THE DESIGN PROCESS Mechanical design process is a systematic iterative decision making process in which a definite process is used for the achievement or conformation of specified purpose and performance through usage of scientific theories and mathematical calculations. The specified purpose and performance must meet or satisfy the need of customers in market. Mechanical design process is required for the following purpose: - To know and analyze the necessity of the people which customer needed most and wanted mostly in market (market demand). - To use best practices, process, techniques that will help achieve quality product. - To reduce high financial risk and secure profit. - To reduce the product cost, simplify manufacturing. - Best utilization of resources such as men, machine, money. - To minimize necessity of design modification after launch of product. - To minimize the failure of product which may cause loss of life, property and prestige. I) Identify need If there is no any need of modification in the product or necessity of new product in the market, then the production of that product would not survive economically, so the product must satisfy the customer's need in the market. In order to identify the need of the product development, one should access the market and should clearly point out the requirement, specification, purpose, performance, quality of the product. Decision regarding either modifying the design of existing product or developing completely a new product should be taken considering various factors such as customer's requirement, manufacturing cost, availability of resource. II) - Plan for the design process Planning is the process used to develop a scheme for scheduling and commiting the resources of time, money and people. It also results in a map showing how product design process activities are scheduled. Planning generates a procedure for developing needed information and distributing it to the correct people at the correct time. Important information includes product requirements, concept sketches, system functional diagrams, component drawings, assembly drawings, material selections, and any other representation of decisions made during the development of product. A plant shows how a project will be initiated, organized, coordinated, and monitored. In order to organize the people and resources for the fulfillment of the goal of the project, a plan must form a member of design team. An individual of a design team will may have a role that will vary with the product development phase, from product to product, and from company to company. Different roll of a design team are listed below: Product design engineer Product manager - Manufacturing engineer Detailer Drafter Technician Material specialist Quality control / quality assurance specialist Industrial engineer Assembly engineer Vendor's or supplier's representative The plan of design is a collection of documents that contains and describes the tasks that should be performed during the design process. For each task, the plan states the objectives, the personnel requirements, the time requirements, the schedule relative to other tasks, projects and sometimes cost estimates. . It helps the design team and management to know how the project is actually progressing relative to the progress anticipated when the plan was first established or last updated. There are five steps to establishing a plan. They are discussed below: 1) Identify the task As the design team gains an understanding of the design problem, the tasks needed to bring the problem from its current state to a final product become more clear. Tasks are often initially thought of in terms of the activities that need to be performed. The tasks should be made as specific as possible. 2) State the objective for each task Each task must be characterized by a clearly stated objective about product, input and activities etc. each task objective must be: - Defined as information to be developed and communicated to others. - Easily understood by all on the design team. -Specific in terms of exactly what information is to be developed. 3) Estimate the personnel time and other resources needed to meet the objectives For each task it is necessary to identify who on the design team will be responsible for meeting the objectives, what percentage of their time will be required, and over what period of time they will be needed. 4) Develop a sequence for the task The next step in working out the plan is to develop a task sequence. Scheduling tasks can be complex. The goal is to have each task accomplished before its result is needed and, at the same time, to make use of all of the personnel, all of the time. Additionally, it is necessary to schedule design reviews. Design reviews need to come at the end of all the phases and may be scheduled more frequently if necessary. Critical Path Method can be used to determine an efficient sequence of activities.Also, the bar chart is the best way to determine the activities of a simple project, and Program evaluation and review technique aids in finding the best estimate of the total time the project will take. 5) Estimate the product development cost The planning document generated can also serve as a basis for estimating the cost of designing the-new product. III ) Understanding the Problem and Developing Engineering Specification While designing a product we have to understand the problem that is to be solved. The ability to write a good set of engineering specifications is proof that the design team understands the problem. There are many techniques used to generate engineering specifications. One of the best and currently most popular is called quality function deployment (QFD). The QFD method helps generate the information needed in the engineering specifications development phase of the design process. Time spent in developing the QFD for new project helps to reduce the time required for completion of the