Metal casting at home

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Igor_toko

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Hello all, I'm Igor. I'm new to this forum. I'm 25 years old and finally have some resources to start this hobby. I have a PLA 3d printer. I recently bought an Emco Unimat 3 mini lathe. I'm now building my own furnace with a steel container, refractory ceramic blanket, and plaster walls.

I'm interested in creating my own scale 4-stroke engines. and I want to experiment with casting my own engine block by using a lost wax method. I thought of 3d printing a mold (considering the shrinkage), then covering the mold with investment plaster, burning it out of the investment, and finally pouring melted aluminum in it.

If someone has experience with similar types of castings, I would greatly appreciate your knowledge exchange. What is the most precise level of detail that I can achieve with this method? As I understand it, the metal has difficulties reaching thin and deep passages due to the thickening as it cools down. Also, what is the superficial tension of the melted aluminum, and how one can make It flow towards the walls and edges of the mold?

I am also thinking of placing the investment mold inside of the furnace, and pouring the metal into the investment while it´s inside the furnace, would it make the aluminum flow better into the mold?

Thank you in advance :)
 

lee webster

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Hi Igor,
There are pla filaments that are suitable for burning out of investment, but they will take a lot of work to prepare them first. Have you checked out the videos of Olfoundryman on youtube? He doesn't use many pla patterns, prefering the old way of doing things. The finish he gets is second to none. Myfordboy is another youtuber well worth checking. He does use pla for almost all his patterns.
Lee
 

GreenTwin

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There is some very significant backyard talent right here on this forum, including investment castings, green sand, bound sand, aluminum, brass/bronze, and iron.

The lastest investment casting thread is located here:


Another interesting investment casting thread is located here:


My backyard gray iron casting work is here:

.
 

GreenTwin

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A quick note on ceramic blanket furnaces, you should coat the interior with a high temperature material such as satanite, to prevent the fibers from becoming airborn, and potentially inhaled.

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GreenTwin

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I have not done lost wax or lost PLA yet, but have been watching closely at how others do it.

The trend these days seems to be towards using lost PLA.

There is a special type of filament that is suppose to burn out cleanly, called Polycast.

Feedback I have seen on Polycast says that it has very little burn out ash, but absorbs water and may need to be dried.

Others I have seen have gotten very good results with burning out PLA.

As "creast" mentions in his 1/8 Rider Ericsson build (link above), the PLA pattern is surrounded by an investment material, with vacuum to help get rid of bubbles, (see his thread for exact details), and then a vacuum assist during pouring.

The lost wax method requires making a mold into which the wax is injected.
I see the lost wax method as more of a mass production thing, and it requires wax, wax pot, etc.

The lost PLA castings I have seen rival lost wax in quality.

I have seen one individual leave the mold heated in the kiln while pouring the metal, but this was with gray iron.
For aluminum, I don't see the need to keep the mold in the kiln.

.
 

GreenTwin

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One trend I see these days is lost-foam.

The industrial lost-foam method uses polystyrene beads which are expanded with heat inside of a metal mold.
The investment material used with lost foam is permeable so as to absorb both the gasses from vaporizing polystyrene, and also absorb liquids from melting polystyrene.

The backyard crowd uses hardware store foam, and while a few have had some success with this type of foam, often I see failures due to the foam not vaporizing very well, exessive gassing, interupted pours, thick toxic smoke, etc.

The backyard application of hardware store foam is not really how lost-foam is done in industry, and so the quality of backyard lost foam castings can vary greatly.

I saw one individual recently who tried the hardware store lost foam with gray iron, and it was a spectacular fail.
Lost foam is used successfully in industry with gray iron, but it is used with expanded polystyrene beads, and a special investment coating material.

The backyard-type hardware store foam method defeats the purpose of the lost foam method, since you have to create every pattern in foam, over and over again with each casting, instead of the industry method of using a metal mold and expanding polystyrene beads into the reusable mold.

I see people spending significant amounts of time making one-off complex hardware store foam patterns, only to burn them up when they pour metal. Totally defeats the repeat-use pattern approach, but perhaps ok for one-off castings.
If the backyard foam casting does not turn out (often it does not), then you have to keep recreating the hardware store foam pattern all over again, potentially numerous times.

I would not totally discount the lost-foam method, but the results I have seen are not consistent enough for me to every try a hardware store lost-foam casting.
I have seen some champion the hardware store foam method as the next big thing in backyard casting, but I don't see that at all, for numerous reasons.

