COALITION RECRUITMENT, PARTICIPATION AND MAINTENANCE Coalition 101.
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![Page 1: Quality Control - ::Gateway Engineering Education Coalition€¦ · PPT file · Web view · 2001-01-31Step 7: Complete control limits using attached table. For X Control Chart.](https://reader031.fdocuments.net/reader031/viewer/2022020302/5ad37db87f8b9a665f8dc3b2/html5/thumbnails/1.jpg)
TOTAL QUALITY MANAGEMENT (Continuous Quality Improvement)
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QUALITY PLANNINGWho is customer?
What do they need?
QUALITY CONTROLEvaluate, compare, act
QUALITYIMPROVEMENT
Establish infrastructure
Who is customer?What Level of Quality do they need?Are they purchasing to Some Quality Specification?Any Safety Considerations?Future Litigation?Ethical Issues?
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QUALITY PLANNINGWho is customer?
What do they need?
QUALITY CONTROLEvaluate, compare, act
QUALITYIMPROVEMENT
Establish infrastructure
QUALITY CONTROL Inspection Destructive Non-destructive Sampling Process Control Monitoring Process (relates to inspection) Feedback Control Statistical Process Control (knowing when the process is out of control) Correction Knowing what to correct when process is out of control
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Cost of Quality Before & After Improvement
0 10 20 30 40 50 60 70 80
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 Time
Series1
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Tools for Quality Control
Check Sheets
Pareto Charts
Why-Why Diagrams
Cause & Effect Diagrams
Flowcharts
Histograms
Scatter Diagram
Control Charts
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Problem Solving Steps
PlanDo StudyAct
Link these Two in Quality Circle
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CHECK SHEETSUsed to keep a record of the number and type of discontinuities over a specified period of time or within a certain batch of product.
PARETO CHARTA graphical representation ranking discontinuities from the most to least significant. Used to help brainstorm what discontinuities, if worked upon first, would be the most likely to produce the greatest improvement in quality.
Class ExampleOur manufacturing procedure is composed of several steps. Several of these
procedures have lead to discontinuities noticed upon inspection. The steps causing defectives are as follows: Caulking 198 defectives Fitting 25 defectives Connections 103 defectives Torque 18 defectives Gapping 72 defective A Pareto Diagram will be developed.
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WHY-WHY DIAGRAMSA systematic representation of causes of why some occurrence happens. Used to guide brainstorming sessions.
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FLOW CHARTSFlow charts are graphical representations of the steps involved in a process. Constructing a flow chart helps give a better understanding of the systems involved.
Process
DecisionData
Process
Process
Terminator
Yes
No
Controltransfer
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CAUSE AND EFFECT DIAGRAMS (Fishbone Diagram)Used in brainstorming session to help identify the causes of quality losses. This diagram is particularly useful after the flow chart and the Pareto diagrams have been developed.
QUALITY(Effect)Cause
Step 1:Decide on the quality characteristic {e.g. Reduction of wobble during machine rotation}Step 2:Set up the fish bone backboneStep 3:Identify main factors causing effect {e.g. Workers, Materials, Inspection, Tools}Step 4: Add Cause to each branch
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Benefits of Cause and Effect Diagram Making diagram is educational in itself Outline relationship Note what samples need to be taken Guide for discussion Causes are actively sought and results written on diagram Appropriate data collected - no time wasted Shows level of technology
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Problem Solving Steps
PlanDo StudyAct
Link these Two in Quality Circle
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CONTROL CHARTS Used to test if the process is in control Used to see if significant changes have occurred in the process over time
“Indiscreet” or “Continuous Data Chart” or “X-R Chart”Measurement at time intervals Measurements compared - control over time. Examples:
Length (mm) Volume (cc)Weight (gm) Power (kwh)Time (sec) Pressure (psi)Voltage (v)
“Discrete Data Charts” or “pn-p charts”Inspection on lot or batch Note # good/defective
# of parts inspected in the lot = nFraction of defective in lot = pNumber of defectives = pn
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- R CHART CONSTRUCTION X
In the manufacturing process for this example parts are being machined with a nominal diameter of 13 mm. Samples are taken at the following times of day: 6:00, 10:00, 14:00, 18:00 and 22:00, for 25 consecutive days. The diameter measurements from these samples are presented on the table in the next slide.
Class Example
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S t e p 1 : C o l l e c t D a t a
S t e p 2 : S o r t d a t a i n t o s u b g r o u p s ( i . e . l o t s , o r d e r # , d a y s , e t c . )
n = s i z e o f t h e s u b g r o u p { i n t h i s e x a m p l e 5 t i m e s p e r d a y ) k = n u m b e r o f s u b g r o u p s { i n t h i s e x a m p l e 2 5 d a y s }
S t e p 3 : F i n d t h e m e a n f o r e a c h s u b g r o u p ( X )
X = X X X X
nn1 2 3 . . . . .
S t e p 4 : F i n d R a n g e f o r e a c h s u b g r o u p ( R )
R = X l a r g e s t v a l u e - X s m a l l e s t v a l u e
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Step 5: Find Overall Mean ( X )
X = X X X X
kk1 2 3 ...
Step 6: Find average value of range ( R ) R = R R R R
kk1 2 3 ...
Step 7: Complete control limits using attached table
For X Control Chart Central Line - CL = X
Upper Control Limit - UCL = X +A2R Lower Control Limit - LCR = X- A2R
For R Control Chart
Central Line - CL = R Upper Control Limit - UCL = D4R Lower Control Limit - LCR = D3R
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Step 8:Plot Chart
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P CONTROL CHART CONSTRUCTION
An inspector at the end of the manufacturing line for the production of car wheel rims, at the end of each shift, inspects the lot of wheel rims made during that shift. On good days when the welder is running properly, over 400 wheels are made per batch. On poor days, as low as 50 to 60 wheels are made per batch. The inspector marks on his/her “check sheet” for each batch the total number of wheels inspected and the number of defects returned for rework in each lot.
Class Example
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Step 1: Collect Data
Step 2: Divide data into subgroups (usually days or lot). Subgroup size should be greater than 50 units.
n = number in each subgroup pn = number of defects in each subgroup
Step 3: Compute fraction of defectives (for %, multiply by 100)
p = pn/n Step 4: Find the Average Fraction of Defectives ( p )
p = ( )( )total defectivestotal inspected
= pnn
Step 5: Compute the Control Limits for each Lot
Central Line CL = p
Upper Control Limit UCL = p + 3p p
n( )1
Lower Control Limit LCR = p - 3p p
n( )1
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Step 6:Draw P Control Chart
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PN CONTROL CHART CONSTRUCTION Class Example
On an assembly line of windshield wiper motors, the inspector selects randomly 100 motors per hour to examine. The inspector notes on the “check sheet” the number of defective motors in each 100 selected.
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Step 1: Collect Data (lot size set constant)
Step 2: Calculate Values p =
npn
CL = p n
UCL = p n + 3 pn p( )1
LCL = p n - 3 pn p( )1 Step 3: Plot Chart
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QUALITY PLANNINGWho is customer?
What do they need?
QUALITY CONTROLEvaluate, compare, act
QUALITYIMPROVEMENT
Establish infrastructure
ISO9000
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