Krajweski Chapter 8-9

© 2007 Pearson Education

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Process Layout

Chapter 8Chapter 8


How Process Layout fits the Operations Management

Philosophy

Operations As a Competitive Weapon

Operations StrategyProject Management Process Strategy

Process AnalysisProcess Performance and Quality

Constraint ManagementProcess Layout

Lean Systems

Supply Chain StrategyLocation

Inventory ManagementForecasting

Sales and Operations PlanningResource Planning

Scheduling


Layout Planning

Layout planning is planning that involves decisions about the physical arrangement of economic activity centers needed by a facility’s various processes. Layout plans translate the broader decisions about the

competitive priorities, process strategy, quality, and capacity of its processes into actual physical arrangements.

Economic activity center: Anything that consumes space -- a person or a group of people, a customer reception area, a teller window, a machine, a workstation, a department, an aisle, or a storage room.


Before a manager can make decisions regarding physical arrangement, four questions must be addressed.

1. What centers should the layout include?

2. How much space and capacity does each center need?

3. How should each center’s space be configured?

4. Where should each center be located?

Layout Planning Questions


Location Dimensions

The location of a center has two dimensions:

1. Relative location: The placement of a center relative to other centers.

2. Absolute location: The particular space that the center occupies within the facility.


Absolute Locations vs. Relative Locations

Original layout

Frozen foods

Dry groceries

Bread Vegetables

Meats

Frozen foods

Dry groceries

BreadVegetables

Meats

Revised layout

Four of the absolute locations have changed but not the relative locations.


Strategic Issues

Layout choices can help communicate an organization’s product plans and competitive priorities.

Altering a layout can affect an organization and how well it meets its competitive priorities in the following ways:

1. Increasing customer satisfaction and sales at a retail store.2. Facilitating the flow of materials and information.3. Increasing the efficient utilization of labor and equipment.4. Reducing hazards to workers.5. Improving employee morale.6. Improving communication.


Performance Criteria

Customer satisfaction Level of capital investment Requirements for materials handling Ease of stockpicking Work environment and “atmosphere” Ease of equipment maintenance Employee and internal customer attitudes Amount of flexibility needed Customer convenience and levels of sales


Types of Layouts

Flexible-flow layout: A layout that organizes resources (employees) and equipment by function rather than by service or product.

Line-flow layout: A layout in which workstations or departments are arranged in a linear path.

Hybrid layout: An arrangement in which some portions of the facility have a flexible-flow and others have a line-flow layout.

Fixed-position layout: An arrangement in which service or manufacturing site is fixed in place; employees along with their equipment, come to the site to do their work.


A Flexible Flow Layout

FoundryMilling

machines

LathesGrinding

Painting Drills

Office

Welding

Forging

A job shop has a flexible-flow layout.


Designing Flexible-Flow Layouts

Step 1: Gather information Space requirements by center Available space Closeness factors: which centers need to be located close

to one another.

Closeness matrix: A table that gives a measure of the relative importance of each pair of centers being located close together.

Step 2: Develop a Block plan: A plan that allocates space and indicates placement of each department.

Step 3: Design a detailed layout.


Gather Information

100'

150'

3 6 4

1 2 5

Current Block Plan

Department Area Needed (ft2)

1. Administration 3,5002. Social services 2,6003. Institutions 2,4004. Accounting 1,6005. Education 1,5006. Internal audit 3,400

Total 15,000

Space Requirements

Example 8.1 Office of Budget Management


100'

150'

3 6 4

1 2 5 Closeness Matrix

Trips between Departments

Department 1 2 3 4 5 6

1. Administration —

2. Social services —

3. Institutions —

4. Accounting —

5. Education —

6. Internal audit —

3 6 5 6 10

8 1 1

3 9

2

1

Departments 1 and 6 have the most interaction.Departments 3 and 5 have the next highest.

Departments 2 and 3 have next priority.

Example 8.1 Office of Budget Management


100'

150'

100'

150'

3 6 4

1 2 5 Proposed Block Plan

First put departments 1 and 6 close together

1

6

Next put departments 3 and 5 close together

5

3

Then put departments 2 and 3 close together

2

4


Weighted-distance method: A mathematical model used to evaluate flexible-flow layouts based on proximity factors.

Euclidean distance is the straight-line distance, or shortest possible path, between two points.

Rectilinear distance: The distance between two points with a series of 90 degree turns, as along city blocks.

