Introduction to Mechanical Design Hanyang University Gyung-Jin Park Preface Design education at the entry level tends to be quite important these days. Yet there seems to be a lack of general education courses. Moreover, it is difficult to find an appropriate textbook for such a course. Hanyang University offers an elementary design course. This volume is developed for the first half semester of the design course of Hanyang University. Therefore, it is not for professionals such as scientists and engineers but for beginners who have not yet been exposed to design. Professionals may want to read it to review elementary aspects. A product is planned in the design process. Design can be viewed from two facets. One is the aesthetic viewpoint and the other is the scientific viewpoint. The beauty of the outer shape is emphasized in the aesthetic design while the logical process should be presented in the scientific design. Engineering designers generally use the latter method. Therefore, engineers need design methodologies that can reasonably explain the design process in an objective way. However, design methodologies are generally domain (discipline or problem) dependent or they do not have definite forms. Axiomatic design is selected as a representative method because it is domain free and has a simple process which is easy to understand. This volume is not for a general explanation of design. It is specifically written for the elementary design course of Hanyang University. Chapter 1 describes what design is. Elements in the design process are introduced and explained. Chapter 2 briefly explains the elements in design and Chapter 3 introduces axiomatic design. Two axioms are presented and a few examples are demonstrated. In the second half of the semester, students conduct a design project by forming teams. How to write project reports are introduced in Chapter 4. Contents I. Introduction to Design ....................................................................................... 1 1.1 What is Design? ......................................................................................... 1 1.2 Analysis vs. Synthesis ................................................................................ 3 1.3 Design Process ........................................................................................... 4 1.4 Exercises ..................................................................................................... 6 II. Elements in the Design Process ....................................................................... 7 2.1 Customer Needs and Market Trends .......................................................... 7 2.2 Functional Requirements ............................................................................ 8 2.3 Design Parameters ...................................................................................... 9 2.4 Process Variables ..................................................................................... 10 2.5 Constraints ................................................................................................ 10 2.6 Exercises ................................................................................................... 11 III. Axiomatic Design .......................................................................................... 15 3.1 Introduction .............................................................................................. 15 3.2 Design Axioms ......................................................................................... 16 3.3 The Independence Axiom ........................................................................ 17 3.4 Application of the Independence Axiom .................................................. 18 3.5 The Information Axiom ............................................................................ 27 3.6 Application of the Information Axiom ..................................................... 29 3.7 Discussion ................................................................................................ 31 3.8 Exercises ................................................................................................... 32 IV. Design Project ............................................................................................... 35 4.1 About the Design Project ......................................................................... 35 4.2 Elements of a Design Project ................................................................... 35 4.3 Team Project and Communication Skills ................................................. 37 4.4 How to Write the Proposal ....................................................................... 38 4.5 How to Write the Progress Report ........................................................... 40 4.6 How to Write the Final Report ................................................................. 41 4.7 Final Presentation ..................................................................................... 41 V. References ....................................................................................................... 43 I. Introduction to Design 1.1 What is Design? Design can be defined in a variety of ways depending on the specific context and/or the field of interest (Suh 2001). It can be an engineering activity, a plan for a product or fashion, a plan in everyday ordinary life, and so on. Therefore, the word “design” is utilized in a broad sense. In this volume, the meaning of design is narrowed to an engineering activity in the planning stage of a product. Since design is a plan, it is performed in the early stage of the engineering process. The overall engineering process is illustrated in Figure 1.1. The total engineering process can be considered as design. In a narrow sense, the design stage resides after the overall planning and before the product is physically made. The corporate strategies are established and market objectives are defined in the Planning Product design Feedback Testing and Refinement Manufacturing Feedback Marketing Figure 1.1. Overall engineering process 2 Introduction to Mechanical Design planning stage. The design activity has a bridge function between planning and manufacturing. In other words, a product is conceptually defined based on the problem definition of the planning stage. Although it occupies a small portion in the entire process, the impact of the design results is fairly large. The history of design is extremely long. It has been performed since cavemen made tools for hunting. Although the history is long, a rigorous method with a definite theory is employed recently. Instead of a standardized method, intuition and unexplained experience have been utilized in design. Even now, there is some doubt as to whether or not there are any definite forms for design theories. Science based design methods are beginning to emerge. Engineering design problems are usually open-ended and ill-structured (Dym and Little 2004). They are open-ended because there are multiple acceptable solutions and a solution can be improved upon. Uniqueness, which is extremely important in mathematics and many analysis problems, does not apply to design problems. In science and analysis, we generally use mathematical formulae in a structured way and obtain a solution. However, there are no such formulae in design. Due to the characteristics, creativity is involved in design because a different designer can make a different design. Engineering design shows the typical characteristics of engineering, which are different from those of sciences. It is noted that the aspects of design are utilized even in the scientific activity, especially when a plan for a scientific process is established. A decision making process is typically involved in design. How do we make a decision or why do we make some specific decisions? What helps us make the decision? What would be rational and logical decisions? Who is a good designer and who is not? According to the manner of the decision making process, there are two viewpoints for the definition of design. In some designs, aesthetic beauty is emphasized. An example would be industrial design. In industrial design, visible shape or user convenience is important. Design is mostly made based on intuition; therefore, science based methods may not be used in this case. In other designs, soundness in engineering is considered. Achievement of target engineering functions is important. Thus, a rational explanation is needed. In this case, science based design methods can be used although it is not always the case. This volume is prepared for college freshmen or sophomores who are not exposed to a specific discipline of engineering or science. They mostly learned general mathematics and sciences through high school education. It is assumed that the readers are familiar with analysis that uses a rigorous method and has a unique solution. The value system of design may confuse them because it is different from what they learned so far. However, it is quite important in that it is a real-world problem. Difficult terminologies and concepts are minimized; therefore, many aspects of this volume might be natural to professionals. Introduction to Design 3 1.2 Analysis vs. Synthesis The spectrum of analysis and synthesis is illustrated in Figure 1.2. Pure mathematics resides at the end of analysis while art is at the extreme of synthesis. Analysis pursues a unique solution of a problem in an analytical way while various aspects