Process Selection and Layout

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McGraw-Hill/IrwinOperations Management, Seventh Edition, by William J. StevensonCopyright © 2002 by The McGraw-Hill Companies, Inc. All rights reserved.

Process Selection and Facility Layout

Chapter 6

Process Selection and

Facility Layout

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Process Selection and System Design

Forecasting

Product and service design

Capacity planning

Facilities andEquipment

Layout

Work design

Processselection

Technologicalchange

Process selection defines the way production is organized, how things will be done

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Process Strategy

• How an organization approaches the process selection process

• Important concerns:– Make or buy?– Capital intensity– Process flexibility

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Introduction

• Make or Buy?– Available capacity– Expertise– Quality Consideration– The nature of demand– Cost

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• Product Variety– How much

• Process Flexibility– What degree will be required

• Volume – Expected output

Process Selection

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Process Types• Job Shops

– Small runs, high variety– Requires skilled labor and flexible

equipment• Batch Processing

– Moderate volume, moderate variety, moderate skill

• Repetitive/Assembly– Semicontinuous– Higher volume, more standardized, less

flexibility and skill required

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Process Types

• Continuous Processing– High volume, highly standardized

• Projects– Nonroutine jobs, limited duration– Large products like buildings

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ProductVariety

High Moderate Low Very Low

Equipmentflexibility

High Moderate Low Very Low

LowVolume

ModerateVolume

HighVolume

Very highVolume

JobShop

Batch

Repetitiveassembly

ContinuousFlow

Variety, Flexibility, & Volume

Job Shop

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• Automation: Machinery that operates automatically, with little or no human intervention• Advantages:

– Consistency– Elimination of negative human factors– Reduced variable costs

• Disadvantages– High initial investment– High fixed costs– Requires high volume to offset costs– Less flexible than human labor– Can hurt worker morale

Automation

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Automation

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

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

(CIM)

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Management of Technology

• Potential effects of new technology:– Improved quality– Increased productivity– Reduced production times– Increased customer satisfaction– Reduced flexibility– Increased fixed costs– Short-term disruptions– Increased training costs– Difficult integration with existing systems

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• Service blueprint: A method used in service design to describe and analyze a proposed service.

• Steps:– Establish boundaries and determine the required level of detail– Identify and describe the steps of a process– Flowchart key process steps– Identify potential failure points– Establish a time frame for service execution and estimate variability– Analyze profitability and zero in on process steps with the biggest impact

Service Blueprint

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

• Important because:– Require substantial investments of time and

money– Involve long-term commitments– Significant impact on cost and efficiency

Layout

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Layout

• Reasons to redesign an existing layout:– Inefficiency– Accidents or safety hazards– Changes in product design– Introduction of new products– Changes in output volume or mix– Changes in regulations

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Basic Layout Types

• Product Layouts

• Process Layouts

• Fixed-Position

• Combination Layouts

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Product Layout• Work divided into a series of standard tasks that every unit goes through• Often uses fixed-path material handling• Entire line can be shut down by one mechanical failure• Advantages:

– High output– Low unit cost– Labor specialization reduces training costs– High utilization rate of labor and equipment

• Disadvantages– Dull, repetitive jobs– Not very flexible to product design or volume changes– Susceptible to shutdowns

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A Flow Line for Production or Service

Flow Shop or Assembly Line Work Flow

Raw materialsor customer

Finished item

Station 2

Station 3

Station 4

Material and/or labor

Station 1Material and/or labor



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A U-Shaped Production Line

1 2 3 4

5

6

78910

In

Out

Workers

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Process Layout• Work divided into departments, each of which handles a given

process• Products follow different paths depending on processing

requirements• Equipment must be more general-purpose• Advantages:

– More flexible– Not as vulnerable to shutdowns– General-purpose equipment often cheaper than specialized

• Disadvantages:– Routing and scheduling can be difficult– Low utilization rates– More costly material handling– Complex jobs can lead to higher supervision costs

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Process Layout

Process Layout - work travels to dedicated process centers

Milling

Assembly& Test Grinding

Drilling Plating

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Functional 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

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Fixed Position Layout

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

• Requires special attention to time materials and workers to prevent clogging up the jobsite

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Design Product Layouts: Line Balancing

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

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Cycle Time

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

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Determine Maximum Output

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

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Determine the Minimum Number of Workstations Required: Efficiency

N = (D)( t)

OT

t = sum of task times

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Precedence Diagram

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.

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Example 1: Assembly Line Balancing

• Arrange tasks shown in the previous slide into workstations.– Use a cycle time of 1.0 minute– Assign tasks in order of the most number of

followers

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Solution to Example 1

W o r k -S t a t i o n

T i m eR e m a i n i n g E l i g i b l e

A s s i g nT a s k

S t a t i o nI d l e T i m e

1 1 . 0. 9. 2

ac

n o n e

ac- . 2

2 1 . 00

bn o n e

b- 0

3 1 . 0. 5. 3

de-

de- . 3

. 5

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Calculate Percent Idle Time

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

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Line Balancing Rules

• Assign tasks in order of most following tasks.

• 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:

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Solution to Example 2

Station 1 Station 2 Station 3 Station 4

a b ef

d

g h

c

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Parallel Workstations

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

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• Requirements:– List of departments– Projection of work flows– Distance between locations– Amount of money to be invested– List of special considerations

Designing Process Layouts

Documents

Process Selection and Layout