PRODUCT DESIGN PROCESS

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1 PRODUCT DESIGN PROCESS Introduction Product design has two aspects: technical design and aesthetic design. Technical design is process of defining all the performance and physical characteristics of a product. Technical design specifies the materials, dimensions and tolerances, and performance standards of a product. Aesthetic design is the process of establishing the sensual and psychological characteristics and benefits of a product. This involves deciding on what the product will look like and feel like, deciding on the color and texture, and the exterior shape or appearance of the product. A company s product design must match the needs and preferences of the customer group targeted by the company s business strategy. Otherwise, the company will lose its customer base and erode its market position. A product design process is series of coordinated activities that results in the creation of a product. A product may be conceived as a system which is a combination of interrelated components that serve a useful purpose. Hence the design of a product is an instance of system design. System design is the conception of a system in its totality. It envisions the whole system and defines its interconnected substructures and components. The critical units of the system are the primary focus at the beginning of the design. Through a process decomposition and refinement, the system is eventually conceived and documented. Idea Development All product designs begin with an idea. The idea might come from a product manager who spends time with customers and has a sense of what customers want, from an engineer with a flare for inventions, or from anyone else in the company. To remain competitive, companies must be innovative and bring out new products regularly. In some industries, the cycle of new product development is predictable. We see this in the auto industry, where new car models come out every year, or the retail industry, where new fashion is designed for every season. In other industries, new product releases are less predictable but just as important. The first source of ideas is the customers, the driving force in the design of products and services. Marketing is a vital link between customers and product design. Market researchers collect customer information by studying customer buying patterns and using tools such as customer surveys and focus groups. Management may love an idea, but if market analysis shows that customers do not like it, the idea is not viable. Analyzing customer preferences is an ongoing process. Customer preferences next year may be quite different from what they are today. For this reason, the related process of forecasting future consumer preferences is important, though difficult. Competitors are another source of ideas. A company learns by observing its competitors products and services and the success rate of these products and services. Remanufacturing Remanufacturing is a concept that has been gaining increasing importance, as our society becomes more environmentally conscious and focuses on efforts such as recycling and eliminating waste. Remanufacturing uses components of old products in the production of new ones. In addition to the environmental benefits, there are significant cost benefits because remanufactured products can be half the price of their new counterparts. Remanufacturing has been quite popular in the production of computers, televisions, and automobiles. Product Design Phases Fig.1 shows a simplified design process model informed by the critical stages in a product development cycle. The process of designing a product is an iterative one involving a review stage that leads to feedbacks and modifications. Graphic modeling is at the heart of the design process and design drafters will be called upon to help create them. Drawing details and complexity grow as the design progresses from the conceptual phase to the prototype phase. 1

2 Fig 1: Product Design Process Design Initiation Design project is initiated when a product need is identified. Product need may arise from: New idea, customer request, market research Inadequate/improved technology: Manufacturing process; materials; machine tools Production cost reduction Mass production capability Safety and reliability Deliverable: Design Brief o Statement of design problem. o Tells what product should do not how it is done Conceptual Design Functional requirements Aesthetic Requirements System design: Units (identify critical units) Ideation drawings (Isometric Sketches, Block Diagrams, Schematic and kinematic diagrams) Concepts and ideas refined Computer Models (Presentation) Activities 1. Brainstorming 2. Record alternatives 3. Generate sketches 4. Streamline viable designs 5. Develop Specifications 6. Estimation Design Preliminary Design Exploration of few viable solutions Choice of candidate solution(s) Refine units/system Component sketches 2

3 Preliminary drawings Computer Models Activities 1. Brainstorming 2. Record alternatives 3. Generate sketches 4. Streamline viable designs 5. Explore viable designs 6. Generate preliminary drawings 7. Chose most promising design 8. Adequacy Design Prototype Design Choose most promising design Refine preliminary units/system Refine preliminary components Detail design analysis and calculations Analysis and optimization Simulations Final drawings Activities 1. Perform detail analysis on most promising design 2. Prepare working drawings 3. Detail Design Prototype Manufacture Design and build tooling Process Design Build full-scale prototype Record manufacturing problems and solutions Record results Prototype Testing Perform experimentations Functionality Operability Reliability Safety Record results Product Development Carefully evaluate test results from computer and prototype Identify possible design and process modifications Perform design improvements May need more build-test activities Finalize best product Production Design Refine units and components Review and revise design analysis Generate production drawings Review and revise process design Redesign and build tooling Review and revise procedures Final technical documents 3

