16. Product Design and CAD/CAM

Transcription

1 16. Product Design and CAD/CAM 16.1 Unit Introduction 16.2 Unit Objectives 16.3 Product Design and CAD 16.4 CAD System Hardware 16.5 CAM, CAD/CAM, and CIM 16.6 Unit Review 16.7 Self Assessment Questions 16.8 Self Assessment Answers 16.1 Introduction Product design serves an important function in the production system. It helps determine the eventual commercial success of a product; it determines how the production system should be created, and exactly what equipment should be bought; and it determines how easily, and how cheaply, the product can be manufactured. The manufacturing support system contains procedures and systems used to manage production and solve the technical and logistical problems associated with designing the products, planning the processes, ordering the materials, controlling work-in-process as it moves through the plant, and delivering products to customers. Product design and its associated use of computer-aided design/computer-aided manufacturing (CAD/CAM) systems, represents one of the most important aspects of the manufacturing support system. In CAD/CAM, both design and manufacturing are tightly integrated into a continuum of activities. Continuing the integration, we have Computer Integrated Manufacturing (CIM), which includes CAD/CAM, but also extends to embrace the business functions of a manufacturing firm. In this unit a discussion and definition of product design and CAD are given, where an analysis of the design process and the actual application of computeraided design principles are highlighted. CAD system hardware is reviewed (see Figure 16.1), before a general introduction to CAM, together with its relationship with CAD, and how it fits into the infrastructure of CIM.

2 Figure 16.1: Components of CAD 16.2 Learning Objectives After completing this unit you will be able to: BULLET LIST List the six processes of the conventional design process Define Computer-aided design (CAD) Specify the benefits of CAD State the relationship between the Product Data Management system, and the CAD system Explain the concept of geometric modelling Classify types of geometric modelling Explain Computer-aided engineering (CAE) software, and list typical applications State how CAD is used to create product prototypes List the hardware used in a CAD system State the types of CAD system configurations that may be used Define Computer-aided manufacturing (CAM) State and explain the two application areas of CAM Explain the concept of CAD/CAM

3 State why CAD/CAM is used in concurrent engineering environments Define Computer-integrated manufacturing, and its scope ENDLIST 16.3 Product Design and CAD Product design is of critical importance to the production system. It contributes more than any other attribute to the overall design and operation of the production system, and its success determines whether the production system will be fit for use in making products over the long term. LEARNING ACTIVIY 16.1 Learn more about these concepts at the following web-sites: Computer-Aided Design (CAD) Computer-Aided Manufacturing (CAM) Computer Integrated Manufacturing (CIM) END LEARNING ACTIVITY The Design Process The general process of design may be seen as an iterative process with six key phases (see Figure 16.2): NUMLIST Recognition of need this involves the realisation that a problem or need exists that may be solved by design. This may mean identifying some deficiency in a current machine design by an engineer, or perceiving some new product opportunity by a salesperson. Problem definition this involves a thorough specification of the item to be designed. Specifications include physical characteristics, function, cost, quality, and operating performance. Synthesis closely related with the following step, analysis, synthesis refers to the bundling of information that occurs after problem definition, and concurrently during analysis, and after re-analysis.

4 Analysis and optimization closely related to the previous step, analysis is concerned with the investigation of design specification information, and the optimization of this information, as well as a synthesis of new information, as required. Evaluation involves measuring the design against the specifications established in the problem definition phase. This evaluation may require the building and testing of prototype models to assess operative performance metrics for the proposed design. This may lead to the re-design of certain or all elements. Presentation this is the final phase, where the design is documented by means of drawings, material specifications, assembly lists, and so on. Documentation means that the design database is created. ENDLIST Figure 16.1: Design Process and Computer aided design

