the philosophy of jit can be traced back to henry ford, but formalized jit originated in japan as...
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The philosophy of JIT can be traced back to Henry Ford, but formalized JIT originated in Japan as the Toyota Production System. W. Edwards Deming’s lesson of variability reduction was a huge influence.
The focus of JIT is to improve the system of production by eliminating
all forms of WASTE.
Just-In-Time Philosophy
JIT is a long-term approach to process improvement. It uses timeliness as a lever to lower costs, improve quality and improve responsiveness. However, JIT requires enormous commitment. It took Toyota more than 25 years to get right!
Just-in-Time
• Downstream processes take parts from upstream as they need.– Get what you want– when you want it– in the quantity you want.
4. Just In Time-- What is It?
• Just-in-Time: produce the right parts, at the right time, in the right quantity – Requires repetitive, not big volume– Batch size of one– Short transit times, keep 0.1 days of supply
Characteristics of Just-in-Time Pull method of materials flow Consistently high quality Small lot sizes Uniform workstation loads Standardized components and work methods Close supplier ties Flexible workforce Line flows Automated production Preventive maintenance
Push versus Pull
• Push system: material is pushed into downstream workstations regardless of whether resources are available
• Pull system: material is pulled to a workstation just as it is needed
From a a « push » to a « pull » System
Work is pushed to the next station as it is completed
SUPPLIERS
CUSTOMERS
A workstation pulls output as needed
SUPPLIERS
CUSTOMERS
From a a « push » to a « pull » System
From a a « push » to a « pull » System
JIT Demand-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 and supply chain
The process continues throughout the entire production process and supply chain
Pull Versus Push SystemsPull Versus Push Systems
A pull system uses signals to request A pull system uses signals to request production and delivery from upstream production and delivery from upstream stationsstations
Upstream stations only produce when Upstream stations only produce when signaledsignaled
System is used within the immediate System is used within the immediate production process and with suppliersproduction process and with suppliers
Pull Versus Push SystemsPull Versus Push Systems
By pulling material in small lots, inventory By pulling material in small lots, inventory cushions are removed, exposing problems cushions are removed, exposing problems and emphasizing continual improvementand emphasizing continual improvement
Manufacturing cycle time is reducedManufacturing cycle time is reduced Push systems dump orders on the Push systems dump orders on the
downstream stations regardless of the downstream stations regardless of the needneed
Waste in Operations1. Waste from overproduction
2. Waste of waiting time
3. Transportation waste
4. Inventory waste
5. Processing waste
6. Waste of motion
7. Waste from product defects
8. Underutilization of people
Streamlined Production
Flow with JIT
Traditional Flow
CustomersSuppliers
Customers
Suppliers
Production Process (stream of water)
Inventory (stagnant ponds) Material
(water in stream)
Reduce VariabilityReduce Variability
Inventory levelInventory level
Process downtimeScrap
Setup time
Late deliveries
Quality problems
Inventory Inventory levellevel
Reduce VariabilityReduce Variability
Scrap
Setup time
Late deliveries
Quality problems
Process downtime
Causes of VariabilityCauses of Variability
1.1. Employees, machines, and suppliers produce Employees, machines, and suppliers produce units that do not conform to standards, are units that do not conform to standards, are late, or are not the proper quantitylate, or are not the proper quantity
2.2. Engineering drawings or specifications are Engineering drawings or specifications are inaccurateinaccurate
3.3. Production personnel try to produce before Production personnel try to produce before drawings or specifications are completedrawings or specifications are complete
4.4. Customer demands are unknownCustomer demands are unknown
Variability ReductionVariability Reduction
JIT systems require managers to reduce JIT systems require managers to reduce variability caused by both internal and variability caused by both internal and external factorsexternal factors
