Drawing Types (e.g. casting vs. machined vs. assembly.... 1

[philipdmartin]

I saw on another thread some discussion about having a casting drawing and a machined drawing if you're using different vendors. In my case I have one vendor doing it all, cast-machine-assemble, and I was wondering can I still have seperate drawings? It seems a lot cleaner if I break the two/three apart. The casting department of the vendor can focus on the casting drawing, the machining department the machining drawing and the assembly area the assembly drawing. Can the casting drawing have datums ABC or should it only have XYZ? I'm assuming the machining and assembly drawing should share the same datums unless functionality comes into play but I'm not sure. I know there's a lot packed in this thread but any thoughts would be extremely helpful. Thank you.

Phil

 

[PeterStock]

I cannot think of a reason why you could not provide two drawings. In fact this provides more flexibility as you can have more than one machining drawing from the casting drawing. The cast datums should be selected from surfaces that remain cast after machining. On the machining drawing locate your machined datums from the same datums used in the casting. All other machined features should be located from your initial machined datums. There may be functional reasons to do something else, but these are the best practices in my opinion.

Peter Stockhausen
Senior Design Analyst (Checker)
Infotech Aerospace Services

http://www.infotechpr.net

http://www.linkedin.com/profile/view?id=30064526&trk=tab_pro

 

[philipdmartin]

Thank you Peter. You stated "On the machining drawing locate your machined datums from the same datums used in the casting.". I'm not sure I follow completely. Do you mean use the same casting datums as machined datums if possible or are you implying something else? Or are you saying establish X-Y-Z on the casting drawing and when I establish A-B-C on the machined drawing relate them back to the X-Y-Z datums through features such as surface, a point, etc.?

Regards,

Phil Martin
Oxford, MI

 

[PeterStock]

Your last sentence is correct, the primary machined datums (your A-B-C) are located from the primary casting datums (your X-Y-Z). The casting datums should remain after machining so that the location of the machined datums can be inspected.

Peter Stockhausen
Senior Design Analyst (Checker)
Infotech Aerospace Services

http://www.infotechpr.net

http://www.linkedin.com/profile/view?id=30064526&trk=tab_pro

 

[SDETERS]

I agree with Peterstock. But if All you are looking for is the final product? Why should you define what the supplier can cast and what the supplier should machine? How do you control what gets machined and what gets as cast? How do you decide on how much stock removal for the machining features? just as long as the final part meets the final print. Sometimes a die caster can match tolerances and cost reduced the part on a as cast dimension versus machining it. Or worst yet machine somthing that you think should be as cast.

 

[KENAT]

If I was going to a single vendor for the 'finished item' I'd be tempted to just detail the finished item and leave it to them to add machining allowance etc.

However, there could be reasons to have separate cast and machining drawings - if nothing else in case of a vendor change in the future. In this case make extra sure and work closely with the vendor.

As Peter says, it may well be appropriate to develop machined datums from your cast datums.

I'd take a look at ASME Y14.8 Casting, Forgings, and Molded Parts which covers this type of thing in detail. It was a great help to me when I had to redesign a casting a couple years back.

Posting guidelines faq731-376

http://eng-tips.com/market.cfm?

(probably not aimed specifically at you)
What is Engineering anyway: faq1088-1484​

 

[looslib]

Product development is a multi-departmental process. Working with a casting vendor who is going to cast, machine and assembly YOUR final product requires communication. You work with them in defining which surfaces remain as-cast and which ones get machined. Drawings of each process level, cast, machine, assembly, allow you to see what each 'final' product looks like. It also allows manufacturing flexibility if your requirements change and you decide to change vendors or bring some of the operations in-house.
I agree with Peter, 3 drawings, with the machined-assembled datums the same and referenced from the cast surface datums.


"Wildfires are dangerous, hard to control, and economically catastrophic."

Ben Loosli

 

[ctopher]

Have a machining drawing, and a separate casting drawing.
The machining drawing can have the material using the casting P/N.

Chris
SolidWorks 10 SP4.0
ctopher's home
SolidWorks Legion

 

[drawoh]

Have a machining drawing, and a separate casting drawing.
The machining drawing can have the material using the casting P/N.

An additional advantage was sort of noted above. Your casting reprents several thousand dollars (euros, yen, roubles?) worth of tooling. It would be nice to leverage this investment, and use the same casting for other stuff. This results in yet another machining drawing that calls up the casting by part number.

Your other option is to have two drawings showing the casting and machining. You can swear up and down to your foundry that the two castings are identical. Not a good idea.

JHG

 

[ptruitt]

ASME 14.8-2009 "Castings, Forgings, and Molded Wachamacallits" is a great Standard, as someone reminded me in another posting.

