Lost wax casting prints
December 12, 2017 05:11PM
I'm looking to do some parts that are going to live under the hood of my car. The temperatures under the hood get rather warm, but the other problem is that I need more strength from the part than any 3D printed part I've ever seen. I've done some stuff with lost wax casting for doing small jewelry pieces, and am playing with the idea of casting parts in aluminum or brass, which are possible with a backyard foundry. This is pretty easy with lost wax, just pack the wax part in your casting sand and pour. I did some poking around and a "lost PLA" process exists, but it's a lot more steps, and seems to be much more work with more risk of fouled parts if any of several things goes wrong with the process, and you don't get to find out until you get your final part. I think that would just make me crazy. On the other hand, maybe that really is the only feasable way to do this.

So I've been thinking what it would take to print in paraffin wax instead.

Wax is too brittle to use a normal extruder with. I don't even want to imagine the problems with trying to feed a 1.75mm line. So I've been thinking of other possible solutions.

1. Pellet extruder. I know that this isn't optimal. Pellet extruders seem to have a lot of issues with things like retraction, and can have problems of dripping. I was thinking that if it's not too bad, that I can likely fix small flaws with a wax model relatively easily, but still, the idea is supposed to be that I won't need to.

2. Custom make an extruder that will feed a larger stick of wax. Shouldn't be a problem to melt a larger stick of wax, say 10mm in diameter, which I should be able to feed and retract. I'd have to make my own sticks to feed it, but for a material like wax, that's not too hard. Because of the larger melting area, I figure that I might end up with some of the same drip problems, but if I control temperature well, I might be okay. For the parts that I am planning, a larger nozzle would probably also be okay, which could mitigate the problem.

3. Just print molds for the wax. If I design parts that can be put into a 2 (or more) part mold, I can print molds for the parts, fill the molds with wax, and then lost wax cast the part. This adds another step, but is still much simpler than the "lost PLA" casting that I was able to find information about. the advantage though is that once I have the molds, I can make several of the same part from one 3D print, which would save a lot of time for things that I want or need multiples of. It makes for a little more limitation on what I can make this way, and of course then there's the need to have mold parts that fit closely together.

MBot3D Printer
MakerBot clone Kit from Amazon
Added heated bed.

Leadscrew self-built printer (in progress)
Duet Wifi, Precision Piezo parts
Re: Lost wax casting prints
December 12, 2017 09:52PM
I don't know if paraffin is suitable for lost wax casting, but the steps should be the same as with lost PLA casting. I'm not sure what the extra steps you're referring to are.
There are some wax filaments available if you look around, made specifically for either sculpting or casting.
Re: Lost wax casting prints
December 13, 2017 02:25AM
Printing molds would often require a lot of support structures. You'd need a dual nozzle setup and ABS/HIPS or PLA/PVA filaments.

Regarding HIPS: you could also print the parts in HIPS and then use lemonene as solvent. Probably much better than the lost PLA method.
Re: Lost wax casting prints
December 13, 2017 04:35AM
Indeed HIPS is a good choice, easy to dissolve or even burn. Parts have to be made as empty and thin wall as possible.

"A comical prototype doesn't mean a dumb idea is possible" (Thunderf00t)
Re: Lost wax casting prints
December 13, 2017 04:46AM
I recently considered mold-lay for a jewelry job. If it works as advertised then that should solve your issue.

However I think if you have a mold that fits inside your foundry any plastic will burn out relatively cleanly at aluminum temps.
Re: Lost wax casting prints
December 13, 2017 05:16AM
Could I suggest using zinc alloy as it gives much finer detail than most aluminium alloy. it is fairly strong and will take under the hood temperatures - it is commonly the material for carburetors. PLA/PHA from Colorfabb makes a good material for the model - see [learn.colorfabb.com] and investment material is always better than sand for the mold - commonly available on eBay at a low price. Melting out and burning out is eased a lot if you use the lightest possible infill for the printed model.

Re: Lost wax casting prints
December 13, 2017 07:44AM
Build an SLA printer? Legitimately more useful then a pellet extruder machine or niche wax-extruders. You can get casting resins used for jewellery that are for SLA machines. Perhaps a bit costly, but probably cheaper then the inevitable research and design costs of a wax extruder.

Or why not make a mould of your printed part? Then you can make it in a range of materials that are more suitable for casting then PLA.
Re: Lost wax casting prints
December 13, 2017 01:27PM
Thanks for comments, I appreciate it.

@Trakyan: I'll look for those filaments. I didn't see any when I was looking before. Because I don't actually need really high resolution, I was looking to put the model directly into the casting sand, directly pouring the aluminum in to replace it. If I want, I can spend time polishing the rough-cast surface afterwards, but I really only need a few small surfaces and bolt/screw holes to have a good finish, and I will want to run a drill and tap through those holes regardless.

@o_lampe: Support structures aren't much of a problem for the things I'm looking at. Mostly I'm looking for brackets to hold things in place, which need some odd shapes to get around other stuff, but making a hollow version inside of a 2 part mold would be easy enough.

@MKSA: Possibly. I'll look into the possibility. Not having to custom-make a printer for doing this type of job would be of great help.

@sungod3k: As stated above, I'm not really looking to put a mold into the foundry, but basically pour molten metal pretty much straight into the casting sand with the model. It's a bit lazy, and does have the issue of losing a bit of resolution, but in terms of some of this design being by necessity trial and error, shortening the development process for the finished product is slightly higher priority. Once I have a working model, It can be worthwhile spending the time to polish the finished product.

