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MMZG 538 Toyota Production

System

Rajiv Gupta

BITS PilaniFebruary 2014

Session 6

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Module 1 Recap of Session 5

Module 2 Pull Production

Rules of Kanban Module 3 Small Batch Production

Level Production

Module 4

Set-up reduction Jidoka

Module 5 Summary and wrap up

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Session 6

Begin Module 1

Recap of Session 5

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Recap

Machine cell design involves the determination of

the number of workers and the assignment of

workers to machines in the cell

Machine cell design cannot be done unless weprepare for it, i.e., we must ensure the proper

systems are in place such as setup reduction, TPM,

quality, etc.

Lean tools are what people attempt to apply whenthey think of TPS. Applying one or two tools in

isolation without full management commitment has a

good chance of failure

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Recap

Inventory is a symptom of other problems in the

system. We use inventory to cover for inefficiencies

and problems. Carrying inventory takes the focus

away from solving the problems so that they do notrecur

Inventory reduction should not be attempted without

working on the root causes for carrying inventory.

Several failed attempts at the reducing inventoryalone can be attributed to this approach.

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Session 6

End of module 1

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Session 6

Begin Module 2

Pull Sceduling

Types of Kanban

Rules of Kanban

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Pull Production

In Push scheduling each work center gets

individual schedule based on a forecast

Push scheduling is typically found with

systems such as MRP/ERP etc.

When there are changes in the requirements,

the system has no means to self correct

The result is confusion, excess inventory andlong lead times

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Pull Production

In Pull scheduling, only one work center

gets scheduled

It pulls material from its upstream

operation

This continues through all upstream

operations

The normal approach is known as Kan

Ban

Borrowed from the grocery industry9

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Types of Kanban

Kanban

Production

Instruction

PartsWithdrawal

In-process kanban for schedulingflow processes

Signal kanban for scheduling

batch processes

Interprocess kanban for

internal purposes

Supplier kanban for

external purposes

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Types of Kanban

In-process kanban used to conveyinstruction to produce small quantities (apitch) to an upstream process

Signal kanban used to convey instructionsto produce a batch to an upstream process.Used when production is in batches due tohigh set ups

Inter-process kanban used to signal theneed to withdraw parts from a storage areaand convey them to a downstreamworkstation in the same facility

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Types of Kanban (contd.)

Supplier kanban used to signal the need

to withdraw parts from an external supplier

to be conveyed to the plant storage or

marketplace

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Kanban Rules

Rule 1

The downstream process should withdraw the

necessary products from the upstream processes

in the necessary quantities at the necessary pointin time

Any withdrawal without a Kanban should be prohibited

Any withdrawal which is greater than the number of

Kanbans should be prohibited

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Kanban Rules

Rule 2

The upstream process should produce its

products in the quantities withdrawn by the

downstream process Production greater than the number of Kanbans should

not be permitted

When several parts are to be produced, the production

should follow the original sequence in which eachKanban has been delivered.

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Kanban Rules

Rule 3

No items are made or transported without a

Kanban (Prevent excess production and

transportation) Rule 4

Always attach a Kanban to the goods (It serves

as a work order

Rule 5

Defective products are not sent to subsequent

process

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Kanban Rules

Rule 6

Reducing the number of Kanbans increases their

sensitivity

Kanbans should be used to adapt to small fluctuationsin demand

Reducing Kanbans reveal existing problems

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Two Kinds of Conveyance

There are two kinds of conveyance in the kanban system:

Fixed time and variable quantity conveyance. Fixed quantity and variable time conveyance.

Fixed time conveyance is preferable when processes aredisconnected and conveyance distances are long.

Easy to follow or "milk run" routes can be readily set up.

External suppliers almost always use this form of conveyance. Fixed quantity conveyance is preferable when processes are

connected (e.g., an assembly line) and conveyance distancesare short, or when lot sizes are large (e.g., stamping).

Toyota uses fixed quantity conveyance for stamped parts andfor large injection-molded parts such as instrument panels.

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Session 6

End of module 2

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Small Batch Production

Batch sizes are a result of long set-up times,

long handling distances, and a focus on unit

costs

As long as product variety was not too much,production in larger batches did not affect

responsiveness of production, e.g., Henry Ford

and his model T

However, as product variety proliferated, large

batch production led to various problems and

inefficiencies in the system

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Small Batch Production

There are two types of batches sizes; production

and transfer batches

A production batch is the quantity that is produced at

one time A transfer batch is the quantity that is moved between

processes at one time

Large batches result in larger inventory

Larger batches result in poor quality feedback

Larger batches result in less responsiveness to

the customer

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Batch Sizes and Inventory

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Batch Sizes and Lead Times

Station 1

Station 2

Station 1

Station 2

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Batch Sizes and Flexibility

Workcenter

Workcenter

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Level Production Tied to Customer

Demand

Takt time = No. of working seconds in a day/Demand per day

This establishes a rhythm for the entire supply chain,through the plant and to the suppliers

Example: Demand for a product is 600 pieces per day.

Assuming a single shift operation, 450 working minutesper shift or 27000 secs per shift.

Takt time = 27000/600 = 45 seconds

i.e., the line should be running at 45 secs/piece

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Level Production Tied to Customer

Demand

The takt time represents the rate of demand. It is sometimes

confused with the machine cycle time. This is incorrect.

Producing at the rate of demand ensures no inventory buildup

while meeting demand.

