CAD CAM Third Edition Solution Manual PDF

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Solution Manual Chapter 1 1. Explain the influence exerted by the computers on the manufacturing scene. The role of computer in manufacturing may be broadly classified into two groups: Computer monitoring and control of the manufacturing process. Manufacturing support applications, which deal essent...

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Solution Manual

Chapter 1 1. Explain the influence exerted by the computers on the manufacturing scene. The role of computer in manufacturing may be broadly classified into two groups: Computer monitoring and control of the manufacturing process. Manufacturing support applications, which deal essentially with the preparations for actual manufacturing and post-manufacture operations. 2. Specify the various stages present in a conventional design process. See Fig 1.2 3. Give a schematic and explain how the application of computers helps in the overall improvement of the design cycle. See Fig 1.10. 4. Explain the importance of engineering analysis in the design cycle. Engineering analysis is shown in Fig. 1.6. The analysis stage is basically an iterative one with modification to the geometric model being carried out until the desired end result is achieved. 5. Briefly describe the role of engineering analysis process in the product design cycle. Various stages in engineering analysis are: Strength analysis: It is necessary to obtain the stresses and strains in the component when it is in service. Using FEA engineers will identify the feasible dimensions of the parts. Kinematic analysis: Kinematic analysis systems allow the user to optimise the product performance by providing a fundamental understanding of how a design will perform in its realworld environment. This understanding, such as how an assembly will behave in motion and how the individual parts move under extreme conditions, provides the necessary insight for creating the best possible product design. Dynamic analysis: Using this, engineers can evaluate the designs for vibration requirements by performing dynamic time, frequency, random, and shock response simulations. Heat/Flow analysis: This would allow for the evaluation of the part in terms of the heat transfer analysis by evaluating the temperature, thermal stresses and the like. Similarly it is also possible to evaluate the flow characteristics by employing the FEA techniques.

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Design for Manufacture and Assembly: This allows for a reduction of the assembly costs and component count along with a reduction of the overall costs while improving the reliability of the product. 6. Briefly explain the computerised product cycle in the manufacturing environment. See Fig 1.11. 7. What are the functions that get benefited by the use of computers in design and manufacturing functions? See Fig 1.11. 8. Define CAD. Explain the reasons for adopting CAD in an engineering organisation. Computer aided design utilises computer as a tool for all functions that are involved in the design process. The main functions that would utilise the computer are: Layout design for the overall assembly Individual component modelling Assembly modelling Interference and tolerance stack checking Engineering drawings CAD is used in an engineering organization because: Computer aided design (CAD) is faster and more accurate than conventional methods. The various construction facilities available in CAD would make the job of developing the model and associated drafting a very easy task. In contrast with the traditional drawing methods, under CAD it is possible to manipulate various dimensions, attributes and distances of the drawing elements. This quality makes CAD useful for design work. Under CAD you will never have to repeat the design or drawing of any component. Once a component has been made, it can be copied in all further works within seconds, including any geometric transformation needed. You can accurately calculate the various geometric properties including dimensions of various components interactively in CAD, without actually making their models and profiles. With the constraint based modelling methods that are prevalent in most of the commercially available CAD systems, it is possible to capture the design intent into the product model beyond the simple geometry. This will help in actually making modifications easily. Also it is possible to try various options, thereby optimising the whole design process. Thus the geometric modelling process can be driven by the physics of the process. Modification of a model is very easy and would make the designer's task of improving a given product simple to take care of any future requirements. Use of standard components (part libraries) makes for a very fast model development work. Also a large number of components and sub-assemblies may be stored in part libraries to be reproduced and used later.

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Professional CAD packages provide 3D (3 dimensional) visualisation capabilities so that the designers can see the products being designed from several different orientations. This eliminates the need of making models of products for realisation and explaining the concepts to the team.

9. Explain with an example various steps in the modern design process. See Fig 1.2.

10. Explain the following steps in the design process: Problem definition, and Engineering Analysis Problem definition: This stage in the design process is the clear definition of the problem and coming up with all possible ideas for solutions. This stage may be carried out in various forms of components as shown in Fig. 1.4. Engineering Analysis: In this stage of design process a thorough analysis of the product is carried out to get as much of information as possible before committing to final manufacturing. For this purpose a large number of computer aids are available as shown in Fig. 1.6. The analysis stage is basically an iterative one with modification to the geometric model being carried out until the desired end result is achieved. 11. Write about prototype development as part of design process. Prototype Development: Before committing the design to manufacture, it is also essential to carryout some physical tests on the part. This will be in addition to the computerised analysis carried out using various facilities as outlined in the earlier stages. The possible components in this stage are shown in Fig. 1.8. Using conventional methods for developing the physical models is often time consuming and expensive. 12. Write down the advantages to be gained by the adoption of CAM. Greater design freedom: Any changes that are required in design can be incorporated at any design stage without worrying about any delays, since there would hardly be any in an integrated CAM environment. Increased productivity: In view of the fact that the total manufacturing activity is completely organised through the computer, it would be possible to increase the productivity of the plant. Greater operating flexibility: CAM enhances the flexibility in manufacturing methods and changing of product lines. Shorter lead time: Lead times in manufacturing would be greatly reduced. Improved reliability: In view of the better manufacturing methods and controls at the manufacturing stage, the products thus manufactured as well as of the manufacturing system would be highly reliable. Reduced maintenance: Since most of the components of a CAM system would include

