Production Planning,Scheduling and Control

7/27/2019 Production Planning,Scheduling and Control

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Production Planning,

Scheduling and Control

Neeti Banga

Asst Professor LD

NIFT


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If a system is working, leave it alone,dont change anything.

John Gall


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Basic components of a production system

Degree of specialization

Bundle type and size

Methods of movement and storage

Production flow and storage

Control


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The degree of sectionalisation

Modern manufacturing can work only by specialization.

Increasing specialization / sectionalisation has some advantages

and disadvantages

GREATER >>>

Personal productivity

Scope for specialized work places, mechanization &

computerization.

Speed or training the operatives


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BUT INCREASED >>>

Need for supervision & formality of work structure

Bundle handling

Work in process, to balance output from individual work places.

Difficulty in identifying source of defects Change of defect manufacture before discovery

Dissociation of worker from finished product

Throughput time

Complexity of prodn system

AND DECREASED >>>

Flexibility of make.

Speed of reaction to changing demand.


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Factories need to set the degree of specialization that gives best

compromise from make through to team workingto full

sectionalisation.

BUNDLE

A bundle is a number of garments which are processed together.

Larger the bundle,smaller is the bundle handling time,but greater the

work in process ,its weight and size.

Usually bundles contain only gmnts to be sewn with same thread

and trimmings. Main requirements of bundle are :

Securityfreedom from creasing and soiling-accessibility


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Bundles

Tied bundles : traditional in mens outerwear, but time is wasted in

tying and untying, looking for parts,gmts become creased and

soiled.

Sewing in chain- for certain depts. this is very cheap and low labor

cost approach. Chain is fed to a bin in front of the machine stand

and removed from it by next operative.

Bags- quite commonly used where bundles are large and creasing

is not important ,as in socks manufacture. Larger bags are dragged

on floor and may become torn too .

Pocketed bags-still used for small parts and trimmings in simple

hanging systems. They are better than tied bundles but less

accessible than pegs and clips. Prevent contamination by lint and

thread from foreign material.


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Bundles

Boxes and baskets- they may cause some creasing but they are

useful with belt conveyers or chutes.

Pocket is usually placed on the outside which holds the

documentation. Frames equipped with wheels can be fitted on

stackable types. Assembly then becomes a trolley Clamps on rails : For long gmnts these permit sewing without

removing the garment from the clamp. Finishing trouser bottom is

good example.

Clamps on cords-pegs were attached on cords to an overhead

rail system..operators can pull cords over the machine and sewoff the rail with trousers hem etc ..there could be more

automated grips that release the garment part as its lifted


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Bundles

Bundle trucks :

These are of 2 types- : big wheeled laundry bins ,e.g. for large bundleof jeans, after sewing and before stone washing; or the clamp

trolleys which serve the previous sewing operations, legs being held

by clamps and other parts being stored in clamps or boxes attached

to trolley .


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Method of movement and storage

Originally all work was carried from one person by hand . Now it

may be conveyed by gravity or by some form of power as well, as

way of saving labor.

By hand : single garments ,tied bundles, garments in bags or boxes.

By chute or roller conveyor : as by hand but usually boxes.

By trolley : wheels set under boxes, clamp trucks, wheeled bins,

combination trolleys.

By Rails: hangers with clamps, boxes or combinations.


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Production flow typesone way-progressive

These may be divided into one way (progressive) or two-way systems .

With one-way systems it is not possible to transport gmnts. back to

previous operations ; they must be transported by hand/ other

methods.

This makes it difficult ,when producing the initial balance ,to

combine diff operations done by same type of machine or which

need similar skills.

Repairs pose a problem, so does transfer of work.

The straight line could be work stations on both sides of the belt

conveyer -upto 2-3 work stations maybe doing the same work. A limited amount of storage occurs after each work station and this

can take form of gravity chutes or work boxes, attached to front of

m/c stands.


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Production flow typesone way-progressive

The progressive bundle unit or PBU has a common storage

system for all work stations engaged in single task .

There is a progression from inflexibility and low work in progressto flexibility and higher work in progress


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Production flow types- two way

There are two main types-

The Sub-type or interflow, in which the garments go around in a

circular route until they reach their addressed destination (selector

type of interflow )

The central storage concept can be as simple as a table, on which

sit bundles of work, surrounded by work stations. The main problem

with this is that bundles are not dealt with in date order.

A more sophisticated version is central pool of bundle trolleys ,and

each type of machine is near these.

Another satisfactory alternative is SATRA conveyor type- the work isstored in a block of roller conveyor belt which can be controlled to

deliver bundles to appropriate work station. Completed work is

returned to rear or store by underside of belt, feeding a gravity roller

conveyor.


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Interflow approach- allows movement b/w every work station and the

bundle trolley bundle trolley central storage system.

-Use of robot trolleys is also a new upcoming concept.

- The selector type is usually a ring of overhead rail, with slidings at

each work station and as a storage area. The work is addressed

from any work station to any other ,by the operative or programmed

chip or mag-stripe card, which provision for a manual override

when this is required.