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Kelly Coffield on YouTube does some of the Best Lost Foam Aluminum casting that I have ever seen...

I use to teach casting at the Houston Museum of Fine arts...

Here is one of his videos casting an Automotive Manifold...



Best Regards,

Preston
 

GreenTwin

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Everyone has their own motivations for what they cast, and how they cast it.

For backyard casting as a hobby, basically anything goes, and efficiency has no real bearing on anything (as long as you can afford the inefficiency).

For me, I make engine parts in gray iron, and so it is critical that there not be any defects or voids in the casting.
I use resin-bound sand, which is not reusable, and so it is again critical that I get it right the first time, and not have any casting failures.

The entire idea behind making castings from patterns is that you can make one high quality pattern, and then reuse that pattern repeatedly, while maintaining the same quality and dimensions for every casting made.

For the backyard lost-foam folks, every pattern has to be hand-made, no two patterns are exactly the same, and the pattern is destroyed with each casting made.
So from a practical and time standpoint, the backyard method of lost-foam castings is perhaps the least efficient method that there is, and it has questionable repeatability as far as accuracy and tolerances.

The density of hardware store foam gives it I think a longer burnout/melt time than the standard expanded bead process, and this seems to cause a very slow mold fill, which is one of the things that you really want to avoid when making castings, because you can get cold joints inside the casting that are not visible.
For a non-structural part, the cold joints may not be critical, but for engine parts, you don't want any cold joints in the casting.

If the idea is that someone just wants to make one of something, and they have unlimited time on their hands, then I think it can be shown that the backyard lost-foam method can be used to make very complex one-off parts (slowly).

The youtube backyard lost-foam videos make for some some interesting discussions, and garner lots of views, likes and subscribers, but from a practical standpoint, that is a lot of wasted effort for a one-off casting, for me anyway.

The spectacular fail I saw recently using the backyard lost-foam method with gray iron sort of highlights the unpredictability of this method.

I guess I would be more interested in a more consistent and reliable lost-foam method that used a metal mold in which polystyrene balls could be expanded, such as how it is done in industry to make engine blocks and such.
The industrial lost-foam method is very impressive, and the same mold can be used thousands of times, and so the efficiency is very high, as is the quality of the castings in both aluminum and gray iron.

For me, it is about the efficient use of time, repeatability, accuracy, and consistency.
I like to be able to section my castings and always have exactly uniform wall thicknesses, with no internal voids or gas defects.

Here are a few videos about the industrial lost-foam process.
I think these videos show the real potential of the lost-foam method, both in the industrial and backyard casting worlds, using aluminum and gray iron.





.
 
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GreenTwin

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The niche for the lost-foam process seems to be very complex parts, with lots of internal passages, and very high difficulty if trying to use the sand casting method.
Here is an example.
As is the typical industry standard, permanent metal molds are used for consistency and accuracy.

 
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agree the “one off” nature of lost foam seems a disadvantage

however I must say the results that Kelly is getting appears outstanding especially the reproduction of fins



which is amazing when Compared to what I have seen from green sand work

his treatise on thin wall aluminium is equally impressive doing the “master test” of cup saucer and spoon



it appears he has processes to make multiple foam patterns. I see routers with jigs and lately cnc cut foam patterns

im a newbie who only has experience with green sand casting aluminium so really only looking from the outside

cheers jeff
 

GreenTwin

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There is a guy out west named Jeff Henise who casts racing motorcycle cylinders in aluminum, and races his motorcycle using his cylinders.

Making a good looking casting is one thing.
Machining that part and using it under racing condtions takes it to a whole new level, and definitely proves that not only do your castings look impressive, but they actually function under very rigorous conditions.

Here is Jeff's channel:

And here are photos of Jeff's cylinder work.
And it shows that you don't need lost foam to make a rather complex engine parts.

Jeff's patterns are reusable, and so they can be used over and over again.

This method makes far more sense to me than a one-off lost foam method, but to each their own I guess.


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GreenTwin

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Jeff is just a genius-grade guy.

He researched sand and binder types, pattern coatings, release agents, and created sand hardness tests, to measure which product worked best.

He posted his tests for many types of foundry sand, some of which used binders.
It is the most comprehensive approach to figuring out the best mold material to use that I have ever seen.

He tried green sand (water-based), Petrobond (oil-based), resin bound sand, and sodium silicate bound sand.
For his bound molds, he used Oaklahoma 85, which is a white ~85 AFS silica sand (often called OK85).

