Problem Solving and Quality Control Tools

• Meaning of Problem

• Steps of Problem Solving Process

• Seven Basic Quality Control (QC) Tools

Problem Solving ProcessA Problem Solving approach focuses employees attention on three activities

• Enabling individual and work group to conduct careful analysis based on numerical and other data to explore potential solutions.

• Planning for the implementation of optimal solution.

• Monitoring the result of their corrective actions.

Steps of Problem Solving Process

1. Identifying and Selecting the Problem. 2. Analyzing the Problem. 3. Generating Potential Solutions. 4. Selecting and Planning the Solution. 5. Implementing the Recommended

Solution.6. Evaluating and Selecting the Solution.

Seven Basic Quality Control (QC) Tools

1. Check Sheet. 2. Histogram. 3. Pareto Chart.4. Cause and Effect Diagram. 5. Scatter Diagram.6. Stratification.7. Control Charts.

Check Sheets

• Simple organized way to collect data as per the frequency.

• Important – when frequent failures at work.

• Data collection based on sample observations in order to identify patterns.

• Used for accountability purpose.

Check Sheets

The main use of Check Sheets are:

• It provides clear picture about how often and what type of problems occur.

• It distinguishes between fact and opinion.

HistogramA diagram showing the frequency of occurrence of a given number or a given range of number is known as frequency distribution diagram or histogram.

Histogram is a bar chart showing the distribution pattern of observations grouped in convenient class interval and arranged in order of magnitude.

Histogram is visual representation of spread of distribution of data.

HistogramThe various types of distributions are:

1. Bell shaped distribution.

2. Double peaked distribution.

3. Plateau distribution.

4. Comb distribution.

5. Skewed distribution.

Histogram1. Bell shaped distribution.

Histogram2. Double peaked distribution.

Histogram2. Double peaked distribution.

Histogram3. Plateau distribution.

Histogram4. Comb distribution.

Histogram5. Skewed distribution.

HistogramGuidelines for Histogram Categories:

Easy to construct but more difficult to interpret. To get meaningful data, select the category size

carefully.Number of data points in

the sampleNumber of categories

Less than 50 5-7

50-100 6-10

100-250 7-12

Over 250 10-12

Pareto Charts (diagrams)

Pareto Charts (diagrams)• Pareto principle was invented by Italian

Economist Alfred Pareto (1848-1923).• He studied the distribution of wealth in

different countries.• He concluded that fairly consistent minority

about 20 percent of people controlled the large majority, about 80 percent of society’s wealth.

• This is called the 80-20 rule and is called Pareto principle.

Pareto Charts (diagrams)

Pareto diagram is a bar chart that illustrates the frequency of reoccurrence or the cost of a set of items.The items are shown in the descending order of importance from left to right.

Pareto Charts (diagrams)

Pareto Charts (diagrams)

Pareto Charts (diagrams)Pareto analysis can be used by system analyst to concentrate on selected activities/ areas for the purpose of exercising control to improve system performance thus reducing wasteful effort in controlling all the activities. Thus Pareto analysis is applicable to different fields to reduce the number of defects and to improve the overall quality of the product and system.

Cause and Effect DiagramThe costs resulting from products or services not conforming to requirements or customer/user needs.

Failure costs are divided into internal and external failure categories.

• A- Internal Failure Costs

• B- External Failure Costs

Cause and Effect Diagram

Cause and Effect Diagram

Cause and Effect DiagramSteps for constructing C & E diagram: 1. Decide on quality characteristics (Effect)2. Draw the back bone from left to right, terminating at the

head and write the quality characteristics (Effect)3. Draw the big bone and write the primary cause.4. Draw the medium sized bone and write the secondary

cause (sub-cause).5. Draw the small bone and write the tertiary cause (cause

which is secondary to sub-cause)6. Ensure that all causes (factors) which influence the effect

(quality characteristics) are displayed in the diagram.

Cause and Effect DiagramAdvantages: 1. The potential cause of a problem becomes readily apparent by

constructing cause and effect diagram. Each effect is evaluated one by one in order to find the true cause of the problem.

2. A task group is constituted for the cause and effect diagram. Thus people work in group for a common objective.

3. Cause and effect diagram reduces defects and thus improves quality.

4. It is constructed by the use of brain storming that enables to develop a wide variety of possible causes for a problem.

5. A clear picture of the process is seen visually. It educates people to improve their skills and helps in understanding the process better.

Scatter Diagram• Scatter diagram or scatter plots are used to determine

whether relationship really exists between two process characteristics and the direction of the relationship.

• A scatter diagram graphically illustrates the relationship between the variables, typically based on quantitative data.

• They reveal bi-variable relationships, that is relationship between pair of variables, such as number of defects per batch against changes in the speed of production line or production time per unit against hours of training.

Scatter Diagram1. Collect at least 30 sets of paired samples of related data (50

to 100 sets are more appropriate) and construct a data sheet.2. Find the lowest and the highest values of X-axis and Y-axis.3. Draw the horizontal and vertical axis and plot the readings. If

the relationship between the two data is of cause and effect, the causes values are usually marked as X and the effect values on Y-axis. X value is an independent variable and the Y a dependent value (variable).

4. Plot the data on the chart. There could be positive correlation, negative correlation or no correlation between variables.

Scatter Diagram

Scatter Diagram

StratificationSegregating a group of measurements, observations or any other data into several sub-groups on the basis of certain characteristics is called stratification. It is an important tool for quality improvement.Stratification is nothing but segregation or reporting the data machine-wise, operator-wise, shift-wise etc. for identifying the influencing factors.

StratificationExample: Breakdown of machines in a plant.

The plant has 110 breakdowns in a year.If this information is properly segregated or stratified, it would enable the management to plan action for systematic plant maintenance.

50 breakdowns in Machine I20 breakdowns in Machine II25 breakdowns in Machine III15 breakdowns in Machine IV

Control Charts

• Originally developed by Walter Shewhart (1920).• Perfected and used by Edward Deming in 1950.• 85 percent of improvement opportunities come from

changes in the system which are management’s responsibility, while 15 percent are within an individual employee’s control.

• A control chart can be used to discover how much variability in a process is due to random variations and how much is due to unique events, in order to determine if a process is under statistical control.

Control Charts

• A control chart is simply a run chart to which two horizontal lines called control limits are added, the Upper Control Limit (UCL) and Lower Control Limit (LCL) on either side of the process average.

Control Charts

There are two types of control charts:

• Variable Control Charts. Samples are expressed in quantitative characteristics units of measurement such as length, weight and time.

• Attributes Control Charts. Sample reflect qualitative characteristics such as is “defective/ is not defective” or “go/ no go”.

Control Charts

Control Charts

Control Charts

Thank You

Seven QC Tools