IENG 217Cost Estimating for

Engineers

Operation Estimating

Operation Cost Elements

Direct Material

Direct Labor

Tooling

Prime Cost

EstimatedOperation

Cost

Turning Operation

Operation Time tpr = total process time = machine time + handling time + tool change time

= tm + th + tc(tm/T)where

tm = machine time

th = time to load/unload machine

tc = time to change a tool

(tm/t) = no. parts that can be produced before a tool change is required

T = life of a tool

Operation Time

cpr = production cost

= batch cost + machine cost + tool cost

cc

Nc t t

t

Tt c

t

T

where

c

total machine operator rate

c of tool

N batch size

prb

bo m h

mc pt

m

b

pt

b

( ) ( )

&

cost of batch setup

c

costo

Machining Time Function of rate of processing

t tool path length feed speed

L

f N

where

f feed inches tooth revolution

N rpm

m

/

( / / )

Machining Time Function of rate of processing

t tool path length feed speed

L

f N

L

fVD

L D

f V

m

/

12 12

Example 3” diameter piece to be turned to 2.8” diameter,

length of stock to be turned is 10”, f = 0.01”/rev., V = cut speed = 200 fpm, d = depth of cut = .2”.

Find machine processing time

Tool Life V

V

t

T

where

n

V cutting speed

T tool life

V ref cutting speed

t ref tool life

r

rn

r

r

FHIK

constant

.

.

n

r

r T

t

V

V

Tool Life

V

V

t

T

TV

Vt

Tt V

V

C

V

r

rn

n rrn

r rn

n

FHIK

1

1

/

/

n

r

r T

t

V

V

Example

HSS cutter; at 250 sfpm tool lasts 30 min; at 100 sfpm tool lasts 60 min. Find tool life eq.

Operation Time

tpr = total process time

= machine time + handling time + tool change time

= tm + th + tc(tm/T)

cc

Nc t t

t

Tt c

t

Tprb

bo m h

mc pt

m ( ) ( )

Operation Time

tpr = total process time

= machine time + handling time + tool change time

= tm + th + tc(tm/T)

cc

Nc t t

t

Tt c

t

Tprb

bo m h

mc pt

m ( ) ( )

Q: Do we want to minimize processing time or do we want to minimize part cost?

Example Turning operation; L=10 inches, D = 3inches to

2.9 inches, feed = 0.1 inch/rev, load and unload = 2 min, cutter change = 3 min, tool life given by

T = 1.7x105 V-1.7, Co = $35/hr, Cpt = $3 / cutter

Example Turning operation; L=10 inches, D = 3inches to 2.9 inches, feed = 0.1

inch/rev, load and unload = 2 min, cutter change = 3 min, tool life given by T = 1.7x105 V-1.7, Co = $35/hr, Cpt = $3 / cutter

nV

D

VV

V fn V V

tL

V VV

f

mf

12 123 2 9

2

1 273

0 1 1 273 1273

10

127378 5 1

. .

. ( . ) .

.

Example

tL

V VV

t t t t t T

VV

x V

V V

mf

pr m h c m

FHG

IKJ

10

127378 5

78 5 2 378 5

1 7 10

78 5 2 001386

1

11

5 1 7

1 1

.

( / )

..

.

. .

. 715

1

1071

578..

.

Vx

V

Operations Analysis Factual time and cost estimating catalogues Product design Process knowledge Operations sheet preparation Time and cost finding

Time Elements Setup time Cycle time

Setup TimeElement Time (hrs)Punch in, study drawing 0.2Turning Equipment First machining tool 0.8 Additional tool 0.3 Collet 0.2 Fixture 0.2Milling Equipment Vise 0.6 Fixture 1.2 Collet 0.5Drilling Equipment Fixture 0.3 Vise 0.1 First Spindle 0.7 Additional spindles 0.4Total Setup Time 5.5

Cycle Time Elements Element Time (min) Time (min)General Start/stop machine 0.10 Air clean part 0.09 Brush chips 0.12 Inspect w/micrometer 0.30 Total General 0.61Turning Equipment Advance/Index turret 0.08 Cross slide adv/index 0.09 Advance stock 0.23 Place guard / start 0.16 Total Turn Specific 0.56Milling Equipment 1.8Drilling 1.2Total Setup Time 4.17

Product Design

Process knowledge

Workstation Ops. No. DescriptionTurret Lathe 10 Turn and cutoffVertical Mill 20 End Mill SlotHorizontal Mill 30 Slab Mill FlatNC Drill Press 40 Drill and Tap Holes

Operations Sheet

Cost Estimates Design Length 18.750Facing Length 0.015Cutoff Length 0.187Total Length 18.952Units / 12 ft bar stock 7.598Units / 12 ft bar stock 7Bars per Lot (200) 28.571Bars per Lot (200) 29Cost per bar (8.178 lb/ft x 12 ft x $1.5/lb) $147.20Lot Cost (bars/lot x cost per bar) $4,268.92Cost per unit (Lot Cost/Lot Size $21.34Material Yield (200 x fl / total length) 89.8%

Setup & Cycle for Operation 10Setup Elements Punch in, study drawing 0.2 First machining tool 0.8 Additional tool 0.3 Collet 0.2 Fixture 0.2Total Setup, Oper 10 1.7

Handling Start/stop machine 0.10 Advance stock 0.23 Brush chips 0.12 Place guard / start 0.16 Advance/Index turret 0.08 Cross slide adv/index 0.09 Inspect w/micrometer 0.30Total Handling 1.08

Machining Times Dimension Depth Length Safety Stc Length Diameter Velocity feed Min Face 1.45 0.015 0.875 1/32 0.906 1.75 350 0.007 0.17 Rough turn 1.15 0.15 16.5 1/32 16.531 1.75 350 0.015 1.44 Rough turn 1.10 0.15 16.5 1/32 16.531 1.45 350 0.015 1.19 Finish turn 1.735 0.025 16.5 1/32 16.531 1.15 350 0.007 2.03 Turn 1.75 0.0075 0.5 1/32 0.531 1.75 350 0.007 0.1 Cutoff 0.187 0.875 1/32 0.906 1.75 350 0.015 0.08Total Mach. Time 5.01Total Cycle Time 6.09

Entry for Opr 10 to Ops Sht. Setup hr 1.7 Hrs/100 units 10.15