Research On Extrusion Process And Extrusion Device Of Ceramic Paste

The Freeze-form Extrusion Fabrication(FEF)process is one of rapid prototyping technologies based on aqueous paste. The FEF parts have higher density, fast binder removing speed and is environmentally friendly. FEF process is intermittent extrusion and there is few research on the intermittent extrusion, especially on the liquid phase migration in paste intermittent extrusion. Therefore, the extrusion process of aqueous ceramic paste for FEF process was investigated in this paper to provide theoretical foundation and data support for FEF device development and freeform fabrication of complicated ceramic parts.The paste extrusion is the foundation of FEF process. To research the extrusion process, a feasible extrusion device is needed before extrusion experiments. A ram extrusion device for aqueous ceramic paste was designed and manufactured firstly. The design principles of device parts were detailed explained.The control software for upper computer and lower computer was programmed to control the extrusion device. The PC was used as upper computer and the human-computer interface is designed by VB for real-time data collection of extrusion force and movement control of stepper motor. The data transmission format and receiving method between upper computer and lower computer was emphatically introduced. The DSP system based on F2812 core was applied to control the low-level software. The modular programs design method was adopted in the software design of the control system. The initialization module, interrupt module, motor control module, communication module and A/D sample module in software was describe. Through the tests of the control software, the control of paste extrusion can achieve the primary purpose for desired continuous and intermittent extrusion control.The flow process and mass transfer mechanism in paste extrusion were characterized by comparing the extrusion force and liquid content of extrudate in different extrusion process parameters. The better extrusion process was given after the experimental results were analysed. In both continuous and intermittent extrusion process, when the extrusion velocity was increased, the extrusion force shows the increasing trend and the liquid phase migration is not obvious. When the extrusion velocity is higher than 0.125mm/s, there is no obvious liquid phase migration. When the extrusion die length is increased, the extrusion force shows the increasing trend and the increasing of force at low extrusion velocity is more obvious than that at high extrusion velocity. The four stage in extrusion process rises with paste loading capacity, but extrusion force showed little change. To solve the salivation problem in stop stage in intermittent extrusion process, the extrusion velocity in steady stage and retreat displacement curves were obtained by many experiments. The"salivation"phenomena is effectively controlled by using this curve.