s7 - 1© 2011 pearson education, inc. publishing as prentice hall s7 capacity and constraint...

S7 - 1© 2011 Pearson Education, Inc. publishing as Prentice Hall

S7S7 Capacity and Constraint Management

Capacity and Constraint Management

PowerPoint presentation to accompany PowerPoint presentation to accompany Heizer and Render Heizer and Render Operations Management, 10e Operations Management, 10e Principles of Operations Management, 8ePrinciples of Operations Management, 8e

PowerPoint slides by Jeff Heyl


Process StrategiesProcess Strategies

The objective of a process strategy is The objective of a process strategy is to build a production process that to build a production process that meets customer requirements and meets customer requirements and product specifications within cost product specifications within cost and other managerial constraintsand other managerial constraints


CapacityCapacity

The throughput, or the number of units a facility can hold, receive, store, or produce in a period of time

Determines fixed costs

Determines if demand will be satisfied

Determines if facilities remain idle


Planning Over a Time Planning Over a Time HorizonHorizon

Figure S7.1

Modify capacity Use capacity

Intermediate-range planning

Subcontract Add personnelAdd equipment Build or use inventory Add shifts

Short-range planning

Schedule jobsSchedule personnel Allocate machinery*

Long-range planning

Add facilitiesAdd long lead time equipment *

* Difficult to adjust capacity as limited options exist

Options for Adjusting Capacity


Design and Effective Design and Effective CapacityCapacity

Design capacity is the maximum theoretical output of a system Normally expressed as a rate

Effective capacity is the capacity a firm expects to achieve given current operating constraints Often lower than design capacity


Utilization and EfficiencyUtilization and Efficiency

Utilization is the percent of design capacity Utilization is the percent of design capacity achievedachieved

Efficiency is the percent of effective capacity Efficiency is the percent of effective capacity achievedachieved

Utilization = Actual output/Design capacity

Efficiency = Actual output/Effective capacity


Bakery ExampleBakery Example

Actual production last week = 148,000 rollsEffective capacity = 175,000 rollsDesign capacity = 1,200 rolls per hourBakery operates 7 days/week, 3 - 8 hour shifts

Design capacity = (7 x 3 x 8) x (1,200) = 201,600 rolls





Utilization = 148,000/201,600 = 73.4%





Utilization = 148,000/201,600 = 73.4%

Efficiency = 148,000/175,000 = 84.6%


Bakery ExampleBakery Example: Estimating Output of : Estimating Output of a New Facilitya New Facility

They are considering adding a second production line and they plan to hire new employees and train them tooperate this new lineEffective capacity on this new line = 175,000 rolls whichis the same on the first lineHowever, due to new hires they expect that efficiency of this new line will be 75% rather than 84.6%

Expected Output = (Effective Capacity)(Efficiency)

= (175,000)(.75) = 131,250 rolls


Capacity ConsiderationsCapacity Considerations

1. Forecast demand accurately

2. Understand the technology and capacity increments

3. Find the optimum operating level (volume)

4. Build for change


Economies and Economies and Diseconomies of ScaleDiseconomies of Scale

Economies of scale

Diseconomies of scale

25 - room roadside motel 50 - room

roadside motel

75 - room roadside motel

Number of Rooms25 50 75

Av

era

ge

un

it c

os

t(d

olla

rs p

er

roo

m p

er n

igh

t)

Figure S7.2


Managing DemandManaging Demand Demand exceeds capacity

Curtail demand by raising prices, scheduling longer lead time

Long term solution is to increase capacity

Capacity exceeds demand Stimulate market

Product changes

Adjusting to seasonal demands Produce products with complementary

demand patterns


Complementary Demand Complementary Demand PatternsPatterns

4,000 –

3,000 –

2,000 –

1,000 –

J F M A M J J A S O N D J F M A M J J A S O N D J

Sal

es i

n u

nit

s

Time (months)

