5 Things to Know Before Buying Lost foam casting equipment

I thought I’d throw this one out there in response to a question that was posed about the merits of lost foam casting. I’d be interested in other member’s views on the subject. For the reasons that follow, I think it’s probably the easiest and most economical point of entry to the casting hobby for most backyard gamers.

Pro’s

• No large heavy tooling to make or store……For me the router templates which are usually just profiles are small, light, and store in very little space. In many cases you can build a library of templates applicable to multiple projects.
• Mold packing is very quick and easy compared to conventional sand casting ….no ramming or heavy lifting and a flask is any container rigid enough to hold the sand. This usually means you don’t have to handle heavy molds because you can scoop it in in manageable amounts. A vibrator is beneficial but wrapping/tapping works to a degree. Now a days, I just dump the spent mold sand on my drive way to let it cool, off-gas, and then shovel it back into my buckets through my sifter. So other than this there is no binder management or sand conditioning to be concerned about…..i.e. no muller is required and other than sifting, no sand conditioning is required.
• If you use a pattern coating such as drywall compound you can use about anything for sand as long as it’s dry and of sufficient refractory.
• Foam castings do not require draft which can be helpful for designing in tooling features from which to locate and grip for post machining of castings.
• Parts that would otherwise have complex coring or parting lines in conventional sand casting are easily handled by gluing pattern features together.
• Pattern Detail: With liquid coatings, casting detail appears to rival lost wax and shell. Foam works very easily but I’ve had to introduce wax (although the foam pattern itself cannot rival the detail of wax) for the finer details such as fillets, embossments, and Lettering/Part marking.

Cons

• Odor: I store my LF sand in 5-gal buckets and with plastic snap lids so there is no storage odor. The odor while casting outdoors is very short lived. I would not under any circumstances recommend casting LF indoors….even small parts.
• Brush coating drywall compound can be slow but it’s very inexpensive and readily air-dries. I need to work on a dippable process, but then you have that to store. Frankly, I can’t see why it just can’t be an 5-gal bucket full of thinned mud that you agitate with a drill-powered paddle before use.
• Machining patterns can be messy. The foam dust travels. I spent this Saturday making improvements to my arm router which included a dust collection system. I also made hot-wire cutter for roughing out machine patterns to reduce the amount of foam that gets machined away. Together the two should make a big difference in speed of fabricating patterns, reducing dust, and clean up. My woodworking machinery earned its space in my shop many years ago so it’s there for the using without additional space.
• Pattern strength: Depends upon the shape. Foam is strong in compression but in general is fragile. Thin shapes can distort during molding and it’s easy to dent or damage a pattern during handling.
• Pattern Detail: This is a relative thing and why I list it as both a Pro and a Con. I don’t think the level of detail that can be reproduced in wax or harder materials is possible…..at least with my techniques. That’s why I introduced wax for fillets and embossments so I have sort of a hybrid process.
• Failure means you not only get to re-make the mold but the pattern too

Areas for (my) further development:

• Dip coating: Might be as simple as lower viscosity mud in a 5-gal bucket….but may also require elevated temp or longer drying cycles.
• Vacuum Assisted Lost Foam. In 90%+ of the cases I think gravity fed pours are adequate. However, I think vacuum assisted LF has real promise to further control and accelerate metal propagation speed which might increase the envelope for LF castings as far as thinner wall thickness, (larger) parts, and (lower) pouring temps.
• Metal Quality: I honestly don’t know if this is a pro or con yet. My preliminary results suggest it’s on par with conventional sand casting.

What sayeth all of you?

Best,
Kelly

The couple of my LF castings I've sectioned and examined under magnification looked as good as any sand casting with which I did the same (years ago) thus my comment above about being "on par". All castings are porous....it's just a matter of degree. Even with close furnace atmosphere control H2 will be present. Degassing certainly helps. Some of my water neck castings "sweat" hot coolant under pressure.......but I don't de-gas and I should, but I still think the issue would persist at least statistically. FWIW, I think conventional sand castings would do the same thing for the same reason and because of the thin walls. Vacuum impregnating castings is pretty much the norm for such in industry.

On machining, I think the selection of alloy and heat treating (if heat treatable and not intended for as cast machining) is more important in this regard than sand or LF process. As soon as the metal in the cup freezes, I de-mold and quench in water to knock the coating off the casting but there's a natural degree of solution heat treatment realized in doing so because it's still very hot. I can easily do the precipitation/age bit because my furnace is electric, but having sat around for a few weeks there's also a natural degree of that as well.

