Does source inspection result in zero defects?

toniriazor · Apr 27, 2024

Bev D said:
It is a very good book that explains the source inspection method very well.
The only caution is the negative perception of “SQC”. SQC and other methods are intended to detect, investigate and solve physics related problems that are not human error based. Source inspection and poke-yoke is perfect for this bu these things cannot address physics based problems. That requires a completely different set of tools. Most companies experience booth types of problems…

Hello Bev, could you please provide an example if possible, so I can get a better understanding what is considered under physics based problems and the tools used to address such problems. I hope you don't mind. Thank you.

Bev D · Apr 27, 2024

toniriazor said:
Hello Bev, could you please provide an example if possible, so I can get a better understanding what is considered under physics based problems and the tools used to address such problems. I hope you don't mind. Thank you.

Start here. Physics problems are those not caused by direct human error. While human error might be at the systemic root of many physics problems it is the physical causal mechanism that must be understood and corrected first. Without that you only have a search for root blame that will be driven by agendas and biases…

toniriazor · Apr 28, 2024

Bev D said:
Start here. Physics problems are those not caused by direct human error. While human error might be at the systemic root of many physics problems it is the physical causal mechanism that must be understood and corrected first. Without that you only have a search for root blame that will be driven by agendas and biases…

Thank you. Wonderful material.

Bev D · Apr 28, 2024

Physics and human behavior are often intertwined in the causal mechanism of a failure. It is critical to point out that it isn’t always necessary to properly identify each factor or step in a. Causal mechanism as behavioral or physics so much as it is essential to keep them in the correct order so we don’t jump to the wrong conclusions…The causal systems of chronic or difficult Problems are often complex and take a torturous path.

If we first look at this question regarding source inspection and apply some critical thinking skills we can understand that the operator will see a missing bolt, a broken or missing bolt ‘head’ and some wrong bolts or cross threaded bolts. They will not see defects that are occluded from view such as a broken bolt in the thread area, a crack or a metallurgical defect/contamination in the non-visual (Threaded area) part of the bolt. Nor will they see a bolt that is of the wrong material properties due to a supplier substitution or a design error that resulted in the wrong type or size or number of bolts. Many of these are physics factors that are initiated or enabled by human behavior/error like substituting the wrong material bolt or an incorrect design choice. Some like a missing bolt are pure human error. Some are a combination of a physics defect (result or Problem) that are directly caused by human behavior/error such as under or over torquing a bolt (not to the specified torque). This will result in a latent defect that will later result in a failure given enough stress (the stress-strength interaction). Human error may be an operator who didn’t follow the instructions, a human error in calibration of the torque wrench or a human error in incorrectly specifying the torque instructions…etc. During my time in the automotive industry and other mechanical assembly processes I have experienced all of these.

In my experience the Problems that are primarily physics based are systemically caused and enabled by human behavior. Problems that are primarily human behavior based are often enabled by physics. Even the simplest looking problem can be quiet complex.

toniriazor · Apr 28, 2024

Bev D said:
Physics and human behavior are often intertwined in the causal mechanism of a failure. It is critical to point out that it isn’t always necessary to properly identify each factor or step in a. Causal mechanism as behavioral or physics so much as it is essential to keep them in the correct order so we don’t jump to the wrong conclusions…The causal systems of chronic or difficult Problems are often complex and take a torturous path.

If we first look at this question regarding source inspection and apply some critical thinking skills we can understand that the operator will see a missing bolt, a broken or missing bolt ‘head’ and some wrong bolts or cross threaded bolts. They will not see defects that are occluded from view such as a broken bolt in the thread area, a crack or a metallurgical defect/contamination in the non-visual (Threaded area) part of the bolt. Nor will they see a bolt that is of the wrong material properties due to a supplier substitution or a design error that resulted in the wrong type or size or number of bolts. Many of these are physics factors that are initiated or enabled by human behavior/error like substituting the wrong material bolt or an incorrect design choice. Some like a missing bolt are pure human error. Some are a combination of a physics defect (result or Problem) that are directly caused by human behavior/error such as under or over torquing a bolt (not to the specified torque). This will result in a latent defect that will later result in a failure given enough stress (the stress-strength interaction). Human error may be an operator who didn’t follow the instructions, a human error in calibration of the torque wrench or a human error in incorrectly specifying the torque instructions…etc. During my time in the automotive industry and other mechanical assembly processes I have experienced all of these.

In my experience the Problems that are primarily physics based are systemically caused and enabled by human behavior. Problems that are primarily human behavior based are often enabled by physics. Even the simplest looking problem can be quiet complex.

These are events that regularly occur during manufacturing and if the standards/procedures are followed (if they exist at all) these events could be reduced and human errors caused by other human errors (like bolt of wrong material properties) avoided to maximum extent and not converted into defects. Something crucial , that Mr. Shigeo Shingo is explaining in his book. My experience shows that operations/controls that are influenced by human judgment fail frequently. As an example we cannot expect that in manufacturing environment an operator will apply proper bolt tightening torque, to do so a robust process must be in place and torque force controlled by the process itself, which parameters again are set by a human. Something unavoidable, I guess.

Again I found your presentation really useful in going deeper into physic defects and the failure modes and effects.

Bev D · Apr 29, 2024

your point is true that we can move up stream of any process and create processes and procedures to help reduce human errors that result in defects or to catch defects before tey result in failure. And this involves many, many other tools beside source inspection of course. FMEA, design processes using DoE to set real specifications and develop processes that will ensure that we meet those specs, better inspection & test methods to help in the development process and catch defects before they are shipped, robust verification and validation methods, measurement systems analysis, true SPC which is intended to find variation before defects are created, poke yoke and single piece flow, robust problem solving methods when defects and failures do occur so can prevent them in the future. And of course you must be able to convince and command others to do these things.

So, it’s not as simple as merely looking, you must know what to look for, how to look and what methods (equipment and statistical, and scientific) you must use to look…

Does source inspection result in zero defects?

toniriazor

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Bev D

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toniriazor

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Bev D

Heretical Statistician

toniriazor

Involved In Discussions

Bev D

Heretical Statistician

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