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Hid_caq + Capp

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    Computer-Aided Process Planning (CAPP)

    Product design is the plan for the product. To convertthe design into a physical entity, a manufacturing plan isneeded. Developing such a plan is called processplanning a link b/n product design and manufacturing.

    Process planning

    Process planning involves determining the mostappropriate manufacturing and assembly processes andthe sequence to produce according to specifications inthe product design.

    The scope and variety of processes are limited by theavailable equipment and technological capabilities. The

    choice of processes is also limited by the details of theproduct design.

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    Process planning is usually accomplished bymanufacturing engineers; (Other titles include industrialengineer, production engineer, and process engineer)who must be familiar with available manufacturingprocesses in the factory and be able to interpretengineering drawings.

    The steps are developed in the most logical sequence.

    Decisions and details included within process planning are:

    Interpretation of design drawings. Analyses of materials,

    dimensions, tolerances, surface finishes, etc. Processes and sequence. Selecting required processes

    and their sequence (brief description).

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    Equipment selections - utilize existing equipmentor purchase the, or invest in new equipment.

    Tools, dies, molds, fixtures, and gages for eachprocessing step. Design, fabrication and contractof these tools is delegated to a tool design / roomdepartment and tool

    Methods analysis. Workplace layout, small tools,material handling and motions must be specified.

    Work standards. Time standards for eachoperation.

    Cutting tools and cutting conditions. formachining operations, with reference to standardrecommendations.

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    Computer-aided Process Planning

    There is much interest by mnfg firms in automating thetask of process planning using computer-aided processplanning (CAPP) systems. An alternative way to replaceshop-trained people who are retiring to do processplanning is needed, and CAPP systems are providing thisalternative.

    CAPP is considered to be part of computer-aidedmanufacturing (CAM). In fact, a synergy results when

    CAM is combined with CAD to create a CAD/CAMsystem. In such a system, CAPP becomes the directconnection between design and manufacturing.

    The benefits of CAPP include:

    Process rationalization and standardization. more logical

    and consistent process plans than manual Increased productivity of process planners. The

    systematic approach and standard process plans in thedata files permit more work.

    Reduced lead time for process planning. provide route

    sheets in a shorter lead time.

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    The benefits of CAPP include:

    Process rationalization and standardization.

    more logical and consistent process plans thanmanual

    Increased productivity of process planners. Thesystematic approach and standard processplans in the data files permit more work.

    Reduced lead time for process planning. provideroute sheets in a shorter lead time.

    Improved legibility. neater and easier to readroute sheets.

    Incorporation of other application programs.interfacing with cost estimating and workstandards.

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    Compu ter-aided p rocess p lann ing systemsare

    designed around two approaches. These

    approaches are called:

    (1) Retrieval CAPP systems and

    (2) Generative CAPP systems.

    Retr ieval CAPP Sys tems A retrieval or variant CAPP system is based on

    GT principles of parts classification and coding.

    A standard process plan (route sheet) is storedin computer files for each part code number

    based on current part routings in use or on an

    ideal process plan prepared for each family.

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    Steps in CAPP

    preparatory phase consists ofthe following steps:

    (1) Selecting an appropriateclassification and codingscheme

    (2) Forming part families and

    (3) Preparing standard processplans for the part families.

    Steps (2) and (3) continue asnew parts are designed and

    added to the company's designdata base.

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    After the preparatoryphase the system is

    ready for use. For a newcomponent which needprocess plan

    Derive the GT codenumber.

    With this code number, asearch is made of thepart family file todetermine if a standardroute sheet exists.

    If the file contains aprocess plan, it isretrieved and displayedfor the user.

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    Generative CAPP Systems

    represent an alternative approach to automated process

    planning. Instead of retrieving and editing an existingplan, a generative system creates the process planbased on logical procedures similar to the procedures ahuman planner would use. In a fully generative CAPPsystem, the process sequence is planned without human

    assistance and without a set of predefined standard plan The generative CAPP system is considered part of

    expert systems, a branch of artificial intelligence. Anexpert system is a computer program that is capable ofsolving complex problems that normally require a human

    with years of education and experience. Processplanning fits within the scope of this definition.

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    Ingredients required

    First, the technical knowledge of manufacturing and the logicused by successful process planners must be captured andcoded into a computer program (knowledge base). Thesystem then uses that knowledge base to solve processplanning problems (i.e., create route sheets).

    second, a computer-compatible description of the partcontaining all of the pertinent data and information needed toplan the process sequence. The possible ways of providing

    this description are:(1) The geometric model of the part that is developed on a CADsystem during product design and

    (2) a GT code number of the part that defines the part features insignificant detail.

    Third, is the capability to apply the process knowledge andplanning logic contained in the knowledge base to a givenpart description to solve a specific problem. This problem-solving procedure is referred to as "inference engine". Byusing its knowledge base and inference engine, the CAPPsystem synthesizes a new process plan from scratch

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    ComputerAided Quality Control

    Au tomated Inspect ion

    Automation of inspection procedure reduces inspection

    time per piece with out fatigue and mental errors.Automated inspection can be defined as the automationof step/s involved in the inspection procedure.

