Robot Parts And Lost Foam Casting
idbruce
Posts: 6,197
Hello Everyone
After being in a programming rut for a while, I put the 3D printer project on hold, and decided to put more concentration on producing my stepper driven linear actuators. Although my current endeavors do not particularly pertain to robots, lost foam casting can be used to make parts for robots, so hopefully Parallax won't mind me being a little off subject, because I am more or less writing about this for the robot builders benefit.
Over the last several years, I have only dabbled with aluminum casting here and there, meanwhile studying the subject of casting quite intensely, and for the first time, I will be attempting lost foam casting. The part that I will be casting, is really quite labor intensive to produce with my limited amount of machinery, requiring a lot of machining and drilling. So instead of machining several components and screwing all the parts together, I have decide to cast it as a single part. Let me just say that the part is fairly small and quite complex (1-1/2 X 1-1/2 X 3).
Since I am considering production, I want to be able to create my molds and cast them as quickly as possible, by any means necessary. In my case, I will have to improvise and create new tools. In many instances, molds are made by cutting large sheets of foam with a hot wire foam cutter, but I will not be using a hot wire foam cutter. As mentioned, the part has a rough dimension of 1-1/2 X 1-1/2 X 3, so instead of buying a huge sheet of foam, I am using small foam blocks used for floral arrangements. These foam blocks will be cut to rough size, with the aid of a band saw, and lightly sanded with a back and forth motion against a sheet of sandpaper glued to a piece of laminated flooring. For further cuts and dissection, I have created custom sawing jigs. These jigs are simply coping saw blades glued to accurately machined spacers, glued to laminated flooring, and may or may not have a back stop. In total, I had to create seven of these particular types of jigs, for the various cutting operations. However, I cannot accurately perform all cutting operations with these jigs, so I am currently in the process of creating a small router table from a Dremel rotary tool and a broken drill press, and instead of using a router bit, for routing, I will be using a carbide PCB drill bit(0.025 Dia.). This router table will be used to cut various rectangular holes and perform various trimming operations, with the aid of router templates.
When the molds are completely machined, all the surfaces will be lightly sanded with an emery board, commonly used on finger nails. After sanding, a sprue, riser, and vents will be added to each mold, although this will require a little experimentation to achieve the best results. Upon adding the previously mentioned items, the mold will be coated with two coats of thinned down lightweight drywall compound. To facilitate faster drying drying times of the drywall compound, I will be creating a makeshift drying chamber from several concrete blocks and a space heater, with a maintained temperature of 100 degrees. When the mold is completely dry, the mold will be placed in a bucket of fine grain sand and then the bucket will be vibrated, so that the sand tightly encapsulates the mold, to prevent mold blow outs. To maintain proper pressure when pouring the molten aluminum, an open ended soup can will be placed over the sprue.
Since I lack the proper facilities to efficiently do my casting, I will be creating several makeshift furnaces. These furnaces will be made by digging several six inch holes in the earth, with a post hole digger, with each one having a diagonally run three inch hole intersecting with the bottom of the six inch hole, to accommodate forced air for a hotter burn. The entire furnace assembly will be constructed from HVAC duct work and surrounded by dirt, with the exception that approximately three inches of the six inch duct will extended above the earths surface. The bottom side of the six inch duct will have a duct cap to facilitate easier cleanup and the top side of the duct will have a duct cap with a two inch hole in the center to help retain heat, but still allow it to burn. For fuel, I will be using charcoal.
I will add more to this thread as I progress.
Any comments?
After being in a programming rut for a while, I put the 3D printer project on hold, and decided to put more concentration on producing my stepper driven linear actuators. Although my current endeavors do not particularly pertain to robots, lost foam casting can be used to make parts for robots, so hopefully Parallax won't mind me being a little off subject, because I am more or less writing about this for the robot builders benefit.
Over the last several years, I have only dabbled with aluminum casting here and there, meanwhile studying the subject of casting quite intensely, and for the first time, I will be attempting lost foam casting. The part that I will be casting, is really quite labor intensive to produce with my limited amount of machinery, requiring a lot of machining and drilling. So instead of machining several components and screwing all the parts together, I have decide to cast it as a single part. Let me just say that the part is fairly small and quite complex (1-1/2 X 1-1/2 X 3).