OK85 is also the sand I use with a resin binder, and I consider it to be the best commercial-grade foundry sand available.

The photos of how he made the cores for the passages for his 2-stroke racing engines are fascinating.

Resin-bound sand can be used for both the mold and the cores, and multi-part cores can be assembled and cemented together, which is the method Jeff used. He uses a zircon refractory wash on his cores to get a very smooth passage finish.
I use a ceramic alcohol-based mold wash, which I spray onto the core(s) and the interior of the mold, and it gives a superb finish, and stops the metal from penetrating the sand.

As as I mentioned, Jeff appears to be self-taught.
He looked at all the options available, tested multiple products and methods, and then picked the best materials for his purpose.

His casting results speak for themselves, and his cylinders functioned very well under high-rpm racing conditions, according to Jeff.

One trick I learned with resin-bound sand is to use a small auto body slide hammer, with a forked end.
I put one or two screws in the pattern, and then lightly tap with the slide hammer, keeping a hand on top of the pattern, not moving the pattern, but breaking the bond between the pattern and the resin sand.

For a small pattern, it can be one screw in the center.
For large patterns, you may need two or more screws, and you basically use the slide hammer all around.
Once the bond has been broken, you can lift out the pattern easily by hand.

You really don't want a slow pull like Jeff does with his extractor, at least not initially, since you can tear the sand by pulling slow.
The light blow of the slide hammer breaks the bond without damaging the resin-bound mold.

I will try to find some more photos of Jeff's motorcycle racing engine work.

.
 
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Igor_toko

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Igor:

If you haven't already found it, you might want to check out The Home Foundry forum. The Home Foundry

Their sub-forums include both lost wax, and lost PLA casting. You'll probably find the answers to most of your questions there.

Don
Hello Don,

Thanks for your reply and for the information. I will read through the posts on that section. I've also seen several projects of people using PLA casting on the forum
 

Igor_toko

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Jeff is just a genius-grade guy.

He researched sand and binder types, pattern coatings, release agents, and created sand hardness tests, to measure which product worked best.

He posted his tests for many types of foundry sand, some of which used binders.
It is the most comprehensive approach to figuring out the best mold material to use that I have ever seen.

He tried green sand (water-based), Petrobond (oil-based), resin bound sand, and sodium silicate bound sand.
For his bound molds, he used Oaklahoma 85, which is a white ~85 AFS silica sand (often called OK85).

OK85 is also the sand I use with a resin binder, and I consider it to be the best commercial-grade foundry sand available.

The photos of how he made the cores for the passages for his 2-stroke racing engines are fascinating.

Resin-bound sand can be used for both the mold and the cores, and multi-part cores can be assembled and cemented together, which is the method Jeff used. He uses a zircon refractory wash on his cores to get a very smooth passage finish.
I use a ceramic alcohol-based mold wash, which I spray onto the core(s) and the interior of the mold, and it gives a superb finish, and stops the metal from penetrating the sand.

As as I mentioned, Jeff appears to be self-taught.
He looked at all the options available, tested multiple products and methods, and then picked the best materials for his purpose.

His casting results speak for themselves, and his cylinders functioned very well under high-rpm racing conditions, according to Jeff.

One trick I learned with resin-bound sand is to use a small auto body slide hammer, with a forked end.
I put one or two screws in the pattern, and then lightly tap with the slide hammer, keeping a hand on top of the pattern, not moving the pattern, but breaking the bond between the pattern and the resin sand.

For a small pattern, it can be one screw in the center.
For large patterns, you may need two or more screws, and you basically use the slide hammer all around.
Once the bond has been broken, you can lift out the pattern easily by hand.

You really don't want a slow pull like Jeff does with his extractor, at least not initially, since you can tear the sand by pulling slow.
The light blow of the slide hammer breaks the bond without damaging the resin-bound mold.

I will try to find some more photos of Jeff's motorcycle racing engine work.

.
Hello Pat J.

Thank you for all your messages and links with references. I saw the videos from Kelly Coffield on lost-foam backyard casting. The results are impressive, but I agree that making the patterns is very tedious, and since I don´t have a CNC mill or router, I will not use that method.

The resin-bound sand casting that you describe sound quite interesting. Since I live in Europe, I don´t know if I can easily access the Oaklahoma 85, but I can try to find sand with a similar composition here. For the resin, which kind of resin should I use and how do you mix the sand with the resin?


Regards.
Igor
 

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