5 The conventional design process consists of six processes: recognition of need; problem definition; synthesis; analysis and optimization; evaluation; and presentation. END Applications of Computers in Design CAD is any design activity involves the effective use of computers to create, modify, analyze, or document an engineering design. It is most commonly associated with the use of an interactive computer graphics system, referred to as a CAD system. CAD provides the following benefits: BULLETLIST Increased design productivity CAD reduces the time required to conceptualize and physically draw product designs; Increased available geometric forms in the design CAD allows the design to choose from a range of geometrical shapes that would normally be outside the manual drawing process. Improved quality of the design the use of a CAD system with appropriate hardware and software capabilities permits the designer to do a more complete engineering analysis and to consider a larger number and variety of design alternatives. The quality of the resulting design is thereby improved. Improved design documentation the output of a CAD system results in better documentation of the design than what is usually seen as practical in manual drafting. Creation of a manufacturing database by creating product design documentation, much of the required database to manufacture the product is also created. Design standardization design rules can be included in CAD software to encourage the designer to utilize company-specified models for certain design features. ENDLIST Computer-aided design (CAD) is any design activity that involves the effective use of a computer to create, modify, analyze, or document an engineering design. END

6 The use of a CAD system creates huge amounts of additional data that is often stored and managed in a product data management (PDM) system. A PDM system consists of computer software that provides links between users and a central database, where engineering design data and related documentation is stored. The PDM system manages the database by tracking the identities of users, facilitating and documenting engineering changes, recording a history of the engineering changes on each part and product, and providing documentation management functions. The output of the CAD system is stored in a product data management (PDM) system. A PDM system consists of computer software that provides links between users and a central database, where engineering design data and related documentation is stored. END The CAD system can facilitate four of the design phases depicted in Figure Geometric modelling is a special use of CAD data to create a mathematical description of the geometry of an object. The geometric model, which contains the mathematical description, is contained in the computer memory; and the CAD system upon accessing the computer memory can display the resultant model as an image on its graphics terminal, allowing the operator to manipulate certain aspects of the geometric model displayed. The operator can create new geometric models from basic building blocks available in the system, can zoomin on certain features of the image on-screen, can move two or more geometric models into close relation to each other, and so on. These capabilities allow the operator to interrogate existing product models, and create new variations on existing products to cater for a wide variety of needs. Geometric modelling creates a mathematical description of the geometry of an object, so that the subsequent description can be displayed as an image on CAD systems, which may be manipulated by the operator. END There are two types of geometric models used in CAD; these are: NUMLIST Two-dimensional modelling dating from the late 1960s and early 1970s, when the first CAD systems began to appear, this is primarily used for design problems, such as flat objects and layouts of buildings. To enable some degree of three-dimensionality, these models were often drawn from various viewpoints, so as to capture the multitude of dimensions on an individual product.

7 Three-dimensional modelling emerging after two-dimensional modelling, these systems are capable of modelling an object in three dimensions according to user instructions, which has been found useful for conceptualising the object, as the three-dimensional model can be displayed in various views and from different angles. ENDLIST Geometric modelling can appear in the form of two-dimensional modelling, and three-dimensional modelling. END Geometric models in CAD can also be classified as wire-frame models, or solid models (see Figure 16.3). Wire-frame models use inter-connecting lines to depict the object drawn; these inter-connecting lines can sometimes be confusing when used on complex part geometries, as multiple overlapping lines may occur. Solid models are objects that have been modelled in solid three dimensions, providing the user with a vision of the object that is similar to its appearance in reality. (a) (b) Figure 16.3: Wire-frame model (a), and Solid model (b) Geometric models in CAD can also be classified as wire-frame models, or solid models. END Engineering Analysis Once a design has been developed, it must then be subjected to engineering analysis. This engineering analysis may include various tests, depending on the product, but may include: stress-strain calculations, heat transfer analysis, or dynamic simulation. These analyses tend to be quite complex, which has led to the development of computer-aided engineering (CAE) software packages, so that complicated engineering analysis may be performed by computer. Computer-aided engineering (CAE) software packages are used to perform complex engineering calculations by computer.

