I ns t i t ut eofManage me nt & Te c hni c alSt udi e s
COMPUTERAI DED MANUFACTURI NG
500
BACHELORI NMECHANI CALENGI NEERI NG www. i mt s i n s t i t u t e . c o m
IMTS (ISO 9001-2008 Internationally Certified) COMPUTER AIDED MANUFACTURING
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COMPUTER AIDED MANUFACTURING CONTENTS:
UNIT-I
01-14
Computer aided manufacturing: Introduction - CAM - Hierarchy Elements of CAM systems - NC in CAM - Rationale for CAD/CAM. Product Development and Design: Introduction - Life cycle of a product Product Cycle - Simultaneous Engineering - Design for manufacture and assembly-DFMA - Rules for the design of parts - Total quality approach.
UNIT -II
15-23
Machine Tool Control: NC of machine tools - Elements of the NC systems - Type of control Systems - Coordinate system - Input Devices Punched Tapes - The NC procedure - NC part programming - ComputerAided Part programming.
UNIT-III
24-34
Machining Centers - Turning Centres - CAD/CAM Integration -NC systems Material Handling - Automated Guided Vehicles (AVGs).
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UNIT-IV
35-49
Group Technology - Part Families - Parts Classification and Coding Coding Systems - Facility Design using GT - Benefits of GT. ComputerAided Process Planning: Introduction - Role of Process Planning Implementation Techniques Process planning Systems - Benefits of CAPP
- Advantages. Master Production Scheduling
- Material
Requirements Planning (MRP) - Manufacturing Resource Planning (MRP II) - Capacity Planning. UNIT-V
50-65
Shop Floor Control System: introduction - Functions of SFC - SFC System . .lust In Time Manufacturing: Definitions - JIT approach Elements - JIT works Effects of JIT Production- Benefits of JIT. FMS: Introduction- Elements - Classification System for FMS - FMS WorkStations -Material handling equipment - Computer control system Applications and Benefits of FMS. Concept of CIM- Evaluation of CIMCIM hardware and software - Introduction to Intelligent Manufacturing System.
UNIT QUESTIONS-
66-67
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UNIT-I UNIT STRUCTURE
1.1
Introduction
1.2
Computer Aided Manufacturing
1.3
Hierarchy
1.4
Elements of CAM system
1.5
NC in CAM
1.6
Rational for CAD/CAM
1.7
Product development and design-Introduction
1.8
Life cycle of a product
1.9
Product cycle
1.10
Simultaneous engineering
1.11
Design for manufacturing and assembly
1.12
Rules for the design of parts
1.13
Total quality approach
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2
1.1 INTRODUCTION: CAM means Computer aided manufacturing. It can be defined as the use of computer systems to plan, manage and control the operations of a manufacturing plant through either direct or indirect computer interface with the plant production resources. 1.2 COMPUTER AIDED MANUFACTURING (CAM): By introducing the computer the following factions are obtained in the manufacturing industries with less manual effort. 1. Planning 2. Managing and 3. Controlling the operations The computer interface with the plant resources either directly. Therefore, the applications of CAM can be broadly classified into two groups, 1. Computer monitoring and control 2. Manufacturing support applications
1. COMPUTER MONITORING AND CONTROL The computer is directly interfaced with manufacturing tool, for monitoring and control the functions in the manufacturing. The distinction between monitoring and control is shown in fig 1.1
Computer
Process Fig.1.1.a. Computer Monitoring
Process Data
Control Signals
Computer
Process Fig.1.1.b. Computer Control
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Fig.1.1. Computer Monitoring and Control 2. Manufacturing Support Application There are indirections, which deal essentially with the preparations for actual manufacturing and post manufacturing operations. In this, the computer is used “off-line� to provide. *
Plans
*
Schedules
*
Forecasts
*
Instruction and
*
Information
By which the resources are utilized more affectivity and economically, the symbolic representation for the CAM as shown in fig.1.2.
Computer
Manufacturing operations
Fig.1.2 CAM for Manufacturing Support The interrelation of CAM activities as shown in Fig.1.3. Factory Shop Floor
Process
Plant
Automatic Measurement & Testing
Quality Control
Materials Handling & Automated Assembly
Robotics Process & Plant Engineering M/c Tool Control Fig.1.3. Interrelation of CAM activities 1.3 HIERARCHY
Production
Material Requirement &
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The computer interface in the manufacturing unit, carried out the following functions, effectively,
Cost estimating
Computer Aided Process Planning
Machinability data system
Computer assisted NC part programming
Development of work standard
Production and inventory planning
Manufacturing control systems.
1. Cost Estimating: By using the computer system, the total expenditure for the new product, is calculated. For this, the material cost, overheads etc are considered.
2. Computer Aided Process Planning: Preparing a list of operation sequence required to process a particular component, root sheet preparation are done with the aid of computer.
3. Machinability Data: It is the information like speed ,feed etc for machining the component.
4. Computer Assisted NC Part Programming: Preparation of NC part program required for machining the component in NC machine using the computer.
5. Development of Work Standards: It is determination of time standard for a particular production operation by using computer.
6. Production and Inventory Planning: The computer determines an appropriate schedule for meeting production requirements.
7. Manufacturing Control Functions: The manufacturing control functions like process control, quality control, shop floor control and process monitoring are done by using computer.
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1.4 Elements of CAM system 1. Numerical control part program by computers. Control program are prepared for automated machine tools. 2. Computer –automated process planning. The computer prepares a listing of the operation sequence required to process a particular product or component. 3. Computer-generated work standards. The computer determines the time standard for a particular production operation. 4. Production scheduling. The computer determines an appropriate schedule for meeting production requirements. 5. Material requirement planning. The computer is used to determine when to order raw materials and purchased components and how many should be ordered to achieve the production scheduling. 6. Shop floor control. In this CAM application, data are collected from the factory to determine progress of the various production shop orders.
1.5 NC in CAM The control systems and machine tools in numerically controlled machine tools have varying complexities and capabilities. In the initial stages, the NC machine tools had NC systems added to the machine but only to control the position of the work piece relative to the cutting tool. The operator had to select the cutting tools, speed and feeds etc. in the next stages, the capabilities of the machine tools improved and in addition to maintaining cutter/workpiece relationship, the material removal was also controlled by the numerical control system. The mechanical design of the machine tool was also improved with the development of recirculation ball screw and better slide ways. These machines are referred to as NC machines. The instructions to the NC machines are fed through an external; medium i.e paper tape or magnetic tape. The information read from the tape is stored into the memory of the control system called ‘buffer storage’ and is processed by the machine step by step. So when the machine is working on one instruction block, the next block is read from the tape and stored in the memory of the machine control system. Since the part cannot be produced without a tape being run through the machine, these machines are also called tape controlled machines. The tape has to be run repeatedly depending on the number of
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components to be produced. Also if there is even a minor change in the design of the component, the tape has to be discarded and new tape with changed programme has to be produced.
1.6 Rational for CAD/CAM
The rational for CAD/CAM arises for the following reasons
To improve the production rate.
To upgrade the firm to manufacture the variety of jobs
It must able to give assembly list.
It must benefit shorter lead time
It must benefit group technology
It must benefit better scheduling
It must improve productivity in manufacturing.
1.7 Product development and design-Introduction
Product development and
design is an essential process made before
manufacturing a component. Effective product development and design is made to improve customer satisfaction and profit of the company. The product design may be made for a new product or for old product which need some improvement. Product design is achieved after getting feedbacks from customer and sales people. The following are the factors to considered for any product design. 1. Material of the product 2. Dimensions and tolerances 3. Appearance of the product 4. Standard of performance 5. Quality of the product.
1.8 Life Cycle of a Product A new product progresses through a sequence of stages from introduction to growth, maturity, and decline. This sequence is known as the product life cycle and
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is associated with changes in the marketing situation, thus impacting the marketing strategy and the marketing mix. The product revenue and profits can be plotted as a function of the life-cycle stages as shown in the graph below:
Introduction Stage In the introduction stage, the firm seeks to build product awareness and develop a market for the product. The impact on the marketing mix is as follows:
Product branding and quality level is established and intellectual property protection such as patents and trademarks are obtained.
Pricing may be low penetration pricing to build market share rapidly, or high skim pricing to recover development costs.
