating and the filling in injection molding.

The main focus of present PhD thesis is to obtain the required knowledge to establish a numerical modeling simulation of the induction heating in the injection molding tool with a fundamental understanding of the underlying mechanisms. To help accommodating this objective was an injection molding tool with simplified part cavities, that resembles part with defects, manufactured including pressure and temperature sensors, together with a glass wall to enable a high speed recording of the filling process both without and with induction heating.

Different models to simulate both the induction heating phenomena and flow of the injected polymer are developed. The emphasis is on analyzing the heat development around the mold cavity, and filling of it. This comprises a detailed characterization of the magnetic properties of the relevant tool materials, together with a solution of Maxwell’s equation with the non-linear magnetic properties and the transient heat conduction equation. The model is compared with experiments, so it is trust worthy and can predict the heat distribution in the cavity surface correctly.

Furthermore, the temperature distribution is used in a flow model to simulate the filling of the cavity with the induction heating. Prior to the modeling of the heating in the filling model, was the filling validated with the high speed video recordings and pressure sensors from the glass mold experiments. There is a good agreement with the real life process and the developed models, and they can be applied to optimize the design of future tools with integrated induction heating coils.