Variability is any deviation from the Variability is any deviation from the optimum processoptimum process
Inventory hides variabilityInventory hides variability Less variability results in less wasteLess variability results in less waste
Performance and WIP Level
• Less WIP means products go through system faster• reducing the WIP makes you more sensitive to
problems, helps you find problems faster• Stream and Rocks analogy:
– Inventory (WIP) is like water in a stream– It hides the rocks– Rocks force you to keep a lot of water (WIP) in the stream
Reduce Lot SizesReduce Lot Sizes
200 200 –
100 100 –
Inve
ntor
yIn
vent
ory
TimeTime
QQ22 When average order size = 100When average order size = 100average inventory is 50average inventory is 50
QQ11 When average order size = 200When average order size = 200average inventory is 100average inventory is 100
Customer orders 10
Lot size = 5
Lot 1 Lot 2
Lot size = 2Lot 1 Lot 2 Lot 3 Lot 4 Lot 5
Reducing Lot Sizes Increases the Number of Lots
Reduce Lot SizesReduce Lot Sizes Ideal situation is to have lot sizes of one Ideal situation is to have lot sizes of one
pulled from one process to the nextpulled from one process to the next Often not feasibleOften not feasible Can use EOQ analysis to calculate Can use EOQ analysis to calculate
desired setup timedesired setup time Two key changesTwo key changes
Improve material handlingImprove material handling Reduce setup timeReduce setup time
Reduce Setup TimesReduce Setup Times
Use one-touch system to eliminate Use one-touch system to eliminate adjustments (save 10 minutes)adjustments (save 10 minutes)Step 4Step 4
Step 5Step 5Training operators and standardizing work Training operators and standardizing work procedures (save 2 minutes)procedures (save 2 minutes)
Repeat cycle until subminute Repeat cycle until subminute setup is achievedsetup is achieved
Initial Setup Time
Step 2Step 2Move material closer and
improve material handling (save 20 minutes)
Step 1Step 1
Separate setup into preparation and actual setup, doing as much as possible while the machine/process is
operating (save 30 minutes)
Step 3Step 3Standardize and
improve tooling (save 15 minutes)
90 min —90 min —
60 min —60 min —
45 min —45 min —
25 min —25 min —
15 min —15 min —13 min —13 min —
——
Kanban
• Japanese for ‘signboard’• Method for implementing JIT• In order to produce, you need both material
to work on, and an available kanban.• Each work station has a fixed # kanbans.
Kanban
• Worker 2 finishes a part, outbound moves over• 2 has a blue tag avaliable, so 2 gets another part to
work on:– 2 takes off 1’s green tag giving it back to 1, and – puts on her blue tag and moves it into position.
Flow of work
32
Kanban
• When 3 finishes a part, – Finished parts move over one spot– He has to have a red tag available to put on,– He gets a part from 2’s outbound pile, – And gives the blue back to 2
Flow of work
32
Kanban
• When 3 finishes a part, – Finished parts move over one spot– He has to have a red tag available to put on,– He gets a part from 2’s outbound pile, – And gives the blue back to 2
• 3’s production will be taken by 4, offstage right.– Tag goes back into 3’s bin
Flow of work
32
Kanban
• Red finishes his part next.
• But 4 hasn’t freed up any of the red kanbans, so there is nothing for 3 to work on now.
• 3 could maintain his machine, or see if 4 needs help
32
32
The Number of CardsThe Number of Cardsor Containersor Containers
Need to know the lead time needed to produce a container of parts Need to know the amount of safety stock needed
Number of kanbans =Number of kanbans =
Demand during Demand during SafetySafetylead timelead time ++ stockstock
Size of containerSize of container
Number of Kanbans ExampleNumber of Kanbans Example
Daily demandDaily demand == 500 cakes500 cakesProduction lead timeProduction lead time == 2 days2 days(wait time + (wait time + material handling time + material handling time + processing time)processing time)Safety stockSafety stock == 1/2 day1/2 dayContainer sizeContainer size == 250 cakes250 cakes
Demand during lead time = 2 days x 500 cakes = 1,000Demand during lead time = 2 days x 500 cakes = 1,000
Number of kanbans = = 5Number of kanbans = = 51,000 + 2501,000 + 250250250
Example
• A switch is assembled in batches of 4 units at an “upstream” work area.
