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Just-in-Time (JIT)

JIT is a manufacturing philosophy!

A collection of methods.

It is just a matter of time.

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A rose by any other name….• ZIPS – zero inventory production system• ZI – zero inventories• MAN – material as needed• MIPS – minimum inventory production system• Kanban• Toyota System• JIT – just in time• CFM – continuous flow manufacturing• Lean manufacturing• Cellular manufacturing

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JIT Origins - the Toyota System• Toyota could not compete with US in terms of

mass production with resulting economies of scale• Strategy to produce many models in small

numbers• To avoid waste, had to be done without large

inventories• Goal was to have each workstation acquire

necessary materials form upstream workstations precisely as need or just in time.– this lead to the kanban system, setup reductions, worker

training, vendor relationships, quality control, etc.

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A Basic Insight

0 0

0 0

2lim lim 0

lim Cost( ) lim 2 0

A A

A A

ADQ

h

Q ADh

Oooh. Why didn’t I think of

that?

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Conventional JIT Thinking

• defects are to be expected

• large lots are economical

• inventory provides safety

• faster production more efficient

• no defects: necessary and attainable

• ideal lot size is one

• safety stock is waste and inventory is evil

• balanced production more efficient

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What does JIT encompass?

• product design

• equipment selection

• material management (inventory)

• quality assurance

• line layout

• productivity improvement

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The 7 Deadly Sins Eliminate Waste!

1. extreme emphasis on high quality (zero defects)

2. reduction of setup times (zero setup times)

3. reduction of lead-times (zero lead-times)

4. reduction of lot sizes (zero lot sizes)

5. removal of work-in-process from stockroom to factory floor (visibility) (zero handling)

6. increased machine reliability (zero breakdowns)

7. smooth production flow (zero surges)

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Multi-functional Worker - 1• Productivity achieved by training workers to have

multiple skills– reduced boredom and fatigue– increased flexibility– gave workers a better “global view”– increased potential for new ideas

• Single worker operates several different machines• Workers move to workstation/machines where

needed• Insufficient WIP to support a single machine

operation• Leads to U-shaped or L-shaped cells

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Drill

Welder

The Manufacturing Cell

Press

Press

Tap Screw

Welder

Rivet

Finish& Inspect

incoming

Outbound

Product Family -part 1 -part 2 -part 3 -part 4

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Plant layout - Cellular Manufacturing

• One worker can see and attend all the machines with a minimum of walking

• Flexible in the number of workers a cell can accommodate allowing adjustments as production rates change

• Workers can “manage” their cells

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Cell design

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Multi-functional Worker - 2• trained in and rotated among all activities

(positions) of the cell• team-leader alternates among cell workers• cell workers trained to perform (daily) preventive

maintenance on equipment• cell workers plan their own production schedule• cell performs quality control and maintains control

charts

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Multi-functional Worker - 3

• given more responsibility

• valued for contributions

• solve problems

• not extension of machine

• records data

• participates in team meetings

A multi-functionalworker on his wayto his cell.

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Group Technology

A manufacturing philosophy in which similar parts areidentified and grouped together to take advantage oftheir similarities in design and manufacture.

lathedepartment

grindingdepartment

millingdepartment

drillingdepartment

traditional process layout

L G

DM

GLDM

group technology cells

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Group Technology Matrix

Part Nbr Chucker Broach L.B. Hob

B.C. Hob

Wash/ trim

Shaver

20 X X X X

21 X X X X X

24 X X X X X

25 X X X X X

30 X X X X

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Cellular/Group Technology

• close machine proximity

• equipment layout

• worker cross-training

• preventive maintenance

• setup reduction

• small lot sizes

• WIP inspection

• lead time reduction

• material handling reduction

• multi-functional workers

• higher capacities

• product mix flexibility

• WIP reduction

• improved quality, fewer rejects

Characteristic Benefit

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Reduced Setup Times

SMED – Single Minute Exchange of DiesPremise: A significant portion of the die/tool changing operation can be performed off-line while the line continuous to operate.

Internal setup – can only be performed while the machine is stopped.External setup – can be performed while the machine isrunning.

