| Summary: | 碩士 === 國立成功大學 === 材料科學及工程學系碩博士班 === 95 === The research is aimed at applying the numerical modeling on the gating and riser designs for investment castings of 17- 4PH stainless steel, and experiments were conducted to verify the results. The commercial available computer-aided engineering software was employed to simulate the mold filling and solidification process in different runner systems, and predict shrinkages. Verification of numerical results was done by actual castings, and shrinkages were analyzed to modify the gating and runner system. Moreover, the simulation of microstructure for 17- 4PH stainless steel was carried out in this study; the results were also testified by the observations of the real castings.
Differential Thermal analyzer, DTA, and Computer-Aided Cooling Curve Analysis, CA-CCA, were adopted to measure the thermal property of 17- 4PH stainless steel, e.g. solidus temp., liquidus temp., the curve of solid fraction versus temp., and latent heat. The experiment data were applied for numerical modeling calculation.
The study case chose a new-style golf putter as a subject. An existed preliminary design of the runner and gating system was obtained by empirical, which composes of a horizontal runner and vertical gates. The experiment results showed inappropriate porosity distribution in the actual casting. The commercial software ProCASTTM was adopted to simulate mold filing and solidification process in the preliminary designed runner system, and predict the defects distribution with hot spot idea. Based on the results of simulation, the reason of defects occurrence was conjectured that the poor gating locations results in cut-off of feeding path; therefore molten liquid cannot feed into the entrapped area during solidification process. Thus, the runner system was improved to get a modified design of runner and gating system, including changing the orientation of castings, making the gates to the horizontal direction, and adding vertical runners to enhance melt flow. The practical production reveals defects were eliminated; the quality of the casting was satisfactory.
In this research, 3D-CAFETM was also used to simulate the nucleation and grain growth of 17- 4PH stainless steel castings. First, a control group was design to conduct experiments, and then a set of suitable parameters for numerical calculating were found out by comparison between the results of experiment and simulation. Applying this set of parameter to the simulation of experimental group, it shows a good correlation between the microstructure of actual 17- 4PH casting and the modeling result. The reliability of these microstructure parameters of 17- 4PH casting under this circumstance was proved.
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