Rapid Prototyping Technology Selection and Application PDF

Rapid Prototyping Technology Selection and Application Kenneth G. Cooper National Aeronautics and Space Administration (NASA) Marshall Space and Flight Center Huntsville, Alabama...

Rapid Prototyping Technology Selection and Application Kenneth G. Cooper National Aeronautics and Space Administration (NASA) Marshall Space and Flight Center Huntsville, Alabama MARCEL MARCEL DEKKER, INC. NEW YORK BASEL DEKKER ISBN: 0-8247-0261-1 This book is printed on acid-free paper. Headquarters Marcel Dekker, Inc. 270 Madison Avenue, New York, NY 10016 tel: 212-696-9000; fax: 212-685-4540 Eastern Hemisphere Distribution Marcel Dekker AG Hutgasse 4, Postfach 812, CH-4001 Basel, Switzerland tel: 41-61-261-8482; fax: 41-61-261-8896 World Wide Web http://www.dekker.com The publisher offers discounts on this book when ordered in bulk quantities. For more infor- mation, write to Special Sales/Professional Marketing at the headquarters address above. Copyright © 2001 by Marcel Dekker, Inc. All Rights Reserved. Neither this book nor any part may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, microfilming, and recording, or by any information storage and retrieval system, without permission in writing from the publisher. Current printing (last digit): 10 9 8 7 6 5 4 3 2 1 PRINTED IN THE UNITED STATES OF AMERICA  MECHANICAL ENGINEERING A Series of Textbooks and Reference Books Founding Editor L. L. Faulkner Columbus Division, Battelle Memorial Institute and Department of Mechanical Engineering The Ohio State University Columbus, Ohio 1. Spring Designer's Handbook, Harold Carlson 2. Computer-Aided Graphics and Design, Daniel L. Ryan 3. Lubrication Fundamentals, J. George Wills 4. Solar Engineering for Domestic Buildings, William A. Himmelman 5. Applied Engineering Mechanics: Statics and Dynamics, G. Boothroyd and C. Poli 6. Centrifugal Pump Clinic, Igor J. Karassik 7. Computer-Aided Kinetics for Machine Design, Daniel L. Ryan 8. Plastics Products Design Handbook, Part A: Materials and Components; Part B: Processes and Design for Processes, edited by Edward Miller 9. Turbomachinery: Basic Theory and Applications, Earl Logan, Jr. 10. Vibrations of Shells and Plates, Werner Soedel 11. Flat and Corrugated Diaphragm Design Handbook, Mario Di Giovanni 12. Practical Stress Analysis in Engineering Design, Alexander Blake 13. An Introduction to the Design and Behavior of Bolted Joints, John H. Bickford 14. Optimal Engineering Design: Principles and Applications, James N. Siddall 15. Spring Manufacturing Handbook, Harold Carlson 16. Industrial Noise Control: Fundamentals and Applications, edited by Lewis H. Bell 17. Gears and Their Vibration: A Basic Approach to Understanding Gear Noise, J. Derek Smith 18. Chains for Power Transmission and Material Handling: Design and Appli- cations Handbook, American Chain Association 19. Corrosion and Corrosion Protection Handbook, edited by Philip A. Schweitzer 20. Gear Drive Systems: Design and Application, Peter Lynwander 21. Controlling In-Plant Airborne Contaminants: Systems Design and Cal- culations, John D. Constance 22. CAD/CAM Systems Planning and Implementation, Charles S. Knox 23. Probabilistic Engineering Design: Principles and Applications, James N. Siddall 24. Traction Drives: Selection and Application, Frederick W. Heilich III and Eugene E. Shube 25. Finite Element Methods: An Introduction, Ronald L. Huston and Chris E. Passerello 26. Mechanical Fastening of Plastics: An Engineering Handbook, Brayton Lincoln, Kenneth J. Gomes, and James F. Braden 27. Lubrication in Practice: Second Edition, edited by W. S. Robertson 28. Principles of Automated Drafting, Daniel L. Ryan 29. Practical Seal Design, edited by Leonard J. Martini 30. Engineering Documentation for CAD/CAM Applications, Charles S. Knox 31. Design Dimensioning with Computer Graphics Applications, Jerome C. Lange 32. Mechanism Analysis: Simplified Graphical and Analytical Techniques, Lyndon O. Barton 33. CAD/CAM Systems: Justification, Implementation, Productivity Measurement, Edward J. Preston, George W. Crawford, and Mark E. Coticchia 34. Steam Plant Calculations Manual, V. Ganapathy 35. Design Assurance for Engineers and Managers, John A. Burgess 36. Heat Transfer Fluids and Systems for Process and Energy Applications, Jasbir Singh 37. Potential Flows: Computer Graphic Solutions, Robert H. Kirchhoff 38. Computer-Aided Graphics and Design: Second Edition, Daniel L. Ryan 39. Electronically Controlled Proportional Valves: Selection and Application, Michael J. Tonyan, edited by Tobi Goldoftas 40. Pressure Gauge Handbook, AMETEK, U.S. Gauge Division, edited by Philip W. Harland 41. Fabric Filtration for Combustion Sources: Fundamentals and Basic Tech- nology, R. P. Donovan 42. Design of Mechanical Joints, Alexander Blake 43. CAD/CAM Dictionary, Edward J. Preston, George W. Crawford, and Mark E. Coticchia 44. Machinery Adhesives for Locking, Retaining, and Sealing, Girard S. Haviland 45. Couplings and Joints: Design, Selection, and Application, Jon R. Mancuso 46. Shaft Alignment Handbook, John Piotrowski 47. BASIC Programs for Steam Plant Engineers: Boilers, Combustion, Fluid Flow, and Heat Transfer, V. Ganapathy 48. Solving Mechanical Design Problems with Computer Graphics, Jerome C. Lange 49. Plastics Gearing: Selection and Application, Clifford E. Adams 50. Clutches and Brakes: Design and Selection, William C. Orthwein 51. Transducers in Mechanical and Electronic Design, Harry L. Trietley 52. Metallurgical Applications of Shock-Wave and High-Strain-Rate Phenom- ena, edited by Lawrence E. Murr, Karl P. Staudhammer, and Marc A. Meyers 53. Magnesium Products Design, Robert S. Busk 54. How to Integrate CAD/CAM Systems: Management and Technology, William D. Engelke 55. Cam Design and Manufacture: Second Edition; with cam design software for the IBM PC and compatibles, disk included, Preben W. Jensen 56. Solid-State AC Motor Controls: Selection and Application, Sylvester Campbell 57. Fundamentals of Robotics, David D. Ardayfio 58. Belt Selection and Application for Engineers, edited by Wallace D. Erickson 59. Developing Three-Dimensional CAD Software with the IBM PC, C. Stan Wei 60. Organizing Data for CIM Applications, Charles S. Knox, with contributions by Thomas C. Boos, Ross S. Culverhouse, and Paul F. Muchnicki 61. Computer-Aided Simulation in Railway Dynamics, by Rao V. Dukkipati and Joseph R. Amyot 62. Fiber-Reinforced Composites: Materials, Manufacturing, and Design, P. K. Mallick 63. Photoelectric Sensors and Controls: Selection and Application, Scott M. Juds 64. Finite Element Analysis with Personal Computers, Edward R. Champion, Jr., and J. Michael Ensminger 65. Ultrasonics: Fundamentals, Technology, Applications: Second Edition, Revised and Expanded, Dale Ensminger 66. Applied Finite Element Modeling: Practical Problem Solving for Engineers, Jeffrey M. Steele 67. Measurement and Instrumentation in Engineering: Principles and Basic Laboratory Experiments, Francis S. Tse and Ivan E. Morse 68. Centrifugal Pump Clinic: Second Edition, Revised and Expanded, Igor J. Karassik 69. Practical Stress Analysis in Engineering Design: Second Edition, Revised and Expanded, Alexander Blake 70. An Introduction to the Design and Behavior of Bolted Joints: Second Edition, Revised and Expanded, John H. Bickford 71. High Vacuum Technology: A Practical Guide, Marsbed H. Hablanian 72. Pressure Sensors: Selection and Application, Duane Tandeske 73. Zinc Handbook: Properties, Processing, and Use in Design, Frank Porter 74. Thermal Fatigue of Metals, Andrzej Weronski and Tadeusz Hejwowski 75. Classical and Modern Mechanisms for Engineers and Inventors, Preben W. Jensen 76. Handbook of Electronic Package Design, edited by Michael Pecht 77. Shock-Wave and High-Strain-Rate Phenomena in Materials, edited by Marc A. Meyers, Lawrence E. Murr, and Karl P. Staudhammer 78. Industrial Refrigeration: Principles, Design and Applications, P. C. Koelet 79. Applied Combustion, Eugene L. Keating 80. Engine Oils and Automotive Lubrication, edited by Wilfried J. Bartz 81. Mechanism Analysis: Simplified and Graphical Techniques, Second Edition, Revised and Expanded, Lyndon O. Barton 82. Fundamental Fluid Mechanics for the Practicing Engineer, James W. Murdock 83. Fiber-Reinforced Composites: Materials, Manufacturing, and Design, Second Edition, Revised and Expanded, P. K. Mallick 84. Numerical Methods for Engineering Applications, Edward R. Champion, Jr. 85. Turbomachinery: Basic Theory and Applications, Second Edition, Revised and Expanded, Earl Logan, Jr. 86. Vibrations of Shells and Plates: Second Edition, Revised and Expanded, Werner Soedel 87. Steam Plant Calculations Manual: Second Edition, Revised and Ex panded, V. Ganapathy 88. Industrial Noise Control: Fundamentals and Applications, Second Edition, Revised and Expanded, Lewis H. Bell and Douglas H. Bell 89. Finite Elements: Their Design and Performance, Richard H. MacNeal 90. Mechanical Properties of Polymers and Composites: Second Edition, Re- vised and Expanded, Lawrence E. Nielsen and Robert F. Landel 91. Mechanical Wear Prediction and Prevention, Raymond G. Bayer  92. Mechanical Power Transmission Components, edited by David W. South and Jon R. Mancuso 93. Handbook of Turbomachinery, edited by Earl Logan, Jr. 94. Engineering Documentation Control Practices and Procedures, Ray E. Monahan 95. Refractory Linings Thermomechanical Design and Applications, Charles A. Schacht 96. Geometric Dimensioning and Tolerancing: Applications and Techniques for Use in Design, Manufacturing, and Inspection, James D. Meadows 97. An Introduction to the Design and Behavior of Bolted Joints: Third Edition, Revised and Expanded, John H. Bickford 98. Shaft Alignment Handbook: Second Edition, Revised and Expanded, John Piotrowski 99. Computer-Aided Design of Polymer-Matrix Composite Structures, edited by Suong Van Hoa 100. Friction Science and Technology, Peter J. Blau 101. Introduction to Plastics and Composites: Mechanical Properties and Engi- neering Applications, Edward Miller 102. Practical Fracture Mechanics in Design, Alexander Blake 103. Pump Characteristics and Applications, Michael W. Volk 104. Optical Principles and Technology for Engineers, James E. Stewart 105. Optimizing the Shape of Mechanical Elements and Structures, A. A. Seireg and Jorge Rodriguez 106. Kinematics and Dynamics of Machinery, Vladimir Stejskal and Michael Valasek 107. Shaft Seals for Dynamic Applications, Les Horve 108. Reliability-Based Mechanical Design, edited by Thomas A. Cruse 109. Mechanical Fastening, Joining, and Assembly, James A. Speck 110. Turbomachinery Fluid Dynamics and Heat Transfer, edited by Chunill Hah 111. High-Vacuum Technology: A Practical Guide, Second Edition, Revised and Expanded, Marsbed H. Hablanian 112. Geometric Dimensioning and Tolerancing: Workbook and Answerbook, James D. Meadows 113. Handbook of Materials Selection for Engineering Applications, edited by G. T. Murray 114. Handbook of Thermoplastic Piping System Design, Thomas Sixsmith and Reinhard Hanselka 115. Practical Guide to