Process Selection

6-1 Process Selection and Facility Layout

William J. Stevenson

Operations Management

8th edition


CHAPTER6

Process Selection and Facility Layout

McGraw-Hill/IrwinOperations Management, Eighth Edition, by William J. StevensonCopyright © 2005 by The McGraw-Hill Companies, Inc. All rights

reserved.


Process selection Deciding on the way production of goods or

services will be organized Major implications

Capacity planning Layout of facilities Equipment Design of work systems

IntroductionIntroduction


Forecasting

Product andService Design

TechnologicalChange

CapacityPlanning

ProcessSelection

Facilities andEquipment

Layout

WorkDesign

Figure 6.1Process Selection and System DesignProcess Selection and System Design


• Key aspects of process strategy– Capital intensive – equipment/labor– Process flexibility– Adjust to changes

– Design– Volume– technology

Process StrategyProcess Strategy


Variety How much

Flexibility What degree

Volume Expected output

Job Shop

Batch

Repetitive

Continuous

Process SelectionProcess Selection


Job shop Small scale

Batch Moderate volume

Repetitive/assembly line High volumes of standardized goods or services

Continuous Very high volumes of non-discrete goods

Process TypesProcess Types


Process TypeJob Shop Appliance repair

Emergency room

Not feasible

Batch Commercialbakery

ClassroomLecture

Repetitive Automotiveassembly

Automaticcarwash

Continuous(flow)

Notfeasible

Oil refineryWater purification

Figure 6.2Product – Process MatrixProduct – Process Matrix


DimensionJob variety Very High Moderate Low Very low

Process flexibility

Very High Moderate Low Very low

Unit cost Very High Moderate Low Very low

Volume of output

Very High Low High Very low

Figure 6.2 (cont’d)Product – Process MatrixProduct – Process Matrix


Automation: Machinery that has sensing and control devices that enables it to operate Fixed automation Programmable automation

AutomationAutomation


• Computer-aided design and manufacturing systems (CAD/CAM)

• Numerically controlled (NC) machines • Robot• Manufacturing cell• Flexible manufacturing systems(FMS)• Computer-integrated manufacturing (CIM)

AutomationAutomation


Layout: the configuration of departments, work centers, and equipment, with particular emphasis on movement of work (customers or materials) through the system

Facilities LayoutFacilities Layout


Requires substantial investments of money and effort

Involves long-term commitments Has significant impact on cost and

efficiency of short-term operations

Importance of Layout DecisionsImportance of Layout Decisions


Inefficient operations

For Example:

High CostBottlenecks

Changes in the designof products or services

The introduction of newproducts or services

Accidents

Safety hazards

The Need for Layout DecisionsThe Need for Layout Decisions


Changes inenvironmentalor other legalrequirements

Changes in volume ofoutput or mix of

products

Changes in methodsand equipment

Morale problems

The Need for Layout Design (Cont’d)The Need for Layout Design (Cont’d)


Product layouts Process layouts Fixed-Position layout Combination layouts

Basic Layout TypesBasic Layout Types


Product layout Layout that uses standardized processing

operations to achieve smooth, rapid, high-volume flow

Process layout Layout that can handle varied processing

requirements Fixed Position layout

Layout in which the product or project remains stationary, and workers, materials, and equipment are moved as needed

Basic Layout TypesBasic Layout Types


Raw materialsor customer

Finished item

Station 2

Station 3

Station 4

Material and/or labor

Station 1




Used for Repetitive or Continuous Processing

Figure 6.4Product LayoutProduct Layout


High rate of output Low unit cost Labor specialization Low material handling cost High utilization of labor and equipment Established routing and scheduling Routing accounting and purchasing

Advantages of Product LayoutAdvantages of Product Layout


Creates dull, repetitive jobs Poorly skilled workers may not maintain

equipment or quality of output Fairly inflexible to changes in volume Highly susceptible to shutdowns Needs preventive maintenance Individual incentive plans are impractical

Disadvantages of Product LayoutDisadvantages of Product Layout


1 2 3 4

5

6

78910

In

Out

Workers

Figure 6.6

A U-Shaped Production LineA U-Shaped Production Line


Dept. A

Dept. B Dept. D

Dept. C

Dept. F

Dept. E

Used for Intermittent processingJob Shop or Batch

Process Layout(functional)

Figure 6.7Process LayoutProcess Layout


Work Station 1

Work Station 2

Work Station 3

Figure 6.7 (cont’d)

Product Layout(sequential)

Used for Repetitive ProcessingRepetitive or Continuous

Product LayoutProduct Layout


Can handle a variety of processing requirements

Not particularly vulnerable to equipment failures

Equipment used is less costly Possible to use individual incentive plans

Advantages of Process LayoutsAdvantages of Process Layouts


In-process inventory costs can be high Challenging routing and scheduling Equipment utilization rates are low Material handling slow and inefficient Complexities often reduce span of supervision Special attention for each product or customer Accounting and purchasing are more involved

