COMPUTER-AIDED MOULD DESIGN MODIFICATION AND TOOL PATH REGENERATION ZHANG LIPING (B. ENG.) A THESIS SUBMITTED FOR THE DEGREE OF PHILOSOPHY DEPARTMENT OF MECHANICAL ENGINEERING NATIONAL UNIVERSITY OF SINGAPORE 2004 ACKNOWLEDGMENTS First and foremost I would like to wholeheartedly thank my supervisors, Professor Andrew Nee Yeh Ching and Associate Professor Jerry Fuh Ying Hsi for their support (morally and academically) and for giving me invaluable guidance, suggestions, encouragement and patience throughout the duration of my graduate study in National University of Singapore. I appreciate very much all they have done for me and I will gratefully remember all forever. Sincere appreciation is expressed to Associate Professor Loh Han Tong and Associate Professor Zhang Yun Feng for their kind words of advice during my research. Thanks are conveyed to National University of Singapore for providing me with the research scholarship and to Department of Mechanical Engineering and CAD/CAM/CAE Center for the use of the facilities. Finally, I wish to express my deepest thanks to some very special people in my life: my husband, Dr. Ding Xiaoming, thank to his love, patience, understanding and great support during my graduate study, for always encouraging me to my best, for never losing faith in my abilities; my son, Ding Changzhao, of his smiles, laughter and understanding; my dear parents and in-laws, for their continuous concern, confidence and moral support. This thesis is specially dedicated to them. I There are many others who have indirectly contributed to my research and although I am not mentioning any name here, I am grateful to all of them. II TABLE OF CONTENTS Acknowledgements……………………………………………………….I Table of Contents………………………………………………………III Nomenclature…………………………………………………………VIII List of Figures………………………………………………………… IX Summary…………………………………………………………… .XIII Chapter Introduction……………………………………………… .1 1.1 Product development processes…………………………………………… .3 1.2 Mould design and modification…………………………………………… .6 1.2.1 Mould structure and subsystems……………………………………… 1.2.2 Mould design………………………………………………………… .8 1.2.3 Mould design modification……………………………………………10 1.3 Tool path generation and regeneration……………………………………11 1.3.1 CNC machines and cutters…….………………………………………11 1.3.2 Tool path generation…….…………………………………………….12 1.3.3 Tool path regeneration…….………………………………………… 13 1.4 Research objectives……………………………………………….…………14 1.5 Outline of the thesis……………………………………………….……… .15 Chapter Literature Review…………………………………………17 2.1 Mould design…………………………………………………….………….18 2.1.1 Parting direction and parting line design…………………………….18 III 2.1.2 Insert design………………………………………………………….21 2.1.3 Mould system and subsystem design……………………………… 23 2.2 Tool path generation.………………………………………………………24 2.2.1 CC-point method…………………………………………………….25 2.2.2 CL-point method…………………………………………………….29 Chapter Mathematical Background of Curves and Surfaces…….34 3.1 Curve parameters………………………………………………………… 34 3.2 Surface parameters……………………………………………………… .36 3.3 Curves on surfaces…………………………………………… .………… 40 3.4 Offset surface…………………………………………………….…………41 Chapter Mould Design Modification………………………………42 4.1 Basic concepts and principles of mould design modification……… .43 4.1.1 Concepts and assumptions of mould design modification……44 4.1.2 Principles of the insert and pocket design…………………….45 4.2 Architecture of the mould design modification system………………48 4.3 Identify the solid bodies of material to be added and removed…… .50 4.4 Identify the mould insert that material needs to be added to or removed from……………………………………………………………51 4.5 Remove material from the mould…………………………………… .53 4.6 Add material to the mould…………………………………………… .53 4.6.1 Create pocket and insert……………………………………….53 4.6.2 Detect interference…………………………………………….60 4.7 Illustrative examples……………………………………………………64 IV Chapter Tool Path Regeneration with the CL-point Method……70 5.1 Terms and notations…………………………………………………….71 5.2 Basic concepts of tool path regeneration………………………………73 5.3 Methodology for detecting affected CL-points……………………… 74 5.4 Tool path regeneration algorithms for CL-point method…………….78 5.4.1 Identifying and replacing affected CL-points…………………80 5.4.2 Calculating scallop height values and adding new CL-points to the modified region……………………………………………86 5.4.2.1 Machining scallop height and step-over size………….86 5.4.2.2 Algorithm for checking the scallop height value and adding new CL-points…………………………………90 5.5 Illustrative examples…………………………………………………….93 Chapter Tool Path Regeneration with the CC-point Method….102 6.1 Terms and basic concepts…………………………………………… 103 6.2 Methodology of identifying the affected CL-points………………….104 6.3 Tool path regeneration algorithms for the CC-point method………108 6.3.1 Identifying and replacing the affected CL-points……………109 6.3.2 Adding new CL-points for the modified region…………… 116 6.3.2.1 Calculating the CL-points with the given tolerance…116 6.3.2.2 Calculating scallop height and adding new CL-points for the modified region………………………………… 119 6.3.2.3 Detecting and removing gouging CL-points……… .119 6.4 Illustrative examples………………………………………………… .119 V Chapter