Supplier wants manufacturing process notes on drawing 2

[LKENNEDY]

We have a supplier who regularly comes back with feedback of specific process notes that he thinks should be included in the product drawing.
E.g. there is a recess on one of our parts, and he asked for a note that says "18 x 5 x 5 recess machined post fabrication" as the part was going to be oxy cut first.

I am very new in my role here so am unsure if what he is asking for is reasonable but have always under the impression that the part/product drawing should contain info critical to form and function -Whichever way the manufacturer decides to make it is not really my concern as long as the parts are coming back within tolerance and passing FAI.
Simply, I don't want to include these type of notes - particularly in case we changed supplier and now the drawing is holding them to someone else's process.

With the same supplier we're having an issue where on one part, they drilled holes to 24mm instead of pre drilling and tapping them to M24. The hole callout was very clear that it is a tapped part and now they are asking for notes on the DXF too so this doesn't happen again.

Again, don't want to include this information, as I see it as completely their fault for relying solely on a DXF and not consulting the drawing we also sent. This has put a lot of pressure on the timeline to get the parts re-done. The rest of the assembly is sitting in the workshop waiting to be finished.
Do I just suck it up and put notes on a DXF for them to try and prevent this happening in the future? Or just insist that they have to read the drawing too. Seems insane to me that they wouldn't look at both. Why am I even sending a drawing if it's not being utilised?

Any help is sincerely appreciated.

 

[3DDave]

As to the holes, make the circles a bit smaller than the minor diameter for an M24, but note the required thread and thread specification. At least if they f' that up they can rework without so much trouble.

The more typical is to have a meeting where they show the process drawing and you look over it. This is not an approval process. It is a "same page" process where, once again, the supplier is reminded the part will be inspected to the drawing. The "same page" is to note discrepancies between the process documents and what the drawing calls for, something their QA should do anyway. Usually to find 0.445 on the process drawing when the part drawing says 0.455, that sort of trouble.

The product drawing shows the characteristics of the finished part unless, exceptionally, the only way to be sure of some characteristic is via some particular process. When a pocket is milled out is not such an exceptional case. Mainly it would be for when a variety of common processes that meet the dimensional requirements damage the part in ways that are difficult to detect, such as requiring use of a drill/ream combination to avoid microcracks that a punch operation might leave.

 

[Burunduk]

Here is what the ASME Y14.5-2018 Fundamental Rules (4.1) section has to say about it:

(e) The drawing should define a part without specifying manufacturing methods. Thus, only the diameter of a hole is given without indicating whether it is to be drilled, reamed, punched, or made by another operation. However, in those instances where manufacturing,
processing, quality assurance, or environmental information is essential to the definition of engineering requirements, the information shall be specified on the drawing or in a document referenced on the drawing.
(f) Nonmandatory processing dimensions shall be identified by an appropriate note, such as NONMANDATORY (MFG DATA). Examples of nonmandatory data are processing dimensions that provide for finish
allowance, shrink allowance, and other requirements, provided the final dimensions are given on the drawing.

 

[Wrenchbender]

What i do to make people happy is add ADVISORY NOTES 1, 2, 3 , etc. You can write anything considered helpful, but it is non-mandatory. Never got any push-back. Its like no one ever thought of it before, duh. Example: PARTS HAVE SUCCESSFULL BEEN FABRICATED BY blah, blah. Keep grammar in passive voice; no commands. Hope that helps.

 

[jassco]

Hi, LKENNEDY:

I agree with your vendor. If you need the recess feature on your part, then you have to define it with appropriate dimensions/tolerances.

Best regards,

Alex

 

[ctopher]

Understanding how the part is made, then dimensioning it correctly, makes a good part.
Sometimes if I'm not clear how the part is made, I will send the vendor a draft copy for their input.

Chris, CSWP
SolidWorks
ctophers home

 

[3DDave]

"ASME Y14.5-2018 Fundamental Rules (4.1) section has to say about it" only applies if they are using ASME Y14.5 and the notation to do so appears on the drawing.

