qc chapter 3

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CHAPTER 3:

CONTROL CHART (1) FOR

VARIABLE


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INTRODUCTION

Visualizing the variations that occur in thecentral tendency and dispersion of a set

of observation.


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VARIATION

The axioms or truism of

manufacturing is that no twoobjects are ever made exactly

alike.


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There are three (3) CATEGORIES ofVariations in piece part production;

1. Within piece

2. Pieceto-piece

3. Time

to

time


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SOURCE of variation;1. Equipment

2. Material

3. Environment

4. Operator


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The source of variation can contribute to

Two (2) TYPES of variations.1. Random causes

inevitable2. Assignable causescan be reduced
http://random%20causes.pptx/http://assignable%20causes.pptx/http://assignable%20causes.pptx/http://random%20causes.pptx/


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CONTROL CHART

Shows variation of single quality char. withinpiece/product .

A chart with statistical Upper and Lower Limits; if theprocess stays within these limit over time it is in controland the problem does not exists.

TWO types:

1. Variable Control Chart (Pembolehubah)2. Attribute Control Chart (Sifat)CHAPTER 4


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VARIABLE CONTROL CHART

The ability that variation within piece can bemeasured by using any necessary measurement

instrument and tools.

Such as; weight, tall, length and etc..


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Objective of Variable Control Chart.

1. For quality improvement.

2. To determine process capability.

3. For decisions in regard to the product process.

4. Current decisions in regard to the production process.

5. Current decisions in regard to recently produced items.


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Two (2) TYPES of Variable Chart.1. Chart - Range

2. Chart - Standard deviation


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Data and Control Chart


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Data Analysis


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Chart Analysis


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1. Center Line (CL)

2. Upper Control Limit (UCL)

3. Lower Control Limit

Data Analysis


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Example 1


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Solution


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SOLUTION

1. Find control limit (CL)


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2. Upper control limit (UCL)

3. Lower Control Limit (LCL

SOLUTION
http://table.pptx/http://table.pptx/http://table.pptx/


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REVISED SOLUTION

Calculate again data to be in controlled (check)

Where;


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Then new standard deviations are;

REVISED SOLUTION


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Thus new Control Limits for the real operationsare;

REVISED SOLUTION


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REVISED SOLUTION


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Then new Upper and Control Limits;

REVISED SOLUTION


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Initiate control charts

results in QI

Less variation in g average

Reduction in Rvariation

Can reduce frequency

of inspection - monitoring purpose

even once/mth.

OBJECTIVE OF REVISED CC


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CHART

1. Centre Line (CL)

2. Upper Control Limit (UCL)

3. Lower Control Limit (LCL)


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SOLUTIONS


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PENYELESAIAN

1. Dapatkan garis pusat (CL) untuk


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2. UCL & LCL

SOLUTIONS


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1. IN CONTROL

When assignable causes eliminated and points plotted arewithin C.L.- process state of control

No points out of control

2. OUT OF CONTROL

A point falls outside control limits

assignable cause present

must be investigated, corrected

STATE OF CONTROL CHART


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Individual parts will be more uniformless variation and fewer rejects

Cost of inspection will decrease Process capability easily attained

Trouble can be anticipated before itoccurs

PROCESS IN CONTROL


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PROCESS OUT OF CONTROL

Patterns1. Change/Jump in level

shift in mean

Causes - process parameterschange, diff / new operator,change in raw material

2. Trend or steady change in level drifting meancommon,

upward or downward direction

tool wear, gradual change intemp. viscosity of chemical

used


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PROCESS OUT OF CONTROL

3. Recurring cycles Wavy, periodic high & low points

Seasonal effects of mtl.

Recurring effects of temp.,humidity (morning vs evening)

4. Trend or steady change in level Many points near or outside

limits due to large difference inmaterial quality and supply.

2 or more machines

Different test method

qc chapter 3

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