The suppliers rate of production should also be matched

to the takt rate. Then the entire supply chain will run in sync.

The actual demand may vary somewhat from day to day, but

this is absorbed by some inventory of finished product.

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Level Production Tied to Customer

Demand

Assume there are 3 products being produced. The deman

per week is 500, 200 and 100. There are several ways in

which this can be accomplished.

500 200 100

This is not leveled production. The production variesfrom day to day.

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Level Production Tied to Customer

Demand

The ultimate schedule would produce the 3 products in sets

of 5, 2, 1. This is called the pitch.

This method of production leveling is called Heijunka.

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Session 6

End of module 3

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Session 6

Begin Module 4

Setup reduction

Autonomation/Jidoka

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Set Up Reduction

Traditional inventory models, such as EOQ, assume

that the set up cost/time is a fixed quantity.

Some large automated lines and presses can take

more than a shift to change over from one product toanother.

With such long set up times, the batch sizes had to

be large. Also, it was impractical to do much load

leveling. Toyota challenged the assumption of fixed setup

times

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Set Up Reduction

Setup Time Die retrieval from storage

Tools readied

Setup person scheduled

Material handling equipment scheduled

Removal of previous die

Installation of new die

Adjustment

Tryout of new die

Moving old die to storage

Time elapsed from good piece to good piece

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Set Up Reduction

Problems with existing method of setup

Scheduling not done in time resulting in long

waiting times.

Non standard procedures. Insufficient training.

Non standard equipment and dies of different

sizes and heights. Searching time.

Different shut heights require longeradjustment.

Tools, nuts, bolts missing.

Excessive adjustment.34

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Set Up Reduction

Steps in set up reduction (SMED) Determine existing setup procedure

Divide activities into internal elements and

external elements Internal elements are those that require the machine tobe stopped

External elements can be performed while the machineis running

Try to convert internal elements to externalelements

Try to improve external elements

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Jidoka

The normal approach when a machine

breaks down or if there is a quality problem isto find a quick solution so that the line does

not stop.

This thinking stems from the numbersmentality that pervades the western

approach to manufacturing (the R orientation)

The focus on keeping production going

prevents the problem from being fully

recognized and addressed. The result is that

the problem will recur in the future

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Jidoka

Problems can occur in production due to a

variety of reasons:

Human error

Lack of proper training/instructions

Lack of proper tools

Quality of incoming parts

Poor design of task

Machine problems

Problems in the material flow

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Jidoka

Human error

Sometimes the worker on the shop floor can make

mistakes as no one is perfect. This may be due to

carelessness, fatigue, or may be just a random

occurrence

Lack of proper training/instructions

In several plants, the only real training a worker

receives is brief instructions and then he/she is sent

to the line to work

This leads to variation in the way in which each task is

completed.

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Jidoka

Lack of proper tools

Due to lack of standardization and work

structuring, or poor 5s/housekeeping, the right

tools are not available at the workplace, whichrequires the worker to improvise. This can and

does lead to mistakes

Quality of incoming parts

Poor quality of incoming parts can lead to

machining and other production problems over

which the worker has no control

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Jidoka

Poor design of task

Due to the result orientation in several

western production plants, the focus is to

maximize production without the concern forhow this is to be achieved.

This leads to shortcuts and pressure on the

supervisors and workers

This results in little effort in the design of tasks

to ensure that it can be consistently

completed by the worker in the time allotted

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Jidoka

Machine problems

If a machine breaks down, instead of ensuring

that proper maintenance be performed, the

focus is to get the machine up and running asfast as possible to minimize the loss in

production

The lack of focus on maintenance results in

subsequent breakdowns in the machine and

the same cycle repeats itself

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Jidoka

Problems in the material flow

When production flow is not smooth, there

may be problems due to non-availability of

parts at a machine When there is a part shortage, attempts are

made to address the problem as fast as

possible, without looking at the root cause,

which may be in the material flow design

The problem will likely recur and the same

cycle repeated43

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Jidoka

The focus in Toyota is first to spend time in the

proper design of the system

However, in order to ensure that the system is

operating as planned, any time there is a systembreakdown, instead of taking shortcuts, the

problem is analyzed to ensure that it does not

recur

This may lead to a short term stoppage in work,but eliminates stoppages in the long term

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Wh Jid k B

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Why Jidoka Becomes

Necessary The focus on numbers

One thing that a plant manager or a supervisor does

not want is a stoppage in production. The machine

loss time is measured by corporate and few

manufacturing personnel will risk their career by

permitting lines to stop

Fear of blame

When a problem occurs, the normal tendency is toask, who is responsible? rather thanwhy did this

problem occur? So people try to hide problems to

prevent being found out

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Jidoka

The Japanese approach is to bring problems to

the surface, analyze the problem going to the

root cause, applying countermeasures and then

monitoring to ensure that the problem does notrecur

The production capacity in a Japanese plant

takes into account a certain number of andon

pulls in a shift. If the number of andon pulls isless than planned, the management feels that

either people are hiding problems or not pushing

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Session 6

End of module 4

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Session 6

Begin Module 5

Summary and wrap up

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Summary

Set-up times can be reduced drastically. Some

of the changes require little or no investments.

Others may require changes to the equipment

Jidoka requires that we shut down a processwhen a problem occurs and take corrective

action to prevent the problem from recurring

If the line stops once and the focus is on

countermeasures preventing the problem, thenthe loss of production is more than offset by the

elimination of future stoppages

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End Module 5

Summary and wrap up

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