Distribution is selective until consumers show acceptance of the product.
Promotion is aimed at innovators and early adopters. Marketing communications seeks to build product awareness and to educate potential consumers about the product. Growth Stage
In the growth stage, the firm seeks to build brand preference and increase market share.
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Product quality is maintained and additional features and support services may be added.
Pricing is maintained as the firm enjoys increasing demand with little competition.
Distribution channels are added as demand increases and customers accept the product.
Promotion is aimed at a broader audience.
Maturity Stage At maturity, the strong growth in sales diminishes. Competition may appear with similar products. The primary objective at this point is to defend market share while maximizing profit.
Product features may be enhanced to differentiate the product from that of competitors.
Pricing may be lower because of the new competition.
Distribution becomes more intensive and incentives may be offered to encourage preference over competing products.
Promotion emphasizes product differentiation.
Decline Stage As sales decline, the firm has several options:
Maintain the product, possibly rejuvenating it by adding new features and finding new uses.
Harvest the product - reduce costs and continue to offer it, possibly to a loyal niche segment.
Discontinue the product, liquidating remaining inventory or selling it to another firm that is willing to continue the product.
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The marketing mix decisions in the decline phase will depend on the selected strategy. For example, the product may be changed if it is being rejuvenated, or left unchanged if it is being harvested or liquidated. The price may be maintained if the product is harvested, or reduced drastically if liquidated. 1.9 Product cycle Product cycle is to examine the various activities and functions that must be accomplished in the design and manufacture of a product. Fig shows the various steps in the product cycle. The cycle is driven by customer and markets which demand the product. It is realistic to think of these as a large collection of diverse industrials and consumer markets rather than one monolithic market. Depending on the particular customer group,there will be differences in the way the product cycle is activated . in some cases, the design functions are performed by the customer and the product is manufactured by a different firm. In other cases, design and manufacturing is accomplished by the same firm. Whatever the case, the product cycle begins with a concept, an idea for a product. This concept is cultivated,refined,analysed,improved and translated into a plan for the product through the design engineering process. The plan is documented by drafting a set of engineering drawings showing how the product is made and providing a set of specifications indicating how the product should perform.
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Product concept
customers and Markets
10
Design engineering
Order new equipment and tooling
Quality control
Production
Drafting
Process planning
Production scheduling
1.10 Simultaneous Engineering: It is a newly emphasized approach that considers design and development of a product concurrently with other related functions of manufacture and support. This approach considers all the factors at the outset e.g., quality, cost, maintenance and repair. It means product design engineering occurs simultaneously with process design engineering. So it yields best-results for both the product developers and consumers.
This approach is getting closer attention because of stringent demands for product quality and shorter times to market. In CIM environment, all relevant information required product design and manufacturing issues can be made available and can be considered simultaneously. Based on current practices, internal partners can work as a unified team from conception to completion of product as ultimate level of concurrent engineering. For implementing the approach of concurrent
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1.11 Design For Manufacturing And Assembly (DFMA)
The concepts of CAD/CAM are now quite mature and the modern industrial units have developed the capability in its widest scope, as such it becomes imperative that the concept of Design for Manufacturing (DFM) has been drawing more and more attention. To be competitive in today’s market-place requires a single engineering effort to integrate the process of design to the process of manufacturing. DFM is basically the integration of product-design activities and process-planning and manufacturing activities, i.e., one common integrated activity through Computer Integrated Process Planning (CAPP). The industry has recognized the fact that it cannot meet the requirements of quality at fairly priced product with isolated design and manufacturing activities.
In Non-CIM environment, the interaction between design and production functions has always been weak. There is not doubt that weak integration gives both the design and manufacturing departments sufficient flexibility and independence in achieving their own goals and objectives independently, but fail to achieve the common objective of quality-product at cost-effective price.
The matured concept of CAD/CAM and CIM-environment has forced the management and engineers to bring changes in their attitude primarily because in long run cost-effective improvement in the product quality are possible through improving the design. It is, therefore, obvious that in CIM-environment, the perfection in product-design cannot be considered without taking into account the manufacturing viewpoint.
Since computers can easily accommodate last minute changes made either in design or subsequently in process planning and production schedule, thus, perfecting the design becomes an easier process. So, the designer must pay more attention to the ideas and drawings from manufacturability point of view i.e., the so designed product can be produced with the available manufacturing resources and
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workforce
provided
detailed
information
on
12
the
capabilities
of
existing
manufacturing – resources is available.
The enormous power of CAD-CAM work station assists in integration of manufacturing resources and design-process to ensure best matching to the needs of customer. DFM emphasizes an easy integration of design and production functions in CAD/CAM environment. DFM simply reinforces the need that within the functional requirements of product, designers shall consider the manufacturability of their design.
Conclusively, it is intended that DFM integrates product-design, processplanning and manufacturing-resources with the objectives of: Identifying the products that are functionally sound and are inherently easy to manufacture. Focusing on component-design for ease of manufacture. Integrate product design with process design to achieve optimum results.
Looking to the complexities involved in the conceptual framework of DFM, it is still convenient to divide the concept of DFM into two components.
DFM guidelines are systematic and codified statement of good-designpractices empirically derived from years of design and manufacturing experience. Derived guidelines are to be strictly followed.
Derive a product with minimum number of parts to achieve higher reliability Develop modular design Minimize part variation Design the parts to achieve the following Design the parts of multi-functional and for multi-use Design the parts for easy fabrication and easy manufacturing (with the available resources). Avoid separate fasteners Minimize assembly direction i.e., design for top-down assembly Maximize compliance to design for easy assembly
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Design for easy handling and packaging.
In the broadest sense, the term DFM includes not only production but also the assembly of components. In plants, where Assembly is the major activity, there also DFM starts from production of components and goes well beyond it, to include assembling and other downstream functions. Such functions are designated as Design For Manufacture and Assembly (DFMA). This concept was developed by Boothroyd and Dewhurst. DFMA also aims to achieve high quality product; easy to use and affordable.
1.12 Rules for the design of parts
1. Design for function: The product designed should perform the various functions expected by the customers. The factors affecting the function of a product are its strength and durability. 2. Design for reliability The product design should work consistently without more troubles. It should function smoothly and efficiently for a long time. 3. Design for maintainability The product design should be easily and economically maintained for a long duration to satisfy the customers. The maintenance of the product should not be complicated.
4. Design for safety The product designed should ensure the safety of the customer. It should give minimum hazard to the customer and the environment. 5. Design for selling The product design should be attractive in appearance. The shape, size, colour of the product should enhance the aesthetic sense among the customer.
