Introduction to Mechanical Engineering Design Through a Reverse Engineering Team Project

Session TA1-1

Introduction to Mechanical Engineering Design through a Reverse Engineering Team Project

Ronald Barr, Thomas Krueger, Billy Wood, Ted Aanstoos, Mostafa Pirnia Mechanical Engineering Department University of Texas at Austin

Abstract

Our group at the University of Texas at Austin has the responsibility for teaching the first course in Mechanical Engineering. The first-year course ME 302, titled “Introduction to Engineering Design and Graphics,” was derived from a traditional Engineering Graphics course with added material that focuses on the engineering design process. The graphics component is based on a computer modeling educational paradigm that includes 2-D computer sketching, 3-D solid modeling of parts, assembly modeling, and the projection of an engineering drawing directly from the 3-D model. Other applications of the paradigm include kinematics animation, finite element analysis, and generation of a rapid prototype directly from the 3-D data base. In order to motivate the freshmen students in the area of engineering design, we have instituted a team project based on the concept of reverse engineering. Reverse engineering is the dissection of a common mechanical assembly into its individual parts, and then studying the geometry and design function of each part. The team activities in the reverse engineering project have been carefully scheduled by our group so that the teams systematically accomplish various phases of the project over the duration of the course, with intermediate due dates for major tasks. The student teams select a mechanical assembly, dissect it into individual parts, make measurements and sketches, build 3-D solid models, apply the solid models to various analyses, and make rapid prototypes. The whole project is eventually documented with sketches, 3-D model printouts, design analysis reports, prototypes, and final drawings.

Introduction to Modern Engineering Graphics Instruction

Within the past two decades, the teaching of 3-D solid modeling has become the central theme in most engineering graphics programs. This recent paradigm shift to 3-D has been facilitated by the development and low-cost availability of solid modeling software that allows the student to focus on the “bigger-picture” approach to engineering graphical communication. In this Concurrent Engineering approach1, the 3-D geometric database serves as the hub for all engineering communication activities (Figure 1). These communications include engineering analysis, simulation, assembly modeling, prototyping, and final drafting and documentation.

Table 1. The Triad of Modern Engineering Graphics Instruction Proceedings of the 2009 ASEE Gulf-Southwest Annual Conference Baylor University Copyright © 2009, American Society for Engineering Education In the Concurrent Engineering paradigm for A. Engineering Graphics Fundamentals graphical communication, the student starts Freehand Sketching with a sketch of an idea. The sketch can then be used to build a solid model of the part. The Generation of Engineering Drawings solid model not only serves as a visualization Dimensioning modality, but it also contains the solid Sectioning geometry data needed for engineering analysis. Typical of these analyses are finite element B. Computer Graphics Modeling Fundamentals meshing, stress and thermal studies, mass Creation of 2-D Computer Geometry properties reports, and clearance-interference Creation of 3-D Computer Models checking. After analysis, the same geometric Building Computer Assembly Models database can be used to generate final communications like engineering drawings, C. Computer Graphics Applications marketing brochures, and even rapid physical Digital Analysis prototypes that can be held in one’s hand. Animation and Simulation Presentations Indeed, an entire Engineering Graphics curriculum could be developed around three Rapid Prototyping and Manufacturing major aspects of instruction: engineering Design Projects/Reverse Engineering graphics fundamentals, computer graphics Presentation Graphics modeling fundamentals, and computer graphics applications. This triad of modern engineering graphics instruction is listed in Table 1.

Figure 1. The Concurrent Engineering Design Paradigm. What Is Reverse Engineering?

Reverse engineering is a systematic methodology for analyzing the design of an existing device or system. It can be used as a means to study the design, and is a prerequisite for re-designing the device or system. Reverse engineering is used to gain information about the functionality and sizes of existing design components. It should be noted that, for student projects, reverse engineering is a legitimate activity. Determining “how something works” is not stealing someone’s ideas, but rather is a beneficial way to enhance the learning process of engineering design for the novice. Reverse engineering is sometimes called mechanical dissection because it involves taking apart or “dissecting” a mechanical system. Mechanical dissection has been promoted for many years as an acceptable activity for engineering students2,3,4. When the student dissects the system, careful sketches of the parts are made. These sketches convey the geometry of the part, and show how the parts fit and work together. This facilitates reassembling of the whole system at a later date. The student needs to carefully measure all of the features on each part during the dissection process so that solid models can be created. Since correct measurements are a significant part of the reverse engineering process, the students learn to use common measurement tools such as scales and calipers.

