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jdougn
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Joined: 18 Mar 2009
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Location: Louisville KY area

PostPosted: Thu Jul 09, 2009 6:15 pm    Post subject: Durable Mold Material Questions Reply with quote

I need your advice on durable mold materials. When my MDF molds went through a straight set of 6 pulls per hour with 3/16" ABS they started delaminating between the layers. Something better must be used before the next set.

What is a cost effective mold material for relatively large molds without sharp corners and limited detail. (Think Jeep Cherokee Fender Flares). I'd like to get at least a few dozen pulls off the mold without worrying about failure and it will need to be drilled, cut and sanded to remove flaws. But, I can't spend over $300USD on molds right now. (Yeah, I know....lol.)


My experience testing a fiberglass shell didn't go well. The fbrgls was a minimum of 1/4" thick with 3 layers of mesh. When 28inHg vacuum and hot 3/16"ABS hit the fbrgls shell it gradually softened and then collapsed. Shocked

What has been your experience with UltraCal30 or HydroStone? I have not used either although I've read extensively on the US Gypsum website, this forum, and related sites. There seems to be a wide range of opinions on the suitablity of plaster based products in general for vac form molds. The local supplier has been out of UltraCal30 for weeks but does have HydroStone.

Something like Freeman Repro 83 or the Freeman aluminum filled 805 would be great but to cast all six molds would take 12 gallons of product if poured solid. With MDF fillers it may take as few as 3-4 gallons but that's still way more expensive than UltraCal30 or HydroStone.

What are your suggestions? Are there other products that have worked well for you?

Thanks, DougN
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speedofsound
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Joined: 21 May 2009
Posts: 56
Location: Memphis, TN

PostPosted: Thu Jul 09, 2009 6:40 pm    Post subject: Reply with quote

I believe this will also rapidly exceed your budget, but I frequently use (and swear by!) Alumilite.

I've done numerous molds cast in Alumilite Black (no fillers/additives), and they've had hundreds of pulls. They look like day one today. It's great stuff!

Try some as your budget allows, and you may find it's worth it to invest in more over time.
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clonesix
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Joined: 19 Jan 2007
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PostPosted: Thu Jul 09, 2009 11:11 pm    Post subject: Reply with quote

for a cost effective method, Ultracal is great. It is gypsum with 20% Portland Cement. It is very durable, and as an added measure, you can cast additional material into one of your pulls, and have extra molds on hand.

Less cost effective method would be fiberglass reinforced polyester, and even more expensive would be fiber reinforced epoxy. (my favorite)
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spektr
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PostPosted: Fri Jul 10, 2009 7:20 am    Post subject: How to build a tool.... Reply with quote

Ok lets make this easier....

Face cast the tools in alumalite or another decent hi temp product. Only cast 1/4 inch thick..... This greatly reduces the product needed. After it cures, get good old fashioned PEA GRAVEL. Fill the mold with dry pea grave and pack it in a bit. Pour a low viscosity resin onto/into the pea gravel. Thes greatly reduces the material cost and still gives you the properties of a solid mold. Gravel a cheap.... I use System 3 epoxy.

If you are worried about vacuum paths, cast in waxed monofiliment fishing line and remove it later.

If you are planning to run the tool HARD or pull parts fast, it needs to be water cooles. so make sure you cast tubing into it to carry coolant. Choose the tubing carefully because you dont get to fix leaks or corrosion later. It needs to be compatable with whatever fluids your molder uses.

This doesn't need to be hard, you just need to get a hold of somebody that understands Tooling for Vac Tools. My Senior Project was the creation of an early Composite Tooling Tech Manual. I'm thinking of updating it for publication. Whaddya think, would you guys buy one?

Scott.
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jdougn
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Location: Louisville KY area

PostPosted: Fri Jul 10, 2009 8:06 am    Post subject: Reply with quote

speedofsound wrote:
I believe this will also rapidly exceed your budget, but I frequently use (and swear by!) Alumilite.

I've done numerous molds cast in Alumilite Black (no fillers/additives), and they've had hundreds of pulls. They look like day one today. It's great stuff!

Try some as your budget allows, and you may find it's worth it to invest in more over time.


Thanks for the recommendation.
Looking at the Alumilite website they have dozens of different products but I think Alumilite Regular is the one you've suggested.

- It lists the pot life as 90 seconds. How would this work on a larger mold like I'm using?
- Also, the Tempurature Resistance is listed at 250 F. ABS must be hotter than that for a successful pull. How will that work or am I misunderstanding the technical information?

Again, thanks for sharing first hand information and Alumilite is certainly a consideration.
DougN
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jdougn
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Joined: 18 Mar 2009
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Location: Louisville KY area

PostPosted: Fri Jul 10, 2009 8:12 am    Post subject: Reply with quote

clonesix wrote:
for a cost effective method, Ultracal is great. It is gypsum with 20% Portland Cement. It is very durable, and as an added measure, you can cast additional material into one of your pulls, and have extra molds on hand.

Less cost effective method would be fiberglass reinforced polyester, and even more expensive would be fiber reinforced epoxy. (my favorite)

Thanks for these ideas. What types of molds have you done in Ultracal and how many pulls have they experienced?
Also, what was done incorrectly when my fiberglass test failed? I did a shell only but I can't imagine doing the entire mold in solid fiberglass. The mold roughly measures 3" wide x 5" tall x 54" long.
Thanks, DougN
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jdougn
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Location: Louisville KY area

PostPosted: Fri Jul 10, 2009 8:32 am    Post subject: Re: How to build a tool.... Reply with quote

Scott, easier is good! However, I sometimes have a time keeping up with your technical knowledge..lol.

spektr wrote:
Ok lets make this easier....

