• Holzer, Clemens
• Schuschnigg, Stephan
• Hentschel, Lukas

Abstract

Material Extrusion (MEX) is a simpler AM technology, affordable also for home use. There are different designs of the dies, and we investigated two designs (MK10 and E3D), with each two variants. We assumed that the forces of the filament are related to the melt pool and not on the friction. For the investigation we used Ansys Polyflow and constructed the nozzle assemblies. We used a highly filled feedstock (55 vol.% 316L steel powder in a polymeric binder) and measured the temperature and shear dependent viscosity and the other material data. The region where we assume solid filament has a temperature dependent slip condition as a boundary, to obtain a smoother transition between the solid area and the melting region. The thermal conditions are different for each variant. The MK10 variants are an all-metal construction and a PTFE tube inside. The E3D version has a shorter or longer PTFE insert. The calculations showed interesting results, especially for the temperatures, whereas the pressures were not satisfactory as the temperature dependent viscosity model had to be adapted to calculate lower temperatures. The temperature of the all-metal design showed that, at low extrusion speeds, the melt pool was approximately 15 mm, while in the PTFE version it was only 10 mm. At higher speeds the temperature in the all-metal does not change much, but in the PTFE the desired temperature cannot be reached. In the E3D version we can see similar results between the long and short PTFE tubes. One thing is the high thermal conductivity of the feedstock at 0.98 W/(m·K), in contrast to polymers having about 0.2 W/(m·K). The MEX printer is set at increasing speeds until the gears can be heard trying to push the filament, but the solid filament is blocked in the die because there is not enough heaHng capacity. This can be heard during trials to achieve maximum prinHng speeds. The next steps are measurements with <br/>a die equipped with a load cell between the die and the gear.

Topics

• impedance spectroscopy
• polymer
• simulation
• melt
• extrusion
• steel
• viscosity
• thermal conductivity
• material extrusion