Microwave rapid debinding and sintering of MIM/CIM parts

Microwave assisted thermal debinding of parts obtained by Metal Injection Moulding (MIM) or Ceramic Injection Moulding (CIM) could benefit from the heating selectivity, having the organic binder to preferentially absorb microwaves, thus accelerating the conventional process, which has to rely on heating by conduction. This is particularly useful when dealing with ceramic powders having low thermal conductivity, but also more conductive materials can be treated faster if the maximum temperature difference inside each part is kept low.Once the organic binder is removed, microwaves at 2.45 GHz can be used to rapidly sinter the obtained brown parts, minimizing grain growth.In this work, microwave assisted debinding and sintering of MIM/CIM parts, made of stainless steel, alumina and titania is studied, using numerical simulation to investigate the presence of localised effects ascribable to the electromagnetic field distribution in the powder compacts.

Thermal debinding of parts obtained by Metal Injection Moulding (MIM) or Ceramic Injection Moulding (CIM) can benefit from the rapid, volumetric and selective microwave-assisted heating, having the organic binder or the metallic powders to preferentially absorb microwaves. This is particularly useful when dealing with ceramic powders having low thermal conductivity, but also more conductive materials can be treated faster if the maximum temperature difference inside each part is kept low. Microwave assisted debinding and sintering of MIM/CIM parts, made of stainless steel and alumina, has been optimized by means of numerical simulation, in order to determine the most favorable load configuration, in terms of heat generation homogeneity and energy efficiency. Rapid microwave-assisted debinding, in the optimized loading conditions, was experimentally achieved, with time reduction from 6 to 8 times, compared to conventional processes. Moreover, in case of MIM, pre-sintering of the brown part occurred, despite the temperature lower than 600°C. The occurrence of this beneficial phenomenon, which improves the brown part mechanical properties, has been ascribed to the electromagnetic field concentration which takes place in the space between the conductive particles, thus promoting rapid binder removal and neck formation.