Lean Systems - OER University - Anvari.Netcbafaculty.org/4_OM/krajewski_om9_ppt_… · PPT file · Web view · 2010-01-27Title: Lean Systems Author: Jeff Heyl Last modified by:

8 – 1Copyright © 2010 Pearson Education, Inc. Publishing as Prentice Hall.

Lean SystemsLean Systems8

For For Operations Management, 9eOperations Management, 9e by by Krajewski/Ritzman/Malhotra Krajewski/Ritzman/Malhotra © 2010 Pearson Education© 2010 Pearson Education

PowerPoint Slides PowerPoint Slides by Jeff Heylby Jeff Heyl


Lean SystemsLean Systems

Lean systems affect a firm’s internal linkages between its core and supporting processes and its external linkages with its customers and suppliers.

One of the most popular systems that incorporate the generic elements of lean systems is the just-in-time (JIT) system.

The Japanese term for this approach is Kaizen. The key to kaizen is the understanding that excess capacity or inventory hides process problems.

The goal is to eliminate the eight types of waste.


Eight WastesEight Wastes

TABLE 8.1 | THE EIGHT TYPES OF WASTE OR MUDAWaste Definition1. Overproduction Manufacturing an item before it is needed.2. Inappropriate

ProcessingUsing expensive high precision equipment when simpler machines would suffice.

3. Waiting Wasteful time incurred when product is not being moved or processed.

4. Transportation Excessive movement and material handling of product between processes.

5. Motion Unnecessary effort related to the ergonomics of bending, stretching, reaching, lifting, and walking.

1. Inventory Excess inventory hides problems on the shop floor, consumes space, increases lead times, and inhibits communication.

1. Defects Quality defects result in rework and scrap, and add wasteful costs to the system in the form of lost capacity, rescheduling effort, increased inspection, and loss of customer good will.

1. Underutilization of Employees

Failure of the firm to learn from and capitalize on its employees’ knowledge and creativity impedes long term efforts to eliminate waste.


Continuous ImprovementContinuous Improvement

Figure 8.1 – Continuous Improvement with Lean Systems


Supply Chain ConsiderationsSupply Chain Considerations

Close supplier ties Low levels of capacity slack or inventory Look for ways to improve efficiency and reduce

inventories throughout the supply chain JIT II In-plant representative Benefits to both buyers and suppliers

Small lot sizes Reduces the average level of inventory Pass through system faster Uniform workload and prevents overproduction Increases setup frequency


Process ConsiderationsProcess Considerations

Pull method of work flow Push method Pull method

Quality at the source Jidoka Poka-yoke Anadon

Uniform workstation loads Takt time Heijunka Mixed-model assembly Lot size of one


Process ConsiderationsProcess Considerations

Standardized components and work methods

Flexible workforceAutomationFive S (5S) practicesTotal Preventive Maintenance (TPM)


Five S MethodFive S Method

TABLE 8.2 | 5S DEFINED5S Term 5S Defined1. Sort Separate needed from unneeded items (including tools, parts,

materials, and paperwork), and discard the unneeded.2. Straighten Neatly arrange what is left, with a place for everything and everything

in its place. Organize the work area so that it is easy to find what is needed.

3. Shine Clean and wash the work area and make it shine.4. Standardize Establish schedules and methods of performing the cleaning and

sorting. Formalize the cleanliness that results from regularly doing the first three S practices so that perpetual cleanliness and a state of readiness are maintained.

5. Sustain Create discipline to perform the first four S practices, whereby everyone understands, obeys, and practices the rules when in the plant. Implement mechanisms to sustain the gains by involving people and recognizing them via a performance measurement system.


Designing Lean System LayoutsDesigning Lean System Layouts

Line flows recommended Eliminate waste

One worker, multiple machines (OWMM)Group technology

Group parts or products with similar characteristics into families


Group TechnologyGroup Technology

Figure 8.2 – One-Worker, Multiple-Machines (OWMM) Cell



Drilling

D D

D D

Grinding

G G

G G

G G

Milling

M M

M M

M M

Assembly

A A

A A

Lathing

Receiving and shipping

L

L L

L L

L L

L

(a) Jumbled flows in a job shop without GT cells

Figure 8.3 – Process Flows Before and After the Use of GT Cells



(b) Line flows in a job shop with three GT cells

Cell 3

L M G G

Cell 1 Cell 2

Assembly area

A A

L M DL

L MShippingD

Receiving

G

Figure 8.3 – Process Flows Before and After the Use of GT Cells


The Kanban SystemThe Kanban System

Receiving postKanban card for product 1Kanban card for product 2

Fabrication cell

O1

O2

O3

O2

Storage area

Empty containers

Full containers

Assembly line 1

Assembly line 2

Figure 8.4 – Single-Card Kanban System



Storage area

Empty containers

Full containers


Fabrication cell

O1

O2

O3

O2

Assembly line 1

Assembly line 2




Storage area

Empty containers

Full containers


Fabrication cell

O1

O2

O3

O2

Assembly line 1

Assembly line 2




Storage area

Empty containers

Full containers


Fabrication cell

O1

O2

O3

O2

Assembly line 1

Assembly line 2




Storage area

Empty containers

Full containers


Fabrication cell

O1

O2

O3

O2

Assembly line 1

Assembly line 2




Storage area

Empty containers

Full containers


Fabrication cell

O1

O2

O3

O2

Assembly line 1

Assembly line 2




Storage area

Empty containers

Full containers


Fabrication cell

O1

O2

O3

O2

Assembly line 1

Assembly line 2



The Kanban SystemThe Kanban SystemK

AN

BA

N

Part Num

ber:1234567Z

Location:A

isle 5B

in 47

Lot Quantity:

6

Supplier:W

S 83

Custom

er:W

S 116

1. Each container must have a card2. Assembly always withdraws from

fabrication (pull system)3. Containers cannot be moved without a

kanban4. Containers should contain the same

number of parts5. Only good parts are passed along6. Production should not exceed

authorization


Number of ContainersNumber of Containers

Two determinationsNumber of units to be held by each container

Determines lot sizeNumber of containers

Estimate the average lead time needed to produce a container of parts

Little’s law Average work-in-process inventory equals the average

demand rate multiplied by the average time a unit spends in the manufacturing process



WIP = (average demand rate) (average time a container spends in the manufacturing process)+ safety stock

WIP = kc

kc = d (w + p )(1 + α)

k = d (w + p )(1 + α)

c

where k =number of containersd =expected daily demand for the partw =average waiting timep =average processing timec =number of units in each containerα =policy variable



Formula for the number of containers

k = Average demand during lead time + Safety stockNumber of units per container

WIP = (average demand rate)(average time a container spends in the manufacturing process) + safety stock


Determining the Appropriate Determining the Appropriate Number of ContainersNumber of Containers

EXAMPLE 8.1 The Westerville Auto Parts Company produces rocker-arm

assemblies A container of parts spends 0.02 day in processing and 0.08

day in materials handling and waiting Daily demand for the part is 2,000 units Safety stock equivalent of 10 percent of inventory

a. If each container contains 22 parts, how many containers should be authorized?

b. Suppose that a proposal to revise the plant layout would cut materials handling and waiting time per container to 0.06 day. How many containers would be needed?


Determining the Appropriate Determining the Appropriate Number of ContainersNumber of Containers

SOLUTIONa.If d =2,000 units/day, p =0.02 day, α =0.10, w =0.08 day, andc =22 units

k =2,000(0.08 + 0.02)(1.10)

22

= = 10 containers22022

b. Figure 8.5 from OM Explorer shows that the number of containers drops to 8.

Figure 8.5 – OM Explorer Solver for Number of Containers


Application 8.1Application 8.1

Item B52R has an average daily demand of 1000 units. The average waiting time per container of parts (which holds 100 units) is 0.5 day. The processing time per container is 0.1 day. If the policy variable is set at 10 percent, how many containers are required?

k = d (w + p )(1 + α)

c

= 6.6, or 7 containers

=1,000(0.05 + 0.01)(1 + 0.1)

100


Other Kanban SignalsOther Kanban Signals

Cards are not the only way to signal needContainer systemContainerless system


Value Stream Mapping (VSM)Value Stream Mapping (VSM)

Value stream mapping is a qualitative lean tool for eliminating waste

Creates a visual “map” of every process involved in the flow of materials and information in a product’s value chain

Work plan and implementation

Future state drawing

Current state drawing

Product family

Figure 8.6 – Value Stream Mapping Steps


Value Stream MappingValue Stream Mapping

Figure 8.7 – Selected Set of Value Stream Mapping Icons


Value Stream MappingValue Stream Mapping

Figure 8.8 – A Representative Current State Map for a Family of Retainers at a Bearings Manufacturing Company


House of ToyotaHouse of Toyota

A key challenge is to bring underlying philosophy of lean to employees in an easy-to-understand fashion

The house conveys stabilityThe roof represents the primary goals of

high quality, low cost, waste elimination, and short lead-times

The twin pillars, which supports the roof, represents JIT and jidoka


House of ToyotaHouse of Toyota

Highest quality, lowest cost, shortest lead time by eliminating

wasted time and activity

Just in Time (JIT) Takt time One-piece flow Pull system

Culture of Continuous

Improvement

Jidoka Manual or automatic

line stop Separate operator and

machine activities Error-proofing Visual control

Operational Stability

Heijunka Standard Work TPM Supply Chain

Figure 8.9 – House of Toyota


Operational Benefits and Operational Benefits and Implementation IssuesImplementation Issues

Organizational considerations Human costs of lean systems Cooperation and trust Reward systems and labor classifications

Process considerationsInventory and scheduling

Schedule stability Setups Purchasing and logistics


Solved ProblemSolved Problem

A company using a kanban system has an inefficient machine group. For example, the daily demand for part L105A is 3,000 units. The average waiting time for a container of parts is 0.8 day. The processing time for a container of L105A is 0.2 day, and a container holds 270 units. Currently, 20 containers are used for this item.

a. What is the value of the policy variable, α?b. What is the total planned inventory (work-in-process and

finished goods) for item L105A?c. Suppose that the policy variable, α, was 0. How many

containers would be needed now? What is the effect of the policy variable in this example?



SOLUTIONa. We use the equation for the number of containers and then

solve for α:

k = d (w + p )(1 + α)

c

so

α = 1.8 – 1 = 0.8

=3,000(0.8 + 0.2)(1 + α)

270

(1 + α) = = 1.8 20(27)

3,000(0.8 + 0.2)



b. With 20 containers in the system and each container holding 270 units, the total planned inventory is 20(270) = 5,400 units

c. If α = 0

k =

= 11.11, or 12 containers

3,000(0.8 + 0.2)(1 + 0)270

The policy variable adjusts the number of containers. In this case, the difference is quite dramatic because w + p is fairly large and the number of units per container is small relative to daily demand.


Lean Systems - OER University - Anvari.Netcbafaculty.org/4_OM/krajewski_om9_ppt_… · PPT file · Web view · 2010-01-27Title: Lean Systems Author: Jeff Heyl Last modified by:

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