06 jit production
TRANSCRIPT
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JIT Production
Henry C. Co
Technology and Operations Management,
California Polytechnic and State University
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Major MPC Approaches
Up to the late 1960s, the EOQ/ROP approach
was the method of choice in production-inventory management (PIM).
During the 1970s, the American Productionand Inventory Control Society (APICS)
campaigned to promote MRP. For the 1980s, APICS promotes JIT
production as the proper method of PIM.
Another contemporary technique for
managing production and inventory is theOptimized Production Technology (OPT)system.
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EOQ/ROP
Developed at Westinghouse by F. W. Harris
in 1915.Event-triggered, uses Calculus to find the
optimal order quantity
Q =
Major deficiencies. Ignores product structure relationships. Does not permit effective rescheduling in response
to dynamic changes in demand or productionactivities.
Reactive [backward looking] rather than proactive[forward looking].
2DS
H
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MRP Resolves EOQ/ROP Deficiencies
Matched sets. structured bill of material provides
"matched sets" of components parts fromwhich to build the end items called for bythe master schedule.
Proactive. Inventory and production management is
guided by firm orders and forecasts offuture demand.
orders for parts are matched with thedemand these parts are expected tosatisfy.
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Nervousness of MRP
Steady stream of changes confronted by
manufacturing companies. Forecasts are wrong!
bill of materials are revised!
parts are scraped!
vendors are late! etc.
A significant change in the final assemblycreates changed requirements in feederoperations that are usually amplifiedbecause of lot size rules, set-ups, queues,
and waiting time. A 10% change at assembly could easily
result in a 100 % change at the front end.
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The Toyota Production System
A manufacturing strategy having a dominant
theme of constantly reduced inventory and asystem of equipment, procedures andattitudes which eliminate waste and promoterespect for people.
Just-in-time manufacturing is a productionphilosophy which calls for the production ofprecisely the necessary units, in thenecessary quantities, at the necessary times.
The kanban system is an MPC system thatsupports JIT manufacturing.
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Kanban System
Developed in the 1970s by Toyota.
Information system that supports JIT production. Kanban is a card, usually put in a rectangular vinyl
envelope, that authorizes the production orwithdrawal of materials.
Consequently, we can think of the kanban system
as a manufacturing planning and control system. Three categories:
pickup information,
transfer information,
production information.
The kanban controls the production of morethan $4.8 billion a year!
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FUNCTIONS RULES FOR USE
Provides pick-up or
transport information.
Subsequent process picks up the
number of items indicated by the
kanban at the preceding stage.
Provides production
information.
Preceding process produces
items in the quantity and
sequence indicated by the
kanban.
Prevents overproductionand excessive transport. No items are made ortransported without a kanban.
Serves as a work order
attached to goods.
Always attach a kanban to the
goods.
Prevents defective
product by identifying
the process making the
product.
Defective products are not
attached with a kanban.
Reveals existing
problems and maintains
inventory control.
Reducing the number ofkanban
heighten their sensitivity.
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Key Elements of Toyota Production
Just-in-time production.
People involvement: Teamwork, Discipline (jobdesign, methods), Supplier involvement.
Total quality control.
Kanban-controlled flow.
Rapid setup to achieve JIT production. Group technology: mixed-model assembly.
Streamlined plant layout.
Capacity reserve to support peak production.
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Total quality.
Quality is everyone's job, each has an immediatecustomer. Many quality-related efforts are moved to the
workers. TQC must become a company culture to be fully
effective.
Work simplification. Preventive maintenance. JIT production control: kanban-controlled. Focused factories.
Supplier network. JIT accounting. Team approach.
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Toyota Focuses on Eliminating Waste
Queues = waste.
Reduce queues a way to discoverproblems and reduce cost.
Waste of overproduction and unnecessary
inventory. Waste of time waiting.
Waste in transportation.
Waste of processing (making defective
products). Waste of movement.
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JIT Production
Uniform production rate.
Purchasing and producing small lots. Quick, inexpensive setups.
Multiskilled workers and flexible facilities.
High quality level.
Effective preventive maintenance.
Continuous improvement.Fix it, even if it ain't broke.
Wake up the sleeping dog! A pull method of coordinating work
centers (e.g., kanban).
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Production Smoothing at Toyota The JIT system works in Toyota because of the unique way
Toyota structure its master production schedule. Master production schedule in MRP seeks economies and
efficiencies through economical lot sizes. at Toyota, the master production schedule is prepared with
the goal of scheduling every product every day. Mixed-model assembly: processing a variety of models of the
same family on the same assembly line.
