7 QC TOOLS
Updated: Sep 11, 2020
1-Stratify data
2-Pareto diagram
3-Cause & effect diagram
4-Histogram
5-Scatter Diagram
6-Check Sheets
7-Control Charts
Will be explained through the creation of a QC Story
QC Story
A procedure for problem-solving
‘Story’ means ‘Logical Flow’
QC Story Steps
1. Define
-Define the problem clearly
Demonstrate the importance of the problem
Show the background of the problem
Explain with data the pain and impact of pain
Define the theme with target
Form a team and appoint a leader
Present and estimated budget
Prepare a schedule
2. Observation
Investigate data
Go to Gemba
Observe both conforming and non-conforming products/situations
How to Collect Data
1.Have Clear Defined Objectives
•Controlling and monitoring the production process
•Analysis of non-conformance
•Inspection
2. What Is Your Purpose
•Collecting as per strata
•Collecting in Pairs (correlation)
3. Are Measurements Reliable
4. Find Right Ways to Record Data
•Arrangement
•Data sheet
A-Check Sheet
What
An easy to understand form used to answer the question “How often are certain events happening?”
Why
Starts the process of translating “opinion” into “fact
When
Gathering data in order to detect patterns. Good point to start most problem-solving cycles.
Purpose of Check Sheets
Simplification of the data collection process
Reduction of recording errors
Ease of analysis
How
•Team agrees as to exactly what event is being observed.
•Decide on the time period during which data will be collected. This could range from hours to weeks.
•Design a form that is clear and easy to use making sure that all columns are clearly labeled and that there is enough space to enter the data.
•Collect the data making sure that observations/ samples are as representative as possible.
B-Pareto Principle
VilfredoPareto (1848-1923) Italian economist
20% of the population has 80% of the wealth
Juranused the term “vital few, trivial many”. He noted that 20% of the quality problems caused 80% of the dollar loss.
Pareto Analysis
What
A bar chart that helps to prioritize actions by arranging elements in descending order of occurrence. Sorts out the “vital few” from the “trivial many”.
Why
•To prioritize actions needed to solve complex problems.
•To separate important from non-important causes contributing to a problem.
When
•Many factors are impacting a problem.
•Attention needs to be directed only to the few factors that account for most of the problems.
How
•Define a problem and collect data on the factors that contribute to it.
•Historical records generally provide sufficient information.
•Classify the data by type, cost, percent, number of occurrences, or whatever is appropriate for the situation.
•Arrange the data in descending order.
How contd.
•Draw bar graph showing constituent ratio on the vertical axis.
•Connect the cumulative percentage of each bar graph to obtain the Pareto curve.
Stratification
What
Stratification is a statistical technique of breaking down values and numbers into meaningful categories or classification.
Why
To focus on corrective action or identify true causes.
When
To identify the cause of the problem if they come from a particular source.
•To analyze root cause in conjunction with other techniques like Pareto diagram histogram and graphs.
How
Regroup original data as per the source of data(e.g.. Machine wise, shift-wise, model-wise, supplier-wise)
•If required collect data a fresh after making the source from which they come.
•Recreate histogram, Pareto charts, and graphs on classified data
3. Analysis
Find out what the main causes are
Set up Hypothesis
Eliminate irrelevant causes
Brainstorming
Cause & Effect Diagram
Mark those with a higher probability
Cause Effect Matrix
Rating and Ranking
FMEA
Test the Hypothesis
Collect data or conduct experiments to the validated hypothesis
List validated causes
Histograms
Control Charts