Engineering Design process

Transcription

1 Engineering Design process Engineering design process is defined, described and illustrated in countless ways, but the core activities are always the same, and could be represented as follows: Problem Definition: re-frame problems, needs analysis, objectives, constraints Concept Generation: designer generates or creates various design concepts Concept Selection: designer selects the optimal design solution Evaluation: designer tests or models the chosen design Refinement :designer creates detailed design for implementation Communication: designer communicates final design to client/users 1. Problem Definition: Problem definition re-frames problem, identify needs, objectives and constraints The needs may come from the following sources The necessity to make a product better or more profitable is a need The establishment of a new product line to satisfy customers is a need Protection of public health and safety is a need An invention that is unexpected and is to be commercialized An opportunity created by new technology, materials and scientific advances A change in rules and regulations. Design objectives are the attributes and behavior that your client or potential users would like to see. That should be determined based on the client s needs. Design Constraints: Design constraints are restrictions or limitations on the design. They may come from the following sources Economic Environmental Ethical and Legal Health and Safety Manufacturability Political and Social Sustainability 2. Concept Generation: Brainstorming is the most common technique for concept generation. The objective of brainstorming is to develop as many ideas as possible in a limited amount of time. Emphasis is on quantity rather than quality. Free expression is essential in a brainstorming session. Evaluation of the ideas can be implemented in later time. Sometimes impractical ideas can inspire more viable ideas. To ensure a good design, multiple concept alternatives need to be generated. The following list can serve as a guideline for brainstorming: No holding back: any idea may be brought to the floor at any time. 1

2 No boundaries: an idea is never too outrageous or way out to mention. No criticizing. An idea may not be criticized until the final discussion phase. No dismissing. An idea may not be discounted until after group discussion. No limit. Another idea is never one too many. No restriction. Participants may generate ideas from any field of expertise. No shame. A team participant should never be made to feel embarrassed for contributing an idea. Strategies to Enhance Creativity: in generating ideas, the following strategies and techniques can enhance creativity. Lateral thinking Question Practice Suspend judgment Allow time Think like a beginner Substitute Combine Adapt Modify Put to other use Eliminate Rearrange or reverse 3. Concept selection: is the process of evaluating concepts with respect to customer and other criteria, comparing the relative strengths and weaknesses of the concepts, and selecting one or more concepts for further investigation, testing, or development. There are unstructured and structured methods for concept evaluation. In unstructured methods, the evaluation and selection may be made by experts, your supervisors, clients based on personal experience and/or preference. Structured methods are more objective comparatively. Decision matrix is an important structured concept selection technique. Concept selection can be roughly broke into two similar stages in application of decision matrix technique, namely concept screening and concept scoring. Concept screening: In concept screening, a concept is firstly chosen as a benchmark; then a relative score of better than (+), same as (0) or worse than ( ) the bench mark product is placed in each cell of the matrix. The summation will indicate the strength of each idea. 2

3 Table 1: concept screening Concept Scoring : Concept scoring uses a finer scale to further evaluate the chosen concepts after the screening stage. A widely accepted scale is the 5 mark scale as bellow. Much worse than reference 1 Worse than reference 2 Same as reference 3 Better than reference 4 Much better than reference 5 A weighting factor can also be added in to the scoring system. Table 2: Concept scoring The concept with the highest mark is potentially a good concept. This is the point of no return for the concept development process, so everyone on the team should feel comfortable that all of the relevant issues have been discussed and that 3

4 the selected concept(s) have greatest potential to satisfy customer s needs and be economically successful. Very careful analysis and reflection on the whole process are needed in order to select a really good concept. Any change to the concept downstream in the design process will be very costly. Sometimes concept tests with physical models and/or computer simulation may be needed after the optimum concept is chosen. 4. Refinement : After choosing the best concept, the next step is to make necessary analysis,/calculation create all technical documents which may include technique drawing package, fabrication manual, manufacturing specification and BOM etc. Solid analysis and calculation is of fundamental importance for a successful design, but varies from projects to projects. We do not talk this topic here. Technique Drawing package: Creating technical drawing packages that meet industrial standards is essential to all engineering disciplines. The package should contain all necessary information for fabricating/manufacturing the device in design. For a typical mechanical device, a package should include, but not limited to, a general assembly drawing, all sub-assembly drawings, drawings for self-made parts, hydraulic schematics and electrical schematics if any, BOM (or part list) including all self-made parts and purchasing parts and a table of contents etc. Traditionally all drawings, including assembly drawings and part drawings, were made by orthographic projection. With more and more popularity of 3-D soft packages, some companies tend to make assembly drawings with explosive 3-D views nowadays. The point for this practice is that the purpose of an assembly drawing is to provide information for assembly, not for manufacturing. Generally, a 3-D model with explosive view can provide the same information, but is much easier to understand than a orthography assembly drawing. For a part drawing, normally just 3-D views are not enough. Common practice is to create three orthographic views accompanied by a 3-D view at the right-upper corner. The reason is that 3-D views are not as good as 2-D views in providing manufacturing information, such as tolerance, dimension, GD&T, surface texture etc. In our design project, the assembly drawing can be prepared by either way (explosive 3-D views or 2-D orthographic views plus a 3-D view). Part drawings have to be made in orthographic views, plus a 3-D view. Numbering system of Drawings: There may be hundreds or even thousands of drawings of assemblies and/or parts in a product. Properly numbering the drawings is essential for effectively organizing the documents. Every company has its own numbering system. You can create your own numbering system in our project if you like. But the following system may be considered. 4

5 } } } And so forth In the above system, the number 12 following the M7926 is the team number. So if you team number is #9, that would become If the number ends with number 0, it is an assembly drawing; if it ends with numbers other than 0, it is a part drawing. 5. Communication: we are not going to talk about communication here. 6. Engineering design Patterns: Traditional Engineering approach: also known as "Serial Engineering". It means the activities in the engineering process are largely sequential, i.e. each discipline performs its own individual function and passes the results to the next discipline in the serial chain. Typically, there is very little or no interaction at all among various disciplines. Thus this leads to problems later in the development cycle. The most obvious barrier is the separation of various functions. There is obvious drawback in this pattern. Most obvious is the process time is pretty long which is very negative for the company s competitiveness. Another problem is if mistakes made in previous sections are found out in downstream sections, the documents have to be returned to the previous section to be corrected. For example, if a mistake is made in design which later is found out in manufacturing, the drawing (design) has to be returned to the design department for correction. This makes the process time even longer and very costly. 5

6 A remedy to the drawbacks is to organize the engineering activities in parallel which is termed as Concurrent Engineering in literature. The basic idea in CE is to take downstream into consideration in upstream activities. For example, the design team in CE may consists of people from manufacturing, fabrication, marketing etc, so that all the requirements in manufacturing, fabrication etc are considered in the design stage. This could significantly reduce the process time and cost. CE has been widely accepted in automotive and aero-plane industry since 1980s. Apparently the design pattern of our project is somewhere in between the two patterns. 6