Student Reverse Engineering Project

The reverse engineering project serves as a semester-long, culminating experience for engineering graphics students at the University of Texas at Austin. Typically, these students are freshmen engineers who have very little background in design or analysis. Hence, the reverse engineering project does not serve as a rigorous analytical challenge, but rather allows them to apply all the tools that they have learned in the graphics course to a real-world design problem. The checklist outlines all the activities expected for the student reverse engineering team project. The following sections detail the chronological events that occur during this reverse engineering project.

Assigning Teams At the start of the semester, the students are asked to fill out a form that includes information like section number, class level, gender, dormitory name, and other scheduling data. They are also required to take the Myers-Briggs Type Indicator (MBTI) on-line, and then to indicate their four- letter MBTI personality rating on the information form. These data are then used by the instructor and teaching assistant (TA) to assign the teams (nominally four students per team) in an equitable fashion that balances team factors such as gender, academic backgrounds, and MBTI types. The team will then have an inaugural meeting in class to exchange contact information, to pick a team leader, and to then begin the project.

Selecting the Engineering Object to be Reverse Engineered The first team task is to pick the engineering object to be reversed engineered. Some judgment is needed to select an object that matches the task at hand. Usually, the instructor will give some advice on what types of objects work well. Table 2 lists some engineering objects that have been successfully used in the past for this reverse engineering team project. For purpose of illustrating the reverse engineering project, a Trailer Winch student report has been selected for this paper.

Table 2. Examples of Acceptable Reverse Engineering Objects

Proceedings of the 2009 ASEE Gulf-Southwest Annual Conference Baylor University Copyright © 2009, American Society for Engineering Education Baby Toy Differential Gear Master Cylinder Shower Massage Head Bathroom Scale Doorknob Assembly Model Car Drive Train Spinning Disk Launcher Beer Faucet Flashlight Oil Pump Sprinkler Head Bicycle Pump Fuel Pump Oscillating Sprinkler Stapler Bolt Cutter Gate Valve Pencil Sharpener Toy Gun Can Opener Hand Tool Pepper Grinder Trailer Hitch Corkscrew Hose Nozzle Piston Assembly Trailer Winch Deadbolt Lock Kitchen Timer Pipe Clamp Vise Grip Desktop Clamp Lug Wrench Ratchet Tie-Down Water Faucet Valve

Charts and Diagrams As part of the process to get started, the team selects a product for the reverse engineering project and then submits a proposal for approval of that product. The students learn within the same week whether their proposal was approved. The students have to quickly plan how to utilize the remainder of the semester, efficiently, to complete the project. To do this, students prepare a Gantt chart for the team to follow. The students review the team activities that are to be completed during the semester. Some of the assignments have multiple activities. The due dates specified in the course syllabus are the deadlines for completion of each activity. Figure 2 shows the Gantt chart that is used for the Trailer Winch design. Students are encouraged to schedule team meetings for the entire semester in the Gantt chart, and to transfer the meetings to the daily planner of each team member

The initial step in the reverse engineering of a product is to analyze the product in terms of inputs and outputs. The exact analytical operation that converts an input into an output is not important at this time. The students are encouraged to not only look at the operation of the product, but to expand the way they consider the use of the product in terms of customer and engineering specifications. A black box diagram is a convenient technique to identify and organize inputs and relate them to the corresponding outputs. Figure 3 shows the Black box diagram for the Trailer Winch. It is recommended that the Black box diagram be developed before the physical dissection takes place.

Subsystems of the product should be identified or surmised before the physical dissection takes place. The dissection process will allow for a better understanding of the subsystems. Some subsystems may have been misunderstood and other subsystems may be found that could not be seen until the interior was exposed. The dissection of the product can be performed with simple tools. For those dissections that require more than just screwdrivers and pliers, the students may utilize the services of the ME department’s machine shop. The students need to document the dissection with notes, sketches, and digital pictures. An exploded assembly of the product will be developed by assembling individual parts. A parts list will then be generated as the product is completely disassembled.

Figure 2. Gantt Chart for Planning the Reverse Engineering Project.

Figure 3. Black Box Diagram Showing the Major Function of the Trailer Winch.