8 END CAE packages in common use with CAD systems include: BULLETLIST Mass properties analysis involving the computation of features on the solid model, such as volume, surface area, weight, and centre of gravity; Interference checking this checks to see if multiple components in a product design would actually interfere with each other in reality; Tolerance analysis this determines how product tolerances would affect product function and performance, how easy it would be to assemble the product, and how variations in component dimensions may affect the overall size of the assembly; Finite element analysis this aids in stress-strain, heat transfer, fluid flow, and other engineering calculations; Kinematic and dynamic analysis this studies the operation of mechanical linkages and analyzes their motions; and Discrete-event simulation this models complex operational systems where events occur at discrete moments in time and affect the status and performance of the system. ENDLIST Common CAE packages include: mass properties analysis; interference checking; tolerance analysis; finite element analysis; kinematic and dynamic analysis; and discrete-event simulation. END Design Evaluation and Review Following comprehensive engineering analysis, the proposed design must be evaluated and reviewed for consistency. Some CAD features that are helpful in evaluating and reviewing a proposed design include: BULLETLIST Automatic dimensioning upon model completion, the CAD software can automatically generate the dimensions of the drawn model;

9 Error checking this checks the accuracy and consistency of dimensions and tolerances, to assess whether the proper design documentation format has been followed; Animation of discrete-event simulation solutions this displays the result as a discrete-event simulation, where input parameters, probability distributions, and other factors can be changed to assess their effect on the performance of the system being modelled; and Plant layout design scores this provides numerical scores for plant layout designs, based upon such factors as material flow, and closeness ratings. ENDLIST CAD features helpful in evaluating and reviewing a proposed design include: automatic dimensioning; error checking; animation of discrete-event simulation solutions; and plant layout design scores. END In many cases, the geometric model is now used to replace the physical prototype that would traditionally be built at this stage. Physical prototypes are usually time-consuming to create, and analyse; and so replacements in the form of rapid prototyping, and virtual prototyping both based upon the geometric model, may be used instead. Evaluating and reviewing a proposed design can use the CAD geometric model to create a prototype, either by rapid prototyping or virtual prototyping. END Rapid prototyping is a term applied to a family of fabrication technologies that allow engineering prototypes of solid parts to be made in a minimum lead time, based upon the CAD geometric model. This is done by dividing the solid object into layers, and then defining the area of each layer. The rapid prototyping process then fabricates the object by starting at the base layer, and building towards the top layer. The fidelity of the approximation that is produced by this method is dependent on the layer thickness used at the start (with greater accuracy achieved with thinner layers used). Virtual prototyping is based upon virtual reality technology, and uses the CAD geometric model to construct a digital mock-up of the product. This mock-up allows the designer to obtain the sensation of the real physical product, without actually building the physical prototype.

10 Rapid prototyping creates a physical prototype by means of segmenting the CAD geometric model into a series of layers, and building to that specification; while virtual prototyping uses the CAD geometric model to construct a digital mock-up of the product. END Automated Drafting CAD may also be used as a presentation application, in that the CAD system can produce highly accurate engineering drawings quickly and conveniently, and also provide associated documentation as necessary. It is estimated that a CAD system increases productivity in the drafting function by about fivefold over manual preparation of drawings. CAD may also be used for automated drafting that is, the creation and presentation of highly accurate engineering drawings. END 16.4 CAD System Hardware Hardware is used in CAD systems is described in Table The relationship between the components discussed is depicted in Figure Hardware Design workstations Digital computer Output devices Table 16.1: Hardware used in CAD systems Description This has the following functions: (1) communication with the computer s central processing unit; (2) continuously generate a graphic image; (3) provide digital descriptions of the image; (4) translate user commands into operating functions; and (5) facilitate interaction between the user and the system. CAD workstation design has an important influence on the convenience, productivity, and quality of user s output. The workstation consists of a display terminal and a set of user input devices, with which the user interacts with geometric model via: entering alphanumeric data; entering system commands to perform various graphics operations; and by controlling cursor position on the display screen. This uses a high-speed central processing unit to process CAD operations. There are several CAD system configurations, such as host and terminal; engineering workstation; and a CAD system based upon a personal computer. These are discussed in the paragraphs below. These include plotters and printers, which generate the output from the CAD system. Plotters include: pen plotters, which are x-y plotters of various type, used to produce high accuracy line drawings; and electrostatic plotters, which are based upon the same principal as photocopying, and produce lower quality drawings. Printers used include inkjet printers, where drawings are produced by high-speed jets

