Final inspection process design for a machine shop setting.

S

sativ

#1
i recently got a job as a quality engineer in a machine shop that fabricates metal parts using CNCs, depending on the customer specs. I am tasked in designing a quality management system from total scratch, for an upcoming ISO 9001certification..
I wonder if you could help me out in the inspection process. since i always go for simplicity, i had chosen FINAL INSPECTION to be the last process prior to shipment. of course there are in-process inspections (done informally by operators, checking dimension after milling,etc.)..
> how can i design an inspection procedure (FINAL) that will not be a hassle to process itself (since some parts have complex forms such that 100% is entirely time-consuming) as well as provide enough confidence in the inspection result...
>> what steps will i take, incase out of sampling i am able to detect a non-conforming product. do i need to inspect all the finish goods?
Thank you.
 
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bobdoering

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#2
>> what steps will i take, in case out of sampling i am able to detect a non-conforming product. do i need to inspect all the finish goods?
Sampling is sampling, and you can not eliminate sampling error. But, final inspection can really only be sampling designed to pick out the higher probability problems. 100% inspection is a phenomenal increase in overhead that is difficult to justify - both in labor and equipment costs. The best way to ensure good product is proper control in the process. The information in the process is far more valuable - especially for machining. Predictive decisions come from sequential data - and that is lost in final inspection.

My suggestion is to look through Statistical process control for precision machining to get a good grasp on the process itself.
 

CarolX

Super Moderator
Super Moderator
#3
i> how can i design an inspection procedure (FINAL) that will not be a hassle to process itself (since some parts have complex forms such that 100% is entirely time-consuming) as well as provide enough confidence in the inspection result....
100% inspection is often very wasteful. I would look at implementing a sampling inspection program at final. My preference is always a C=O plan.

>> what steps will i take, incase out of sampling i am able to detect a non-conforming product. do i need to inspect all the finish goods?
Thank you.
A C=0 plan requires you to reject the lot and sort out the defects.

Hope this helps a bit.
 
B

Boscoeee

#4
i recently got a job as a quality engineer in a machine shop that fabricates metal parts using CNCs, depending on the customer specs. I am tasked in designing a quality management system from total scratch, for an upcoming ISO 9001certification..
I wonder if you could help me out in the inspection process. since i always go for simplicity, i had chosen FINAL INSPECTION to be the last process prior to shipment. of course there are in-process inspections (done informally by operators, checking dimension after milling,etc.)..
> how can i design an inspection procedure (FINAL) that will not be a hassle to process itself (since some parts have complex forms such that 100% is entirely time-consuming) as well as provide enough confidence in the inspection result...
>> what steps will i take, in case out of sampling i am able to detect a non-conforming product. do i need to inspect all the finish goods?
Thank you.

I am curious how do you define "final inspection"? I believe that will drive the extent of inspection needed.

Do you have a First Article Process to qualify the process?

Do you have First Piece Inspection program in place?

Do you have a in process inspection program in place?

Answers to this questions may lead other to provide more help!

Good Luck going forward!

With regards to "hassle", I am not sure how you can design an effective inspection system that does not appear to be a hassle (burden) to the work force. IMHO, the goal should be a cost effective program that provides the assurance the customer requirements are met nothing more, noting less.
 

Project Man

Involved In Discussions
#5
> how can i design an inspection procedure (FINAL) that will not be a hassle to process itself (since some parts have complex forms such that 100% is entirely time-consuming) as well as provide enough confidence in the inspection result...
I work in the same environment you do and we have recently revised our QMS as part of our process to become ISO certified. We have three levels of inspection at the Quality Manager level: 1. First Article Inspection 2. In-Process Inspection 3. Final Inspection. After the FA (first artcle) everything is inspected on a lot sample basis. We will sometimes require the operator to document measurements through out the production run. These are reviewed by the QM.
 

bobdoering

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#7
With regards to "hassle", I am not sure how you can design an effective inspection system that does not appear to be a hassle (burden) to the work force. IMHO, the goal should be a cost effective program that provides the assurance the customer requirements are met nothing more, nothing less.
Good point - that is a good difference between inspection and control. Inspection tells you if you made good parts - not very interesting, feels like a hassle. Control gives feedback that the process needs adjustment (when done correctly, before any bad parts are made.) To a good operator, that should be valuable information of ongoing interest.
 

Wes Bucey

Quite Involved in Discussions
#8
Some good answers so far.

From the description given in the first post, we are dealing with a contract machining environment. Almost by definition, the use of CNC machining and turning centers describes a precision machining environment.

In a precision machining environment, it is not a good practice for in-process inspection to be informal, rather, it should be part of a well-thought out Control Plan for each different product, taking into consideration such things as critical characteristic dictated by the customer and machining "checkpoints" before a final dimension.

Following are links to posts about some practices I deployed in a precision machining environment - perhaps something similar will work for your organization.

Wes Bucey on an efficient shop - empowerment (This is a single post (#18) in a longer thread - the url leads directly to the post - it is associated with a follow-up in post #20)
http://elsmar.com/Forums/showpost.php?p=105469&postcount=18
Wes Bucey on quoting and empowerment (This is a single post (#20) in a longer thread - the url leads directly to the post)
http://elsmar.com/Forums/showpost.php?p=105566&postcount=20

In process and final inspection:

Re: Inspection Dimensional Check Sheets - Over 500 part numbers

Who inspects?
I, too, ran a shop where primary responsibility...

Control Charts
In my high tech machining business (1990 -2000),...

What makes sense?
In point of fact, I have seen several operations...

 

Jen Kirley

Quality and Auditing Expert
Staff member
Admin
#9
When I worked in a machine shop, our CNC machinists checked the tight tolerance features of their parts frequently based on tool wear, and variation introduced by the environment: temperature and humidity. We could never say we achieved process control, so sampling per ANSI would not work, and if too many parts went by without a check he was apt to lose some.

So, as Wes said a customized inspectionplan could be needed to address the likelihood of certain characteristics going out of tolerance and why.
 

bobdoering

Stop X-bar/R Madness!!
Trusted Information Resource
#10
When I worked in a machine shop, our CNC machinists checked the tight tolerance features of their parts frequently based on tool wear, and variation introduced by the environment: temperature and humidity. We could never say we achieved process control, so sampling per ANSI would not work, and if too many parts went by without a check he was apt to lose some.
That is often the case with traditional attempts at CNC controls, but process control in CNC is very possible when done correctly. The real problem in machining is the sorts after a broken tool. Often final inspection sampling will pick up the results of ineffective sorts for that condition - because the sorts are just that bad.

As was mentioned in one of the threads, sampling is god for finding very bad conditions. For very good conditions, sampling will not pick up the rare problem. And, it falls into "inspecting in quality" approach. That is why control and capability are the goal.
 
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