pull-push system and jit and lean
DESCRIPTION
Pull-Push System and JIT and LeanTRANSCRIPT
Computer Integrated manufacturing Systems ENGR 4440
What is Inventory?
Inventory (n) - 1: an itemized list of current assets; 2: the quantity of goods or materials on hand: STOCK
Merriam Webster’s Collegiate Dictionary, 10th ed.
Inventory - any of the materials used directly in the manufacture of a finished product
Computer Integrated manufacturing Systems ENGR 4440
Types of Inventory
$ Invested
$ $ $Flexibility
high medium low
1 2 4 53 ...
Finished Goods Raw
Materials
Work-In-Process
Computer Integrated manufacturing Systems ENGR 4440
Why Have Inventory?
Variability
Large Inventories
High Costs
- Customers- Suppliers- Competitors- Mfg. Process
- “Just-In-Case”
{
Computer Integrated manufacturing Systems ENGR 4440
Why Have Inventory?In
ven
tory
Lev
el
Work-In-Process
Computer Integrated manufacturing Systems ENGR 4440
Managing Inventory
Two ways to attack the problem...
ReduceSources ofVariability
ImplementInventory
ManagementSystem
...best solution: Do Both!
Computer Integrated manufacturing Systems ENGR 4440
Identify “Rock”
Form Teams
ReceiveTraining
Document/Analyze Process
ImplementImprovements
Adjust Process or System
EnhancedPerformance
Inventory Management: Variability Reduction
Computer Integrated manufacturing Systems ENGR 4440
Inventory Management: System
A systematic method of purchasing, controlling, using,and distributing the three classes of inventory: - Raw Materials - Work - In - Process (WIP) - Finished Goods
1 2 4 53 ...
Finished Goods Raw
Materials
Work-In-Process
Computer Integrated manufacturing Systems ENGR 4440
To build the right product,
at the right time,
in the right quantity
to meet customer demand
subject to
At the right cost
To meet company profitability goals
Purpose of Inventory Management Systems
Computer Integrated manufacturing Systems ENGR 4440
Inventory Management Philosophies
I. Push System: Manufacturing Resource Planning (MRP II) Links demand for parts to demand for finished goods through standard lead times and bills-of-material via computer systems;Production is triggered by a schedule
II. Pull System: Just-In-Time (JIT) Links demand for parts to demand for finished goods through series of calculated buffers via simple visual cards/containers known as kanban; Production is triggered by demand
Computer Integrated manufacturing Systems ENGR 4440
Inventory Costs
Opportunity cost
Carrying costs
Obsolescence
Design changes
Operating costs Handling Space People Paperwork Equipment Damage
Excess inventory is the root of all evil.
K. Suzaki, The New Manufacturing Challenge
Computer Integrated manufacturing Systems ENGR 4440
Key Inventory Measure
Inventory Turns = Gross Annual Sales
Avg. On-Hand Inventory
Inventory Turns: Harley Davidson
05
10152025
1 2 3 4 5 6Year
Annu
al
Turn
sA
nn
ual
T
urn
s
Computer Integrated manufacturing Systems ENGR 4440
Key Inventory Measure
Company Inventory Turns Turn Days
Avg. U. S. manufacturer 7 - 8 45 - 52
Harley Davidson 21 17
Black & Decker 37 10
Avg. U. S. grocery store 50 7
Toyota 80-100 3.7 - 4.7
Southland (7-11 stores) 300+ ~1
Computer Integrated manufacturing Systems ENGR 4440
Push Systems
Product is pushed through the manufacturing process in batches large enough to: A. Meet present and future demand B. Compensate for problems in process
Trigger: Schedule, based on Forecast & Actual Customer Orders
“Just build it, They’ll buy it!”