Finite Elements: A Solid Mechanics Approach, Steven M. Lepi 116. Applied Computational Fluid Dynamics, edited by Vijay K. Garg 117. Fluid Sealing Technology, Heinz K. Muller and Bernard S. Nau 118. Friction and Lubrication in Mechanical Design, A. A. Seireg 119. Influence Functions and Matrices, Yuri A. Melnikov 120. Mechanical Analysis of Electronic Packaging Systems, Stephen A. McKeown 121. Couplings and Joints: Design, Selection, and Application, Second Edition, Revised and Expanded, Jon R. Mancuso 122. Thermodynamics: Processes and Applications, Earl Logan, Jr. 123. Gear Noise and Vibration, J. Derek Smith 124. Practical Fluid Mechanics for Engineering Applictions, John J. Bloomer 125. Handbook of Hydraulic Fluid Technology, edited by George E. Totten 126. Heat Exchanger Design Handbook, T. Kuppan 127. Designing for Product Sound Quality, Richard H. Lyon 128. Probability Applications in Mechanical Design, Franklin E. Fisher and Joy R. Fisher 129. Nickel Alloys, edited by Ulrich Heubner 130. Rotating Machinery Vibration: Problem Analysis and Troubleshooting, Maurice L. Adams, Jr. 131. Formulas for Dynamic Analysis, Ronald Huston and C. Q. Liu 132. Handbook of Machinery Dynamics, Lynn L. Faulkner and Earl Logan, Jr. 133. Rapid Prototyping Technology: Selection and Application, Kenneth G. Cooper Additional Volumes in Preparation Reciprocating Machinery Dynamics, Abdulla S. Rangwala Reliability Verification, Testing, and Analysis of Engineering Design, Gary S. Wasserman Maintenance Excellence: Optimizing Equipment Life Cycle Decisions, edited by John D. Campbell and Andrew K. S. Jardine Mechanical Engineering Software Spring Design with an IBM PC, Al Dietrich Mechanical Design Failure Analysis: With Failure Analysis System Software for the IBM PC, David G. Ullman For my loving wife, Jennifer. Thank you for your support and patience while I finished this writing. Preface Well, first off, thanks for buying this book! And, if you are only considering buy- ing this book, or at least took the time to pick it up and read the preface, hey, thank you, too! Regardless, at this point you are hoping I don't ramble through the whole text like this, so let's get down to business, shall we? This book was written by a technical professional who, for over seven years, has personally operated, modified, tweaked, repaired, and advanced at least one of every domestic rapid prototyping system on today's market. Just what is rapid prototyping? Well, here it refers to a collective set of manufacturing technologies that build parts in additive fashion, by growing slices of a material from the bot- tom to the top of the part, directly from computer-driven data. My mechanical and materials engineering background has given me the desire to take the machines apart and see what makes them tick, and on most machines in this book I have done just that. I will not give out any trade secrets of any vendors or countries, only practical knowledge that, with a good bit of work, most anyone could probably find on their own, if only they had the time. Where I lacked expertise I tried to get information from more experienced folks in that niche, namely Curtis Manning for the ModelMaker chapter, Pat Salvail on the investment casting chapter and case study, and Anthony Springer for facilitating the wind-tunnel case study. This text covers each rapid prototyping system at a fundamental level, that is, down to the basic operation of the machines along with typical uses and the pros/cons of each. The book covers not only the domestic systems that I have worked with, but also brief segments for foreign systems, as well as international progress in the rapid prototyping realm that I picked up with some savvy Internet surfing. Finally, just in case I haven't completely covered something you are looking for, I've added a comprehensive recommended reading list of some of the best in iv Contents rapid prototyping texts on the market. So, happy reading, and I hope you find what you are looking for in these pages! Kenneth G. Cooper, AST Contents Preface Hi 1 What Is Rapid Prototyping? 1 1.1 Rapid Prototyping Defined 1 1.2 Origins of Rapid Prototyping 2 1.3 The Design Process 3 1.4 The Rapid Prototyping Cycle 4 1.5 Where the Technology Is Today 6 1.6 A Sample Application of Rapid Prototyping 8 1.7 Rapid Prototyping Processes 9 1.8 Key Terms 10 UNIT I CONCEPT MODELERS 12 2 The JP-System 5 13 2.1 JP-5 Hardware 14 2.2 JP-5 Operation/Build Technique 15 2.3 Finishing a Part 23 2.4 Typical Uses of the JP-5 Process 24 2.5 Materials Properties 25 2.6 Key Terms 25 3 Ballistic Particle Manufacturing 26 3.1 System Hardware 26 3.2 Ballistic Particle Manufacturing Operation 27 3.3 Ballistic Particle Manufacturing Build Technique 29 vi Contents 3.4 Finishing of Ballistic Particle Manufacturing Parts 29 3.5 Typical Uses of Ballistic Particle Manufacturing Parts 30 3.6 Advantages and Disadvantages 32 3.7 Key Terms 32 4 The Model Maker Series 33 4.1 Model Maker System Hardware 33 4.2 Model Maker Operation 37 4.3 Advantages and Disadvantages of the Model Maker 42 4.4 Key Terms 43 5 Multi Jet Modeling 44 5.1 System Hardware 44 5.2 Multi Jet Modeling Process Operation 45 5.3 Typical Uses of Multi Jet Modeling 47 5.4 Advantages and Disadvantages of Multi Jet Modeling 48 5.5 Key Terms 48 6 3D Printing (Z402 System) 50 6.1 Z402 System Hardware 50 6.2 Z402 Operation 52 6.3 Build Technique 55 6.4 Postprocessing 59 6.5 Typical Uses of Z402 Parts 62 6.6 Advantages and Disadvantages of the Z402 62 6.7 Key Terms 62 7 The Genisys Desktop Modeler 64 7.1 History of the System 65 7.2 System Operation 65 7.3 Typical Uses of Genisys Parts 66 7.4 Advantages and Disadvantages of Genisys 66 UNIT II FUNCTIONAL MODELERS 67 8 Fused Deposition Modeling 68 8.1 Fused Deposition Modeling System Hardware 68 8.2 Fused Deposition Modeling Operation 73 8.3 Typical Uses of Fused Deposition Modeling Parts 85 Contents vii 8.4 Fused Deposition Modeling Materials Properties 86 8.5 Advantages and Disadvantages 87 8.6 Key Terms 87 9 Laminated Object Manufacturing 89 9.1 System Hardware 89 9.2 Laminated Object Manufacturing Operation 91 9.3 Laminated Object Manufacturing Build Technique 96 9.4 Finishing a Laminated Object Manufacturing Part 102 9.5 Typical Uses of Laminated Object Manufacturing 105 9.6 Advantages and Disadvantages 107 9.7 Laminated Object Manufacturing Materials Properties 107 9.8 Key Terms 108 10 Stereolithography 110 10.1 The Stereolithography Apparatus 110 10.2 Stereolithography Apparatus Operation 113 10.3 Relation to Other Rapid Prototyping Technologies 114 10.4 Applications of Stereolithography Parts 115 10.5 Advantages and Disadvantages 116 10.6 Key Terms 116 11 Selective Laser Sintering 118 11.1 History of Selective Laser Sintering 118 11.2 Selective Laser Sintering Technology 118 11.3 Purpose of Selective Laser Sintering 120 11.4 Current State of Selective Laser Sintering 121 11.5 Impact of the Technology 129 11.6 Interrelation with Other Technologies 130 11.7 Future of the Selective Laser Sintering Technology 130 11.8 System Update 131 11.9 Key Terms 131 12 Laser Engineered Net Shaping 132 12.1 Build Materials 132 12.2 Build Process 132 12.3 System Statistics 135 12.4 Postprocessing 135 12.5 Materials Properties 136 12.6 Typical Uses 136 viii Contents 12.7 Advantages and Disadvantages 137 13 Pro Metal System 138 13.1 Pro Metal System Hardware 13 8 13.2 Pro Metal Operation 140 13.3 Build Technique 141 13.4 Postprocessing 142 13.5 Typical Uses of Pro Metal 143 13.6 Materials Properties 146 13.7 Advantages and Disadvantages of Pro Metal 146 13.8 Key Terms 146 14 Other Functional Rapid Prototyping Processes 148 14.1 Precision Optical Manufacturing 148 14.2 Laser Additive Manufacturing Process 149 14.3 Topographic Shell Fabrication 150 14.4 Direct Shell Production 151 UNIT III SECONDARY RAPID PROTOTYPING APPLICATIONS 153 15 Casting Processes 154 15.1 Investment Casting 154 15.2 Sand Casting 157 15.3 Permanent-mold Casting 158 16 Rapid Tooling 160 16.1 Direct Rapid Prototyping Tooling 160 16.2 Silicone Rubber Tooling 161 16.3 Investment-cast Tooling 162 16.4 Powder Metallurgy Tooling 162 16.5 Spray Metal Tooling 163 16.6 Desktop Machining 165 17 Reverse Engineering Using Rapid Prototyping 166 17.1 Process 166 17.2 Other Reverse Engineering Applications 167 18 Case Study: Wind-tunnel Testing with Rapid Prototyped Models 169 Contents ix 18.1 Abstract 169 18.2 Introduction 170 18.3 Geometry 172 18.4 Model Construction 172 18.5 Facility 175 18.6 Test 177 18.7 Results 178 18.8 Baseline Models 178 18.9 Replacement Parts 179 18.10 Cost and Time 179 18.11 Accuracy and Uncertainty 179 18.12 Conclusions 181 18.13 Bibliography 183 19 Case Study: Rapid Prototyping Applied to Investment Casting 184 19.1 Introduction 184 19.2 Background/ Approach 184 19.3 Test Results 185 19.4 Cost Comparisons 193 19.5 Conclusions 193 19.6 Key Terms 195 19.7 References 197 UNITIV INTERNATIONAL RAPID PROTOTYPING SYSTEMS 198 20 RP Systems in Israel 199 20.1 Solid Ground Curing 199 20.2 The Objet Quadra 200 21 Rapid Prototyping Systems in Japan 203 21.1 Stereolithography 203 21.2 Laminated Object Manufacturing 203 21.3 Other Rapid Prototyping Systems 203 22 Rapid Prototyping Systems in Europe 206 22.1 Germany 206 22.2 Sweden 207 22.3 Belgium 208 x Contents 23 Rapid Prototyping Systems in China 209 23.1 Stereolithography 209 23.2 Laminated Object Manufacturing 210 23.3 Fused Deposition Modeling 210 23.4 Selective Laser Sintering 210 23.5 Multifunctional Rapid Prototyping Manufacturing System 210 APPENDICES 212 Appendix A Rapid Prototyping System Cross Reference Chart 213 Appendix B Direction of the Rapid Prototyping Industry 215 B. 1 Design Technologies 216 B.2 Materials and Fabrication Technologies 216 B.3 Integration Technologies 218 B.4 Summary 219 Appendix C Recommended Rapid Prototyping Publications 220 Index 223 Rapid Prototyping Technology 1 What Is Rapid Prototyping? 1.1 Rapid Prototyping Defined Rapid Prototyping (RP), as defined in this text, refers to the layer- by-layer fabrication of three-dimensional physical models directly from a computer-aided design (CAD). This additive manufacturing process provides designers and engineers the capability to literally print out their ideas in three dimensions. The RP processes provide a fast and inexpensive alternative for producing prototypes and functional models as compared to the conventional routes for part production. The advantage of building a part in layers is that it allows you to build complex shapes that would be virtually impossible to ma- chine, in addition to the more simple designs. RP can build intricate internal structures, parts inside of parts, and very thin-wall features just as easily as building a simple cube. All of the RP processes construct objects by producing very thin cross sections of the part, one on top of the other, until the solid physical part is completed. This simplifies the intricate three- dimensional construction process in that essentially two-dimensional slices are being created and stacked together. For example, instead of trying to cut out a sphere with a detailed machining process, stacks of various-sized "circles" are built consecutively in the RP machine to create the sphere with ease. RP also decreases the amount of operation time required by humans to build parts. The RP machines, once started, usually run 1 2 Chapter 1 unattended until the part is complete. This comes after the operator spends a small amount of time setting up the control program. Af- terwards, some form of clean up operation is usually necessary, gen- erally referred to as post processing. Nonetheless, the user inter- vention times still remain far less than that for traditional machining processes. You can imagine the cost and time savings involved with such a process. Models can usually be built within hours, and the build materials for most processes are generally inexpensive. Some RP machines are small and environmentally friendly so that they can be placed directly into a designer's office, just like a common photo- copy machine! Finally, having access to accurate, functional proto- types to verify concepts in the beginning phases of a project is an invaluable resource to any institution in the business of producing physical components. 