Disadvantages of Process LayoutsDisadvantages of Process Layouts


Cellular Production Layout in which machines are grouped into a

cell that can process items that have similar processing requirements

Group Technology The grouping into part families of items with

similar design or manufacturing characteristics

Cellular LayoutsCellular Layouts


Dimension Functional CellularNumber of moves between departments

many few

Travel distances longer shorter

Travel paths variable fixed

Job waiting times greater shorter

Throughput time higher lower

Amount of work in process

higher lower

Supervision difficulty higher lower

Scheduling complexity higher lower

Equipment utilization lower higher

Table 6.3Functional vs. Cellular LayoutsFunctional vs. Cellular Layouts


Warehouse and storage layouts Retail layouts Office layouts

Other Service LayoutsOther Service Layouts


Line Balancing is the process of assigning tasks to workstations in such a way that the workstations have approximately equal time requirements.

Design Product Layouts: Line Design Product Layouts: Line BalancingBalancing


Cycle time is the maximum time allowed at each workstation tocomplete its set of tasks on a unit.

Cycle TimeCycle Time


O utput capac ity = O TC T

O T operating tim e per day

D = D es ired output ra te

C T = cyc le tim e = O TD

Determine Maximum OutputDetermine Maximum Output


N = (D)( t)

OT

t = sum of task times

Determine the Minimum Number Determine the Minimum Number of Workstations Requiredof Workstations Required


Precedence diagram: Tool used in line balancing to display elemental tasks and sequence requirements

A Simple Precedence Diagrama b

c d e

0.1 min.

0.7 min.

1.0 min.

0.5 min. 0.2 min.

Figure 6.10

Precedence DiagramPrecedence Diagram


Arrange tasks shown in Figure 6.10 into three workstations. Use a cycle time of 1.0 minute Assign tasks in order of the most number of

followers

Example 1: Assembly Line BalancingExample 1: Assembly Line Balancing


WorkstationTimeRemaining Eligible

AssignTask

RevisedTime Remaining

StationIdle Time

1 1.00.90.2

a, ccnone

ac-

0.90.2

0.2

2 1.0 b b 0.0 0.0

3 1.00.50.3

de-

de-

0.50.3 0.3

0.5

Example 1 SolutionExample 1 Solution


Percent idle time = Idle time per cycle(N)(CT)

Efficiency = 1 – Percent idle time

Calculate Percent Idle TimeCalculate Percent Idle Time


Assign tasks in order of most following tasks.

Count the number of tasks that follow Assign tasks in order of greatest positional

weight. Positional weight is the sum of each task’s

time and the times of all following tasks.

Some Heuristic (intuitive) Rules:

Line Balancing RulesLine Balancing Rules


c d

a b e

f g h

0.2 0.2 0.3

0.8 0.6

1.0 0.4 0.3

Example 2Example 2


Station 1 Station 2 Station 3 Station 4

a b ef

d

g h

c

Solution to Example 2Solution to Example 2


1 min.2 min.1 min.1 min. 30/hr. 30/hr. 30/hr. 30/hr.

1 min.

1 min.

1 min.1 min. 60/hr.

30/hr. 30/hr.

60/hr.

1 min.

30/hr.30/hr.

Bottleneck

Parallel Workstations

Parallel WorkstationsParallel Workstations


Information Requirements:1. List of departments2. Projection of work flows3. Distance between locations4. Amount of money to be invested5. List of special considerations6. Location of key utilities

Designing Process LayoutsDesigning Process Layouts


1 3 2

30

170 100

A B C

Figure 6.12

Example 3: Interdepartmental Work FlowsExample 3: Interdepartmental Work Flowsfor Assigned Departmentsfor Assigned Departments


Author’s note: The following three slides are not in the 8e,

but I like to use them for alternate examples.


Process Layout - work travels to dedicated process centers

Milling

Assembly& Test Grinding

Drilling Plating

Process LayoutProcess Layout


Gearcutting

Mill Drill

Lathes

Grind

Heattreat

Assembly

111

333

222

444

222111444

111 3331111 2222

222

3333

111

444111

333333333

44444

3333

3322

222

Functional LayoutFunctional Layout


-1111 -1111

222222222 - 2222

Ass

embl

y

3333333333 - 3333

44444444444444 - 4444

Lathe

Lathe

Mill

Mill

Mill

Mill

Drill

Drill

Drill

Heat treat

Heat treat

Heat treat

Gear cut

Gear cut

Grind

Grind

Cellular Manufacturing LayoutCellular Manufacturing Layout


Flexible ManufacturingFlexible Manufacturing

VD7

Process at Trek Bikes


Location/CriteriaLocation/Criteria

PS11

Guitar site location


Process OverviewProcess Overview

AB2

Aluminum tubing, suppliers at Hillerich & Bradsby

Process Selection

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