1.13 Total quality approach
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Quality is excellence which leads one firm’s product to dominate another and to guarantee its survival by establishing a new standard of quality. In this sense quality is a mark of excellence, persistence and maintained over long periods of time. Such excellence is, of course a function of habits, culture and values and may thus vary from person to person and from time to time. The concept and vocabulary of quality are difficult to express. Different people interpret quality differently. Few can define quality is measurable terms that can be operationalized. When asked what differentiates their product or service the banker will answer”service”, the health care worker will answer “quality health care”, the hotel or restarunt employee will answer “customer satisfaction”, and the manufacturer will simply answer “quality product”. There is an old saying in management which says” if you cannot measure it, you cannot manage it “, and so it is with quality. If the strategic management system and the competitive advantage are to be based on quality, every member of the organization should be clear about its concept, definition and measurement as it implies to his job. Harvard Professor David Garvin, in his book Managing Quality summarized five principle approaches to defining quality 1. Transcendent 2. Product based 3. User based 4. Manufacturing based 5. Value based
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UNIT-II
UNIT STRUCTURE
2.1 Machine tool control 2.2 Elements of the NC systems 2.3 Types of control systems 2.4 Co-ordinate system 2.5 Input devices 2.6 Punched tape 2.7 The NC procedure 2.8 NC part programming 2.9 Computer aided part programming
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2.1 Machine tool control In the numerically controlled machine table are dine automatically with the help of electric motors. For examples, in case of a CNC lathe the longitudinal and traverse movements of the tool are controlled by two motors fitted on the machine i.e. one for longitudinal movement and the other for traverse movement of the tool. In addition, the speed of the spindle motor is also controlled by the part programme. The machine may have a tool magazine, so that tool changing is done automatically. Also the other functions like machine ON/OFF, coolant ON/OFF, etc. are controlled through the part programme. The motors used for controlling the speed, feed and depth of cut are either servomotors or stepper motors which enable the user to select any desired speeds and feeds. 2.2 Elements of the NC systems An numerical control system consists of the following three basic elements 1. Program of instructions The program of instruction is the detailed step by step set of directions to tell the machine tool what to do. It is coded in numerical or symbolic form on some type of medium. The different input media are punched cards, punched tape, magnetic tape, and even 35 mm motion picture film. 2. Machine control unit(MCU) It consists of the electronics and control hardware that read and interpret the program of instructions and convert it into mechanical actions of the machine tool. The elements of control unit includes
Tape reader
A data buffer
Signal output channel to the machine tool
Feedback channels from the machine tool
Sequence control
Control panel
3. Machine tool. It is the part of the NC system which does useful work. The machine tool contains worktable, slides and spindles with separate individuals servomotors and controls to drive them independently. The different linear movement of the slides and spindles are specified with respect to the co-ordinate axis X, Y, Z. It also
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carries the cutting tool, work fixtures and other auxiliary equipments needed for the operation. 2.3 Types of control systems The different types of control system are, (i)
Point-to-point control system
(ii)
Straight line control system
(iii)
Continuous path or contouring control system
(i)
Point-to-point control system Point-to-point is one where accurate positional control is required only to place the machine slides in fixed position and the machine tool slide is required to reach a particular fixed coordinate point in the shortest possible time. The machining operations are performed as specific points and there is no machining while the machine table/slides move from one point to the next. No machining takes place until the machine slides have reached the programmed coordinate point and slide movement ceases. Since there is no machining when the machine slides move from one
point to other
point, all the slide movement are made in rapid traverse to save time. Also the path movement is not important but care must be taken to ensure that the cutting tool should not hit the workpiece while moving from one position to the next. The movement along different axis may be sequential or simultaneous and each axis is controlled independently. The simultaneous movement along the axis results in reduced cycle time. It is suitable for drilling, boring, tapping, punch presses and jig boring machines.
(ii)
Straight line control system Straight line or straight cut CNC system is an extension of point –to –point control system with the provision of machining along a straight line as in case of milling and turning operations. This is obtained by providing movement at controlled feed rate along the axis in the line of motion. It is possible to machine along diagonal lines with movement in two axis at a controlled feed rate. However, in such cases the control system must be
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capable of calculating and displacing the slides simultaneously at suitable feed rates to reach the desired points because in this case the feed rates along different axis will have to be different. (iii)
Continuous path or contouring system The contouring system is a high technology and most versatile control systems. The contouring system generates a continuous controlled motion of the tool and workpiece along different coordinate axis. This control system enables the machining of profiles, contours and curved surface. A system designed for continuous path machining can, of course, be used for point-to-point and straight line machining but that will result in under utilization of the system. In contouring system, the movement of several machine slides has to be controlled simultaneously so that their relative positions and velocities are established at every point and continuously throughout the operation.
2.4 Co-ordinate system
X
Z
X
Z
X Y
Y
Y
The purpose of the co-ordinate system is to provide a means for locating the tool in relation to the workpiece. In NC or CNC system it is necessary to CO-ordinate the tool in relation to the workpiece. To plan the sequence of positions and movements of cutting tool in relation to the workpiece it is necessary to establish a standard axis system by which the relative positions can be specified. The axis system are defined on the basis of three dimensional Cartesian co-ordinate system. Some co-ordinate positions are shown in fig. the +ve direction of the axes is arrived by using the right hand convention method.
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For drilling,milling,boring and similar machines the co-ordinate system of axes is established with respect to the machine table. Two axes ,x and y are defined in the plane of the table as shown in fig. The z axis is perpendicular to this plane and movement in Z direction is controlled by the vertical motion of the spindle. The +ve and –ve directions of motion of tool relative to table along these as shown in the fig. In addition to the three linear axes,these machines have three rotational axes. They are defined as A,B,C axes. These axes specify angles about the X,Y,and Z axes respectively. The +ve and –ve direction of rotation angular movement is fixed by right hand thumb rule.using the right hand with the thumb pointing in the +ve linear axis direction the fingers of the hand are curled to point in the positive rotational direction. 2.5 Input devices It consist of the electronics and control hardware that read and interpret the program of instructions and convert it into mechanical actions of the machine tool. The input devices are tape reader,a data buffer,signal output channel to the machine tool,feed back channels from the machine tool, sequence control and control panel.
2.6 Punched tape
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Punched tape is widely used for feeding the programme to numerical control systems. There are various types of paper tapes used in NC system but the standard format for tape size and configuration, issued by Electronic Industries Association of USA (EIA) and international standards Organization (ISO) , are universally accepted. A standard tape is 25 mm wide. The punched tape has capacity for storing 10 characters per 25 mm length. A punched tape is shown in fig. there are 8 tracks on the tape, which are used for punching the information in coded form. The edge adjacent to track 1 is called reference edge. A row of small holes between track 3 and track 4 is used for feeding the tape into the tape reader. The information required to machine the component is punched on the tape b a tape punching device.
2.7 The NC procedure To utilize numerical control in manufacturing, the following steps must be accomplished: Process planning The engineering drawing of the workpart must be interpreted in terms of the manufacturing processes to be used. This step is reffered to as process planning and it is concerned with the prepration of a route sheet.the route sheet is a listing of the sequence of operations which must be performed on the workpart along with the required machining data like speeds,feeds,depth of cut,tools used,etc. it is called a route sheet because it also lists the machines through which the part must be routed in order to accomplish the sequence of operations. Part programming: Part programmer plans the process for the portions of the job to be accomplished by numerical control.part programmers have knowledge about the machining processes and they have been trained to programme for numerically controlled machine tools. They are responsible for planning the sequence of machining steps to be performed by NC and to document these in a special format. There are two ways to develop programme for numerical control machines: 1. Manual part programming 2. Computer –assisted part programming.
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In manual part programming,the machining instructions are prepared on a form called a part programme manuscript.the manuscript is a listing of the relative cutter/workpiece positions which must be followed to machine the workpiece.in computer-assisted part programming , much of the tedious computational work required in manual part programming is transferred to the computer. This is especially appropriate for complex workpiece geometries and jobs with many machining steps.use of the computer in these situations result in significant saving in part programming time. Tape preparation: A punched tape is prepared from the part programmers process plan. In manual part programming, the punched tape is prepared directly from the part programme manuscript on a typewriter like device equipped with tape punching capability. In computer assisted part programming, the computer interprets the list of part programming instructions,performs the necessary calculations to convert this into a detailed set of machine tool motion commands and then controls a tape punching device to prepare the tape for the specific NC machines. Tape verification: After the punched tape has been prepared,some method is usually provided for checking the accuracy of the tape.sometime the tape is checked by running it through a computer programme which plots the various tool movements on paper. In this way,major errors in the tape can be checked.the “acid test� of the tape involves trying out on the machine tool to make the part.foam or plastic material is sometimes used for this try out. Programming errors are not uncommon, and it may require two to three attempts before the tape is supposed to be correct and ready to use.
Production: The final step in the numerical control procedure is to use the part programme in production. This involves ordering the raw workparts, specifying and preparing the tooling and any special fixturing that may be required and setting up the numerically controlled machine tool for the job. The machine tool operator’s function during production is to load the raw workpart in the machine and establish the starting position of the cutting tool relative to the workpiece. The numerical control system then takes over and machines the part according to the instructions
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on tape. When the machining of part is completed, the operator removes it from the machine and loads the next part.
2.8 NC part programming
PROGRAM WRITING: Data required for programming: To prepare the manuscript for manual part programming the programmer needs to collect the following data. 1. Machine tool specifications 2. Cutting tool specifications 3. Work measurements 4. Work material specifications 5. Speed, feed details 6. Sequence of operations
PART PROGRAM STRUCTURE:
The information contained in the program can be dimensional or nondimensional like speed,feed,auxiliary functions etc., The basic unit of a part program input to thecontrol is called a block. Each block contains adequate information for the machine to perform a movement and for functions. Block in turn are made up of words. Each word consists of a number of characters. All the blocks are terminated by the block and character.