1.2 Origins of Rapid Prototyping RP stems from the ever-growing CAD industry, more specifically, the solid modeling side of CAD. Solid modeling is the branch of CAD that produces true three-dimensional objects in electronic for- mat. A solid model has volume and is fully enclosed. It can be as- signed materials properties such as mass and density, and the ge- ometry data can be output in various formats to accommodate RP, stress analysis software packages, and, of course, computer numeri- cally controlled machining (CNC). Before solid modeling was introduced in the late 1980s, three-dimensional models were created with wireframes and sur- faces. A wireframe is an approximate representation of a three- dimensional object, such as one would sketch with a pencil or on the chalkboard. Wireframes are sometimes deemed as two-and-a- half dimensional, for the fact that they only appear to be three- dimensional. Later on, the wireframes could actually have sur- faces for visual enhancement and analysis. For example, a cube would be represented by six squares joined at the edges in three- dimensional coordinate space. But not until the development of What Is Rapid Prototyping? 3 true solid modeling could innovative processes such as RP be de- veloped. Charles Hull, who helped found 3D Systems in 1986, devel- oped the first RP process. This process, called stereolithography, builds objects by curing thin consecutive slices of certain ultravio- let light-sensitive liquid resins with a low-power laser. This con- cept of layer additive construction has been capitalized on by vari- ous institutions in many different ways, which all have collectively been termed RP. With the introduction of RP, CAD solid models could sud- denly come to life. Designers and engineers now have the power to go through several iterations of a design in order to get the best possible performance for their needs. 1.3 The Design Process In order to understand where RP fits into the manufacturing stream, it is best to begin with a description of a typical design process. Although the techniques for approaching a design-to-manufacture cycle may vary from business to business, a general path is taken by most of them for a mass-production item. 1 The Concept. Any new product, or improvement of an old product, must start out as a concept, or idea. The source for such a concept may be based on a need, desire, or may simply be a random thought that entered someone's mind. However it came to be, in order to become a reality, the concept must be carried through the design-to-manufacture process. 2 Preliminary Design. A preliminary design can range from a simple sketch on a napkin, to a two-dimensional drawing or even to a CAD solid model of the part needing to be built. The design can go through much iteration during this phase, as the designer determines the feasibility of the product through dis- cussing with colleagues and co-workers and presenting to man- agement, for instance. Other preliminary checks can now be performed with computers such as stress analysis, interference and fit, as well as visualization. RP can be useful in this phase by allowing the designer to have a physical representation to 4 Chapter 1 help demonstrate the product's use and functions. This use of RP is referred to in this text as concept verification. 3 Preliminary Prototype Fabrication. Once a design has been given the go-ahead, a prototype must be fabricated to check out the design. Before RP, this phase of the design-to-manufacture process was carried out either by hand working or machining, both of which can be time consuming and expensive. Enter RP. Durable plastic or similar models can be fabricated quickly for fit-check analysis to determine if the design is the correct size, shape, etc. for the necessary application by demonstrating with a physical model. This step may repeat several times until the proper design is acquired. With the inexpensive RP alternative, it is now less of a burden to reiterate as opposed to before. 4 Short-run Production. Sometimes, a short-run production se- quence may be necessary to further proof a part before entering into final production. Anywhere from ten to a few hundred parts may be manufactured and distributed for testing, verification, consumer satisfaction, etc. RP can be used in this phase for pro- ducing several small prototypes or, through a process often termed rapid tooling, be used to make several hundred parts in- expensively. It is crucial that any mistakes or flaws in the de- sign are found during or before this stage, otherwise it could be- come very costly. For small runs of parts, this can even be the last phase of a program, without going to an expensive tradi- tional tool at all. 5 Final Production. In this final step of the process, parts are typi- cally either machined, injection molded, or cast in large num- bers. The patterns for injections, or tooling, are usually ma- chined from aluminum or steel so that they can be used several thousand, even hundreds of thousands, times. With the devel- opment of direct metal and ceramic processes, RP may yet reach this phase in the near future. 1.4 The Rapid Prototyping Cycle As previously mentioned, RP can be useful in several steps of the design process. This segment describes the cycle from CAD design What Is Rapid Prototyping? 5 to the prototype part, which is actually embedded in the design pro- cess (Figure 1.1). CAD Design STL Fife Output ffuffd'Process Fife Transfer Figure 1.1 The RP cycle begins with the CAD design, and may be repeated inexpensively several times until a model of the desired characteristics is produced. The first step is the CAD file creation. The final file or files must be in solid model format to allow for a successful prototype build. From the CAD file, an export format called the.STL file must be created. The.STL file, so named by 3D Systems for STereoLithogra- phy, is currently the standard file format for all U.S. RP systems. STL files are triangulated representations of solid models. The indi- vidual triangles are represented by simple coordinates in a text file format. STL files are usually stored in binary format to conserve disk space. 6 Chapter 1 After the.STL file is created, it must be prepared differently for various types of RP systems. Some systems can accept the.STL file directly, whereas others require preprocessing. Preprocesses include verifying the.STL file, slicing, and setting up parameters for machine control. Preprocessing is usually done at a computer sepa- rate from the RP system to save time and to avoid tying up valuable machine time. After the.STL has been preprocessed and saved into a new slice file format, the new file can then be transferred to the RP sys- tem. File transfer can be done several ways, from manually transfer- ring by disk or tape to network transfer. Since more complicated files are usually very large, a local area network or Internet connect is now almost essential for easy file transfer. Once the final file formats are transferred to the RP device, the build process occurs. Most RP machines build parts within a few hours, but can run unattended for several days for large parts. Upon completion of the build process, post processing of the part must occur. This includes removal of the part from the ma- chine, as well as any necessary support removal and sanding or fin- ishing. If the finished part meets the necessary requirements, the cycle is complete. Otherwise, iterations can be implemented in the CAD file and the cycle is repeated. 1.5 Where the Technology is Today As you can probably see, RP is a very powerful utility for prototype modeling in today's high-speed design-to-market workplace. Quick and inexpensive prototypes are the reason the technology was in- vented, as it is still a very important function to accommodate. RP is an excellent prototype-run alternative, but since its creation, as all good technologies do, it has branched out into even more useful ap- plications, including casting, tooling, reverse engineering, and direct hardware fabrication. What Is Rapid Prototyping? 7 7.5.7 Direct Use With the stronger plastics and even metallic materials used in some of the RP processes, parts can be produced that will withstand respectful amounts of stress and higher temperature ranges. These parts can be applied in applications such a transonic wind-tunnel testing, as will be described in a later case study; snap-fit compo- nents, such as clasps or buckles; electronics devices; medical de- vices; and so on. The capability to print a part in hours and plug it directly into an application is a powerful advantage to any manu- facturing, design, or similar business. Figure 1.2 shows a laser- welding shield built with RP, which was directly used to shield the laser cartridge from the bright flashes caused by welding. Figure 1.2 This 3-inch laser shield was prototyped in approximately 2.5 hours. 