project. Based on the QFD, the steps that is followed to prepare the specification are described below: Step 1: Identify the customers: Who are they? We must first determine exactly who the customers are. For most design situations there is more than one customer; for many products the most important customers are the consumers, the people who will buy the product and who will tell other consumers about its quality. There is usually more than one class of customers to be considered in a design situation. The consumer, the designer's management, manufacturing personnel, sales staff, and service personnel must also be considered as customers. Additionally, standards organizations should be viewed as customers, as they too may set requirements for the product. For many products there are five or more classes of customers whose voices need to be heard. Step 2: Determine the customer’s requirement: what do the customer want ? Once the customers have been identified, the next goal of the QFD method is to determine what is to be designed. That is, what is it that the customers want? Typically the consumers want a product that works as it should, lasts a long time, is easy to maintain, looks attractive, incorporates the latest technology, and has many features. Typically, the production customer wants a product that is easy to produce (both manufacture and assemble), uses available resources (human skills, equipment, and raw materials), uses standard parts and methods, uses existing facilities, and produces a minimum of scraps and rejected parts. Typically, the marketing/sales customer wants a product that meets consumers' requirements; is easy to package, store, and transport; is attractive; and is suitable for display. In this way what type of consumer wants what type of product should be analyzed. Step 3: Determine relative importance of the requirements: who versus what The next step in the QFD technique is to evaluate the importance of each of the customer’s requirements. This is accomplished by generating a weighting factor for each requiremet and the weighting factor provides the information about how much effort, time, and money to invest in achieving each requirement. Step 4: Identify and Evaluate the competition: how satisfied is the customer now? This step determines how the customer perceives the competition's ability to meet each of the requirements. It creates an awareness of what already exists (the "now"), and, second, it reveals opportunities to improve on what already exists. In some companies this process is called competition benchmarking and is a major aspect of understanding a design problem. In benchmarking, each competing product must be compared with customers' requirements (now vs. what). Step 6 : Generate engineering specifications: how will the customer's requirement be met? The goal here is to develop a set of engineering specifications from the customer’s requirements. These specifications are the restatement of the design problem in terms of parameters that can be measured and have target values. Without such information the engineers cannot know if the system being developed will satisfy the customers. Step 6: Relate customer's requirements to engineering specifications: Hows measures whats This step describes how engineering parameters are related with customer’s requirements. Many parameters will measure more than one customer’s requirement. Step 7: Identify relationships between engineering requirements: how are the hows dependent on each other? Engineering specifications may be dependent on each other. It is best to realize these dependencies early in the design process for efficient design of the product. Step 8: Set engineering targets: how much is good enough? The last step in the QFD techniques to determine a target value for each engineering measure. As the product evolves, these target values are used to evaluate the product's ability to satisfy customers' requirements. IV) CONCEPT GENERATION Concept is an idea that is developed sufficiently to evaluate physical principles confirming that the product will meet the target set as a primary goal which satisfies the customer requirement. Concepts can be represented as sketches, block diagrams, textual descriptions, clay or paper models, or other forms that give some indication of the manner in which the functions are achieved with the least commitment. Generating multiple ideas is better than generating only one idea for concept generation of a product because multiple ideas produces multiple options and probability which will help get optimized concept for the efficient production of the product. functional decomposition and concept variant generations are the basis of technique of concept generation and can be used to generate concepts. Functional decomposition is designed to further refine the functional requirements; concept variant generation aids in transforming the functions to concepts. The function tells what the product must do, whereas its form, or structure, conveys how the product will do it. Function, subfunction and alternative functions should be created on the basis of customer requirements and purpose of product. After creation, concepts should be generated from each alternative function. Now, the concepts generated from alternative functions should be combined into complete conceptual design. To create prime creativity, the engineer should study various pre-invented ideas so that, unknowingly, re-creation of the same old idea is not created. So for the study of various creation and idea, following sources presented below for concept ideas can be studied: 1) Using patent as an idea source : Patent literature is a good source of ideas. The easiest way to do patent searches is on CASSIS (Classification and Search Support Information System), a computer index to the patent number. 