Note: MRP II is a Push System
customer
Computer Integrated manufacturing Systems ENGR 4440
MRP II Strengths
Well suited for variable demandWorks in both Make-To-Stock and
Make-To-OrderProvides integrated manufacturing
management systemHandles large number of parts easilyWidely used & accepted
Computer Integrated manufacturing Systems ENGR 4440
MRP II Weaknesses
Assumes infinite plant capacity Requires accurate lead times Requires accurate forecasts No limit to WIP inventory Lack of robustness (i.e., easily “disturbed”) Requires accurate Bill-of-Materials
Computer Integrated manufacturing Systems ENGR 4440
Pull Systems
Product is pulled through the manufacturing processat the rate of customer demand; Finished Goods arereplenished through a linked series of tactical buffers (kanban) that offer control of Work-In-Process inventory.
Trigger: Customer Purchase of Goods
“If they buy it, We’ll build it!”
customer
Computer Integrated manufacturing Systems ENGR 4440
One Piece Flow - Pull System
One order at a time
Order in = Order out
First in - first out
Produce what you need - not what you can
Lot size reduction
Simplified scheduling
Computer Integrated manufacturing Systems ENGR 4440
Cross Training and Load Leveling
Opens system constraints or bottle necks
Better utilizes all resources
Improves communication
IMPROVES productivity
Computer Integrated manufacturing Systems ENGR 4440
Pull System
A Trigger to Signal:
• What to Build
• When to Build
• How Much to Build
Kanban
Computer Integrated manufacturing Systems ENGR 4440
Pull System Strengths
Continual visibility Simple, low cost production scheduling tools Controlled / Calculated buffers Reduced dependence on specific
item forecast
Computer Integrated manufacturing Systems ENGR 4440
Pull System Weaknesses
Requires relatively steady demand Not Useful for Make-To-Order: FG Relies on manufacturing process Not as widely understood
Computer Integrated manufacturing Systems ENGR 4440
Which System is Best?
There is no “Silver Bullet”!
You must find the appropriate systemfor your business environment
Computer Integrated manufacturing Systems ENGR 4440
Ch 26 Just-In-Time and Lean Production
Sections:
1. Lean Production and Waste in Manufacturing
2. Just-in-time Production Systems
3. Autonomation
4. Worker Involvement
Computer Integrated manufacturing Systems ENGR 4440
What is Lean Production?
Lean production means doing more work with fewer resources
Adaptation of mass production in which work is accomplished in less time, smaller space, with fewer workers and less equipment
Based on the Toyota Production System The term "lean production" was coined by researchers
at Massachusetts Institute of Technology
Computer Integrated manufacturing Systems ENGR 4440
Structure of Lean Production System
Taiichi Ohno's structure of the Toyota Production System
Computer Integrated manufacturing Systems ENGR 4440
Activities in Manufacturing
1. Actual work - activities that add value to the product
2. Auxiliary work - activities that support the value-adding activities
3. Muda (waste) - activities that neither add value nor support the value-adding activities
Computer Integrated manufacturing Systems ENGR 4440
Muda (Waste)
Taiichi Ohno’s seven forms of waste:
1. Production of defective parts
2. Production of more parts than needed (overproduction)
3. Excessive inventories
4. Unnecessary processing steps
5. Unnecessary movement of people
6. Unnecessary handling of materials
7. Workers waiting
Computer Integrated manufacturing Systems ENGR 4440
Keys to Eliminating Waste
1. Just-in-time production
2. Autonomation (automation with a human touch)
3. Worker involvement
Computer Integrated manufacturing Systems ENGR 4440
Just-In-Time Production
Production and delivery of exactly the required number of each component to the downstream operation in the manufacturing sequence just at the moment when the component is needed
Minimizes: Work-in-process Manufacturing lead time
Computer Integrated manufacturing Systems ENGR 4440
Requisites for JIT
1. A pull system of production control
2. Setup time reduction for smaller batch sizes
3. Stable and reliable production operations
Computer Integrated manufacturing Systems ENGR 4440
Pull System of Production Control
A system in which the order to make and deliver parts at each workstation in the production sequence comes from the downstream station that uses those parts
JIT is based on a pull system of production control Alternative is a push system in which parts are produced
at each station irrespective of the immediate need for those parts at the downstream station
Computer Integrated manufacturing Systems ENGR 4440
Kanban System
Toyota’s way of implementing a pull system of production control
Kanban means “card” in Japanese Two types of kanbans:
1. Production kanban – authorizes upstream station to produce a batch of parts
2. Transport kanban – authorizes transport of the parts to the downstream station
Computer Integrated manufacturing Systems ENGR 4440
Operation of a Kanban System
1. Station i + 1 removes next P-kanban from dispatching rack. This P-kanban authorizes it to process a container of part b. A material handling worker removes the T-kanban from incoming container of part b and takes it back to station i.
