Do engineering drawings imply solid and uniform parts?

[iusedtobehydrogen]

If I were to have a drawing of, let's say a cube, and the material specified was simply "ABS", and after sending the part to a vendor I recieved an average quality 3D print instead of a solid piece, could the part be said to be out of spec?
In my view, the discontinuities inherent in normal 3D printed parts would mean the part is out of spec. In other words, if really did want a solid piece for strength reasons or any other reason, I would not have to specify that it not be 3D printed. But a friend from work who is a drafter disagreed. What say you?

 

[JStephen]

I believe that ASTM A6 and/or A20, some of the stainless standards, define plate, strip, bar, etc. But yes, those terms do have definite meanings in various standards. I think the mill catalogs also made that distinction in the past.

The short answer is, you're communicating information, and your drawing needs to include whatever information needs to be communicated TO THAT PERSON.
I can detail a part, send it out to our welding shop, and after fabricating 10,000 other parts that I've also detailed, I have a pretty good idea of what they need, and they have a pretty good idea of what I intend. If I draw a cube, they don't have to ask "is that machined or forged or heat-treated or what". If I'm sending it off to somebody I've never dealt with, that may not be the case.
A similar issue is use of abbreviations, acronyms, welding/finishing/inspection symbols, tolerances, etc.

 

[dgeesaman]

Big picture view: I see this is as a grey area. The designer and the manufacturer both have to have their common sense hats on.

- If a manufacturer decides to convert to 3D printed material in a new application without agreement, they are incompetent. Full stop. 3D printed material is generally much weaker, porous, and more flexible owing to its reduced density.
- If a buyer / sourcing specialist decides to get a part quoted at a vendor that only offers 3d printed materials, the buyer made a mistake.
- As an engineer/designer, I suppose that some of my designs could be 3d printed or sintered/DMLS. Currently, on our drawings we assume no 3d printing unless we explicitly request it and we've been safe because the printed option costs more. But that is not adequate protection. Should I make any more complicated small parts I might want to add a note excluding 3D printing methods.
- The material standards groups have not caught up with this possibility AFAIK. For metals, there are plate and bar specs that preclude other methods of manufacturing of the raw material, but I'm as guilty as they come for simply putting "316L S/S" or "A-36 C/S" on a drawing so that I don't force the vendor into plate when they'd rather use bar or vice-versa. And there are plenty of material standard specifications that have only chemical specifications.**
- Some corporations have corporate standards that clarify the above. If your company has approved vendor lists or standard terms/conditions on your POs maybe you can formalize these issues via that paperwork.
- Perhaps welding specifications are a useful precedent. If you require an air-tight weld or a weld with complete joint penetration, you need to specify more than a continuous weld symbol or specify a weld prep that merely allows CJP. Unless there is an 'air tight' or 'CJP' required on the drawing, they don't owe you that. Ditto for any other particular weld quality requirement - indications, spatter, grinding, etc, etc.

My takeaway is that it might be wise to add "3D PRINTED MATERIAL IS NOT ACCEPTABLE UNLESS SPECIFIED OTHERWISE" on all of our drawing title blocks. Easier to get ahead than pretend I didn't know this was a possibility.

** Edited to add: maybe this is the argument - if a 3D printed material contains any measurable void space, compare how much air is allowed in the chemical composition for the material grade you specified. It's not an argument I feel a reasonable person needs to make, but if you want to get pedantic this seems like a clear way to settle it. "12-15% Chromium, .10-.13" Carbon, ... balance is Iron" should eliminate highly porous materials.

 

[ctopher]

dgeesaman,
Good suggestion. I like the note "3D PRINTED MATERIAL IS NOT ACCEPTABLE UNLESS SPECIFIED OTHERWISE". I may add it to our templates.

 

[mfgenggear]

Generally it is material chosen as follows.
Acceptable met lab properties.
Conducive to material cost savings
Conducive to to manufacturing

For example
A shop with a lathe with live tools can utilize
Round or square bar material. With a hydralic bar feeder. That can load 12 ft bars.
Can face , mill and part off , with one setup
Reducing handling , and machine load.
As long as it meets or exceeds the above criteria.
If it is a one time only one part for assembly fit up , and evaluation it could be possibly used if it meets the above criteria.

Model shops (considered engineering)
Will utilize many manufacturing methods
To get the job done for fitup.
In production , manufacturing could be
Utilized to be lower in cost, time and delivery.

 

[TDWS]

If I were to have a drawing of, let's say a cube, and the material specified was simply "ABS", and after sending the part to a vendor I recieved an average quality 3D print instead of a solid piece, could the part be said to be out of spec?
In my view, the discontinuities inherent in normal 3D printed parts would mean the part is out of spec. In other words, if really did want a solid piece for strength reasons or any other reason, I would not have to specify that it not be 3D printed. But a friend from work who is a drafter disagreed. What say you?

You can specify the material and processing technology of the product, or specify the processing or other technology in the order.