Proceedings of the 2009 ASEE Gulf-Southwest Annual Conference Baylor University Copyright © 2009, American Society for Engineering Education As the product is being dissected, the students identify the subsystems first, then the individual components are identified. Students assign a name and number to each part of the product, and create a parts list. From this information the subsystems and individual parts can be organized into a fishbone diagram. The fishbone diagram shows the relationship between the subsystems and the parts. The head of the fish is labeled the project name, Trailer Winch in this case, and a spine is drawn. Ribs angle off of the spine to represent each subsystem. Minor ribs come off of each subsystem rib to represent every component part of the subsystem. There should be a minor rib to account for every individual part (or set of identical parts) found during the dissection. Figure 4 shows the Fishbone bone diagram for the Trailer Winch.

Figure 4. Fishbone Diagram for the Trailer Winch.

Sketching the Parts Throughout the entire Reverse Engineering process, much thought has been given to the possible changes that could improve the efficiency and durability of the whole system as well as individual subsystems and parts. This starts with the students taking apart the mechanical system, studying the subsystems that allow it to function, and inspecting the individual parts. Part of this process includes measuring geometry and sketching isometric pictorials of the individual parts, as well as sketching the parts assembled together. The following preliminary documents are then produced in order to better understand and visualize each individual part as well as the overall mechanical assembly: 1. Isometric sketches of all individual parts, 2. An exploded-assembly sketch that depicts all the parts (see Figure 5), and 3. A parts list of all components of the assembly (see Figure 6).

Figure 5. Exploded Assembly Sketch.

Figure 6. Parts List for the Assembly.

Proceedings of the 2009 ASEE Gulf-Southwest Annual Conference Baylor University Copyright © 2009, American Society for Engineering Education Building Solid Model Parts and Assemblies The students will have a good understanding of the parts after the exploded assembly sketches and the individual isometric sketches of each part have been made. The students generally have a team meeting during the next lab session and request digital calipers from the professor. The students utilize the calipers to get the gross dimensions of the individual parts and the size and location dimensions for the details. The students sketch the dimensions onto the isometric sketches until there is enough detail present to construct an accurate computer model of each part. Figure 7 shows the computer model of the handle for the Trailer Winch.

Figure 7. Computer Model of the Trailer Winch Handle.

The students divide the dimensioned sketches among the team members. Each team member is responsible for modeling several component parts. The students work together to model their individual parts and make sure that the parts are oriented properly so an assembly drawing can be made by compiling the part files into a single assembly file. Care is taken to adhere to the dimensions taken from the real parts to assure accurately sized and constructed components. Properly constructed parts will mate in the assembly as they mate in the real product.

The course prepares the students to make intricate computer models. The students have had concerted practice in making difficult profiles into extruded and revolved parts. The students are capable of making accurate internal and external threads. Each part is constructed and saved as a part (.SLDPRT) file. Each part is also saved as a stereo-lithography (.STL) file to be emailed to the teaching faculty member. Each faculty member sequences, scales, and orients these files, and then sends them to the rapid prototyping machine. As each part is modeled the students are able to assign the appropriate material to the part and then run a mass properties report for each individual part. These mass properties reports will be included in the final written report. Figure 8 shows the computer model of the Trailer Winch pinion gear.

Figure 8. Computer Model of the Trailer Winch Pinion Gear.

Each part will be submitted with the original sketch, the CAD model, the mass properties report, and dimensioned orthographic views. The students will use the individual part files to reconstruct the product as an assembly. The parts can be aligned and mated to resemble the finished product, or they may be aligned but exploded. To construct the assembly the students bring their files to one computer and sequentially open them and insert them into an assembly file. Parts are mated as necessary, with the most common mate being cylindrical components and the holes they fit into concentrically. The completed assembly is placed into a title block sheet. The title block is completed, the parts are identified by the leader, and a parts list is provided. Figure 9 shows the Trailer Winch computer assembly model.

Figure 9. The Trailer Winch Computer Assembly Model.

Mass Properties Report and Design Analysis One objective of the project is to have the students assess the overall suitability of a design from a materials performance point of view. The starting point for this assessment is the Mass Properties Report. After a part model is complete, the students assign material properties, including the material type and mass or weight density, depending on system of units used. Stock materials can be chosen from a library or custom materials can be defined. The software then automatically generates the Mass Properties Report, which includes the calculated mass, volume, and surface area of the part, as well as principal axes and moments of inertia at various locations (center of mass, output coordinate system). The mass properties report can also be generated for an assembly, in which case overall properties are given and the resulting density is volume-averaged over all parts in the assembly. Figure 10 shows a Mass Properties report.