A block may contains any or all of the following: Optional block skip(l) Sequence or block number (N) Preparatory functions(G) Dimensional information (x,y,z,A,B,C) Decimal point(.) Feed rate (F)
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Spindle speed (S) Tool number (T) Tool offset function(D) Miscellaneous functions (M,H etc.) End of block(EOB/*) 2.9 Computer aided part programming The manual part programming is a time consuming process and needs an expert part programmer who should have through knowledge of the various machining processes, materials, speed and feeds, part programming codes and capabilities of various machine tools.etc., Manual part programming is a labour oriented task and needs skilled programmers. Also, if a person is expert in programming one machine, he will not able to develop part programme for another machine, since the format or the type of information required by the two machines may be different. With the modern NC/CNC machines where more than three axes are to be controlled it may not be possible to develop part programmes by manual programming method. All these problems have been overcome and part programming has been considerably simplified with the use of computer aided part programming, where the computer generates the part programme required to machine the component. The process of generating part programmes in computer aided part programming is partly done by part programmer and partly by the computer. Advantages of computer aided part programming: (i) Part programming is considerably simplified. (ii) The part programmes generated are accurate and efficient (iii) All arithmetic calculations are done by the computer, resulting in saving in time and elimination of errors. (iv) The part programming for different machines can be done by a single person, which can then be post processed for specific machines. (v)
Such system can deal with many axes for simultaneous movement.
(vi) If new machines are added, only a post processor may be needed to integrate the new machines with the existing system. Computer aided part programming languages are APT and COMPACT II.
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UNIT-III UNIT STRUCTURE
3.1 Machining centres 3.2 Turning centres 3.3 CAD/CAM Integration 3.4 NC systems material handling 3.5 Automated Guided Vehicles
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3.1 MACHINING CENTRES These are very important types of CNC machines. They are multi functional machines. They are equipped with Automatic Tool Changer (ATC). They are capable of doing milling, drilling, reaming, tapping, boring, counter boring, and allied operations without operator help for changing the tools. Machining centres are classified according to the spindle configurations as
Horizontal spindle machining centres
Vertical spindle machining centres
Universa machining centres
HORIZONTAL SPINDLE MACHINIG CENTERS: Its configuration is shown in fig 3.1. These machines are generally single spindle machines.
These are bed type machines.
They are equipped with automatic tool changer.
In this type of machines
X- axis traverse is provided by table or column
Y-axis traverse is provided by spindle head.
Z-axis traverse is provided by saddle or column or head stock or spindle head.
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y-Axis servo motor +y Automatic Tool changer
Column
-y Spindle
-X
+X
Table
+Z -Z
Fig 3.1 These machines are used with rotary indexing table to do multifac machining at different angles in a single set up. The axis of rotary table is parallel to Y- axis and is called as ‘B’ axis.
VERTICAL SPINDLE MACHINING CENTRE:
Its configuration is shown in fig 3.2
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Z-axis servo motor Tool magazine Z
Spindle
Y X Table Fig 3.2
These machines are also bed type single spindle machines
These are equipped with ATC or multispindle with turret head
In this type of machines,
X- axis traverse is provided by table or column
Y-axis traverse is provided by spindle or column or ram.s
Z-axis traverse is provided by head stock.
These machines are used with rotary indexing table.its axis is parallel to X axis and is called as A axis. These machines are not suitable for large width job as this increase the throat distance. UNIVERSAL MACHING CENTRES These are similar to horizontal machining centres but with the spindle axis capable of tilting from horizontal to vertical position continuously under computer control.this constitutes the fifth axis of the machine. In some machines, it is possible to tilt the lable instead of spindle. The
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workpiece may be automatically loaded and unloaded. The fifth axis is essential for machining of some components which require the cutter axis to be perpendicular to the surface being machined. 3.2 TURNING CENTRES CNC lathe are called turning centers. They are generally classified as
Horizontal machines and
Vertical machines.
The horizontal turning centres are again classified as
Chucking machine
Shaft lathes
Universal lathes
HORIZONTAL CHUCKING MACHINE
They have shorter beds and single saddle.
They have drum type turret to hold ID and OD tools.
They have two axis control. One is Z- axis parallel to the spindle. Another is X-axis perpendicular to the axis spindle.
Now a days, there is chucking machines with two turrets one for ID and other for OD.
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SHAFT LATHES
It is intended mainly for between centre work
They have hydraulic or pneumatic operated tailstock and roller studies for supporting the work piece. Tooling is mainly for external working.
They have two axis controls , one is Z-axis parallel to the spindle. Another is X-axis perpendicular to the spindle axis.
UNIVERSAL LATHES These machines are suitable for both chucking and for bar work. A 4 axis machine has two turrets. Each turret is mounted on an independent slide. This helps to do maching with two tools. Some lathes have rotating tools in the turret. This is used for drilling, milling, reaming, taping, and boring etc. these machines have in addition to the conventional X and Z axis. CNC control of the spindle rotation i.e., C axis.
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VERTICAL CNC LATHES: These are widely used for machining heavy jobs. Some of thes machines can also be used for milling operations. TOOLING SYSTEM IN CNC LATHE Turning centers have turret heads with the capacity of 8 to 16 tools for tooling. On receiving tool change command from the program, turret moves to a fixed tool change position and then the required tool (numbered tool) comes to the cutting position by the rotation of turret head. Some machines have two turret heads, one for external working tools and the other for internal tools. Some machines have an automatic tool changer with outstation tool magazine and a tool clamping arrangement on a slide. 3.3 CAD/CAM INTEGRATION
Geometric Modelling
Tool and fixture design
Engineering Analysis
Numerical control programming
Data base
Interactive Graphics Design review and evaluation
Computer aided process planning
Production Automated Drafting
Production planning and scheduling
INTEGRATED CAD/CAM ORGANISATION
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In the conventional manufacturing cycle, design activities were separated from manufacturing activities. Engineering drawings were prepared by the design people and were supplied to production department. The manufacturing people should study the drawing and prepare data to plan, manage and control the manufacturing. It is actually a two step procedure. That is both time consuming and involved duplication of effort by design and manufacturing personals. To avoid this drawback, the integrated CAD/CAM is established. In the integrated CAD/CAM system, a direct link is established between product design and manufacturing. The aim of this system is not only to automate certain phase of design and certain phase of manufacturing, but also to automate the transmission of data from design to manufacturing. The integrated CAD/CAM organization is shown in fig. The CAD creates the document of the model and database contains geometry
data,bill
of
materials,partslists,material
specification
etc.
this
is
automatically transformed to CAM systems for its activities.
3.4 NC SYSTEM S MATERIAL HANDLING The numerically controlled machines are capable of performing a number of operations using different tools, on different faces of a component in a single setting. This requires that the component should be accessible from different sides without changing of clamps or re-positioning of component. The work holding device has to bear multidirectional cutting forces. So additional demands are made on work holding devices in numerically controlled machine tools. To reduce the clamping/unclamping time, hydraulic and pneumatic actuation is widely used in work holding devices. In general, awork holding device for CNC applications should have the following features: 1. It should restrict the linear and rotary motion of the component. 2. It should facilitate quick loading and unloading of the component.
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3. It should be fool proof i.e. it should ensure that component cannot be loaded wrongly. 4. It should not interfere with the cutting tools. 5. It should permit number of operations on different planes in a setting. 6. It should provide for easy removal of chips. 7. It should be adaptable to automated loading or unloading of components. 8. It should be safe.
3.5 Automated Guided Vehicles It is an independently operated self-propelled vehicle guided along defined pathways in the floor.it is normally powered with batteries. The material handling system using AGV is known as automated Guided Vehicle System(AGVS). In this material movement takes place automatically and also there is interfaces with other automatic systems to form an Integrated Material Handling System. AGV components/working of an AGV For the functioning of an AGV it contains the following as its components. 1. Vehicle guidance and routing components. 2. Traffic control and safety components. 3. System management components.
Vehicle guidance and routing components Guidance system: it refer to the method by which the AGVS path. This wire is supplied with electric signal which creates a magnetic field along the path.sensing this magnetic field by the corresponding sensors in the AGV,AGV follows the path independently .it is shown in fig.
