Expanding Mechanical Design and Fabrication Horizons
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D.W.WILSON,L.E.BAILEY,ANDC.E.BENNETT Expanding Mechanical Design and Fabrication Horizons Dale W. Wilson, Leslie E. Bailey, and Clifford E. Bennett The capability to develop prototype hardware systems is improving steadily as computer technology is dramatically enhancing design, fabrication processes, and tools. Designers now make extensive use of sophisticated 3D solid modeling programs to visualize design concepts, perform engineering analysis, and communicate detailed design data through networked file transfers. Numerically controlled computerized machine tools are then programmed using the design data to produce parts faster and with greater accuracy than ever before. New laser machining, electrical discharge machining, and rapid prototyping technology are enabling the fabrication of small, precision components not possible using traditional methods. The result is faster product development cycle times and lower costs. (Keywords: Casting, Computer-aided design, Computer-aided machining, Electrical discharge machining, Finite-element analysis, Laser machining, Rapid prototyping.) INTRODUCTION At this dawn of the 21st century, the key challenges display, control, information management, and mate- facing engineers responsible for the development of rials fabrication technologies. prototype mechanical hardware systems have expanded Product development is an iterative yet creative beyond the purely technical realm. Today research process linking design and fabrication processes. Im- engineers must creatively deliver increasingly complex provements in the product design process have instruments and systems in less time and at lower costs occurred through the use of more efficient tools, en- than ever before. This trend is expected to continue hanced communications capabilities, and design and well into this century as industry attempts to capitalize fabrication process improvements. Most of these en- on emerging computational and information technol- hancements have been powered by the rapidly increas- ogies. To remain competitive in meeting these chal- ing capability of affordable computer technology. lenges, the Mechanical Services Group (TSM) of the While the improvements in design and fabrication Engineering, Design, and Fabrication Facility within automation have been evolutionary, the collective the Technical Services Department (TSD) has imple- impact of these changes has the potential to be rev- mented a continuous stream of evolutionary improve- olutionary if used to full advantage. To better under- ments in mechanical design and fabrication methods stand how this revolutionary improvement in product that take advantage of emerging computer modeling, development can be achieved, this article describes 506JOHNS HOPKINS APL TECHNICAL DIGEST, VOLUME 21,NUMBER 4 (2000) EXPANDING MECHANICAL DESIGN AND FABRICATION HORIZONS the significance of the key advancements in design, design tools are shown in yellow (Fig.1), while those analysis, and fabrication tools and how they interact to impacted by advanced fabrication capabilities are reduce design cycle times and development costs. shown in blue. Much of the design process can now be achieved in “virtual” space using 3D solid modeling, analysis, and mechanical simulations. Computer de- THE PRODUCT DEVELOPMENT sign and analysis tools enhance the visualization of PROCESS concepts, speed up the evaluation of expected per- Product development is a complex process that can formance, and streamline communication of design be realized in many different ways. A simple block information. Design concepts and variations can be diagram of a prototype product development process is explored on the computer screen, before prototype shown in Fig. 1. The process defines how ideas are hardware is fabricated. For small, simple development turned into a physical prototype by repeatedly following efforts, savings in time and cost are small, but for larger, an ordered sequence of steps. The arrows show how more complex programs, time and cost savings can be concepts and solutions from each stage are evaluated exponentially more significant. Experience has shown and redone, if necessary, to achieve the design require- that gains in efficiency achieved by using modern com- ments. There are three ways to significantly reduce puter-aided design (CAD) tools can quickly be erased product development times and costs: (1) shorten the by increases in design iterations if the design process time it takes to perform each step in the process, (2) is loosely controlled. reduce the number of iterations in the design process, The savings are especially significant when the and (3) conduct steps in a parallel, substantially over- design process is linked to the fabrication process. Once lapping mode instead of in series. This third “holistic” a design has been introduced into the fabrication stage, approach1 has the most dramatic impact on develop- further changes to it become very costly. Also, some ment cycle times by accelerating the whole process. designs are easier and more cost-effective to produce The process steps most significantly impacted by the than others, and the practice of “design for manufac- advanced features and capabilities of new computer-based ture” takes on a more significant role in performing cost-effective prototype fabrication. Effective design for manufacture requires collaboration among engineers, designers, and fabricators early in the conceptual design stage. Inherently this process generates change, and the Need recognition modern computer design tools minimize the impact of such changes. Advances in design tools have contrib- uted to the efficient and successful design support of the Problem Near Earth Asteroid Rendezvous (NEAR),2 Advanced definition Composition Explorer (ACE) and Thermosphere-Iono- sphere-Mesosphere Energetics and Dynamics (TIMED) Design spacecraft, the Seafloor Characterization and Mapping synthesis Pod (SCAMP), and the highly publicized Integrated Storage System developed for the Advanced Natural 3 Preliminary design Gas Vehicle (ANGV) Project. and analysis ADVANCED DESIGN TOOLS Detailed design CAD and Solid Modeling Tools State-of-the-art CAD systems offer many advantag- Prototype model es to the design team. Concepts can be generated and evaluation analyzed in a virtual environment, and digital images can be enhanced to display photorealistic renderings. Final Many design concepts and variations can be explored design on the computer screen, and any changes can be cap- tured automatically and implemented quickly. Anima- tion and simulation software can be applied to explore Product mechanical characteristics of mechanisms for motion paths and interferences. Moreover, designs are stored as Figure 1. Simplified schematic block diagram showing the key computer data files that can be used as a starting point steps in a typical linear prototype product development process. for future revisions of hardware. Solid modeling greatly JOHNS HOPKINS APL TECHNICAL DIGEST, VOLUME 21, NUMBER 4 (2000) 507 D. W. WILSON, L. E. BAILEY, AND C. E. BENNETT enhances the designer’s ability to create and manipu- Product Data Management late assemblies. The volume, mass, center of gravity, Product data management (PDM) systems provide and moments of inertia can be calculated by the CAD a means for organizing and storing the CAD files pro- program by assigning appropriate properties to the duced by a design so that they can be accessed for future solid. Geometric interference can also be quickly as- use. This capability is absolutely essential for configu- sessed and quantified to check tolerances. Cutaway ration-managed design to preserve the CAD databases views can be generated (Fig. 2) to show hidden detail. and associated documentation and to promote disci- These capabilities facilitate the more efficient evolu- plined, formal communications of design information. tion and understanding of complex hardware designs. Currently, all drawings and design databases are ar- TSD currently uses Parametric Technology Corpo- chived in an Oracle-based PDM system. As long as the ration’s Pro/Engineer (Pro/E) software, which is pow- databases are compatible with the current software in erful, fast, and robust. Changes to the computer rep- use, the information can be retrieved and reused by the resentation of the hardware are made by merely CAD package as a basis for new or modified designs. retyping a dimension. In Pro/E, related geometry, di- In addition, the drawings are archived in a neutral mensions, and numerically controlled (NC) program- plotter format so that they can be displayed and replot- ming information are all driven by parameters. When ted well into the future as read-only files. The PDM a parametric change is made, the associated down- stores all types of data, allowing the archiving of mem- stream data are updated automatically. Parametric os, special assembly instructions, and reports generated means that geometry changes are driven by predefined for a program. This ancillary information can be very physical parameters such as length, width, and height. valuable in preserving important insights about a de- Both the initial design and later modifications can be sign, especially if it is going to be used again. Since APL created with record efficiency. In addition, the para- often uses design heritage to reduce time and costs, the metric information is associative, i.e., the numbers used PDM is an important tool to ensure that important to create the original geometry stay