Graphics Education Needed for Upper Division Courses in Mechanical Engineering Design

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1 Graphics Education Needed for Upper Division Courses in Mechanical Engineering Design B-C. Ng, G. S. Agoki Department of Engineering and Computer Science Andrews University Abstract Engineering graphics are taught in the first year of the engineering program at Andrews University. This paper shows that students in the mechanical engineering program continue to use this skill in their upper division classes as well as in their extra-curricular activities such as SAE student chapter. In the manufacturing process course, the engineering students are tasked to design and subsequently produce a casted product as part of their project. This project requires students to produce a 3-D pattern for initial evaluation. To produce this 3-D pattern, students will need to convert the graphic files into a format that can be read by the 3-D printer. After evaluation of the 3-D pattern, and approval from the instructor, students will go back to the drawing board to design a two-piece mold and subsequently produce a 3-D mold to receive the molten metal necessary to form the casting. This paper will also review courses such as Machine Design and Finite Element Methods taught at Andrews University that require students to have proficiency in the use of a CAD graphic software, as they are required to produce drawings of machine elements either for assembly (Machine Design) or for analysis (Finite element Analysis). Students participating in the Annual SAE Student Competition such as Mini Baja Competitions need to show their designs or modifications. These are usually done using one of the CAD graphic software. Introduction Engineers and scientists nowadays can create complex designs using sophisticated analysis techniques such as Computer-Aided-Design (CAD), Finite Element Methods (FEM), solid modeling, simulations, dynamic animation, database tools, and general data visualization capabilities. Michael B. McGrath, et. al., (1991) credited this to the arrival of the computer age and the demand by the industry to be competitive. Most of these techniques require the use of engineering graphics to accomplish the task comfortably. Engineering graphics has been in both the technology and engineering education with the graphics being employed both as the final outcome and intermediate stage for numerous technological design activities (Wiebe, E. N., et. al., 2001). Thanks to the knowledge and skill in the use of engineering graphics, engineers can use it Galveston, Texas

2 to communicate ideas of components as to its shape, size, dimensional tolerance as well as layout, among many other things. Project work is often used in the engineering program to allow students to integrate certain areas of their undergraduate training or to direct them to apply their knowledge to solve a problem. As mentioned by Nathan Scott, et. al., (2003), these projects will have varying complexity, but all will relate in some way to the fundamental theories and techniques of their discipline. Students are more likely to retain the knowledge gained by this project-based learning more readily than through traditional textbooks. Engineering graphics has a role in most of these projects as the student needs to be able to model objects or their designs in 2-D or 3-D space and have it printed for discussion among team members. At Andrews University Department of Engineering and Computer Science, the authors use group or individual projects as part of the learning processes in the upper division mechanical engineering program courses. In all these projects, students are assumed to have some proficiency in the use of engineering graphics software. Manufacturing Processes Class Project Mechanical engineering students take a manufacturing processes course as part of their major program requirements. One of the topics taught in this course is the subject of casting and casting processes. After students are taught about the robust design requirement in casting, they were tasked to design a paperweight that would be produced by a casting process. The project takes the students from visualizing their concept of the paperweight design to pouring molten metal into their 3-D printed mold to obtain the finished cast product. The mechanical engineering students must be able to work visually and use any of the computer aided drafting (CAD) software to represent the paperweight designs in space with reasonable accuracy. After consultation with the instructor, their designs were printed using a 3-D printer and the 3-D patterns were further evaluated and mistakes identified. Students then go back to the drawing board where the mold patterns, along with the necessary gates, runners and risers for the molten metal to flow into the mold cavity, were then designed and 3-D print two halves molds were produced. Two sample models of the graphical representation of the students paperweight designs, a gear and a mounting stand combination set with Andrews University Engineering etched into the mounting stand and a half gear with Andrews University etched on the side are shown in Figure 1. 66th EDGD Mid-Year Conference Proceedings 189