In the paint strip method,suitable paint is painted along the AGVS path. The optical sensor available in the AGV senses this path and moves independently.
There are microprocessor control systems provided in the AGV to avoid its moving away the path and collision.
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Routing system: it is concerned with the problem of selecting the correct path among the alternative paths available to a vehicle(eg. From a junction point) .There are two methods avaible for this. i)
Frequency select method-current in the different paths will be of different frequencies
ii)
Path switch select method-current in the other parts will be switch off.
Traffic control and safety components Traffic control:it relates to the prevention of collision between vehicles traveling along the same path.it is done by a Block control system. This blocking system works in two ways. i)
Using on-board vehicle sensing devices to sense the presence of vehicle ahead.
ii)
Zone blocking: Here,the AGVS path layoutis dived into number of zones. Entering of one vehicle to a zone which is already with another vehicle will be avoided.
Safety: It relates the collision of vehicle on human being who is on the way. It is also possible by suitable sensors on the AGV or some bumber like thing in front of the AGV to touch and feel the presence of human being to stop the vehicles. Also there may be warning signals from the AGV. 3.System Management: It relates to the moving of an AGV to the exact to the exact point of dispatch or delivery at the correct time of need.it is possible with the following.
i)
Providing with on-board control panels on the AGV itself
Each guided vehicle is equipped with some of 0n-board control panel. It serves the purposes of manual vehicle control,vehicle programming and other functions. It gives flexibility to cope with the changes and variations in delivery requirements. ii)
By using remote control call stations
This arrangement help to call the nearest available AGV to the load/unload point at the time of requirements.from that point it is moved to the dispatch station using on-board control panel facility. Some remote controls have the facility to
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programme the dispatch while the AGV is called to the load/unload point. It leads to an automated system of dispatching.
iii)
By using computer control
This arrangement helps automatic vehicle dispatching as per preplanned schedule of pickups and deliveries and/or in response to call form the various load/unload stations. It gives a full flexible AGV system. AGV benefits: 1. Flexibility:path of AGV can be easily altered or modified. 2. Real time monitoring and control: Computer controlled AGVS are closely watched and whenever required same may be called for urgent needs. 3. Good safety: It is safe because of its low speed, sensor capacity and warning arrangements. 4. Good maintenance: It has the provision of advance indication of faults and so maintenance becomes easy. 5. Best suitable for programmable automation and FMS.
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UNIT-IV UNIT STRUCTURE 4.1 Group technology 4.2 Part families 4.3 Part classification and coding 4.4 Coding system 4.5 Facility design using GT 4.6 Benefits of GT 4.7 Computer Aided process planning-Introduction 4.8 Role of process planning 4.9 Implementation techniques process planning systems 4.10 Benefits of CAPP 4.11 Advantages 4.12 Master production scheduling 4.13 Material requirements planning (MRP) 4.14 Manufacturing resource planning (MRPII) 4.15 Capacity planning
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4.1. GROUP TECHNOLOGY [G.T] Group technology (GT) is a manufacturing concept in which similar parts are identified and grouped together in parts groups or parts families to take advantage of their similarities in manufacturing and design. By grouping similar parts into families, manufacturing personnel can improve efficiency. GT can also improve the productivity of design personnel by decreasing the amount of work and time involved in designing new parts by simple modifying the design of the already existing part. 4.2. PART FAMILIES: A part family is a collection of parts which are similar either because of geometric shape and size or because similar operation steps are required in their production. The part family concept is central to design - retrieval systems and most computer – aided process schemes. The parts which are similar in their design characteristics are grouped in a family referred to as a design part family. Fig 4.1. The parts which are similar in their manufacturing characteristics are grouped in a family referred to as a manufacturing part family Fig. 4.2. The characteristics used in classifying parts are referred to as “attributes”.
Materi : Steel
Materi : A1
Tolera : 0.2
Tolera : 0.55
Finish
: Two coats primer
Finish
: sand & buff
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Fig 4.1 Design Part Family The figure 4.1. and 4.2. are the good example for part family concept. The above two parts design characteristics (attributes) are same, because they have mostly the same shape and size.
Fig.4.2. Manufacturing Part Family Material - CI Tolerance
Material - CI - ď‚ą 0.5
Tolerance
- ď‚ą 0.5.
Hence, these two parts are represented as design part family. Also these parts are manufactured by different process. The above two parts are different in size and shape but these two parts may be machined in the shaping machine because of the similarity in manufacturing characteristics. Hence, these parts are coming under the manufacturing parts family. Also, in the figure 4.3. the parts are shown with different in design attributes and similar in manufacturing attributes.
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Fig 4.3. Parts with Similar manufacturing process requirement but different design attributes
The main advantages of grouping parts into families is explained with reference to fig. 4.4.
Fig. 4.4 shows a process type layout for batch production in machine shop. The various machine tools are arranged by their functions as lathe section, milling machine section, drilling machine section and so on. During machining the parts has to move between these sections repeatedly several time. This results to the greater amount of material handling large in process inventory, more setup time, longer lead times, high cost etc.
Fig 4.4. Process Type Layout
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Fig . shows a production shop of same capacity as above. But here the machines are arranged in cells. Each cell is organized with machines required to manufacture parts of a particular families. It gives the advantages of reduction in material handling, less in process inventory, lower setup time, shorter lead time, low cost, less floor area etc.
4.3. PARTS CLASSIFICATION AND CODING SYSTEM: Parts classification and coding is a method in which the various design and / or manufacturing attributes of parts are identified, listed and assigned a code number. Three types of parts classification and coding systems are available. 1. System based on Part Design Attribute: It is used for design retrieval and to promote the design standardization.
2. System based on part manufacturing attributes: This method is useful for computer-aided process planning, tool design and other production related functions.
3. System based on both design and manufacturing attributes: In this, both design and manufacturing attributes are considered. 4.4. CODING SYSTEMS: The coding system widely used are, 1. The CODE system (Manufacturing data systems) - 8 digit hexadecimal semi poly code. 2. TNC (Brixsch – Birn Type developed for General motors) - 6 digit mono code 3. D CLASS (Design and Classification information system) - 8 digits hybrid code 4. MICLASS -12 digits decimal poly code
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5. OPTIZ (Dr. H. Opitz, Aachen, West Germany) -9 digit decimal semi – polycode version 6. The K.K.-3 system 7. CUTPLAN 8. Multi Class 9. Part Analog System 10. Brisch system
1. THE CODE SYSTEM:
The CODE system has 8 digits. For each digit
there are 16 possible values (0 to 9 and A to F) which are used to describe the part’s design and manufacturing attributes.
The initial digit position indicates the basic geometry of the part and is called the major provision of the CODE system. This digit would be used to specify whether the shape was a cylinder, flat piece, block or other. The interpretation of the remaining seven digits depends on the value of the first digit, but these remaining digits form a chain type structure. 1. Digit : Specifies the basic structure of the part either cylinder, flat piece or block etc. nd
2. 2
rd
and 3
digit: Basic geometry and principal manufacturing process of the
part. th
th
th
3. 4 , 5 and 6 digits:
Secondary manufacturing process e.g., threads,
grooves, slots etc. th
th
4. 7 and 8 digits: Overall size of the part. 2. MICLASS SYSTEM (Metal Institute Classification): The MICLASS system has the number range from 12 to 30 digits. The first 12 digits are universal code that can be applied to any part. UP to 18 additional digits can be used to code data that are specific to the particular company or industry. For example, lot size, piece time, cost data and operation sequence might be included in the 18 supplementary digits. The attributes of first 12 digits are given below: st
1 digit nd
Main shape rd
2 and 3 digit Shape elements
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th
4 digit th
41
Position of shape elements th
5 and 6 digits Main dimensions th
7 digits
Dimension ration
th
8 digits th
Auxiliary dimension th
9 and 10 digits th
th
11 and 12 digits
Tolerance codes Material code
The unique features of the MICLASS system is that parts can be coded using a computer interactively. To classify a given part design, the user responds to a series of questions asked by the computer. The number of question depends on the complexity of the part. On the basis of the response to its questions, the computer assigns a code number to the part. 3. DCLASS CODING SYSTEM: The DCLASS part family code is comprised of eight digits partitioned into five code segments as shown in figure. Basic Shape
B
1
Form Feature
1
2
Size
Precision Material
3
4
A
1
The first segment, composed of three digits, is used to denote the basic shape. The form feature code is entered in the next segment, it is one digit in length. This code is used to specify the complexity of the part, which includes features (such as holes and slots) heat treatments and special surface finishes. 4. The OPTIZ coding system: In this system alphanumeric symbols are used to represent the various attributes of a part. The optiz system uses characters in 13 places to code the attributes of parts and hence, to classify them. The digits places are represented as follows. The form code represent the design attributes The supplementary code represents the manufacturing attributes The secondary code represent the process type.
