What is the root cause analysis?

What is Root Cause Analysis?

Root Cause Analysis is an in-depth technique for identifying the most relevant, controllable and significant cause of a problem. If we take action on that cause then the problem will not repeat due to that cause.

3 Requirements of the Root Cause:

Root cause,requirement for root cause
  • The root cause must be relevant to the problem. If it is not relevant to the problem then it is not the root cause.
  • It must be controllable. If the root cause is not controllable then it is not the root cause.
  • It must be significant.

What are the 5 Whys of Root Cause Analysis?

Five whys were invented by Sakichi Toyoda in 1920. There are 2 categories for why why analysis.

Occurrence:

The first category is related to the process that made the defective part. Why did it occur? We focus on the real root cause of occurrence here. So that when we take action on that real root cause the problem will not be repeated.

Detection:

The second one must address the detection system that was not able to detect the defective part.

  • Why did the outflow happen?
  • Why was it not detected in our factory?
  • Why did the part go to the customer? So in this category, we focus on the second step detection.

5 Whys are not always necessary to reach the root cause of the problem. It may take less or more than 5 whys to get to the root cause. It could be 4 whys or 6 whys. It will depend upon the complexity of the problem.

Stop asking why if your common sense says you have reached the controllable step of a process, relevant document, policy or a concerned person ( operator or supervisor)

As this tool is purely observation-driven, just keep asking the next why till you feel that the root cause has now become evident.

Useful Tools for determining Root cause analysis:

Practical Examples of Root Cause Analysis :

Case Study 1 :

Problem: Flat Tyre of a Car

Why 1Why 2Why 3Why 4Why 5Root Cause
Nails on the garage floorNails cartoon split openCartoon got wetRain through a hole in the garage roofRoof tiles are missingThe roof is not a part of the daily checklist

Case Study 2:

Problem: The CNC Machine stopped

Why 1Why 2Why 3Why 4Why 5Root Cause
The overload circuit trippedThe pump was seizedMetal chips damaged the shaftChips entered the lubrication systemNo filter on the inlet pipeThe sump design is not OK

Case Study 3:

Problem: Rod Length under size on Band saw cutting

Why 1Why 2Why 3Why 4Why 5Root Cause
Rod movement lessLimit switch plunger not movingPlunger jammedChips got into the plungerNo cover on the plunger and limit switchMachine design not OK

Case Study 4:

Problem: Blowhole in Aluminum casting

Why 1Why 2Why 3Why 4Why 5Root Cause
Casting filling is not OKMolten metal does not reach the effective areaCasting ends before filling areaCasting design as per modelDesign not adequateGate opening design is not adequate

Case Study 5:

Problem: Punching out in Sheet metal parts

Why 1Why 2Why 3Why 4Why 5Root Cause
Part shiftedLocator gauge shiftedLocator looseBolt looseHardened bolt not usedNo checkpoint in the design for the use of hardened bolt

Case Study 6:

Why why for the occurrence of a Blow Hole in the Pressure die casting process due to air entraption:

Why-1Why is air entrapped during metal flow?
AnsSleeve filling ratio more ( 55%)
Why-2 Sleeve filling ratio more ( 55%)?
AnsEffective sleeve area less
Why-3Effective sleeve area less?
AnsPlunger dia less (50mm)
Why-4Plunger dia less (50mm) ?
AnsAs per standard practice, the die was designed according to the model and past history data are not considered

Root Cause: As per standard practice, the die was designed according to the model and past history data are not considered

Case Study 7:

Crack in sheet metal part

Why why analysis for the occurrence of a crack in sheet metal parts:

Why-1Why crack on parts after bending?
AnsHeavy burr on the edge of the blank
Why-2 Heavy burr on the edge of the blank?
AnsThe cutting edge of the die worn out
Why-3The cutting edge of the die worn out?
AnsCutting edge worn out before the defined resharpening frequency
Why-4Cutting edge worn out before the defined resharpening frequency?
AnsTool resharpening frequency not reviewed as per past history

Root cause: Tool resharpening frequency should be revised as per past history.

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