Production Planning,Scheduling and Control
Transcript of 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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Basic components of a production system
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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Basic components of a production system
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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Production flow types- two way
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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Production flow types- two way
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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Planning , Scheduling and Controlling
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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Planning , Scheduling and Controlling
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