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12345
6789
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ABCD Secondary Code Supplementary Code Form Code
4.5 Facility Design using GT Design of the machine cell is critical in cellular manufacturing. The performance of a GT cell
depends on its design. An effective cell design is
governed by the following. 1. Types of machine cell a) Single machine cell b) Group machine cell with manual handling c) Group machine cell with semi-integrated handling d) Flexible manufacturing system
2. Cell layout a) U –shape layout b) In-line layout c) Loop layout d) Rectangular layout 3. Key machine concepts 4.6 BENEFITS OF GT: 1. GT provide the manufacturing feed back 2. It helps to reduce part proliferation and cost estimation. 3. It reduces the lead time, production delays, and set up times. 4. It improves the material handling system, communication, product quality and production supervision. 5. It is used in process selection, tool selection and material flow. 6. It helps to bring new technology to the attention planners by automatically offering newly acquired equipment. 7. It is used in production control for group scheduling, stock accounting and WIP inventory purpose.
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8. Reduces design duplication. 9. Facilitates NC part programming 10. Provides for better machine tool utilization 11. Reduce design duplication.
4.7. COMPUTER AIDED PROCESS PLANNING : The process planning contains the following activities Selection of Process Selection of operations sequences Selection of machines and tools Selection of work holding devices, jigs and fixtures Determination of grouping of operations Determination of cutting parameters and tolerances Selection of gauges and inspection inertia Selection of time standard and setup time
Mostly these that information are collected by the person, hence this activity is called as manual process planning.
It is obvious process planning can be a very complex and time consuming job requiring a rage amount of data. In addition. if different planners were asked to develop a process plan for the same part, they would provably come up with different plans, with no. optimum method for manufacturing the part.
To eliminate the limitations of process planning, computer aided process planning (CAPP) is used to rationalize the process.
4.8 Role of Process Planning Process planning is concerned with determining the sequence of individual operations needed to produce a given part or product. CAPP accomplishes the following three functions with the help of computer. 1. Planning the process 2. Determining the cutting conditions and
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3. Setting the time standards. A CAPP system offers the potential for reducing the routine clerical work of manufacturing engineers. At the same time it provides the opportunity to generate production routings which are rational, consistent and perhaps even optimal. 4.9 Implementation techniques process planning systems Two techniques to CAPP are traditionally recognized. The variant approach and the generative approach. Many CAPP systems combine both approach. Variant CAPP system: The variant approach to process planning is comparable with the traditional manual approach where a process plan for a new part is created by recalling, identifying and retrieving and existing plan for a similar part and making the necessary modifications for the new part.
User enters part code No.
Process plan
Part Family search
Part family Matrix File
Standard Machine Routing Retrive
Machine Routing File
Standard operation Retrive
Operation sequence File
Process plan for matter
Other application Programs
Fig Variant CAPP System
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In some variant systems parts are grouped into a number of part families, characterized by similarities in manufacturing methods and thus related to group technology. For each family, a standard process plan, which includes all possible operations for the family is stored in the system. Through classification and coding, a code is built up by answering a number of predefined questions. These codes are often used to identify the part family and the associated standard plan. The standard plan is retrived and edited for the new part. The variant approach is widely used(e.g.) CAPP,MIPLAN. Advantages of variant CAPP 1. It increases the information management capabilities. 2. It requires less time and less labour for complicated activities. 3. It is incorporated with planners manufacturing knowledge. 4. In this system,process plan can be quickly evaluated. 5. It has a structure for the companies specific needs. 6. The investment is less and development time is shorter. 7. The development costs and hardware costs are lower. Generative CAPP system: In the generative approach, process plans are generated by means of decision logies,formulae,technical algorithms and geometry based data. The rules of manufacturing and the equipment capabilities are stored in a computer system. When using the system, a specific process plan for a specific part can be generated without any involvement of a process planner. For generative system, input can come either a text, input where the user answers a number of questions in English or English-like dialogue or as graphic input. This type of system is mostly oriented toward large project.especially for companies which have a number of products in small lot sizes, the generative approach is attractive.
4.10. Benefits of CAPP Several specific benefits can be expected in the planning department implementation of computer aided process planning. ď ś Fewer calculation error due to human error.
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Reduced clerical effort in preparation of instructions. Use of the latest revisions of part drawings. More-detailed, more-uniform process plan state me produced by word processing techniques. More effective use of inventories of tools, gauges, fixture and a concomitant reduction in the variety of the items. Immediate access to up-to-data information from a center database. More retailed, more uniform process plan steam produced by would processing techniques.
4.11. Advantages 1. Reduces the process planning time. 2. Reduces the skill required of a planner. 3. Reduces the process planning and manufacturing cost. 4. Creates more consistent plans. 5. Increase Productivity.
4.12. MASTER PRODUCTION SCHEDULE (MPS) The master production schedule is a macro level documents which sets top-level priorities for what will be manufacturing and when, looking at the material requirement from the MPS provide greater flexibility in reelecting the over production plans of management in a dedicated production schedule, allowing planning production to be on prelisted demand. The MPS has several important uses: 1. It is used, to Co-ordinate the activities mark engineering manufacturing and fiancé. 2. It is used to control the plant facilities, equipment vendors and costs. 3. To balance the customer needs with plant capacities 4. It specifics the part to be made. 5. It reduces the long lead time. 6. It general format of a MPS is shown in fig. Week Number
8
9
10
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Product P1
50
Product P2
60
Product P3
60
Product P4
75
47
100 25 90 100
Etc Fig. Master Production Schedule 4.13 Material Requirements Planning (MRP) MRP is a computational technique that converts the master schedule for end products into a detailed schedule for the raw materials and the components used in the end products. The detailed schedule indicates the quantities of each raw material and the component items. It also tells when each item must be ordered and delivered so as to meet the master schedule for the final products. MRP is an effective tool for minimizing unnecessary inventory investment and also useful in production scheduling and purchasing of materials. MRP is an appropriate technique for the inventory control of dependent demand items. 4.14 Manufacturing Resource Planning (MRP II) It is the improved form of MRP(Material Requirement Planning).MRP was strictly a materials and part planning tool and its calculations based on the MPS(Master Production Schedule). The introduction of computers to the manufacturing system neds linking of MRP with different software packages of computer intergrated production management system. The software packages of MRP thus developed is known as MRP II (Manufacturing Resource Planning II).
The Manufacturing Resource Planning(MRP II) is defined as a computerbased system for planning, scheduling and controlling the materials,resources and supporting activities needed to meet the MPS. MRP II is a “closed loop system� that integrates and coordinates all of the major functions of the business including financed to produce. The term right products at the right time. Closed loop system means the inclusion of feedback mechanism of various aspects of the MRP II. That is, MRP II is a shop floor control system. Following are the applications of MRP II system:
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Management planning: It includes the functions such as business stategy, aggregate production planning, master production scheduling, rough 窶田ut capacity planning and budget planning. Customer service: It includes sales forecasting order entry, sales analysis and finished goods inventory. Operation planning: This is the MRP with the addition of capacity planning activity. Operation execution: It includes purchasing , production, scheduling and control,WIP (Work in Progress) inventory control, shop floor control and labour hour tracking. Financial functions: It includes cost accounting, accounts, receivable, account payable, general ledger and pay roll. 4.15 Capacity Planning It is concerned with determining what labour and equipment capacity is required to meet the current master production schedule and future production needs of the firm. Capacity planning is typically performed interms of labour and machine hours available. The master schedule is transformed into material and component requirements using MRP. Then these requirements are compared with the available plant capacity. If the schedule is incompatible with capacity, adjustments must be made either in the master schedule or inplant capacity. Capacity adjustments can be accomplished in either the short term or the long term. For short term adjustments, decisions on the following are needed. 1. Employment level. 2. Number of work shifts. 3. Labour over time. 4. Sub contracting 5. Inventory stock pilling. 6. Order backlogs.