Aggregate production schedule. One-year horizon. Updated monthly; marketing and finance input.
MPS has a three-month horizon. First month shows daily schedule for the final assembly of
each model. Next two months lso in daily time-buckets, but in terms of
model family. Daily schedules are determined by dividing the number of
units required for the month by the number of working days inthe month.
Same production for each item each day.
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Illustration
Forecasts for next two weeks:
50% of the sales will be Product A, 25% will be Product B, and
25% will be Product C:
Typical U.S. plant: Make Product A for 5 straight days,
Change over to Product B for two and a half daysProduce Product C for the balance of the week
Under the JIT system: make Product A, followed by Product B, followed
by Product A, followed by Product C, and the cyclerepeats.
The goal is to schedule every product every day,and in a sequence which intermixes all products.
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JIT MPS: Future Resembles Past
OthersWeek 1 A A A A A A A A A A
A A A A A A A A A A
Week 2 B B B B B B C C C C
B B B B C C C C C C
Toyota (JIT)
Week 1 A B A B A B A B A B
A C A C A C A C A C
Week 2 A B A B A B A B A B
A C A C A C A C A C
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A Two Card Kanban System
Consider a multi-stage system.
The output of workstation A is the input toworkstation B. Each filled container at the outgoing stocking point
of A has a production (P) kanban; At the incoming stocking point in B, each has a
withdrawal (W) kanban.
At workstations B (the customer): As each container is opened, B detaches the W-
kanban and deposits it in a withdrawal post(either a box or a board).
At fixed intervals (e.g., 2 hours), a material
handler (called "mizusumashi" at Toyota) picks upthe W-kanban at the withdrawal post; takes theW-kanban and the corresponding number ofempty containers to the outgoing stock point atworkstation A.
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Order-Picking at the outgoing stocking point ofWorkstation A: The material handler:
Picks up the corresponding number of filled containers.
Detaches the P-kanban from each filled containers atthe outgoing stock point.
Deposits the detached P-kanban in a receiving post.
Attaches a W-kanban to each of these filled containers. Transports the filled containers to Workstation B.
Production at Workstation A: Each kanban card deposited in the P-kanban post
authorizes workstation A to produce one container.
Attaches the production kanban to each filledcontainers, store at the outgoing stock point.
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Two Card Kanban
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Pull & Push Systems
Push system (conventional production system).
To maintain a high level of utilization (i.e., to keep theworkstations working), materials are pushed from eachstage to the succeeding stage(s).
When something goes wrong in some intermediatestage, inventory builds up in the up-stream stages.
Pull system (kanban-controlled) Production at each stage is triggered by its successor
stage(s), and this process is carried all the way to theraw material acquisition stage.
Production is controlled (i.e., pulled) by demand, asinformation of demand flows backwards from the finalstage (the final assembly) to the initial stage (the raw
material acquisition). at each work center, all requests for production are
made through the kanban cards.
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Number of kanban Needed
Number of kanban cards =
AD = average daily demand for the month. WT = waiting time.
PT = processing time for one container. CQ = container quantity -- limited to
maximum of 10% of day's demand. PV = policy variable (determined by
management) up to 10% of day's demand. WT + PT = time interval between order
picking.
( ) ( )CQ
PVPTWTAD ++ 1
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Kanban and EOQ/ROP
Observations by Walter Goddard of
Oliver Wight Educational Associates,Inc.
Both are reactive systems designed to
replenish inventory -- the quantityused is the quantity ordered -- not inanticipation of future orders (MRP).
Kanban system: linked replenishment.
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Linked Replenishment
The conventional EOQ/ROP system ignored
the product structure/bill-of-materialsrelationships among the component parts.the demand of each component item isassumed to be independent of each other.Hence, items are replenished independently.
With the kanban system, production of anitem is "pulled" by the demand for the itemat the succeeding stage. Last stage = the final assembly, which is planned
in the master production schedule. If something is not used in the final assembly, no
replenishment action will take place. Replenishment is therefore linked with the master
production schedule, just like in MRP.
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Quick Setups at Toyota
To make:
10,000 coronas a month, consisting of5,000 sedans, 2500 hardtops, and 2500wagons.
20 days/month means producing 250
sedans/day, 125 hardtops/day, and 125wagons/day.
Die-change time
In 1940's die-change time was 2-3 hours. In the late 1960's, it was cut to 3
minutes.
A 50 fold decrease!