Lost Foam Aluminum Casting - Page 1
Forum section: electronics / projects

author: sourcecharge
author_rank: Regular Contributor
timestamp: July 16, 2018, 10:24:32 am
content: So, a while back, I was looking to "roll my own" 1.8KW PS and I did the noob mistake by trying to do it using basically a linear regulator.here is the original thread:https://www.eevblog.com/forum/projects/1800w-50v-power-supply/It basically was for a 1800W ZVS Induction Heater. I had changed the design of the regulator to a switching regulator, but never actually made it because I got lazy and I decided to just buy a 2.5KW PS that has all the little dodads that make it work right. That 1.8KW ZVS induction heater runs like a champ with 50V and 50A, not one problem, (knock on wood), ever.(edit: the 1.8kW ZVS Induction heater was slightly modified with 10 AWG solid copper wire soldered directly into the pcb because the connector was 30A max, the pcb's traces from the irfp260's sources and drains to the tank caps and output posts were all beefed up with 14 AWG copper wire and alot of extra solder, also, a 48V fan died, so I got 12V fans with greater cfm, and the gate resistance dividers were all dropped down in increase efficiency. The gate voltages and the fans are now driven by a separate 13.8V PS ensuring that the gates are always supplied with enough voltage. Lastly I've got a switch that turns on the gate voltage, but also switches to ground when turned off, ensuring the circuit turns off. whew, that was alot)Since then, it's been easy to melt about 18.8 inch^3 worth of aluminum in a 2 inch diameter crucible. When the buckets are full of water for cooling, it's just 5 switches to flip on and 10 mins later, I've got a crucible full of molten aluminum.I have a 6 inch diameter crucible but I still need to make the coil and modify it for transport and pouring. Kinda hesitant about doing it though because the danger level is exponentially increased when the volume is that much.anyways, the whole point was so that I could start making castings from 3d printed wax filament, but found that the toaster oven wont melt it out. A self cleaning oven probably would do the trick, but using the one I eat out of is dumb, and getting another one is too expensive and requires a lot of room.So I've wanted to do Lost Foam Casting with expandable polystyrene using PETG filament 3d printed negative molds.This process would be far more efficient for 3d printing and much faster setup times because it only requires the foam to be put into sand, without the plaster surrounding it. The plaster is only needed if you need a complex object.The problem is, I can't find it anywhere for consumer use anywhere.I found something called poly-fil micro beads, and tried them out, then found that they did not expand at all, (even though they say not to wash them)now after more research, I've found that the pentane is actual put inside the beads while being made. Therefore any bead wont work unless it already has this pentane in it.Anyone have any knowledge or experience in this?I was thinking about getting some pentane liquid and submersing the micro beads in it to see if they would take on the "blowing agent" pentane.Doubtful that it will work, but there just seems like there must be an easier way of casting foam for casting aluminum.Here is a sample video of what I'm talking about:

author: tooki
author_rank: Super Contributor
timestamp: July 16, 2018, 07:02:49 pm
content: I wanna say I’ve heard of people using spray insulation foam for the same purpose, it being something readily available for home use.

author: sourcecharge
author_rank: Regular Contributor
timestamp: July 16, 2018, 09:05:27 pm
content: The expanding insulation foam here is made out of polyurethane, and if you heat that stuff, it creates hydrogen cyanide.Is that what you were talking about?If it is, I don't think that it is probably something I want to test.

author: tooki
author_rank: Super Contributor
timestamp: July 16, 2018, 10:56:11 pm
content: Bah, what’s a little HNC among friends?! :pHonestly I don’t remember if it was urethane foam or something else.A bit of googling found an alternative foam, called icynene, which claims to have less toxic combustion products (primarily CO2and CO, they claim). No idea whether it exists in a home can form, though.

author: tooki
author_rank: Super Contributor
timestamp: July 16, 2018, 10:57:20 pm
content: What about some food based foam? There are many that dry hard, like meringue.

author: rhb
author_rank: Super Contributor
timestamp: July 17, 2018, 02:56:56 am
content: 3D print your object.Spray it with a release agent.Cast a mold using plaster of paris which has had a vacuum pulled on it to eliminate bubbles.Dry the mold in an oven at 250 F for 10-12 hours, more if it's large.Cast the aluminum, but be careful in case you didn't dry the plaster long enough.You can get die casting quality finishes this way for prototypes. It's also used to make kirksite dies for forming things like aircraft fuel tanks.If you don't need a fine surface finish, just 3D print patterns and ram up as normal practice in greensand.I've attached a few pages from:Casting Kaiser Aluminum2nd ed, 1965If you have complex parts with reentrants, make plastic master, make a silicone mold of the master, make a wax pattern using the silicone mold as in normal lost wax.

