diak14.basics of capability

8/10/2019 Diak14.Basics of Capability

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8-1

IsProcessCapable

?

IsProcessCapable

?

The

QualityImprovementModel

Use SPC toMaintainCurrentProcess

Collect &Interpret

Data

SelectMeasures

DefneProcess

Is

ProcessCapable?

Is

ProcessCapable?

ImproveProcess

Capability

IsProcessStable

?

Investigate& i!

SpecialCauses

"o

#es

"o

#es

Is Process Capable?

Purpose$Determine t%eae'uacy o( t%eprocess )it% respect

to customer*management nees+



8-,

IsProcessCapable

?

IsProcessCapable

?Capable Process

stable process t%at meets customer re'uirements+

8 22 242 4 6 10 12 14 16 18 20 26 28 30 32

.un /rer

UCL

CL

LCL

Control C%art

0o)er Spec Upper Spec arget

2istogram

Capability assessments for unstable processes, may not

be indicative of how the process is actually performing.



8-3

IsProcessCapable

?

IsProcessCapable

?

Assessing Process Capability

Counting Measures %e average percent e(ectives+

%e average number o( e(ects+

Instrument Measures Comparing bot% t%e center o( t%e process an t%e

process variation



8-4

IsProcessCapable

?

IsProcessCapable

?

Capability Assessment for Counting Measures

“Order Entry Process

Is this process adequate as is?

Should it be improved?

Week

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14151617181,9

otal

# Errors

15,,181913

,71,,4,,88

,6

16,91916

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9

5

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15

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"umbero( =rrors

Control C%art



8-5

IsProcessCapable

?

IsProcessCapable

?

Measures of Process CapabilityCp =

Specification RangeTrue Process Range

= USL - LSL6

c

Cpk =

Distance from process averageto closest specification limit

12 True Process Range

= min (USL - x , x - LSL)3σc

Problem: We are assuming the process has a target that isin the center of the specification range, and thatthe process is in fact centered on that target.

Note: a negative result is possible if the process average is outside specifications

Benefits: • Optimal values are attained by running exactlybetween specs.• Can (must) be used for 1-sided specifications

Cp

< 1.0→

Process is not capable of meeting specs

Cp = 1.0 → Process is marginally capableCp > 1.0 → Process is capable of meeting specs

Cpk < 1.0 → Process is not capable of meeting specs

Cpk = 1.0 → Process is marginally capableCpk > 1.0 → Process is capable of meeting specs

Warning Capability assessments for unstable processes,may not be indicative of how the process is actually



8-6

IsProcessCapable

?

IsProcessCapable

?

2o) muc% material is out o( spec?

In t%e s%ort term?

In t%e long term?

!"#

!"##"#

#"#

Process Capability


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IsProcessCapable

?

IsProcessCapable

?Process Capability $atios

Voice of The Customer

Voice of The Process

USLUSLLSLLSL



IsProcessCapable

?

IsProcessCapable

?


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IsProcessCapable

?

IsProcessCapable

?

Process Capability % The "trategy

Centering –The Process Is On Target

Spread – Reduce The Variation

LSL USL

&efects&efects



IsProcessCapable

?

IsProcessCapable

?

' (ey Metrics for Measuring Capability

C Min( X-LSL

3

USL- X

3 pk =

, )

c

LSLUSLC p

σ 6

−

=

cσ cσ

Process Capability $atios



IsProcessCapable

?

IsProcessCapable

?Process Capability $atios % Concept

Total ToleranceC

Process Spreadp

c

LSLUSLC p

σ 6

−

=


http://slidepdf.com/reader/full/diak14basics-of-capability 12/198-1,

IsProcessCapable

?

IsProcessCapable

?

A Short-term Capabiit! stud! co"ers a reati"e!

short period of time #da!s$ %ee&s' genera!

consisting of () to *) data points+ The actua

number depends on the sub,ect under stud!+

Is The Process

In Control ?

Is It Producing

Defects ?

)*)+'*'+,*,+*+

)-

).

'-

'.

Observation /umber

I n

d i v i d u a l 0 a l u e

12)+34+

)3+"#2)53)4

%)3+"#2')36.

CP 7 CP( Measure "hort%term Capability



IsProcessCapable

?

IsProcessCapable

?

A ong-term capabiit! stud! co"ers a reati"e! ong

period of time #%ee&s$ months' genera! consisting of

))-.)) data points+ Again$ the actua amount depends

on the sub,ect under stud!+

Is The Process

In Control ?

Is It Producing

Defects ?

,++*++

*+

.+

)+

'+

Observation /umber

I

n d i v i d u a l 0 a l u e

12))36+

)3+"#2.53,'

%)3+"#2'+3.-

#ong Term Performance

S%ort termCapability



IsProcessCapable

?

IsProcessCapable

?

A 8urther #oo9 at Capability

Compare the estimates of the process de"iations

from the short-term and ong-term data

/hat is the difference bet%een the short-term and the

ong-term data0

/hat impication does this ha"e in doing capabiit!

studies0

/hat is the difference bet%een the short-term and theong-term data0

/hat impication does this ha"e in doing capabiit!

studies0

Descriptive Statistics

Variable N Mean StdDevshort ter 3! 30.6 2.23

lon" ter #$! 33. !.!!



8-15

IsProcessCapable

?

IsProcessCapable

?

Measures of Process PerformanceP p =

Specification Range

True Process Range = USL - LSL

6σs

Ppk =

Distance from process averageto closest specification limit

12 True Process Range

=min (USL - x , x - LSL)

3σs

Problem: We are assuming the process has a target that isin the center of the specification range, and thatthe process is in fact centered on that target.

Note: a negative result is possible if the process average is outside specifications

Benefits: • Optimal values are attained by running exactly

between specs.• Can (must) be used for 1-sided specifications

P p < 1.0 → Process Performance is not meeting specs

P p = 1.0 → Process Performance is marginally meeting specs

P p > 1.0 → Process Performance is meeting specs

Ppk < 1.0 → Process Performance is not meeting specs

Ppk = 1.0 → Process Performance is marginally meeting specs

Ppk > 1.0 → Process Performance is meeting specs



8-16

IsProcessCapable

?

IsProcessCapable

?

Performance vs3 Capability

These data sho% that the process$ if %e controed can

perform much better than it current! is

*+.+)+'+,+

,.

,)

,'

,,

,+

Inde:

C

O ' % " h r t

CO' #evels for ** Time Points&ays "ales Outstanding for ** &ays

& " O



8-18

IsProcessCapable

?

IsProcessCapable

?

Process Performance $atios

The P-fami! of indices are computationa! the same as

the C-fami! of 3capabiit!4 indices$ but use the obser"ed

ong-term standard de"iation+

% Min( X-LSL

3

USL- X

3 pk =

, )

s

LSLUSL p P

σ 6

−

=

sσ sσ



8-1

IsProcessCapable

?

IsProcessCapable

?

;A$/I/<===;A$/I/<===

Statistical ssumptions Mae In Capability

Stuies

1+ Data Comes From a Stable ProcessData Comes From a Stable Process

I( not> )or< to)ars getting t%e process incontrol

Dont espair> you can still ma<e someassumptions about your process in t%emean time

diak14.basics of capability

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