Applying the Weighted- Distance Method


Distance Measures

Rectilinear DistanceRectilinear Distance

ddABAB = |= |xxAA –– x xBB| + || + |yyAA – – yyBB||

Euclidian DistanceEuclidian Distance

ddABAB = (= (xxAA –– x xBB))22 + ( + (yyAA – – yyBB))22

© 2007 Pearson Education© 2007 Pearson Education

Example 8.2 Load Distance Analysis

Current Plan Proposed Plan

Dept Closeness Distance DistancePair Factor, w d wd Score d wd Score

1,2 3 1 3 2 61,3 6 1 6 3 181,4 5 3 15 1 51,5 6 2 12 2 121,6 10 2 20 1 102,3 8 2 16 1 82,4 1 2 2 1 12,5 1 1 1 2 23,4 3 2 6 2 63,5 9 3 27 1 94,5 2 1 2 1 25,6 1 2 2 3 3

ld =112 ld = 82

Calculating the WD Score


Line Flow Layout

Station 1 Station 2 Station 3 Station 4

A production line has a line-flow layout.


Designing Line-Flow Layouts

Line balancing is the assignment of work to stations in a line so as to achieve the desired output rate with the smallest number of workstations. Work elements are the smallest units of work that can be

performed independently. Immediate predecessors are work elements that must be

done before the next element can begin. Precedence diagram allows one to visualize immediate

predecessors better; work elements are denoted by circles, with the time required to perform the work shown below each circle.


Line Balancing Example 8.3Example 8.3

Green Grass, Inc., a manufacturer of lawn & garden equipment, is designing an assembly line to produce a new fertilizer spreader, the Big Broadcaster. Using the following information, construct a precedence diagram for the Big Broadcaster.


Line Balancing Green Grass, Inc.Green Grass, Inc.

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AA Bolt leg frame to hopperBolt leg frame to hopper 4040 NoneNoneBB Insert impeller shaftInsert impeller shaft 30 30 AACC Attach axleAttach axle 5050 AADD Attach agitatorAttach agitator 4040 BBEE Attach drive wheelAttach drive wheel 66 BBFF Attach free wheelAttach free wheel 2525 CCGG Mount lower postMount lower post 1515 CCHH Attach controlsAttach controls 2020 D, ED, EII Mount nameplateMount nameplate 1818 F, GF, G

TotalTotal 244244

WorkWork Time Time Immediate ImmediateElementElement DescriptionDescription (sec) (sec) Predecessor(s) Predecessor(s)


Desired Output and Cycle Time

Desired output rate, r must be matched to the staffing or production plan.

Cycle time, c is the maximum time allowed for work on a unit at each station: 1

rc =


Theoretical Minimum

Theoretical minimum (TM ) is a benchmark or goal for the smallest number of stations possible, where total time required to assemble each unit (the sum of all work-element standard times) is divided by the cycle time. It must be rounded up

Idle time is the total unproductive time for all stations in the assembly of each unit.

Efficiency (%) is the ratio of productive time to total time.

Balance Delay is the amount by which efficiency falls short of 100%.


Output Rate and Cycle TimeExample 8.4

Green Grass, Inc. Desired output rate, r = 2400/week Plant operates 40 hours/week r = 2400/40 = 60 units/hour

Cycle time, c = 1/60

= 1 minute/unit

= 60 seconds/unit

1

r


Calculations for Example 8.4 continued

Theoretical minimum (TM ) - sum of all work-element standard times divided by the cycle time.

TM = 244 seconds/60 seconds = 4.067 It must be rounded up to 5 stations

Cycle time: c = 1/60 = 1 minute/unit = 60 seconds/unit

Efficiency (%) - ratio of productive time to total time.

Efficiency = [244/5(60)]100 = 81.3%

Balance Delay - amount by which efficiency falls short of 100%.

(100 − 81.3) = 18.7%


Line Balancing Big BroadcasterBig Broadcaster

cc = 60 seconds/unit = 60 seconds/unitTM = 5 stationsTM = 5 stationsEfficiency = 81.3%Efficiency = 81.3%

S1

S2S3

40

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S1 A A 40 20

S2 B,C C 50 10

S3 B,F,G B 30 30E,F,G F 55 5

Cumm IdleStation Candidate Choice Time Time


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S5S4 66

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Green Grass, Inc. Green Grass, Inc. Line Balancing SolutionLine Balancing Solution

cc = 60 seconds/unit = 60 seconds/unitTM = 5 stationsTM = 5 stationsEfficiency = 81.3%Efficiency = 81.3%

The goal is to cluster the work elements into 5 workstations so that the number of work-stations is minimized, and the cycle time of 60 seconds is not violated. Here we use the trial-and-error method to find a solution, although commercial software packages are also available.