11 Secondary Storage of ink impacting the paper. This includes various storage devices attached to the CAD system to store programmes and data files. The storage mediums used can include: magnetic discs, magnetic tape, floppy discs, external harddrives etc. Figure 16.4: Configuration of a typical CAD system The hardware used in a CAD system includes: design workstations; digital computers; output devices, such as plotters and printers; and various secondary storage devices. END 16.5 CAM, CAD/CAM, and CIM We can now give more precise explanations of the terms CAM and CIM and their relationships to CAD Computer-Aided Manufacturing Computer-Aided Manufacturing (CAM) is the effective use of computer technology in manufacturing planning and control. It is closely associated with certain functions in manufacturing engineering, such as process planning and numerical control (NC) part programming. It is applied in two broad categories: manufacturing planning, and manufacturing control. Computer-Aided Manufacturing (CAM) is the application of computer technology to the areas of manufacturing planning and control. END Manufacturing planning concerns the use of CAM to support the production function, without a direct connection between the computer and the process.

12 Effective planning is achieved off-line ; that is, the computer is used to provide information for planning and managing production activities, without directly accessing the process in real-time. Important applications of CAM in manufacturing planning are outlined in Table Application Computer-aided process planning (CAPP) Computer-aided NC part programming Computerized machinability data systems Computerized work standards Cost estimating Production and inventory planning Computer-aided line balancing Table 16.2: Applications of CAM for manufacturing planning Description This is concerned with creation and dissemination of route sheets that list the sequence of operations and work centres required to produce the product and its components. We discussed numerical control in unit 5. This application supports the creation of computer-assisted part programmes for numerical control, which represents a more efficient solution for their creation over traditional manual methods. This is concerned with creation and dissemination of part programmes that can determine optimal cutting conditions for machine tools in the factory. These are computer packages that can be deployed to determine time standards for direct labour jobs in the factory. They supersede tedious manual time-and-motion studies used to perform the same task. This is a programme that can estimate the cost of a new product, by computerizing several of the key steps required to prepare the estimate (such as the application of labour and overhead rates to the sequence of planned operations). Functions here include maintenance of inventory records, automatic re-ordering of stock items when inventory is depleted, production scheduling, maintaining current priorities for the different production orders, material requirements planning, and capacity planning. This programme helps to find the best allocation of work elements among stations on an assembly line. Can be used in situations where the line balancing problem is particularly complex and difficult, owing to the number of workstations, and complicating factors. Applications of CAM for manufacturing planning include: Computer-aided process planning (CAPP); Computer-aided NC part programming; Computerized machinability data systems; Computerized work standards; Cost estimating; Production and inventory planning; and Computer-aided line balancing. END Manufacturing control uses CAM applications to manage and control the physical operations of the factory. Here computer systems are developed that can be used to implement the manufacturing control function. Important applications of CAM in manufacturing control are outlined in Table Table 16.3: Applications of CAM for manufacturing control Application Process monitoring and control Description This is concerned with observing and regulating the production equipment and manufacturing processes in the plant. They

13 Quality control Shop floor control Inventory control Just-in-time production systems include the control of transfer lines, assembly lines, numerical control, robotics, material handling, and flexible manufacturing systems. This includes a variety of approaches to maintain the highest possible quality levels in the manufactured product. They include the use of quality functional deployment techniques. This refers to the use of production management techniques to collect data from factory operations, and the deployment of this data to aid the control of production and inventory in the factory. This is concerned with maintaining the most appropriate levels of inventory in the face of two opposing objectives: minimizing the investment and storage costs of holding inventory; and maximizing service to customers. Just-in-time (JIT) production systems deliver the right number of components to downstream workstations, at the right time. JIT refers to both production operations and supplier delivery operations. Applications of CAM for manufacturing control include: process monitoring and control; quality control; shop floor control; inventory control; and just-in-time production systems. END CAD/CAM The integration of CAD functions with CAM applications gives us the acronym CAD/CAM. CAD/CAM is concerned with engineering functions in both design and manufacturing; it denotes an integration of design and manufacturing activities by means of computer systems. Since the way a product is manufactured depends upon the specific design that is supplied, the combining of CAD with CAM in CAD/CAM, creates a direct link between product design and product manufacture that can be exploited in the production system. Conventional practices, practiced for many years in industry, saw design and manufacturing as essentially separate functions: engineering drawings were created by the design department, and these were later used by manufacturing engineers to develop the process plan. This two-step procedure was timeconsuming and duplicated the efforts of design and manufacturing personnel. The application of CAD/CAM removed this problem. In an ideal CAD/CAM system, it is possible to take the design specification of the product as it resides in the CAD database, and convert it automatically into a process plan for making the product. As such, therefore, CAD/CAM operates as a system that facilitates concurrent engineering practices.

