9. just in time

8/4/2019 9. Just in Time

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The McGraw-Hill Companies, Inc.,

1

Chapter 11

Just-in-Time and

Lean Systems

LEANPRODUCTION


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2

Leanproduction

can be defined as an integratedset of activities designed toachieve high-volume productionusing minimal inventories of rawmaterials, work in process, andfinished goods.

It also involves the elimination ofwaste in production effort

Lean is also based on the logic

that nothing will be produced


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3

FEATURES OF LEANPRODUCTION

WHAT IT IS?Management philosophyPull System through the plant

WHAT IT DOES?Attacks waste (time, inventory, scrap)Exposes problems and bottlenecksAchieves streamlined production

WHAT IT REQUIRES?Employee participationIndustrial Engineering

Total Quality ControlSmall Lot SizesContinuous Improvement

WHAT IT ASSUMES?Stable environment


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4

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 of operationsmanagement that seeks to eliminatewaste in all aspects of a firmsproduction activities: human

relations, vendor relations, and themanagement of materials andinventory

Little JIT focuses more narrowly onscheduling goods inventory and


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5

Pull Logic

Customers

Sub

Sub

Fab

Fab

Fab

Fab

Vendor

Vendor

Vendor

Vendor

Final

Assembly

Here the customer starts

the process, pulling an

inventory item from Final

Assembly

Here the customer starts

the process, pulling an

inventory item from Final

Assembly

Then sub-assembly

work is pulled

forward by that

demand

Then sub-assembly

work is pulled

forward by that

demand

The process continues

throughout the entire

production process

The process continues

throughout the entire

production process


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Waste in Operations

1. Waste from overproduction

2. Waste of waiting time

3. Transportation waste4. Inventory waste

5. Processing waste

6. Waste of motion

7. Waste from product defects


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7eliminationof waste

1. Focused factory Networks

2. Group Technology

3. Quality at source

4. Uniform Plant loading (Heijunka)

5. JIT production

6. Kanban Production control

7. Minimized set up times

N t k


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8Networks:Plant designed for onepurpose can be constructedand operated moreeconomically

CoordinationSystem

Integration

These are smallspecialized plantsthat limit the rangeof products produced(sometimes only onetype of product for anentire facility).

These are smallspecialized plantsthat limit the range

of products produced(sometimes only onetype of product for anentire facility).

Some plantsin Japanhave as fewas 30 andas many as1000employees

Some plantsin Japanhave as fewas 30 and

as many as1000employees

Mi i i i W t G T h l (P t


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9Minimizing Waste: Group Technology (Part1)

Using Departmental Specialization for plant layout can cause

a lot of unnecessary material movement

Using Departmental Specialization for plant layout can cause

a lot of unnecessary material movement

Saw Saw

Lathe PressPress

Grinder

LatheLathe

Saw

Press

Heat Treat

Grinder

Note how the flow lines are going back and forthNote how the flow lines are going back and forth


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Minimizing Waste:Group Technology (Part 2) Revising by using Group Technology Cells can reduce

movement and improve product flow

Revising by using Group Technology Cells can reducemovement and improve product flow

Press

Lathe

Grinder

Grinder

A

2

BSaw

Heat Treat

LatheSaw Lathe

PressLathe

1


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11

Suppose we operate a production plant thatproduces a single product. The schedule ofproduction for this product could be

accomplished using either of the two plantloading schedules below.

Heijunka is the levelling of production byboth volume and product mix. This system

does not build products according to theactual flow of customerorders. Heijunka takes the total volume oforders in a period and levels them out so the

same amount and mix are being made each

Suppose we operate a production plant thatproduces a single product. The schedule ofproduction for this product could be

accomplished using either of the two plantloading schedules below.

