Sheet Metal Inspection - Constrained or Not Constrained

[CarolX]

Re: Sheet metal inspection - restrained or unrestrained

Thanks everyone for your input.......and I will try to answer some of the questions that have arisen here, but I really was just needed to know if anyone else had this issue before. I know that sheet metal is a small field, and not a lot of folks know the issues involved with sheet metal fabrication, including engineers.


So let me start with this - we are a commercial sheet metal job shop. It is an extremely competative filed. On a regular basis, we see drawing that are dimensioned incorrectly from most of our customers. +-.005 on a process that can achieve, at best, +-.010 repeateble. If we went back to our customers - they would see this as an anoyance, and take their business elswhere. There are a hundred shops that would take their work, no question or complaints.

There is a lot of backroom politics with this customer, and way to many details to go into. Bottom line is we were shoved on them by their parent division, and they didn't like that.

As to the methods used for inspection to verify hole location - we us a piece of equipment that is specialized for sheet metal called Fabrivision - it is a flat part digitizing scanner and it verfies the punched part in the flat against the engineering CAD file. The accurance of the scanner is +-.002.

So I hope this answers most of the questions that have come up.

 

[apestate]

Re: Sheet metal inspection - restrained or unrestrained

That's true Hawat, but imagine the climate. I'm in the same boat, so I can describe somewhat.

This is why I feel that poorly defined requirements are a poison to manufacturing:

A large customer of yours has title block tolerances that are absurd. No other supplier has tried to get them to update their prints, because frankly, they didn't care whether or not the parts were to spec. All they care is that they get accepted.

The customer rejects any pleas for print changes because they don't have the engineering staff to enact changes. Their prints were done poorly and remain poorly done. Their other suppliers aren't complaining.

Meanwhile, the supplier is producing parts and checking 4 parts out of a run of 300. The QA techs know that at least a third of those parts are out of tolerance. They're forced to fudge numbers or look the other way (for example checking five first articles to get a good one), because if they had complete integrity, they'd be a huge problem and snag in the company.

The operators know that, on average, at least a third of what they're making is out of spec. They don't have any trust in management at this point, and will fudge numbers and hide problems because otherwise they will be fired for making scrap. The operators mistrust QA techs because when the QA techs reach a breaking point and finally flag something as out of tolerance, the operators know it's like handing out speeding tickets at the Indy 500.

Everyone knows that the product requirements do not really matter, because the customer is accepting them and using them all the time. The end use of the product is a manure spreading fan for instance. The customer might even view your company as a high-quality producer, even though 1/3 of the product doesn't meet the poorly defined requirements.

The customer knows that they can reject parts almost at will, because there will almost always be something wrong with a part. Therefore, if the shoddy blueprinting doesn't define the proper requirement, such as the part must be some kind of flat to fit in drawer slots, they can reject the part because of a finish or hole size or location that makes no difference whatsoever. It's possible this goes on without the critical characteristic ever being communicated!

The quality manager knows all this, and has to eat it once in a while. All they can do is reason with the customer and take a beating when they have to, and update their internal requirements to the critical characteristics that should have been on the print in the first place.

THE SAME THING IS HAPPENING AT YOUR CUSTOMER'S PLANT.

Could you imagine returning every request for quote with a request for tolerance review? Even if you're 1 in 3 suppliers with the opportunity to quote, it looks bad.

Could you imagine asking the customer to review their tolerances on 700 different parts you make for them? The Emperor wears no clothes, except this time you kill the messenger.

Could you imagine improving your process to produce mundane sheet metal stampings and similar kit to absurdly tight tolerances? You might as well offer to update all the customer's prints yourself, because that's about the size of it.

I really understand where you're coming from, Hawat. I had that pride of workmanship and integrity as well, when I was in precision machining. I wasn't FORCED to make scrap. I miss that.

This has slowly changed as I've adapted to the product of the company I work for now, and it's abysmally depressing.

But! I'm glad to see you posting so well recently.

The Cove's activity is about the only thing that keeps me sane, so let me know if sometimes I'm releasing insanity into the forum.

 

[Coury Ferguson]

Re: Sheet metal inspection - restrained or unrestrained

Overtoleranced or not, when you agree to produce a product to a spec, you sadly agree to produce to the spec.

I'm still somewhat interested in hearing the method used. I'm trying to get a visual for the part in my head, and basically all I'm getting is a piece of sheet metal with some details stamped out. If that's the case, are you just using calipers from the edges of the part?

If you would read how Carol responded to part of your question (which just might be a time thing in posting) she said that Corporate forced (maybe not that type of language) them to use her company and they weren't to happy about this (already negativity has been started). Even though I am sure that during the review of the Contract/PO and the drawing this tolerance may have been missed during product review and being that the drawing is also old could have also been a Cause. These can be be missed by the best of us during the Review (Product Realization) phase.

But using any common sense from the Engineering group the tolerance of +/- .005 is way too tight for this application even with the tolerance block. This application (design) should have been designed for manufacturability from the get go.

You can not inspect quality into the product it has to be built into the product, from design through the final product stage.

 

[True Position]

Re: Sheet metal inspection - restrained or unrestrained

Maybe working with transmission components all day has made me a bit jaded, but I've worked on more open tolerance jobs. One with an atmosphere much like Atetsade talked about. I still stood my ground and forced the decision to ship not to print material on the production manager.