Jet ski engine sales

Figure S7.3



4,000 –

3,000 –

2,000 –

1,000 –


Sal

es i

n u

nit

s

Time (months)

Snowmobile motor sales


Figure S7.3



4,000 –

3,000 –

2,000 –

1,000 –


Sal

es i

n u

nit

s

Time (months)

Combining both demand patterns reduces the variation

Snowmobile motor sales


Figure S7.3


Tactics for Matching Tactics for Matching Capacity to DemandCapacity to Demand

1. Making staffing changes

2. Adjusting equipment Purchasing additional machinery

Selling or leasing out existing equipment

3. Improving processes to increase throughput

4. Redesigning products to facilitate more throughput

5. Adding process flexibility to meet changing product preferences

6. Closing facilities


Demand and Capacity Demand and Capacity Management in the Service Management in the Service

SectorSector Demand management (scheduling

customers)

Appointment, reservations, FCFS rule

Capacity management

(scheduling workforce)

Full time, temporary, part-time staff


Bottleneck Analysis and Bottleneck Analysis and Theory of ConstraintsTheory of Constraints

Each work area can have its own unique capacity

Capacity analysis determines the throughput capacity of workstations in a system

A bottleneck is a limiting factor or constraint

A bottleneck has the lowest effective capacity in a system

S7 - 23


Bottleneck ManagementBottleneck Management

1. Release work orders to the system at the pace of set by the bottleneck

2. Lost time at the bottleneck represents lost time for the whole system

3. Increasing the capacity of a non-bottleneck station is a mirage

4. Increasing the capacity of a bottleneck increases the capacity of the whole system


Process Times for Stations, Process Times for Stations, Systems, and CyclesSystems, and Cycles

The process time of a stationprocess time of a station is the time to produce a unit at that single workstation

The process time of a systemprocess time of a system is the time of the longest process in the system … the bottleneck

The process cycle timeprocess cycle time is the time it takes for a product to go through the production process with no waiting

These two might be quite

different!


Process Times for Stations, Process Times for Stations, Systems, and CyclesSystems, and Cycles

The system process timesystem process time is the process time of the bottleneck after dividing by the number of parallel operations

The system capacitysystem capacity is the inverse of the system process time

The process cycle timeprocess cycle time is the total time through the longest path in the system


A Three-Station Assembly LineA Three-Station Assembly LineProcess time of stationsProcess time of stations: 2, 4 and 3 min/unit: 2, 4 and 3 min/unitProcess time for the systemProcess time for the system: 4 min/unit: 4 min/unitProcess Cycle TimeProcess Cycle Time= 2 + 4 + 3 = 9 min/unit= 2 + 4 + 3 = 9 min/unitSystem Capacity System Capacity = ¼*60(min)= 15 units/hour= ¼*60(min)= 15 units/hour

Figure S7.4

2 min/unit 4 min/unit 3 min/unit

A B C

QuickTime™ and a decompressor

are needed to see this picture.


Capacity AnalysisCapacity Analysis Two identical sandwich lines

Lines have two workers and three operations

All completed sandwiches are wrapped

Wrap

37.5 sec/sandwich

Order

30 sec/sandwich

Bread Fill Toast

15 sec/sandwich 20 sec/sandwich 40 sec/sandwich

Bread Fill Toast

15 sec/sandwich 20 sec/sandwich 40 sec/sandwich


Capacity Capacity AnalysisAnalysis Wrap

37.5 sec

Order

30 sec

Bread Fill Toast

15 sec 20 sec 40 sec

Bread Fill Toast

15 sec 20 sec 40 sec

It seems that the toast work station has the longest processing time – 40 seconds, but the two lines work in parallel and each deliver a sandwich every 40 seconds so the process time of the toast work station is 40/2 = 20 seconds per sandwich.

Order: 37 seconds, Combined Assembly:20 seconds, Wrapping:37.5 seconds

With 37.5 seconds, wrapping station has the longest processing time and it is the bottleneck. So process time of the system is 37.5 sec.