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Interflow approach- allows movement b/w every work station and thebundle trolley bundle trolley central storage system.

-Use of robot trolleys is also a new upcoming concept.

- The selector type is usually a ring of overhead rail, with slidings at

each work station and as a storage area. The work is addressed

from any work station to any other ,by the operative or programmed

chip or mag-stripe card, which provision for a manual override

when this is required.


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Mechanization

The movement of work from one place to another can be timeconsuming ,although it does provide employment for less able or

those operatives waiting for work .

Most common was-conveyor belt-but essentially straight line and

restriction to output of slowest worker. It became common to switch

off power to allow manual sliding of bundles or work forwardthemselvesfor flexibility.

Overhead rails now provide common methods of transport

economical and safe, permits gmt parts to be hung (reducing

creases and adding ease of access).

Also its easy to link to computerized system


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Computerization

Most modern computerized approaches use

mechanized hanging rail type.

UPS or Unit production System came into vogue in

1980s.

A feature of many is some means for operative to

call from the next bundle.


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Computerization

The characteristics of such systems are :

flexibility For ability to cope with rapid style changes/balancing

problems

Little WIP High capital cost of installation means that storage forWIP is limited. This is claimed as an advantage and is

valid to extent that increased flexibility does reduce

need for high WIP

Fast

throughput

A direct result of lower WIP


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Computerization

The characteristics of such systems are :

space

saving

partly due to lower WIP and partly due to hanging rail

system

reducedhandling

as mainly handled by hanging rail systems

high

quality

FIE or flexible intermediate examining ,is possible,

with rapid return of defective work to work station

concerned. Positioning of the intermediate examiningpositions can be changed frequently ,to respond to

changing defect generation systems.


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Production planning and control

Function of this dept:

Prodn planning and control is : The process by which flow of

raw material or part finished product is planned, regulated and

monitored .

The dept with this label is responsible for rest of the management

for:

1. Allocating work in most profitable way .

2. Providing information as to progress of orders.

3. Adjusting the production schedules to suit changingcircumstances .


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Production planning and control the tasks

Draft guidelines For confirmation by senior management

Evaluate prodn

capacity

Especially with respect to specialist and bottleneck

operations

Make long term

prodn plans

Using the marketing plan but with modifications to

suit the prevailing state of work in hand

Schedule prodn In accordance to prodn plan with modifications to

suit prevailing state of prodn.WIP to be agreed

within limits

Originate orders

for raw materials

Notifying the purchasing office the dates on which

items are required.

Load order as

required

To meet realistic delivery dates ,with proper

documentation ,takign care that scarce resources

are fully utilised.


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Production planning and control the tasks

Monitor

progress

in order to adjust plans and to inform other sections

of management.

Provide

an

information

exchange

laying emphasis on ease of management and sales

staff


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Production planning and control the dangers

PPC function is too often undervalued or treated as merely a clericalactivity . Main areas of weakness are in :

Records- duplication and ommission

Responsibility: poorly defined

Computers: not used or overvalued, with inadequate software

and inaccurate input.


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Range and scope of PPC in textiles and clothing

It is based on variety of specialization of the production units

Spinningthere is less spl in prodn unit and little affected by

operative skill

Weaving-flow of process is from warping to weaving to mending.

Diff types of weaving mc exist with diff applications and need tobe managed.

Dyeing and finishing: Typical flow includes-scouring,

stentering,dyeing,application of various finishes, printing etc

Knitting: variety of m/c exist .prodn line may extend to linking to

cut and sew. operative skills may be important in performance.Mending skills may be needed.


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Planning , Scheduling and Controlling

Planning

Basis shd be market forecast .

Agreement is necessary about whether the prodn unit

can cope up with expected sales, in terms ofoverallvolume and in terms of specialized plant and

operatives.

Action may be done like- revising plans, purchasing

needed machines,train staff, obtain or lease newpremises or lease unwanted onesetc


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Scheduling

As per company policies, work will be allocated to prodn capacity

according to agreed plan, as orders are confirmed ,or bycombination of the two.

Schedules are drafted in detail.


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Controlling

Production rarely goes as per schedule, especially where the

work processes are complex and dependant on performance ofindividuals.

Orders may be cancelled, rush orders may come up.

Inefficiency can easily occur ,unless preliminary work is done

thoroughly and the routine of change is covered by computerized

ways. Balancing is part of this process.


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Key factors in Controlling & Scheduling

Throughput

time/ unit

E.g. in meters of cloth or sms of work/minute

Work in

process

delays

When there are number of processes ,it is

usual to use work in process to buffer against

fluctuations in output, each will cause anextension in throughput time.

Critical paths Some processes occur in parallel, some one

after another. Some part of any process

governs the time taken for process as whole.