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integrated diagnostics and monitoring facilities, they would require less maintenance compared to the conventional manufacturing methods. Reduced scrap and rework: Because of the CNC machines used in production, and the part programs being made by the stored geometry from the design stage, the scrap level would be reduced to the minimum possible and almost no rework would be necessary. Better management control: As discussed above, since all the information and controlling functions are attempted with the help of the computer, a better management control on the manufacturing activity is possible. 13. Briefly explain the various categories of manufacturing activities. We can broadly categorise the industrial manufacturing activity (for only mechanical engineering industries i.e. making discrete components) into: Mass production ─ large lots e.g. automobiles In this, the volume of production is very high, ranging from a few thousand to millions per annum. The very high volume justifies the use of special purpose machines and transfer lines to decrease the cost of production substantially. Batch production ─ medium lot sizes e.g. industrial machines, aircrafts, etc. Batch production refers to the making of jobs in medium lots, say 100 to 1000, for a component type. Thus, transfer lines may not be used in their production, but special purpose machines which can be easily modified by the use of jigs and fixtures for such jobs can be utilised. Job shop production ─ small lots or one off, e.g. prototypes, aircrafts, etc. Job shop production refers to the manufacture of very small lots, often of single jobs. This may be required in special situations for the purpose of proving a design, making prototypes, in tool making, or for special purpose applications. 14. What do you understand by CIM and Lean Manufacturing? CIM: Computer Integrated Manufacturing. There are a number of advantages to be gained by employing computer applications in individual domains of the product cycle. It is possible to utilise computers in all aspects of the product cycle as shown in Fig. 1.10. However the synergy can be obtained by integrating all the functions through the computer such that all the incremental improvements that are possible can be improved manifold which is termed as Computer Integrated Manufacturing or CIM. Lean Manufacturing: In spite of a number of improvements having been achieved through the employment of computer and other automation efforts, there is a large amount of waste involved in the production, which finally increases the unnecessary costs. Japanese manufacturers have recognised this fact, and developed methodologies that lead to the reduction of waste during the mass manufacturing operations. In lean manufacturing the products are manufactured as required and not for stocking. By following this philosophy throughout the product cycle it will be possible to reduce the amount of storage at each stage and there by reduce a large amount of the hidden costs in the final product. 15. What are the various processes that should be considered in getting the problem identification phase of the product design?

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Problem Identification: The starting point of the design process is the identification of the needs of an unsatisfied demand for a particular product or conceptually a new idea to start a fresh demand. At this stage it is possible to identify some of the basic questions related to the product such as who, what, where, when, why and how many should be answered with fair accuracy. In order to provide answers to the above questions, the design team may have to explore a number of sources and methods as shown in Fig. 1.3. 16. Briefly explain about the importance of six sigma in manufacturing operations. Six Sigma is considered as the most important business tool that has transformed many ideas of management in the recent past. Six Sigma was originally started as a defection reduction process, but progressed into as a comprehensive statistically-based method to reduce variation in electronic manufacturing processes in Motorola Inc in the USA. Now it is practically adopted by a majority of industries as well as all walks of life such as government departments and hospitals. In industries even a new brand name of “Lean Sigma” is coined to combine the concepts Lean Manufacturing and Six Sigma. The UK Department for Trade and Industry defines Six Sigma as "A data-driven method for achieving near perfect quality. Six Sigma analysis can focus on any element of production or service, and has a strong emphasis on statistical analysis in design, manufacturing and customer-oriented activities."

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 Chapter2 1. What is the structure of a computing system? The computing system in operation can be compared to a human being in terms of its operating characteristics. The basic configuration of a typical computing system is shown in Fig. 2.1. The heart of any computing system is the central processing unit (CPU). It is in the CPU that all the necessary functions of a computer are carried out. The main functions performed in the CPU are arithmetic and logic operations. The CPU communicates with the external world through input/output devices or in short I/O devices. These are similar to the sensory organs by which a human being maintains contact with the outside environment. These are also collectively called peripheral units. Through an input device, the user would be able to communicate with the CPU, either to give certain data or to control the operation of the CPU. The output device is a means through which the CPU gives the results of the computations. 2. What do you understand by the CPU? The central processing unit is the nerve centre for any computing system. Based on the software it organises the information processing for any given application. 3. Describe the functioning of a central processing unit with the aid of a block diagram. The flow of information in the CPU is presented in Fig. 2.2. The program containing the necessary sequence of instructions to the CPU resides in the main memory of the computer, the location of which is specified to the CPU in the form of a program counter. The instructions are in the form of low-level commands, which comprise the repertoire of any given CPU, called instruction set. The instruction set consists of instructions for moving the memory contents, performing arithmetic and logic operations and other miscellaneous commands. 4. What is the importance of a CPU in a computing system? The central processing unit is the nerve centre for any computing system. Based on the software it organises the information processing for any given application. 5. How do you distinguish between a CPU and a microprocessor? The concept of the CPU with mainframe computers and mini computers is essentially a printed circuit board (PCB) consisting of a number of devices (chips). A CPU fabricated as a single integrated circuit (chip) is termed a microprocessor. 6. Explain the following terms with reference to microprocessors: (a) word, (b) system clock, and (c) address. (a) Word: It is the number of individual bits acted upon by the CPU at a given time. The length of a data word normally depends on the length of the word used by the CPU.

