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Drum-buffer-rope SystemVs
Just In Time Systems
Production and Operations Management
DBR system
• DBR is “a planning and control system that regulates the flow of work-in-progress materials at the bottleneck or the capacity constrained resources(CCR) in a productive system”
• To achieve this optimum flow, the entry of materials into production is synchronized with the current production rate of CCR
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Key terms
• Capacity constraint resource (CCR): Resource with the least capacitylimits the organization's ability to meet product
volume, product mix or demand fluctuationsIt is the least capable resource in the system but
at a the time can still be of higher capacity than the market demand
• Bottleneck: CCR whose capacity or output rate is less than market demand
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DBR is based on key principles of TOC :
1. Identify The System Bottleneck(s) Physical or Managerial
2. Exploit The Bottleneck(s) Elevating the bottleneck An hour added in bottleneck is an hour for the system
3. Subordinate All Other Decisions To Step 2 Every other component must be adjusted to support maximum effectiveness of the constraint
4. Elevate The Bottleneck(s)Rigorous improvement efforts on constraints to improve their performance
5. Do Not Let Inertia Set In04/10/2023 4
Drum:
Capacity constraint resource schedule
It is effectively the master production schedule which establishes the "drum beat" and control for the entire system
linked to market demand
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60 70 40 60
Capacity Constraint Resource(Drum)
A CB D
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Buffer:
placed before the CCR ensuring that the constraint is never starved
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6070 40 60
Capacity Constraint Resource(Drum)
BufferA B C D
time buffer is created to ensure that work-in- progress arrives at the CCR well before it is scheduled to be processed
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Rope : • Communication from Drum to upstream• connects the CCR to the material release
point• ensures that raw material is not inserted
into the production process at a rate faster than the CCR can accommodate
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6070 40 60
Capacity Constraint Resource(Drum)
Buffer
Rope
A B DC
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EXAMPLE
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Drum-Buffer-Rope System with CCR
Material Release
Schedule
Process ACapacity
800 units/week
Process C Capacity
700 units/week
Process B Capacity
500 units/week
Shipping Schedule
Market Demand650 units/week
CCR (bottleneck)
Non-constraint Non-constraint
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STEPS
STEP 1:
Identify the CCRs in the system
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Drum-Buffer-Rope System with CCR
Material Release
Schedule
Process ACapacity 800 units/week
Process C Capacity
700 units/week
Process B Capacity
500 units/week
Shipping Schedule
Market Demand650 units/week
CCR (bottleneck)Non-constraint Non-constraint
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STEP 2:
Develop a Drum or a schedule for the CCR which is in-line with the needs of the market
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Drum-Buffer-Rope System with CCR
Material Release
Schedule
Process ACapacity 800 units/week
Process C Capacity
700 units/week
Process B Capacity
500 units/week
Shipping Schedule
Market Demand650 units/week
CCR (bottleneck)Non-constraint Non-constraint
Drum
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STEP 3:
Create Time-buffers at critical locations
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Drum-Buffer-Rope System with CCR
Material Release
Schedule
Process ACapacity 800 units/week
Time Buffer
Inventory
Process C Capacity
700 units/week
Process B Capacity
500 units/week
Finished goods
inventoryShipping Schedule
Market demand 650 units/week
Constraint Buffer CCR (bottleneck)
Non-constraint
Non-constraintShipping Buffer
Drum
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STEP 4:
Use logistical ropes tied to the CCR drum schedules for each resource
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Drum-Buffer-Rope System with CCR
Material Release
Schedule
Process ACapacity 800 units/week
Time Buffer
Inventory
Process C Capacity
700 units/week
Process B Capacity
500 units/week
Finished goods
inventoryShipping Schedule
Market demand 650 units/week
Constraint Buffer CCR (bottleneck)
Non-constraint
Non-constraintShipping Buffer
DrumROPE
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Just-In-Time
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Definition
“A philosophy of manufacturing based on planned elimination of waste and continuous improvement of productivity ……”
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A repetitive production systemin which the processing and movement of
materials and goods occurjust as they are needed!
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The Primary Elements
to have only the required inventory when needed
to improve quality to zero defects
to reduce lead times by reducing setup times queue lengths, and lot sizes
to incrementally revise the operations themselves
to accomplish these things at minimum cost04/10/2023 24
Pull system (Kanban)
• In a push system, such as an MRP system, we look at the schedule to determine what to produce next
• In a pull system, such as JIT, we look only at the next stage of production and determine what is needed there, and then we produce only that
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Pre-JIT: Traditional Mass Production
Big lot sizesLots of inventory”PUSH” material to nextstage
Lowerper unit
cost
Big purchase shipments
Big “pushes” of finished goodsto warehouses or customers
???
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Post-JIT: “Lean Production”
Smaller lotsFaster setupsLess inventory, storage space”PULL” material to next stage
Minimalor no
inventoryholding
cost
Smaller shipments
Goods are pulled out ofplant by customer demand
Tighter coordination along the supply chainGoods are pulled along
— only make and ship what is needed
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Synonyms
• IBM - Continuous Flow Manufacturing• HP - Stockless Production
- Repetitive Manufacturing System
• GE - Management by Sight• Motorola - Short Cycle Manufacturing• Japanese - The Toyota System• Boeing - Lean Manufacturing
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Advantages
• Inventory levels are drastically reduced:free up working capital for other projectsless space is neededcustomer responsiveness increases
• Total product cycle time drops• Product quality is improved• Scrap and rework costs go down• Forces managers to fix problems and
eliminate waste .... or it won’t work!04/10/2023 29
Summary
• Management philosophy• Pull system though the plant
• WHAT IT IS
•
• Employee participation• Industrial engineering/basics• Continuing improvement• Total quality control• Small lot sizes
• WHAT IT REQUIRES
• Attacks waste• Exposes problems and bottlenecks• Achieves streamlined production
• WHAT IT DOES
• Stable environment
• WHAT IT ASSUMES
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JIT & DBR- Comparison
JIT
1. JIT requires the plant to be balanced so each task has the same output level
2. JIT creates batches of equal size
DBR
1. DBR uses a buffer in front of the constrained resource to reduce the build-up of unnecessary WIP and allow for a continuous flow of products through the system
2. DBR allows different sized batches, making it better suited for use in a job order shop that takes custom orders of differing sizes
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References
• Operations Management – Krajewski, Ritzman, Malhotra
• http://maaw.info/ArticleSummaries/ArtSumHuff01.htm
• http://maaw.info/ArticleSummaries/ArtSumHuff01.htm
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Thank you
Ashwath PutturBakul Sanakal
SarahVinay Darbi
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