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Defect Concentration Diagram


Vishwadeep Khatri
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Defect Concentration Diagram is a graphical tool used to identify & mark the location of defects and then to analyze their causes. The defects are marked on a picture or a diagram of the product usually along with frequency of the defects.

 

An application-oriented question on the topic along with responses can be seen below. The best answer was provided by Mohamed Asif and Sourabh Nandi.

 

Applause for all the respondents - Mohamed Asif, Sourabh Nandi, Aritra Das Gupta, Sudhir Gayakwad.

Question

Q 290. Process defects could be analyzed using a process map review. Similarly product defects could be analyzed using a Defect Concentration Diagram. Provide use-cases of Defect Concentration Diagram with suitable examples.

 

Note for website visitors - Two questions are asked every week on this platform. One on Tuesday and the other on Friday.

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Defect Concentration Diagram / Problem Concentration Diagram is one of the "Magnificent Seven" SPC tools. It is also referred as Location Plot or Defect Location Check Sheet.


Defect Concentration Diagram is a graphical tool that is used in analyzing the causes of the unit defects.
It can be used and applied to any process, it shows the picture of the unit/product (or item of interest) and associated defects in the unit, in all relevant views. Location and frequencies of various defects are clearly given in visuals. Defect data segregated based on location.


294452627_DCDSBSR.thumb.jpg.4f79926f124a8e07a49c03fc650e187e.jpg

The diagram is further analyzed to determine if the defect location of the unit provides any useful information about the potential causes of the defects. This is repeated with enough sampling of units, to study patterns of defect and to set the focus area of improvement.

 

It is widely used during,

  • Problem identification (data collection phase)
  • When analyzing a part for potential defects
  • When a part has multiple defects
  • when problems arise after purchase of parts

Defects to a large outspread affects shipping decisions and Defect classification is a vital step associated with Inspection. Based on the severity of the defect, it is usually classified as Minor, Major and Critical.
Minor Defects - Don’t affect the function/form of the item
Major defects - Affect the function, performance or appearance of a product
Critical defects - Unusable and/or could cause harm to the user


2031252792_DefClassi.jpg.84276cb93d7de813017934fda9603146.jpg

 

Analysis Actionable:
Based on the study, it would help the product manufacture to make decisions like
Asking supplier to correct quality issues – Ask for replacement of the supplied item
Re-inspect – ensuring to correct the defects
Callback products – Keeps customer safe
Chargeback suppliers - Re-inspection and Re-work cost
Destroy unusable goods - prevent defective goods getting into grey market

 

It help to a great extend in product improvement for example,

A smartphone manufacturer can analyze defect concentration diagram of unusable/defective smartphone which the customer returned during warranty to study the type, frequency, severity and also the pattern of the defects to strengthen and improve the smartphone in the subsequent release.

 

Recent Advancement:
Usually inspection is performed manually by human and it could be sometimes unstable and insufficient. Surface defects, such as scratches, cracks and dents are common during manufacturing process.

 

Defect identification methods have improved a lot in recent times. 

998107826_DCDATMV.thumb.jpg.1b7d548dee40a82964543fab367c807c.jpg

 

One such improvement is Automatic Surface Defect Inspection System for Automobiles Using 3D Machine Vision Methods with integrated software’s which gives Defect Concentration Diagram in multi dimension.

 

To reduce the number of Rejects, it is necessary to know not only the percentage but also the location and the types of defects. Defect Concentration Diagram is a great tool to locate the type, frequency, location and the pattern of the occurring defect.

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Defect Concentration Diagram 

Also, know as: check sheet, concentration diagram, location diagram, defect location, defect map

 

Description 
Statistical process control involves seven essential tools for quality control. One quality control tool is called the defect concentration diagram. A defect concentration diagram is a type of check sheet using an actual image of the object or area where problems could occur. During data collection, observed defects, mistakes, or problems are marked within the picture. 

 

When to Use 
• When we investigate defects, mistakes, or problems that occur on a physical object or within an area. 
• Especially when we suspect that the physical pattern of occurrence might provide clues to the cause of the problem.