2) Finding ideas in reference books and trade journals: Most reference books give analytical techniques that can be useful and many good ideas are published in trade journals that are oriented toward a specific discipline and designed oriented trade journals also can be found. 3) Using experts to help generate concept We can find someone with expertise in that domain and after interaction with them we can grab the ideas about the product. 4) Brainstorming as a source of ideas: Brainstorming, initially developed as a group-oriented technique, can also be used by an individual designer. What makes brainstorming especially good for group efforts is that each member of the group contributes ideas from his or her own viewpoint. The rules for brainstorming are quite simple: a. Record all the ideas generated. Appoint someone as secretary at the beginning: this person should also be a contributor. b. Generate as many ideas as possible, and then verbalize these ideas. c. Think wild. Silly, impossible ideas sometimes lead to useful ideas. d. Do not allow evaluation of the ideas;just the generation of them. This is very important. Ignore any evaluation, judgment, or other comments on the value of an idea and chastise th 5) Using a 6-3-5 method : A drawback to brainstorming is that it can be dominated by one or a few team members . The 6-3-5 method forces equal participation by all. This method is effectively brainstorming on paper and is called brainwriting by some. To perform the 6-3-5 method, arrange the team members around a table. The optimal number of participants is the "6" in the method's name. In practice, there can be as few as 3 participants or as many as 8. Each takes a clean sheet of paper and divides it into three columns by drawing lines down its length. Next, each team member writes 3 ideas for how to fulfill a specific agreed-upon function, one at the top of each column. The number of ideas is the "3" in the method's name. These ideas can be sketched or written as text. They must be clear enough that others can understand the important aspects of the concept. After 5 minutes of work on the concepts, the sheets of paper are passed to the right. The time is the "5" in the method's name. The team members now have another 5 minutes to add 3 more ideas to the sheet. This should only be done after studying the previous ideas. As the papers are passed in 5minute intervals, each team member gets to see the input of each of the other members, and the ideas that develop are some combination of the best. After the papers have circulated to all the participants, the team can discuss the results to find the best possibilities. There should be no verbal communication in this technique until the end. 6) Using existing products and concepts as idea Source: Since many hundreds of engineering hours have been spent developing the features of existing product, one of the best sources of ideas is to look at existing product, and we can get the ideas about manufacturing process, material type, geometrical property and other modification ideas. V) CONCEPT EVALUATION In this process a best concept is chosen for the implementation from collection of concepts in such a way that the least resources is expended fro the implementation. The difficulty in concept evaluation is choosing a concept for which time is spent although we have limited data and knowledge on the basis of which we have to select one. Based on concept evaluation to make a decision about which concept to select following four techniques described below can be used: 1) Evaluation based on feasibility judgment : A concept may be feasible or not feasible or working if something happens. An experienced designer can evaluate a concept whether it is feasible or not and can select other concepts for further processes which are feasible. 2) Evaluation based on technology-readiness assessment In order for a technology to be used in a product, it must be ready. If a technology is to be used in a product, it must be mature enough. 3) Evaluation based on go/no-go screening Once it has been established that the technologies used in a concept are mature, comparison of each alternative is done with customer requirements. Each customer requirement must be transformed into a question to be addressed each concept. The questions should be answerable either go (yes) or no-go (no). This method helps to determine either the concept is worth modifying or eliminating. This evaluation rapidly points out the weak areas in a concept and also generates new ideas. 4) Evaluation based on a decision matrix This method is effective for comparing alternative concepts that are not refined enough for direct comparison with engineering specifications. Steps to be followed in decision matrix are as follows - Choose the criteria for comparison - Select the alternatives to be compared - Generate score for each alternatives - Compute the total score and analyze the score - Select the best concept which weights high score VI) Product Design Phase The goal of this phase is to refine the concepts already generated into quality products like giving flesh to what was the skeleton of an idea. Documentation measures progress in product development, and drawings, bill of materials are produced during the product design phase. Drawing is a necessary part of the product design phase, which is used for the data communication among designers, manufacturing personnels. Layout drawing, assemble drawing, detail drawing are the varieties of drawing. A layout drawing is a working document that supports the development of the major components and their relationships. A layout drawing is frequently changed during design phase. Layout drawing often becomes obsolete as detail drawings and assembly drawings are developed. However, if the product is being developed on a CAD system, the layout drawing's data file becomes the basis for the detail and assemblv drawings. As the product evolves on the layout drawing, the detail of individual components develops, and these are documented on detail drawings. In detail drawing all