casting datums

[swforge1]

Hi all,
Has anyone experience with casting datum specification? The part has one flat surface for a primary datum, all else has necessary draft angles. How do I spec B and C datums? On machining drawing, I can add datum surfaces but for casting what is standard practice? Thanks

 

[KENAT]

ASME Y14.8 is probably what you need to look at - assuming you work to ASME drawings standards (14.5, 14.100 etc.).

Simplistically, datum targets as explained in section 4.6 of ASME Y14.5M-1994 get used in these types of situations. Y14.8 gives some more 'applied' guidance.

Posting guidelines faq731-376

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

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

 

[fsincox]

swforge1,
Ten years ago, special cast datums were very common on high production complex cast items like engine blocks, I am not in automotive anymore, but do to the part's complexity and a desire for thinner wall sections, I will assume they still do.
Basically, your choice of approach will depend on the part complexity, the quantity produced and how important it is to you to be able to verify the original established relationship.
Frank

 

[drawoh]

swforge1,

I have only done a couple of castings. Let's if one of the experts chip in.

The problem with castings is that they are inaccurate, and their faces are not reliably orthogonal, even if you specified them that way. Read up on datum targets. Make sure everyone is fixturing your part the same way.

Casting manuals recommend designing in physical datum points.

Make sure your datum points or targets are not machined off.

JHG

 

[SDETERS]

How are you going to hold the part to machine it? There is many different ways of specifiying the cast datums. Just do not machine your as cast datums away. If you do you will not have anything thing to check your part to if something goes terrible wrong. We usually have three datum targets on the flat sealing surface as X. Then use a couple of the cored holes as the Y and Z. Just depenends what the part looks like and the function. Our Cored holes uses self tap screws in assembly.

 

[SDETERS]

Another tip is to spread the datums out over the entire part and get the biggest triangle you can. Do not put your datums close and or next to each other.

 

[swforge1]

Thanks to all

 

[DeanD3W]

I think using datum feature letters X, Y, & Z is pretty common in the casting or forging industries, but I think in 10 or 20 years it will become much less common (or will go away, I hope).

Since Y14.5-2009 now includes the use of X, Y, and Z axes to represent a datum reference frame, the use of datum feature letters X, Y, and Z on the same drawing will cause confusion. At least on a drawing with DRF axes labeled, which are very helpful for more than the just the reason described in Y14.5-2009, I think letters other than X, Y, or Z for the datum features would be a better choice.

Dean

http://www.d3w-engineering.com