14 CAD/CAM is concerned with engineering functions in both design and manufacturing; it denotes an integration of design and manufacturing activities by means of computer systems. END The term concurrent engineering defines a system whereby the whole life cycle of a product is considered concurrently. The pressure to decrease design and development time-scales is leading companies to conduct the design, development, analysis and the production of manufacturing information in tandem. Within this setting, advances such as CAD/CAM help to avoid certain problems occurring, such as a lack of quality design or a lack of communication between design and manufacturing personnel, as everybody understands and appreciates what everyone else is doing. The organisation of the company in the case of a concurrent engineering approach is usually dictated by product group rather than by individual function, with applications such as CAD/CAM being cross-functional, rather than being department-specific. The concurrent engineering practice involves work through multi-disciplinary teams comprising expertise from every area of the organisation, from materials right through to marketing and sales. There may also be input from outside specialists. This is opposed to the conventional engineering approach, whereby the responsibility for the product moves from department to department. For example, the materials personnel may purchase the raw materials, which they see as suited to the finished product, but this may not comply with the expectations of the maintenance people or the production engineers. In the concurrent engineering approach the materials, production and maintenance staff would all be working together, enhancing communication on a project team. Leadership of such teams will vary according to the stage in the product life cycle. Concurrent engineering defines a system whereby the whole life cycle of a product is considered concurrently. CAD/CAM is an example of an application widely used in concurrent engineering. END Computer-Integrated Manufacturing Computer-integrated manufacturing (CIM) includes all of the engineering functions of CAD/CAM, but it also includes the firm s business functions that are related to manufacturing. The component geometry developed through the use of CAD systems may be reused in the generation of manufacturing instructions for numerically controlled production processes, and in the planning of manufacturing operations through computer aided process planning (CAPP). This is in line with our discussion above.

15 Further, they suggest that these activities in turn feed information, together with bill of materials information, from CAD, into an activity called computer aided production management (CAPM). All of these manufacturing activities are integrated through the use of computer aids and a shared database. They are collectively known in industry as CIM, and they can be summarised in a graphical format as shown in Figure The computer aids the interface between design and manufacture through the interaction between CAD and CAM, by developing computer aided process plans. There are problems with this approach: computer plans are trying to generate and automate process plans for manufacturing, while the ideal scenario would be to automate the techniques of design for manufacture and design for assembly in the CAPP system. Examples are techniques for product/process analysis that gives the manufacturer an influence or input into the design. CAPP systems constitute both process planning and product/process analysis with influences from CAD and CAM. CIM Environment Market needs CAD Geometry CAM Bill of materials Geometry Priority Manufacturing Manufacturing strategy CAPP Routes CAPM Manufacturing cell capability profile Cell capacity profile Figure 16.8: Data Exchange in a CIM Environment Computer-integrated manufacturing (CIM) includes all of the engineering functions of CAD/CAM, but it also includes the firm s business functions that are related to manufacturing. END Comparing the scope of CIM to the more limited scope of CAD/CAM, is instructive (see Figure 16.9). The ideal CIM system applies computer and communications technology to all the operational functions and information processing functions in manufacturing, from order receipt through design and production, to product shipment. CAD/CAM, on the other hand, is not so allembracing, and does not cover what may loosely be termed the business