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Setup Reduction

1. separate internal from external setup2. convert as much as possible of internal setup to

external setup3. obtain all necessary tools, fixtures, and dies

before stopping the machine4. eliminate the adjustment process by using jigs,

fixtures, or sensors5. abolish the setup entirely by using a uniform

product design, producing various parts at the same time, or maintaining parallel machines

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Techniques for reducing setup times

• use of jigs

• quick-release bolts

• standardized tools and dies

• color coding schemes

• parallel operations (2 workers setup in parallel)

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Lead Time Reduction

• Lead time– total time required to complete one unit of a

product beginning with receipt of customer order and ending with customer receipt of the order.

• Value-added– any activity or operation required to ensure that

a product is manufactured or assembled in conformance to specifications.

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Lead Time Reduction

Supplier Administrative Manufacturinglead time lead time lead time+ +

supplier office reduced setup timesinvolvement synchronization reduced material

handling

LEAD TIME REDUCTION

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Vendor Relations

• single source suppliers

• long term agreements

• partners in profit

• quality and reliability emphasized– no incoming inspection

• vendor must implement JIT

• many items delivered in small quantities

just deliver on the hour, every hour with no defects

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Management by Eye

• Applying visual methods at each manufacturing unit to record and monitor its activities.– input and output bins

– reject bins

– production and quality control charts

– vendor (supplier) performance

• Use of display boards, charts, lights, gauges, meters, plaques, and awards.

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Traditional Quality Control

from vendors

incominginspection

Finalinspection

manufacturing to customers

rejects

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Drill

Welder

Continuous Quality Control – stage 1

Press

Press

Tap Screw

Welder

Rivet

Inspect

incoming

Outbound

RejectBin

rework

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Drill &Inspect

Welder &Inspect

Continuous Quality Control - stage 2 (poka-yoke –foolproof operations)

Press &Inspect

Tap &Inspect

Screw &Inspect Welder &

Inspect

Rivet &Inspect

incoming

Outbound

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Total Quality Management

• Process control (including SPC) responsibility given to workers

• Easy-to-see quality with visual displays, gauges, meters, awards (green, yellow, red)

• Insistence on compliance – quality comes first then output• Line stop – any worker has the authority to stop the

production line• Correct own errors – whoever produced the defective

items gets to fix it• 100 percent inspection – inspect every part• Continual improvement – strive for zero defects

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Equipment Maintenance

• reactive• breakdown based• performed during

production shifts• solely maintenance

personnel

• proactive (PM/pred maint)• schedule based• performed on 3rd shift or

non-production time• operator participation and

responsibility

Traditional JIT

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Kanban (card)

• synchronize production process• only parts or products required to fill a customer order

are produced• when a part is removed from final inventory, the last

work station in the line is given authorization to replace the part

• authorization signal is sent upstream replacing WIP as they are used

• operator requires both parts and an authorization (Kanban) to produce

The production/control system associated with JIT

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Kanban (2- card system)• Move cards – authorize transfer of a container• Production cards – authorize production of one

container• Card contains

– Kanban number– part number– name and description of part– place where card is used– the number of units in a container

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Kanbans = WIP

Customerorder

supplierraw

material

subassemblyfinal

assembly

material flowauthorization(production) card

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Kanbans We are tryingto figure outhow many Kanbanswe need.

y = number of kanbansD = demands per dayL = average lead-time in (fraction of) daystp = average processing time per containertw = average wait + transportation time per containera = container capacitys = safety factor <= 10%

single card systemL = tp + tw

y = DL(1 + s) / a = (DL + w) / a

(move card) yT = D tw (1 + s) / a

(produce card) yP = D tp (1 + s) / a

WIP = a y

note: DLs = w = buffer stock

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JIT Summary

Small WIP Inventories decrease cost

improve prod efficiency

identify quality issues quickly

increased worker idle time

decrease production rate

Kanban information flow

efficient lot tracking

cheap implementation

predetermined WIP levels

slow to react to demand changes

ignores future demand patterns

other reduced inventories

improved vendor relationships

decrease in multiple sourcing

lack of competition

feature advantages disadvantages

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Conclusions

• JIT works well only in favorable manufacturing environments– little or no demand variability– reliable vendors– small setup times– high quality

• primary benefit – creating favorable environment?• process of implementing JIT more beneficial than JIT

itself ?• Hybrid system

– use MRP to pull long-lead time items and purchases into the factory

– use JIT within the factory

Just-in-time will solve all of our manufacturing

problems!

