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01113-lean

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IntroductionJIT is one of the tool of Lean manufacturing, which was first,developed by the Japanese in the early 1970s.

The Toyota manufacturer plant was the first to adopt the

technique, by its leader Taiichi Ohno.

Researchers have labeled JIT as a philosophy with threemain objectives:

1. reducing the inventories2. making quality better and3. providing on time production and shipment of products.

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P ush and P ullM RP is the classic push system. The M RP systemcomputes production schedules for all levels based onforecasts of sales of end items. Once produced,subassemblies are pushed to next level whether needed or not.

JIT is the classic pull system. The basic mechanism isthat production at one level happens when initiated by arequest at the higher level. That is, units are pulled

through the system by request.

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Just- In-Time (J IT)

Defined

JIT can be defined as an integrated set of activitiesdesigned to achieve high-volume production usingminimal inventories (raw materials, work in process,and finished goods)

JIT also involves in the elimination of waste in

production effort

JIT also involves in the timing of productionresources (i.e., parts arrive at the next workstationjust in time)

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J IT and Lean ManagementJIT can be divided into two terms: Big JIT and Little JIT

Big JIT (also called Lean M anagement ) is a philosophy of operations management that seeks to eliminate waste in all

aspects of a firms production activities: human relations,vendor relations, technology, and the management of materials and inventory.

Little JIT focuses more narrowly on scheduling goodsinventory and providing service resources where and whenneeded

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J IT P ull systemIt is dangerous to summarize JIT as a concept because of its breath butmost applicable definition is:

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MRP vs. J ITThese methods offer two completely different approaches to basicproduction planning in a manufacturing environment. Each hasadvantages over the other, but neither seems to be sufficient on itsown. Both have advantages and disadvantages, suggesting that bothmethods could be useful in the same organization.

Main Advantage of MR P over J IT: M RP takes forecasts for endproduct demand into account. In an environment in which substantialvariation of sales are anticipated (and can be forecasted accurately),M RP has a substantial advantage.

Main Advantage of JIT over MR

P: JIT reduces inventories to aminimum. In addition to reducing inventory cost, there are substantial

side benefits, such as improvement in quality and plant efficiency.

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MRP - Merits & DemeritsAdvantages Disadvantages

MR P | PUSH

A llows M anagers to managei.e. plan and control things

Can lead to large inventories

Requires maintenance of largeand complex databases

A llows for the planning andcompletion of complexassemblies as sub-componentsare delivered only by scheduledneed

Can generate large quantities of scrap before errors arediscovered

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J IT - Merits & DemeritsAdvantages Disadvantages

J IT | PU LL

Limited and known Final

Inventory

Every job is a High Stress

Rush order

Worker only consume their time& Raw M aterials on what isactually needed

Setup times will greatly impactthroughput

Each piece has a definite placeto go and immediate feedback isgiven

A ny problem will lead tounhappy customers

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K anbanK anban is Japanese word for card or signboard. It is a technique for building a control mechanism into the manufacturing system itself.There are number of kanban techniques which can be employed. Thesimplest form is known as K anban Squares.

The squares are painted between the work centres for each item in

production. When a downstream kanban square is empty, this is thesignal for the material to be processed. The great virtue of thistechnique is its simplicity.

There are several other methods of applying pull control in addition tokanban squares (eg. K anban cards).

In pull system, control is an integral part of the manufacturingsystem while in push system (MR P ), the control is a separateentity controlled externally.

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K anban

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Two Card K anbanThis is a more sophisticated approach. This technique depends onusing production (P) and withdrawal (W) kanban cards and standardcontainers. The kanbans contain simple information relating to the partsto be produced. The cycle can be represented as five-stage procedure.

1. A n empty container arrives at an output queue from a downstream

workcentre. A ttached to this container is W kanban.

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Two Card K anban2. The W kanban authorizes material withdrawal and a full container issent to the workcentre downstream. The P kanban attached authorizesthe workcentre to manufacture product.

3. The workcentre completes a batch of product. The P kanban is nowattached to the full container at the output queue.

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Two Card K anban4 . The empty container in the input queue is sent to the upstreamworkcentre along with its attached W kanban.