16 functions of the factory. Thus, at higher levels, CIM subsumes CAD/CAM, and adds functions of its own. Figure 16.9: The scope of CAD/CAM and CIM CIM has a wider scope than CAD/CAM, so that at higher levels CIM subsumes CAD/CAM and adds functions of its own. END A specific examination of the computerized elements of a CIM system may also be analysed (see Figure 16.10). Here we can see the elements of CAD and CAM being captured within the CIM remit, at different stages of design and manufacturing. CIM adds a series of computerized business systems that account for peripheral elements entering and exiting the manufacturing system, proper. Customer orders are initially logged by an order entry system, with product specifications being derived from this, and acting as initial input to the design function, where CAD functions may occur. The output of the design department, in its turn, serves as input to manufacturing engineering at both control and planning levels, and both product and process planning is performed in detail. Full implementation of CIM results in the automation of the information flow through every aspect of the company s organization. During the process, accounting and payroll activities ensure that personnel, product and production considerations are fully in line with planned expenditure; while at process end, customer billing completes the operation of the CIM architecture.

17 Figure 16.10: Computerized elements of a CIM system CIM adds a series of computerized business systems that account for peripheral elements entering and exiting the manufacturing system, alongside those that emerge from CAD/CAM. END 16.6 Unit Review BULLETLIST Product design, and associated CAD/CAM systems, are important parts of the manufacturing support system. The conventional design process consists of six processes: recognition of need; problem definition; synthesis; analysis and optimization; evaluation; and presentation. Computer-aided design (CAD) is any design activity that involves the effective use of a computer to create, modify, analyze, or document an engineering design. Benefits of CAD include: increased design productivity; increased available geometric forms in the design; improved quality of the design; improved design

18 documentation; creation of a manufacturing database; and design standardization. The output of the CAD system is stored in a product data management (PDM) system. A PDM system consists of computer software that provides links between users and a central database, where engineering design data and related documentation is stored. Geometric modelling creates a mathematical description of the geometry of an object, so that the subsequent description can be displayed as an image on CAD systems, which may be manipulated by the operator. Geometric modelling can appear in the form of two-dimensional modelling, and three-dimensional modelling. Geometric models in CAD can also be classified as wire-frame models, or solid models. Computer-aided engineering (CAE) software packages are used to perform complex engineering calculations by computer. Common CAE packages include: mass properties analysis; interference checking; tolerance analysis; finite element analysis; kinematic and dynamic analysis; and discrete-event simulation. CAD features helpful in evaluating and reviewing a proposed design include: automatic dimensioning; error checking; animation of discrete-event simulation solutions; and plant layout design scores. Evaluating and reviewing a proposed design can use the CAD geometric model to create a prototype, either by rapid prototyping or virtual prototyping. Rapid prototyping creates a physical prototype by means of segmenting the CAD geometric model into a series of layers, and building to that specification; while virtual prototyping uses the CAD geometric model to construct a digital mock-up of the product. CAD may also be used for automated drafting that is, the creation and presentation of highly accurate engineering drawings. The hardware used in a CAD system includes: design workstations; digital computers; output devices, such as plotters and printers; and various secondary storage devices.

19 Different types of CAD system configurations may be used, including: host and terminal configurations; engineering workstation configurations; and CAD systems based on the use of personal computers. Computer-Aided Manufacturing (CAM) is the application of computer technology to the areas of manufacturing planning and control. CAM can be considered to have principal application areas: manufacturing planning, and manufacturing control. Manufacturing planning uses CAM in an off-line setting; that is, computers are used to support planning and management activities, without a direct connection being maintained between the computer and the process. Applications of CAM for manufacturing planning include: Computer-aided process planning (CAPP); Computer-aided NC part programming; Computerized machinability data systems; Computerized work standards; Cost estimating; Production and inventory planning; and Computer-aided line balancing. Manufacturing control uses CAM applications to manage and control the physical operations of the factory. Applications of CAM for manufacturing control include: process monitoring and control; quality control; shop floor control; inventory control; and just-in-time production systems. CAD/CAM is concerned with engineering functions in both design and manufacturing; it denotes an integration of design and manufacturing activities by means of computer systems. Concurrent engineering defines a system whereby the whole life cycle of a product is considered concurrently. CAD/CAM is an example of an application widely used in concurrent engineering. Computer-integrated manufacturing (CIM) includes all of the engineering functions of CAD/CAM, but it also includes the firm s business functions that are related to manufacturing. CIM has a wider scope than CAD/CAM, so that at higher levels CIM subsumes CAD/CAM and adds functions of its own. CIM adds a series of computerized business systems that account for peripheral elements entering and exiting the manufacturing system, alongside those that emerge from CAD/CAM. ENDLIST