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MRP versus JIT

A Comparative Analysis

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Push (MRP) System

-difficult to control-irregular deliveries-requires large storage-frequent stock-outs-large batches

The work center produces to a forecast (dependent demand)regardless of whether the parts are needed immediately.

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Pull System

from supplier to customer

-demand oriented-small, manageable quantities-uniform load

The work center produces only when output is needed by the next stage of production.

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Push versus Pull

• work releases are scheduled (SOR)

• schedules prepared in advance

• directly accommodates customer due dates

• MRP must be regenerated – demands pushed down

• work releases are authorized (kanban)

• authorization initiated by a customer demand

• forced to accommodate customer due dates by matching production against demands– uses excess capacity (e.g.

overtime) to accommodate MPS changes

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Pull vs. Push

1 2 3buffer buffer

push system

decoupling of stages

1 2 3

pull system

rawmaterial

customers

information flow

material flow

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MRP versus JITMRP dayproduct 1 2 3 4 5 6 7 8 A 500 500 0 0 0 0 0 0B 200 200 200C 120 120 120

JIT dayproduct 1 2 3 4 5 6 7 8 A 500 0 0 500 0 0 0 0B 0 200 0 0 200 0 200 0C 0 0 120 0 0 120 0 120

JIT or each day A 125B 75C 45

JIT repeat 25 times a dayA A A A A B B B C C

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The Bottom Line(s)

• MRP– static system– high inventories

particularly WIP– push system– long production runs– few setups– long lead times– specialized workers– organized by function

• JIT– dynamic (continuous

improvement – kaizen)– zero inventories– pull system (Kanban)– short production runs– frequent setups– short lead times– flexible workforce– organized by product

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What went wrong? US decline in market share

Continued perception of inferior qualitylarge trade deficits

An introspection of American manufacturing

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A General Observation

• Top management along with the best and brightest minds focused on marketing and finance rather than operations– Short-term profit is primary objective– Strategies for long-term health of the company

are largely ignored

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Traditional Methods (inventory control and scheduling)

• Invalid and simplified assumptions– constant, known setup cost (exogenous) and demands

– infinite capacities

– no product interactions (dependent demands)

• Emphasis on the mathematics rather than the applications– stylized standard problems became focus of research

– algorithms and computational speed dominated

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Trouble with MRP?

• Inventory turns (sales/average on-hand inventory) have not shown an upward trend under MRP

• Survey and anecdotal evidence continue to show problems with MRP/ERP

• Common problems include:– lack of top management commitment– lack of education on those using the system’– Unrealistic master production schedule– Inaccurate data (BOM, inventory position)

• Flawed Model– not in the detail but in the basics– deterministic with infinite capacity

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Trouble with JIT?• Is JIT transportable to US manufacturers?

– a set of beliefs and attitudes embedded in a culture?– or a collection of methods and slogans?

• Difficulty implementing the pragmatic nuts and bolts methods of JIT– does form a complete system– is not off the shelf technology– requires a coherent set of operating policies– requires a revolutionary change– Toyota spent 25 years developing JIT

• JIT contains multiple, conflicting objectives– quality, regularity of flow, flexibility, worker involvement, zero

waste, zero inventory, etc.– what are the trade-offs, precedence's?

• JIT has proven to be neither simple nor inexpensive

Say it isn’t so.

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The JIT Bottom Line

• The American JIT as described in the literature is a loosely coordinated collection of techniques infused with an inspiring stream of romantic rhetoric.

• A metaphor: US JIT is like a father faced with assembling a complex toy for his son but without the instruction manual. He has components, but some may be missing and others may be extra. He has enthusiasm, because his child is anxious for the toy, but he does not precisely know what the toy should be or do. The resulting toy may or may not please the son.– Hopp and Spearmen, Factory Physics

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No easy solution

Gosh. Manufacturing is complex, large, stochastic, multi-objective,

rapidly changing, and highly competitive. How am I ever going to become a successful production

engineer?

Towards a science of manufacturing