4 Fit Selection After design sizes are determined, the fits between mating parts need to be considered. The functional requirement of a fit depends on the tightness between the mating components and this controls the required tolerance on the components. Determining tolerances on components is a standard engineering task [54]. Reference may be made to previous drawings or general engineering practice when determining fits. Fits have been standardized nationally and internationally and the International Standardization Organization (ISO) standards are the most preferred. ISO recommends two fits systems of Hole-basis and Shaft-basis and 18 tolerance grades. In Hole-basis system, the size of hole is fixed while the shaft size can change to meet tightness requirement of a fit. In Shaft-basis system, the shaft size is fixed while the size of hole can change to meet tightness requirement for a fit. The position of the reference or basic size for a tolerance group is indicated by a letter. Capitalized or upper-case letters are used for holes while lowercase or small letters are used for shafts. The tolerance grade is indicated by a number. A Fit is made up of a combination of letters and numbers such as H9-f8. Hole-basis system is generally preferred by manufacturers because it minimizes the variety of cutting tools such as drills, reamers, broaches, and gauges required for production activities. Smaller tolerances and fine surface finishes require use of highprecision machine-tools, therefore production cost becomes higher. Hence small tolerances and high surface finish need to be justified when specified. Drafting Details The last task in a design project is drafting, a documentation process by which design intents are translated into industrial standard drawings and notes and or specifications. Two types of drawings are critical in drafting: namely design and working drawings. Design drawings show functional sizes and fits which are usually indicated with symbols. Fits for mating parts are important for functionality; so design drawings should indicate fits. Design drawings are transformed into working drawings during detailing by a drafter where actual tolerances are shown on detail component drawings. Working Drawings Working drawings are used to build or construct the designed product. They consist of two parts in mechanical design, namely assembly and detail drawings. Detail drawings are prepared as multiple 2D views annotated drawings of a single component with complete dimensions, tolerances and notes for construction, manufacturing and inspection. The practice in the industry at this time is to prepare a detail drawing for each custom component. Having multiple detail drawings on a single sheet is discouraged due to the changes that may occur in some components. Assembly drawings are prepared for mechanisms, devices, units, and products. They show the relative positions of components when assembled for functional use. An assembly drawing must include all components in a product that normally consist of standard and custom parts. These parts are listed in a bill of materials (BOM) or parts list. All custom parts in an assembly drawing must be accompanied by a detail drawing. However, standard parts in an assembly drawing do not need detail drawings but proper specifications are required for each of them so that the purchase order can be prepared correctly. Standard parts are bought from other companies or vendors. Written instructions in working drawings are called specifications. In general, specifications may provide technical requirement information on parts, manufacturing, and assembling processes. They may include material type and grade, processing methods, surface finish, heat-treatment, etc. Specifications may appear as general notes or are put together as separate documents as is commonly done in architectural projects. They should be clear and easily understood. The design drafter should add specifications to a working drawing as needed, but the correctness of the specifications is the responsibility of the designer or engineer 4

5 Working drawings are precise engineering drawings that show dimensions, general and geometric tolerances, surface finish grades, and special manufacturing requirements such as heat treatment. Mating dimensions must have specified tolerances and so are parts designed for interchangeable manufacture. Working drawings must show enough views to completely describe an object for manufacture or construction without ambiguity. They must be clear, concise, complete, and accurate, so fits shown by symbols in design drawings are converted to numeric values. Tables of standard or preferred fits and tolerances are useful during drafting. A working drawing set is package of all the detail drawings, assembly drawings, and specification documents, if any, in a design project. A drawing set completely communicate the design intent. Some CAD packages are able to generate a drawing set for a project. Product Decomposition System Breakdown -System (Assembly) -Units (Subassembly) -Mechanisms (Subassembly) Units (Subassembly) Mechanisms (Subassembly) Parts (Detail). Fig. 2: Product breakdown An engineered product is made up several parts or components which can be considered as a system, a combination of objects that actively work together to serve a common purpose. A product may be decomposed into units or subassemblies. A unit is a subsystem or portion of a system that alone can perform one or more functions. A unit consists of devices and a device can perform an identifiable function in a unit. Units have one or mechanisms and a mechanism can transmit force and or motion from one point to another. A mechanism consists of individual parts or components. A part performs a useful function only when used within a mechanism or device. Fig.2 depicts the breakdown of a product. The product is an assembly of units and a unit is an assembly of devices. A device is an assembly of mechanisms and components. Mechanisms, devices, and units are subassemblies relative to the product which is the assembly. Part Breakdown A part consists of features and segments. Segments are primitive forms of specifics sizes. Hence before we can construct a part, we must identify the segments and features. There are special features likes screw threads, bosses, lugs, etc. Once the part segments and features are identified, then the form primitives can be created. Normally, these form primitives will be modified by adding features to them to obtain the desired component. Each component in an assembly must first be created before they can be brought together into devices and units 5