author: texaspyro
author_rank: Super Contributor
timestamp: July 17, 2018, 03:58:15 am
content: Hot aluminum and plaster of paris are not always friends. During WWII resistance fighters used to mix plaster and powdered aluminum and cast the mixture into blocks (bar of soap size was popular). When ignited they would burn through engine blocks, etc with the heat of a thermite reaction.

author: calexanian
author_rank: Super Contributor
timestamp: July 17, 2018, 05:09:33 am
content: I use electric heating elements and ceramic blanket inside a stainless tub to melt aluminum now. Its easier. ZVS induction heaters don't last very long I have found. something always goes wrong or shorts out right when you are at a critical time it seems. also you can use any crucible in an electric furnace. Additionally I found the graphite clay crucibles to be too variable and brittle.As far as the foam the better solution is to dip the foam in quick set drywall joint compound, let it dry, pack it with the sand, bake/burn out the foam (I use my furnace set to lower temp) then after that cools cast it. you run less risk of the aluminum blowing back out if a vent plugs with melting foam and gas pressure coming back at you. Also the parts require very very little secondary grinding or cleaning.just my experiences.

author: sourcecharge
author_rank: Regular Contributor
timestamp: July 17, 2018, 05:38:23 am
content: Tooki, icynene is made out of the caster plant, and I don't want anything to do with that....thank you though.meringue, would certainly be interesting but I don't think it would hold it's shape very well.rhb, I originally though of doing the lost pla, then the lost wax, using the wax filament. Both require the plaster but need high temperature to melt out the 3d print because the 3d print is embedded into the plaster. It's a waste of time doing it this way because each print for something usable usually takes 8 to 20 hours depending on the print.The drying time of the plaster is another 24 to 48 hours and the burn is another 5 hours, that's if you've got a furnace. Then, after you cast, you lose your "investment" and in order to make more of the same object, you have to go through the same process.The plaster mold idea, which by mold I'm guessing something that allows the object to be removed without damaging the plaster. This seems reasonable be lacks the ability to do some slightly unsymmetrical objects, let alone complex objects.I would really like to have the ability to do complex objects. Thanks for the suggestion though.texaspyro, one of the first things I did when I started to use metal crucibles was review the safety of using them.Powered aluminum and plaster will not make what you are thinking. It requires rust. That is why I used a wire wheel on the inside of the crucible before I started melting anything. Now the aluminum is coating it and I don't think too much rust will accumulate.Plaster that has not fully dried, is not a good because it could crack the mold, and if you try to cast before the plaster is somewhat dry, you risk the mold having trapped water, and when the water boils and can't escape it causes the plaster to violently break apart.calexanian, are you casting EPS or cutting it? I know what you mean about the plaster, sand, and burnout, and ya you're right about that. But if the part does not need to be good looking, I've seen some rather good youtube videos of aluminum castings from foam being directly into the sand without any plaster at all or burnout. The aluminum burns out the foam.This is why I am mainly interested in is being able to make foam positives from 3d printed negative molds.Anyways, anyone has any experience or knowledge about making expandable beads for Lost Foam Aluminum Casting?This obviously would be very useful for DIYers as parts could be made over and over again with the same 3D printed mold.I have found pentane online and I think there might be a supply shop in town, but I have to check the local laws and statutes first before I try it.I don't see why this would be regulated or banned, so I'm thinking I might be able to try this out soon.Here is an example of "the right way" lost foam aluminum casting:And here is an example of "simple" lost foam aluminum

author: Biff383
author_rank: Regular Contributor
timestamp: July 17, 2018, 06:38:12 am
content: If you need raw EPS beads let me know. I can get you some for the cost of postage.

author: sourcecharge
author_rank: Regular Contributor
timestamp: July 17, 2018, 07:10:23 am
content: That's a very kind offer, but I would rather never give my personal information out to anyone on the internet.Thank you though....Do you have a distributor that you could recommend that deals in small quantities?

author: Mr. Scram
author_rank: Super Contributor
timestamp: July 17, 2018, 07:31:01 am
content: Quote from: texaspyro on July 17, 2018, 03:58:15 amYou need to be careful with substances what hold water indeed. Aluminium is relatively cool when it comes to casting metals, but molten iron has enough energy to release the water out of concrete. Having steam suddenly violently appear from dry concrete can be a nasty surprise.Even with aluminium, steam exploisions are a real danger. A minimal amount of water can turn in a massive amount of gas in an instant. Make sure anything that goes in or near the furnace is absolutely dry. You wouldn't be the first to learn about the disadvantages of getting hot liquid metals thrown in your face.