Since I am considering production, I want to be able to create my molds and cast them as quickly as possible, by any means necessary. In my case, I will have to improvise and create new tools. In many instances, molds are made by cutting large sheets of foam with a hot wire foam cutter, but I will not be using a hot wire foam cutter. As mentioned, the part has a rough dimension of 1-1/2 X 1-1/2 X 3, so instead of buying a huge sheet of foam, I am using small foam blocks used for floral arrangements. These foam blocks will be cut to rough size, with the aid of a band saw, and lightly sanded with a back and forth motion against a sheet of sandpaper glued to a piece of laminated flooring. For further cuts and dissection, I have created custom sawing jigs. These jigs are simply coping saw blades glued to accurately machined spacers, glued to laminated flooring, and may or may not have a back stop. In total, I had to create seven of these particular types of jigs, for the various cutting operations. However, I cannot accurately perform all cutting operations with these jigs, so I am currently in the process of creating a small router table from a Dremel rotary tool and a broken drill press, and instead of using a router bit, for routing, I will be using a carbide PCB drill bit(0.025 Dia.). This router table will be used to cut various rectangular holes and perform various trimming operations, with the aid of router templates.
When the molds are completely machined, all the surfaces will be lightly sanded with an emery board, commonly used on finger nails. After sanding, a sprue, riser, and vents will be added to each mold, although this will require a little experimentation to achieve the best results. Upon adding the previously mentioned items, the mold will be coated with two coats of thinned down lightweight drywall compound. To facilitate faster drying drying times of the drywall compound, I will be creating a makeshift drying chamber from several concrete blocks and a space heater, with a maintained temperature of 100 degrees. When the mold is completely dry, the mold will be placed in a bucket of fine grain sand and then the bucket will be vibrated, so that the sand tightly encapsulates the mold, to prevent mold blow outs. To maintain proper pressure when pouring the molten aluminum, an open ended soup can will be placed over the sprue.
Since I lack the proper facilities to efficiently do my casting, I will be creating several makeshift furnaces. These furnaces will be made by digging several six inch holes in the earth, with a post hole digger, with each one having a diagonally run three inch hole intersecting with the bottom of the six inch hole, to accommodate forced air for a hotter burn. The entire furnace assembly will be constructed from HVAC duct work and surrounded by dirt, with the exception that approximately three inches of the six inch duct will extended above the earths surface. The bottom side of the six inch duct will have a duct cap to facilitate easier cleanup and the top side of the duct will have a duct cap with a two inch hole in the center to help retain heat, but still allow it to burn. For fuel, I will be using charcoal.
I will add more to this thread as I progress.
Any comments?
Comments
We had a lot of fun sand casting ali at school. I did quite a few lost foam castings using shapes hacked out of big lumps of white polystyrene. Using saws, hot wire cutters, soldering irons, whatever.
From what I can remember:
1) It's a great process for making one offs. But when you need to make many of the same thing you have the problem of having to cut new foam forms all the time. For that it's better to use removable wooden forms. But then that limits the complexity of the shapes you can cast.
2) We did not think hard about runners and risers. Just a put them where the "maxima" were in your design when in place for casting. Just think about how metal flows in and air moves out.
3) We used "sharp" sand. Not the "round" sand you find on the beach. The later will not lock itself together and stay put nicely. The sand was also a bit damp so that it sticks to itself and holds the shape (not too damp, then you have an explosion on your hands). What that means is that I can't imagine a vibration table shaking it down into position. It does not move and flow like that so easily. No, we just packed the sand around the forms carefully to ensure no voids were left and everything was packed tight.
4) Being only 14 there was no great study of the casting process for us. We just did it. Of course our teacher knew some magic. Like what was that stuff we threw into the molten ali whilst it was melting in the furnace. Some kind of flux and slag separator. Sadly I don't recall what it was.
As it stands now, the most time consuming part of the process is cutting my rough block down to size. Once I have that rough block, with the various jigs, I can cut out the other main features, in about three minutes, but that does not include my rectangular holes and various trimming, which might take an additional minute or two, once I get my router table built. I am truly surprised how fast it goes with the use of the saw jigs.
The use of dry sand in combination with vibration is a common industry practice. Just shake a bowl sugar a couple of times to see how much it compacts.
I believe it is Borax that is used as flux, if I remember correctly. I has been a while since I last casted.
I'm sure you are right. I am not up to speed with industrial casting techniques. Surprised though because the sand we used back in the day certainly would not flow like sugar. It would just sit there in the shape you gave it. Which of course is what you want it to do while casting.
In my limited experience of getting processes like this running nicely it's a black art made up of experience, experiment, trial and error, on going tweaking and a little bit of science thrown in
But if you really desire fine detail and precise parts, making an original in wax, building a mold of the right kind of plaster around it, and then melting the wax out in a kiln will product better results.
This is commonly used in jewelry and dental work where details are precise. Though they use gold and silver, I have done both bronze and aluminum.
Wax is available from jewelry makers supply houses and comes in a variety of hardnesses as different projects demand different characteristics. About the only other item needed is a small electric kiln, though I suspect that one could just salvage an old oven to burn out the wax.... just be sure it is in a place where a wax fire is no big deal.