6 Assembly Drawing Techniques Assemble components to make devices Assemble devices to make units Assemble units to make product Design Reviews Design reviews assess the progress of the design work, monitors design and development, assure that all requirements are met, and provide feedback of information to all concerned. Design reviews are conducted by teams and involve examination and discussion of the relevant aspects of product design. Issues dealing with product assembly, unit assemblies, and components are addressed to ensure that all requirements are met. Concurrent engineering is the guiding principle of modern design reviews. This requires all stakeholders to be represented in the review team. Members, however, should not be involved in the day-to-day design efforts but have adequate skills and knowledge at least comparable to the actual design team members. Design projects vary in scope and relevance but even the relatively simple designs need a minimum of three reviews: conceptual, preliminary and prototype: see Fig. 8. Conceptual review deals with the basics of the design project and defines its direction. Several promising design options are generated at this stage so conceptual review has a major impact on the design final outcome. Preliminary design finalizes the conceptualization process of a few of the options from conceptual review. A best solution selection is made at the end of this review. The prototype review is a final review activity and focus on eliminating all errors in the design carried out on the best solution from preliminary review. At the end of this review, detail and assembly drawings (prototype working drawings) for prototype manufacture are sent for revision or correction after which approval for construction is granted. Preliminary and prototype reviews have lesser impact than conceptual review on project outcome. A complex product design will certainly require more reviews in between the three mentioned above. When a prototype is built and test results are satisfactory, production working drawings are prepared and released. Drawing Revisions Revisions are made on design models and drawings due to customer requests, design changes, manufacturing process changes, production tools changes, and errors. It is very important to maintain accurate records of changes to design documents and drawings. Revisions may be done on detail and assembly drawings. Once a design or drawing is approved, changes must be initiated with an engineering change request (ECR) or engineering change order (ECO) which must have an assigned reference number. An ECR can be made by any department and is a formal request to make change(s) to approved design model or drawing. The indicated document is located and retrieved with the ECR attached and it is then changed, checked, and approved. Desired change(s) may be redlined, labeled or surrounded with clouds in the drawing. Drawing revision may need changes in dimensions but the drawing scale should be maintained. Some revision may be a redrawing of an old one without dimensional changes. This may be necessary because of loss, destruction or degradation. The revision record of the old drawing may be transferred to the new drawing with an added note of REDRAWN WITHOUT CHANGE. When drawings are revised with changes to the old ones, the revision letter or number must be incremented to the next. Once the change(s) are completed, an engineering change notice (ECN) is issued with an ECN number assigned. The notice should state the type of change and why. Revisions are usually summarized in a revision block on the drawing sheet and new prints are issued after the changes have been made. The old prints are archived with OBSOLETE or SUPERCEDED or REPLACED BY in the title block along with the new drawing number replacing them. Companies usually have standard forms for ECR, ECO, and ECN. 6