8 Chapter 1 1.6 A Sample Application of Rapid Prototyping As a quick scenario, lets say a mechanical engineer has designed a pump housing for a certain type of racing engine. To get a proto- type model conventionally, he would have to create numerous pages of detailed two-dimensional drawings, with various cross-sectional views, dimensions, and other specifications. He then would possi- bly create a three-dimensional model on the computer to allow for visual verification by the model maker. The model maker would take the printed drawings and specifi- cations and then proceed to cut the prototype housing out of a block of material using some type of machining process. After many man- hours of labor as well as a lot of time for transportation of the part from station to station within the shop, the model is returned to the engineer. But alas! He discovers that the housing will not fit properly on the pump due to an unforeseen dimension of the surrounding parts. Now he has to start the process all over again. You can see where this can be very costly and time consuming. With RP, the engineer could have created the three- dimensional CAD drawing (without any of the detailed two- dimensional drawings), downloaded directly to the RP machine in his office or lab, and then returned the next morning to find a pro- totype waiting for him to use. Upon discovering any flaws in the design he can quickly up- date the computer model and download again to get the correct part built in a matter of hours, saving time, money, and a lot of heart- aches. This enhances the process of concurrent engineering, or "getting it right the first time." The obvious advantages of RP can thus be said to be speed, cost, and ease of mind. Many businesses are discovering these unique and powerful processes on a daily basis, including such pro- fessions as automotive, aerospace, medical, electronics, military, architectural, and more. And with such a wide cross section of techniques available, the processes can be molded and improved to fit each industry's needs. What Is Rapid Prototyping? 9 1.7 Rapid Prototyping Processes As the RP market expands, there are now many national and inter- national companies manufacturing and selling RP processes. New technologies are being introduced at a growing rate, and thus this text will try to do them justice. Each process has its own section, with a breakdown of the system operation, part finishing, typical uses, etc. Some systems have very short chapters, either due to the simplicity of operation or perhaps vendor-proprietary information. Also included are some case studies involving a cross section of the technologies used in wind-tunnel testing, investment casting, and other applications. 1. The JP-System 5 (JP5), by Schroff Development, builds models from CAD data using label paper and a knife plotter. JP5 is a simple and inexpensive modeler for creating rough three- dimensional models. 2. Ballistic Particle Manufacturing (BPM), now a historic compo- nent of the RP legacy, printed wax models by firing micro droplets of molten wax from a moving jet onto a stationary plat- form. BPM is currently not available due to a collapse of the manufacturer in late 1997, but is still held under a valid patent. 3. The Model Maker (MM), Model Maker II (MM2) and Rapid Tool Maker (RTM) by Sanders Prototype, Inc. produce highly accurate wax patterns using ink-jet printing technology with molten wax. 4. Multi-Jet Modeling (MJM), by 3D Systems, Corp., uses ink-jet printing technology with many jets enclosed into a single print head to produce concept models. 5. Direct Shell Production (DSP), used by Soligen, Inc., uses binder printing technology developed by MIT. The binder is printed onto layers of ceramic powder to produce investment shells directly from CAD. 6. The Z402 system by Z-Corp also uses MIT three-dimensional printing technology to build very fast concept models from a starch-like material. Also, the ProMetal system by Extrude Hone technology builds metal parts this way. 10 Chapter 1 7. Fused Deposition Modeling (FDM), by Stratasys, Inc., produces models from wax or ABS plastic using motion control and ex- trusion technology similar to a hot glue gun. Also, the Genisys system uses FDM-like technology to build nylon concept mod- els. 8. Laminated Object Manufacturing, by Helisys, Inc., builds physi- cal models by stacking sheets of paper or plastic material and cutting away excess material with a laser. 9. Stereolithography, by 3D Systems, Corp., is the oldest RP sys- tem, and builds models by curing epoxy resins with a low power laser. 10. Selective Laser Sintering, by DTM, Corp., can build with a vari- ety of materials, and works by selective melting together powder with a laser into a desire shape. 11. Laser Engineered Net Shaping, by Optomec Design Co., builds parts directly from metal powders, by fusing the powder to- gether with a laser beam. 12. Other functional RP systems covered are Precision Optical Manufacturing, Laser Additive Manufacturing Process, and Topographic Shell Fabrication. 13. Brief coverage is given to international systems from Israel, Ja- pan, Europe, and China. 1.8 Key Terms Post processing. Cleaning operations required to finish a part after removing it from the RP machine. Preprocessing. CAD model slicing and setup algorithms applied for various rapid prototyping systems. Prototype. An initial model fabricated to prove out a concept or idea. Rapid prototyping. Refers to the layer-by-layer fabrication of three- dimensional physical models directly from a CAD. What Is Rapid Prototyping? 11 Solid modeling. The branch of CAD that produces true three- dimensional objects in electronic format. Wireframe. An approximate CAD representation of a three- dimensional object. Unit! Concept Modelers Concept modelers, often called office modelers, are a class of rapid prototyping (RP) system designed specifically to make models quickly and inexpensively, without a great deal of effort. The sys- tems are usually small, inexpensive, quiet, and require very little or no training to operate. For these reasons, the systems are targeted to reside in design office environments, where they can ideally be op- erated much like a standard printer, only the prints from these sys- tems are in three dimensions. 12 The JP-System 5 The JP-System 5 (JP-5) is perhaps the simplest of all rapid prototyping (RP) processes. The JP-5 is nothing more (and nothing less) that a pen plotter that uses a knife blade and label paper instead of pens and draft paper. The JP-5 is manufactured by Schroff De- velopment, Inc., and provides possibly one of the most economical bases for rapid prototyping on the market today. The system is a ta- ble-top unit, as is shown in Figure 2.1. Figure 2.1. The JP-System 5 is a table-top unit that runs from a PC. 13 14 Chapter 2 2.1 JP-5 Hardware The JP-5 operates from a personal computer as small as a 486/33 with 8 MB RAM (not included), and is very simple to use. The system comes in two sizes, the larger of which builds parts typically within a 12" X 18" cross sectional area. The JP-5 plotter is controlled through a serial port on the computer, by the JP-5 soft- ware. 2.7.7 Software The software used to operate the JP-5 is actually embedded into a computer-aided design (CAD) package called Silver Screen. The JP-5 software accepts the standard.STL file, as well as Silver Screen CAD files. JP-5 slices the file and can be configured to run different materials as well as size ranges. 2.7.2 Build Materials The build material supplied with the JP-5 is label paper. The label paper has adhesive on its underside, which is protected before use by a glossy sheet of backing. The paper comes in sheets that are 24" x 36" for the larger system. The JP-5 can use other materials that are in the same "peel-and-stick" configuration. 2.1.3 The Plotter System The JP-5 plotter is a Graphtec single-pen plotter. The plotter is set up to either be sheet fed, as is the case with JP-5, or roll fed for standard pen plotting. The JP-5 is supplied with stainless steel cut- ting blades that fit in a modified pen holder. The pen holder allows the blade to be adjusted for cutting depth, and also gives the blade freedom to swivel. This swivel action, or free rotation, allows the blade to cut curvatures without a stepping motion. The plotter moves the paper back-and-forth in the -y direction, while the blade is controlled in the -x direction. This results in the two axis motion used to cut the cross sections of the parts being built. JP-System 5 15 2.1.4 The Assembly Board The assembly board is a piece of three-quarter inch thick parti- cle board, and is used to align the sheets of paper for final fabrica- tion of the parts. It has many threaded holes across its surface, into which the alignment pins can be placed. There are several align- ment pins, which can also be attached end to end to make taller parts. Alignment pin configurations can be set in the JP-5 software, and the typical setting is for two or three alignment holes per slice. Also with the assembly board is an application board, which is a small board used to press the sheets together to get good bonding between layers. 2.2 JP-5 Operation/Build Technique 2.2.I CAD File Preparation The JP-5 starts with a CAD file, which can either be drawn up in Silver Screen or any other CAD package that puts out the stan- dard.STL file format. The JP-5 operating software is started up from Silver Screen, and the file you wish to build is opened. The CAD file must be converted from the three-dimensional format into horizontal two-dimensional slices, which will control the plotter motions. The CAD file is represented graphically in the software, and you have several operations you can execute before building the part. It is important to note that the style for assembling models on the JP-5 will vary from user to user, and the following is just one of those styles. 2.2.1.1 Scaling/Part Size JP-5 allows you to scale parts to the size you wish to build. Parts can either be scaled uniformly across the -x, -y, and -z coor- dinates, or be scaled in a combination thereof. When scaling down it is important to note smaller features that may not be distinguish- able at smaller sizes. 16 Chapter 2 2.2.1.2 Orientation/Positioning When building with the JP-5, the position of the parts can play an important role in the ease fabrication scheme. JP-5 allows you to rotate parts to a desired position before slicing and building. One consideration is the height of the part. If a part can be placed with the shortest dimension in the -z direction, it will require the least amount of slices and therefore take less time and effort to put to- gether. Another aspect of orientation takes into account the shape of the part. It is usually effective to place larger cross sections near the bottom of the build, so that overhangs do not have to be supported. If a large cross section were to be placed on top of a significantly smaller one, the edges of the top slice would sag due to lack of physical support. This concept is demonstrated in Figure 2.2. Curved surfaces provide another need for orientation. If it is practical concerning the number of slices, curves will be smoother if placed in the cutting plane. Sometimes a trade-off between curve accuracy and build layers can be achieved by rotating the part at a slant. 2.2.1.3 Slicing Once the parameters are set, the software goes through a "slic- ing" function, which basically takes the drawing and cuts it into horizontal cross sections approximately 0.005" thick (the thickness of the paper). For larger parts, there may only be one slice per sheet of label paper. However, smaller parts have many slices per sheet. This will result is having sub sections of the part being built per sheet, which will then be assembled after all of the sheets have been cut. When the slicing is complete, the instructions can be down- loaded to the plotter for building the part. Figure 2.3 shows the slices of a gear model in the JP-5 software. JP-System 5 17 Figure 2.2 1) A sample of the need for supports when rapid prototyping a model. 