System Implementation and Case Studies…………… 128 7.1 The computer-aided mould design modification and tool path regeneration system…………………………………………………… 128 7.1.1 The platform…………………………………………………….128 7.1.2 The architecture of computer-aided mould design modification and tool path regeneration system………………………………… .130 7.1.3 The user interface……………………………………………….133 7.1.4 The mould design modification module……………………… .133 7.1.5 The tool path generation and regeneration module…………… 134 7.2 Case studies…………………………………………………………… .136 7.2.1 Case 1……………………………………………………………136 7.2.2 Case 2……………………………………………………………142 Chapter Conclusions and Recommendations……………………149 8.1 Conclusions……………………………………………………………….149 8.1.1 Mould design modification…………………………………… .150 8.1.2 Tool path regeneration………………………………………… 150 8.2 Recommendations……………………………………………………… 151 8.2.1 Mould design modification…………………………………… .151 8.2.2 Tool path generation…………………………………………….152 8.2.3 Tool path regeneration………………………………………… 152 List of Publications from this Study………………………………….154 VI References…………………………………………………………… .155 VII NOMENCLATURE 2D Two Dimensional 3D Three Dimensional C The Boundary of Mould Modification Region Co The Boundary of Affected CL-points CAD Computer-Aided Design CAE Computer-Aided Engineering CAM Computer-Aided Manufacturing CAD/CAM Computer-Aided Design and Manufacturing CAD/CAM/CAE Computer-Aided Design/Manufacturing/Engineering CC Cutter Contact CC-point Cutter Contact point CL-point Cutter Location point CLSF Cutter Location Source File CNC Computer Numerical Control EDM Electrical Discharge Machining EC Engineering Change MRR Metal Removal Rate UFUN User-Function UG Unigraphics VIII List of Figures Figure 1.1 Plastic part development processes…………………… ………………4 Figure 1.2 A typical injection mould structure……………………… ……………7 Figure 1.3 A general mould design process…………………………… ……… Figure 2.1 Parting lines and parting surfaces………………………………… …19 Figure 2.2 The iso-parametric method……………………………………………26 Figure 2.3 The inverse tool offset method………………………………… …….31 Figure 3.1 The Frenet frame……………………………………… …………… 35 Figure 4.1 Different shapes of inserts and pockets…………………………… …47 Figure 4.2 Framework of the mould design modification system…… ………….49 Figure 4.3 Material to be added to or removed from designed mould……………50 Figure 4.4 Cavity and core are affected by product design modification…………51 Figure 4.5 Designed insert and pocket……………………………………… … 57 Figure 4.6 An ejector hole interferes with the pocket…………………………….58 Figure 4.7 Fix the insert with screw or welding process………………………….59 Figure 4.8 Lifter and cooling holes………….……………………………………61 Figure 4.9 Minimum distance between pocket and other holes………………… 63 Figure 4.10a Old product file……………………………………………………… 65 Figure 4.10b New product file.…………………………………………………… .65 Figure 4.10c Old cavity.…………………………………………………………… 66 Figure 4.10d Modified cavity……………………………………………………… 67 Figure 4.10e Old core .…………………………………………………………… 68 Figure 4.10f Modified core………………………………………………………….69 Figure 5.1 Cutter contact (CC) and cutter location (CL) points………………… 72 IX Chapter System Implementation and Case Studies CAM functions and with the algorithm developed in this research are 61634.2 mm and 62296.1mm, respectively. Original tool paths Figure 7.9c Tool paths with replaced points and added lines before and after modification 148 CHAPTER CONCLUSIONS AND RECOMMENDATIONS 8.1 Conclusions To shorten the new product development time, the design of a new product may be changed many times during the mould design and manufacturing processes. With the existing CAD systems, the mould design cannot be modified automatically if the design parameters are lost when the part is transferred from one CAD system to another. When the mould design is changed, the tool path that covers the affected region needs to be regenerated. With the existing CAM systems, when the tool path is regenerated and error-prone in NC-machining, all the CL-points will need to be recalculated, which is very time-consuming. To solve these problems, this research has developed a computer-aided Mould Design Modification and Tool Path Regeneration System. With this system, when the design of a plastic part is changed, the mould design can be modified automatically with different methods according to the mould machining status. The tool path can then be regenerated efficiently by reusing the unaffected CL-points. New theories, methodologies and algorithms for mould design modification and tool path regeneration have been developed in this research. The system has been tested with several industrial parts. It is proven that the system can efficiently modify mould design and regenerate tool paths according to the mould machining status. The 149 Chapter Conclusions and Recommendations contributions of this research can be summarized into two areas: mould design modification and tool path regeneration, as will be discussed in the following subsections. 