STATISTICAL QUALITY CONTROL 1

• STATISTICAL QUALITY CONTROL
  OPERATION MANAGEMENT
  BUSINESS STATISTICS
  
  
• MEANING OF QUALITY
• QUALITY MAY BE DEFINED AS THE SUM TOTAL OF FEATURES OF PRODUCT WHICH INFLUENCES THE ABILITY TO SATISFY A GIVEN DEMAND.
• QUALITY IS DETERMINED BY THE CUSTOMER. THE QUALITY OF PRODUCT OR SERVICE IS A CUSTOMER PERCEPTION OF THE DEGREE TO WHICH THE PRODUCT OR SERVICE MEETS HIS OR HER EXPECTATION.
• DIMENSIONS OF PRODUCT QUALITY:-

1. PERFORMANCE
2. FEATURES
3. RELIABILITY
4. SERVICEABILITY
5. APPEARANCE
6. CUSTOMER SERVICE SAFETY

• QUALITY CONTROL

1. QUALITY CONTROL IS AN APPROACH TO PREVENT THE EFFECTS RATHER THAN DETECTING THE DEFECT. THE ULTIMATE AIM OF QUALITY CONTROL IS TO PROVIDE PRODUCTS WHICH ARE DEPENDABLE,SATISFACTORY AND ECONOMICAL. QUALITY CONTROL SYSTEM IS DESIGNED TO ENSURE ECONOMICAL PRODUCTION OF PRODUCTS OF UNIFORM QUALITY WHICH IS ACCEPTABLE TO CUSTOMER.
2. QUALITY ASSURANCE:_ACTIVITY OR PROVIDING ADEQUATE CONFIDENCE THAT A PRODUCT OR SERVICE WILL SATISFY GIVEN REQUIREMENT FOR QUALITY.IT COVERS QUALITY PLANNING,QUALITY CONTROL,QUALITY IMPROVEMENT,QUALITY AUDIT AND RELIABILITY,

• ENSURING QUALITY

1. CONTROL OF ENGINEERING QUALITY
2. CONTROL OF PURCHASED MATERIAL QUALITY
3. CONTROL OF MANUFACTURING QUALITY
4. ACTIONS SUPPORTING THE PRODUCT AFTER DELIVERY

• STATISTICAL QUALITY CONTROL
• IS THE APPLICATION OF STATISTICAL TECHNIQUES TO ACCEPT OR REJECT PRODUCTS ALREADY PRODUCED OR TO CONTROL THE PROCESS AND THEREFORE THE PRODUCT QUALITY WHILE THE PART IS BEING MADE.

1. ACCEPTANCE SAMPLING
2. PROCESS CONTROL

• STATISTICAL QUALITY CONTROL FOR PROCESS CONTROL
• SQC IS USED FOR CONTROLLING QUALITY DURING PRODUCTION IN MASS PRODUCTION INDUSTRIES WHICH PRODUCE STANDARD PRODUCT. SQC IS BASED ON PROBABILITY THEORY.
• COMMON KNOWLEDGE WHEN SEVERAL IDENTICAL PARTS ARE MANUFACTURES,SOME ARE LARGE AND SOME ARE A LITTLE SMALL BUT MOST WILL BE SAME.
• SQC FOR PROCESS CONTROL
• D
• 
• 
  
• VARIATION IN SIZES BETWEEN .995 AND 1,005 WITH MOST MEASURING 1 INCH ARE DUE TO CHANCE CAUSES. VARIATION MAY OCCUR DUE TO

1. CHANCE VARIATIONS : RESULT FROM MINOR CAUSES THAT BEHAVE IN RANDOM MANNER AND PRODUCE SLIGHT DIFFERENCE IN PRODUCT FEATURES.THESE ARE INHERENT AND CAN NOT BE CONTROLLED OR PREVENTED.
2. ASSIGNABLE CAUSES:THOSE VARIATION THAT MAY BE ATTRIBUTED TO SPECIAL NON RANDOM CAUSES FOR EXAMPLE CHANGE IN THE CHARACTERISTICS OF INPUTS SUCH AS RAW MATERIAL,IMPROPER MACHINE SETTING,CHANGE IN TEMPERATURE ETC ASSIGNABLE VARIATION CAN BE DETECTED AND CORRECTED.

