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Computer Integrated Manufacturing:Computerized Manufacturing Planning
Systems
CHAPTER 2:
2.1 Computer Aided Processes Planning (CAPP)
2.2 Computer Integrated Production Planning Systems
2.3 Material Requirements Planning (MRP)
2.4 Capacity Planning System
UNIVERSITI TEKNOLOGI MARA
FACULTY OF MECHANICAL ENGINEERING
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Process PlanningDetermining the most appropriate manufacturing
processes and the sequence in which they should be
performed to produce a given part or productspecified by design engineering.
Limitations imposed by available processing
equipment and productive capacity of the factory
must be considered. Parts or subassemblies that cannot be made internally
must be purchased from external suppliers.
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Details in Process Planning Processes and sequence - process plan should briefly
describe all processing steps used on the work unit
in the order they are performed.
Equipment selection - try to develop process plans
that utilize existing plant equipment.
Otherwise, the part must be purchased, or new
equipment must be installed in the plant.
Tools, dies, molds, fixtures, and gages - design is
usually delegated to the tool design group, and
fabrication is accomplished by the tool room.
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More Details in Process Planning Methods - hand and body motions, workplace layout,
small tools, hoists for lifting heavy parts.
Methods must be specified for manual operations(e.g., assembly) and manual portions of machine
cycles (e.g., loading and unloading a production
machine).
Production costs - often accomplished by cost estimatorswith help from the process planner.
Cutting tools and cutting conditions for machining
operations.
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The Route SheetThe document that specifies the details of the
process plan.
The route sheet is to the process planner what theengineering drawing is to the product designer.
Route sheet should include all manufacturing
operations to be performed on the workpart, listedin the order in which they are to be performed.
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Route Sheet
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Computer-Aided Process
Planning (CAPP) During the last several decades, there has been
considerable interest in automating the process
planning function by computer systems. Shop people knowledgeable in manufacturing
processes are gradually retiring.
Tradition process planning is very timeconsuming and not efficient.
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Computer-Aided Process
Planning An alternative approach to process planning is
needed, and computer-aided process planning
(CAPP) systems provide this alternative. Requires extensive software and good
coordination with CAD/CAM & other aspects.
Efficient tool for planning & schedulingmanufacturing operations.
CAPP is especially good for small volume, high
variety parts production.
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CAPP SystemsComputer-aided process planning systems are designed
around either of two approaches:
1. Retrieval systems (variant/derivative system)
2. Generative systems
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Retrieval CAPP Systems Also known as variant CAPP systems.
Based on GT and parts classification and coding.
A standard process plan is stored in computer files for each part code
number .
The standard plans are based on current part routings in use inthe factory, or on an ideal plan prepared for each family .
For each new part, the standard plan is edited if modifications
are needed.
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Retrieval CAPP Systems - continued
If the file does not contain a standard process planfor the given code number, the user may searchthe file for a similar code number.
By editing an existing process plan, orstarting from scratch, the user develops a newprocess plan that becomes the standard planfor the new part code.
Final step is the process plan formatter.
Formatter may call other applicationprograms: determining cutting conditions,calculating standard times, or computing costestimates.
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Generative CAPP Systems Rather than retrieving and editing an existing plan from a
data base, the process plan is created using systematicprocedures that might be applied by a human planner.
In a fully generative CAPP system, the process sequenceis planned without human assistance and without
predefined standard plans.
Designing a generative CAPP system is a problem in
expert systems- computer programs capable of solvingcomplex problems that normally require a human withyears of education and experience.
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Cost Savings of CAPP Reduction in process planning effort
Saving in direct labor
Saving in material
Saving in scrap
Saving in tooling Reduction in work-in-process
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Benefits of CAPP
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Process standardizationCAPP leads to more
logical and consistent process plans than
traditional process planning, more complete and
detailed process plans. Increased productivity of process planners.
Reduced lead time to prepare process plans.
Improved legibility over manually written route
sheets.
CAPP programs can be interfaced with other
application programs, such as cost estimating,
work standards, and others.
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Material Requirements Planning
System (MRP) A computer-based system for managing inventories & delivery
schedules of raw materials & tools.
