Contolling Electronic Cad Data

[macduff]

Happy New Year Everyone!

I was wondering if there and ASME specification for controlling electronic data. Looking mostly for a generic drawing note.

Here's my dilemma:
For our complex parts we make drawings with only critical dimensions applicable to the design and have a drawing note referencing the cad model as follows:

THIS DRAWING SHALL BE MAINTAINED AND REVISED ELECTRONICALLY
THROUGH THE 3D SOLIDMODEL AND SHALL HAVE THE SAME REVISION
LETTER. THE 3D MODEL MAY BE USED FOR RAPIDPROTOTYPING OR
ANY OTHER CAD SERVICES NEEDED FOR PRODUCIBILITY OF THIS PART.

My co-workers want to use this note:

GEOMETRY OF PART PER SOLIDWORKS FILE USE FOR MANUFACTURING AND DATA VERIFICATION. MODEL: XXX-XXXX-XX.SLDPRT PART MODEL
TAKES PRECEDENCE OVER DRAWING PART IS MODELED AT NOMINAL DIMENSIONS.

A couple of things......one; I don't like the p/n in the note because it's just one more thing to edit and miss revising a drawing. two; our quality system hear requires us to buy and inspect hardware to drawings, not electronic data. I'm referencing ".....PART MODEL TAKES PRECEDENCE OVER DRAWING....." which conflicts our quality standard.

What your take on this? Also, any aerospace spec referencing controlling electronic data would be helpful.

All the Best,




Colin Fitzpatrick (aka Macduff)
Mechanical Designer
Solidworks 2009 SP 3.0
Dell 490 XP Pro SP 2
Xeon CPU 3.00 GHz 3.00 GB of RAM
nVida Quadro FX 3450 512 MB
3D Connexion-SpaceExplorer

 

[drawoh]

macduff,

How is your inspector going to decide which parts to accept or reject?

You need tolerances.

JHG

 

[macduff]

Hmmm...........that's a good point. Our critical dimensions labeled on the drawing do have tolerances assigned, but the remaining part (3D model) does not. That's another issue I have to address.

Besides that, what's your take on the initial thread? Is there an aerospace spec out there you can point me too? How about the comment on ".....PART MODEL TAKES PRECEDENCE OVER DRAWING....." when our buyers buy to the print and quality dept inspects to the print.

Colin Fitzpatrick (aka Macduff)
Mechanical Designer
Solidworks 2009 SP 3.0
Dell 490 XP Pro SP 2
Xeon CPU 3.00 GHz 3.00 GB of RAM
nVida Quadro FX 3450 512 MB
3D Connexion-SpaceExplorer

 

[drawoh]

macduff,

I am not aware of such a standard. There is a standard for dimensioning and tolerancing of 3D models, but this involves you applying the tolerances, and getting the rapid prototype guys to read them.

How about a drawing note?

"UNLESS OTHERWISE SPECIFIED, ALL FACES LOCATED TO WITHIN 0.2mm WITH RESPECT TO DATUMS A, B AND C."

JHG

 

[KENAT]

Our notes are:

x. DIGITAL PRODUCT DEFINITION PREPARED IN ACCORDANCE WITH ASME Y 14.41-2003.
y. THIS DRAWING SHALL BE USED WITH MODEL (INSERT PART NUMBER) (REVISION PER THIS DRAWING) FOR COMPLETE PRODUCT DEFINITION. MODEL GEOMETRY IS BASIC.

I created these after reviewing the info here on this site, asking my own questions on Model Based Dimensioning, and trying to read through ASMe Y14.41. From memory I based them on something in ASME Y14.41 but I can't recall the details and don't have time to look at the standard right now.

Tolerances are placed on the drawing. For some cast or molded points this has been in the form of an overall surface profile tolerance.

14.41 is a bit dissapointing from a designers point of view, as it's almost more a list of what the software needs to do, but it's the most relevant spec I can think of.

There have been a number of threads generally relating to this topic I suggest you take a look, for instance thread1103-239768.

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[ctopher]

I do similar to KENAT.
I also add one line above the title block "CAD FILE: XXXXXX, REV X".
This is updated when revs change so the machinist or assembler knows which to use. It is easy to find on the dwg face.