2) A sample model with overhangs. 3) Exag- gerated slice of the model in the given orientation. The ledges have nothing to keep them from falling. 4) Optimum orientation for the sample part. 2.2.2 Plotting The plotter accepts the instructions from the computer one slice at a time, which allows the user to manually load paper for each slice. All slices except the mask are only cut partially through the label paper on the peel-away side, so that each cross section of the part can be peeled away from the backing and adhered to the previ- ous layer. Alignment holes preset to match the peg scheme on the assembly board are cut completely through the paper and backing. The first cut is a "mask" of the part, and is cut completely through the label paper and the backing. The mask is typically a rectangular stencil that encompasses the area of the initial slice of the actual part. The mask is used after the first slice is positioned and anchored. 18 Chapter 2 Figure 2.3 Gear slices in JP-5 software. Next, the first part slice is cut. Figure 2.4 shows the slice being traced on the label paper (a pen was used to enhance the cut edges). The software automatically mirrors the first slice so that it will align with the second and subsequent slices properly, since the remaining sheets will be placed opposite the first one. The backing is not peeled from the first slice. The first sheet is placed with the backing side down on the assembly pegboard with pins properly aligned through the alignment holes. This sheet is taped around the edges to the assembly board with masking tape to prevent any movement along the pegs. Figure 2.5 shows the first sheet being applied to the board. The now upward-facing surface of sheet one has no adhesive for the next layer to stick to, so the mask is needed. The mask is placed on the assembly pegboard, using the registration pins, over the first slice, and spray adhesive is applied to the top of the first slice to give the second slice an adherent surface to start on. Figure 2.6 shows the mask being applied. JP-SystemS 19 Figure 2.4 Gear slices being traced with the JP-5. Figure 2.5 First slice of the gear placed on the assembly board. 20 Chapter 2 The mask stencil is now removed, revealing rectangular patches of adhesive on the top of the first sheet. The part is now ready for the second layer. The second layer of paper is placed in the JP-5 and is cut like the first slice. After the cut, it is extremely helpful to peel the entire label from the second sheet except the ac- tual cross section of the part, as in Figure 2.7. Figure 2.6 Mask adhesive being applied to first gear slice. JP-System 5 21 Figure 2.7 Peeling away excess label around gear cross sections. You now have the second sheet with only the part cross sec- tions remaining, and you are ready to proceed to the next step. Since the label side is cut, but the backing isn't, placing the sheet label side down onto the square patch of adhesive will now allow you to peel the backing away, leaving the cross section attached to the first sheet, with its own adhesive side now exposed. Figure 2.8 shows the second layer being applied. Having the excess backing peeled from the second sheet keeps it from sticking to the spray adhesive in places undesired. 22 Chapter 2 Figure 2.8 Applying subsequent layers to the gear model. Now the third and all remaining slices are cut through the label side, the excess labels are peeled away, and the sheets are placed label side down and peeled to leave the cross section sticky side up for the next layer. The alignment pegs allow the cross sections to be set properly, ensuring a well-built part dimensionally. Keep in mind, however, that the part accuracy is only as good as the coordi- nation of the operator. Smaller parts may be built with several cross sections "per page." In this case the excess label removal and adhesion step may become a little more complicated, but it still works well. This proc- ess also requires subassembly steps, as it is only building sections of the part with the first sequence of sheet addition. The subassemblies typically have sub alignment holes so that they can be properly stacked together once the sheet peeling and adhesion step is com- pleted. Figure 2.9 shows the finished gear (white), along with other parts made with the JP-5. JP-System 5 23 Figure 2.9 Finished JP-5 parts. All are approximately one-quarter inch thick. 2.3 Finishing a Part Once the JP-5 part has been completely assembled, it should be sealed to prevent moisture from being absorbed into the paper. Moisture can cause the parts to warp, sag, or deform. Different sealers can be used, including sanding sealers and varnishes or poly- urethane sprays, but the simplest method suggested by the manu- facturer is to use ordinary school glue brushed on with a small paintbrush. The glue hardens, leaving a nice glossy seal around the part, which helps the appearance as well, however, care must be taken to protect the part from dirty surfaces before the glue dries. Figure 2.9 shows some finished JP-5 parts. 24 Chapter 2 2.4 Typical Uses of the JP-5 Process 2.4.1 Preliminary Design The JP-5 produces simple, inexpensive models that are best used in preliminary design environments, where dimensional accu- racy and durability are less of an issue. It basically gives a designer a solid part he or she can hold and observe, as opposed to a flat drawing on a sheet of paper or computer screen. Unfortunately, the lack of automation tends to defer some designers and businesses, as the process would effectively consume at least one person's attention on a full-time basis, and most firms don't have the manpower to dedicate to spending so much time in producing simple models. 2.4.2 Education Because of the attractive low pricing of the JP-5, it tends to of- ten find its way into various educational facilities, typically on the collegiate level. It is an excellent demonstration of the concepts of layer-by-layer fabrication, because it allows the user the step-by-step interaction with the layers and cutting processes. The interface is easily taught and learned, and the student can get a feel (literally) of prototype modeling from CAD design. Students can design and fab- ricate mechanical components as class projects, for instance, which gives them experience in operating CAD systems for solid model- ing, as well as designing for ease of manufacture. There are many universities now using the JP-5 as a teaching and learning instru- ment. 2.4.3 Research On the research end, the simplicity of the system targets the JP- 5 as a prime candidate for studying the effects of laminating stronger materials together in a rapid prototyping environment. Since the RP industry is in a constant shift toward the actual manufacturing of hardware, RP materials other than the ones currently used must continuously be studied, tried, and tested to meet the demands of the ever-growing needs of the manufacturing world. JP-5 allows one to experiment with basically any sheet-form material that can be cut JP-System 5 25 with a knife blade. Results from these studies can lead to advance- ment in materials capabilities for the more automated RP processes, where lasers and continuous feed come into play, along with various other parameters. 2.5 Materials Properties The JP-5 parts are actually fairly rugged once they are sealed with glue. Since the parts are only paper and glue, there haven't been many official tests done on the parts for tensile and compression strengths. The parts can survive being handled and dropped, but would probably not be used in many testing applications. For one, the dimensional tolerance relies heavily on the user, and at best probably is still approximately ±0.1 inches. Also, any exposure to fluids or pressures may result in delamination of the paper between layers. Regardless, the application of verifying a concept visually is well filled by these parts. 2.6 Key Terms Plotter system. For the JP-5, the plotter system consists of a com- puter and a modified Graphtec pen plotter with knife blades. Assembly board. A large peg board with threaded holes at regular intervals that match pegs used for JP-5 part assembly. Part orientation. The most crucial preprocessing step of the JP-5 system setup, consisting of placing the part in relative three- dimensional space whereas the build time and support geometry are both optimized. For more information on JP-5 contact Schroff Development at 913- 262-2664. Ballistic Particle Manufacturing BPM Technology, Inc., in Greenville, SC developed ballistic particle manufacturing (BPM). There are only a few BPM systems on the market due to the collapse of the company in late 1997, how- ever the patent is still held by the inventor at Stereology Research, Inc. in Easley, SC. The systems that are used are mainly for rapid prototyping (RP) research, or for concept verification models. Bal- listic particle manufacturing was marketed as one of the most af- fordable RP processes at that time, with very inexpensive build ma- terials. Ballistic particle manufacturing was represented as an "office modeler," since the build material was non toxic, the system was compact, and there was no need for solvents or post curing proc- esses. Ballistic particle manufacturing's role in the RP environment was as one of the pioneers of ink-jet based, office-friendly systems, which several vendors now supply to the market. 3.1 System Hardware The BPM Personal Modeler came with all hardware and soft- ware enclosed in a single compact unit. The footprint area of the entire system was only about 24" x 20", as it was expected to be used in an office environment. The BPM is controlled by a MS- DOS based 486/PC, which is housed within the unit on a unique slide and foldout tray. The system has a modem and a serial port for transferring files. The controlling software, which is used for slicing and building the models from the.STL files, is an MS-DOS™ based 26 Ballistic Particle Manufacturing 27 program that is set up for very little user interaction. Figure 3.1 shows the BPM system. 3.2 Ballistic Particle Manufacturing Operation The BPM utilizes ink-jet or droplet based manufacturing (DBM) techniques, where it builds models by firing micro-droplets of molten wax material from a moving nozzle or jet onto a station- ary platform. The platform is then lowered and the process is re- peated until a three-dimensional object is printed. Most parts are built as a hollow shell, although down to a 0.25 inch internal cross hatch may be used. Figure 3.1 The BPM Personal Modeler has all its components built into a slim cabinet. 28 Chapter 3 3.2.1 Software The BPM software is very easy to use for building parts. Es- sentially, the.STL file is opened, and if the file is in the proper ori- entation and scale, clicking the Print command starts the model building, just like printing to a regular desktop printer. After a prompt for a Crosshatch size (or none), the BPM slices the file, homes out the machine, and begins printing. 