3 .. Figure 1. Student-designed paper weight models using CAD software. The 3-D prints of their designs were shown in Figure 2. 3-D printing took about two hours followed by another couple of hours for the curing to complete. Within 4 hours, the students could see, touch and feel the 3-D paperweight models that they had designed. From the 3-D prints, the students could evaluate their designs and make the necessary corrections. In this case, it was found that the logo Andrews University Engineering on the mounting stand was a little too shallow/small causing the letters to smudge and this needed to be made deeper into the casting. At this point, with the 3-D print, the student and instructor would consider the best way to design the two halves mold and how the runner, riser and gate could be added to the design. Figure 2. 3-D models of the student-designed paperweights. CAD drawings of one of the two paperweights mold are shown in Figure 3. Note that in the initial mold design, risers and runners were not included in the mold for allowing the molten Galveston, Texas

4 metal to be poured into the mold. Students had to redesign the mold to have these runners and risers added before printing the 3-D models. Figure 4 shows the 3-D mold of the gear and mounting stand combination set. Note that the gear mold had been modified to include a runner (hole) shown clearly on the bottom left mold. With the completion of the 3-D molds, the students went ahead and made the necessary preparation for the pouring of the molten metal into the mold cavities. Once the castings were sufficiently cooled, it could be removed from the molds and further evaluation of the castings could be done. Students learn first-hand what kinds of defects (see Figure 5) occurred when the molds were not made correctly; like insufficient draft angles, or the opening to the runner is too small. From this class project involving the use of 3-D printing, the students were able to progress from the design stage to the finished product in a relatively short period of time. All in all the students were able to grasp the fundamental concepts of casting easily with the hands-on experiences gained from this class project. The 3-D printer recognizes many of these CAD drawing formats; so it is easy to print the 3-D pattern but what is important is that all the modifications on the paperweight pattern and the mold do require that the student be proficient in the use of the CAD software.. Figure 3. CAD drawing of the gear and mounting stand combination set mold. Note that there was no provision made for the pouring of the molten metal into the mold. 66th EDGD Mid-Year Conference Proceedings 191

5 Figure 4. 3-D mold of the gear and mounting stand combination set. Note that the gear mold had been modified to include a runner (hole) shown clearly on the bottom left mold Figure 5. Figure shows a portion of the mounting stand protruding out of the mold. Misrun and flash were observed on this casting as identified by the arrow Galveston, Texas

6 Machine Design: Finite Element Analysis of Machine Components Machine Design is another upper level mechanical engineering major course. Part of this course involves the study and analysis of mechanical components. Mechanical components in the form of simple bars, beams, etc., can be analyzed quite easily by basic methods of mechanics that provide closed-form solutions. Actual components, however, are rarely so simple, and the designer is forced to less effective approximations of closed-form solutions, experimentation, or numerical methods. There are a great many numerical techniques used in engineering applications for which the digital computer is very useful. In mechanical design, where CAD software is heavily employed, the analysis method that integrates well with CAD is finite-element analysis (Budynas Nisbett, 2011). In this Machine Design Course, the students are exposed to some of the fundamental aspects of Finite Element Analysis (FEA), and are then tasked to analyze a load cell of the forceplate assembly (see Figure 6), using both the basic methods of mechanics followed by a FEA. This load cell assembly measures the amount of load asserted on the plate using a set of strain gages attached to one of the bars identified as B in Figure 6. Figure 6. Image of the load cell and an exploded view of the load cell showing the upper and lower channel as well as the bar where the strain gages will be attached. To complete the project, the students work as a team to analyze one of the components shown in Figure 6, including the pins used to mount the components together to form the force plate assembly. The students are given the blueprints of the parts (after the initial calculation by hand) to analyze the component using Algor, an FEA software. In order to run the program in the Algor, the student will need to able to model the part in 3-D space using either one of the CAD software and importing the file to Algor or model the part directly into the Algor software which is integrated into Autodesk. In either case, the student will need to use his or her background in engineering graphics to be able to use the software 66th EDGD Mid-Year Conference Proceedings 193