System capacity per hour is (1/37.5)*3,600 seconds = 96 sandwiches per hour

Process cycle time is 30 + 15 + 20 + 40 + 37.5 = 142.5 seconds


Capacity AnalysisCapacity AnalysisExample S4, pg.322Example S4, pg.322

Standard process for cleaning teeth

Cleaning and examining X-rays can happen simultaneously

Customerpays

6 min/unit

Customer Checks in

2 min/unit

A Lab Ass Develops

X-ray

4 min/unit 8 min/unit

Dentistre-processes

A Lab Ass.TakesX-ray

2 min/unit

5 min/unit

DentistExaminesX-ray andprocesses

HygienistCleans

the teeth

24 min/unit


Capacity Capacity AnalysisAnalysis All possible paths must be compared

Cleaning path is 2 + 2 + 4 + 24 + 8 + 6 = 46 minutes, X-ray exam path is 2 + 2 + 4 + 5 + 8 + 6 = 27 minutes

Longest path involves the hygienist cleaning the teeth, so the process cycle time is 46 min. The patient will be out of door after 46 min.

Bottleneck is the hygienist at 24 minutes which is the process time of the system

System capacity is (1/24)*60 min = 2.5 patients/per hour

Checkout

6 min/unit

Check in

2 min/unit

DevelopsX-ray

4 min/unit 8 min/unit

DentistTakesX-ray

2 min/unit

5 min/unit

X-rayexam

Cleaning

24 min/unit


Break-Even AnalysisBreak-Even Analysis

Technique for evaluating process and equipment alternatives

Objective is to find the point in dollars and units at which cost equals revenue

Requires estimation of fixed costs, variable costs, and revenue


Break-Even AnalysisBreak-Even Analysis Fixed costs are costs that continue

even if no units are produced Depreciation, taxes, debt, mortgage

payments

Variable costs are costs that vary with the volume of units produced Labor, materials, portion of utilities

Contribution is the difference between selling price and variable cost



Costs and revenue are linear functions Generally not the case in the

real world

We actually know these costs Very difficult to verify

Time value of money is often ignored

AssumptionsAssumptions


Profit corri

dor

Loss

corridor

Break-Even AnalysisBreak-Even AnalysisTotal revenue line

Total cost line

Variable cost

Fixed cost

Break-even pointTotal cost = Total revenue

–

900 –

800 –

700 –

600 –

500 –

400 –

300 –

200 –

100 –

–| | | | | | | | | | | |

0 100 200 300 400 500 600 700 800 900 10001100

Co

st in

do

llars

Volume (units per period)Figure S7.5



BEPx = break-even point in unitsBEP$ = break-even point in dollarsP = price per unit (after all discounts)

x = number of units producedTR= total revenue = PxF = fixed costsV = variable cost per unitTC= total costs = F + Vx

TR = TCor

Px = F + Vx

Break-even point occurs whenBreak-even point occurs when

BEPx =F

P - V



BEPx = break-even point in unitsBEP$ = break-even point in dollarsP = price per unit (after all discounts)

x = number of units producedTR= total revenue = PxF = fixed costsV = variable cost per unitTC= total costs = F + Vx

BEP$ = BEPx P

= P

=

=

F(P - V)/P

FP - V

F1 - V/P

Profit = TR - TC= Px - (F + Vx)= Px - F - Vx= (P - V)x - F


Break-Even ExampleBreak-Even Example

Fixed costs = $10,000 Material = $.75/unitDirect labor = $1.50/unit Selling price = $4.00 per unit

BEP$ = =F

1 - (V/P)$10,000

1 - [(1.50 + .75)/(4.00)]



Fixed costs = $10,000 Material = $.75/unitDirect labor = $1.50/unit Selling price = $4.00 per unit

BEP$ = =F

1 - (V/P)$10,000

1 - [(1.50 + .75)/(4.00)]

