Finite Element modeling of Microwave-Assisted Hot Press process in a multimode furnace

In this paper, Microwave-Assisted Hot Press (MAHP) process in a multimode microwave furnace using double-action compaction for two samples including Al-Al2O3 composite and Alumina ceramic was simulated. Firstly, cold press process for two samples was simulated. The constitutive relations of porous compacts during the compaction process were derived with respect to the yield criterion of Gurson-Tvergaard-Needleman (GTN) model. Secondly, to simulate the microwave heating process, a frequency domain calculation was used to calculate the electromagnetic field in the furnace. Then, the temperature variation of samples was calculated according to the dielectric permittivity and thermal parameters. The result was that the difference between such parameters as permittivity and conductivity, in different powder systems led to different times needed to reach the required temperature for the hot pressing process. Furthermore, compared to Alumina ceramic, more heating uniformity of the composite specimen was seen. Finally, by using green density distributions and temperature gradient extracted from microwave heating process, the hot press process of two compactions was simulated. In the process of compaction, Von Mises stress, density distributions resulted. For hot-pressed Alumina ceramic, the Mises stress at the corners of the compact reached 45% to 50% of the applied pressure and decreasing towards the center of the circumference of the compact. However, for hot-pressed Al-Al2O3 composite, the value at the corners of the compact was about 25% of applied pressure. Also, Alumina ceramic specimen during the hot press had a relative density of 96% in the outside region and a relative density of 95% in the central region where this number for Al-Al2O3 composite compact was derived to be 98% in central region.