IENG 217 Cost Estimating for Engineers
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Transcript of IENG 217 Cost Estimating for Engineers
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IENG 217Cost Estimating for
Engineers
Estimating
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Nature of the estimate Timeliness Purpose Accuracy Effort Accountability
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Universal Methods Opinion
Guesstimating, TLAR Conference
Delphi, Sales Force Composite, Exec. Dec.
Comparison Cc(Dc) < Ca(Da) < Cb(Db)
Unit
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Comparison
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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
,
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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
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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
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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
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Operational Methods Cost estimating relationships Time estimating relationships Performance time data
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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
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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
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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.
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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
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Performance Time Data Time Study Work Sampling
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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
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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
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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
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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%
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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
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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
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Carriage / Support Assembly
Element Test I Test II ConclusionLoad Carriage Machine CarriageUnload CarriageAlign to supportSpot Weld AssemUnload / Store