Converts the master production schedule for end products into
a detailed schedule for the raw materials and components used
in the end products.
The detailed schedule indicates:
Quantities of each item to be ordered.
When the order must be placed.
When the order must be delivered to achieve the master
schedule .
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MRP Operational Model
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MRP Inputs Starts process with the MPS (master production schedule) which provides the
quantity of each model or product required in future periods. This required
production quantity becomes the driver of plans for all material items and
subassemblies that make up the product. Two additional inputs, BOM and current inventory, provide critical
information for an effective MRP system. Inputs must be accurate and timely.
Eg. Parts from vendors arrive daily and when they arrive the inventory
control system has to be updated to provide timely information for planners.
BOM provides with the part number and quantity of all parts required to
build and assemble the product.
Inventory control system supplies the projected on-hand balance of all parts
and materials listed on the BOM. (how much on hand, where it is stored and
the status of material)
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MRP Inputs The system can either be manual or computer aided
driven by data supplied to it.
The critical data needed by the MRP system includemanufacturing order information that incorporates the
critical information in the master schedule: the specific
quantities of products to be made and when they are due,
item number, description, planning lead times, costs, etc.
Purchased order data provide information on what
material is currently on order and the status of open
purchase orders.
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MRP Outputs The results or outputs can be generalized into 2 information
streams:
The primary output is the system-generated plan forfuture purchase orders for the material needed to
produce the quantities of products shown in the master
schedule (production order schedule for finished
products).
The order will become the plan that drives theproduction on the shop floor. Capacity Requirements
Planning (CRP) is a computer-based extension of the
MRP process to calculate planned workloads.
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MRP Outputs Manufacturing planners can evaluate the
projected workload and assess the capability of
manufacturing to complete the planned work. Theresults of the CRP process are used to determine
short-term capacity needs for equipment and
labor skills.
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MRP Output Reports
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Order releases - authorize placement of orders planned by
MRP system
Planned order releases in future periods Rescheduling notices, indicating changes in due dates for
open orders
Cancellation notices - indicate that certain orders are
canceled due to changes in the master schedule Inventory status reports
Exception reports, showing deviations from schedule,
overdue orders, scrap, etc.
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Material Requirements Planning Benefits:
Improved customer service
Reduction in past-due orders
Better understanding of capacity constraints
Significant increases in productivity
Reduction in lead time
Reduction in the inventory for finished goods, raw materials, component
parts and safety stock
Reduction in WIP
Elimination of annual inventory
Significant drops in annual accounting adjustments for inventory
problems
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Manufacturing Resource
Planning (MRP-II) Controls all aspects of manufacturing
planning through feedback.
System is complex, able to produce final
production scheduling of monitoring actual
results in terms of performance and output,
& comparing results against the masterproduction schedule.
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Enterprise Resource Planning
(ERP) An extension of MRP-II. An effective method for
planning & control of all the resources needed in
a business enterprise to take orders for products,produce them, ship them to the customer and
service them. It coordinates, optimizes, and
integrates all information sources & widely
diverse technical and financial activities in amanufacturing organization.
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Capacity Requirements Planning
System (CRP) Capacity Planning: the process of determining the
amount of capacity required to produce in the
future. The function of establishing, measuring and
adjusting limits or levels of capacity. Detail
amount of labour and machine resources required
to accomplish the tasks of production. May show
insufficient capacity during specific time periods.
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Just-In-Time Production /
Manufacturing Definition: Elimination of all waste and on continuous
improvement (Kaizen) of productivity. It encompasses the
successful execution of all manufacturing activities
required to produce a final product, from design
engineering to delivery, and includes all stages of
conversion from raw material onward.
Primary elements are: only required inventory when
needed; to improve quality to zero defects; to reduce lead
times by reducing set-up times, queue lengths and lot
sizes; revise the operations incrementally; and minimize
activity costs.
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Just-In-Time Manufacturing First Implemented in Japan.
Eliminate sources of manufacturing waste.
Receive supplies Just-In-Time. Produce parts Just-In-Time.
Produce subassemblies Just-In-Time.
Produce and deliver finished products Just-In-Time to be
sold.