Computer Integrated manufacturing Systems ENGR 4440
Operation of a Kanban System
1. At station i, the material handling worker finds the container of part b, removes the P-kanban and replaces it with a T-kanban. He then puts the P-kanban in the dispatching rack at station i.
Computer Integrated manufacturing Systems ENGR 4440
Operation of a Kanban System
1. The container of part b that was at station i is moved to station i + 1 as authorized by the T-kanban. The P-kanban for part b at station i authorizes station i to process a new container of part b, but it must wait its turn in the dispatching rack. Scheduling of work at each station is determined by the order of P-kanbans.
Computer Integrated manufacturing Systems ENGR 4440
Setup Time Reduction
Starting point in setup time reduction is recognition that the work elements in setup are of two types:
1. Internal elements – can only be done while the production machine is stopped
2. External elements – do not require the machine to be stopped
Computer Integrated manufacturing Systems ENGR 4440
External Work Elements
Can be accomplished while previous job is still running Strategy:
Design the setup tooling and plan the changeover procedure to permit as much of the setup as possible to consist of external elements
Examples: Retrieve tooling for next job from tool crib Assemble tools for next job Reprogram machine for next job
Computer Integrated manufacturing Systems ENGR 4440
Internal Work Elements
Use time & motion study and methods improvement to minimize the sum of the internal work element times
Use two workers rather than one to accomplish the changeover
Eliminate adjustments in the setup Use quick-acting fasteners rather than bolts and nuts Use U-shaped washers instead of O-shaped washers Design modular fixtures consisting of a base plus insert
tooling that can be quickly changed for each new part style Base part remains attached to production machine
Computer Integrated manufacturing Systems ENGR 4440
Examples of Setup Reduction
Setup time
Equipment type Before After Reduction
1000 ton press 4 hr 3 min 98.7%
Transfer line 9.3 hr 9 min 98.4%
Punch press 2 hr 3 min 97.5%
Machine tool 6 hr 10 min 97.2%
45 ton press 50 min 2 min 96.0%
Computer Integrated manufacturing Systems ENGR 4440
Stable and Reliable Production Operations
Production leveling - distribute changes in product mix and quantity as evenly as possible over time
On-time delivery of components Defect-free components and materials Reliable production equipment Workforce that is cooperative, committed, and cross-
trained Dependable supplier base
Computer Integrated manufacturing Systems ENGR 4440
Autonomation
“Automation with a human touch” Production machines operate autonomously as long as
they are functioning properly When they do not function properly (e.g., they produce a
defect), they are designed to stop Autonomation topics:
1. Stop the process
2. Error prevention
3. Total Productive Maintenance (TPM)
Computer Integrated manufacturing Systems ENGR 4440
Stop the Process
“Jidoka” Japanese word meaning machines that are designed to
stop automatically when something goes wrong Stop the process when:
Defective parts are produced Required production quantity has been completed
Avoids overproduction
Computer Integrated manufacturing Systems ENGR 4440
Error Prevention
“Poka-yoke” Japanese word meaning prevention of errors using low
cost devices to prevent or detect them Common mistakes in manufacturing:
Omitting processing steps Incorrectly locating a part in a fixture Using the wrong tool Neglecting to add a part in assembly
Computer Integrated manufacturing Systems ENGR 4440
Poka-Yoke Functions
Performs 100% inspection for the following: Workpart deviations Processing and methods deviations Counting and timing functions Verification of steps during work cycle
When an error or other exception is identified, the poka-yoke responses are either or both of the following: Stops the process when an error or problem is detected Provides an audible or visible warning to alert operator