Other Considerations

In addition to balancing a line, managers must also consider four other options:

1. Pacing: The movement of product from one station to the next as soon as the cycle time has elapsed.

2. Behavioral factors of workers.3. Number of models produced: A mixed-model line

produces several items belonging to the same family.

4. Cycle times depend on the desired output rate, and efficiency varies considerably with the cycle time selected.


Creating Hybrid Layouts

Layout flexibility is the property of a facility to remain desirable after significant changes occur or to be easily and inexpensively adopted in response to changes.

A One-worker, multiple-machines (OWMM) cell is a one-person cell in which a worker operates several different machines simultaneously to achieve a line flow.

A Cell is two or more dissimilar workstations located close together through which a limited number of parts or models are processed with line flows.


Group Technology (GT)

Group Technology (GT) is an option for achieving line-flow layouts with low-volume processes; this technique creates cells not limited to just one worker and has a unique way of selecting work to be done by the cell.

The GT method groups parts or products with similar characteristics into families and sets aside groups of machines for their production.


Before Group Technology

Drilling

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Milling

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Assembly

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Lathing

Receiving and shipping

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Jumbled flows in a job shop without GT cellsJumbled flows in a job shop without GT cells


Applied Group TechnologyLine flows in a job shop with three GT cells Line flows in a job shop with three GT cells

Cell 3

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Cell 1 Cell 2

Assembly area

A A

L M DL

L MShipping

D

Receiving

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Warehouse LayoutsOut-and-back Pattern

The most basic warehouse layout is the out-and-back pattern. The numbers indicate storage areas for same or similar items.

Dock Aisle

Storage area

Storage area

3 5 5 6 4 2 7

1 5 5 4 4 2 7


Warehouse LayoutsZone System

Click to add titleZones Zones Control

station Shipping doors

Tractor trailer

Tractor trailer

Overflow

Feeder lines

Feeder lines


Office Layouts

Most formal procedures for designing office layouts try to maximize the proximity of workers whose jobs require frequent interaction.

Privacy is another key factor in office design.

Four common office layouts:

1. Traditional layouts

2. Office landscaping (cubicles/movable partitions)

3. Activity settings

4. Electronic cottages (Telecommuting)


Lean SystemsLean Systems

Chapter 9Chapter 9


How Lean Systems fits the Operations Management

Philosophy

Operations As a Competitive Weapon

Operations StrategyProject Management Process Strategy

Process AnalysisProcess Performance and Quality

Constraint ManagementProcess LayoutLean Systems

Supply Chain StrategyLocation

Inventory ManagementForecasting

Sales and Operations PlanningResource Planning

Scheduling


Toyota Production System (TPS)

Toyota Production System (TPS) is one of the most admired lean manufacturing systems in existence.

They have a process of continuous improvement. Work is completely specified as to content, sequence, timing,

and outcome. Services and goods do not flow to the next available person or

machine, but to a specific person or machine. Employees are stimulated to experiment to find better ways to

do their jobs. Improvements to the system must be made in accordance with

the scientific method, under the guidance of a teacher, at the lowest possible organizational level.


Lean Systems

Lean systems are operations systems that maximize the value added by each of a company’s activities by paring unnecessary resources and delays from them.

Just-in-time (JIT) philosophy The belief that waste can be eliminated by cutting unnecessary capacity or inventory and removing non-value-added activities in operations.

JIT system: A system that organizes the resources, information flows, and decision rules that enable a firm to realize the benefits of JIT principles.


Pull method of work flow Quality at the source

Small lot sizes

Uniform workstation loads

Standardized components & work methods

Close supplier ties

Flexible workforce

Line flows

Automation

Five S

Preventive maintenance

Characteristics of Lean Systems


Push and Pull Systems of Work Flow

Push method: A method in which production of the item begins in advance of customer needs.Example: A buffet where food is prepared in

advance. Pull Method: A method in which customer

demand activates production of the service or item.Example: A restaurant where food is only

prepared when orders are placed. Lean systems use the pull method of work

flow.


Pull method of materials flow Quality at the source Small lot sizes Uniform workstation loads Standardized components & work methods Close supplier ties Flexible workforce Line flows Automation Five S Preventive maintenance



Quality at the Source

Quality at the source is an organization-wide effort to improve the quality of a firm’s products by having employees act as their own quality inspectors, and never pass defective units to next stage.

One approach for implementing quality at the source is to use poka-yoke, mistake-proofing methods aimed at designing fail safe systems that minimize human error.

Another approach for implementing quality at the source is a practice the Japanese call jidoka, and andon, which gives machines and machine operators the ability to detect when an abnormal condition has occurred.