@leadinglights: Yes, that would be a superior material, but the additional resolution isn't necessary, and it's more difficult to do the machining work like drilling/tapping afterwards in the zinc alloy. Aluminum is very easy to polish, and is plenty strong enough. A smooth finish is not critical for most of the parts, but being able to try several different shapes, often with the same pour is important to me.

@Origamib: Yeah, I had considered SLA, but since I'm currently tearing down and rebuilding my I3, and it's not really important that it be useful for anything else right now, I am considering making it useful for this specific purpose. And yeah, I am considering doing pretty much exactly that. Make a mold in order to make a wax model, then use that to cast from. Still much faster than firing a plaster mold.

A bit of information about what I'm doing: It's not really relevant to the general theme of the forum, but might give an idea of the things that I'm looking at.

I have plenty of aftermarket goodies under the hood of my car.

Currently, some parts (intercooler, intercooler piping, oil cooler) are held in place by braces to factory mounting points by pieces of flat rod bent to connect up, with bracing welded in where the rod just wasn't quite strong enough. It works, but a purpose built brace would work better and might not rattle on the parking lot speed bumps. A sandcast rough surface wouldn't be worse than the sandcast exterior of some of the aluminum parts already present, particularly if they're put in matching powdercoat.

Some parts (Boost controller solenoid, aftermarket gauge senders, added relays) are bolted to the fender well at odd angles using the closest useable mounting locations. I'd like to clean these up so that they look more presentable. Again, either a rough cast powder coat would be acceptable, or I can spend some time with sand paper making a polished aluminum part for some in very visible locations, like the top of the intake manifold. Even a faithful accurate replica of the 3D print would need polishing in this way.

Some parts (The wires for the wideband O2 sensor, exhaust gas temperature probe, oil cooler) are under the car, and things are held in however I managed to put them in at the time, and appearance really isn't important at all, but it would be nice to have a good rigid mounting method for parts that are exposed to heat.

Some parts are factory (heater and radiator hoses, power steering lines, wiring harness) and just need to be held out of the way where they interfere with the aftermarket stuff. Again, powder coated sand cast will be fine.

I have a casting box that's about 2' by 1' by 1' I can probably fit 3-4 parts in the sand with risers if I'm directly packing them in sand. I can maybe do 2 per pour if I'm doing fired molds. this means a lot more cycles with the foundry, and a much longer re-cast process if something goes wrong, plus the additional chance that something will go wrong. To me, it doesn't seem worth the added accuracy when you consider that the best that I can get is a more accurate reproduction of the texture of the 3D printed part.
Re: Lost wax casting prints
December 15, 2017 07:08AM
Why not just print parts in Polycarbonate? It'll withstand heat up to 115°C (240°F) and should be enough for most places under the hood. Since your thermostat opens at around 87°C(190°F) your motor shouldn't be getting much hotter than than that anyway. And from what I've read, you just want to print parts to clean up wiring and mount components to the chassis. Well within spec of what Polycarbonate can handle.

I already use TPU and Polycarbonate under the hood of my car, haven't had any problems yet! If you want to have a look at what I've done, take a look
here TPU Intake adapter
here crankcase breather inlet

Both parts live not far from the turbocharger, so they get a good amount of heatsoat after parking the car, still nothing polycarbonate can't handle.

Build Log - DDDE 330x330x300mm Ultimaker
Re: Lost wax casting prints
December 18, 2017 11:53AM
@jerryjs8: Not too bad an idea. For some of it, I want the rigidity of metal, which is going to be much higher than any thermoplastic can manage, and if the stresses on it are too much for 1" by 1/8" steel flat bar to manage without unacceptable flexing, I can't imagine a 3D printed part itself being strong enough to manage, but a cast aluminum arm (not flatbar) will do the job nicely. For some of the other parts, I want to be able to polish it up and make it shiny. Honestly, I could probably even use ABS for some of the routing stuff. Some of the factory parts were ABS (though injection molded ABS is certainly stronger than printed ABS will be) in locations that I'd have stuff.

Honestly, there are some of the things that are on a really low priority list for being cast, like holders for the boost controller solenoid that I will probably prototype in ABS and leave that way for a really long time before I'd even bother casting, just because doing so would be a pain.

However if I do have a setup for doing lost wax sand casting, there are things that I might not need done that way that I might do anyway, because once polished up, they would look really nice. No way that anything 3D printed can match the look of polished aluminum. smiling smiley

MBot3D Printer
MakerBot clone Kit from Amazon
Added heated bed.

Leadscrew self-built printer (in progress)
Duet Wifi, Precision Piezo parts
Re: Lost wax casting prints
December 19, 2017 02:27AM
Printed ABS can be cured with Acetone afterwards. That would make the part stronger and reduces the layer marks. Then the molded parts wouldn't look like 3D printed anymore. ( If molding is still neccessary )
Re: Lost wax casting prints
December 29, 2017 08:23PM
What o_lampe said.

Made complete pump housings and impellers from 3d printed ABS when I was a designer for a Spa company.
Juiced them with acetone, more like painted acetone on with a brush, then painted with enamel. High temp Rustoleum from a rattle can worked great.
Parts looked like they were molded, and stood up under real world pressures and temps. Trick is to have as many shells (outer profiles) as possible, layer height didn't seem to matter.
Never had an impeller fail over 60 plus revisions, and 200 plus trials machining them to various diameters.
Had one or two housings fail after some extreme abuse, 200 GPM at 40 PSI will soak a room in no time grinning smiley
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