T5 is in reach at home but T6 is more difficult. I think you really must have the need for that extra little bit of strength to warrant T6. T5 machines and polishes well but you're never going to get to the level of the best wrought aluminum alloys. My castings thus far have machined satisfactorily and hold threads as well as any aluminum castings I've used. Neither LF nor conventional sand casting is the best process for critically stressed parts and that's why the design guides recommend higher safety factors be applied for parts manufactured with these processes due to alloys, porosity, and flaw population.

I'm accumulating a quite few parts to be machined and I'll post up results in the near future.

Best,
Kelly

I must say I am pretty surprised at the success you are having with the foam.
Your methods sort of take it from the very crude backyard "YT" sort of thing to a very viable process.

Your statement above is also true, and points out he benefit of a pattern with green sand; ie: you can tweek a wood pattern and make a new mold pretty quickly.

I think part of it is in what you are set up to do.
I am set up for green sand type molds, and I would have to rethink the whole process in order to go to foam.
If someone was set up for foam, then it would make a lot more sense to use that process.

One solution to the heavy sand/mold/flask situation is to use bound sand with a custom-fit flask, and make the mold very thin; no more than 1" thick in any one spot.
I generally start with a square wood flask, and add spacers inside to reduce the amount of sand used. The spacers can be taped in place if just a few molds need to be made, which greatly speeds the custom flask process.

And I plane 3/4" thick wood to standard heights, such as 1", 1.5", 2", etc., so that I can easily add filler pieces into a flask.
My flasks (generally the cope) are often only 3/4" thick, and relatively lightweight, and the bound sand allows for this.

But seeing your foam work really demonstrates the potential of LF-type castings, and proves that there is a whole lot that can be done in that arena, and far more can be done than I think most people realize.

Agreed, horses for courses. That's part of what I was trying to get at with the post, applicability of the process. I would not use it for jewelry either and that's probably a close cousin to your emblems. The other bit is just that there doesn't seem to be many people doing LF, at least here and AA. A little more on YT but most of that doesn't seem to be a very serious attempt at making quality parts.

If I knew I was making 50-100 of my thermostat housings that would probably be core and sand too, but ya know, having made the router templates (which also didn't take long), it doesn't take me long at all to make those small foamies with the jigs and if it was only that many per year and I was only going to cast 10-20 at time, it might not be so clear cut. For now it is because I'm not set up for traditional sand casting.

The tubular water necks I've made are somewhat a different matter because that would be a much more complicated pattern and core box for even 50+ pcs. That is one thing about lost foam....it sort of offers the design freedoms of lost wax investment or shell and maybe even a little more so because my method of making a foam pattern seems less laborious then making a master then a rubber or plaster mold, then wax patterns, then shelling, and casting them. LF would be a lot less laborious without detailing and coating the foam patterns but also yield a lower quality result. The coating labor could be greatly reduced by dip versus brush and I intend to work on that. I try to machine in all fillets where possible but at complex intersections of assembled pieces I'm stuck with wiping in wax fillets and embossment applique. So I see LF can sort of be a tweener between LW shell and sand casting as far as economy and ease of use.

I think the potential metal quality and finish is greater with LW and shell. I think LF is less total labor than LW and way less without detailing and coating the pattern.
Coated LF seems to be on par with Petrobond as far as finish potential but LF seems limited by pattern finish whereas Petrobond more so by the mold.
In volume, traditional sand casting and hard tools is the clear economic winner, but unless the part is small, few have the home resources to process that much sand, molds, and metal.

I spent a day making the templates & a set of foam patterns for the carb plenum. Now I can reproduce multiples of those foam patterns in an hour......the pattern detailing is more involved. When I shared that piece with my old foundry friends, their first impression from ten feet was they were looking at investment casting. Then when they look closer and see it isn't quite as refined, they ask how the expendable pattern was made. And then when I tell them it's LF and I have 8-12 hours of total invested time, and the next ones will come much easier......they like it.

Best,
Kelly

I have been playing around with lost foam for a few years, though less so in the more recent past. Kelly, you have covered pretty much all the pros and cons I can think of. I'll chip in my 2¢ here, but you covered it pretty well from where I sit.