Long term capacity requirements include the following decisions:
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1. New plant construction. 2. New more productive modern m/c’s 3. Purchase of existing plants from other companies. 4. Selling off existing facilities which will not be needed the future.
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UNIT-V UNIT STRUCTURE
5.1 Introduction 5.2 Functions of SFC 5.3 SFC system 5.3.1 Order release 5.3.2 Order scheduling 5.3.3 Order progress 5.4 Advantages of scheduling 5.5 Just In Time manufacturing-Definition 5.6 JIT approach 5.7 JIT Elements 5.8 JIT work effects of JIT production 5.9 Benefits of JIT 5.10 FMS: Introduction 5.11 Elements 5.12 Classification system for FMS 5.13 FMS workstations 5.14 Material handling equipments 5.15 Computer control system 5.16 Applications of FMS 5.17 Benefits of FMS 5.18 Concepts of CIM 5.19 Elements of CIM 5.20 CIM hardware & software 5.21 Introduction to intelligent manufacturing system.
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5.1 SHOP FLOOR CONTROL SYSTEM-INTRODUCTION Production management systems are concerned with planning and control of the manufacturing operations. The functions of production planning, development of the master schedule, capacity planning and MRP all deal with the planning objective. Systems that accomplish the control objective are often referred to as “Shop Floor Control” (SFC) 5.2 Functions of SFC The functions of a SFC system are: 1. Priority control and assignment of shop orders. 2. Maintain information on work-in-process for MRP. 3. Monitor shop order status information. 4. Provide production output data for capacity control purpose. 5.3 SFC system The factory-wide information control system is shown in fig 5.1. The input of the SFC system is the collection of production plans. A typical SFC system consists of three phases: 1. Order release 2. Order scheduling 3. Order progress.
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52
MASTER SCHEDULE ENGG/MFG DATA BASE MRP, CAPACITY PLANNING
SHOP FLOOR CONTROL
RAW
FACTORY PRODUCTION OPERATIONS
FINISHED PRODUCTS
MATERIALS
FIG 5.1 1 .Order release: The order release phases of SFC provide the documentation needed to process a production order through the factory. It consists of: Material requisition Route sheet Job cards Move tickets Part lists 2. Order scheduling: The order scheduling module assigns the production orders to the various work centres in the plant. It executes the dispatching function in production planning and control.
It is used to solve two problems in production control 1.
Machine loading and 2. Job sequencing. Allocating the orders to the work centre s is named as machine loading. Determining the order in which the jobs will be processed through a given work centre. To determine the sequence, priorities has to be fixed. Priority rules are: Earliest due data Shortest processing time
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Least slack time Critical ratio Slack time: it is defined as the difference between the time remaining until due to the process time remaining. Critical ratio: it is defined as the ratio of the time remaining until due date divided by the process time remaining. 3.Order progress: The order progress module monitors the status of the various orders in the plant,work-in-process etc., its function is to provide information that is useful in managing the factory based on data collected from the factory. The various information reports are: Work order status reports Progress reports and Exception reports 5.4 Advantages of Scheduling 1. Machine idle time is reduced 2. Labour idle time is minimised 3. There is no slack in the work movements 4. Every operations should be carried out in the specified m/c in correct time with correct quantity. 5. Plant capacity is optimized. 5.5 Just in time manufacturing-Definition Just in time is an operations management philosophy. JIT means that the right number of parts would be delivered to the right shop floor operation at the tight time. It is also defined as the methodology by which, the overall productivity of plant is increased by eliminating the waste. 5.6 JIT approach The secret of JIT success lies in the following factors: 1. Workers co-operation and devotion to work. 2. Strict adherence to time schedule of various activities. 3. Competitive production cost. 4. Stringent quality control 5. Use of information system called Kanban.
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JIT seeks to design the manufacturing system to optimize the production 100% good unit.
5.7 JIT elements The basic elements of the JIT philosophy are 1. Flow layout 2. Mixed model scheduling 3. Small lots and minimum set up times 4. Buffer stock control 5. Quality 6. Production and process simplification 7. Preventive maintenance 5.8 JIT work effects of JIT production JIT begins with a master schedule drawn for one to three months. This is communicated to the production personnel on the shop floor and to the suppliers, with in the production month, the master schedule is levelled on daily basis. This is done by identifying the products into runners, repeaters and strangers. These terms reflecting the volume and frequency of decreased runners denotes high volume products and strangers denote occasionally produced products. 5.9 Benefits of JIT 1. Productivity improvement 2. Set-up time reduced 3. Inventory reduction 4. Quality is improved 5. Space savings 6. Lead time reduction 5.10 Flexible Manufacturing System (FMS) A flexible manufacturing system (FMS) is an individual machine or group of machine served by an automated material handling system, that is computer controlled and has a tool handling capability. The key element necessary for a manufacturing system to quality as an FMS are as follows 1. Computer control 2. Automated material handling capability
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3. Tool handling capability The objectives of FMS are 1. To have a good management control 2. To maximize the utilization of resources 3. To provide flexibility in producing small and medium batch type parts 4. To improve the grouping of operations in the workstation 5. To provide flexible manufacturing ability for part family components 5.11 Elements of FMS The FMS consists the following components to evaluate the manufacturing flexibility 1. Work station 2. Load and unload stations 3. Work places transport equipment 4. Pallets 5. Fixtures 6. Tool transport 7. Robots 8. Buffer storage at workstations 9. Fixtures 10. Other storage facilities 11. Human operators 12. Computer control system WORK STATION The work stations vary according to the type of parts being produced. Mostly NC and CNC are used in the FMS. Similarly other types of processing equipments like inspection station, washing machines, single purpose machine etc., are used in the FMS. LOAD AND UNLOAD STATIONS Parts have to be introduced into the system at some point and there are usually load and unload stations, where parts are placed on pallets, usually by human operator.
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WORKPIECES TRANSPORT EQUIPMENT Work pieces must be transported from the load positions to the productive equipment and back of unloading. Three types of equipments are in common use namely, conveyors, vehicles and robots. PALLETS Work pieces are normally held in pallet of some sort for transport and locating on machine tables. Two types of pallets are commonly used. One type of pallet is used for carrying a batch of small parts and other type is used for the single or more parts are accurately located purpose. FIXTURES Fixtures are used to locate the parts precisely on pallets. Several type of part may be sufficiently similar to make use of the same fixture, the fixtures may permanently bolted on the pallets or they may be removed from the pallet when a part requiring a different fixtures. TOOLS Most operation requires some form of tooling specific to the particular operation being performed. Machining centers have tool magazines in which a set of tools can be held so that operation on work piece can be performed.
TOOL TRANSPORT The supply of tools to the machine may be done manually, but more recent systems include a tool transport system as well as a work piece transport system. Robots are frequently used as part of tool supply operation. ROBOTS Robots may be either stationary of mobile. There are several types of mobile robots, principally mounted on the floor or on rails. BUFFER STORAGE AT WORKSTATIONS Most system includes some form of buffer storage at work stations. This permits work piece to be brought to a machine while it is operating on the previous part. HUMAN OPERATOR Operator may be required to do the following activities
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Loading and unloading the parts
Tool preparation Clearing faults
System monitoring Operating the computer
CONTROL COMPUTER The basic functions of a control computer are to give instructions to the machines and transport devices, so that the parts are moved and processed as required. 5.12 Classification system for FMS 1. Random FMS 2. Dedicated FMS 3. Engineered FMS 4. Modular FMS 5.13 FMS work stations There are various types of machines are used in the FMS workstations 1. Machining centres 2. Head changers 3. Head indexers 4. Milling module 5. Turning module 6. Assembly workstation 7. Inspection stations 8. Sheet metal processing machines 9. Forging stations MACHINING CENTRES A machining centre is a multipurpose CNC machines tool that has an automatic tool changing capability. Machining centres have multi-axis and can be operated alone, as part of FMS. END CHANGER It is a special machining tool with the capability to change tool heads. The tool heads are usually multiple spindle tool modules that can be stored in a rack or
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drum. Located on or near the machine, they are used to perform simultaneous multiple drilling and related machining operations on a workpart
HEAD INDEXERS It is similar to the head changer except that the tool heads are larger enough to permit them to be moved in between the spindle drive and the tool storage location. MILLING MODULE These are special milling module and to achieve higher production levels than a machining centres. The milling module can be horizontal or vertical with multispindle. TURNING MODULE The turning modules are designed to rotate the finger print tool around the work. This is used when the parts made on FMS are held in a pallet. ASSEMBLY WORKSTATIONS Flexible automated assembly systems are used for products made in batches. Industrial robots are most appropriate for this purpose. INSPECTION STATIONS Inspection can be incorporated in to a FMS, either by including an inspection operation at a given work station, CMM, special inspection probes and machine vision on a FMS.