@Loopy - I am also interested in lost wax casting, because of the fine detail that you mention. I will be using lost wax casting to capture the profiles of timing belts for belt clamps. I can now make pretty accurate belt clamps with my drill press and a fly cutter, but this process is also very time consuming, and I want precision clamps.
As an additional side note, they now have a wax filament for 3D printers. Here is a YouTube video about the new product:
As mentioned in the first post, I am using a rotary tool as my router, and even though I used the word "Dremel", it is actually just a cheap knock-off. I also mentioned that I am using a broken drill press as the base for my router table, having the motor and drill housing removed, so basically I am just using the base, the adjustable column, and the table.
The cheap rotary tool had a threaded removable nose to enable the attachment of various possible attachments. To attach the rotary tool to the table of the drill press, I removed the nose, then I inserted the threaded portion of the rotary tool through the center hole of the drill press table, and then reattached the nose. It was practically a perfect fit, however now I had to compensate for the nose above table height. Without rushing for a solution, I spent some time to think about the problem, because not only did I have to overcome the height discrepancy, but I also needed something to quickly register my templates in respect to the bit being used. While looking around for a solution, I came across an 80MM X 80MM X 25MM cooling fan for a PC. The fan housing provided ample height for clearing the nose portion of the rotary tool, it provided four accurately spaced holes for mounting and registering my templates, and these four holes were spaced according to the center of the fan motor which would be replaced by the center of my router bit.
I began my work by cutting out the center supports and removing the fan motor. Now that I had a nice support for my templates, it became necessary to accurately center it in respect to the center of the router bit. To accommodate simple centering, I cut a thin piece of plastic to a diameter slightly larger 80MM. After center drilling the plastic, I then attached the plastic to the rotary tool sanding disk holder and chucked it up in the drill press. Using sandpaper, I then turned the plastic down to match the outer dimensions of the fan housing (80MM DIA.). Utilizing a PCB drill bit, which corresponded to the size of the center hole within the center of the plastic disc, I chucked the bit and plastic disc to the rotary tool. After aligning the fan housing with the now centered plastic disc, I then secured the fan housing to the drill press table with a hot melt glue gun.
As it stands now, I believe I now have a nice table for my rotary tool, which will enable attachment and removal of templates. For those that may need a similar table for their rotary tool, I highly suggest the use of a fan housing.
It is now time to make my templates
So I finished one template and performed my first cutting test on the table, using a PCB drill bit. I am happy to say that it cut well and very accurately. After cutting out a rectangle, from 3/8" thick foam, I only had to lightly dress the cut with a fine emery board.
Although I have more templates to make, I am now very curious to see just how well the foam will sand, utilizing the grinding stones included with the rotary tool. If the grinding stones work well, then that will open up some other possibilities.
I will keep you informed.
Now I will have to investigate to discover what types of stone profiles are available with an 1/8" shank for the rotary tool and 1/4 shank for the drill press.
Yes. Go here: https://oshpark.com
Interesting find Heater.
@Everyone
Alright.... The other day I purchased several pieces of 8" duct work, so that I could start constructing my "in-ground" furnace, but since I have been working on something else, I have had several days to think about various ways of constructing it. This morning I came up with a completely different idea for constructing the furnace and I immediately went to work on it, and at this point, I have a new prototype. With the exception of waiting for some furnace cement to cure and adding a coat of high temperature paint, this baby is ready for burial and testing.
I am fairly certain that this furnace should work well for melting 1 pint ~ 1 quart of aluminum, and would probably be a good starting furnace, for those eager to try casting. Providing the furnace works well, I will most likely start selling them on the Novel Solutions website for about $50. So please let me know if you might be interested.
Items that will not be included, if I sell them these "in ground" furnaces:
Just this evening, out in the depths of the forest, I was huffing and puffing into our little charcoal grill to get some life into it for a bbq.
Strangely I could not help but think of you.
I just finished building my forced air system and it looks good. Now it's a bummer, because I have to wait.
Hmm...Seems you need 1.2 US pints to make a proper Imperial Pint.
Your beers must be depressingly small:)
Keep in mind that I am using a similar container for the current furnace, as to my previous setup.... The main difference with this furnace is that the earth will insulate and retain heat, so it should be much more efficient. Additionally, in the past I did not cover the furnace, but I will now, which will also make it more efficient.
This container is 7" DIA. X 8" TALL. The crucible stands off the bottom of the container approximately 1-5/8" and lets also say the crucible is 4" DIA. X 6-1/2".
