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Introduction
JIT 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 three
main objectives:
1. reducing the inventories2. making quality better and
3. providing on time production and shipment of products.
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Push and Pull
MRP is the classic push system. The MRP systemcomputes production schedules for all levels based onforecasts of sales of end items. Once produced,subassemblies are pushed to next level whetherneeded 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 (JIT)
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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JIT and Lean Management
JIT can be divided into two terms: Big JIT and Little JIT
Big JIT (also called Lean Management) is a philosophy ofoperations management that seeks to eliminate waste in all
aspects of a firms production activities: human relations,vendor relations, technology, and the management ofmaterials and inventory.
Little JIT focuses more narrowly on scheduling goods
inventory and providing service resources where and whenneeded
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JIT Pull systemIt is dangerous to summarize JIT as a concept because of its breath but
most applicable definition is:
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MRP vs. JIT
These 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 MRP over JIT: MRP takes forecasts for endproduct demand into account. In an environment in which substantialvariation of sales are anticipated (and can be forecasted accurately),MRP 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 & Demerits
Advantages Disadvantages
MRP| PUSH
Allows Managers to manage
i.e. plan and control things
Can lead to large inventories
Requires maintenance of large
and complex databases
Allows for the planning and
completion of complex
assemblies as sub-components
are delivered only by scheduled
need
Can generate large quantities of
scrap before errors are
discovered
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JIT - Merits & Demerits
Advantages Disadvantages
JIT | PULL
Limited and known Final
Inventory
Every job is a High Stress
Rush order
Worker only consume their time
& Raw Materials on what is
actually needed
Setup times will greatly impact
throughput
Each piece has a definite place
to go and immediate feedback is
given
Any problem will lead to
unhappy customers
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KanbanKanban 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. The
simplest form is known as Kanban 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 this
technique is its simplicity.
There are several other methods of applying pull control in addition to
kanban squares (eg. Kanban cards).
In pull system, control is an integral part of the manufacturing
system while in push system (MRP), the control is a separate
entity controlled externally.
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Kanban
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Two Card KanbanThis is a more sophisticated approach. This technique depends on
using production (P) and withdrawal (W) kanban cards and standard
containers. The kanbans contain simple information relating to the parts
to be produced. The cycle can be represented as five-stage procedure.
1. An empty container arrives at an output queue from a downstream
workcentre.Attached to this container is W kanban.
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Two Card Kanban2. The W kanban authorizes material withdrawal and a full container is
sent to the workcentre downstream. The P kanban attached authorizes
the workcentre to manufacture product.
3. The workcentre completes a batch of product. The P kanban is now
attached to the full container at the output queue.
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Two Card Kanban4. The empty container in the input queue is sent to the upstream
workcentre along with its attached W kanban.
5. The upstream workcentre is authorized to send a full container.
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Single Card KanbanThis 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 can
be considered to be a hybrid push-pull system.
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OtherKanban TechniquesThere are number of other techniques available for implementing a pull
system. Some companies use signal kanbans. Here, when inventory
reaches a predetermined level a kanban is hung on a signal post where
it is highly visible.
Finally, some companies have
developed methods for transmittingthe signal to produce to a remote
location. This can be accomplished
in variety of ways;
1. Lights
2. Semaphore3. Rolling coloured golf balls down
transparent tubing
Example of a Kanban Card
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Determining the Number of
Kanbans Needed
Setting up a kanban system requires determining
the number of kanbans cards (or containers)
needed
Each container represents the minimum production
lot size
An accurate estimate of the lead time required toproduce a container is key to determining how
many kanbans are required.
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Example ofKanban Card
Determination: Problem Data
A switch assembly is assembled in batches of4 units from
an upstream assembly area and delivered in a special
container to a downstream control-panel assembly
operation
The control-panel assembly area requires 5 switch
assemblies 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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Example ofKanban Card
Determination: Calculations
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Pre-requisites forKanban
Kanban is a very simple yet efficient means of control. There arehowever, a number of pre-requisites before Kanban can be employed
as the sole means of control.
Repetitive Manufacture: Clearly, Kanban cannot be used in an
engineer to order environment.
Machine Layout: Kanban cannot be used in a functional layout.
Small lot sizes: In practice, for Kanban to be successful it is
essential that lot sizes are small. It means short changeover times.
Stable Demand: Kanban cannot respond to highly fluctuating level
schedules.
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Traditional vs. JIT Approach
Traditionally, in the West, problems have been seen as
something to be avoided. In factories, problems such as
poor quality, unreliability of machines etc, have been
addressed by the use of safety stocks.
Sophisticated techniques have been developed to
determine the appropriate level of these stocks.
In addition to this, companies have invested in complexcomputer systems for planning and control that help to
avoid such problems in manufacturing.
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Traditional vs. JIT ApproachThis approach is sometimes likened to
a ship negotiating a river (river androcks analogy). The Western approach
is to increase the level of water to
allow the ship to pass. Where some
obstacles are too large to be covered,
radar is used to avoid the problems.
The JIT approach is fundamentally
different. Here, the root cases of the
problems are attacked using a variety
of techniques (e.g. TQM, TPM and
SMED). Then, stock levels arereduced and this reveals other
problems which themselves are
attacked. This process is repeated
indefinitely, leading to continuous
improvement (orK
aizan).
The Classical Approach
The JIT Approach
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Examples ofSuccessful
JIT SystemsToyota 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 next
node, or they are part of an assembly for the next node.
This philosophy has allowed Toyota to keep a minimum amount ofinventory which means lower costs.
It also means that Toyota can adapt quickly to changes in demand
without having to worry about disposing of expensive inventory.
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Examples ofSuccessful
JIT SystemsDell has also used JIT principles to make its manufacturing process
a success.
Dells approach to JIT is different in that they leverage their suppliers
to 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 simply
assembled by Dell quickly and then shipped to the customer.
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Summary
While there is no generally accepted definition of JIT, it is best
thought of as a approach that attempts to eliminate waste.
It is a decentralised approach that means people at all levels in
the organisation are involved in decision-making.
JIT is the most influential idea in industry in the last twenty
years.
It is a philosophy that requires changes not only to plant and its
layout, but also attitudes throughout organizations.
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Tools & Technologies
In order to support competitive
priorities and manufacturingobjectives companies may
implement different technologies
and tools in their systems.
Some of which are listed.