7 effectively. Figure 7a shows the model of the bottom plate and 7b is the analyzed FEA of the plate and Figure 8 shows some of the FEA of the other parts of the load cell. Figure 7. a) Graphic model of the bottom plate and b) the completed FEA of the same plate showing the stress concentration. Figure 8. Various FEA of the various parts of the load cell completed; a) the loading of the top plate in the FEA, b) the FEA of the pin and c) the FEA of the center bar. As shown in this section, skill in the use of engineering graphics software is necessary as the engineering student continues in his/her engineering program in the upper level courses. Without the proficiency skills in engineering graphics early in the engineering program, the student will have a harder time trying to complete this FEA project. Society of Automotive: Design of Roll Cage Each year the Society of Automotive Engineers (SAE) organizes a Mini Baja Competition to provide SAE student members with a challenging project that involves designing, building, testing, and racing a vehicle within the limits of the rules. The off-road vehicle must survive the severe punishment of rough terrain and sometimes even water at such competition Galveston, Texas

8 Figure 9 shows one of the vehicles designed by the engineering students at the start of the 4-hour endurance race in Florida. One of the important safety concerns in building such off-road vehicle is the roll cage. This cage must be designed and fabricated to prevent any failure of the cage s integrity and causing injury to the driver during collision or when the vehicle rolls over during the race. As such the student must be able to build the roll cage to meet certain criteria. Figure 9 shows the off-road vehicle, design by students from Andrews University, at the start of the 4-hour endurance race. In building the roll cage, students use the CAD software to model their intended design in 3-D space taking into consideration all the necessary minimum space/clearance around the driver. An isometric drawing of the roll cage is shown in Figure 10. Once the team members are agreeable with the design, they make the necessary bending of the tubes to the correct angles and cut them to the correct dimensions. This requires the student to reposition the isometric drawing in 2-D with the cages positioned in different viewing directions so that the true length and angle is shown. Figure 11 shows a section of the roll cage with the correct angles between the tubes. With a large plotter, the roll cage drawings can be printed in stages or in different viewing directions. The printed paper is then used as a template when building the actual vehicle. This process involving the design of the roll cage to repositioning the drawings so that the correct angles and dimensions of the tubes can be measured, strongly indicates that the SAE student members must be proficient in the use of a CAD software in order to make the necessary drawings, both in isometric view as well as in 2-D space. 66th EDGD Mid-Year Conference Proceedings 195

9 From these three examples, it clearly shows that mechanical engineering students must have the foundation in engineering graphics firmly grounded early in their engineering programs in order for them to successfully complete in their upper level class projects. Figure 10 Isometric drawing of the roll cage used for the SAE Mini Baja Competition. Figure D drawing of the roll cage showing the correct angles between the tubes Galveston, Texas

10 Conclusion This paper clearly outlines the continued use of engineering graphics in upper division mechanical engineering courses in class projects as well as in extra-curricular activities such as SAE student chapter. Students working on 3-D printing that involves modification of the design will need to be proficient in the use of the CAD software. Without the proficiency skills in engineering graphics early in the engineering program, the student will have a harder time trying to complete this FEA project. The mechanical engineering students must have the foundation in engineering graphics firmly grounded early in their engineering programs in order for them to complete successfully in their upper level class projects. References Budynas Nisbett, Shigley s Mechanical Engineering Design, Ninth Edition, The McGraw Hill Companies, Inc. Nathan Scott, Roger Hadgraft, Vojislav (Vic) Ilic, Australasian J. of Engng. Educ., online publication , Michael B. McGrath, al. et., Computer Graphics, Volume 25, Number 3, July Wiebe, E. N., Clark, A. C., & Hasse, E. V., Scientific Visualization: Linking science and technology education through graphic communications, The Journal of Design and Technology Education, 6(1), 40-47, th EDGD Mid-Year Conference Proceedings 197