Some projects also include a finite element study of key parts or on the assembly as a whole. In such studies, student teams assign realistic boundary constraints as well as fixed or distributed loads on the part or assembly so as to mimic what the real assembly might see in normal duty. Resulting stress, strain, and/or deformation color 3-D plots are then studied to reveal high stress areas. Alternately, design check studies can also be run to show performance of the assembly against a stated margin of safety criterion. Students are asked to evaluate the efficiency of their model, and to suggest ways in which the design of parts could be modified to improve overall design efficiency of their project (e. g. reduce peak stress concentrations, reduce total mass, etc).

Mass properties of CRANK ARM (2) ( Part Configuration ‐ Default ) Output coordinate System: ‐‐ default ‐‐ Density = 0.2854 pounds per cubic inch Mass = 0.4896 pounds Volume = 1.7153 cubic inches Surface area = 18.9277 inches^2 Center of mass: ( inches ) X = ‐0.3781 Y = 0.1050 Z = ‐0.5578

Principal axes of inertia and principal moments of inertia: ( pounds * square inches ) Taken at the center of mass. Ix = (0.9603, 0.0001, 0.2789) Px = 0.1290 Iy = (0.2789, 0.0003, ‐0.9603) Py = 1.5414 Iz = (‐0.0002, 1.0000, 0.0003) Pz = 1.5879

Moments of inertia: ( pounds * square inches ) Taken at the center of mass and aligned with the output coordinate system. Lxx = 0.2388 Lxy = 0.0001 Lxz = 0.3782 Lyx = 0.0001 Lyy = 1.5879 Lyz = 0.0000 Lzx = 0.3782 Lzy = 0.0000 Lzz = 1.4316

Moments of inertia: ( pounds * square inches ) Taken at the output coordinate system. Ixx = 0.3966 Ixy = ‐0.0193 Ixz = 0.4815 Iyx = ‐0.0193 Iyy = 1.8102 Iyz = ‐0.0286 Izx = 0.4815 Izy = ‐0.0286 Izz = 1.5069 Figure 10. Mass Properties Report for the Crank Arm.

Making Rapid 3-D Prototypes of the Object Once the solid models are produced in a computer modeling software package, the parts can be saved in the STL format. There are various ways to then produce physical models. Physical models can be made using CAM, laser sintering, or by means of a 3-D printer. In our program, we print the students’ STL files on a Stratasys Dimension BST 3-D printer. The students send their STL files to their instructor, who load the printers and control what is being printed. Figure 11 shows examples of 3-D parts from the Trailer Winch assembly that were produced on our 3-D Stratasys printer system.

Figure 11. 3-D Rapid Prototypes of Several parts for the Winch Assembly.

Creating Dimensioned Orthographic Drawings of the Parts Another objective of the project is to familiarize the student with the purpose and practice of engineering drawings as part of the design documentation effort. This is done through the development of multi-view orthographic drawings from solid models. The student sets drawing preferences (e. g. ANSI or ISO style, units, tolerance, precision) and converts the part/assembly 3-D model into a set of orthographic views in a 2-D drawing document. Then, the student constructs consistent, complete, non-redundant dimensions in the appropriate views following conventional dimensioning practice. Shaded isometric, auxiliary, and/or section views should be added to the drawing for clarity if needed. To document assembly properties, an overall annotated exploded assembly drawing should be included, with a bill of materials defining the individual parts of the assembly. Figure 12 shows the individual part drawing of the Crank Arm.

Figure 12. Dimensioned Orthographic Drawing of the Crank Arm.

Submission of the Final Team Report At the end of the semester, the students compile all of the interim reports along with their dimensioned drawings and their redesign recommendations and bind them into a final report. The students are required to find a suitable box that will hold the bound report and the printed prototypes (Figure 13). We have found that unless you have these items turned in together as a unit, it is hard to keep all of the parts of the project in the same place. The final checklist (Figure 14) helps the students in this final submission requirement.