20 16.7 Self-Assessment Questions NUMLIST What are the six processes of the conventional design process? What is Computer-aided design (CAD)? What are the benefits of CAD? What is the relationship between the Product Data Management system, and the CAD system? What is meant by the concept of geometric modelling? Classify types of geometric modelling. What is Computer-aided engineering (CAE) software? List typical applications of CAE software. How is CAD used to create product prototypes? What hardware is used in a CAD system? What are the different types of CAD system configurations that may be used? What is Computer-aided manufacturing (CAM)? What are the two application areas of CAM? What is meant by the concept of CAD/CAM? Why is CAD/CAM used in concurrent engineering environments? What is Computer-integrated manufacturing (CIM)? What is its scope? ENDLIST 16.8 Answers to Self-Assessment Questions NUMLIST The conventional design process consists of six processes: recognition of need; problem definition; synthesis; analysis and optimization; evaluation; and presentation.

21 Computer-aided design (CAD) is any design activity that involves the effective use of a computer to create, modify, analyze, or document an engineering design. The benefits of CAD include: increased design productivity; increased available geometric forms in the design; improved quality of the design; improved design documentation; creation of a manufacturing database; and design standardization. The output of the CAD system is stored in a product data management (PDM) system. A PDM system consists of computer software that provides links between users and a central database, where engineering design data and related documentation is stored. Geometric modelling creates a mathematical description of the geometry of an object, so that the subsequent description can be displayed as an image on CAD systems, which may be manipulated by the operator. Geometric modelling can appear in the form of two-dimensional modelling, and three-dimensional modelling. Geometric models in CAD can also be classified as wire-frame models, or solid models. Computer-aided engineering (CAE) software packages are used to perform complex engineering calculations by computer. Common CAE packages include: mass properties analysis; interference checking; tolerance analysis; finite element analysis; kinematic and dynamic analysis; and discrete-event simulation. Evaluating and reviewing a proposed design can use the CAD geometric model to create a prototype, either by rapid prototyping or virtual prototyping. Rapid prototyping creates a physical prototype by means of segmenting the CAD geometric model into a series of layers, and building to that specification; while virtual prototyping uses the CAD geometric model to construct a digital mock-up of the product. The hardware used in a CAD system includes: design workstations; digital computers; output devices, such as plotters and printers; and various secondary storage devices. Different types of CAD system configurations may be used, including: host and terminal configurations; engineering workstation configurations; and CAD systems based on the use of personal computers. Computer-Aided Manufacturing (CAM) is the application of computer technology to the areas of manufacturing planning and control.

22 CAM can be considered to have principal application areas: manufacturing planning, and manufacturing control. Manufacturing planning uses CAM in an off-line setting; that is, computers are used to support planning and management activities, without a direct connection being maintained between the computer and the process. Manufacturing control uses CAM applications to manage and control the physical operations of the factory. CAD/CAM is concerned with engineering functions in both design and manufacturing; it denotes an integration of design and manufacturing activities by means of computer systems. The term concurrent engineering defines a system whereby the whole life cycle of a product is considered concurrently. The pressure to decrease design and development time-scales is leading companies to conduct the design, development, analysis and the production of manufacturing information in tandem. Within this setting, advances such as CAD/CAM help to avoid certain problems occurring, such as a lack of quality design or a lack of communication between design and manufacturing personnel, as everybody understands and appreciates what everyone else is doing. The organisation of the company in the case of a concurrent engineering approach is usually dictated by product group rather than by individual function, with applications such as CAD/CAM being cross-functional, rather than being department-specific. Computer-integrated manufacturing (CIM) includes all of the engineering functions of CAD/CAM, but it also includes the firm s business functions that are related to manufacturing. CIM has a wider scope than CAD/CAM, so that at higher levels CIM subsumes CAD/CAM and adds functions of its own. ENDLIST