    Alternative ways in which automated inspection can be:

    1. Automated presentation with an operator performing the

    examination and decision with possible errors.2. Automated examination and decision by an automaticmachine, with manual loading.

    3. Completely automated inspection system

    Automated inspection can be statistical sampling or

    100%. With either inspection, automated systems cancommit inspection errors, just as human inspectors.

    The full potential of automated inspection is achievedwhen it is integrated in the mnfg process, inspection is100% and when the results lead to some positive

    action.

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    The positive actions cantake either or both of twopossible forms,

    (a) Feedback pro cesscont ro l. Data are fed backto the precedingmanufacturing processresponsible for the quality

    characteristics to allowcompensating adjustments,to reduce variability andimprove quality. If theautomated inspectionindicate drift in output of the

    process, corrections can bemade in the inputparameters to bring theoutput back to the nominalvalue.

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    (b) Parts so rtation. Parts aresorted according to qualitylevel: acceptable versusunacceptable quality. There

    may be more than two levels(e.g., acceptable, reworkable,and scrap). Sortation andinspection may beaccomplished

    to both inspect and sort at thesame station

    to locate one or moreinspections along theprocessing line, with a single

    sortation station near the endof the line. Inspection data areanalyzed and instructions areforwarded to the sortationstation indicating what actionis required for each part.

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    Coord inate measur ing machines (CMM)

    Coordinate metrology is concerned with

    the measurement of the actual shape and

    dimensions of an object and comparing it

    with desired shape and dimensions, as

    might be specified on a part drawing.coordinate metrology consists of the

    evaluation of the location, orientation,

    dimensions, and geometry of the part.

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    Coordinate measuringmachine (CMM) is anelectromechanical system

    designed to performcoordinate metrology. ACMM consists of

    a contact probe that can bepositioned in three-

    dimensional (3-D) spacerelative to the surface ofwork; and

    thex, y, and zcoordinatesof the probe can be

    accurately recorded toobtain dimensional dataconcerning the partgeometry.

    Coord inate measu ring machines (CMM)

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    CMMs are most appropriate for applications possessingthe following characteristics:

    Many inspectors performing repetitive manual inspection

    operations to reduce labor cost and increase throughput.

    Post-process inspection. inspection performed after themanufacturing process.

    Measurement of geometric features requiring multiple

    contact points. Multiple inspection setups are required if parts are

    manually inspected

    Complex part geometry.

    High variety of parts to be inspected. Repeat orders; once the part program has been

    prepared, subsequent parts from repeat orders can beinspected using the same program.

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    the advantages of using CMMs over manualmethods are:

    Reduced inspection cycle time- inspection

    procedures are speeded and labor productivityis improved.

    Flexibilityto inspect a variety of partconfigurations with minimal changeover time.

    Reduced operator errors in measurements andsetups.

    Greater inherent accuracy and precision thanthe manual surface plate methods.

    Avoidance of multiple setups all measurementscan be made in a single setup.

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    Machine vision

    Machine vision can be defined as the acquisition ofimage data, followed by the processing and interpretation

    of these data by computer for some useful application. Vision systems are either 2-D (quite adequate for most

    industrial applications) or 3-D.

    Functions machine vision system:

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    Functions machine vision system:

    1. Image acquisition and

    digitization-is

    accomplished using a

    video camera and

    digitizing system to

    store data for

    subsequent analysis.The image obtained is

    divided into pixels. The

    pixel value (light

    intensity) is converted into digital value by

    analogue-to-digital

    converter.

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    Machine Vis ion Appl icationsAre divide into three categories:

    (1) Inspect ionconstitutes about 80% of machine visionapplications either on-line/in-process or on-line/post-

    process. The applications are almost always in massproduction. Typical industrial inspection tasks include:

    Dimensional measurement- determining the size ofcertain dimensional features of parts usually moving atrelatively high speeds on a moving conveyor.

    Dimensional gauging - gauging function rather thanmeasurement.

    Verification of the presence of components in anassembled product.

    Verification of hole location and number of holes in apart.

    Detection of surface flaws and defects - revealing Flawsand defects on the surface as a change in reflected light.

    Detection of flaws in a printed label. a poorly locatedlabel or poorly printed text, numbering, or graphics onthe label.

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    Other Machine Vision Applications.

    2 Part identification applications to recognize

    and perhaps distinguish parts so that someaction can be taken; such as part sorting,counting different types of parts and inventorymonitoring. Reading of 2-D bar codes andcharacter recognition represent additional

    identification applications.3 Visual guidance and control- a vision system

    is teamed with a robot to control the movementof the machine. Examples include seam

    tracking in continuous arc welding, partpositioning and/or reorientation, bin picking,collision avoidance, machining operations, andassembly tasks.

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    Assignment 2

    Discuss the Application of Computers in

    the Following Production Functions: Sales forecasting

    Marketing

    Accounting Distribution

    Work measurement

    Management

    Education

    Plant design and Layout


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