Pros...

Easiest way to get into casting. All you need other than a way to melt and pour metal is a bucket of sand and some styrofoam. You can use free EPS packaging material for sprues and pieces where the beaded texture won't matter or if you're a really gentle touch with the sandpaper, or maybe buy a sheet of 2" XPS blue/pink foam insulation board that could last for a few years of weekend fun. It's easy to machine without needing much special equipment - you can manually mill out patterns for plaques and such with just a small drill press with a cutter bit in it, or even with a Dremel tool with a cheap plastic router attachment screwed onto it, or even just carve it by hand with sharp blades and files and sandpaper, if you are careful. Glue guns can be had at the dollar store and work great for assembling patterns. A paper towel or TP tube can be used as a sprue to get the metal right into the part similar to your metallic tape cones (but less conical). Hot wire cutters are easy to build on the cheap if you don't have a bandsaw to cut out patterns with. It can be so simple, or you can put more into it if you want to, just like with any other casting method - better sand, better foam carving tools, experimenting with coatings, sand vibration tools like your bucket or I've even seen where some people have tried getting some interesting sand fluidizing air hose setups to work, etc. So there's lots of room to have fun growing into it.

Cons...

Remaking foam patterns because you're too stubborn to figure out how to copy one of several cheap and easy to build pyrometer threads and poured too cold again really SUCKS! But that is not really lost foam's fault, is it? I would have had more to say here about how reliable results and thin walled parts are impossible for the home gamer if this were several months ago, but meanwhile you've gone and proved that simply isn't so. You're definitely not wrong about how messy and smelly it can be either!

Possible areas needing more research...

About the crusty sand lumps that come out of the lost foam bucket. Were you saying or implying in one of your lost foam posts somewhere that you don't get those when you pour hot enough, or am I misremembering? That is very interesting, something to watch out for. I remember on AA, metalbynevin (a guy with a good number of successful lost foam pours under his belt) had a theory that polystyrene vapour residue builds up in the sand, and that once it reaches a certain concentration, it can cause or aggravate sand float defects which sometimes occur if you pour the soup can Kush tool too full when the pattern isn't buried under a heavy enough load of sand to counteract the hydraulic pressure. If true, I can see how it would be easy to misdiagnose as such. I don't know if there is any validity to that, it was only briefly discussed, but if so, maybe it is possible the sand may need to be replaced (or burned clean?) every so often. If that is a real thing, perhaps it is only of concern if you've been pouring cool enough to see a lot of those tell-tale sand lumps?

Jeff

My 1/2 tubes are machined on both sides. I machined a female plug they just press into with friction fit, but I use small amounts of packing tape so they don't get sucked out of the fixture. My carb plenum is also machined on both sides and its just a friction fit on an internal MDF plug. I think the next time I may just try PoP and vacuum. If you machine the one side of the foam pattern and cast it at the parting line in PoP, then either fire or just use acetone or lacquer thinner to remove the foam pattern and you should have a real nice fitting machining fixture. You can use a lost foam plug immersed in the plaster that is cooked out to create a vacuum plenum in the plaster or simply set the plaster fixture on a wooden plenum and drill small wholes through the PoP for the vacuum. In some of my fixtures the foam fits so snug that I have to drill a couple finger holes in the back side so I can remove the foam patterns without destroying them.

I used the above method to make machine fixtures for tough to grip castings but I powder coated the casting and then used urethane resin instead of PoP. The powder coat increased the surface dimensions enough to easily accommodate casting variation yet accurately position it. I used toggle clamps instead of vacuum for clamping. -Worked slick.

Best,
Kelly

Lost foam casting is often used to cast small to medium complex products from some metal alloy materials. The final products maintain high precision and good surface finish.

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Continue series blog of casting technology of Vietnam Cast Iron, this article will bring a brief and concise summary about the lost foam technology which often used to cast high detailed products.

The author will provide a detailed explanation including definition, advantage & disadvantage, and application of the lost foam process so that everyone could be easy to have a clear idea about this metal casting technology either you are an expert or freshman to this mechanical industry.

What is Lost Foam Casting?

Lost foam casting is a type of evaporative pattern casting. This method is quite similar to investment casting which uses wax instead of foam in the pattern making process.