 

Procedure 
1. Decide what object or area is observed. Develop operational definitions. 
2. Decide when data are going to be consolidated and for how long. 
3. Design the pattern. Draw an outline picture of the objective or a map of the space, showing all significant features. Make it large and uncluttered enough that data will be collected directly on the image. 
4. If different varieties of defects, mistakes, or problems are observed, settle on symbols for every kind. Put a legend on the shape showing the symbols and what they mean.
5. Test the diagram for a brief test period to confirm it collects the acceptable data and is straightforward.
6. Every time an observation occurs, record it on the diagram. 
7. When the information collection period is over, analyze the information for patterns and trends that may indicate causes. If a visible analysis is inconclusive, we will measure distances between occurrences and analyze those measurements statistically. 

 

Example 
This tool is most common use is to mark defects on a picture of a manufactured object coming off an assembly line. In another example, insurance personal and vehicle repair facilities use pictures of cars to show damaged locations clearly. Here is an example of a non-manufacturing application.

 

A Pharmacy team trying to reduce shoplifting created a defect concentration diagram (Refer to the below figure ) to study how store layout contributed to the problem. Using a diagram of the store, we can mark locations where shoplifted commodities had been presented. When they analyzed the diagram, they observed clustering around the edges of the store, but they could not relate the pattern to aisle length, type of merchandise, or clerk location. Finally, a team member suggested adding to the diagram the positions of monitoring cameras. A pattern became clear based on sight-lines from the cameras.

 

646364140_Figure-Defectconcentrationdiagramexample..JPG.554d7a89417465660c2290c50acab4e2.JPG

Considerations

  • A common way to layout the check sheet is to create a table with descriptions of what we are observing (events, problems, types of errors) in an exceeding column down the left-hand side (or a row across to the top). Divide the remains of the page into columns (or rows) for accessible data collection. These might represent dates, times, locations of defects, or any other category that we wish to use to examine the data later.
  • Consider what information about the sources of the data might be necessary for the analysis. Plan the check sheet so that data is apprehended. It is easier to capture information when the data is generated than to try to reconstruct it later. Sometimes it is impossible to capture additional information later. See stratification for ideas about the information we might need to capture
  • When designing the form, use illustrations whenever possible, making the check sheet easier to use and can reveal patterns during the later analysis. For example, to collect data on damaged packages, include a description of the package and have data collectors put an X where we see the waste. 
  • Think about how data is received or how we are going to want to research it later and consider keeping separate sheets for various aspects of the gathering or analysis. For instance, if different people handle international and domestic shipments, use separate check sheets for international and domestic shipment errors.
  • Keep the check sheet near the purpose where the information to be recorded will occur. As an example, if we monitor forms of telephone interruptions, keep the check sheet next to the phone. This insistence helps us to gather the information consistently.
  • If observations occur frequently, we may opt to record samples instead of every observation. In step 2, decide when and observation are recorded. We may plan to use an amount (every 30 minutes) or a frequency (every fifth phone call).
  • A checklist could be a variation, sometimes called a confirmation check sheet.

Defect Concentration Diagram

  • A object might be a fabricated item rolling off an assembly line, an item that might have been damaged during shipment handling, or a form that operators or customers must fill out.
  • An area might be an office building, a laboratory, a warehouse, or a store (retail and storage areas).
  • To scrutinize errors made in filling out a form, use a copy of the form as the defect concentration diagram.
  • Include just enough detail on the picture so that the problem is located clearly, but not enough that the picture is too cluttered to highlight.
  • Use marker pens to mark the defects, so they are easily seen on the black and white illustrations. (But this should not be used if we need to photocopy the completed diagram for analysis or presentation.)
  • When we analyze the data, try to look at the patterns that are not distinct. For example, turn the diagram upside down. Alternatively, have someone unfamiliar with the object or area look at the diagram. Alternatively, add more detail to the diagram—a detail that was initially left out to unclutter the picture— and see if a pattern becomes apparent.
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Defect concentration diagram can be defined as a visual representation as to where the maximum defect is found for a product. For service the same can be done by a process mapping.

 

For a product the same can be done by defect concentration diagram. This helps to identify which part of the product has the maximum defect. This will help the team to focus or channelize the effort to remove these defects.

 

Defect     Concentration diagram is done in any of the 3 scenarios: - 

 

1.When data collection is being done to identify and quantify the problem. This helps to understand the magnitude of the problem and the effort that will be required to rectify the same. This will also help to understand what the benefits will be. 

2.Helps to identify which part of the assembly is leading to the increase in defects being produced. Which will help in fixing the same.