• TWO DIFFERENT WAYS OF CONTROLLING THE QUALITY OF THE PRODUCT.

1. THROUGH 100 % INSPECTION
2. THROUGH SAMPLING

• STATISTICAL TOOL APPLIED IN PROCESS CONTROL IS CONTROL CHARTS.
• THE PRIMARY OBJECTIVE OF PROCESS CONTROL ARE :

1. TO KEEP THE MANUFACTURING PROCESS IN CONTROL SO THAT THE POPULATION OF DEFECTIVE UNITS IS NOT EXCESSIVE
2. ASSITING IN DETERMINING WHETHER A STATE OF CONTROL EXIST

• ACCEPTANCE SAMPLING
• INSPECTION FOR ACCEPTANCE PURPOSE IS CARRIED AT MANY STAGES IN MANUFACTURE FOR EXAMPLE INSPECTION ON INCOMING MATERIAL,PROCESS INSPECTION AT VARIOUS POINTS IN THE MANUFACTURING OPERATIONS,FINAL INSPECTION BY MANUFACTURER AND ULTIMATELY BY PURCHASERS.
• MUCH OF THE ACCEPTANCE INSPECTION IS CARRIED ON SAMPLING BASIS BY USING STATISTICAL STANDARDS TO INFER FROM THE QUALITY OF THE SAMPLE WHETHER THE WHOLE LOT IS ACCEPTED OR REJECTED. THE STANDARD IN ACCEPTANCE INSPECTION ARE SET ACCORDING TO WHAT IS REQUIRED OF THE PRODUCT RATHER THAN BY THE INHERENT CAPABILITIES OF THE PROCESS

• CONTROL CHARTS

1. PROCESS CONTROL THROUGH CONTROL CHARTS
2. CONTROL CHARTS FIRST DEVELOPED BY DR WALTER A SHEWHART OF THE BELL TELEPHONE LABORATORIES DURING 1920 ARE HORIZONTAL EXTENSIONS OF THE BELL SHAPED CURVE
3. CONTROL CHART IS A STATISTICAL DEVICE PRIMARILY USED FOR THE STUDY AND CONTROL OF REPETITIVE PROCESS
4. THE ORIGINATOR WALTER A SHEWART: THE OBJECTIVE
5. DEFINE THE GOAL OF STANDARD FOR THE PROCESS
6. MAY BE USED AS INSTRUMENT TO ATTAIN THE GOAL
7. IT MAY SERVE AS A MEANS OF JUDGING WHETHER THE GOALS HAS BEEN ACHIEVED.

8. A CONTROL CHART IS ESSENTIALLY A GRAPHIC DEVICE FOR PRESENTING DATA FOR SHOWING THE FREQUENCY AND EXTENT OF VARIATIONS FROM THE ESTABLISHED STANDARDS OR GOALS.
9. CONTROL CHARTS ARE SIMPLE TO CONSTRUCT AND EASY TO INTERPRET AND THEY INFORM WHETHER THE PROCESS IS IN CONTROL AND OUT OF CONTROL
10.  A CONTROL CHART CONSISTS OF THREE HORIZONTAL LINES:-

• 
  

1. UPPER CONTROL LIMIT(UCL)
2. LOWER CONTROL LIMIT(LCL)
3. A CENTRAL LINE (CL)TO INDICATE THE DESIRED STANDARD OR LEVEL OF THE PROCESS

• 
  
• ADVANTAGE OF SQC

1. IT HELPS PREVENT DEFECTS FROM OCCURRING
2. AVOIDANCE OF THE RISK OF ACCEPTING A BAD LOT
3. REDUCTION OF COST  AS THE INSPECTION IS DONE ON  THE BASIS OF SAMPLE
4. GREATER EFFICIENCY
5. EASY TO APPLY
6. ENABLES PROCESS TO BE BROUGHT INTO CONTROL