Back to the topic at hand though, CarolX, your gage doesn't meet the 10 to 1 standard for usability of a gage. When you put the part into your gage, does it accept or reject it? So far you've only said your customer has rejected them.

 

[CarolX]

Re: Sheet metal inspection - restrained or unrestrained

Back to the topic at hand though, CarolX, your gage doesn't meet the 10 to 1 standard for usability of a gage. When you put the part into your gage, does it accept or reject it? So far you've only said your customer has rejected them.

Sorry if this is about to sound harsh - but this thread has gotten way off topic.

This thread was not intended as a disucusion of the measurment equipments capapbility - just a question about restraining sheet metal during inspection.

 

[Coury Ferguson]

Re: Sheet metal inspection - restrained or unrestrained

Sorry if this is about to sound harsh - but this thread has gotten way off topic.

This thread was not intended as a disucusion of the measurment equipments capapbility - just a question about restraining sheet metal during inspection.

Carol, not harsh, the truth.

Now everyone should know that sometimes we (even me) stray from the OP. This is Human Nature (opinions, techniques and so forth). This is the nature of the beast, and I know we really didn't have an answer to the original question of: Specifications to reference, which we now seem to understand that there isn't a specification or standard we can fall back on.

It is a Customer and Supplier Issue of a inspection technique which both parties can agree on.

 

[True Position]

Re: Sheet metal inspection - restrained or unrestrained

Yes, but this topic moving off topic has been one of the most interesting topics I've seen in this (the inspection/test) forum in a while. The questions related to the sheet metal were answered two pages ago, but it branched out into an excellent thread on how often stuff is run at deviations, and was actually heading in my opinion into a pretty good discussion of measurement strategies for sheet metal.

How interesting would: 'Is there a standard to let me restraint sheet metal' 'No' 'Thanks' have been?

The point of a discussion forum is occasionally the freeform places it can go.

As to Coury's statement that the choice of techniques is between a supplier and a customer. That's only true if you let the customer know of your machines accuracy and they accept that you are deviating from worldwide standard procedures.

No harshness was intended towards anybody in any of my posts, I'm just interested in the problem, resolution, and such, sometimes I come across as 'difficult' or a bit of a jerk. It's usually just enthusiasm and interest in the problem.

 

[CarolX]

Re: Sheet metal inspection - restrained or unrestrained

The questions related to the sheet metal were answered two pages ago,

I respectfully disagree - If I tally the reponses, I get..

2 in restrained plus my opion here makes it 3.

3 for unrestrained.

50/50 split here.


Anyway - I appreciate all the suggestions. As I stated, there is a lot of politics involved. Going to customer and requesting a drawing change, or to get them to agree to a specific method of inspection, or really, any type of agreement is just not an option. It is such a combative situation that we have been dealing with for over 3 years. The owner of my company was raked over the coals about a month ago because of all our "quality" problems. Once we cleaned up their data (more than half of the charged rejects were not chargable), we found our reject rate with this division is about .001%....but in their eyes - we are their worst supplier....but why do we keep getting orders?????

Bottom line - the customer is using the parts, and the owner will probably flip his lid when he sees what they rejected and why. I would just like to give him some reference material. Looks like that does not exist.

 

[Marc]

Re: Sheet metal inspection - restrained or unrestrained

I have been in your position quite a few times, Carol. I've done a lot of contracting where in part I was asked in because of internal politics. I have followed this thread with much interest because I have gone through situations quite similar.

Most of the times I was involved in situations like this I wrote a 'History Report' and included data details as well as an explaination of the situation with potential solutions and gave it to top management. Usually I knew going in I was coming in as a 'Hired Gun' which I will admit made it easy for me to 'tell it like it is'. I remember working with a metal forming company where we had over 50% scrap on a part. As I went back through the history of the part for my report, I found that Alcoa had even run tests in simulation software that predicted all the problems we ended up having on a 'Deep Draw' aluminum part. The customer specified the alloy and tests BEFORE the contract was accepted showed where there would be cracking and other issues including a color 3D output of the stress areas of the part as the die drew down. But, sales wanted the customer more for its name ("Company X is one of our customer!") than for the amount of business. As I followed through the history the APQP process was followed, but as time went on the contract was accepted by sales, who 'sold' upper management, despite everyone from the material supplier to the engineers involved saying it can't be done. Then about 3 years later, as losses were being scrutinized, upper management had a hissy fit over the scrap. They didn't want to listen to what I said, but eventually they came around to 'reality' to some degree. However, one day in a meeting the plant manager yelled at me, including using the 'F' word (yes, there were female personnel present), for the failure to reduce scrap. I literally got up, said "I quit", packed up my stuff and walked out.

As you know you're in a no-win situation where you can only present the facts. I personally sympathize with you and wish you the best.

As far as the thread goes, I have had a lot of parts where we had to measure in a 'restrained condition' which often led to non-issues being categorized as significant issues. For what it's worth, although the thread has veered off topic, it has been valuable to me.

 

[CarolX]

Re: Sheet metal inspection - restrained or unrestrained

IAs you know you're in a no-win situation where you can only present the facts. I personally sympathize with you and wish you the best.

Thanks Marc. Fortunately, the owner of my company knows sheet metal. That is why I said he will hit the roof when he sees this reject. Most like his word will be something along the lines of "Those folks don't have a clue" in words that I can't type here. And this is where his real talent will come in....he is a wolf in sheeps clothing. He can make a used car salesman look like a rookie. I just wanted to give hime some technical ammo.