Conclusions

Our current educational paradigm for Engineering Design Graphics is a fulfillment of 20 years of work to deliver a robust course based on the solid modeling approach to engineering design. During this journey, many obstacles to realize this paradigm were encountered. These obstacle included incompatible software and hardware systems, user-unfriendly analysis software that frequently crashed, high costs for prototyping equipment, and lack of training for instructors. Nonetheless, gradually these hurdles were overcome, and the Concurrent Engineering Design paradigm (as originally envisioned in earlier versions of Figure 1) is now fully functional for design graphics education5. Even more noteworthy is that this educational paradigm offers a rich opportunity for graphics applications and projects for our engineering students beyond the graphics fundamentals. In addition to building solid models and assemblies, they can also analyze the models, perform kinematic animations, and print 3-D parts. This paper illustrates a reverse engineering student project that not only exercises the graphics and modeling fundamentals, but also extends the student activities to analysis and prototyping. In doing so, the teaching environment for Engineering Graphics can now be extended deeper into design practices that will serve the students well in later engineering courses. Proceedings of the 2009 ASEE Gulf-Southwest Annual Conference Baylor University Copyright © 2009, American Society for Engineering Education

Figure 13. Submission of the Final Project Report.

Figure 14. Final Project Checklist.

1. Barr, R., Juricic, D., and Krueger, T. (1994): “The Role of Graphics and Modeling in the Concurrent Engineering Environment,” Engineering Design Graphics Journal, Vol. 58, No. 3, pp. 12-21. 2. Sheppard, S.D. (1992): “Dissection as a Learning Tool,” Proceedings of the 1992 Frontiers in Education Conference, IEEE Press. 3. Mickelson, S.K., Jenison, R.D., and Swanson, N. (1995): “Teaching Engineering Design Through Product Dissection,” Proceedings of the 1995 ASEE Annual Conference, Anaheim. 4. Lieu, D.K. and Sorry, S. (2009): Visualization, Modeling, and Graphics for Engineering Design (Chapter 8: Design Analysis), Delmar Carnage Learning, New York. 5. Krueger, T. and Barr, R. (2007): “The Concurrent Engineering Design Paradigm is Now Fully Functional for Graphics Education,” Engineering Design Graphics Journal, Vol. 71, No. 1, pp.22-28.

RONALD BARR Dr. Ronald E. Barr is Professor of Mechanical Engineering at the University of Texas at Austin, where he has taught since 1978. He previously taught at Texas A and M University. He received both his B.S. and Ph.D. degrees from Marquette University in 1969 and 1975, respectively. His research interests are in Binominal Analysis, Biomechanics, and Engineering Computer Graphics. Barr is a recipient of the ASEE Chester F. Carlson Award, the Orthogonal Medal, and the EDGD Distinguished Service Award. Barr is a Fellow of ASEE and served as ASEE President from 2005-2006. He is a registered Professional Engineer (PE) in the state of Texas. THOMAS KRUEGER Dr. Thomas Krueger is a Senior Lecturer in the Mechanical Engineering Department, The University of Texas at Austin. He received his BS in Ed in 1966 and his M.Ed. and PhD in 1971 and 1975 respectively from Texas A&M University. Since 1994 he has taught Engineering Design Graphics. Dr. Krueger is Member of ASEE, SME and ASME. BILLY WOOD Mr. Billy H. Wood is a Senior Lecturer in the Mechanical Engineering Department of the University of Texas at Austin. He received his BSET in 1974 and his MARCH in 1977 from Texas A&M University. He joined the ME department at UT in September 1980. He taught engineering and architectural design graphics until 2000 and has continued to teach engineering design graphics ever since. During this time he spent twelve years as the Undergraduate Advisor for the ME department. He was promoted to Senior Lecturer in the fall of 2008. TED AANSTOOS Mr. Ted A. Cantos is a Senior Lecturer in the Mechanical Engineering department at UT Austin. He follows 23 years as a Research Engineer/Scientist at the Center for Electro mechanics, specializing in energy storage and power conditioning equipment. His teaching includes introductory and advanced engineering design and university-wide signature courses on engineering topics. He is also a PhD candidate in the LBJ School of Public Affairs, addressing the impact of international technical standards. Mr. Cantos is a Guest Researcher for NIST, a Fellow in ASME and a registered professional engineer in Texas. MOSTAFA PIRNIA Mr. Mustafa Purina is a Senior Lecturer in the Mechanical Engineering Department, The University of Texas at Austin. He received his BS in Physics in 1963 and MS in Nuclear Physics in 1965 from Tehran University, Tehran, Iran. He received a fellowship from American Nuclear Energy Commission to study and research operation and design of Nuclear Reactors in the Nuclear Engineering Department at Penn State University in 1967-1968. Since 1981 he has taught Engineering Design Graphics in the Mechanical Engineering Department as well as College and Engineering Physics in the Physics Department at Austin Community College. His research areas of interest include design, analysis and prototyping of mechanical parts.