Small Lot Sizes

Lot: A quantity of items that are processed together.

Setup: The group of activities needed to change or readjust a process between successive lots of items.

Single-digit setup: The goal of having a setup time of less than 10 minutes.





Uniform Workstation Loads

A lean system works best if the daily load on individual workstations is relatively uniform.

Service processes can achieve uniform workstation loads by using reservation systems (e.g., scheduled surgeries) and differential pricing to manage the demand.

For manufacturing processes, uniform loads can be achieved by assembling the same type and number of units each day, thus creating a uniform daily demand at all workstations.

Mixed-model assembly produces a mix of models in smaller lots.





Line Flows and Automation

Line Flows: Managers of hybrid-office and back-office service processes can organize their employees and equipment to provide uniform work flows through the process and, thereby, eliminate wasted employee time.

Another tactic used to reduce or eliminate setups is the one-worker, multiple-machines (OWMM) approach, which essentially is a one-person line.

Automation plays a big role in lean systems and is a key to low-cost operations.





Five S (5S)

Five S (5S) A methodology consisting of five workplace practices conducive to visual controls and lean production.

1. 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 is 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.


Continuous Improvement with Lean Systems


The Single-Card Kanban System

Kanban means “card” or “visible record” in Japanese & refers to cards used to control the flow of production through a factory.

General Operating Rules:Ø Each container must have a card.

Ø The assembly line always withdraws materials from fabrication (pull system).

Ø Containers of parts must never be removed from a storage area without a kanban being posted on the receiving post.

Ø The containers should always contain the same number of good parts. The use of nonstandard containers or irregularly filled containers disrupts the production flow of the assembly line.

Ø Only nondefective parts should be passed along.

Ø Total production should not exceed the total amount authorized on the kanbans in the system.


Example 9.1 Westerville Auto Parts Company produces rocker-arm assemblies for use in the steering and suspension systems of four-wheel-drive trucks.

A typical container of parts spends 0.02 day in processing and 0.08 day in materials handling and waiting during its manufacturing cycle.

Daily demand for the part is 2,000 units. Management believes that demand for the rocker-arm assembly is uncertain enough to warrant a safety stock equivalent of 10 percent of inventory.

Determining the Determining the Number of ContainersNumber of Containers


Calculations forCalculations for Example 9.1Example 9.1

k k = = dd( ( ww + + pp )( 1 + )( 1 + ) )

cc

dd = = 20002000 units/day units/day pp = = 0.020.02 day day = 0.10 = 0.10ww = = 0.080.08 day day cc = = 2222 units units

Westerville Auto PartsWesterville Auto Parts

k k = = 20002000( ( 0.080.08 + + 0.020.02 )( 1 + 0.10 ) )( 1 + 0.10 )

2222

k k = 10 containers= 10 containers

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


Calculations forCalculations for Example 9.1Example 9.1

k k = = dd( ( ww + + pp )( 1 + )( 1 + ) )

cc

dd = = 20002000 units/day units/day pp = = 0.020.02 day day = 0.10 = 0.10ww = = 0.060.06 day day cc = = 2222 units units

Westerville Auto PartsWesterville Auto Parts

k k = = 20002000( ( 0.060.06 + + 0.020.02 )( 1 + 0.10 ) )( 1 + 0.10 )

2222

k k = 8 containers= 8 containers

Proposed change from 0.08

b. 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?


Value Stream Mapping

Value stream mapping (VSM) is a qualitative lean tool for eliminating waste (or muda) that involves a current state drawing, a future state drawing, and an implementation plan.

Product family

Current state drawing

Current state drawing

Future state drawing

Future state drawing

Work plan & implementation

Work plan & implementation

Value stream mapping (VSM) spans the entire value chain, from the firm’s receipt of raw materials to the delivery of finished goods to the customer.


Selected Set of Value Stream Mapping Icons


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


Organizational Considerations

The human costs: Lean system implementation requires a high degree of regimentation, and sometimes it can stress the workforce.

Cooperation & Trust: Workers and first-line supervisors must take on responsibilities formerly assigned to middle managers and support staff.

Reward systems and labor classifications must often be revamped when a lean system is implemented.

Existing layouts may need to be changed.


Process ConsiderationsInventory & Scheduling

Schedule Stability: Daily production schedules in high-volume, make-to-stock environments must be stable for extended periods.

Setups: If the inventory advantages of a lean system are to be realized, small lot sizes must be used.

Purchasing and Logistics: If frequent, small shipments of purchased items cannot be arranged with suppliers, large inventory savings for these items cannot be realized.

Krajweski Chapter 8-9

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