The foam pattern was first used in metalworking in . Although this mold casting technique is not as popular as other methods such as sand mold casting or permanent casting, it maintains outstanding advantages, especially in casting complicated and precise molds.

Unlike traditional methods which include the pattern withdrawn process before casting and require skillfulness in the pattern removal step, with respect to the lost foam method, the pattern is evaporated when the molten metal is poured into helping to reduce these considerations.

The lost foam casting process

The lost foam casting technology included 5 steps: designing the pattern; applying insulation painting; placing the pattern into the sand flask; pouring the molten metal; and collecting the castings.

How a lost foam pattern is made?

Firstly, a pattern is designed from polystyrene foam. This type of foam plays an important role in this casting method. It is a good thermal insulator and chemical resistance, enable working normally at the temperature below 75 oC.

Depending on difficulty and details of the product, the foam pattern can be made from different manners.

For highly detailed casting patterns, the foam pattern is partly made and glued together. For the small volume, foundries often make patterns by hand-cut or machined from a solid foam block. If the pattern is simple enough, a hot wire foam cutter can be applied.

In case the volume is large, the pattern can be mass-produced by a process similar to injection molding.

Polystyrene beads are injected in a pre-heated aluminum mold at low pressure. After that steam is applied leading to polystyrene expands more to fill the empty cavity and then form the pattern or a section. The final pattern is approximately 97.5% air and 2.5% polystyrene.

Casting process

Once the pattern is formed, it is coated with insulation paint, placed in a flask and surrounded in un-bonded sand and compacted.

The covering paint works to increase the durability of the mold surface, protect from erosion, and broken. Whereas, the flask is designed suitably for this method so that when the molten metal is poured into the mold, the gas generated by foam burning is withdrawn completely.

After molten metal is poured into the foam pattern, the foam pattern is burned out and the casting is formed.

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What are the advantages of the lost foam casting process?

Lost foam casting maintains excellent advantages in comparison with other metal casting methods.

1. It is able to cast very complicated castings.
2. It is advantageous for guaranteeing high precision and smooth surface finish.
3. Casting by the lost foam technique guarantees nearly no errors or defects.
4. Generally, this method is also more economic than investment casting because it involves a few steps. Applying the lost foam process, the foundries can save a lot of labor and production costs.

What could be disadvantages of the lost foam casting process?

Except from numerous advantages, there are two main limitations of the lost foam casting technology.

1. Firstly, the pattern costs can be high for low volume applications.
2. Another disadvantage is the patterns are damaged or distorted easily because of its low strength. 

Application of Lost Foam Casting

Lost foam technique can apply in various materials ranging from alloy steel, carbon steel, alloy cast iron, ferrous alloy to alloy aluminum.

Ignore a few limitations, there are various advantages found in the lost foam method. Because of its precise casting ability, this process is often preferable to cast complicated and detailed products.

It is applied in a variety of industries ranging from the arts, computer technology, agriculture, national defense, automotive, to civil areas.

For many cast products cylinder heads, cylinder blocks, pipe fittings, valves, fire hydrants, motor starters, 3D models, gearbox details and more the lost foam casting process is the perfect match.

High detailed and complex lamp posts, gas burners, fences, pump housing, aluminum castings, pan support, etc. are also often processed by the lost foam casting.

Lost foam casting in Vietnam

Together with sand casting, the lost foam technology is most widely and popular applied in metalworking foundries in Vietnam because of its economic effectiveness and good quality.

Vietnam Cast Iron is the leading company in metalworking. We supply custom-designed products meeting international standards within fields as following:

• Urban Decoration
• Agriculture Machinery
• Construction Industry
• Transportation
• Marine
• Water Supply and Drainage

Our productions are mainly made from cast iron, ductile iron, carbon steel, and aluminum; and processed by three main innovative technologies including Green Sand, Lost Foam, and Furan Sand.

With respect to the lost foam technique, we often recommend this method for high-detailed products. The outcome delivers tight tolerances, good surface finish, and save cost for the buyers.

Lost foam technology is an efficient and economic process. At Vietnam Cast Iron, with numbers of high skillful and expert labors and high-tech machinery, we could manufacture almost any products by the lost foam process, from a lamppost, manhole cover, pump housing to trash bin, fence, gas burner, etc.

We work with our customers to decide the best casting processes resulting best quality for final products and minimizing the buying cost.

Request a quote to get more information on how our casting service can match your project requirements.

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