×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Drawings for casting

Drawings for casting

Drawings for casting

(OP)
I have made a model / drawing of something we are now machining out of solid stock.. Because there is so much waste we are thinking of having this cast.

I have never seen a drawing showing cast dimensions.. Can anyone point to some possible samples.. possibly something like a pillow block bearing.. most of it will remain with a cast finish yet some parts must clean relative to the cast areas / pockets etc..  How does one show this on a drawing?

Thanks for your time
Ralph

RE: Drawings for casting

Not sure how others do it or even if this follows any set standard, but in automotive we just model extra solids where machining is required and make them a different colour for clarity.

Does anyone still supply drawings for castings these days?
 

RE: Drawings for casting

I've done something similar before. If you're unfamiliar with casting, work with your (potential?) supplier. You'll need to determine your critical areas as far as datums, dims and surface finish are concerned. You'll also have to look at how it's going to be cast so you can determine draft. Generally, "Draft as needed" will suffice.  

Jeff Mirisola, CSWP, Certified DriveWorks AE
http://designsmarter.typepad.com/jeffs_blog

Follow me on Twitter

RE: Drawings for casting

Yes, definately get advice from the foundry, most have different ways of doing things.

RE: Drawings for casting

(OP)
Thanks all.. We are potentially going to have these made in China.. so if there was some "standard" I would like to use it.
Remodeling / sizing the whole thing, dimensioned only to the cast areas seems to be the best option.

RE: Drawings for casting

Ask for sample drawings from potential suppliers.  If that is not feasible, then I would create drawings of the finished part showing the machined surfaces and let them figure out how to get there.  

The only other trick is figuring out how to specify acceptable prosity.  For that I recommend you get your vendor picked out!

-b

RE: Drawings for casting

Ralph2,

   I strongly agree with ctopher's suggestion.  His 3D model follows your fabrication process, making documentation more logical.   If your machining is done by a different vendor than your casting, you absolutely need two separate drawings.  Make sure both of your vendors have the same set of datum features to work to.  Foundries recommend casting datum targets into the part.

    Another issue is that you might want to do a different machining process on your casting to make to new part.  Ctopher's method makes this easy.

               JHG

RE: Drawings for casting

This is the sort of thing where inserted parts work well.  Design your casting in its finished state.  Then, insert finished casting into new part using Insert --> Part, and add material to machined surfaces.  "Move face" and "Replace face" work well for this.

RE: Drawings for casting

I prefer the Insert > Part method for this. The inserted part being the "raw material" for the machined part.

I dislike the assembly method because it creates an assy where one does not actually exist, but I understand the usefulness of having the "raw material" called up in a BOM.

Whichever method best suits the product and company procedure is the one which should be used.

cheers

RE: Drawings for casting

Specifying details of the fabrication process with your drawing is only good if you know more about it than the vendor.  In doing so you make assumptions about the manufacturing process that may not be borne out.  The end effect is that you are tying the vendor's hands by specifying unnecessary detail and may get higher costs or no-quotes as a result.

Doing it in the model is fine (and how I'd do it), just don't show it on the drawing.

-b

RE: Drawings for casting

(OP)
Thanks guys... appreciate the different points of view and points to consider

RE: Drawings for casting

There is an organization in the US National American Die Casters Assosiation, NADCA and they have quite a bit of litterature about castings, from design considerations to documentation and material selection.

I would recommend using the same supplier for both the machining and casting.  If anything goes wrong there will be a lot of finger pointing and only have 1 supplier that is 1/3 less fingers to sort out.

RE: Drawings for casting

Here's may take on this:

A lot of cast supplies are not really into finishing/machining a cast part. Some suppliers will do targeting machining (another subject) for best possible cast to machine fit. I would find a machining supplier to purchase/procure the cast part, and then send you the finished part. Similar to what GRF stated.

I don't know what type castings you're designing or what materials you're using, but do have a couple recommendations:

Sand Cast (Aluminum) - Use .120 nominal cast to machine cleanup on faces and diameters. There's a lot of shifting of casting cores especially if it's a complex housing. If you have small internal core sticks, make sure your wall thickness are no thinner than .190. The cast supplier will love you for this. Wall thicknesses will also depend on internal pressures of your design.

Investment Cast (Aluminum) - Use .060 nominal cast to machine cleanup on faces and diameters. Investment Castings are a lot more accurate than Sand castings, and also cost more because of tooling.

The best idea is what the others commented on. Find a cast supplier and deal directly with them. DO NOT define parting lines; let the cast supplier do that for you. It will save you a lot in tooling cost. If you have a problem were there located, talk with the cast supplier. Also, keep in contact with the cast supplier at all times. Notify them of any changes immediately. It could save you thousands of dollars in tooling charges.

Hope this helps,


 

Colin Fitzpatrick (aka Macduff)
Mechanical Designer
Solidworks 2008 SP 4.0
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

RE: Drawings for casting

No one mentioned having different configurations of a part file "as cast" and "as machined" where cuts are made and suppressed for the two setups. Is there a reason to not do it this way?
"who does it that way"

--
Hardie "Crashj" Johnson
SW 2008 SP4
Nvidia Quadro FX 1000
AMD Athalon 1.8 GHz 2 Gig RAM

 

RE: Drawings for casting

SnowCrash,
Users and companies have different methods of modeling castings and machinings. My preference is to have the casting as the master, and insert it into another SW part to do my machining operations. My color preference is: exterior casting surfaces color gray, interior casting core surfaces color light blue and machining surfaces color red. I try and stay away using configurations in this case. This is just my opinion.
 

Colin Fitzpatrick (aka Macduff)
Mechanical Designer
Solidworks 2008 SP 4.0
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

RE: Drawings for casting

Ralph2,
I would recommend having a cast drawing separate from the machining drawing. I know some aerospace companies have it combine into one drawing, but makes it difficult to interpret base on its complexity.
 

Colin Fitzpatrick (aka Macduff)
Mechanical Designer
Solidworks 2008 SP 4.0
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

RE: Drawings for casting

I've only had experience with 2 cast parts.  Both were done using configurations as SnowCrash asked about.  The default config was the "as received" cast part, the machined version was the other config.  This worked fairly well back on SW00 and SW06.

RE: Drawings for casting

Ralph2,

   Now, we are getting really detailed about this, and outside the scope of this SolidWorks forum.

   Find a textbook on Design for Manufacture And Assembly (DFMA).  Read up on how you should minimize the number of parts.  A carefully designed casting can be very complicated, and perform a lot of functions, each of which, otherwise, would require a separate part, which must ordered, fabricated, stocked, kitted and attached to your final product.  

   The best strategy for machining is to not do machining.  Make the sloppy casting tolerances work in your assembly.  Make the surface finishes work in your assembly.  If you must machine your casting, make sure that all the machining can be done in one setup.  If it takes four or five setups to machine your casting, it be easier just to CNC machine the thing from billet.

               JHG

RE: Drawings for casting

Depending on geometry limitations, die casting is a lot more accurate than the sand or investment casting.  The upfront cost is greater but the piece price is cheeper, and the part to part variation is minimal.

RE: Drawings for casting

Part of the reason to choose making a casting is that you're machining so much that in casting to near net the actual wasted material is greatly reduced.

With material costs as they've been for the last 10 years it's very economical even with a few machining operations.

They type you need is going to depend on what you need, and what kind of quantities you need.  Do some research, send your part out (as is) for quotes from casting companies.  Don't be afraid to ask for any thoughts to make the part easier for them to make without losing functionality.

James Spisich
Design Engineer, CSWP

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources