Error Proofing Verification - Layered Audit Question

BradM

Staff member
Admin
#11
Suppose you have a process where you push a pin in a hole to a depth of 1 inch. I was considering whatever mechanism controls the press depth (lvdt, encoder etc…) to be the error proofing device.
IMO, error proofing is performing A DMAIC or other type analyses to ascertain the applicable variables and controlling them. Above, there are multiple facets that would need to be identified to minimize/eliminate error. The mechanism to measure distance, depth, etc. would be one tool. The sharpness of the pin, temperature, density variations of the material, etc. would all come into play.

Does that sound close?
 
Elsmar Forum Sponsor
#12
This thread has taken an interesting 'twist'.

One of the challenges that automotive suppliers have is that we don't get to discuss terminology, 'correctness' of application etc. or other, deeper, philosophies. The customer wants error proofing to be done as part of LPA's and that means 'testing' the system with a reject part (or similar) to see if the equipment etc is capable of letting it go on, unchecked.
 

Helmut Jilling

Auditor / Consultant
#13
This thread has taken an interesting 'twist'.

One of the challenges that automotive suppliers have is that we don't get to discuss terminology, 'correctness' of application etc. or other, deeper, philosophies. The customer wants error proofing to be done as part of LPA's and that means 'testing' the system with a reject part (or similar) to see if the equipment etc is capable of letting it go on, unchecked.

I agree. Let's not overthink this. Any device that protects the customers, or reduces the possibility of making bad parts, is a good thing. Go with it.
 

BradM

Staff member
Admin
#14
Thank you Andy, very much. I have been rambling a bit in this thread, as I have been unclear what the intentions/ requirements are of the OP. NOTE: That is not meant negatively towards anyone, just means I have a lack of understanding on this particular application.

Andy (or others), please if you don't mind, elaborate on this process/application in the automotive industry.

Too, a bit about LPA would benefit me also
 
V

vanputten

#15
I am not over thinking anything. The differnece between error prevention (poka yoke, mistake proofing, error proofing) and escape controls (error detection) is not an advacned concept. It is a very important concept.

In all of the literature I have read, the main purpose of mistake proofing is to ensure no errors are made. If no errors are made, then there is no need to detect errors and stop them from escaping.

Advance Product Quality Planning put the emphasis on the process design to ensure quality output. Same thing for mistake proofing - the main prupose is to ensure quality output so the organization should not have to dedicate excess resources to inspection and escapes. Spend time and effort to prevent erros as opposed to spending time detecting them.

The Layerd Process Audit question should concentrate more on verifying that controls are in place to prevent errors and less emphasis on inspections to detect errors already made.

Regards,

Dirk
 
#16
I'll try to help....I've got some similar fixtures.
Let's say that your automatic fixture twists a potentiometer clockwise until it gets a signal from a multimeter that the voltage is in specification. Can you unplug the connection between the two? Can you put an insulator between your part and the measuring fixture so it never gets a signal? So you've got a pot twister and a meter, somewhere there must be a power supply to turn the part on. Can you turn off the power supply to your parts so they never turn on? What happens? Be creative.

We had an "error-proof" system that worked something like this...until we figured out that the power supply had failed and was running at 1/2 the set input and every pot was set wrong. We had to add a check of of the input voltage to the existing output check in our test software.
 
#17
No problem, Brad:

Simply put, a Layered Process Audit is a check of a workstation (or similar) in a manufacturing process (assembly, welding, etc) by various 'layers' of management from line supervision to the top manager of the facility, to watch the operator 'doing' the process. These are done at a frequency which ranges from per shift (supervisor) to weekly/monthly. A simple audit checklist ensures the same topics are covered each time plus any actionable items found, which are, in effect, escalated to top management each time they do an LPA.

An error proofing audit is a type of LPA but done by specific individuals (process technicians etc.) Typically it consists of running a known reject part down the process to 'trigger' any error proofing systems such as position detectors, vision systems, etc. Other systems rely on proximity detectors which can be 'fooled' and tested to see if the line still functions and will 'accept' defective parts.

The underlying reason for these 'audits' is to re-inforce operators 'following work instructions'............because some people think that's why we get poor product quality!

There are other threads here about LPA's (I don't know how to link them:eek: )
 

Helmut Jilling

Auditor / Consultant
#18
I am not over thinking anything. The differnece between error prevention (poka yoke, mistake proofing, error proofing) and escape controls (error detection) is not an advacned concept. It is a very important concept.

In all of the literature I have read, the main purpose of mistake proofing is to ensure no errors are made. If no errors are made, then there is no need to detect errors and stop them from escaping.

Advance Product Quality Planning put the emphasis on the process design to ensure quality output. Same thing for mistake proofing - the main prupose is to ensure quality output so the organization should not have to dedicate excess resources to inspection and escapes. Spend time and effort to prevent erros as opposed to spending time detecting them.

The Layerd Process Audit question should concentrate more on verifying that controls are in place to prevent errors and less emphasis on inspections to detect errors already made.

Regards,

Dirk

What I meant by overthinking was that the terms are used somewhat interchangeably, to the point where the differences are lost in context.

However, I trust we all agree there are different levels of execution, regardless of which term is applied.

The best approach is a system that prevents the error from even occuring. Sometimes that is not possible, or feasible. Many times, the best we can do is put automated inline sensors and inspection equipment to 100% check the output, without adding labor. This does not prevent the making of bad parts, but prevents them from passing.

Regardless of which term we assign to that, it still protects the customer, but is not as ideal as preventing it in the first place.

Either way, the customer receives benefit. The Layered Audits are supposed to verify these systems work.
 
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