and other workers
Computer Integrated manufacturing Systems ENGR 4440
Total Productive Maintenance
Goal: zero breakdowns TPM = integration of preventive and predictive
maintenance to avoid emergency maintenance Emergency maintenance = repair equipment that
breaks down Preventive maintenance = routine repairs to avoid
breakdowns Predictive maintenance = anticipating malfunctions
before they occur
Computer Integrated manufacturing Systems ENGR 4440
Equipment Availability Curve
Typical U-shaped availability curve for a piece of equipment during its life
Computer Integrated manufacturing Systems ENGR 4440
Overall Equipment Effectiveness
Measure that includes availability (reliability), equipment utilization, yield of good product, and operating capability
OEE = A U Y ros
where OEE = overall equipment effectiveness
A = availability (proportion uptime)
U = equipment utilization (time equipment is used relative to available time)
Y = yield of good product = 1 - q, where q = fraction defect rate
ros = operating capability (actual speed / design speed)
Computer Integrated manufacturing Systems ENGR 4440
Worker Involvement
Components: Continuous improvement Visual workplace Standard work procedures Total productive maintenance
Computer Integrated manufacturing Systems ENGR 4440
Continuous Improvement
“Kaizen” Japanese word meaning continuous improvement of
production operations Usually implemented by worker teams, sometimes called
“quality circles” Encourages worker sense of responsibility Allows workers to gain recognition among colleagues Improves worker’s technical skills
Computer Integrated manufacturing Systems ENGR 4440
Visual Management and 5S
Principle: the status of the work situation should be evident just by looking at it Objects that obstruct the view are not allowed Build-up of WIP is limited to a specific height Andon boards located above the assembly line indicate
the status of the workstations Worker training includes use of photos and diagrams to
document work instructions
Computer Integrated manufacturing Systems ENGR 4440
Worker Involvement through 5S
Japanese word
Seiri
Seiton
Seiso
Seiketsu
Shitsuke
English equivalent
Sort
Set in order, simplify access
Shine, sweep, scrub
Standardize
Self-discipline, sustain
Computer Integrated manufacturing Systems ENGR 4440
Standardized Work Procedures
Three components:
1. Cycle time – actual time required “Takt time” – reciprocal of demand rate adjusted for
available shift time
2. Work sequence Basically the same as a standard method
3. Standard work-in-process Minimum number of parts to avoid waiting of
workers
Computer Integrated manufacturing Systems ENGR 4440
Takt Time and Cycle Time
Takt time defined
Ttakt = EOT / Qdd
where Ttakt = takt time
EOT = effective daily operating time
Qdd = daily quantity demanded
In the Toyota Production System, the work must be designed so that the operation cycle time is consistent with the takt time
Computer Integrated manufacturing Systems ENGR 4440
Standard Operations Routine Sheet
Shows the machines that must be visited by the worker during each work cycle
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U-shaped Work Cell
Allocation of work at nine machines between three workers in a production work cell
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Operations Routine Sheets
Allocation of work at nine machines for three workers in a production work cell
Computer Integrated manufacturing Systems ENGR 4440
Standard Work-In-Process Quantity
Defined as the minimum number of parts necessary to avoid workers waiting
Factors that affect the standard WIP quantity: If quality inspections must be performed as distinct
steps, then additional parts must be provided If processing includes heating of parts, then additional
parts must be provided for heating and cooling time If the worker's work sequence is in the opposite
direction of the part processing sequence, then at least one workpart must be held between machines to avoid waiting time
Computer Integrated manufacturing Systems ENGR 4440
HW # 6
26.2, 26.3, 26.4, 26.12