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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