= = $22,857.14$10,000

.4375

BEPx = = = 5,714F

P - V$10,000

4.00 - (1.50 + .75)



50,000 –

40,000 –

30,000 –

20,000 –

10,000 –

–| | | | | |

0 2,000 4,000 6,000 8,000 10,000

Do

llars

Units

Fixed costs

Total costs

Revenue

Break-even point


MultiproductMultiproduct Break-Even Break-Even AnalysisAnalysis

BEP$ =F

∑ 1 - x (Wi)Vi

Pi

Each product’s contribution is weighted by Each product’s contribution is weighted by its proportion of salesits proportion of sales

where V = variable cost per unitP = price per unitF = fixed costs

W = percent each product is of total dollar salesi = each product


Multiproduct ExampleMultiproduct Example

Annual ForecastedItem Price Cost Sales UnitsSandwich $5.00 $3.00 9,000Drink 1.50 .50 9,000Baked potato 2.00 1.00 7,000

Fixed costs = $3,000 per month





Sandwich $5.00 $3.00 .60 .40 $45,000 .621 .248Drinks 1.50 .50 .33 .67 13,500 .186 .125Baked 2.00 1.00 .50 .50 14,000 .193 .096 potato

$72,500 1.000 .469

Annual WeightedSelling Variable Forecasted % of Contribution

Item (i) Price (P) Cost (V) (V/P) 1 - (V/P) Sales $ Sales (col 5 x col 7)





Sandwich $5.00 $3.00 .60 .40 $45,000 .621 .248Drinks 1.50 .50 .33 .67 13,500 .186 .125Baked 2.00 1.00 .50 .50 14,000 .193 .096 potato

$72,500 1.000 .469

Annual WeightedSelling Variable Forecasted % of Contribution

Item (i) Price (P) Cost (V) (V/P) 1 - (V/P) Sales $ Sales (col 5 x col 7)

BEP$ =F

∑ 1 - x (Wi)Vi

Pi

= = $76,759$3,000 x 12

.469

Daily sales = = $246.02

$76,759312 days

.621 x $246.02$5.00 = 30.6 31

sandwichesper day


Reducing Risk with Reducing Risk with Incremental ChangesIncremental Changes

(a) Leading demand with incremental expansion

Dem

and

Expected demand

New capacity

(c) Attempts to have an average capacity with incremental expansion

Dem

and

New capacity Expected

demand

(b) Capacity lags demand with incremental expansion

Dem

and

New capacity

Expected demand

Figure S7.6



(a) Leading demand with incremental expansion

Expected demand

Figure S7.6

New capacity

Dem

and

Time (years)1 2 3



(b) Capacity lags demand with incremental expansion

Expected demand

Figure S7.6

Dem

and

Time (years)1 2 3

New capacity


Reducing Risk with Reducing Risk with Incremental ChangesIncremental Changes(c) Attempts to have an average capacity

with incremental expansion

Expected demand

Figure S7.6

New capacity

Dem

and

Time (years)1 2 3


Expected Monetary Value Expected Monetary Value (EMV) and Capacity Decisions(EMV) and Capacity Decisions

Determine states of nature Future demand

Market favorability

Analyzed using decision trees Hospital supply company

Four alternatives



-$90,000Market unfavorable (.6)

Market favorable (.4)$100,000

Large plant

Market favorable (.4)

Market unfavorable (.6)

$60,000

-$10,000

Medium plant



$40,000

-$5,000

Small plant

$0

Do nothing





Large plant



$60,000

-$10,000

Medium plant



$40,000

-$5,000

Small plant

$0

Do nothing

EMV = (.4)($100,000) + (.6)(-$90,000)

Large Plant

EMV = -$14,000





Large plant



$60,000

-$10,000

Medium plant



$40,000

-$5,000

Small plant

$0

Do nothing

-$14,000

$13,000

$18,000

s7 - 1© 2011 pearson education, inc. publishing as prentice hall s7 capacity and constraint...

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