3.2.2 Part Orientation If the part does need manipulating before the build, the soft- ware has the capability to do so. Parts can be scaled, rotated, and/or translated to a desired orientation. The software will prompt if the part is too big for the build envelope, and will even give a scale factor, which will bring the part down to the maximum possible build size. The part orientation in terms of support structures is less of an issue with the BPM. The unique five-plane build motion eliminates the need for much of the supports, and what little remain are auto- matically generated during the slice function. This build process is described later in the BPM Build Technique section. Basically, the main concerns are surfaces with large radii of curvature, which should be placed in the -x, -y building plane for better curve definition. This orientation eliminates the stair-stepping effect of the layer-by-layer manufacturing process. 3.2.3 Crosshatching The Crosshatch setting represents the distance, or air gap, be- tween the raster fill lines in a "solid" structure. For instance, if a solid cylinder.STL file is built with BPM, it will actually only build the walls and the ends, with an open egg-crate type structure inter- nally. This egg-crate structure is the aforementioned raster fills, and thus the size of the openings is the Crosshatch setting. If the cylinder file were to be built with no Crosshatch size specified, the BPM will only build the walls and the ends, much like an unopened soup container. Ballistic Particle Manufacturing 29 3.2.4 Calibration The BPM is calibrated through the software as well. If parts are not building smoothly or correctly, the calibration sequence can be initiated fairly easily. This sequence prints a series of line pat- terns in the -x and -y direction, distinguished by printed numbers at each group of three lines. The line groups are viewed with a magni- fying glass to determine which set is equally spaced, and then the corresponding number is entered in to correct the jetting properties. 3.3 Ballistic Particle Manufacturing Build Technique The BPM process has five planes of motion for printing the wax material. The -x and -y motion is provided by a carriage sys- tem that moves the single jetting head front to back and side to side while printing. This action results in a thin layer of wax represent- ing the contour of a cross section of the part. The z axis is provided by a platform mounted on screw leads, which enable it to be low- ered to allow for the next cross section to be built. These three planes of motion are present in most RP systems. The last two degrees of motion are what set the BPM system apart from others. The build jet can flip to fire almost completely horizontally. This motion is what eliminates the need for supports. As in the hollow closed cylinder example, the top surface can be jetted without supports because the flip motion of the jet allows material to be deposited sideways, in a horizontal plane. This unique capability is complemented with the capability of the head to rotate in the -x, -y plane for horizontal printing in the -x or -y plane. 3.4 Finishing of Ballistic Particle Manufacturing Parts BPM parts are not intended to be finished, as they must be handled with care. The parts can be painted with a water-based paint using an airbrush, but that is about the extent of finishing that can be performed without damaging the part. 30 Chapter 3 Figure 3.2 The BPM head flips to build at an angle, which elimi- nates most supports (Courtesy of BPM, Inc.). 3.5 Typical Uses of Ballistic Particle Manufacturing Parts BPM parts are mainly used for concept visualization. Due to the weakness of the material, the parts aren't well equipped for use as functional components. The visualization aspect is a valuable in- sight however, as a three-dimensional model can provide the neces- sary comfort zone in designing to manufacture. Ballistic Particle Manufacturing 31 Figure 3.3 This compressor scroll model made by the BPM process was painted with water-based acrylic to give a metallic appearance. Figure 3.4 These concept models were made using BPM process. The dime shows scale. 32 Chapter 3 3.6 Advantages and Disadvantages The advantage of the BPM was the capability to build parts that required minimal post-processing from a low toxicity standpoint. The BPM system was also presented as a low-power consumption device, and the low cost of the system and materials made the use in smaller design firms with low budgets a probable target. In the event that another company buys the patent and revives the system, it will again probably be sold as a "printer," because of its user-friendly interface, non toxicity, and low cost per part opera- tion. 3.7 Key Terms Part orientation. An essential part of typical RP processes, the BPM could build parts in most any orientation with its 5-axis capa- bility. Cross-hatching. A time and material saving technique, in which parts are built with a hollow shell surrounding a corrugated grid structure. Now used in several RP techniques. Calibration. In order to maintain repeatability and accuracy, ink-jet based RP systems, including the BPM, must go through a standard print calibration of a series of lines or intersecting lines that are then checked by the user and adjusted accordingly. Finishing. Typically consists of sanding, polishing and painting. The BPM parts were too fragile to perform these operations, except for water-based airbrush painting. The Model Maker Series The Sanders Model Maker (MM) series captures the essence of the ink-jet printing technology, and builds in a layer-by-layer fash- ion, similar to other rapid prototyping (RP) systems. The MM uses several different types of data file formats but has only one base type for the build and support materials, wax. The MM was devel- oped by Sanders Prototype, Inc. (SPI), a subsidiary of Sanders De- sign in Wilton, NH, in the early 1990s with the intention of revolu- tionizing the industry as it pertains to accuracy and precision. 4.1 Model Maker System Hardware The MM system has evolved through three "models," Model Maker (original model), Model Maker II (MMII, second genera- tion), and recently Rapid Tool Maker (RTM). The original modeler has a build envelope of 7" x 7" and the MMII has an envelope size of 13" x 7", whereas the RTM has a 12" x 12" working area. While both MMs are desktop models, the RTM is a self contained unit with an onboard computer. Figure 4.1 shows an MM unit and an MMII unit. 4.1.1 Software Both modelers utilize MW (MW) software, manufactured by SPI, to prepare and manipulate the incoming file for use in the MM machine. The software can be operated through a variety of work- stations, from UNIX to PC , and the current modeler has an on- board computer that can function alone after it receives the pre- 33 34 Chapter 4 pared file from a "dummy" PC whose sole purpose is for file slic- ing and preparation. Figure 4.1 The MM and MMII by Sanders Prototype, Inc. 4.1.2 Build Materials Both models use a build and support material to produce a 3-D model. These materials are wax based with the support having a lower melting point than the build. This insures that during post- processing, the support material will melt away leaving only the part, made of build material. Each material has its own heated res- ervoir and is very sensitive to contamination, which means handling should not occur (See Figure 4.2). 4.1.3 The Print-head The print-head assembly consist of the print-head, print-head cap, purge spout, purge spout cap, cable, and saddle (see Figure 4.3). Model Maker Series 35 There are two print-heads, one for building the part and the other for generating the necessary support. This support depends on the geometry of the part and can be produced around the entire part or just on certain areas. The jets sit on a carriage that enables them to move in the X and Y direction (left to right), while the stage moves in the Z direction (up and down). There are two proc- esses that enable the materials to be transported to the print-heads. 1) Material is pumped to the feed lines by compressed air within the reservoir during the purge operation 2) There is an actual si- phon that is conducted from the reservoir to the feed lines, to the print-head during the model build. The feed lines are heated, as are the print-heads. This heating of reservoirs, feed lines, and print- heads is necessary to have a continual flow of material. Figure 4.2 Build and support reservoirs for the MM. 36 Chapter 4 Figure 4.3 Print-head assembly of the MM. 4.1.3.1 Print-head Cap The print-head cap is comprised of the top that closes the jet off and the connecting portion of the jet to the feed lines. This cap must be screwed on tightly to make sure the jet compartment is air tight and the connection to the feed line must be secure if there is to be a consistent and even flow of material. 4.1.3.2 Print-head Purge Spout and Cap The purge spout is very important. It enables the user to purge the jet to assure there is a proper amount of material within the jet. If there is a air bubble in the material it is also necessary to purge by connecting a plastic tube to the spout and implementing the purge command for 2 seconds. Immediately after, remove the tube and replace the cap to eliminate excess air entering into the print-head body. This process should be done prior to every build and as the primary method to correcting a printing malfunction of the jet as- sembly. Model Maker Series 37 4.1.3.3 O-ring The o-ring is a seal between where the print-head cap screws into the print-head body assembly. It prevents leaking of material and the introduction of air into the body chamber. 4.1.3.4 Print-head Body The print-head body is where the extra material is stored until it is printed onto the substrate surface. This is a very small space, therefore, an air bubble could cause a jet interruption and possibly a failure. 4.1.3.5 Saddle The saddle secures the entire print-head assembly to the car- riage. There is a locking device on the MMII that helps insure that the print-head is properly positioned to produce optimal printing re- sults. 4.1.3.6 Tip The tip is the orifice through which the material is printed. Never rub or touch this orifice with your hands or any other sub- stance, this will damage the jet and cause it to be inoperable. The proper substance to use to remove any debris from the tip is the cor- ner of a Kim wipe. 4.2 Model Maker Operation 4.2.1 CAD File Preparation Prior to actually building the part, the STL file must be trans- lated into the software language used by the MM. This software is MW and is used for the purpose of preparing and manipulating the file so that the MM can build it. The file, after being read into MW, produces a picture of the file on screen in the Cartesian coordinate system (-x , -y , and -z). A box appears around this grid with a bar that has many functions that allow the user to put the part in its de- sired orientation. From this box you can perform slicing functions, zoom functions, layer thickness alterations, part positioning, part sizing and other build parameters. The MW software is very useful 38 Chapter 4 and gives the user ultimate control over the end product. Figure 4.4 shows an STL file as viewed by MW. Figure 4.4 The STL file is viewed with MW before preparation to run. 4.2.1.1 Positioning the Model There are several factors to consider when positioning the part. Among them are the distance the cutter travels, special features, detailing, opening edges, time to build, and the quality of the model. All of these can be changed as it pertains to the specific character- istics desired for the part. The fundamental rule for positioning is to have the longest length of the part parallel to the cutter. 