author: Biff383
author_rank: Regular Contributor
timestamp: July 17, 2018, 07:58:42 am
content: Nope, we get them in 2000 lb. bags.

author: tooki
author_rank: Super Contributor
timestamp: July 17, 2018, 08:32:46 am
content: Quote from: sourcecharge on July 17, 2018, 05:38:23 amYou know that castor oil is used widely in industry? It’s not made of ricin! And moreover... it’s a product made for use in residential construction, with known combustion characteristics...Quote from: sourcecharge on July 17, 2018, 07:10:23 amI’m starting to think you may be... overcautious? Is “paranoid” too much?

author: sourcecharge
author_rank: Regular Contributor
timestamp: July 17, 2018, 08:53:13 am
content: Quote from: Biff383 on July 17, 2018, 07:58:42 amdamn!knew it....Question, do you guys add the blowing agent to the EPS or does it already have the blowing agent in it?

author: sourcecharge
author_rank: Regular Contributor
timestamp: July 17, 2018, 08:59:34 am
content: Quote from: tooki on July 17, 2018, 08:32:46 amya, i forgot about castor oil, so no WMDs right?I'll look more into it. if burning icynene foam is safe, experimentation would be required to see of aluminum could melt through it. Thanksand ps, "nope"...

author: Biff383
author_rank: Regular Contributor
timestamp: July 17, 2018, 09:20:04 am
content: They add it when they make the stuff. I've never been up to the plant, but I hear that it is an interesting process. We just expand and mold and cut.

author: sourcecharge
author_rank: Regular Contributor
timestamp: July 17, 2018, 09:38:51 am
content: Quote from: Biff383 on July 17, 2018, 09:20:04 amWell, thanks anyway, btw, how much is the EPS bag for 1 ton?Just curious..

author: Biff383
author_rank: Regular Contributor
timestamp: July 17, 2018, 09:45:43 am
content: Right now it's a little over a dollar a pound, but we are getting a price break for buying a lot at one time. I think we have about 100 tons on the floor right now, and more comes in every week.

author: sourcecharge
author_rank: Regular Contributor
timestamp: July 17, 2018, 09:51:06 am
content: your company should distribute it as a side business for little guys that want to do backyard projects...your company could mark it up 400% to 500% and people would buy it if they could get only 1 to 10 lb bags..just saying...

author: Biff383
author_rank: Regular Contributor
timestamp: July 17, 2018, 10:44:52 am
content: I'll bring it up with management, it could have something to do with liability. Pentane isn't the greatest thing to work with. EPA dosen't like it at all, we burn most of the fumes.

author: sourcecharge
author_rank: Regular Contributor
timestamp: July 17, 2018, 11:14:19 am
content: Quote from: Biff383 on July 17, 2018, 10:44:52 amJust tell them that every customer has to sign or accept non liability agreements and also give out the proper documentation regarding the EPA standards for home and business practices.If amazon can ship pentane, expandable polystyrene bead should be able to ship too...just look at one of the reviews, someone said it came broken!https://www.amazon.com/Pentane-n-Pentane-CP-98-32oz/dp/B012B9AW8C

author: Mr. Scram
author_rank: Super Contributor
timestamp: July 17, 2018, 12:04:37 pm
content: Don't forget that dealing with little guys means a lot of overhead for a given amount and generally a lot of pain dealing with people. I know a fair few companies that don't do it for that reason. It's just too much of a hassle for what you earn.

author: rhb
author_rank: Super Contributor
timestamp: July 17, 2018, 01:53:20 pm
content: The "make a master, make a flexible mold, make a wax investment" is how jewelers make multiples of the same design. Any of the jewelry supply houses can supply the materials.Casting large kirksite (a zinc-tin alloy) in plaster molds was used extensively during WW II to make dies for aircraft fuel tanks. The dies will last for about 10,000 pieces if well designed, which is a lot more than the number of aircraft of a design that were built in many cases.The example in one of my books was a 2000 lb die set.As I noted, you *do* have to dry the mold before pouring hot metal into it. For the 2000 lb die it probably took a couple of days to dry. Though if the plaster is just the facing of a stout wooden mold it would dry more quickly.I think most people use a ceramic kiln for wax burnout of investment castings. For small work a large junk electric stove burner in a suitable refractory housing should make short work of burnout of the 3D printer wax for a one off.

