Experimental study on the ice pattern fabrication for the investment casting by rapid freeze prototyping (RFP)

The process of investment casting has come to occupy a key position in the range of modem metal casting techniques. Wax pattern is widely used in the investment casting. However, there exist some problems and technical difficulties in using it such as wax pattern expanding, ceramic shell cracking, etc. A new investment casting technology, named freeze cast process (FCP), has demonstrated the possibility and advantage of investment casting with ice patterns. But how to make ice patterns is really an important concern in the FCP process. RFP is a novel, environmentally conscious solid freeform fabrication process that can generate three-dimensional ice patterns by selectively depositing and rapidly freezing water layer by layer. With RFP it is possible to make ice patterns with better accuracy and more flexibility directly from CAD models in a short time, without the cost and other issues of mold making. In this paper, the current status of the experimental study of the RFP process was introduced. The effect of different processing parameters on the layer thickness and layer width was studied quantitatively and thoroughly. These parameters include: frequency of pulse signal, stagnation pressure, scanning velocity, distance between nozzle and building surface, duty cycle of pulse signal, layer offset (slant angle), environmental temperature, scanning trajectory, and depositing material. And further the effect of the processing parameters on the dimension accuracy and surface roughness were analyzed qualitatively. The optimal parameters were chosen and used to fabricate complex ice patterns based on these experiments and analyses. Finally, an example was given to demonstrate that an ice pattern can be used to make the metal prototype. The fabricated metal prototype has a very good appearance, although surface roughness and dimensional accuracy have not been measured. The experiment results showed that RFP provides an enabling way to quickly make ice patterns for the investment casting with better quality and more flexibility. (C) 2002 Elsevier Science B.V. All rights reserved.