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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