5. The upstream workcentre is authorized to send a full container.

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S ingle Card K anbanThis technique is simpler as only withdrawal kanbans are used. The

five stage cycle is shown below. The process is similar to two cardkanban except production is controlled externally. This approach canbe considered to be a hybrid push-pull system.

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O ther K anban TechniquesThere are number of other techniques available for implementing a pullsystem. Some companies use signal kanbans. Here, when inventoryreaches a predetermined level a kanban is hung on a signal post whereit is highly visible.

Finally, some companies have

developed methods for transmittingthe signal to produce to a remotelocation. This can be accomplishedin variety of ways;

1. Lights2. Semaphore3. Rolling coloured golf balls down

transparent tubing

Example of a Kanban Card

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Determining the Number of K anbans Needed

Setting up a kanban system requires determiningthe number of kanbans cards (or containers)needed

Each container represents the minimum productionlot size

A n accurate estimate of the lead time required toproduce a container is key to determining howmany kanbans are required.

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E xample of K anban CardDetermination: P roblem Data

A switch assembly is assembled in batches of 4 units froman upstream assembly area and delivered in a specialcontainer to a downstream control-panel assembly

operationThe control-panel assembly area requires 5 switchassemblies per hour

The switch assembly area can produce a container of switch assemblies in 2 hours

Safety stock has been set at 20% of needed inventory

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E xample of K anban Card

Determination: Calculations

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P re-requisites for K anbanK

anban is a very simple yet efficient means of control. There arehowever, a number of pre-requisites before K anban can be employedas the sole means of control.

Repetitive Manufacture: Clearly, K anban cannot be used in anengineer to order environment.

Machine Layout: K anban cannot be used in a functional layout.

S mall lot sizes: In practice, for K anban to be successful it isessential that lot sizes are small. It means short changeover times.

S table Demand: K anban cannot respond to highly fluctuating levelschedules.

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Traditional vs. J IT Approach

Traditionally, in the West, problems have been seen assomething to be avoided. In factories, problems such aspoor quality, unreliability of machines etc, have beenaddressed by the use of safety stocks.

Sophisticated techniques have been developed todetermine the appropriate level of these stocks.

In addition to this, companies have invested in complexcomputer systems for planning and control that help toavoid such problems in manufacturing.

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Traditional vs. J IT ApproachThis approach is sometimes likened toa ship negotiating a river (r iv er and rocks analogy). The Western approachis to increase the level of water toallow the ship to pass. Where someobstacles are too large to be covered,

radar is used to avoid the problems.

The JIT approach is fundamentallydifferent. Here, the root cases of theproblems are attacked using a varietyof techniques (e.g. TQ M , TP M andS M ED). Then, stock levels arereduced and this reveals other problems which themselves areattacked. This process is repeatedindefinitely, leading to continuous

improvement (or K

aizan).

The Classical Approach

The JIT Approach

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E xamples of S uccessful

J IT S ystemsToyota is considered by many to be the poster child for JIT success.

The Toyota production strategy is highlighted by the fact that raw

materials are not brought to the production floor until an order isreceived and this product is ready to be built.

No parts are allowed at a node unless they are required for the nextnode, or they are part of an assembly for the next node.

This philosophy has allowed Toyota to keep a minimum amount of inventory which means lower costs.

It also means that Toyota can adapt quickly to changes in demandwithout having to worry about disposing of expensive inventory.

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E xamples of S uccessful

J IT S ystemsDell has also used JIT principles to make its manufacturing processa success.

Dells approach to JIT is different in that they leverage their suppliersto achieve the JIT goal.

Dell is able to provide exceptionally short lead times to their customers, by forcing their suppliers to carry inventory instead of

carrying it themselves and then demanding (and receiving) shortlead times on components so that products can be simplyassembled by Dell quickly and then shipped to the customer.

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S ummaryWhile there is no generally accepted definition of JIT, it is bestthought of as a approach that attempts to eliminate waste.

It is a decentralised approach that means people at all levels inthe organisation are involved in decision-making.

JIT is the most influential idea in industry in the last twentyyears.

It is a philosophy that requires changes not only to plant and itslayout, but also attitudes throughout organizations.

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Tools & TechnologiesIn order to support competitivepriorities and manufacturingobjectives companies mayimplement different technologiesand tools in their systems.

Some of which are listed.