Computer Integrated Manufacturing: Computerized Manufacturing Planning Systems

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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 systemscomputer 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


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

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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

Computer Integrated Manufacturing: Computerized Manufacturing Planning Systems

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