I have seen people use entire charcoal briquettes, but I bust mine up, because the space is cramped, and I want to put as much fuel in there as possible, so that I can avoid unnecessary refueling. The broken up charcoal briquettes first fill the bottom 1-5/8" under the crucible, and then the area surrounding the crucible is also filled with broken briquettes. If I am not mistaken, I occasionally had to add a little more fuel while burning, but I could be wrong.
A ball park guess.... 10~15 briquettes.
EDIT: OOPPS my bad, you did say a pint.... I would say 10~15 would do a quart
I recall that back in school our gas powered furnace, which probably held about a pint in the crucible seemed to be consuming gas at a ferocious rate. There was a veritable tornado of hell fire going on in there. With an appropriately satisfying roaring sound
For investment plaster (the actual plaster mould), there are lots of formulas listed in dentistry, jewelry making, and sculpture. Aluminum is relatively a lower temperature casting, so the kind of investment plaster that actually makes the mold may be less critical.
Sand-casting with traditional wooden blanks that are packed with sand, then the wood mold removed --- uses special recipes of sand with certain clay or resin mixes to make the sand hold up to being opened for removing the wood prior to casting.
The big advantage of foam is the sand does not require as much special treatment. The main drawback is the surface of the casting takes on the rough texture of the foam.
Lost wax can eliminate that rough texture and makes production of multiple duplicate parts easier to achieve. But it requires that extra step of melting and burning the wax out of the investment mold before you can pour. It is still wise to bury the investment mold in a box of sand for safety.
I have experience casting bronze in lost wax for art sculpture and the higher melting temperature makes it more of a hazard than aluminum. The higher the temperature and the larger the casting, the greater the danger as there is more energy in the molten material to cause trapped gas to burst the mold.
Since my last post and as it pertains to the in ground furnace, I have been making jigs and altering my process for making these furnaces, as well as altering the design of the furnaces. I am now on the home stretch of completing the third prototype and I believe this one will be the final design.
I have been doing my best to cut down production time and costs, so that I may offer the furnace at a reasonable price. At this point in time, it is looking like it will be right around $60 with free shipping to any of the 48 lower states.
In the near future, I will be producing several YouTube videos, which will demonstrate furnace "planting", furnace use, and creating a few simple things from molten aluminum. Since I am not a robot owner, I will simply create a few shapes for some of my equipment designs, however, the process can be used for making parts for your robots.
In Ground = The furnace is below the earth's surface
The answer is simplicity. Just dig a hole, set the furnace, add a couple pipe nipples, fill surrounding area with dirt, adapt to blower unit, add charcoal, and ignite. Considering a trip to the hardware store, a person could be melting some serious aluminum within an hour or two, with little fuss.
No hope of making such a hole around here without some dynamite. This country is built on solid granite!
I like the grass in your diagram. I imagine that is not there after the job is done
The furnace I am making should work above ground also, because it will be very similar to my last setup, which worked well, without being buried, but I think it will be more efficient, when surrounded by earth for insulation.
For those folks that may want the insulating properties, but are surrounded by concrete, granite, or other formidable obstacles, there is always the option of just building a small and simple sandbox to place the furnace in.
As mentioned earlier, the furnace should work fine above ground and without insulation, but for comparisons sake, when I make my videos, I will fire up two of these furnaces, where one will be in ground and the other will be above ground. Hmmmm... but for comparison, they would both need identical sources of forced air.... Oh well, I guess it will not be a true comparison then, but I will demonstrate both above and below ground metal melting.
I no longer intend to offer an "in ground" furnace, instead I will be making above ground furnaces, mounted to a 12" X 12" patio block. The patio block will provide stability for the furnace assembly and two sides of the patio block will have a handles, for easier carrying and placement.
The new furnace assembly should be able to accept quite a few full size charcoal briquettes and it will also include a lid to help retain the heat. Additionally, I have also decided to include a crucible, a crucible handling and pouring tool, and a lid remover. The furnace should weigh approximately 20LBS. (including the patio block), it will be stable, and should melt about a quart and a half of aluminum.
It is getting better with each prototype.
I believe graphite works well for crucibles, although I have never used it. As I am sure you are aware, graphite crucibles requires the use of tongs.
The crucibles that I will be constructing, will most likely be made from 5" diameter stainless exhaust tubing, and having two eyelets welded to the outside, so that the crucible can be picked up and poured with a tool, similar to that shown below.
I now have most of my production jigs completed and it won't be long before I can make these furnaces at a decent pace.
Additionally, I have also created a nice forced air blower assembly for the furnace, which can be quickly attached to a 12VDC lawn tractor or car battery, with large alligator clips, however I am also thinking about creating another version of the blower, which will accept a 12VDC power adapter, so that an extension cord may be utilized instead of a battery.
As a side note, I have decided not to include the crucibles and pouring tool, simply because I am getting to eager to proceed.
Anyhow, just trudging along