4.2.1.2 Configuration Selection This is a very important factor prior to building a part. This particular feature is accessed through the Config button on the MW window. This notebook contains the database of settings that de- termine how the model is built. Different parameters can be set with five tabs on the screen. These tabs are: Configuration, Units, Ma- chine, Memory, and Build. Model Maker Series 39 4.2.1.2.1 Configurations Under this tab you are able to scroll through several configura- tions for slice thickness for each machine type (MM or MMII). Each configuration has an ID number that allows you to customize the slice thickness depending on the model being prepared. Figure 4.5 shows the configuration grid. Figure 4.5 The configuration notebook in MW. 4.2.1.2.2 Units The Units tab allows you to select the units in the configuration program and alters the way dimensions are interpreted in the ge- ometry files. The choices are inches, millimeters, and centimeters. 4.2.1.2.3 Machine The Machine tab allows you to select the current machine you are building on (MM or MMII). 40 Chapter 4 4.2.1.2.4 Memory This tab allows the user to select the amount of memory de- pending on the part size and complexity. The larger and more intri- cate the model, the more memory required. The machine require- ments are at least 16 MB of RAM and preferably 32 MB of RAM. To make it simple most parts can be sufficiently completed by se- lecting the Memory Default button. 4.2.1.2.5 Build This tab has default values for building the model. The user can auto center the model in -y, offset the model in -x and -y; set number for multiple copies and distance between each; offset the jet velocity and acceleration; add cooling time; adjust the temperature; skip layers between jet checks; adjust cutter feed rate; and set multi- ple layer cutback depth. 4.2.1.3 Fill The next important area is the Fill Notebook. This notebook is divided into three sections, the first tells you the ID number, slice thickness, and configuration chosen in the Configuration Notebook. The second area shows you the slice thickness and the start/stop height. The last section deals with support. It enables the user with the ability to have maximum to minimum support. If the part is fragile or has many overhangs, you may consider choosing support around the entire part, whereas if it is a more rigid/sturdy part you would only use support where it is needed. This will also be a de- termining factor in the timeliness of the post-processing procedure. There is a box to check for eliminating extra cooling in between lay- ers, the number of initial support layers, and continuing extra sup- port to the top of the model. In addition, you can also reinforce the support walls by adjusting the excess-support control button. 4.2.1.4 Slicing The MM utilizes Bview as a viewer of the.MM2 and.BIN files generated by MW. This viewer displays slice cross sections and their respective fill patterns. A digital readout at the bottom of the screen gives the ability to extract measurements from this file. This information is helpful in determining the files integrity and getting a view of slice-by-slice formation. This slice-by-slice file is Model Maker Series 41 the code the machine will use to generate a layer-by-layer creation of the model. To access this function you must select the Bview button from the menu. There are several different functions that you can implement to render the model and file exactly how you desire it to be prior to building. The Navigation buttons allow you to view the model slice by slice or at 10 percent increments, the Automated Control button gives you a real time build slice by slice, the Zoom buttons allow you to adjust the view of the model on the screen, and the Pan buttons allows you to adjust the -x and -y plane views of the model. Together, all of these functions give the modeler com- plete control over not only how the machine will build the part, but the customization of the part prior to the build. 4.2.1.5 Send to Model Maker After slicing and orientation, the model must be sent to the on- board computer of the MMII. In order to do that the operator must choose the MM=> button, which will send the complete file to the MMII as Job.MMII. In order to send the file you must choose a file name, the printer, and then select the OK button. Once this is done it is now time to physically prepare the machine to build the model. 4.2.2 Building a Part Once the part has been delivered to the MMII it is time to pre- pare the machine for building. Initially, you can check the material reservoirs to determine if you need to add any build or support mate- rials. You can get a graphical representation by selecting on your opening screen. The computer will tell you if additional mate- rial is needed and how much to add. Once you have added the ma- terial(s), allow 45 minutes for the material to be liquefied in the res- ervoir before use. But while you are waiting you can check the op- tical tape receptacle to make sure it is empty and you can mill the substrate. To do so, select from the initial screen (Run MM), select , and then , this will allow you to choose the mill command and level your substrate. Mill the original surface (dull finish) of the substrate until it has a clean, bright finish. This en- sures that the surface is level. The next and most important step is to check the jet-firing status. Before each use, perform a manual 42 Chapter 4 purge to refill the jet reservoir with material and make sure that the proper amount of air is within the reservoir also. Cut a 3-inch piece of plastic tubing, remove the purge cap, and place the tube on the purge spout. Hold the cylindrical tube over the tube and under choose the respective jet you are purging (build or support). Once the jet has been selected, another menu will appear that will prompt your actions, from this menu, choose the purge command. Allow the jet to purge until you get an even flow of material into the tube container and allow it to flow for 2 to 3 seconds, then press any key to stop the purge. Immediately remove the tube from the spout and reapply the cap. After making sure that the jets are firing properly, go back into new build, select the file you want, and build. 4.2.3 Post-processing The post-processing procedure is a process that must be moni- tored very carefully. When setting your initial temperatures you must be careful because the support material has a lower melting point than the build material. Either you can use a porcelain bowl- like container, a hot plate, and a thermometer, or you can purchase a sonicator with heat control and a built-in digital thermometer. If you purchase the latter, remember that the sonication produces its own heat, so additional heat may or may not be necessary depending on the part size. Post-processing is a hands-on process that involves time and attention. Allow the part to sit in the recommended VSO solvent solution at 35° C for 30-minute increments. Depending on part size you may want to play with the temperature settings and the time you allow it to soak in VSO. You want the support material to be mushy so that you can easily remove it with a tool of your prefer- ence (be careful not to destroy part surface). When all the support (red) material has been removed, you may re-finish your surface, paint it, or leave it as is. Remember, this process takes time, if you rush it you could sacrifice the integrity of your part. 4.3 Advantages and Disadvantages of the Model Maker The power of the MM family of systems lies primarily with the production of small, intricately detailed wax patterns. The jewelry Model Maker Series 43 and medical industries have capitalized on this advantage due to their needs for highly accurate, small parts. Perhaps the most apparent drawback of these systems are the slow build speed when it comes to fabricating parts larger than a 3- inch working cube. This is primarily due to the fact that the layer thickness required to achieve the high-dimensional accuracy is typi- cally an order of magnitude thinner than standard RP systems. The result: the parts take 10 times longer to build. Many concerns have been raised over the progression of the technology as to system operation reliability issues. More often than not, however, jet failures and failed part builds can often be traced back to a misunderstanding of the process operation and an over- loading of the machine's true capacity. 4.4 Key Terms Print head. The print head is the heart and soul of the MM systems, as most other components of the hardware can be obtained off-the- shelf. Configuration. The main venue in the MW software for changing operating parameters of the MM system. Fill. A large contributor to the final build time and material required for a part, the fill can be varied from solid to hatched. Post-processing. The final cleanup of models after removal from the MM machine, post-processing requires several steps and direct user intervention in order to acquire a finished project. For more information on the Model Maker, please contact Sanders Prototyping at 1-603-429-9700. Multi Jet Modeling The ThermoJet and the Actua 2100, both made by 3D Systems in Valencia, CA, fall into the growing area of the rapid prototyping (RP) market known as concept modeling. Both systems apply the Multi Jet Modeling (MJM) build style to produce wax prototypes with an array of ink jets. The systems are one of the least expensive in the line of RP technologies. They are also safe and clean enough to operate directly in a design office environment. The ThermoJet is actually a replacement to the Actua 2100, but there are still several Actua units in operation throughout the world. 5.1 System Hardware The ThermoJet/Actua 2100 comes as a single self-contained unit (excluding the control computer), and is about the size of a large photocopy machine. One of the more unique features of the ThermoJet/Actua 2100 is the ability to network the system much like a standard printer. This allows the download of build files into a queue from various areas of the office. Parts are "printed" out in the order they are received the same way that documents are printed out on the standard printer. The ThermoJet/Actua 2100 also does not require any post-processing units, as the support removal is done easily by hand. The key component of the MJM process is the material deliv- ery system. The wax billet is loaded into a reservoir inside the cabi- net of the machine. The material is kept molten there and is siphon- fed to the multi-jet head. The Actua 2100 multi-jet head has four 44 Multi Jet Modeling 45 rows of 24 jets each, a total of 96 jets for print-on-demand capabil- ity, whereas the ThermoJet systems have over 300 jets spanning the entire cross section of the part build area for a faster build capability. 