Casting/sand cast design techniques

I've worked a lot in plastic part, injection mold and die cast design. Now
I'm trying to apply some of this to the sand cast process. I worked with
someone recently who has a particular way of doing it which instinctively
looks inefficient, but I'm unclear how best to improve it. His process is
as follows:
- build casting (engineered part) w/o draft
- build "template" (casting with core areas filled in)
- build "core template" (modeling empty space in casting)
- build "pattern" by cutting casting at the PL - add draft here
- build core patterns to make cores
- create halves of cast from drafted patterns
- assemble halves of cast and cores
- create a test part from halves of cast and cores
- compare test part to original cast part design
Intuitively, I want to start with a casting that has the draft on it, and
create the halves of the cast and the cores from there, then make the
patterns from that. Basically I'm trying to work like I do with injection
mold process.
How are other people manufacturing sand cast parts doing this?
thanks in advance...
matt
Reply to
matt
Loading thread data ...
Matt,
You're right, the process is almost identical. The difference is that the casting "should" have two configurations, as cast, and machined. The casting model should represent the real world just like any other process. All of the cores/cavities should be taken directly from the model. All feature changes, or additions/subtractions to the cores/cavities, should be made to the model, not the tool components.
It sounds like your friend is very knowlegable of old school pattern making, and He's trying to model this process. No big deal if that's what he's comfortable with, but it is convoluted. Problems may arise if someone else has to work on the data. Also, design changes will be much more prone to error.
Regards
Mark
Reply to
MM
"MM" wrote in news:wYTnb.384$ snipped-for-privacy@newssvr14.news.prodigy.com:
Exactly right. He's an old timer to be sure, and I think he got his start in the wood pattern-making business many moons ago, moved to board drafting, then Cadkey, then Pro/E, then SW. I assume he developed this way of working from his Pro days.
The only problem I see with trying to do it the same way as you would do a plastic part is that on the casting, if you have areas where you need to use draft to add material at the PL, SW can't do that. Well, it *can* do it using Step Draft, but only on one side of the PL, not on both.
I've put in an enhancement to see if we can get a draft feature that will add material to both sides of the PL, based on a neutral plane at a given distance from the PL.
The old timer's method gets around this limitation by essentially making the two sides of the PL separate pattern parts, so he can change draft however he likes without worrying about the other side. The disadvantage here is obviously that you have to keep track of what you've done where to make sure the PL matches on the patterns for the two sides.
Any ideas about that?
matt.
Reply to
matt
Matt,
Can't you use multi-bodies to some advantage for this ???
Regards
Mark
Reply to
MM
"MM" wrote in news:d9Vnb.17975$6O7.4080 @newssvr29.news.prodigy.com:
hmmm
yes, I suppose you could. Split the part at the PL, make the draft, and join it back together. a bit of a kloodge, but it would work.
If anyone else wants to chip in, I welcome more suggestions!
matt
Reply to
matt
Matt, contact a fellow named Bernie Mares. You can find a post or two of his in the Google archives of this newsgroup. He owns a casting shop in Portland (OR) and can tell you reams about the approach he takes and the reasons for it.
'Sporky'
matt wrote:
Reply to
Sporkman
Agreed on this as a first step, but I figure once and include the draft, shrink factor and rough stock from the start.
Setting the cores and coreprints would be part of the first step, this is actually building the inside features of the part as well.
The parting line is developed in the same first stage, everything is related from the parting line, the cope and drag halves of the "pattern/mold halves" as well as chucking on a finished part for workholding and machining etc. You must know where there may be a bit of flash or possibly grind. Shrink factor must also be added, if you forget to figure shrink the project will be doomed.
Still part of the first operation, the cores form the void that will become the inside features of the casting.
I create the casting with draft, shrink and all features. The parting is established first, draft works from the parting onto both halves. I build a seperate set of surfaces inside the casting that represent the machine stock that is to be removed, remember, you are making a casting that becomes the machined part. In sand castings, often you may need to build a few thou clearance into the parting depending on the squeeze pressure available on the equipment. I spent 18.5 years building patterns etc for a cast iron foundry. Food for thought anyway, Michael
Reply to
Michael
OK, I'll take a stab at it.
First of all, I suppose it's too much to ask to model the part with draft from the start. All this talk of `adding draft afterwards' gets me a little cranky. Pretty easy to do, I guess. (make me cranky, I mean.)
As for the other problem, how about creating surfaces all the way around and then thickening them to the main part? I have done this a couple of times. It's a little time-comsuming, but I've had some success with it. The advantage to this is you will end up with 2 definite configurations of the machined part and the `as-cast' part.
I'll think a bit more about it and check here in the morning to see what other ideas pop up.
jk
Reply to
John Kreutzberger
I have a related die casting question: From a tooling standpoint (from the toolmakers view on life, i.e. machining the EDM tooling) is it better to put radii in the sketch so that the radii decreases with "pocket" depth (I have been cut-extuding with a draft angle), or is it better to add the radii after the fact (and end up with "constant" radii)? The design I'm working on has about one inch deep pockets so I would like to start with a .062 corner radii (in the "sketch"), but the radii at the bottom of the pocket ends up very small (.005). Would I be better off adding radii "after the fact", or increasing the starting radii in the sketch, or.....? Jim W.
Reply to
JimW
This issue has come up a lot and is a very good question. Unfortunately, there is not a set answer. In general, I think it is better to but on the radii later for a constant radius for the reason you state. (gets small at the bottom.)
However, for large corner radii when a constant wall section is desired it can sometimes make sense to put the radius in the sketch before extruding and then shelling.
jk
Reply to
John Kreutzberger

PolyTech Forum website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.