dimensions must be toleranced for each component. Materials and manufacturing detail must be in clear and specific language and also special processing must be spelled out clearly. Since the detail drawings are a final representation of the design effort and will be used to communicate the product to manufacturing, each drawing must be approved by management. A signature block is therefore a standard part of a detail drawing. The goal of an assembly drawing is to show how the components fit together. In assembly drawing, each component is identified with a number or letter keyed to the bill of materials. Some companies put their bill of materials on the assembly drawings; others use a separate document. The bill of materials (BOM), or parts list, is like an index to the product and separate list of bill of material is usually kept for each assembly. There are six pieces of information on a bill of materials: 1) The item number or letter 2) The part number 3) The quantity needed in the assembly 4) The name or description of the component 5) The type of the material of the component 6) The source of the component. VIII) Product Generation In this phase, manufacturing process and material selection are determined to convert a best concept into a product. In the selection of material and manufacturing process, at first, the quantity of the product to be manufactured greatly influences the selection of the manufacturing processes to be used. For a product that will only be built once, it is difficult to justify the use of a process that requires high tooling costs. Secondly, prior-use knowledge for similar applications influences majorly the selection. Knowledge and experience are the third influence on the choice of materials and manufacturing processes. Limited knowledge and experience limit choices. Probably the most compelling point in the selection of a material is its availability. Therefore selection of material and manufacturing process must evolve parallel with the evolve of the shape of the product. As a product matures, its layout, details, materials, and production techniques are refined (become less abstract). IX) Product Evaluation for Performance This phase of the design process is the last chance to design quality into the product.Before launching the product it is necessary to evaluate the performance of product by comparing with the engineering specification prepared in previous design process. Engineering specifications are the numerical value, based on which performance, behaviour of the product is compared. The measurement of performance should list out the parameters that should be changed in order to meet the requirement of product. The evaluation of performance should be presented in numerical value so it can be compared quantitatively so the comparision becomes easier. Evaluation process should include the manufacturing variations, aging effect and environmental changes. Evaluation can be performed by investigating through analytical model, testing of physical model, and representation with graphical model. Evaluation of performance can be done also in computer by simulation method. In simulation process, various parameters can be altered by giving input and corresponding result can be found and it provides the suggestion in change of parameter. X) Product Evaluation for Cost, Manufacture, Assemble, and Other Measure It is important to generate a cost estimate early in the design process as possible and to compare with the original cost requirements. In the conceptual design phase or beginning, a rough cost estimate is generated, and as the product is refined the cost is also refined and for redesign process the estimate cost is fairly accurate for minor design change or for the design which has not extreme change. As the design matures, cost estimations converge on the final cost. Mostly, every company has a purchasing or cost-estimating department whose duty is to estimate the cost of the manufacture and purchase. Designer also should share the responsibility to estimate the cost where various concepts and design are presented for manufacture. as establishing the shape of comProduct evaluation for manufacture helps establish the components to allow for fficient, highquality manufacture. It specifies the manufacturing process for manufacturing of the component, and ensures the component form supports the manufacturing process. It also ensures the best tooling and fixturing required for manufacturing process. Product evaluation for manufacture measures the ease of assembly with which a product can be assembled efficiently. It increases the efficiency in retrieval, handling and mating of components while assembly. The following guideline can be applied for efficient assmebly: 1) Overall component count should be minimized. 2) Assembly should contain minimum use of separate fasteners. 3) Design the product with a base component ( single ) for locating other components. 4) Do not require the base to be repositioned during assembly. 5) Make the assembly sequence efficient. 6) Avoid components that are more difficult to retrieve. 7) Design components for a specific type of retrieval, handling, and insertion. 8) Design all components for end to end symmetry. 9) Design all components for symmetry about their axes of insertion. 10) Design the all components to mate through straight line assembly, all from the same direction. 11) Make use of chamfer, fillet, leads to facilitate insertion and alignment. 12) Maximize component accessibility. Product should be designed in such a manner that the reliability of the product should be high so the availability and utilization of the product is efficient. Also the product should be design considering the environmental emphasizing concern for energy, pollution, and resource conservation in processing raw materials for products. Recycling, re-usability, and disposal after end of its life cycle should also be considered while designing.
