Common practice in casting design

I'm looking to gather information on what some of the casting
designers in the group do when they approach a casting design problem.
I've done a few aluminum castings this year, but I am beginning to
fell like I may not be going about it in the most efficient manner.
What I have been doing is to design the part in its machined state
(all of my castings have had significant machining done as finishing
operations). Designing in it machined state allows me to readil
control the position of the machined interfaces realtive to other
parts in the assembly. When I have finished the design of the
assembly and parts, I create a configuration or separate part that
will become the as-cast part. I add machine stock to this to this
part and fix draft problems that I may have left out in the finished
model.
I have found that I do not like the configuration route because I run
into problems with feature suppression and finding parent child
relationships that I didn't expect. Perhaps this is really just
exposing flaws in my modeling techniques...I'm not sure. I do not
consider myself a casting expert, and am definitely learning as I go.
Since there is no one at my company to show me a better way, I am
turning to the collective intelligence of this group. I then plan to
document what I find into a best practices instruction sheet for my
fellow designers to use in the future.
Any input or experiences that can be shared would be appreciated.
MHill
Reply to
MHill
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I don't design castings, but I DO design die casting dies. I think you are doing it backwards. My opinion is that you should first model the `as-cast' part ; complete with all draft. THEN make your configuration for the machined part. I am almost positive that you will have fewer problems this way. After all, machining is "taking away material". Always easier to do than adding it. Even with a 3-d model.
Just my 2 cents. YMMV.
jk
Reply to
John Kreutzberger
MHill wrote in news: snipped-for-privacy@4ax.com:
The way I like to work is to make the part as cast first, and then add features to remove material to make the as machined. Using this method, I never have problems with the configurations. You need to have a scaled up config anyway to account for the shrink. Making cast or molded parts is always a game of rock, paper, scissors anyway, between the fillets, draft and shell. Complicating it by doing the machined features first is too much for me to mess with.
That way makes more sense to me since it follows the manufacturing method.
I can see where you would have problems going the other way, because creating drafted faces from the machined detail could be a real bear.
matt
Reply to
matt
Two responses so far and both are saying the same thing. I have a feeling this trend may continue.
I absolutely agree that removing material for the machined features makes the most sense from a manufacturing standpoint. I haven't done it that way because it was easier to design in context if I was designing to the machined state. I will have to experiment with this and see how it works out for me.
Am I hearing that using a configuration is better than a separate part?
MHill
Reply to
MHill
Check this thread out about exactly the issue you describe:
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IMO, from a design perspective it is best to design the finished part. Then use methods (insert part, for instance) to build the cast part from that. Document your design intent, not the (current) manufacturing process).
This is the same methodology as everyone seems to recommend for sheet metal: Model what you want and let the manufacturers figure out how to build it (just keep communication open to ensure you don't design an impossible part).
I understand how this can be difficult to manage and I understand why others do it 'the other way.'
Reply to
Arlin
Arlin wrote in news: snipped-for-privacy@News.CIS.DFN.DE:
Arlin:
I think I actually do it that way, but I build it in such a way that the two can be separated. I'm thinking about how the mold will be made while I'm designing the part, and I try not to model anything that I won't be able to mold. If I've done a good job, when I'm done designing the finished part, all I have to do is suppress and maybe reorder a couple of features to get the cast part.
matt
Reply to
matt
MHill wrote in news: snipped-for-privacy@4ax.com:
I'm just saying that I'm accustomed to doing it that way. It is also viable to use the as cast as a base part in another as machined part, but if you do that, you still have to have scaled and unscaled configs of the as cast (if you are building the molds as well). If you don't have to worry about compensating for shrink, then that simplifies things.
matt.
Reply to
matt
Matt,
Unfinished first and machined later works for one component models. However, if the process involves designing a complicated machine, the components are usually modeled in their finished states. I don't know how one would go about designing a complete machine as unfinished components (castings, weldments, etc ...) and then circle back around and create a finished machine assembly. That would be complicated.
Fundamental difference between product/mold and machine design.