Face cast the tools in alumalite or another decent hi temp product. Only cast 1/4 inch thick..... This greatly reduces the product needed. After it cures, get good old fashioned PEA GRAVEL. Fill the mold with dry pea grave and pack it in a bit. Pour a low viscosity resin onto/into the pea gravel. Thes greatly reduces the material cost and still gives you the properties of a solid mold. Gravel is cheap....
Scott.

How would you "face cast" the mold shape I'm using? My internet search turned up stuff about body casting.
Also if using an epoxy, I'd planned on suspending a rough shape of MDF to fill the majority of the void then pouring epoxy around the MDF. An alumalite/MDF mold would allow for drilling additional vent holes if needed and future modification. Will an alumalite/MDF mold work? How do you anchor an alumalite/gravel mold to the base?
Thanks for the input, DougN
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jdougn
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Joined: 18 Mar 2009
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Location: Louisville KY area

PostPosted: Fri Jul 10, 2009 8:35 am    Post subject: Re: How to build a tool.... Reply with quote

spektr wrote:
Ok lets make this easier....
This doesn't need to be hard, you just need to get a hold of somebody that understands Tooling for Vac Tools. My Senior Project was the creation of an early Composite Tooling Tech Manual. I'm thinking of updating it for publication. Whaddya think, would you guys buy one?

Scott.

Because it's coming from a reliable source on knowledge I might be interested. What types of topics would the Manual cover?
dn
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spektr
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Joined: 07 Jan 2008
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PostPosted: Fri Jul 10, 2009 8:41 am    Post subject: Face Casting. Reply with quote

Think of a box with an open top. It has 5 sides. To face cast it the easy way, try this. Pour the bottom and let it cure. Lay the box on its side and use cardboard or masking tape kind of stuff to make a dam at the open end and pour each side seperately. 5 pours, not a lot of material used. After you are done you have a "hollow mold". fill it appropriately and you are done. Face casting lets you conserve material and get other stuff like cooling and internal vac plenums installed. An internal plenum can link many aluminum tubes to a model airplane fuel tank embedded in the tool with a larger tube coming out to simplify plumbing. Internal cooling tubing can also be installed before you pour the solid. Epoxy sand is also quite useful......

You anchor the tool to the mold base by casting elevator bolts into the mold, heads in, threads out. Grease em up so they dont get coated or you will meed to run dies over them after youre done..



Scott.
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jdougn
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PostPosted: Fri Jul 10, 2009 9:18 am    Post subject: Reply with quote

Scott, I now follow what you're getting at with the face casting. I'd use the inside of a good clean pull of the ABS as a type of master. With the multi-direction curves on the molds I think it would also work to use mold release suitable for the selected epoxy on an insert that controls the thickness of the epoxy between the ABS outer and the inner insert.

Using elevator bolts cast into the epoxy makes sense. That's the same thing we do when we're anchoring bolts into a concrete base for light poles in parking lots. duh... Laughing

The idea of casting cooling tubes into the mold isn't something I'd probably do soon but is really interesting. Would it work to fasten the cooling tubes to an MDF core filler then pour epoxy? I'll have to see what material Bob Owings Patterns recommends. This could be really interesting!

Thanks again for exceptional advice!
DougN
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spektr
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PostPosted: Fri Jul 10, 2009 9:55 am    Post subject: trust me... Reply with quote

Doug..
If you have to make a wooden insert plug, use Jelutong or Bass wood.
MDF has NO PLACE in any production tooling. It debonds at a low temp, it is horribly hygroscopic and will grow mold when damp. It is unstable over time. Remember that it is fine sawdust and glue. It's OK if you arent asking it ot do a lot, and it has its place for low volume slow production and prototyping, but the cost benefit ratio is all wrong. The few bucks you save in cost in my mind arent worth the potential of production issues with the tool while it is on the machine. There are 4 casts to think of that you might be missing. The cost of lost machine time by running the part slower than a "normal tool" would allow. The cost of actually fixing the tool breakdown. The cost of part variability as the tool degrades over time, stuff like customer satisfaction with surface finish, secondary operation costs like extra hand work. Fourth, and probably most important to you...... The loss of TIME you could be working on your next effort. Delaying the next project impacts future revenue negatively.....

Scott.
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jegner
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Joined: 30 May 2003
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Location: Texas, USA

PostPosted: Fri Jul 10, 2009 10:54 am    Post subject: Reply with quote

Production molds are another creature all together, and one option that Doug takes about is a foundry or machine resin. There is an old thread somewhere here, but I'm on my lunch break and don't have time to search for it, but it talks about this very topic.

Another option might be the use of a expanding, self skinning urethane foam. Like Foam-It-8 from Smooth-on.
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vacunoob
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Joined: 03 Apr 2009
Posts: 49
Location: Hickory, NC

PostPosted: Mon Jul 13, 2009 4:20 am    Post subject: Reply with quote

@ spektr- Just curious where are you located?

For my mold making I've been using Smooth-on's Task 3. I wonder if that's similar to what Spektr is using?

http://www.smooth-on.com/Urethane-Plastic-a/c5_1120_1157/index.html

The process is mix, degas, pour, pressurize, heat.

I've never face-cast. Though, I've inserted displacement blocks (a.k.a. blocks of wood) to decrease the amount of resin needed to fill the dammed area.
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spektr
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PostPosted: Mon Jul 13, 2009 6:55 am    Post subject: Reply with quote

I used to be in Texas, but moved back to the Pac NW to go back to Boeing for a while. Currently in Mount Vernon.
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jegner
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PostPosted: Mon Jul 13, 2009 8:49 pm    Post subject: Reply with quote

finally had time to do that search:

BCC 8002 gray resin from http://www.bccproducts.com/ is what Doug Walsh suggests for a production mold material.
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