Heijunka is the levelling of production byboth volume and product mix. This system

does not build products according to theactual flow of customerorders. Heijunka takes the total volume oforders in a period and levels them out so the

same amount and mix are being made each

Uniform Plant Loading(heijunka)


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Monday Production

Tuesday Production

Wednesday Production

Chan eover

UNLEVELEDPRODUCTION

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UNLEVELEDPRODUCTION

Figure 1 gives an example of traditionalunlevelled production, for Company X thatmanufactures tractors. The line makes small,medium, and large tractors. The medium are thebig sellers and are made early in the week,

Monday through part of Wednesday. There is achangeover and the small tractors are madeWednesday through Friday morning. Afteranother changeover the largest tractors, which arein smallest demand, are made Friday afternoon.

This typical unlevelled method creates fourproblems:

Customers usually do not buy productspredictably. If the customer decides to buy the

large tractors early in the week the plant is introuble.

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14

LEVELED PRODUCTION

Figure 2 represents an example of mixedmodel levelled production. By reducing thechangeover time and employing other Leanmethods, the plant is able to build thetractors in any order they want to on theirmixed model assembly line. The four benefitsof levelling the schedule is:

Flexibility to make what the customer wantswhen they want it.

Reduced risk of unsold goods.

Balanced use of labour and machines.

Smoothed demand on the upstream

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15Monday Production

Tuesday Production

Wednesday Production

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16

Quality at source

Quality at the source means do it right thefirst time and when something goes wrong,stop the process or assembly line

immediately. Factory workers becometheir own inspectors, personallyresponsible for the quality of their output.

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Minimizing Waste: Just-In-TimeProduction

Management philosophy Pull system though the plant

Hydraulic Push Systems

WHAT IT IS

Employee participation Continuing improvement

Small lot sizes

WHAT IT REQUIRES

Attacks waste

WHAT IT DOES

Stable environment

WHAT IT ASSUMES

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Inventory Hides Problems Justas Water in a Lake Hides Rocks

Scrap

Setuptime

Latedeliverie

s

Qualityproble

ms

Process

downtime

Scrap

Setuptime

Latedeliverie

s

Qualityproble

ms

Process

downtime

Inventorylevel

Inventorylevel

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Scrap

Work in process inventory level(hides problems)

UnreliableVendors

CapacityImbalances

Lowering InventoryReduces Waste

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Scrap

Reducing inventory revealsproblems so they can be solved.

UnreliableVendors

CapacityImbalances

WIP


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Scrap

Reducing inventory revealsproblems so they can be solved.

UnreliableVendors

CapacityImbalances

WIP


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T L I


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To Lower Inventory,Reduce Lot Sizes

Time

Inventory Level

Lot Size200

Lot Size80

Average

inventory =100

Averageinventory =

40

Average inventory = (Lotsize)/2

23e uc ng o zes


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Customerorders 10

Lot size = 5

Lot 1 Lot 2

Lot size = 2

Lot 1 Lot 2 Lot 3 Lot 4 Lot 5

e uc ng o zesIncreases the Number ofLots

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Whi h I


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Which IncreasesInventory Costs

Lot Size

Cost

Holdin

gCost

TotalC

ost

Setup Cost

OptimalLot Size

SmallerLot Size

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U l S t C t


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Unless Setup Costsare Reduced

Lot Size

Cost

Holdin

gCostTot

alCost

Setup Cost

Originaloptimallot size

Newoptimallot size

26Lower Total Cost Requires


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26Lower Total Cost RequiresSmall Lot Sizes and LowerSetup Costs

Lotsize

Sum of

orderingand holdingcost

T1

T2

S2

S1

Cost

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Minimizing Waste: KanbanProduction Control Systems

Storage PartA

Storage PartA

MachineCenter

AssemblyLine

Material Flow

Card (signal)Flow

Withdrawalkanban

Once the Production kanban isreceived, the Machine Center

produces a unit to replace the

one taken by the Assembly Line

people in the first place

This puts thesystem back

were it was

before the item

was pulled

The process begins by the Assembly Line

people pulling Part A from Storage

Productionkanban

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Respect for People

Level payrolls

Cooperative employee unions

Reliable Subcontractor networks

9. just in time

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