Peter Truitt

 

[fcsuper]

What ctopher is referring to is a make-from drawing. Have the cast drawing for the initial part, then have a machine drawing that makes the final machined product from the cast part.

Matt Lorono, CSWP
Lorono's SolidWorks Resources & SolidWorks Legion
Follow me on Twitter

 

[ctopher]

Thanks Matt.
That is what I was referring to.

Chris
SolidWorks 10 SP4.0
ctopher's home
SolidWorks Legion

 

[philipdmartin]

Thank you everyone for your input on this topic.

I'd like to take it to the next level that I'm facing and that's I have a machined drawing, a casting drawing and 4 purchased component drawings. Now there's the need for the assembly drawing showing all of those pieces put together. I want to dimension the assembly drawing such that the supplier knows what to check for a capability study and ongoing SPC checks. I'll end up using new dimensions but also dimensions from the casting and/or the machined drawings so do I have to show them in parentheses as a reference dimension or with no parentheses? My understanding is a reference dimension does not get measured but I want it measured. On top of that, what's the best way to determine what dimensions should be measured on an assembly?

Regards,

Phil Martin
Oxford, MI

 

[PeterStock]

If you need them inspected on the assembly drawing, make them regular toleranced dimensions.

Note that in the CAD system of my choice, when you show a dimension from a part in the assembly instead of creating it in the assembly, if you modify it to display differently that it was in the part drawing, you have just changed the part drawing without intending to. I suggest creating most dimension in assembly drawings instead of showing them.

Peter Stockhausen
Senior Design Analyst (Checker)
Infotech Aerospace Services

http://www.infotechpr.net

http://www.linkedin.com/profile/view?id=30064526&trk=tab_pro

 

[looslib]

That 'feature' can be turned off in Pro/E. I have heard of many companies scrapping parts at the manufacturing level bacause they left that option on and the NC programmer made a slight change to a dimension to ease his job.


"Wildfires are dangerous, hard to control, and economically catastrophic."

Ben Loosli

 

[drawoh]

philipdmartin,

Let us assume you are on 3D CAD of some sort. You have a 3D model of your casting. You have attached a casting drawing to it. You have also attached your casting to an assembly, and at this assembly level, you are making cuts as per your machining requirements. Your machining drawing is attached to this. Perhaps you are attaching thread inserts as well.

The first thing you need is a common set of datums. The casting manuals I have read recommend casting in datum target features. If you have a consistent set of datum targets, the foundry and machine shops can fixture to the same points. Don't forget that casting is not as accurate as machining.

Your casting drawing must be a fully dimensioned and toleranced fabrication drawing.

Your machining drawing shows modifications to an existing part. It does not hurt to provide a few reference dimensions of the casting. Only your machined features require properly toleranced dimensions.

Critical specifications should be shown in one place only. At inspection time, a critical cast-in, unmachined feature should be inspected from the casting drawing. This is completely feasible if you specify datum targets as I noted above.

All of this is easily done with SolidWorks. I would be surprised if the other 3D CAD packages could not do it.

JHG

 

[ptruitt]

I hope your internal policies for design configuration, quality, and purchasing are in good shape. If not, I can see this becoming a blame-game, both internally and with the supplier. Are you ready to do supplier audits and corrective action? As I expressed in another posting, I would use the ST symbol, but not inspection instructions (or other processes, with some exceptions) on design documents. Work with the Quality groups (yours and your supplier's) to develop an appropriate quality plan with dedicated Quality documents.

Peter Truitt

 

[drawoh]

ptruitt,

Why would casting and machining be different from any other fabrication process?

The main problem I can see is that the OP can produce crappy fabrication drawings for the casting. If the tolerances all are ±.005", then the foundry cannot achieve them.

It appears that the OP has not done castings before. He will need to establish a relationship with a reliable foundry.

Specify castable tolerances. Make sure the design works with them. Give the fabrication job to someone competent.

JHG

 

[ptruitt]

If I was the QA manager, I might want the purchasing contract to mandate special inspection reports covering agreed upon inspection criteria initiated at the foundry and additional special inspection criteria generated at the machine shop. I might do additional audits of both reports although I would expect that the machine shop was doing their own audits of the foundry. Why discover bad parts at the assembly level?

(I don't mean to say I am sure that Phil will be running into trouble, but I get suspicious whenever I hear of folks measuring parts at the assembly level.)

Peter Truitt

 

[KENAT]

You're wanting to reinspect part dimensions at the assy level? Sounds a little odd.

Posting guidelines faq731-376

http://eng-tips.com/market.cfm?

(probably not aimed specifically at you)
What is Engineering anyway: faq1088-1484​