3.Helps in understanding what are the defects in a product and work on removing the same. This will help the company to increase customer satisfaction and reduce Cost of Poor Quality.

 

Example 1- 
image.png.4fd00017ae1722c993e895a0f95ef11f.png

 

The above diagram shows that which area in the car door has the maximum defects. This can be very vital for a car door supplier to quantify the total defect which will help in understanding the magnitude of the problem.

This can also be used to identify which production stage the defects are produced as each section of the car door is produced at a stage. This also helps to understand which part of the product has defects and what can be a potential impact.

For Example, if the lock of the has a defect there can be serious safety and life hazard and can lead to litigation. Despite the defect being less the manufacturer will have to work on the same first so that there is no defect.

The next focus can be on the glass fitting which if faulty can lead to customer dissatisfaction as it might result in leakage during rainy season.

 

 

Example 2- 
 

image.png.8ee1243a9a60e5e4e36516d2276ab6bb.png

 

A shirt manufacturer can use this technique to identify the number of defectives and defects. He can use the defect concentration diagram to understand where the maximum defects are and what are the defects.

In the above example of shirt, the maximum defects are concentrated towards the sleeves. The defect which is there is mark. There is a total of 12 defects for mark ,8 defects for flaw and 4 defects for tear. This will also help him to understand what happens incorrectly when a sleeve is being made which results in an increase in error for mark.

These techniques can be very useful in identifying defects and helping resolve the problem. Post implementation of solution the same methodology can be applied to check whether there has been an overall reduction in defect count as well as the defect concentration.

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Nowadays we all are very much familiar with a map shown on local news channel or national news channel with few areas shown in Red, few in Orange and rest in Green. The colors depict the severity of Covid 19 (number of cases) in those areas.

Red = highly severe – large number of infected cases.
Orange = moderately severe – Medium, number of infected cases,
Green = Low severity – Very less number of cases.

Depending upon the severity the rules for movement of peoples, doing the business in those areas are decided by government. Accordingly peoples are permitted as below,

Red – No business, no movement, complete restrictions.

Orange – Low movement, business of essential goods under moderate restrictions,

Green – High scale movement and business with regular restriction.

Thus it is easy to understand map which is shown on regular basis on TV news channels or in the news paper. It is a very effective way of communication to all concerned to take required actions.

Actually what is this map showing? Areas with severity of covid 19 spread. Or simply percentage of concentration of Covid 19 cases in different areas to guide local authorities to take appropriate actions and peoples to decide their course of action. As this journey of medical treatment, preventive actions and changes in basic habits, exercise goes the percentage of cases will go reducing day by day and red zone becomes orange, orange to green and eventually all green.

We all are engaged in the business of manufacturing defect free products. Manufacture defect free products is also a long journey and most of the time initial products are containing defects.

Quality control (QC) plays the most important task to bring defect free products.

There are 7 QC tools which comes to our help in analyzing defects initially so that we can reduce and eliminate them to make a defect free product.

1. Histogram, 2. Pareto Char, 3. Ishikawa Diagram, 4. Scatter plot,

5. Defect Concentration diagram, 6. Control charts, 7. Check sheet.

Let us discuss Defect Concentration Diagram-

A defect concentration diagram is the visual representation by a diagram or a map which shows the places on the product, where there are defects occurring. It also shows the frequency of the defects. Initially it is a plain diagram or picture or map. As analysis goes the diagram is filled with the places where defects are occurring along with number of defects at a particular location.

Use of the Defect concentration Diagram-

It is an effective research tool which is majorly used during the data collection phase of Problem Identification or measure phase of the DMAIC.

Steps involved –

1. Define the defect or defects being analyzed. It brings clarity about defect or defects for inspector. It brings standardization for common understanding.

2. Making a diagram, map or the picture of the product to be investigated.

3. Mark the particular location where defect occurs with designated sign (colored) each time it occurs while getting investigated. Thus the particular location is getting with marks of a particular defect and also the number of times it comes.

4. After sufficient period of time analyses the defect with respect to location on the diagram and number of time it occurs. This count will give the severity of defects.

*** Please have a look at following figure where different signs show the different defects and the number shows the frequency to show the severity of occurrences
image.png

 

 

Further Action Plan –

               Depending upon the location there could be action taken on design parameter and production methods to control the frequency of occurrence.

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