IENG 217Cost Estimating for

Engineers

Estimating

Nature of the estimate Timeliness Purpose Accuracy Effort Accountability

Universal Methods Opinion

Guesstimating, TLAR Conference

Delphi, Sales Force Composite, Exec. Dec.

Comparison Cc(Dc) < Ca(Da) < Cb(Db)

Unit

Comparison

Unit

CC

n

where

C average per unit of design

C value of design i dollars

n design i unit

ai

i

a

i

i

cost

,

Unit Metal machining cost may be related to

length of the bar stock that is turned on a lathe. Actual tickets yield

Design Ci, $ Length

1 20 22 30 33 60 4

Total 110 9

Unit Metal machining cost may be related to

length of the bar stock that is turned on a lathe. Actual tickets yield

Ca = 110/9 = $12.22 / in.

Design Ci, $ Length

1 20 22 30 33 60 4

Total 110 9

Unit Cost

Fails to apply principle of economy of scale Accounts for slope only Regression: Ca = -23.3 + 20(length)

Cost per Bar Stock Length

0102030

40506070

0 1 2 3 4 5

Inches

Co

st (

$) Actual

Estimate

Operational Methods Cost estimating relationships Time estimating relationships Performance time data

Cost Estimating Relationships Parameters

Ca = -23.3 + 20(length)

bar stock length ( 5 inches ) used in CER ( $76.70 ) is often called a parameter – it is not

CER is actually a parametric equation

Cost Estimating Relationship

CI x V x C x in ft

S x hr x Mpcur

( / ) ./ .

/ .

1000 12

60 min

where

C power cost per foot

I welding current,amperes

V welding voltage

C utility power cost,dollars per KWhr

S travel speed of arc welding process,in. per minute

M machineefficiency, percentage

pc

ur

Cost Estimating Relationship Typical arc welder draws 200 amps

for a 20 volt arc welding process. If we have a 10 in/min welding travel speed and a 95% machine efficiency, estimate the cost per foot of a weld if the utility costs are $0.08 per KWhr.

Cost Estimating Relationship

WWII military aircraft constructed of aluminum (regression; 10 contractors)F A S Q

where

F flight test operations base year

number of flight test airframes

D

0 001244

1970

1 160 1 371 1 281.

, ( )

. . .

cost

A=weight without engines, fuel, pounds

S=maximum airspeed, nautical miles / sec

QD

Performance Time Data Time Study Work Sampling

Performance Time Data Alg.

1. Collected several measurements from ops.2. Classify elements into common group3. Regress element time against one or more

independent causal variables4. Determine if TER is constant or variable5. If TER is constant, determine value6. If TER is variable, convert to time table or eq.7. Collect all constant variable elements for

operation8. If accuracy is acceptable, use information for

estimating designs

Constant or Variable ? 5 time measurements taken on a

manual handling task

Weight, lb. 1 3 4 5 7

Time, min. .15 .20 .30 .40 .50

Regression yields . .y x 0 06 0 0625

Constant or Variable ? Test 1

Test 2

%max min

min

y y

yx P

100 1

%

y

yx P

y total dependent value for x of operationelements

ave

t

t

100 2

Constant or Variable ? 5 time measurements taken on a manual

handling task (test 1, P1 = 100%)

Weight, lb. 1 3 4 5 7

Time, min. .15 .20 .30 .40 .50 yhat .1225 .4975

.4975 .

..max min

min

y y

y

1225

12253 06 306%

Carriage / Support Assembly

Element Parameter (xi) a b

Load Carriage Carriage Length 0.20 0.08Machine Carriage Carriage Length 1.20 0.20Unload Carriage Support girth 0.40 0.04Align to support Support girth 0.15 0.10Spot Weld Assem No. Welds 0.15 0.12Unload / Store Carriage Length 0.30 0.02

Regression

Carriage / Support Assembly

Element xmin xave xmax ymin yave ymax

Load Carriage 5.00 6.20 8.00 0.60 0.70 0.84Machine Carriage 23.00 27.20 29.30 5.80 6.64 7.06Unload Carriage 7.00 7.40 8.20 0.68 0.70 0.73Align to support 5.30 7.20 8.40 0.68 0.87 0.99Spot Weld Assem 12.40 15.20 18.80 1.64 1.97 2.41Unload / Store 6.80 7.00 7.20 0.44 0.44 0.44

SUM = 9.83 11.32 12.47

Carriage / Support Assembly

Element Test I Test II ConclusionLoad Carriage Machine CarriageUnload CarriageAlign to supportSpot Weld AssemUnload / Store