SHEET METAL PROCESSING MACHINES It consists of punching, shearing, bending, and forming operations
FORGING STATIONS It consists of a heating furnace, forging press and trimming stations. 5.14 Material Handling Equipments The material handling equipments used for various FMS layout are given in table. Either automatic storage or retrivel system is used for storage.
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S.No
Layout
Material handling system
1.
In-line
Conveyor and shuttle system
2.
Loop
Conveyor system
3.
Ladder
Conveyor system AGV’s
4.
Open field
AGV’s
5.
Robot centered cell
Robots
Material handling and storage system (MHSS) MHSS deals with 1. Functions of material handling system. 2. FMS layout. 3. Material handling equipment. 4. FMS material storage. 1. Functions of material handling system: MHSS in a FMS should perform the following functions. Random movement of work parts between workstations. The parts must be capable of moving from any one machine in the system to any other machine. 2. Handle a variety of workpart configuration: Pallets and fixtures are used to transfer prismatic (cube, prism) parts. Robot is used to transfer rotational parts (cylindrical and spherical) 3. Temporary storage: Each machine in FMS must have a queue of parts to be processed to increase the machine utilization. Such parts are temporarily stored. 5.15 Computer control system The operation of a FMS is computer controlled. The various functions to be performed by the computer control are:
Control of each workstations
Distribution of control instruction to workstation
Production control
Traffic control
Shuttle control
Work handling system monitoring
Tool control
System performance monitoring and reporting
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5.16 Application of FMS Some of the applications of FMS installations are in the following areas 1. Machining works 2. Assembly works 3. Sheet metal- press working 4. Forging 5. Plastic injection moulding 6. Welding 7. Textile-machinery manufacturing
5.17 Benefits of FMS 1. Reduced cycle time 2. Decreased direct and indirect labours costs 3. Reduced work-in process inventory 4. Higher machine utilization 5. Flexibility within a family of parts 6. Lower manufacturing lead times 7. Improved product quality 8. Reduced space requirements 9. Reduced number of tools and machines required 10. Quicker response to market change.
5.18 Concepts of CIM Computer Integrated Manufacturing (CIM) is a management philosophy in which the functions of design and manufacturing are rationalized and coordinated using computer, communication and information and technologies.
CIM includes all of the engineering functions of CAD/CAM but it also includes the business functions of the firm as well. The ideal CIM system applied computer technology to all of the operational functions and information processing function in manufacturing from order receipt, through design and production to product shipment.
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Sequence of functions in CIM: The component of the integrated computer system is shown in fig. Customer orders are centered into a computerized order-entry system. The order with part specifications is fixed into product design department. In which, the new product is designed in the CAD system. In the CAD system, the Bill of materials, detailed part drawings and assembled drawings are created. The document from the design department (CAD) serves as input to the manufacturing engineering. In this process planning, tool design and similar activities are accomplished to prepare for production. The manufacturing activities are carried out by using the computers. The output from manufacturing engineering provides the input to the production planning and control, where the materials requirements planning and scheduling is performed using the computer system. 5.19 Elements of CIM The CIM system has the following five important elements such as 1. Product design 2. Production planning 3. Production control 4. Production equipment and 5. Production process These elements must be integral part of the manufacturing system to be automated, optimized and integrated by applying the computer. 1. Product design: It is the initial database for production of a proposed product. In a CIM system, this is accomplished through activities such as geometric modelling and CAD. The cost constraint and the capabilities of existing production equipment and processes must be kept in mind during the design process. 2. Production planning: It takes the data based established by product design and enriches it with production data and information to produce a plan for product production.
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The cost incurred and production equipments capabilities should be key consideration for generating an optimized plan. 3. Production control: This requires further enrichment of the data base with performance data and information about the production equipment and process. In a CIM system, this requires activities such as modelling,simulation and computer aided scheduling of the production activity. 4. Production equipment: Production equipment further enriches the data based with equipment and process data and information,resident either in the operator or equipment to carry out production process. In CIM system, the equipment consists of computer controlled process machinery such as CNC machine tools, FMS, Robots, AGVs etc.,
5. Production process: Production process, that creates the finished products are carried out by production equipment. This is done under the guidance of the data, information and knowledge resident in the operator. In a CIM system, these process consists of material removal , material forming, etc., accomplished by the computer.
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Marketing
Product Design
Information
Planning CIM
Finance
Purchase Warehousing Manufacturing Automated work Centre
Major elements of CIM system 1.20 CIM hardware and software CIM hardware comprise the following 1. Manufacturing Equipments (i)
workstations
(ii) cells (iii) DNC/FMS (iv) Work handling &tool handling device (v) Storage device (vi) Sensors 2. computers, Controllers, CAD/CAM systems, work stations/terminals, printers, plotters, modems, cables connectors etc., 3. Office equipments: Computer-Plotter-etc. CIM software comprises the following: 1. Management information system(MIS) program 2. Marketing program 3. Sales program 4. Finance program
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5. DBMS program 6. Design program 7. Analysis program 8. Communication program 9. Monitoring program 10. Production control program 11. Inventory control program 12. Bar code program 13. Order entry program 14. Process planning program 15. Manufacturing facilities program etc. 5.21 Introduction to intelligent manufacturing system An expert system is a computer program that relies on knowledge and reasoning to perform a difficult task usually undertaken only by a human expert. The expert system technology has emerged from research in Artificial Intelligence (AI) The expert system approaches is to task knowledge from human experts and represent it as a knowledge base , which can then be processed to solve difficult problems in the same way the expert world. A knowledge base is formulated and enclosed in such a way that the system readily explain why is it arrived at and its answer. Artificial Intelligence It is the endeavor to construct computer system that perform tasks that are considered to require intelligence.AI is the study of how to make computers do thing at which at the moment people are better. The major components of an AI system are shown in fig. The main areas of pure AI research are -
Problem solving and search
-
Common sense reasoning and deduction
-
Knowledge representation
-
Learning
-
System architecture
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Areas
such
as
Robotics.
Natural
65
language
processing,
image
understanding, automatic programming, planning and decision support and considered
applications
of
the
core
AI
concepts.
Heuristic search
Knowledge representation
Factory production
AI programming language and tools
AI hardware
Major components of AI system
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UNIT QUESTIONS
UNIT-1 QUESTIONS 1. Define CAM. 2. What is the need of CAM? 3. What are the elements of CAM systems 4. Define Simultaneous Engineering. 5. What are the advantages of CAM? 6. Define Total Quality Approach 7. Briefly explain the life cycle of a product.
UNIT-II QUESTIONS
1. What are the different types of control system? 2. What are the elements of the NC system? 3. What is the use of punched tape? 4. What are the advantages of computer-aided part programming.
UNIT-III QUESTIONS
1. Explain turning centre with a neat sketch. 2. Sketch the vertical machining centre 3. Explain universal machining centre. 4. What is AGV? Explain it. 5. Give the benefits of AGV. 6. What are the types of AGV?
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UNIT-IV QUESTIONS 1. Define group technology. 2. What do you mean by part families? 3. Write the benefits of GT. 4. What are the data required for MRP? 5. What are the benefits of MRP? 6. What are the benefits of CAPP? 7. Define capacity planning.
UNIT-V QUESTIONS 1. What are the components of an FMS? 2. What are the FMS workstations? 3. What is JIT? 4. Explain the MRP II. 5. What are the elements of JIt? 6. Explain Order Release.
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