Chris
SolidWorks 09 SP4.1
ctopher's home
SolidWorks Legion

 

[KENAT]

Thanks Chris, I meant to say, you may be able to parametrically call up the PN & rev from file properties which may help reduce chance of it being missed at a revision or a typo being made.

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[MechEng2005]

A decent portion of my drafting time is spent on clarifying and indicating the assumed. For example, I often need to go back and add weld symbols to drawings I created myself or I am checking for co-workers. There may be a dozen other identical weld symbols on the drawing, and it's obvious that the pieces need to be welded, and it will be done even if the weld symbol were absent. Also, we do most of the fabrication in-house, so I'm a short walk from the fabricator if questions arise.

The point of my rant is that drawings are intended to make things completely unambiguous. I am against referring to the model for use in inspection. Part of my job as a drafter/engineer is to know when to include (for example) the dimension from the left edge of a part to a hole or the right edge. If inspection is working from a model, it's up to them where to measure from.

I have in tight situations supplied a hand drawn sketch from the field for fabrication of simple parts. This was certainly quicker than even 2d drafting or 3d modeling. However, there is a reason that everything is not produced with "napkin sketches".

-- MechEng2005

 

[KENAT]

MechEng - there are types of parts that are very time consuming, if not almost impossible, to truly fully define with a 2D drawing. The curved surfaces on automobiles or aircraft being the classic example, but the curvy plastic parts on many consumer items may be even more common. The old approaches of defining lots of cross sections or similar still required the tool maker to 'fill in the gaps' to some extent in some cases so left some ambiguity.

For these types of parts MBD is a real bonus, even in the current state. Tolerances (including datum’s etc.) and other non geometric data still need to be defined, that has not changed.

True MBD has a way of recording this information in the model and - importantly - communicating this to other users of the data. However, because of the inadequacies of current CAD programs, the problems of not everyone using the same file format, the need for ‘rules of use’ on how to interpret models and some other issues not fully addressed by 14.41 etc. hybrid model/drawing is supported by 14.41 and from what I’ve seen is probably the best approach for most folks at this stage.

Of course, many folks see MBD as an opportunity to half ass it without addressing things like Tolerancing, but these people probably half a$$ed their drawings to so whether it’s worse is debatable.

This has been discussed in depth in the other threads I mentioned, including input from folks in automotive and aerospace that live in the MBD world.

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[SDETERS]

We have this note on our drawings ALL FEATURES NOT DIRECTLY DIMENSIONED TO BE CONTROLLED BY (Company Name)3D MODEL TO (Catch all Profile and Positional tolerances). DIRECTLY DIMENSIONED FEATURES TAKE PRECEDENCE OVER THE 3D MODEL.

We use this mostly on our Complex parts such as Die castings, lost foam and plastic parts. We dimension what is functional and or critical to the parts function. Then we let the rest of the part be controlled by the 3D model. If we meet the the critical dimensions on the drawing we have a good feeling that the rest of the part meets the profile of the 3D model. But this requires good 3D modeling practice putting in all fillets, draft and accurate 3D model geometry.

 

[ewh]

As usual, I have to agree with KENAT. The real world is not made of geometric primitives, and lofted surfaces can be very difficult to define using dimensions on a drawing. Granted, aircraft did use to be designed in that manner, but it took many many sections and cross sections to define the surfaces, making for more of a book than a drawing. That time and effort is avoided by inspecting to CAD models, especially when designing engine vane components with extreme geometry changes. As noted, MBD is no guarantee of a properly defined part, but neither were board drawings. Tolerancing must still be defined somewhere.
On our drawings, one of the standard notes states that the solid model is the master definition and takes precedence. We also reference any customer files that were the basis for the part in the general notes.
In the drawing title block there ia space allocated for the actual "as filed" file names (drawing and model) to be listed. These are associative to the files used, so there is no confusion when working on preliminary files or otherwise oddly named unreleased files.
Below the title block is a note specifying what CAD system was used in the drawing creation (I think that this may be covered by a standard somewhere).

"Good to know you got shoes to wear when you find the floor." - [small]Robert Hunter[/small]

 

[KENAT]

OK, looking at 14.41-2003 3.3.2e says that the drawing shall reference the model. I don't see suggested wording in the text (didn't look too deeply though) however, several examples use essentially the same text I gave above.

