Machine Design: Redesigned

Machine design is a cornerstone foundation course in any Mechanical Engineering program. The traditional objective of this course is to engage students with analysis techniques to guard against specific failure modes or to predict a product’s life cycle based on a loading scenario. Generally, the course is taught by introduction of a topic first, e.g. static failure criteria, then examples are presented and homework sets are assigned to allow students to practice and sharpen their problem solving skills. The current methodology lacks the implementation of the complete engineering design process and the integration of other knowledge domains such as manufacturing. Additionally, the current course structure does not usually stimulate creativity necessary for the design process (ideation) or train students on decision making based on objective criteria. This paper presents an enhanced course structure developed over the past few years for a more comprehensive approach to machine design. The new course structure is hinged on the application of engineering design process, knowledge integration from prior courses as well as industrial practice, and adoption of design matrices as an objective decision making tool. We have retained many of the traditional pedagogies used in teaching machine design and supplement this educational experience with a significant project component based on current customer-need or economical challenge. Through the project students learn to: 1) create the design envelop based on a provided statement or requirement document; 2) define specific, meaningful, and measurable goals; 3) synthesize creative ideas to solve the problem; 4) perform a patent search to verify the innovative nature of their ideas; 5) produce a design matrix with evaluation criteria based on the goals and expected functionality; and 6) perform an in depth engineering analysis based on mechanics of materials, manufacturability, assembly, and packaging. The inclusion of an intensive writing and presentation experience with critical feedback engages students in a continuous reflection on the elements of the complete design process throughout the entire semester. It was found that this approach produces students who are better prepared for their senior design projects and engineering practice. Students noted an increase in their understanding of machine design concepts as an integration of all their prior preparatory training. The effectiveness of the revised course structure was evaluated through a survey of previous and current students. Introduction and background Prior to 2011, one of the common concerns of the Mechanical Engineering department’s senior students was the inability to “engineer” or practice “design.” This was also echoed by capstone project instructors. In other words, our students were not prepared to work on their senior design projects, unless they had prior industrial or volunteering experiences. Students were found to be unable to develop ideation and design skills independently prior to enrolling in their required culminating experience [1]. At our university, four different Mechanical Engineering capstone projects are available, all of which are competition-based. These projects include: Society of Automotive Engineers Formula Car Design and Competition, Intelligent Ground Vehicle Competition sponsored by IGVC, American Society of Mechanical Engineers Human Powered Vehicle Design and Competition, and AUVSI Unmanned Aerial Vehicle Competition. P ge 26102.2 2 The inability of engineering graduates to engineer and design hampers the industrial productivity in the United States [1], since these students lack the ideation, design and practical skills that are in great demand by current employers. This issue is rooted in the lack of preparatory courses that inculcate the design process in our students early in their educational program. The traditional focus is on the important appropriate scientific and analytical techniques with little regard to the complexity of the design process and its applications. Traditionally, machine design courses, where design in some instances is first introduced, are focused on the analysis of stresses due to applied loads, static failure theories for ductile and brittle materials, fatigue, and analysis of mechanical components, such as shafts, fasteners, gears, etc. [2]. Notably, mechanical design textbooks are full of practical knowledge but it is presented solely from the perspective of performing a careful detailed analysis. Academic professors without considerable industrial experience promotes the basics of problem solving, in other words the ‘science of analysis’ [2]. Those academicians with extensive industrial experience understand the critical role design plays in the understanding of mechanical design and are able to share this experience with their students but may not possess the breadth of experience to cover all of the content equally in a full term course. As a result a large gap exists between the senior design experience and industry expectation and the knowledge attained in a typical machine design course. The design process, sometimes referred to as the design cycle, exposes engineering students to two important lessons: 1) the design is iterative process [3]; and 2) design is a process of tradeoffs. In a typical design exercise, more than one solution exists and an engineer is expected to objectively evaluate all suitable solutions and decide on which to move forward with, i.e., tradeoff. Thereafter, the selected conceptual design is modeled and analyzed in detail. The design cycle thus consists of two symbiotic phases: synthesis and analysis. Furthermore, the design will continuously evolve through many iterations until the final design meets all the established design criteria. If an engineering student approaches a project beginning with the foundation of the design process, involving iteration and trade-off through synthesis and analysis, the result is an engineer who is ready to contribute to the workforce on the first day on the job. Figure 1: Engineering Design Cycle (modified from [3]). Figure 1 depicts one model of the steps of the design process [3]. The design project topic is introduced at the earliest opportunity at the start of the term. The project topic may range from relatively simple to extremely complex in its subtleties. The intent is to stimulate ideation and P ge 26102.3 3 finding solutions to issues that arise every step of the way in teamwork setting. Each group consists of 3-5 students. The project provides a term long framework whereby all of the elements of mechanical design can be introduced with contextual relevance. It begins with the definition of the overall objective of the project. In this step, the design requirement document is carefully reviewed and questions or concerns are articulated and communicated to the customer (the instructor). In our experience, most students never contemplate additional possibilities or alternatives when a design task is assigned. This is of high importance to the consumer or contractor who is expecting to be involved in the decision making process even though they might not completely comprehend the complexities of a proposed design. In the requirement document, the overall customer need, problem or challenge is specified as well as the machine functionality, design constraints, rules and regulations, and allocated resources such as budget and timeline. Once the requirement document is well-understood, the design team needs to define the overall design goal. It is encouraged that specific, meaningful, and measureable (SMM) goals to be defined. Here, in an academic setting, the professor can assist the students in thinking, focusing on and defining SMM goals in design courses. The second step is choosing an appropriate design strategy, in which the decision must be made whether the product is going to be mechanical, electrical, software, or hybrid, such as an automated machine or process. The design approach must be decided as well, whether top-down or bottom up. Additionally, decisions must be made regarding manufacturing processes versus the use of commercially available components. The third step is collecting information and conducting research about the design strategy and all components and subsystems. Moreover, in this step, research needs to be conducted about theories, techniques, and scientific principles to facilitate the subsequent steps in the design. We argue that devoting appropriate time and effort in the first three steps of the process will have a significant impact on the design by shortening the overall project time and reducing the number of iterations required. The result will be a more efficient process leading to the final product design that meets all the required design criteria. Put another way, the first three steps in design process should be allocated enough resources, in effect time, funds, effort, expertise, to achieve “lean design,” and making informed decisions. Only then, initial design attempts are done. If the preceding steps are executed correctly, the initial attempts will satisfy the design requirements with implied novelty, involving creative and innovative solutions. In the initial attempt and based on the research, the designer is now considering the manufacturing, assembly, and the packaging as well as the loading scenarios. These first four steps constitute the synthesis phase of the design cycle. Subsequently, the selected solution can be analyzed based on the loading scenarios and environmental conditions to define the shape, size, and materials.