Flat Patterns in type design drawings. 3

[Cmott]

Flat Patterns in type design drawings.
Does anyone do this? For me I think it is a manufacturing process and should not be on a type design drawing, any thoughts on this?
I work at an Aerospace manufacturing company.

 

[3DDave]

That was my question.

<rant> He didn't care. He was looking to eliminate engineers working for him by eliminating their work, plus turn this in as a bonus worthy concept to middle management. The same middle management that, on that same contract that required delivery of the drawing package, told upper management that they'd gotten a verbal agreement that no such delivery was req'd and turned back the Level III package allocation as a straight up profit to the corporate coffers.

He moved to a 'cost cutting' group that mainly looked to cut costs by choosing concepts that failed to work, so no money was saved; but a lot of money was wasted on useless concepts. The big clue was him taking only the new grads. The ones with all the best ideas, but no experience and no concept of the word "NO." They mostly were laid off after his failure, and so, finally was he. But not before a large amount of damage was done.

Same project also put weld details on weldment drawings, but absent weld fixtures or final assembly dimensions, had a lot of problems that were solved on the assembly line with grinders. Not a good feeling to watch a mounting lug get ground down to fit because the weldment was oversize. As different welders worked on the items, the factory would generate ECRs to change the weldment details to account for each welder's technique. The weld schedule was detailed - one to three passes, no order to the welds, no particular preheat, etc, for the greatest warpage variation they could muster.
</rant>

 

[tbuelna]

In the aerospace industry, which typically works to AS9100 QA standards, it is not permissible to accept a non-conforming part without engineering/MRB approval. Nor is it acceptable for manufacturing to deviate from a controlled process used to produce a component that is part of a qualified/certified product without approval. If manufacturing wished to make a change to the design or process, the correct procedure would be to submit a change request to engineering. Or if manufacturing/QA wished to accept a non-conforming part, the correct procedure would be to submit an NCR and request engineering/MRB to disposition the non-conforming parts accordingly.

 

[3DDave]

MRB was chaired by manufacturing and mostly approved drawing changes to ensure there was no non-conforming material. Quality also reported to manufacturing. Any engineer objecting to the arrangement found they were dis-invited to all program meetings and had no program work because of 'attitude' problems. Why fix a factory when you can torpedo an engineer?

On one quick-turn design I asked the manufacturing engineer in charge if he wanted a flat pattern and was given a definitive 'We don't need your help.' Two days later I see the part on a table and another manufacturing engineer comes by. I ask what he thinks of the part and tells me the 'stupid engineer' (not realizing it was me) didn't even give them a flat pattern.

 

[tbuelna]

Yes, MRB is usually chaired by manufacturing, and QA is typically part of manufacturing. But QA can only submit an NCR or DR to engineering. It is up to engineering to disposition the non-conforming parts. Engineering decides whether the parts will be used as-is, scrapped, or reworked. Engineering must also provide written justification for the decision, instructions for reworking the part, and any documentation needed for effectivity/configuration management requirements. Stress approval is always required when dispositioning parts, unless they are scrapped.

 

[berkshire]

Some years ago I worked in the experimental department of Grumman American in Georgia, we would find parts that did not fit and would mark up the prints so that they and an ECR could be turned back to engineering.
We got told " If we catch you marking up prints you will be terminated." Have you got any idea how hard it is to write an ECR without the drawing?
Then the engineers would say , " Why didn't you just mark up the print?",
There are some fights you just cannot win.
B.E.

You are judged not by what you know, but by what you can do.

 

[tbuelna]

Here's a situation I had a few years back working on a NASA program at Boeing. All the parts we needed to have machined were contracted out to vendors. Boeing used on-site inspectors to check the parts produced by the vendors. If there was a non-conformance with any part the source inspector would submit a DR to the cognizant engineer (ie. me). The source inspector always put pressure on me to accept the parts as-is because they were under pressure from the vendor to not reject any deliverable products. Boeing suppliers were subject to a very strict quality control process, and any rejected products would affect their standing as a Boeing supplier, and that could cost them lots of money in lost business.

The problem I faced was that if I accepted a slightly out-of-tolerance part in order to keep the vendor happy, I would be forced to submit a written justification explaining why this part that does not conform to my design is acceptable to use. If I did this manufacturing would typically respond with an ECR asking to change my design to allow the larger tolerance. The cost of processing an ECN would greatly anger my manager and would be immediately rejected. So I was stuck in a difficult situation with this type of problem.

 

[ewh]

berkshire,
That was why I included the caveat that it was not an aerospace company that used this method, where it would never fly. ;-)

"Know the rules well, so you can break them effectively."
-Dalai Lama XIV

 

[berkshire]

Ewh,
I understand,
It always amazed me, that the situation I described had gone through the DC10, to the MD11, without ever being discovered.
B.E.

You are judged not by what you know, but by what you can do.

 

[dgapilot]

Seems to me that the non-conforming parts from MRB end up in the "spare parts pool" and they let the operator deal with the non-conformance. At the repair stations I worked for, we paid extra to not have PD holes on the skins we purchased. They would never line up right!

All that said, Type Design is the end product. The method of attaining that end product should be up to the entity building it. Yes, you need traceability, but you also need manufacturing flexibility. At one manufacturing facility (PMA house), almost all the jobs in the machine shop were routed for CNC equipment. Problem was, we didn't have enough CNC equipment to make all the parts. The machine shop supervisor (me) would look at the flow I the shop and offload jobs from the CNC machines to the manual or automatic lathes or mills just to get the parts out the door.

Since the Manufacturing Engineers wrote the routings, and the Cost Accountants used those routings to develop costs for the product, the incentive was there to manufacture the product for the lowest cost - highest profit. On paper it was nice, lower product prices - in actuality, costs went up since we didn't have capacity.

That's the main reason you don't want process documentation to be part of type design data unless that process impacts the end product features.

 

[tbuelna]

The OP mentioned the situation involved an "aerospace manufacturing company". Most aerospace manufacturers are now AS9100 compliant, which means working to a documented/validated/controlled process from start to finish. This would include some QA activity to verify conformance of the flat pattern blanks to any associated documentation used to produce them. This documentation often includes requirements specifically for producing the flat pattern such as material specifications, raw material grain orientation, or definition of features such as bend reliefs that might have an effect on the finished part's structural properties. Any features of the flat pattern defined by its engineering/manufacturing documentation, and that remain unmodified/unaltered when it is finally incorporated into the end item product, are still controlled at the flat pattern level. For example, if the flat pattern documentation defines the material alloy requirement, it cannot be re-defined on a later drawing. Thus the type design data package for the certified end item (assuming 14 CFR 21.31 applies) might need to include this flat pattern documentation.

There is an excellent post above from debodine that is worth reading which shows the relevant section of 14 CFR 21.31.

 

[dgapilot]

As a DAR, when I go out to do a conformity inspection, I'm only looking at the top level drawing and sub drawings to show conformity to the Type Design, not the method of production, and compare that design to the part in my hand. 21.31 requires "The drawings and specifications, and a listing of those drawings and specifications, necessary to define the configuration and the design features of the product shown to comply with the requirements of that part of this subchapter applicable to the product;", and " Information on dimensions, materials, and processes necessary to define the structural strength of the product". How a given manufacturer develops their FAA quality system is independent of and could be a subset of their QS or ISO quality system. It is usually best to not mix them.

There is no need for manufacturing engineering data about how a part is produced to be included in the Type Design under 14 CFR 21.

 

[Cmott]

Thanks for all the replies and providing me with some ammo.