Free Quality C Charts
-
Upload
ahmad-bassiouny -
Category
Education
-
view
1.219 -
download
0
description
Transcript of Free Quality C Charts
Develop a Count Chart
Amanda Christensen, BYU MBA Class of 2009
Professor: Dr. Tom Foster
What Will Be Covered• Communicate Number of Defects
– Collect Data– Graph Data
• Find Nonrandom Patterns– Calculate the Average– Determine Limits
• An Example and an Exercise
The Tool Defined• C Chart Graphs Number of Defects
– Clean Presentation
• Determines Whether a Process is in Control– Visual Determination
Brainstorming Exercise
How can this tool be used in your organization?
Communicate Number of Defects• Collect Data
– Number of Defects per Unit– Number of Defects per Inspection Lot
• Graph Data– X-Axis Represents Number of Inspected
Products– Y-Axis Represents Number of Defects
Find Nonrandom Patterns• Calculate the Average
– Find Average Number of Defects per Unit or Lot (C Bar)
– Add Line to Graph Representing C Bar. This is the Central Line.
Find Nonrandom Patterns• Determine Limits
– Find Standard Deviation of Data– Upper Control Limit
• UCL = c bar + 3*(√c bar)
– Lower Control Limit• LCL = c bar – 3 *(√c bar)
• Add Limit Lines to the Graph
Next Steps• Determine if Process is Random or
Nonrandom
• Evaluate Process if Necessary
Collide Shoes
A Real World Example
Collect Data
Record Date and Number of Defects per Shoe
11-Oct6
10-Oct1
9-Oct2
8-Oct4
7-Oct7
6-Oct6
5-Oct2
4-Oct2
3-Oct3
2-Oct5
1-Oct2
DateDefects
Graph Data
C Chart - Collide Shoes
012345678
10/1
/200
7
10/8
/200
7
10/1
5/20
07
10/2
2/20
07
10/2
9/20
07
11/5
/200
7
11/1
2/20
07
11/1
9/20
07
Date
Def
ects
Calculate the Average• Find C Bar• Add C Bar, Central Line, to Graph
C Chart - Collide Shoes
012345678
10/1/
2007
10/8/
2007
10/15
/2007
10/22
/2007
10/29
/2007
11/5/
2007
11/12
/2007
11/19
/2007
Date
Def
ects
Determine Limits• Find Standard Deviations, Then Use
Formulas:• UCL = c bar + 3*(√c bar)• LCL = c bar – 3 *(√c bar)
• Standard Deviation = 1.53• UCL = 7.53• LCL = -1.64
Find Nonrandom PatternsC Chart - Collide Shoes
012345678
10/1
/200
7
10/8
/200
7
10/1
5/20
07
10/2
2/20
07
10/2
9/20
07
11/5
/200
7
11/1
2/20
07
11/1
9/20
07
Date
Defe
cts
Gentry Bolts
An Exercise
Collect Data• Record Number
Inspected and Number Failed
10700
5450
10300
91000
4500
7800
6600
# Failed# Inspected
Graph the Data
Gentry GraphC Chart - Gentry Bolt
0
2
4
6
8
10
12
600 800 500 1000 300 450 700
# Failed
Next Steps• Calculate the Average• Find Standard Deviation• Calculate Upper and Lower Limits
• UCL = c bar + 3*(√c bar)• LCL = c bar – 3 *(√c bar)
Graph the Central Line and UCL and LCL
Find Nonrandom Patterns
C Chart - Gentry Bolt
0
2
4
6
8
10
12
14
16
600 800 500 1000 300 450 700
# Failed
Central Line
UCL
Summary• Communicate Number of Defects
– Collect Data– Graph Data
• Find Nonrandom Patterns– Calculate the Average– Determine Limits
Readings List• Calculating the (Almost) Exact Control
Limits for a C-Chart. By: Kittlitz Jr., Rudolf G.. Quality Engineering, Jul-Sep2006, Vol. 18 Issue 3, p 359-366, 8 p.
• Statistical Methods for SPC & TQM. By: Derek Bissell.
• Statistical Process Control and Quality Improvement. By: Gerald M. Smith