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?

 

[CWB1]

Yes, but you need to provide a specific material spec.

Manufacturing process is irrelevant bc it doesnt change your material spec, hence why its left off design prints.

 

[EdStainless]

rd1957, We have revising AMS to address this sort of thing.
First is to prohibit cutting bar from plate.
And then we added working about following original orientation (L, T, ST, LT) when cutting plate.
In the metals industries (coiled steel and stainless) it is common to 'or equivalent process'.
I have lost count of how many times it wasn't equivalent enough for our use.

 

[dik]

Unless shown by hidden lines, I would suggest...

 

[mfgenggear]

It's common to machine dastardly size anything to remove rolling , or manufacting imperfections depending on the product type.

 

[mfgenggear]

In my line of work the spec will dictate bar, forged or plate
And it's not allowed to substitute

 

[IRstuff]

The drawing is the specification, period; if you want something, or want to prevent something, then it should be on the drawing. We have notes, datums, etc., on our drawings. In our ME world, a classical prose specification is called a "Book-form" drawing.

Since your drawing does not specify either density, nor surface finish, nor any mechanical properties, a 3D printed cube would meet the letter of the requirement. Were I inclined to be annoying, I might be tempted to give you a hollow ABS box and have you try to prove to me that your drawing specified something else.

 

[CWB1]

rd1957, We have revising AMS to address this sort of thing.
First is to prohibit cutting bar from plate.

That sort of nonsense is the reason why companies have to waste so much time carving up society standards into usable corporate standards rather than simply referencing the society standard as a whole.

Shape is not part of a material spec. If critical, that's a lower-level print or specific source callout on an assembly print.

 

[mfgenggear]

CW
Not really correct and it depends on the contract requirements or if is a safety issue or not. Tensile strength , charpy, and met lab
In my line if work is very critical or can be.
Commercial with safety or non safety issues
Can also apply. Making gadgets with no issues no contract requirement other than
Reliabily nock your self out. This can be debated.

 

[3DDave]

How the material is formed can have a huge effect on the performance of the material. Resulting shape is a large part of how the material is formed.

 

[mfgenggear]

Oh, you wanted the properties to be OK through the thickness? I've had the opposite. Part did not need such critical properties, but did need to be made real soon. So nothing happens from the Quick Response Shop. Similar issue, .375 thick required. None on hand, don't want to order a big piece for just a little one. I say, is there 0.500 on hand? Sure, plenty. Can you machine that down? Uh, yeah, I guess. Bang head, mine, because I need to work with these guys for a long time.

Yes a great example is using forged raw material for high stress components.
Lost wax or investment castings for
Cost savings of machining or material cost.

 

[MintJulep]

Do engineering drawings imply solid and uniform parts?​

No, they do not; but for a long time we've mostly agreed to assume that they do.

With the advances in additive manufacturing it's probably time to stop agreeing to that assumption and start making more complete drawings or drawings + specification.

 

[EdStainless]

CWB1, In AMS many specs are tied to design properties.
So product form really does matter.
The post by rd1957 is now gone, but sending someone a plate where the L direction was originally the ST is asking for failure.
Very different properties in those directions.

 

[3DDave]

CWB1, In AMS many specs are tied to design properties.
So product form really does matter.
The post by rd1957 is now gone, but sending someone a plate where the L direction was originally the ST is asking for failure.
Very different properties in those directions.

Not gone, but the scroll-back function is replaced here with pagination.

 

[mfgenggear]

Yep longitudinal and transverse u and y properties.

 

[CWB1]

We're discussing print detailing but FWIW, I agree on the material science.

Despite many attempts there's been no consistent, specific definitions for shapes. Adding "bar," "plate," etc onto a material callout adds nothing and is often confusing, just like "AL," "STL," etc, hence why its bad practice. If the shop needs to start with specific stock, that stock needs to be treated as a separate, lower-level part and explicitly defined. Process requirements also need to be defined if applicable. Otherwise, you may get a part machined from "bar" that was cut from "plate" bc the terms are vague and the practice common.

 

[3DDave]

If I ask for a part to be made from bar stock, I know that the grain alignment and grain distribution will have a certain characteristic. I could request that a micrographic analysis be made by sectioning the finished part and specifying that same information in a few hundred pages attached to the drawing or, get this, I could rely on the specification for "bar stock" that it was made to produce those alignment and distributions.

Notice however that the name "bar" isn't the guide. It is the material specification that is called out for "bar stock" that guides it and if someone fails to use material meeting that specification and uses something that isn't qualified that is normally considered fraud. In government contracts that is called material substitution and can result in fines or prison sentences.

If one likes, that is the separate lower level and that is already common practice.

 

[MintJulep]

If I ask for a part to be made from bar stock, I know that the grain alignment and grain distribution will have a certain characteristic.

As far as I know, "plate", "bar" etc. are colloquial terms that are nowhere defined in a citable standard. I'd be happy to learn differently.

Although those terms might get you what you hope for most of the time, all they get you is an argument when you don't get what you hope for.

If grain alignment and such is important for your part, then your drawing needs to explicitly identify what you need relative for your part.

 

[3DDave]

Like:

ASTM A663/A663M-17
Standard Specification for Steel Bars, Carbon, Merchant Quality, Mechanical Properties

ASTM A615/A615M-22
Standard Specification for Deformed and Plain Carbon-Steel Bars for Concrete Reinforcement

 

[mfgenggear]

AMS specifications for bar steels include chemical composition, mechanical properties, and shapes. AMS specifications are used to ensure that steel bars meet certain standards.

AMS specifications for bar steels

• AMS 6257
  This specification covers the chemical composition of steel bars, forgings, and tubing. It includes elements like carbon, manganese, silicon, and chromium.
  
  
• AMS 6370
  This specification covers low-alloy aircraft-quality steel bars, forgings, and rings. It includes the chemical composition and mechanical properties of the steel.
  
  
• AMS 5639
  This specification covers 304 stainless steel bars, tubes, forgings, and more. It includes the chemical composition and mechanical properties of the steel.
  
  
• AMS 6427
  This specification covers 4330M alloy steel bars, which are known for their strength, toughness, and fatigue resistance. It includes the material properties of the alloy steel.
  
  
• AMS 6484
  This specification covers steel bars, forgings, and tubing. It includes the mechanical properties of the steel, such as tensile strength and elongation.
  
  
• AMS 6471
  This specification covers low-alloy steel bars, forgings, and tubing that can be heat-treated using the nitriding process.
  

AMS 6257 | Steel Bars, Forgings, and Tubing - Titanium Industries


Titanium Industries, Inc.

 

[EdStainless]

In the systems that I work with bar and plate are defined.
The various spec have size limits and manufacturing methods requirements.
In aerospace I have seen drawings with L, T, and ST marked on them.

In other products there are often not such definitions.
We used to have plastic coil end-turn supports made.
The print listed a composition per an ASTM specification.
It said that they were 'solid, made from extruded bar or injection molded'.