Pull systemparts are produced to order and the
production is matched with demand for the final assembly
of products.
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Advantages of JIT Low inventory carrying costs.
Fast detection of defects in the production
or the delivery of supplies and, hence, low
scrap loss.
Reduced inspection and reworking of parts.
High quality parts produced at low cost.
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Kanban The implementation of JIT involved kanbanvisible
records. Two types of cards:
Production cardauthorizes the production of onecontainer or cart of identical, specified parts at a
workstation.
Conveyance or move cardauthorizes the type or
one container or cart of parts from that particular
workstation to the workstation where the parts will
be used.
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Group Technology First developed in Europe in early 1900s.
Definition: GT is manufacturing philosophy that justifiessmall and medium-size batch production by capitalizing
on design and/or manufacturing similarities amongcomponent parts.
Parts can be grouped and produced by classifying intofamilies based on geometry (external & internal shapes,surface finish, dimensional tolerances, etc) and production
/ manufacturing characteristics (primary processes,secondary and finishing processes, etc.). GT coding givenon all parts and components.
The production equipment is organized into machine cellsand specializes in the production of a part family calledcellular manufacturing.
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Group Technology Two tasks to carry out:
Identifying the part families. Review all part drawings andgrouping the parts into families.
Rearranging production machines into machine cells.
Benefits:
Promotes standardization of tooling, fixturing and set-ups.
Reduces material handing because the distances within amachine cell are much shorter than within the entire factory.
Shorter lead and set-up times.
Reduces work-in-process and finished-goods inventories.
Simplifies production planning and control.
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Part Families Ten parts are different in
size, shape, and material,
but quite similar in terms ofmanufacturing.
All parts are machined
from cylindrical stock by
turning; some parts requiredrilling and/or milling.
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Traditional Process Layout
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Cellular Layout Based on GT
Each cellspecializes in
producing one
or a limited
number of
part families.
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Database in CIM The enterprise must have the automation systems and
computers in all department areas linked to a Product
Development Management system through an information and
data network. PDM system is designed to organize and supportthe shared database.
It controls the BOM (information on individual parts, sub-
assembly and materials) in a hierarchical system called a
product structure. The technique used is called a relationaldatabase since part data are linked to numerous files related to
the part, assembly and product. The links could be to CAD
models, CAD drawings, vendor specifications or analyses
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Data Interfaces It addresses the sharing of CAD and other product and
engineering data across the enterprise. The process includes (1)
creating the product with CAD, (2) converting the CAD part
geometry and attributes file to the format required by otherdepartments, and (3) saving the different versions of the
drawing files in the product structure.
The part geometry and specifications created in CAD are used
by production machines in manufacturing, manufacturingresource planning (MRPII) software systems in production
planning and control, and text and graphics documentation
software systems in marketing and other front office
departments.
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Enterprise Network Linking to a common data storage is done through LAN.
The structure and operation of LAN covers the topology,protocols and media.
Topology refers to the shape of the network and is eitherphysical (the way it is wired) or logical (the way it ismade to work)bus, ring, star, tree topology.
Protocols refers to the rules and encoding specifications
for sending data and whether the network uses a peer-to-peer or a client-server architectureEthernet (LANarchitecture using either a bus or star topology, supports10 megabits per second, IEEE 802.3), Token ring
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Enterprise Network (Used with ring topology , IEEE 802.5)
Media indicates how devices are interconnected
(twisted-pair wire, coaxial cable, etc) Learn more in Chapter 3.
Electronic data communications must extend
beyond internal divisions. Frequently used
technology for external networks is electronicdata interchange (EDI).
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Computer Simulation of
Manufacturing Processes & Systems Simulation takes 2 forms:
A model of a specific operation intended to
determine the viability of a process or to optimize orimprove its performance.
Models multiple processes and their interactions to
help process planners and plant designers in the
layout of machinery and facilities.
Examples: process viabilityformability of sheet-
metal in dies, process optimizationto identify hot
spots, minimize defects, etc.
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Inventory Types of inventory encountered in
manufacturing:
Raw materials
Purchased components
In-process inventory (work-in-process)
Finished products