quality

Quality

Er.Sartaj Singh Bajwa

Quality

• Quality– The extent to which a product or service is able to

meet customer needs and expectations.• Customer’s needs are the basic standard for

measuring quality• High quality does not have to mean high price.

• ISO 9000– The quality standards of the International Standards

Organization.


Quality Control Process

1-Prepration of policies regarding quality

2-Fixation of quality standard relating to material & process

3-Designing the production system

4-Inspection and control of materials

5-Inspection and control of process

6-Production of goods and services

7-Inspection of final product and service


Objectives of Quality Control

• Increased sales volume• Increased profits• Improving the company`s image• Improving the production system• Better procurement of material• To reduce the cost of inspection and losses


Quality Circles

• Small group of employees who meet regularly for solving problems related to cost , quality , efficiency , equipment ,tools etc.

• In QC it is believed that each individual worker is responsible for quality and productivity


Inspection

• Process of examining an object for identification or checking it for verification of quality and quantity

• Functions Of Inspection :

1 – To maintain quality of RM , WIP , FG

2 – To locate the defective items

3 – To prevent losses

4 – To detect sources of weakness


Types Of Inspection

• Vendor place inspection ( For raw material )

• In process inspection

1–Trial run inspection ( to check tool & M/C )

2–First off inspection(items produced at first step are checked )

3–Inspection by self control(checking the operations)

4–Floor inspection(semi-finished goods are checked)• Final inspection• Post sales quality evaluation ( items rejected by customers

should be analyzed)


Control Charts

• Whole production line is divided in sub groups such that variation in the quality , in each sub group is attributed to some change

• Factors considered while making of the sub groups :

1- Each sub group should be homogeneous2- Sample should not be taken at regular

intervals


Control Charts• Characteristics/Quality on Y axis• Quantity/number on X axis


Interpretations of Control Chart

• If all the points lie within UCL & LCL then the process is said to be in control

• If one or more points lie beyond UCL & LCL then the process is said to be out of control

• If points lie predominantly on one side of the central line then we cannot derive any conclusion


Types Of Control Charts

• Control chart for variables

1 – M or Mean charts

2 – R or Range charts

• Control chart for attributes

1-P chart (to calculate the number of defective items)

2–C chart (to calculate the number of defects)


Control Chart For Variables

• When the quality characteristics is capable of direct quantitative measurement then the control chart is known as chart for variables.

• Eg life of an item , diameter of a screw• Variables in these charts should be such that it

can be measured and expressed in numbers.• It includes : Control chart for Mean

Control chart for Range


Control Chart For Mean

• Basic assumption here is that variability of the characteristic is under control

• Mean(M) and standard deviation(sigma) of each sub group is calculated with size of the sample(n) to be known then Charts are given by :

UCL = M+3 (sigma/square root of n)

CL = M

LCL = M-3 (sigma/square root of n)


Control Chart For Range

• Basic assumption here is that variability of the characteristic is out of control

• Value of d and standard deviation(sigma) of each sub group is calculated , with size of the sample(n) to be known then Charts are given by :

UCL = d2*sigma+3d3*sigma

CL = d2*sigma

LCL = d2*sigma-3d3*sigmaEr.Sartaj Singh Bajwa

Control Chart For Attributes

• In this we cannot have direct quantitative measurement and the items can be classified only as good or bad , accepted or rejected

• Eg quality of cloth


Plotting the P Chart• Calculate p (fraction defective in the lot) in

sample of size n• p = no. of defective items found , q=1-p

total no. of items

Control charts are given by :

UCL = p + 3*square root of(pq/n)

CL = p

LCL = p – 3*square root of(pq/n)


Plotting the C chart

• Calculate c ( average no. of defects per unit )

C= mean of the given frequency

Control charts are given by :

UCL = c + 3*square root of c

CL = c

LCL = c – 3*square root of c


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