NMO
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Hello all – a quick preface. My brain officially reach maximum password retention today and I couldn't for the life of me remember my old account password for "switch." Unfortunately it's tied to an email I no longer have access to so password reset was not an option, and thus "NMO" was born! Just wanted to re-introduce myself.

I am reaching processes and materials for a furniture project. It's essentially a storage bin/coffee table – overall dimensions seen in attachment if you're curious.

The difficult part is finding a process and material, preferably suited to low volume production, that allows for the sides to remain completely vertical (ie. no draft angle). The sides being vertical is critical to the modular nature of the part. Aluminum would be the ideal material in terms of performance and aesthetics, but at this point I'm open to ideas.

So far I have:

-deep drawing aluminum or steel
-v process sand casting aluminum
-slip casting ceramic
-rotomolding plastic

Are there any other obvious choices that I'm overlooking?

Thanks for any help.

N
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sprockets
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These are not great options (in fact they are pretty much useless), but . . .
  • Machining (go macbook pro on this thing!)
  • SLS
  • 3D printing
  • Molding or casting with machining after
  • Extrude sides, stamp bottom, and attach together


    Deep drawing would likely need a tiny draft, albeit something crazily small like 0.05°. Very likely your best option.
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hatts
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If the process could be controlled enough, you could do a two part operation of stamping a rounded bottom, cutting & folding the sides, and then welding the seams. Would be expensive.

However, cheap in plastic: vac-form the rounded base and then manually cut the sidewall flaps, bend flaps up and cement in place.
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chevisw
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I think one thing you need to do is tell us what is the desired cost for the part you want?

That will help you figure out the process, because 0 degree draft is gonna cost you more then having draft.

You may want to think bent metal with welded corners, but you will spend money on grinding.....
iab
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^^^

I was thinking something similar. Mold the bottom and back. Bend metal for the sides and front. Or mold the bottom, bend metal for the sides, front and back with a single seam. Offset and spot weld or weld and grind the whole seam.

Andbobsyeruncle.
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nxakt
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Not sure if it works with rectangles, but no reason I can see why not, impact extrusion.

http://www.core77.com/blog/object_cultu ... _25056.asp
NMO
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Thanks everyone. Definitely some options discussed that I hadn't considered.

I do like the stamped base and welded loop idea, and impact extrusion seems rather awesome.

I just realized that fiberglass could very well fit the bill too.

To answer your costing question: low startup cost is more important than low part cost at this point, as I will just be making a small run to begin. The tooling cost for a process like deep-drawing is therefor a bit of a barrier.

N
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Just bend some steel on a brake press and weld up the corners.
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Depending on volume, you could make it out of urethane in a silicone mold. If you split the side of the mold that makes the outside along the long axis (done by pouring it in two steps) you should be able to remove that mold half without need for draft. You'll see a parting line though. For the inside you could either have tapered walls (if the inside doesn't need to be zero draft), which may not work since 229mm at any draft might cause enough thickness variation (call your urethane supplier) or you could have a removable core inside that mold half. Once you remove that core the remaining silicone will likely be floppy enough to come out. It'll also save you on silicone, since that's a decent sized part.

You'll have to CNC or rapid prototype a pattern to make the mold. I know it's not aluminum, but there are a lot of grades of urethane out there and it's tough stuff.
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Scott Bennett
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nxakt wrote:Not sure if it works with rectangles, but no reason I can see why not, impact extrusion.
I was going to say the same thing, except I think the tooling cost would kill it for low volume. 914 is right, unless you're planning to make thousands of these (or at least hundreds), hand fabrication is probably your only option if you need it in aluminum.

Investment casting would work if you can come up with a way to make the wax master without draft. It's too big to 3D print realistically, so that would require some thought.

Also, unless you're planning to contain explosions, 10mm thick aluminum looks like massive overkill. This is about 60-70 pounds of aluminum, your material cost alone could be over $250.
NMO
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@scott – I actually am now thinking about investment casting using lost foam. The pattern would be reasonably easy to cut from foam (CNC router for the base, CNC hot wire the flat sections, then glue together). It's pretty large for investment casting but actually could work. And yes, cutting the material thickness down would make a lot of sense too, though I'm not sure how thin the foam could get and still remain usable for the pattern.
seurban
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I just came across this today - have you looked into vacuum sand casting (V-process)? It's biggest selling point seems to be zero draft, plus high accuracy, relatively fine surface finish, and long pattern life.

http://en.wikipedia.org/wiki/Sand_casti ... um_molding
http://www.aandbfoundry.com/processes/v ... s-casting/
http://www.mccannsales.com/book/vprocess.pdf
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Kinda off topic - but for passwords management. Since you happened to forget your old account. These programs work great.

Mac: https://agilebits.com/onepassword
Windows: https://lastpass.com/index.php?fromwebsite=1
emmanuel carrillo - emmanuelcarrillo.com
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I'm not sure what your material requirements are, but for plastics I'd go for vacuum forming. Pretty cheap and easy. Draft required but forgiving.

For sheet metals and quantities of 400 or more, I'd start looking at hydroforming as its tooling costs are cheaper than deep draw or stamping. Small draft required.
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Lmo
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I'm just curious... why do you think that "fiberglass" would not need draft in a one-piece mold?

Another idiosyncrasy, with any plastic, is that it hates to be formed flat. If you don't "tell" it which way to shrink it will choose it's own direction, and not necessarily the same one each time.
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