7 QC Tools.doc

8/14/2019 7 QC Tools.doc

1/4

The following are the 7 QC Tools :

1. Pareto Diagram

2. Cause & Effect Diagram

3. Scatter Diagrams

4. Histogram

5. Graphs

6. Contro Charts

!. Chec" Sheets

1) Pareto Diagram

Pareto Diagram is a too that arranges items in the or#er of the magnitu#e of

their contri$ution% there$ i#entifing a fe' items e(erting ma(imum

infuence. )his too is use# *uait impro+ement for prioriti,ing pro-ects for

impro+ement% prioriti,ing setting up of correcti+e action teams to so+epro$ems% i#entifing pro#ucts on 'hich most compaints are recei+e#%

i#entifing the nature of compaints occurring most often% i#entifing most

fre*uent causes for re-ections or for other simiar purposes.

2) Cause & Effect Diagram

Cause/an# Effect Diagram is a too that sho's sstematic reationship

$et'een a resut or a smptom or an effect an# its possi$e causes. 0t is an

effecti+e too to sstematica generate i#eas a$out causes for pro$ems an#

to present these in a structure# form. )his too 'as #e+ise# $ Dr. ouro0shi"a'a an# as mentione# earier is aso "no'n as 0shi"a'a Diagram.

3) Check Sheets1. s measurement an# coection of #ata forms the $asis for an anasis%

this acti+it nee#s to $e panne# in such a 'a that the information coecte#

is $oth ree+ant an# comprehensi+e.

2. Chec" sheets are toos for coecting #ata. )he are #esigne# specific to

the tpe of #ata to $e coecte#. Chec" sheets ai# in sstematic coection of

#ata. Some e(ampes of chec" sheets are #ai maintenance chec" sheets%atten#ance recor#s% pro#uction og$oo"s% etc.


2/4

4) Graphs

Graphs of +arious tpes are use# for pictora representation of #ata. Pictora

representation ena$es the user or +ie'er to *uic" grasp the meaning of the

#ata. Different graphica representation of #ata are chosen #epen#ing on the

purpose of the anasis an# preference of the au#ience. )he #ifferent tpes

of graphs use# are as gi+en $eo'

S.No Tpe of Graph Purpose

1. Bar Graph To compare sizes of data

2. Line Graph To represent changes of data

3. Gantt Chart To plan and schedule

4. Radar Chart To represent changes in data (efore

and after!". Band Graph #ame as ao$e

%. &ie Chart 'sed to indicate comparati$e eights

). *#+ Graph To represent data using s,mols

!) "istogram

Histograms or re*uenc Distri$ution Diagrams are $ar charts sho'ing the

#istri$ution pattern of o$ser+ations groupe# in con+enient cass inter+as an#arrange# in or#er of magnitu#e. Histograms are usefu in stu#ing patterns

of #istri$ution an# in #ra'ing concusions a$out the process $ase# on the

pattern.

#) Co$tro% Charts

aria$iit is inherent in a manufacturing processes. )hese +ariations ma

$e #ue to t'o causes

i. an#om 7 Chance causes 8un/pre+enta$e9.ii. ssigna$e causes 8pre+enta$e9.

Contro charts 'as #e+eope# $ Dr. :ater . She'hart #uring 1;2


3/4

Contro chart ma"es possi$e the #iagnosis an# correction of man

pro#uction trou$es an# $rings su$stantia impro+ements in the *uait of the

pro#ucts an# re#uction of spoiage an# re'or".

0t tes us 'hen to ea+e a process aone as 'e as 'hen to ta"e action to

correct trou$e.

'S(C CNCEPTS *

a. Data is of two types :

aria$e / measure# an# e(presse# *uantitati+e

-ttriute /uanlitati$e1 Mean and Range :

0 ean is the a$erage of a sugroup

R Range is the difference eteen the minimum andmaimum in a sugroup

1 Control Charts for Variables

Charts depleting the $ariations in 0 and R ith time are non as 0 and R charts. 0 and R charts are used for $ariale data hen

the sample size of the sugroup is 2". hen the sugroup size islarger5 s Charts are used instead of R charts here s is the standardde$iation of the sugroup.

1 Control Charts for Attributes

The control charts for attriutes are pchart5 npchart5 cchart and uchart. Control charts for defecti$es are p and np charts. & charts areused hen the sample size is constant and np charts are used henthe sample size is $ariale. *n the case here the numer of defectsis the data a$ailale for plotting5 c and u charts are used. *f thesample size is constant5 c charts are used and u charts are used for

$ariale sample sizes.

+) Scatter Diagram:hen so+ing a pro$em or anasing a situation one nee#s to "no' the

reationship $et'een t'o +aria$es. reationship ma or ma not e(ist

$et'een t'o +aria$es. 0f a reationship e(ists% it ma $e positi+e or


4/4

negati+e% it ma $e strong or 'ea" an# ma $e simpe or compe(. too to

stu# the reationship $et'een t'o +aria$es is "no'n as Scatter Diagram. 0t

consists of potting a series of points representing se+era o$ser+ations on a

graph in 'hich one +aria$e is on @/a(is an# the other +aria$e in on A/a(is.

0f more than one set of +aues are i#entica% re*uiring more points at the

same spot% a sma circe is #ra'n aroun# the origina #ot to in#icate secon#

point 'ith the same +aues. )he 'a the points ie scattere# in the *ua#rant

gi+es a goo# in#ication of the reationship $et'een the t'o +aria$es. ?et us

see some common patterns seen in Scatter Diagrams an# the concusions

one can #ra' $ase# on these patterns. Diagrams 6 to 11 sho' some of the

more common patterns.

,) Stratificatio$

Data coecte# using chec" sheets nee#s to $e meaningfu cassifie#. Suchcassification heps gaining a preiminar un#erstan#ing of ree+ance an#

#ispersion of the #ata so that further anasis can $e panne# to o$tain a

meaningfu output. Beaningfu cassification of #ata is cae# stratification.

Stratification ma $e $ group% ocation% tpe% origin% smptom% etc.

Documents

7 QC Tools.doc