author: texaspyro
author_rank: Super Contributor
timestamp: July 17, 2018, 05:06:43 pm
content: Quote from: sourcecharge on July 17, 2018, 05:38:23 amA thermite reaction requires a metal and an oxide to react. It does not have to be aluminum and iron oxide. Magnesium / copper oxide produces more heat than AL/iron oxide and is particularly energetic. Not sure if AL/plaster is a true thermite reaction, but it works the same. The solid plaster / AL mold may not cause problems since the materials are not well mixed.

author: sourcecharge
author_rank: Regular Contributor
timestamp: July 18, 2018, 12:48:00 pm
content: Quote from: Mr. Scram on July 17, 2018, 12:04:37 pmthey might actually give him a raise and a promotion if this idea works!Quote from: rhb on July 17, 2018, 01:53:20 pmI don't see why I can't use EPS, it really shouldn't be this hard. Someone has to sell expandable polystyrene beads for consumer use. I can't believe I'm the only one that can see the potential consumer use of such a process. The time to make the required part would be 1 hour compared to 2 to 3 days. And that's only if you have one 3d printed negative mold.Quote from: texaspyro on July 17, 2018, 05:06:43 pmya, I was very cautious about the rust, didn't want molten aluminum going through the bottom of it. I've heard that a 1 to 2 day drying time is optimal if you are going to use plaster, but I'm hoping to not even have to use plaster, just sand and a positive EPS object from a 3d printing negative mold.

author: sourcecharge
author_rank: Regular Contributor
timestamp: July 20, 2018, 07:57:41 pm
content: Gone fishing!

author: jmelson
author_rank: Super Contributor
timestamp: July 20, 2018, 08:06:55 pm
content: Quote from: sourcecharge on July 18, 2018, 12:48:00 pmUnless you need extreme detail on the part, like a display plaque , you do not need the investment. I've seen lost foam casting done with simple sand molds, and it worked very well for mechanical parts. This was done with styrofoam insulation board machined on a CNC router. You put the foam master in the casting sand and pack more sand around it. Make a few holes for risers and vents, and pour the molten aluminum or other metal into the mold. the styrofoam immediately flames up and is gone in several seconds. The smoke from that DOES look pretty nasty, though.The casting sand is mixed with some form of motor oil and additives to make it sticky.Jon

author: sourcecharge
author_rank: Regular Contributor
timestamp: July 21, 2018, 09:40:00 am
content: Quote from: sourcecharge on July 20, 2018, 07:57:41 pmhttps://www.ebay.com/itm/Expandable-Polystyrene-EPS-Beads-High-Impact-Foam-For-Floating-Fishing-Lures/263681639645?hash=item3d64a684dd%3Ag%3AJz4AAOSwlSda9whP&_sacat=0&_nkw=expandable+eps&_from=R40&rt=nc&_trksid=m570.l1313

author: CopperCone
author_rank: Super Contributor
timestamp: July 21, 2018, 03:41:28 pm
content: My recommendation for anyone that wants to get into casting is to go to home depot and buy a bunch of roofing lead first, then experiment with casting lead.It is alot safer then aluminum in terms of heat hazard so you can get used to handling molten metal, making molds, using crucibles, pouring metal..when you get a hang of that then go for aluminum.I recommend doing open face molds for a while before going to covered molds. My choice is to set sand with sodium silicate and CO2.Casting is one of those things that seems really easy but if you miss a step or detail you can get injured pretty bad.. for instance if you are casting a closed mold that has moisture in it, you can get aluminum/steam shooting out at you, steam explosions, all sorts of bad shit. Take it slow and actually observe the properties of the stuff you are working with.. I really get a sense here that people are getting too complicated too quickly in this thread for a newbie. Someone just melting a kilogram of aluminum and pouring a complex mold for the first time in their life is asking for trouble.Watching all of MrPete222's videos about casting is a good primer I think:https://www.youtube.com/channel/UCKLIIdKEpjAnn8E76KP7sQg(just search his channel for casting).But seriously start with lead. I studied it alot before I started doing small castings but it was still different because you just feel different when you are pouring a buncha liquid metal, wearing all the safety equipment, feel the heat, etc.

author: rhb
author_rank: Super Contributor
timestamp: July 21, 2018, 08:30:18 pm
content: Be *very* careful about working practices shown on YouTube. There are people who pour aluminum in their kitchen and others who pour iron on their concrete shop floor. Amazingly some of them seem to have gotten away with such dangerous practices for a long time.Steve Chastain has some very good books on metal casting which I highly recommend:http://stephenchastain.com/store/Lindsay Books reprinted a lot of good books, but alas, he retired and closed the business.David Gingery also wrote some good books:http://gingerybooks.com/