 

[Burunduk]

"The drawing should define a part without specifying manufacturing methods" is a recommendation anyway, so even if they do use and reference Y14.5 on their drawings, there is no obligation to follow this practice. However it is good to take into consideration even if they don't work per Y14.5 because there is good reasoning behind it. Once designed and documented a part can be produced for decades, during which vendors and processes may change, but the geometry, function, and other characteristics can stay the same. For example, nowadays many companies are moving to 3D printing of parts that were machined. So, all the "FABRICATED blah blah MACHINED blah blah" nonsense that may be on the drawings of these parts becomes irrelevant, and there is either a need to update the drawings or to ignore parts of them, with only the info indicated as "NONMANDATORY (MFG DATA)" not becoming a problem.

 

[3DDave]

Yes, that is a great truism to keep in mind.

 

[CheckerHater]

"The drawing should define a part without specifying manufacturing methods"

"However, in those instances where manufacturing, processing,... is essential to the definition of engineering requirement, it shall be specified on the drawing..."

"For every expert there is an equal and opposite expert"
Arthur C. Clarke Profiles of the future

 

[Burunduk]

CH, your quote says "shall" when it's essential for an engineering requirement. Nor for the convenience of a specific vendor.

 

[CheckerHater]

We need ASME standard on how to draw the line between the two.

"For every expert there is an equal and opposite expert"
Arthur C. Clarke Profiles of the future

 

[3DDave]

Would have been better to write:

The engineering documentation should not specify manufacturing methods unless the method is required to produce a particular result.

They write as if paid by the word and in complete ignorance that this applies to means of communication other than drawings.

 

[Burunduk]

"unless the method is required to produce a particular result"
What qualifies as a valid "particular result"? Is any intended result legit for making an exception from this convention? If so what is the point of this guideline?

 

[CheckerHater]

There is no point. As there is no guideline. "You shouldn't do that unless you shall do that" is not exactly a guideline.

"For every expert there is an equal and opposite expert"
Arthur C. Clarke Profiles of the future

 

[3DDave]

"What qualifies as a valid "particular result"? Is any intended result legit for making an exception from this convention? If so what is the point of this guideline?"

Great question. What on any contract is to produce a particular result?

What is "essential to the definition of engineering requirement" ?

If one wishes to criticize, perhaps starting by being consistent in reasoning is a place to start.

For certain there may not be an engineering requirement. It may be an aesthetic requirement.


So, the question back: What qualifies as "essential to the definition of engineering requirement"? Is any intended result legit for making an exception from this convention? If so what is the point of this guideline?

Please contact ASME with your enlightened views on that point.

 

[3DDave]

"You shouldn't do that unless you shall do that"

is not the guideline.

When one removes the conditions to each part the sentence is changed.

Sure, it's a stupid clarification in Y14.5, as much of Y14.5 is stupid in other ways, to include guidance that is intended to stop fights, but phrased in a way that people can use the guidance to start them.

If a checker says "NO MANUFACTURING METHODS ON THE DRAWING, EVER" how is the engineer supposed to include those that are required for performance on the drawing? And if the standard says only if it is required, then there isn't a litmus test for what it means to be required (or the longer "essential to the definition of engineering requirement")

 

[drawoh]

LKENNEDY,

A very important issue is what your inspector should do. All the dimensions and finishes are good, but the hole specified as DRILL[ ]1/4 clearly has been cast in place, punched, or reamed, or gnawed out by Marvin the hyper-gerbil. Part rejected?

--
JHG

 

[3DDave]

For example - on the 737 there is a hole that is to be formed by drilling undersize, then reamed, and then an expander is placed into the hole to produce the final size.

The drill is done because one cannot make a hole with a reamer. The reamer is used to remove any axial scratches from drilling, and the expander is used to ensure a compressive load is left in the hole perimeter; all to preclude the formation of fatigue cracks.

Unless there is some method to measure that compressive load that is cheap and reliable, and microscopic inspection to check for linear scratches and marks, then not having other methods raise concerns about which parts were treated what way is worth it.

As I recall Spirit was called onto the carpet because fittings on in-service aircraft were found to have fatigue cracks originating at these holes, which had passed dimensional inspection, but weren't formed using the required process.

 

[Burunduk]

"What is "essential to the definition of engineering requirement"?"

Specific heat treatments, surface finishes, or any process with a unique outcome on the finished part, such as knurling, engraving, or laser marking. These are some manufacturing methods defined for the product by engineering. You don't tell the manufacturer what process to use when there are several different common methods to achieve the same result.