Introducing Plastic Product Design Into the Machine Design Curriculum

Session 2566 Introducing Plastic Product Design into the Machine Design Curriculum Reginald G. Mitchiner, Ph.D., and John T. Tester Mechanical Engineering / Industrial and Systems Engineering Virginia Polytechnic Institute and State University Blacksburg, VA 24060 Abstract We present our paradigm of plastic product design as a necessary part of the mechanical engineering design curriculum and how these concepts have been a historical part of the mechanical engineering educational agenda, though in other venues. We discuss the practical and accreditation problems associated with incorporating the "new" design features in an existing machine design course. A separate design course, dedicated to plastic product design, is also outlined. This last alternative is likely the best bridge from a machine design curriculum without plastics concepts to one with metallic/nonmetallic product design. 1 Introduction Plastic products† are a dominant part of the manufacturing world. It is very likely that you the reader could, at this moment, reach out and touch a plastic product from where you sit. Yet, mechanical design curricula at universities, as a general rule, do not have plastic product design integral in their construction. The mechanical design curriculum has embedded within it the classical theory associated with metallic products; usually these products are assumed to be manufactured via metal-removal processes, if their manufacture is assumed in any manner at all. As practicing mechanical design engineers, we (the authors) have frequently been required to design products with a plastic component as part of their basic structure. One of the authors' primary functions for several years was to design solely plastic products as part of electronic product packaging. The engineering knowledge required for such design tasks did not come from the traditional college curricula. Instead, such knowledge was obtained through many extension courses, plastic vendor training, and seminars. Indeed, the Virginia Tech Mechanical Engineering Department does not have plastic product design integral to any of the classes in the mechanical design course structure. Plastic product design has its origins in a related field: Casting design. This is especially true we consider injection molding as the predominate process for plastics design. Both design disciplines have many similar design features: Draft angles, sprue locations, coring, cooling accountability and so on. The more seasoned of this article's authors recalls that the typical mechanical engineering curriculum of the past required casting processes and design as a fundamental requirement for graduating mechanical engineers. 3.376.1 Page † In the context of this article, we consider only thermoplastic products. Thermoset products are not within the scope of this discussion. Some thirty to forty years ago, most mechanical engineering programs (indeed the many of the premier programs of the Midwest—Illinois, Ohio State, Purdue, Michigan State, among others) included significant metal castings and processing experiences in required coursework. These universities maintained extensive laboratories which provided practical as well as theoretical experiences for the student. Over the intervening years, however, we have lost the provision to the mechanical design student of an integrated approach to mechanical structure design with the requisite considerations of formation. Many factors and forces have contributed to this shift in mechanical engineering undergraduate program direction. This paper is responsive to those forces tending to reassert integrated design and formation for the new millenium. There are a few engineering programs which contain a solid basis in plastic product design. Most notable of the research-level universities is the University of Massachusetts, Lowell. Their engineering college has an entire department devoted to plastics engineering1. Though their curriculum shows a predominance of rheology-oriented coursework, there are at least two classes devoted to plastic product design at the undergraduate level. There are several engineering technology-oriented programs with a healthy emphasis on plastics technology. Western Washington University's Plastic Engineering Technology program is a good example2. This course of study covers various plastic manufacturing technologies and design tools, in preparation for the students' bachelors degrees in Manufacturing Engineering Technology. Their laboratories are fully equipped in order to provide a thorough, hands-on educational experience for the Plastics Technology student. The previous two programs do not address our concerns, however, because these programs are not mechanical engineering programs. They are instead accredited under their own genre of plastics engineering or plastics/manufacturing engineering technology. The question remains, then: How can a mechanical engineering department prepare a student for plastic product design, without devoting major resources towards such an effort? 2 Course Structure Alternatives We see two alternatives for incorporating plastic product design in our curriculum: a) Integrate the material in one or more existing courses. b) Create a new, separate course, devoted to the topic. The first alternative appears to be the easiest to implement on the surface, but has several disadvantages. The second alternative may seem more difficult to integrate into an existing course offering, but will likely provide long-term benefits to both the students and the department. 2.1 Integration into Existing Courses We use our own Department of Mechanical Engineering (ME) at Virginia Tech as a basis for exploration. There are four courses into which plastics design concepts might be introduced in Virginia Tech's ME curriculum: Introduction to CAD/CAM, Mechanical Design I, Mechanical Design II or Machine Design3. Before discussing these classes separately, there are some concerns 3.376.2 Page associated with changing the course structure. The first, and probably most important from a college point of view, is ABET accreditation. These courses, to various degrees, affect the accreditation of the Mechanical Engineering bachelors degree. Tampering with the course content significantly could be perceived as highly risky to university personnel dedicated to preserving such accreditation. Of greater immediate impact to the instructing professors is the question: "What material is cut out of the course in order to make room for the plastics design topics?" This question is valid and relates to both the accreditation issue as well as the personal preferences of the professor. Being in a semester format, Virginia Tech's course content can provide a range of information for a given course. Nevertheless, most instructors would still contend that there is never enough time to impart all the topics they feel necessary to give to the students in a specific class timetable. Noting the above problems, let's assume that they can be satisfactorily addressed. We now want to examine how well such concepts could fit into the existing course structures. The first course, Introduction to CAD/CAM, gives the students an introduction to a computer- graphics design package which is integrated with a CNC computer package. This course is structured around the concept of taking a class project from design on CAD to manufacture on a CNC machine. Introduction of plastic product design concepts in this would require a complete overhaul of the course's concept. Furthermore, the department does not have the facilities (i.e., an injection molding machine) to finalize the final class product designs, whereas CNC machines are readily available for such tasks. Two consecutive courses, Mechanical Design I and II, emphasize static and fatigue loading concepts in various components, including fasteners, springs, bearings, gears, shafts and brakes. Fatigue analysis instruction is considered a strength in Virginia Tech's Mechanical Engineering Department's approach towards mechanical design. Introduction of plastic product design concepts do not fit snugly into this course paradigm; plastics design (in our view) is more of a guidelines approach to component features. Such guidelines do not usually impact the fatigue analysis concept. Integration of this topic into the class would not be a smooth nor easy fit. Machine Design is devoted to the analysis of machine components, such as bearings, gears, contact stresses, plates, rotating disks, press fits, torsion, springs and so on. This course would seem to be the best fit for a plastics design introduction. Some concepts of "design for manufacturing" (DFM) are brought to bear in this class; plastic product design is heavily oriented towards DFM. In addition, some aspects of plastic part assembly could be integrated here as well. The main drawback to integration into this course is the fact that this course is a graduate-level offering. Seniors with certain qualifications are allowed to take the course as an elective, but not all undergraduate engineering students are eligible or required to do so. If we believe that plastics design is important to the fundamental education of the student, then even modification of this course may be insufficient to answer our educational needs. Page 3.376.3 Page 2.2 A Separate Course Offering The above discussion leads us to believe that the instruction of plastic product design would be best served by introducing a new elective into the curriculum. This new course, arbitrarily

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