5.2 Multi Jet Modeling Process Operation 5.2.7 System Software The software for the Thermo Jet/Ac tu a 2100 system is very user-friendly, where user input is kept to a minimum. It is available on the PC platform, and accepts the standard STL RP file format. Basically all of the slicing and operating parameters are default set- tings that normally do not have to be changed. Parts can be nested in the -x, -y plane with a unique auto-nesting capability, and are then essentially "printed" into functional, accurate wax parts. Figure 5.1 shows the latest Thermojet system. Figure 5.1 The ThermoJet MJM System (Courtesy of 3D Systems). 46 Chapter 5 5.2.2 Build Technique The MJM process builds parts by printing thin consecutive lay- ers of the molten wax in the shape of the part cross sections. Like most RP systems, the parts are built onto a movable z stage, which lowers as the part is "printed." Currently, the Actua 2100 system prints with a layer thickness of 0.0039 inches, or three passes of 0.0013 inches, whereas the ThermoJet system prints multiple passes of thinner layers for higher resolution. The multi-jet head traverses in the x axis direction (left to right), as the printer gantry that houses the head increments the width of the affective print area in the y di- rection. The multiple jets are turned on and off where needed at precise intervals, which allows for an accurate final article in the xy plane. The final z dimensions suffer a slight amount of inaccuracy on the lower side due to support removal, yet the upward facing sur- faces have excellent surface quality. Figure 5.2 shows the MJM process. Figure 5.2 The multi jet modeling process (MJM) (Courtesy of 3D Systems). Multi Jet Modeling 47 5.2.3 Postprocessing MJM process parts are fairly easy to post process. The sup- ports are built with the part build material, yet are strategically shaped for easy removal. The entire support structure consists of very fine columns of the build material that reach from the build platen up to any overhanging surfaces. These columns are thin enough that most of them can be "rubbed" off the part with your finger, and the rest can be sanded away. Again the upward-facing surfaces already have excellent surface quality (detailed enough to print a full-scale business card with raised print), so all of the post processing needed is on the underlying surfaces where the supports have been removed. For best results, the parts can be placed into a freezer for an hour prior to support removal. This causes the fine supports to become brittle and hence much easier to rub off. Care must be taken not to fracture the part itself, however. After the quick support removal, the parts are complete. They require no post curing, infiltrating, or dipping. They are nontoxic and can be handled immediately after processing. 5.3 Typical Uses of Multi Jet Modeling The MJM system was designed specifically for concept mod- eling in the office environment. The models can be built quickly and effectively, and are durable enough to demonstrate designs in presentations and meetings. The MJM process parts are also dimen- sionally stable enough to use for limited fit-check analysis applica- tions. Another use of the MJM process parts developed later for a more practical test hardware application. The wax makeup of the build material makes it applicable as an investment casting pattern material. The glossy surface finish and easy melt-out provide for clean, crisp metal castings. As materials develop for the MJM process systems, they may begin to play a larger part in the more functional prototyping roles. Until then they will continue to serve an important component in the concept-modeling and casting realm. Figure 5.3 shows some sam- ple MJM parts. 48 Chapter 5 Figure 5.3 Sample parts from the MJM process (Courtesy of 3D Systems). 5.4 Advantages and Disadvantages of Multi Jet Modeling The advantages of the MJM systems include speed, afforda- bility, reliability, ease-of-use, cleanliness, crisp resolution, and net- working capability. All of these features stack up to make for a very robust RP system. The key disadvantages are not unlike those experienced by other RP systems, which include low-strength material, rough sur- faces on the support material side of parts, and the moderately high cost of the build material. Unfortunately, also, even though the post processing required has been significantly reduced in the Thermojet system, sometimes designers still find the effort required to clean up the parts is more than what fits into their working schedules. Thus the systems may tend to be used less than what would be ideal to maximize the de- sign-to-manufacturing experience in a corporation. 5.5 Key Terms Ink-jet technology. The same basic technology as used in desktop publishing printers, ink-jet technology provides the core process for concept modeling RP systems. Multi Jet Modeling 49 Networking. In this case, networking refers to electronic file trans- fer networks, such as local area networks (LANs), over which STL data can be transferred to the RP system. The MJM systems maxi- mize the use of networking by allowing print queues, in which op- erators from remote computer workstations can send multiple parts to the systems to be manufacturing consecutively. Concept modeling. Applying fast, inexpensive RP systems to the concurrent engineering design loop by providing physical verifica- tion models to designers, salesmen, etc. For more information on MJM systems, contact 3D Systems at 805-295-5600. 3D Printing (Z402 System) Three-dimensional printing, or 3DP, is an MIT-licensed proc- ess, whereby liquid binder is jetted onto a powder media using ink jets to "print" a physical part from computer aided design (CAD) data. Z Corporation (Z Corp) incorporates the 3DP process into the Z402 system. The relatively inexpensive Z402 is directed toward building concept-verification models primarily, as the dimensional accuracy and surface roughness of the parts are less than higher end systems. The initial powder used was starch based and the binder was water based, however now the most commonly used powder is a new gypsum based material with a new binder system as well. Models are built up from bottom to top with layers of the starch powder and binder printed in the shape of the cross sections of the part. The resulting porous model is then infiltrated with wax or an- other hardener to give the part dexterity. The Z402 is the fastest modeler on the market, with speeds 5 to 10 times faster than other current rapid prototyping (RP) systems. 6.1 Z402 System Hardware The Z402 is currently available in only one size, which can build models up to 8" x 11" x 8". The overall size of the modeler is approximately 3' X 4', so it can fit in a fairly confined area. Parts built with the starch material can be hardened to fit the application necessary. Wax infiltration gives the parts some strength but also leaves them usable as investment casting patterns. Stronger infil- 50 3D Printing (Z402 System) 51 trants, such as cyanoacrylate, can be used to provide a durable part that can survive significant handling. Since the starting point of this writing, Z Corp has advanced their 3DP system in several ways. First, they released updated print cartridges (Type 3) that last longer along with stronger infiltrants for durable parts. Secondly, a new material and binder system called ZP100 Microstone was released that provides stronger models di- rectly from the machine with little or no postprocessing or infiltrant. Finally, an automated waxer was released that helps control the wax infiltration process if necessary. The modeler has several important components, including the following: 1. Build and Feed Pistons. These pistons provide the build area and supply material for constructing parts. The build piston lowers as part layers are printed, while the feed pis- ton raises to provide a layer-by-layer supply of new mate- rial. This provides the z motion of the part build. 2. Printer Gantry. The printer gantry provides the xy motion of the part building process. It houses the print head, the printer cleaning station, and the wiper/roller for powder landscaping. 3. Powder Overflow System. The powder overflow system is an opening opposite the feed piston where excess powder scraped across the build piston is collected. The excess powder is pulled down into a disposable vacuum bag both by gravity and an onboard vacuum system. 4. Binder Feed/Take-up System. The liquid binder is fed from the container to the printer head by siphon technique, and excess pulled through the printer cleaning station is drained into a separate container. Sensors near the contain- ers warn when the binder is low or the take-up is too full. The Z402 is operated through the COM port of a PC Worksta- tion (not included), although the system has an onboard computer that can be used for diagnostics if necessary. The Z Corp slicing software is provided with the purchase of a Z402 system, and is compatible with Windows 98 and Windows NT. 52 Chapter 6 Z Corp also sells a postprocessing package necessary for detail finishing and strengthening of the parts produced by 3DP. The package includes a glove box with air compressor and air brushes for excess powder removal, a heating oven to raise the temperature of the parts above that of the wax infiltrant and a wax-dipping unit that melts the wax and provides a dipping area for the parts. Figure 6.1 shows the Z402 system. Figure 6.1 The Z-Corp Z402 3D printing system. 6.2 Z402 Operation The Z402 has a very user-friendly interface, where very few commands are necessary to build a part. Since the parts are built in a powder bed, no support structures are necessary for overhanging surfaces, unlike most other RP systems. 6.2.7 Software The Z402 starts with the standard STL file format, which is imported into the Z Corp software where it is automatically sliced 3D Printing (Z402 System) 53 and can be saved as a BLD (build) file. When a file is first imported into the software, it is automatically placed in an orientation with the shortest -z height. This is done as the fastest build capability, like other RP systems, is in the -x, -y direction. The part can be manu- ally reoriented if necessary for best-part appearance. Multiple STL files can be imported to build various parts at the same time for maximum efficiency. The default slice thickness is 0.008", however the value can be varied to fit the needs for particular parts. Objects can be copied, scaled, rotated or moved for optimum