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15

JIT andLean Operations

15-2

Learning Objectives

Explain what is meant by the term lean operations system.

List each of the goals of JIT and explain its importance.

List and briefly describe the building blocks of JIT. List the benefits of the JIT system. Outline the considerations important in converting

a traditional mode of operations to a JIT system. List some of the obstacles that might be

encountered when converting to a JIT system.

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JIT/Lean Production

Just-in-time (JIT): A highly coordinated processing system in which goods move through the system, and services are performed, just as they are needed,

JIT lean production

JIT pull (demand) system

JIT operates with very little “fat”

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Goal of JIT

The ultimate goal of JIT is a balanced system.

Achieves a smooth, rapid flow of materials through the system.

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Summary JIT Goals and Building BlocksFigure 15.1

Product Design

ProcessDesign

PersonnelElements

Manufactur-ing Planning

Eliminate disruptions

Make the system flexible Eliminate waste

Abalancedrapid flow

UltimateGoal

SupportingGoals

Building Blocks

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Supporting Goals

Eliminate disruptions

Make system flexible

Eliminate waste, especially excess inventory

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Sources of Waste

Overproduction Waiting time Unnecessary transportation Processing waste Inefficient work methods Product defects

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Kaizen Philosophy

Waste is the enemy Improvement should be done gradually and

continuously Everyone should be involved Built on a cheap strategy Can be applied anywhere

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Kaizen Philosophy

Supported by a visual system Focuses attention where value is created Process oriented Stresses main effort of improvement should

come from new thinking and work style The essence of organizational learning is to

learn while doing

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Big JIT – broad focus Vendor relations Human relations Technology management Materials and inventory management

Little JIT – narrow focus Scheduling materials Scheduling services of production

Big vs. Little JIT

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JIT Building Blocks

Product design Process design Personnel/organizational

elements Manufacturing

planning and control

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Product Design

Standard parts

Modular design

Highly capable production systems

Concurrentengineering

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Process Design

Small lot sizes Setup time reduction Manufacturing cells Limited work-in-process Quality improvement Production flexibility Balanced system Little inventory storage

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Benefits of Small Lot Sizes

Reduces inventory

Less storage space

Less rework

Problems are more apparent

Increases product flexibility

Easier to balance operations

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Single-Minute Exchange

Single-minute exchange of die (SMED): A system for reducing changeover time

Categorize changeover activities Internal – activities that can only be done while

machine is stopped External – activities that do not require stopping

the machine

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Production Flexibility

Reduce downtime by reducing changeover time

Use preventive maintenance to reduce breakdowns

Cross-train workers to help clear bottlenecks

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Production Flexibility

Use many small units of capacity Use off-line buffers Reserve capacity for important customers

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Quality Improvement

Autonomation Automatic detection of defects during

production

Jidoka Japanese term for autonomation

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Production Flexibility

Balance system: Distributing the workload evenly among work stations

Work assigned to each work station must be less than or equal to the cycle time

Cycle time is set equal to the takt time Takt time is the cycle time needed to match

customer demand for final product

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Personnel/Organizational Elements

Workers as assets

Cross-trained workers

Continuous improvement

Cost accounting

Leadership/project management

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Manufacturing Planning and Control

Level loading Pull systems Visual systems Close vendor

relationships Reduced transaction

processing Preventive maintenance

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Pull/Push Systems

Pull system: System for moving work where a workstation pulls output from the preceding station as needed. (e.g. Kanban)

Push system: System for moving work where output is pushed to the next station as it is completed

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Kanban Production Control System

Kanban: Card or other device that communicates demand for work or materials from the preceding station

Kanban is the Japanese word meaning “signal” or “visible record”

Paperless production control system

Authority to pull, or produce comes from a downstream process

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Kanban Formula

N = DT(1+X)C

N = Total number of containersD = Planned usage rate of using work centerT = Average waiting time for replenishment of parts plus average production time for a container of partsX = Policy variable set by management – possible inefficiency in the systemC = Capacity of a standard container

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Limited Work in Process

Benefits Lower carrying costs Increased flexibility Aids scheduling Saves cost of rework and scrap

Two general approaches Kanban – focuses on individual work stations Constant work-in-process (CONWIP) – focuses

on the system as a whole

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Traditional Supplier Network

BuyerBuyer

SupplierSupplierSupplierSupplier SupplierSupplier SupplierSupplier

SupplierSupplier

SupplierSupplierSupplierSupplier

Figure 15.4a

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Tiered Supplier NetworkFigure 15.4b

SupplierSupplier

SupplierSupplier

SupplierSupplier

SupplierSupplierSupplierSupplier SupplierSupplier

BuyerBuyer

SupplierSupplierFirst Tier Supplier

Second Tier Supplier

Third Tier Supplier

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Preventive Maintenance and Housekeeping

Preventative maintenance: Maintaining equipment in good condition and replacing parts that have a tendency to fail before they actually fail.

Housekeeping: Maintaining a workplace that is clean and free of unnecessary materials.

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Housekeeping Five S’s

1. Sort

2. Straighten

3. Sweep

4. Standardize

5. Self-discipline

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Comparison of JIT and Traditional Systems

Factor Traditional JIT

Inventory Much to offset forecast errors, late deliveries

Minimal necessary to operate

Deliveries Few, large Many, small

Lot sizes Large Small

Setup; runs Few, long runs Many, short runs

Vendors Long-term relationships are unusual

Partners

Workers Necessary to do the work Assets

Table 15.3

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Transitioning to a JIT System

Get top management commitment Decide which parts need most effort Obtain support of workers Start by trying to reduce setup times Gradually convert operations Convert suppliers to JIT Prepare for obstacles

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Obstacles to Conversion

Management may not be committed Workers/management may not be

cooperative Difficult to change company culture Suppliers may resist

Why?

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Why Suppliers Resist JIT

Unwilling to commit resources Uneasy about long-term commitments Frequent, small deliveries may be difficult Burden of quality control shifts to supplier Frequent engineering changes may cause

JIT changes

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JIT in Services

The basic goal of the demand flow technology in the service organization is to provide optimum response to the customer with the highest quality service and lowest possible cost. Eliminate disruptions Make system flexible Reduce setup and lead times Eliminate waste Minimize WIP Simplify the process

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JIT II: a supplier representative works right in the company’s plant, making sure there is an appropriate supply on hand.

JIT II

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Benefits of JIT Systems

Reduced inventory levels

High quality

Flexibility

Reduced lead times

Increased productivity

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Benefits of JIT Systems

Increased equipment utilization

Reduced scrap and rework

Reduced space requirements

Pressure for good vendor relationships

Reduced need for indirect labor

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Smooth flow of work (the ultimate goal) Elimination of waste Continuous improvement Eliminating anything that does not add

value Simple systems that are easy to

manage Use of product layouts to minimize

moving materials and parts Quality at the source

Elements of JIT

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Poka-yoke – fail safe tools and methods Preventative maintenance Good housekeeping Setup time reduction

Cross-trained employees

A pull system

Elements of JIT