7 Revisions of drawings from solid models are easier and faster to make, especially in CAD packages with bidirectional associativity of data between part models and assembly models. The changes could be made in a part file and these will reflect in the assembly and drawing files when they are updated. This may be as simple as reopening the files or by selecting an update button after the files are opened. Changes made in assembly files likewise propagate to the other model files. Document File Formats File formats are schemes used to arrange bits in digital files for data storage and retrieval. They can be identified from a file extension which is usually the three letter appendage after the period mark (.) in a filename. Different file formats are available for electronic files of the same type digital data. A document usually contains both text and images and defaults to a text file if no images are present. There are several text formats available, but some are platform dependent. Also format compatibility for formatted documents is an issue in many instances and when available, there may not be 100% conversion. Table 4 shows the common document file formats and extensions. Table 1 Common document formats File Format File Extension Text File Format (TXT).txt Microsoft Word Document (DOC).doc Rich Text Format (RTF).rtf Hypertext Markup Language (HTML).htm, html Word Perfect Document (WPD).wpd Portable Document Format (PDF).pdf PDF is a product of Adobe Acrobat Systems Inc. and it became an official ISO standard in June, Acrobat 8 3D offer the capability to open and convert 2D or 3D CAD files into a PDF at a fraction of the original file size (e.g. 100 to 1). 3D PDF is suitable for view-only files, review/markup or distribution of precise geometry with reasonable security. Acrobat Reader (free software) is needed to view the pdf document, however, pdf writer from Acrobat Systems Inc. is not free. Purely graphic or video documents have special file formats. Vector graphics have several file formats. In fact, most CAD software providers use proprietary file formats, however, the need for compatibility of model and drawing data from different CAD packages is driving the use of neutral CAD file formats. The Standard for Exchange of Product Model Data (STEP) is a CAD file format developed by ISO (ISO 10303) and covers product life cycle namely: geometry, manufacturing, quality, testing, maintenance, etc. STEP can be used to exchange data between CAD, CAM, PDM (Product Data Management)/EDM (Enterprise Data Management) and other systems. ANSI CAD file format is Initial Graphics Exchange Specifications (IGES). The Drawing Exchange Format (DXF) developed by Autodesk used to be a popular format for CAD data exchange. DXF and IGES standards represent model data in ASCII format but this is not an efficient way of representation. Similarly, raster graphics have several popular file formats such as the Joint Photographic Experts Group (JPEG or JPG); Bit Map (BMP); Graphic Interchange Format (GIF); and Tagged Image File Format (TIFF). Popular video file formats for purely video documents include Windows Media, Quick Time, AVI, and MPEG4. MPEG4 is the file format for video information that can store both audio and video data. Video clips take up a lot of space. A normal video file has a capacity of MB. MPEG4 can reduce the video file size to that of a normal audio MP3 file, which is around 5-6 MB. 7

8 Table 2: Common video file formats Video File Format File Extension Windows Media (Microsoft).asx Quick Time (Apple).mov RealPlayer.rp? AVI (Microsoft).avi MPEG4 (Joint Photographic Experts Group).mpg Summary Design Initiation is the first step in a design project. A design project is often initiated with a meeting (call it intent meeting) in which a need for a product is identified. Product need may arise from new ideas, market research, or customer request. Inadequate or improved technology in material processing, materials, machine-tools, etc. can lead to a design project initiation. Likewise are the needs for production cost reduction, mass production capabilities, safety, reliability, or environmental issues. Requirements of the product are discussed and a design brief is formulated. A design brief is a statement of a design problem that expresses the need to be satisfied but not how it will be satisfied. It states what a product would do and not how it will do it. Conceptual Design is a follow up of design initiation. In this phase, focus is on system design and perceived critical units (Fig. 6) of the system are identified. Brainstorming section(s) are conducted so as to generate many alternative design solutions as possible. Conceptualization drawings (pictorial and orthographic sketches, block diagrams, schematic diagrams, kinematic diagrams, etc.) and visualization computer models are generated. Design concepts and ideas are refined and initial specifications are developed. A few promising design options are identified for the preliminary design phase. Preliminary Design phase explores in greater depth a few viable solutions identified in the conceptual phase with the goal of identifying the best or most promising design option. Layout diagrams and drawings are used for refined studies. Quantitative analysis is done on critical subassemblies and components. Preliminary engineering computer models and drawings are prepared for review. Preliminary drawings usually include basic dimensions determined from functional and structural integrity considerations. Cost, manufacturing, safety, etc. considerations are used to identify most promising design solution. Prototype Design phase involves performing detail analysis and optimization on the most economical and promising design option from the preliminary phase. Animations and simulations are done to ensure soundness and functionality of the design. Aesthetics are improved upon and final engineering models and drawings are prepared. Prototype drawings are scaled assembly and detail drawings used for construction of a full-scale first time product of the design. They normally include dimensions, tolerances, notes and specifications. Prototype drawings are the initial working drawings of the product development cycle. When product prototype is created as 3D solid model, a virtual product is created. It gives the same visual and physical appearance as a full-scale physical model. A virtual product has an electronic database with the product assembly and solid model parts in proper functional relationships. A virtual product database is accessible to different departments: engineering, manufacturing, marketing, management, etc. Documents Release is done after all corrections are made to product models, drawings, and associated documents. When a product is designed in a CAD environment, the model data is stored in a master database called the virtual database. The master database is a reference for manufacturing, marketing, engineering, etc. It simplifies design changes, communications, documentation and help to shorten time to 8

9 market for products. The release of appropriate design documents leads to the construction of the initial or first prototype of the product. Tests are conducted on the prototype and analysis of results done to verify performance and design specifications. Design and manufacturing errors if any identified during construction are recorded and improvements recommended. Several improved prototypes may have to be developed before specifications are met and satisfactory performance is achieved. Then production models, drawings, and documents are prepared for release. 9