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(b) System clock: Speed with which a microprocessor operates. (c) Data is the name given to any information that is written or retrieved by the microprocessor from the memory. Data can be a part of the program, constant parameter values required for the execution of the program, or results of computation. 7. Describe the various types of semiconductor memory devices used in micro computers. ROM - Read only memory, PROM - Programmable ROM, RAM - Random access memory in its various forms EPROM - Erasable programmable ROM, and EEPROM - Electrically erasable and programmable ROM. Flash memory 8. What are the input devices more commonly employed for general graphics applications? Keyboard, Mouse, Light pen, Joystick, Digitizer Tablet, and Scanner 9. Describe the following input devices: (a) digitizer, (b) tablet, (c) mouse, and (d) light pen. (a) Digitizer: A digitizer is the most widely used input medium by the CAD designer. It is used for converting the physical locations into coordinate values so that accurate transfer of data can be achieved. (b) Tablet: A tablet is essentially a low resolution digitizer having a small work area. (c) Mouse: Mouse is a pointing device with a number of buttons attached to it for inputting the geometric data and easy access of the menu items. (d) Light pen: A light pen resembles a fountain pen in the method of holding, but it works on the principle of light. It detects the presence of light on the screen. Since the light pen points to the graphic display directly, it is a natural graphic interactive tool. 10. Specify a digitizer for the CAD application and justify your choice. The selection of a digitizer is in terms of size, resolution, accuracy, linearity and repeatability. See Table 2.2. 11. What are the various constructional methods employed in the making of a digitizer? A digitizer consists of a rectangular smooth surface area which is to be converted into locational data. Electro magnetic and electric resistance technologies are generally used for this conversion process.

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12. What are the various display devices that are used for displaying graphic information? Present their merits and demerits. Cathode ray tube (CRT) display These are low cost, highly refined, but bulky in size. Plasma panel display Though they are small and flat, they consume a large amount of power and also the resolution is not very good. Liquid crystal display (LCD) Their main advantage is that they occupy very small desktop space while reducing the power consumption. 13. Explain the functioning of Liquid Crystal Display terminals as used in CAD. LCD consists of two sheets of polarized glass. Each sheet of glass has a film on one side which gives the glass its polarizing properties, while a special polymer is applied on the other side which will set small, microscopic grooves into the surface. The grooves must be in the same direction as the polarization of the glass. A coat of nematic liquid crystal is added on top of this polymer such that the molecules of the crystal align with the direction of the microscopic grooves. Then, the two pieces of glass are arranged in such a way that the polarization of the second sits at a right angle from that of the first. Since the liquid crystal is twisted nematic, each molecule is slightly twisted as compared to the level right below it. The uppermost level of molecules will be aligned with the grooves on the upper glass, making them at a 90 degree angle from the ones on the bottom. Electrodes are embedded into the LCD to administer the electric current. When a current passes through them the liquid crystal untwists blocking the light and when the current is not passed the reverse takes place. 14. Explain the importance of aspect ratio in computer display terminals. Aspect ratio is the ratio of display screen width to that of the height. CRT terminals were all produced with an aspect ratio (ratio of longer side to the shorter side) of 4:3. However with the larger LCD (> 19 inch) have wide format with a 16:9 aspect ratio. This format provides a longer screen while reducing the height, thereby reducing the amount of scrolling one has to do for wider documents. This will be good for some application where the width is more, for example for draughting work. 15. What do you understand by the word interlacing in connection with display terminals? Explain its importance. In some low-cost display devices, decreasing the refresh rate to half at 30 Hz reduces the cost of the monitor. This gives rise to a flickering of the image as in each of the cycles only half of the screen image is refreshed, instead of the full one by omitting alternate lines. This is termed interlaced refreshing. In this mode, in the first cycle, alternate lines are refreshed as shown in Fig. 2.12 whereas in the second cycle the other lines are refreshed. This reduces the overheads on the display control and consequently the costs, but is not suitable for dynamic displays where the display changes fast.

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16. What do you understand by raster scanning? Why is it preferred to the storage tube in the display of graphics information? In the raster scan displays, the complete screen is divided into a matrix of pixels as shown schematically in Fig. 2.8. Each square in the Fig. 2.8 represents one pixel. The electron beam generates a single dot at the centre of this square. The display is generated by identifying which pixels need to be bright for a given vector and then the full screen display is obtained by scanning the complete screen horizontally line by line as shown in Fig. 2.9. 17. Give a brief description of scanners as used in engineering application. A scanner digitally scans images or text present on a paper optically and converts it into a digital image as a bit map. The scanner consists of a CCD (Charge Coupled Device) array which takes the image in the form of dot...