This is the critical path.Bottleneck

operations

It is essential to identify the processes for

which limited capacity restricts output


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Key factors in Controlling & Scheduling

Plant utilization How much of the avlbl time is predicted to be

used effectively and how much is likely to be

wasted in repairs? because there is not suitable

work OR no suitably skilled person to run it ?

minimum

order size

we may accept an order for a few profitable item

but only for a large number of a product of

marginal profitabilitydepends on per unit value

effects of

changeover

if one style or type of product is replaced by

another-what is the typical expected loss of

output? Or changing from dark to light thread

waste

percentage

e.g. cloth utilization in cutting, combined with the

predicted loss of garments in rejects and cloth

returns.


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General capacity calculation

Example- 1

Factory has 200 line machines,

Work time= 40 hrs per week Machinist work= bottleneck

Product can be made on anym/c.

Potential output =

200 x 40 x60 = 4,80,000 sms

(std minutes of work per week)


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General capacity calculation

Example- 2

Factory has 200 line machines,

Work time= 40 hrs per week

Attendance= 95% only

Operators do job they are trained for 80% of

time= 80% utilization Average performance = 90 BSI

If output of people not performing upto std is alsoadded, the overall output may increase more- but itsbetter to take a pessimistic view when calculatingcapacity as there maybe unexpected problems.

Potential output =

200 x 40 x60x

0.95 x 0.80 x 0.90

= 3,28,320 sms

(std minutes of

work per week)


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Production capacity for diff parts of prodn

organization

Cutting room- area that can e cut on one table in one day isbased on

-cutting machinery allocated

-skill of the cutters

-depth of the lay---as size of order increases the size of lay increasesand range of sizes and colors will decrease.

- Will be restricted by thickness of material, cutting accuracyrequired ,and presence or otherwise of a vacuum system to putthe block tight .

Based on all this ,fty can prepare a table and link it to a computer, topredict how long an order shd take to complete, as per prodn

units avlbl.Such a table is calledcapacity or skills inventory.

Group of workers ,with common level of productivity are calledoneunit-and this is called as skill center


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Analyzing a multi-style factory

E.g.- A company makes ladies dresses and jackets . Hence the cutting room has little difficulty in coping

with variations of style since types and weights of the

leather skins do not vary much over the range.

In order to promote efficiency each line is givenspecific groups or styles or garment families to sew

,as far prodn schedule would allow.


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Computerization

Use of computers to handle the PPC function isessential to any large organization.

Managers must understand the software completelybefore buying it.

Always essential to run the old system parallel with thenew for a period, despite the heavy work load it placeson the staff.

Computers are invaluable in the making of fastdecisions, based on very recent information.

Main drive is to reduce inventory and throughput time. Quick response is mainly concerned with the latter

and is particularly important in those industries which,like ours, have a high fashion element.


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MRP (Materials requirement Planning )

It is a system of information based on requirementsof direct materials and part-finished product, interms of type, volume and the dates by which themanufacturing unit will require them.

A master time schedule is prepared for a given timeperiod.

In one approach ( regeneration) the completeschedule is renewed ready for the beginning of anew time period.

In other (net change) only those aspects that havechanged are recalculated and represented .


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MRP II (Manufacturing Resource Planning )

It is also a similar system relating to goods of the required typeand volume, at a specified place, at a specified planned time.

It is dependant on the master plan for that style.

It is a rigid system which takes no account of cancelled orders,machine breakdowns, or other irregularities.

It actually forced prodn managers to abandon old methods andbe more planned and organized.

As time has gone MRP II has been successfully modified towardsthe just in tie approach (JIT).


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JIT (Just in Time )

(JIT) Just in time is a pull system of production, so actualorders provide a signal for when a product should bemanufactured.

Demand-pull enables a firm to produce only what is required, inthe correct quantity and at the correct time.

This means that stock levels of raw materials, components,

work in progress and finished goods can be kept to aminimum.

This requires a carefully planned scheduling and flow ofresources through the production process.

Its origin lies in Japan .

This system has been modified to incorporate forward planning

and so there is convergence between JIT and MRP II.


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JIT (Just in Time )

Modern manufacturing firms use sophisticated production schedulingsoftware to plan production for each period of time, which includesordering the correct stock.

Information is exchanged with suppliers and customers through EDI(Electronic Data Interchange) to help ensure that every detail iscorrect.

Supplies are delivered right to the production line only when theyare needed.

For example, a car manufacturing plant might receive exactly the rightnumber and type of tyres for one days production, and the supplier

would be expected to deliver them to the correct loading bay on theproduction line within a very narrow time slot.


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Advantages of JIT

1. Lower stock holding means a reduction in storagespace which saves rent and insurance costs

2. As stock is only obtained when it is needed, less

working capital is tied up in stock3. There is less likelihood of stock perishing, becoming

obsolete or out of date

4. Avoids the build-up of unsold finished product thatcan occur with sudden changes in demand

5. Less time is spent on checking and re-working theproduct of others as the emphasis is on getting thework right first time


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Disadvantages of JIT

1. There is little room for mistakes as minimal stock iskept for re-working faulty product

2. Production is very reliant on suppliers and if stock isnot delivered on time, the whole production schedule

can be delayed3. There is no spare finished product available to meet

unexpected orders, because all product is made tomeet actual orders however, JIT is a veryresponsive method of production

Production Planning,Scheduling and Control

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