• delivered in a bin to a “downstream” control-panel assembly area that requires 5 switch assemblies/hour.
• The switch assembly area can produce a bin of switch assemblies in 2 hours.
• Safety stock = 10% of needed inventory.
2.75 or 3 4
5(2)(1.1) C
dL (1S)
k size of container Expected demand during lead time + safety stock
Scheduling Small LotsScheduling Small Lots
AA BB CCAA AAAABB BB BB BB BB CC
JIT Level Material-Use ApproachJIT Level Material-Use Approach
AA CCAA AAAA BB BB BB BB BB CC CCBB BB BB BBAA AA
Large-Lot ApproachLarge-Lot Approach
TimeTime
Minimizing Waste: Uniform Plant Loading
Not uniform Jan. Units Feb. Units Mar. Units Total
1,200 3,500 4,300 9,000
Uniform Jan. Units Feb. Units Mar. Units Total
3,000 3,000 3,000 9,000
Suppose we operate a production plant that produces a single product. The schedule of production for this product could be accomplished using either of the two plant loading schedules below.
How does the uniform loading help save labor costs?
or
Mixed Batch Example• Company produces
three products with a mixed model assembly line.– Operates 16 hours per
day for 250 days/yr.– Determine the mixed
model MPS for a daily batch.
– Determine minimum batch MPS and the mix schedule for a day.
Products Forecasts (year)
1 20,000
2 10,000
3 5,000
Calculations
#1 #2 #3
Year Forecast 20000 10000 5000
Daily Batch divide by 250 80 40 20
Hourly Batch divide by 16 5 2.5 1.25
Minimum Batch MPS 4 2 1
For every unit of #3 (minimum batch), we need twice as many #2 and 4 timesAs many #1 so for minimum batch:Produce during each day produce #1,1,1,1,2,2,3 - repeated 20 times
Characteristics of JIT Partnershps
• Few, nearby suppliers• Supplier just like in-house upstream process• Long-term contract agreements• Steady supply rate• Frequent deliveries in small lots• Buyer helps suppliers meet quality• Suppliers use process control charts• Buyer schedules inbound freight
• Promote flow with little WIP• Facilitate workers staffing multiple machines• U-shaped cells
• Maximum visibility• Minimum walking• Flexible in number of workers• Facilitates monitoring of work entering and leaving cell• Workers can conveniently cooperate to smooth flow and
address problems
Cellular Layout
Inbound Stock Outbound Stock
Group TechnologyAn engineering and manufacturing philosophy that identifies physical similarities of parts and establishes their effective production. Assignment of individual products to
product families
Group Technology (Part 1)
• 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
Group Technology (Part 2)• Revising by using Group Technology Cells can reduce movement and
improve product flow • Revising by using Group Technology Cells can reduce movement and
improve product flow
Press
Lathe
Grinder
Grinder
A
2
BSaw
Heat Treat
LatheSaw Lathe
PressLathe
1
Group Technology (con’d)
• A set of machines dedicated to processing one or more family• Arrange machines in a narrow U• Workers rotate among several machines
Group Technology (con’d)
Advantages Reduce cycle time
Move time Queue timeSet up time
Adjust the output rate by increasing or decreasing the number of workers in a cell
Facilitate job trainingPromote job satisfaction
Typical Benefits of JIT• Cost savings: inventory reductions, reduced scrap, fewer
defects, fewer changes due to both customers and engineering, less space, decreased labor hours, less rework.
• Revenue increases: better service and quality to the customer.
• Investment savings: less space, reduced inventory, increased the volume of work produced in the same facility.
• Workforce improvements: more satisfied, better trained employees.
• Uncovering problems: greater visibility to problems that JIT allows, if management is willing to capitalize on the opportunity to fix these problems.
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