Kman
Reply to
Kman
Having done a few complex castings I'll throw in my 2 cents.
If the casting must become part of a complex multi part assembly then:
1. Create an assembly that defines the connectivity/bounding surfaces for the components. The assembly will contain datum planes, axes, envelope parts, etc. to define design intent. Envelope parts can be used to define the mechanical connectivity before the casting is completed.
2. Hang the casting(s) on the assembly, i.e., top down approach with minimal incontext features. Use the assembly to get the important interface information and then work in the part for speed.
3. Keep the casting simple if it is complex till enough of the whole assembly is firmed up, then refine the casting, but make sure to consider draft and parting line issues early.
4. Add machining operations last. There are several very good reasons for this.
a. If the casting is complex (and most will be because of draft and fillet issues consider doing the machining operation on a derived part for speed.
b. Adding material to a model that is machined first can cause all ki nds of issues with sliver edges, etc. It will probably be easier to cut aw ay the casting.
c. Having the casting part first will speed up your cycle time as y ou can let your castings drawings out while finishing the machined portion. There is some risk to this, but some people have schedules that demand the risk.
4. Draft and possibly fillets will likely be your biggest time consumer especially in conjunction with lofts and sweeps. Know how to use the Atomic Bomb of Fillets.
MHill wrote:
Reply to
kellnerp
(snipped good advice added to my tips folder)
Which is ???
Reply to
Art Woodbury
MHill,
I have just finish creating a guideline for this. I will give you the quick and dirty.
My approach is for long-term revision and understandability of the design.
- FIY - My method for deciding when to use a config and when to create a new part/assy. Use Configs for family of parts when only dimensions of existing features are modified. When new features require to be managed with configurations then try and opt to use base parts or new parts/assemblies. ---------
1 - Create your as CAST design. This will be used as a BASE PART for your machined casting. This becomes a base part you can use to create any new-machined part. Sometimes one casting is machined to create many different new parts...extremely dangerous to control with configurations and risky.
2 - Create a new part, go to INSERT, BASE PART and select your casting. All the features in this part are only for the creation of the new part. (I created the requirement that all machining features are to be colored RED.) It is clear to any user what has been done and what needs to be machined. Revisions are clear and cannot affect other machined part versions or the casting.
This method is currently being used with much success. Remember to consider the reason why to use a configuration and what benefits you will have.
Always try and use a MASTER set of layout sketches to capture the design intent when creating the casting. This resolves the need to create a machined version first and then adding material for the casting.
I currently have a co-worker re-working an complex casting from the configuration setup to the separate part setup. He has learned the hard way the benefits of having a manageable design.
Jorge Medeiros Mech Design Eng
Reply to
Jorge Medeiros
You'll have to see Ed Eaton about that one. It is his baby and it works wonders. I think it is part of his Curvy Stuff series which you can find from the newsgroup and download.
Oh, alright I will try to explain it.
Most fillet failures are caused by a number of edges coming together in what it euphemistically called a complex geometry failure. The idea is to extrude a wall of material into the part centered on this failure point then fillet up to the wall. After the fillets are in the intersection edge of the extrusion and the part is picked and the fill surface command is used to make a surface. That surface is then used to trim away the extrusion and hopefully leave a smooth blended surface between the part and the adjacent fillets.
I have sometimes had to use this four or five times to get a single fillet to work.
Art Woodbury wrote:
Reply to
kellnerp
Atomic bomb fillets-
I think Paul is referring to a section in the filleting tutorial that can be found through the 'tutorials' link at
formatting link

Atomic bomb filleting is a really terrific technique for working through tough filleting situations (it just saved my rear this morning, ironically enough) that came to my attention in Jason Pancoasts 'art of filleting' presentation at SW World. The histrionic name is just how I refer to them - I don't think that Jason had any name for the process.
Reply to
Edward T Eaton
Paul & Ed,
Thanks very much for the explanation. I downloaded "Curvy Stuff" some time ago and must have missed or forgotten the technique.
In addition to having you two among the "A" list of experts on this NG, I'm very fortunate to have Jason (and Keith Pedersen and Joe St.Cyr) answer my VAR's support line. I just doesn't get any better.
Thanks again,
Art W.
Reply to
Art Woodbury

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