8.1.1 Mould design modification A new mould design modification module that can automatically modify the mould design for parametric and non-parametric parts according to the mould machining status has been developed in this research. With the developed module, the mould design modification does not rely on the product parameters that increase with the complexity of the product and the mould. Therefore, the developed module is not sensitive to the complexity of the plastic part and the designed mould. The mould design may need to be modified at different mould machining stages. Different methods have been developed to modify the mould design according to the mould machining status. When an insert needs to be designed to add extra material, the system automatically detects the interference between the pocket to be designed and the existing holes. Different pockets, inserts and fasteners can be designed based on the interference detection result. 8.1.2 Tool path regeneration New tool path regeneration algorithms have been developed in this research. With these algorithms, the affected and unaffected CL-points can be identified efficiently. The affected CL-points are then removed and replaced by new CL-points. Since the unaffected CL-points are used to machine the modified mould directly, the tool path regeneration time can be reduced greatly. 150 Chapter Conclusions and Recommendations Four propositions have been proposed and proven in the thesis for tool path regeneration. The propositions indicate two important properties of a gouge-free tool path: 1) the affected CL-points are enclosed by a boundary of CL-points that correspond to the interference-free boundary of the modified region; 2) when projected onto the XY-plane, if one CL-point is ‘before’ another, their corresponding CC-points follow the same topology. With these propositions, the affected CL-points can be efficiently identified by only noting their x- and y-values. The tool path regeneration algorithm is related to the tool path generation method. Since the tool path generation methods can be categorized into CC- and CL-point methods, two different tool path regeneration algorithms have been developed for them respectively. The tool path regeneration algorithms were implemented with the parallel tool path and CC-curve tool path generation methods. These algorithms can easily be applied to other tool path generation methods. 8.2 Recommendations The system developed in this research has solved some of the mould design modification and tool path regeneration problems. However, it does not cover all aspects in these areas, more research is needed in mould design modification, tool path generation and regeneration, as will be discussed in the following subsection. 8.2.1 Mould design modification This research emphasizes on modifying the mould design for the core and cavity. Sometimes, the change of the plastic part design may affect the parting line and the parting surfaces. More research is needed to develop algorithms that can efficiently 151 Chapter Conclusions and Recommendations and optimally identify the parting line for the modified profile based on the given parting direction and the unaffected parting lines. The plastic design modification may also lead to new undercuts. More research is needed to develop algorithms to automatically and optimally design sliders and lifters based on the given parting direction and the designed mould structures. When an insert is to be created, the optimal design of the insert which affects the quality of the moulded plastic part least is also an issue to be studied further. 8.2.2 Tool path generation With the existing algorithms, when a tool path row is to be planned, the maximum scallop height value for this row needs to be identified point by point. A challenging problem is how to identify the point with maximum scallop height value from the surface and the CC-curve information directly. This can be applied to generating tool paths efficiently and selecting cutters more accurately without generating the tool paths. 8.2.3 Tool path regeneration With the system developed in this research, as it is assumed that the original tool path has been developed by other systems (e.g., the commercial CAM software), the user needs to input the original machining parameters before the tool path can be regenerated. If these parameters can be stored in the original tool path file when it is generated, these parameters can be retrieved directly from the file, which will reduce the tool path regeneration errors caused by user input. 152 Chapter Conclusions and Recommendations In this research, tool path regeneration was focused on 3-axis machines with ball endmills. It will even be more time consuming and error-prone to generate tool paths for 4-axis and 5-axis CNC machines. More research is needed to develop algorithms that can efficiently identify and replace the affected CC-points from the generated CLpoints for them. Flat and fillet end-mills are also used in tool path generation for mould machining, especially for rough machining. New algorithms need to be developed to identify and replace the affected CL-points for these types of cutters. 153 RELATED PUBLICATIONS 1. Zhang, L. P., Fuh, J.Y.H. and Nee, A.Y. C. “Tool path regeneration for mold modification.” Computer-Aided Design, 35(9), pp.813-823, 2003. 2. Zhang, L. P., Fuh, J.Y.H. and Nee, A.Y. C. “A Tool Path Re-Generation Algorithm For Die & Mold Machining”. Proceedings of the 10th International Manufacturing Conference, Oct. 2002, Xiamen, China, Panel1-205. 3. Zhang, L. P., Nee, A.Y. 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S., “Automated Generation of Lifters for Injection Moulds”, International Journal of Advanced Manufacturing Technology, 19, pp.537–543, 2002. 163 [...]... curves and surfaces for mould design modification and tool path regeneration The mould design modification system is introduced in Chapter 4 The tool path regeneration algorithms for CL-point and CC-point tool path generation methods are introduced in Chapter 5 15 Chapter 1 Introduction and Chapter 6, respectively Chapter 7 presents the computer- aided mould design modification and tool path regeneration. .. tool path regeneration method is related to the tool path generation method, and the tool path methods can be categorized into CC- and CL-point methods, two different tool path regeneration algorithms are developed for them respectively From this research, a computer- aided Mould Design Modification and Tool Path Regeneration System has been developed to modify the mould design and regenerate tool paths... mould is modified, the entire tool path that covers the modified region will have to be recalculated This could take as much time as for generating a new tool path Therefore, the process of mould design modification and tool path regeneration in NC programming is still very tedious, time-consuming and error-prone This research aims at developing a Computer- Aided Mould Design Modification and Tool Path. .. work-piece after design modification …………….121 Figure 6.7d Regenerated tool paths with replaced points and added lines after design modification ……………………………………………………….122 Figure 6.7e Tool paths with added lines before and after design modification 123 Figure 6.8a Part surface of T-cover mould before design modification ……….124 Figure 6.8b Tool paths of T-cover mould before design modification ………... transferred from one format to another, and the design parameters may be lost during file transformation When the mould designer receives the plastic part, he/she will study and analyze the mould capability and then design the mould If the design of a plastic part is found to be not suitable for moulding, it will be returned to the product designer for modification When the mould is designed, the material... this research is to develop a mould design modification and tool path regeneration system that can solve the above two problems This research will focus on the following two issues: (1) Mould design modification Develop a mould design modification system that 14 Chapter 1 Introduction can automatically and efficiently modify a mould design based on the designed mould and the mould machining status The... 6.8c Part surface of T-cover mould after design modification …………125 Figure 6.8d Regenerated tool paths with replaced points after design modification ……………………………………………………….126 Figure 6.8e Tool paths of T-cover before and after design modification ………127 Figure 7.1 Framework of the mould modification and tool path regeneration system……………………………………………………………… 131 Figure 7.2 New product selection………………………………………………... the CAM department 1.2.3 Mould design modification When the design of a plastic part is changed, the mould design will need to be modified Since a mould has been designed and some mould inserts may have been machined, the mould design modification method is different from the mould design method Besides the geometrical and functional constraints, the structure of the designed mould also needs to be considered... work-piece after modification ………………………94 Figure 5.12d Regenerated tool paths with replaced points and added lines after modification …………………………………………….………… 95 Figure 5.12e Tool paths before and after modification with replaced points and added lines……………………………………………… ………………….96 Figure 5.13a Part surface of bezel mould before modification ………………… 98 Figure 5.13b Tool paths of bezel mould before modification …………………….98... a design tool in most mould manufacturing companies Several mould design systems have been developed to automate some of the mould design processes and shorten the design time Figure 1.3 shows a general mould design process: Upon receiving the design of the 8 Chapter 1 Designed product model Introduction Shrinkage Determine parting direction and parting line Select the mould type and mould machine Design . of T-cover mould before design modification ……….124 Figure 6.8b Tool paths of T-cover mould before design modification ……… 124 Figure 6.8c Part surface of T-cover mould after design modification …………125. developed for them respectively. From this research, a computer-aided Mould Design Modification and Tool Path Regeneration System has been developed to modify the mould design and regenerate tool. Since the tool path regeneration method is related to the tool path generation method, and the tool path methods can be categorized into CC- and CL-point methods, two different tool path regeneration