Worcester Polytechnic Institute Optimized Design of Gating/Riser System in Casting Based on CAD and Simulation Technology By Feng Liu A Thesis Submitted to the Faculty of the WORCESTER POLYTECHNIC INSTITUTE in partial fulfillment of the requirements for the Degree of Master of Science in Manufacturing Engineering By _____________________ Feng Liu December 2008 APPROVED: Prof. Yiming (Kevin) Rong, Advisor, Associate Director of Manufacturing and Materials Engineering, Abstract Casting as a manufacturing process to make complex shapes of metal materials in mass production may experience many different defects such as porosity and incomplete filling. How to improve the casting quality becomes important. Gating/riser system design is critical to improving casting quality. The objective of the research presented in this thesis is to optimize gating/riser systems based on CAD and simulation technology with the goal of improving casting quality such as reducing incomplete filling area, decreasing large porosity and increasing yield. Therefore in the thesis, an optimization framework is presented based on CAD and simulation technology. Given a CAD model of part design and after converted to a casting model, it is the first step to evaluate castability of the casting design. Then the runner and risers are represented parametrically, and CAD models generated by varying parameters can be used in the simulation. After analyzing simulation results, the gating/riser system design is optimized to improve casting quality. In the thesis, one engine block is used to verify the effectiveness of the optimization method. Compared with the initial design, it is found that the optimized casting design can decrease porosity around 18% while the yield increases 16%. i Acknowledgement It is a great pleasure to express my gratitude to the people who have helped me during my pursuit of master degree in Manufacturing Engineering Department at Worcester Polytechnic Institute. My deepest gratitude goes to Professor Yiming (Kevin) Rong, my advisor. Professor Rong stimulates my interest of working in the area of computer aided casting process optimization with this specific approach, and guides me through the whole process. Without his support and encouragement, this thesis can never been completed. My special thanks go to the advisory committee members. I would also like to thank Dr. Qigui Wang and Mr. Gerald Baker at GM for their assistance in my research. I appreciate the great help from Dr. Gang Wang for his professional suggestions on my research work and the preparation of my thesis. The financial assistantship from WPI is highly appreciated. I would also cherish the support from my wife and my family. ii Table of Contents Chapter 1 Introduction .......................................................................................................................... 1 Chapter 2 Background ........................................................................................................................... 3 2.1 Sand Casting Processes .................................................................................................................... 3 2.2 Sand Casting Process Design ........................................................................................................... 4 2.3 Quality Problems in Sand Casting Process ...................................................................................... 7 2.4 Gating/Riser System ......................................................................................................................... 9 2.4.1 Gating System ........................................................................................................................10 2.4.2 Riser .......................................................................................................................................12 2.5 Current Gating/Riser Design and Optimization Methods ...............................................................16 2.6 Castability Analysis ........................................................................................................................17 2.6.1 Importance of Castability Analysis ........................................................................................17 2.6.2 Current Castability Analysis Methods ...................................................................................18 2.7 Problems Remained In Castability Analysis And Gating/Riser Design And Optimization ............20 2.8 Thesis Objectives ............................................................................................................................20 Chapter 3 System Framework ..............................................................................................................22 3.1 Workflow of the System Framework ..............................................................................................22 3.2 Castability Analysis ........................................................................................................................23 3.3 Casting Design Matrix ....................................................................................................................24 3.4 Casting System Design ...................................................................................................................25 3.5 Simulation Results Analysis and Gating/Riser Optimization ..........................................................25 Chapter 4 Castability Analysis .............................................................................................................26 4.1 Castability Analysis Workflow .......................................................................................................26 4.2 Modulus Based Castability Analysis Method .................................................................................27 4.3 Part Feature Recognition .................................................................................................................29 iii Chapter 5 Gating/riser Optimization ...................................................................................................31 5.1 Optimization Objectives and Initial Conditions ..............................................................................32 5.2 Flow Chart of Optimization Process ...............................................................................................33 5.2.1 Runner Optimization ..............................................................................................................35 5.2.2 Riser Optimization .................................................................................................................49 Chapter 6 Summary and Conclusion ...................................................................................................54 6.1 Summary .........................................................................................................................................54 6.2 Conclusion ......................................................................................................................................55 6.3 Future Work ....................................................................................................................................55 Reference ......................................................................................................................................................57 iv List of Figures Figure 2.1 Production steps in a typical sand casting process .................................... 3 Figure 2.2 Schematic illustration of a sand mold ....................................................... 4 Figure 2.3 Examples of sand casting .......................................................................... 6 Figure 2.4 Some defects in sand casting ..................................................................... 7 Figure 2.5 Example of porosity .................................................................................. 8 Figure 2.6 Cold-shut defect......................................................................................... 9 Figure 2.7 Misrun defect ............................................................................................. 9 Figure 2.8 Typical gating/riser system...................................................................... 10 Figure 2.9 Progressive solidification can cause a shrinkage..................................... 13 Figure 2.10 Too large feeding distance can cause shrinkage .................................... 16 Figure 2.11 Several castability guidelines examples ................................................ 19 Figure 3.1 Computer aided system workflow ........................................................... 22 Figure 4.1 Castability analysis flowchart.................................................................. 26 Figure 4.2 CAD model used to illustrate the calculation of modulus ....................... 27 Figure 4.3 Split body................................................................................................. 28 Figure 4.4 Example of calculating modulus ............................................................. 28 Figure 5.1 Current gating/riser system design .......................................................... 31 Figure 5.2 Flow chart of optimization process ......................................................... 34 Figure 5.3 Runner and its parameters ......................................................................