Engineering Design Process in the Mechanical Engineering Program at Cal Maritime: An Integrated Approach Teaching and Learning in the Maritime Environment Conference The California Maritime Academy Vallejo, CA 94590 Mansur Rastani Cal Maritime Academy Mechanical Engineering Department Vallejo, CA 94590 Nader Bagheri Cal Maritime Academy Mechanical Engineering Department Vallejo, CA 94590 Garett Ogata Cal Maritime Academy Mechanical Engineering Department Vallejo, CA 94590 1 AbstractU The capstone design project has become an integral part of the mechanical engineering (ME) program at Cal Maritime. Students in the program take three courses in sequence starting in the spring semester of their junior year. The first course, Engineering Design Process, introduces the students to the ten tasks involved in the design process. These tasks are introduced and taught in five stages as follows: 1) Problem Definition, 2) Conceptual Design, 3) Preliminary Design, 4) Detailed Design and prototyping, and 5) Communication Design. The details of each task are introduced and discussed. Students implement the first three stages in their second course, Project Design I, and the last two stages in their third course, Project Design II. Successful completion and understanding of these courses are the key to completing the ME program requirements as well as on-time graduation at Cal Maritime. IntroductionU Definition: Engineering design is an iteration process of devising a system to meet a set of desired needs. The design process begins with an identified need, which can be initiated based on any of the following sources: Observable deficiency (i.e., A car bumper that gets easily damaged in low speed collisions) Product improvement (i.e., A system for improving traction on ice without studs or chains) New products (i.e., A more effective alarm clock for reluctant students) Change in law (i.e., An average automobile gas mileage of 25 miles per gallon of gasoline) When a new design problem is begun, very little is known about the solution, especially if the problem is a new one for the designer. As work on the project progresses, the designer’s knowledge about the technologies involved and the alternative solutions increase. Thus, the goal during the design process is to learn as much about the evolving product as early as possible in the design process because during the early phases changes are least expensive. The systematic methodology of the evolutional engineering design process consists of five stages as follows: 1) Problem Definition In this stage the objectives, constraints, and the functional requirements of the designed objects are clarified through qualified terms by the customers, which in turn are converted into measurable engineering parameters. 2) Conceptual Design In this stage using brainstorming method and morphological tool, from information compiled in prior phase, concepts are created, evaluated, and design alternatives are selected. 3) Preliminary Design In this stage the product architecture (form and shape) is performed, materials are selected, and engineering analysis is carried out. 4) Detailed Design & Prototyping In this stage the preliminary design is refined through design for manufacturing, design for assembly, and design for safety & reliability. Detailed drawings, bill of materials and final design review are executed. 5) Communication Design This is the last stage of the design process that includes the final written report and oral presentation. Each stage has been itemized into instructional tasks as set of languages that we can use to describe how those designed objects came to be. 2 ProblemU Definition Stage This stage involves tasks 1A, 1B, 2, and 3. Each task is described below: TaskU 1A: Identifying User Requirements / Clarifying Design Objectives This task presents a method for comprehensively identifying a set of customer needs. The goals of the method are to: 1 • Ensure that the product is focused on customerTPF F PT needs • Identify implicit needs as well as explicit needs • Provide a fact base for justifying the product specifications • Ensure that no critical customer need is missed or forgotten • Develop a common understanding of customer needs among members of the development team. A team should be able to identify customer needs without knowing how it will eventually address those needs. Also note that we choose to use the word need to label any attribute of a potential product that is desired by the customer. Other terms used in industrial practice to refer to customerU needs U include customerU requirements, design attributes, and design objectives.U The latter is the terminology used in this course. Objectives are usually expressions of the desired attributes and behavior that the potential users would find attractive. They are normally expressed as "being" statements that say what the design will be, 2 as opposed to what the design must doTPF F.PT Identifying customer needs is itself a process, for which we present a three-step method as follow: 1. Gather data on customer needs. 2. Organize the needs into a hierarchy of primary, secondary, and if necessary, tertiary needs (Objective Tree). 3. Establish the relative importance of the needs (Weighted Objective Tree). StepU 1. Gathering data on customer needs Means for gathering data includes: 1. Literature Review on Similar Products 2. Market Research 3. Bench Marking 4. Interviews & Focus Groups 5. User Survey 6. Consulting Expertise 7. Questioning and Brainstorming 8. Reverse Engineering on Competitive products (Dissection) 9. Watching Customers Use an Existing Product 10. Web Sites for Similar Products StepU 2. Organize the needs into a hierarchy of primary, secondary, ……. needs (Objective Tree). The results of step 1 may end up to a large number of need statements. Working with such a long list of detailed needs is difficult. The goal of this step is to organize these needs into a hierarchical list. Group the need statements according to the similarity of the needs they express. The list will typically consist of a set of primary needs, each one of which will be further characterized by a set of secondary needs. In some cases, the secondary needs may be broken down into tertiary needs as well. The primary needs are the most general needs, while the secondary and tertiary needs express needs in more detail. The groups of need statements are clustered according to the similarity of the needs they express, and then organized in hierarchical order by assigning a head-objective to a group of sub-objectives. 1 TP PT Word “customers” refers to: manufacturers, marketing staff, distributors, retailers, and the end users. 2 TP PT Functions are the things a design supposed to do, the actions that it must perform. Functions are usually expressed as "doing" terms. We will discuss functions in greater details later in task 2. 3 ObjectiveU Tree:U The above hierarchical list can then be put in an objective tree form, which is a graphical depiction of the objectives for the artifact. The top-level goal in an objective tree, which we represent as a node at the peak of the tree, is decomposed or broken down into sub-goals that are at different levels of importance or that include progressively more detail, so the tree reflects a hierarchical structure as it expands downward. An objective tree also shows that related sub-goals or similar ideas can be clustered together, which gives the tree some organizational strength and utility. StepU 3. Establish the relative importance of the needs (Weighted Objective Tree). So far we have assumed that all of the design objectives are equal, whereas it is almost certain that some objectives will be worth more than others. We use a fairly simple technique, pair-wise comparison, which can be used to rank a cluster of objectives that are at the same level in the objective tree. It is important to keep in mind that the pair-wise comparison method should be applied in a "top-down" fashion, so that the higher-level objectives are compared and ranked before those at lower levels. Each design objective is listed and is compared to every other objective, two at a time. In making the comparison the objective that is considered the more important of the two is given a 1 and the less important objective is given a 0. A rating of 1/2 is given for objectives that are equally valued. The total number of possible comparisons is N= n(n-1)/2, where n is the number of objectives under consideration. The ratings are added and the total score for each one of the objectives are listed. In the resulting scores, if the smallest score for an objective is a zero, it is changed to one, which in turn moves up the scale for the other scores by one. The reason for doing this is simply due to the fact that an objective cannot have a zero value. TaskU 1B: Identifying Constraints Constraints are restrictions or limitations on a behavior or a value or some other aspect of a designed object's performance. Constraints are important to the designer because they limit the size of design space by forcing the exclusion of unacceptable alternatives. For example for a ladder design project, any design that fails to meet OSHA standards will be rejected. Objectives and constraints sometimes seem to be interchangeable, but they are not. On the other hand, objectives and constraints are closely related. Constraints limit the size of the design space, while objectives permit the exploration of the remainder of the design space (i.e. expand the design space). Constraints are usually expressed in measurable, quantitative terms, such as dollars, pounds, cubic feet, Psi, etc, whenever possible. Tools for identifying constraints, are listed below: 1. Identify sponsor-imposed constraints 2. Identify any compatibility constraints (with existing equipment, or mating parts) 3.