"THIS DRAWING SHALL BE USED WITH MODEL 123-4567 FOR COMPLETE PRODUCT DEFINITION"

I added the "MODEL GEOMETRY IS BASIC" because we mostly use this on complex parts that have some kind of overal profile tolerances. In this case the overal profile tolerances is given as 'UNLESS OTHERWISE STATED' so that any tolerances explicitly defined on the drawing take precedence.

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[SDETERS]

What happens when your 2D drawing and your 3D model dimensions do not match? For example you have a hole dimensioned with a basic dimension on the 2D print at 1.000 and on the 3D model the hole moved to 1.050 because it was associated with geometry that got changed. The hole was not suppose to move but it moved anyway. Who flips the bill for moving the hole back to the proper spot in the tooling. Assuming the supplier moved the hole and included it in the original change tooling costs. This has happened to us that is why we use the 2D over the 3D model. It could be argued the other way around also. It is just a headache when the model and the 2D drawing do not match.

 

[KENAT]

The drawing in most 3D solid modelling CAD systems I've used is directly driven by the model. So, unless someone fudged the drawing or there is a configuration control issue, then what you describe shouldn't happen.

While I'm not sure how well it's been implemented, for parts that aren't MBD but we supply the model to help with CNC programming, I've made it clear to operations that our PO's or T's & C's should state that the model is supplied for reference only and that the drawing should take precedence. This is mainly to address concerns I have over our configuration control.

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[ewh]

What happens when your 2D drawing and your 3D model dimensions do not match?

This is the reason our drawings contain the note proclaiming that the solid model is the master definition and takes precedence. It is really more of an insurance policy, as our procedures should prevent any disconnect between the model and the drawing, but mistakes have been known to happen.

"Good to know you got shoes to wear when you find the floor." - [small]Robert Hunter[/small]

 

[macduff]

Guys, I'll be back tomorrow with my comments. All your comments are awesome! Thanks, and see you tomorrow.

best,

Colin Fitzpatrick (aka Macduff)
Mechanical Designer
Solidworks 2009 SP 3.0
Dell 490 XP Pro SP 2
Xeon CPU 3.00 GHz 3.00 GB of RAM
nVida Quadro FX 3450 512 MB
3D Connexion-SpaceExplorer

 

[fcsuper]

We are currently applying within the title block a generic Profile FCF with ALL OVER to the basic model, with notes similar to what is stated above.

In my view, the drawing should supersede the model...this is because anything you bother to put on the drawing is only there because of some criticality. When the drawing says nothing, then the model is law per the general notes and the profile FCF. Also, sometimes (even these days...though not that common anymore) particular shapes cannot be created in the CAD software and need to be described on the drawing itself.

Matt Lorono
Lorono's SolidWorks Resources & SolidWorks Legion

http://groups.yahoo.com/group/solidworks & http://twitter.com/fcsuper

 

[ewh]

...particular shapes cannot be created in the CAD software and need to be described on the drawing itself.

Wow, never saw one of those. I've had some very difficult shapes to create in CAD, but time, effort, imagination and a powerful CAD system always saw me through. I can't understand how it would be easier to define them on a drawing though.

"Good to know you got shoes to wear when you find the floor." - [small]Robert Hunter[/small]

 

[macduff]

Matt and Sdeters,
I agree with your comments. The drawing shall take precedence over the cad model. But.....it must follow the way your quality procedures are set up. This is getting into the nuts and bolts to my question. If your Qual procedure is set up to buy and inspect to the drawing, then obviously you must follow that. Most of the aerospace companies follow this beacause of FAA regulations. If your Qual procedure is set up to buy and inspect to cad model, you must follow that. Most of the automotive companies do this, and also no drawings are created.

Great comments by everyone, and thanks!

Colin Fitzpatrick (aka Macduff)
Mechanical Designer
Solidworks 2009 SP 3.0
Dell 490 XP Pro SP 2
Xeon CPU 3.00 GHz 3.00 GB of RAM
nVida Quadro FX 3450 512 MB
3D Connexion-SpaceExplorer

 

[ewh]

We make the solid model the master mainly to expedite fabrication. This is where the design is created and modified. Tooling, machining and inspection all reference the solid model. Any tolerancing is referenced on the drawing (which is hopefully reviewed before chips are cut).
Of course, YMMV.

"Good to know you got shoes to wear when you find the floor." - [small]Robert Hunter[/small]