Simulation of die filling for the wax injection process: Part I. Models for material behavior
- PDF / 756,529 Bytes
- 5 Pages / 612 x 786 pts Page_size
- 28 Downloads / 236 Views
07/08/2004
5:41 PM
Page 755
Simulation of Die Filling for the Wax Injection Process: Part I. Models for Material Behavior J.-C. GEBELIN, M.R. JOLLY, A.M. CENDROWICZ, J. CIRRE, and S. BLACKBURN This article is the first of two articles dedicated to the modeling of wax injection for the investment casting (or lost wax) process. It will present several models that have been established in order to describe the behavior of the wax during the injection in a die. The first part of the article presents the modeling of the rheology of the wax, and the second part presents the modeling of the thermophysical properties of the wax. These models will be validated in the second article by comparison of the results from experimental and numerical work, the numerical work being carried out using the models presented here. The quality of these models will then be assessed in the second paper.
I. INTRODUCTION
INVESTMENT casting is one of the oldest manufacturing processes, and has been used for several thousands of years. Through the ages, it has evolved, and even though it is a more controlled process now than 3000 years ago, it is not yet fully understood. In the modern investment casting process, a male pattern is manufactured from wax, or other polymeric materials, usually by injection molding into a die that contains a female impression of the final component shape. The die may also contain a friable ceramic core. The pattern is then coated (invested) with a shell of ceramic particles bound with inorganic materials. The shell is de-waxed and fired, after which metal is poured into it. There are no split lines in such castings and the process is primarily used for near-net-shape production of high integrity components. Probably one of the oldest casting processes, investment casting, is now used when the highest level of detail and quality is required. The mold is hot when metal is poured, usually between 0.75 and 1.0 Tm of the alloy, and this aids the filling of very thin sections. For example, the trailing edge on a turbine blade may have a radius of 0.1 mm, and the minimum section thickness of an aerofoil may be between 0.3 and 0.8 mm. At these dimensions, the controlling factor for complete filling of the casting becomes the surface tension, and so the wetability couple of the shell and liquid alloy becomes important. The level of detail achievable is potentially very high and the surface finish is extremely good for a nonpressurized process. It is possible to achieve good tolerances, but controlling the process brings substantial engineering challenges, as there are many stages to complete, each with its own source of errors. The capability of the process is very wide. Extremely small components weighing just a few grams can be cast for dental implants or jewelry; conversely, some industrial and aerospace components can weigh up to several hundred kilograms. Investment casting in a vacuum or inert gas is J.-C. GEBELIN, Research Fellow, M.R. JOLLY, Senior Research Fellow, A.M. CENDROWICZ, Research Associate, and S. BLA
Data Loading...
