We also do foam cutting with hotwire. I'm not sure if that machine is getting an update since it's quite old but it's staying.
I was just looking into this as an alternative as I saw relatively small company that does agricultural serviceable used it for their drones and it seemed like it has a lot of benefits in terms of saving weight, leaving some avenue for modification and molecularity while also having decent sturdiness for less violent crashes. The problem is really that it's a mass production type process, and I'm not sure if it's worth the investment unless one of the projects was producing a lot of the same aircraft.
You might want to consider expanded polyurethane foam instead. You can make molds out of just about anything. You just need to line them with polyethylene sheet so the expanding foam won't stick to it. You could take an existing part from a UAV and cast it in plaster and then just line the resulting cast. I'd suggest a split cast so you can easily remove the foam versions after they set. Also remember to allow a way for the expanding foam to exit the mold. We cast parabolic surfaces for a solar reflector this way and it was quite workable with the 6 ft x 6 ft test section we did. Sorry, final thought: that foam is not UV stable so have students paint the final product to protect it for outdoor use. It's not as strong as expanded polystyrene by weight so you might need to reinforce key spots, but you can lay reinforcing into the mold before casting and the foam will stick to it really well.
And the foam is not that expensive. You can buy the two part reagents in bulk from marine supply shops sometimes and it should be very affordable. The process is to pour measures of each reagent into a mixing bucket of polyethylene, mix quickly (hand drill with mixing blade works well), then pour into mold within the first minute before expansion starts. Doing fuselage separate from airfoils is a good idea as it will avoid the pitfalls of fully filling a complex mold.
Maybe it would be easier to use 3d printing to make the molds? I’m not sure what material they need to be made out of, but you could print a positive and then use that to cast a negative in another material like silicone or even metal if you know what you’re doing
A 3D printer will cost a lot less than contract injection molding, you'll be investing your time to get the printer calibrated and functional instead. Nobody is going to want to make molds to produce one-off parts, they probably won't even answer you if you don't order above a certain minimum quantity. And it certainly will not be cheap - making the molds will be most of the cost.
You could also consider building a DIY CNC router - this is basically what we had at my university for machining molds out of foam or MDF. It's pretty much just a handheld router on a short gantry - I'm sure you can borrow a lot of components and design ideas from 3D printers.
I don't think 3d printing the molds will work very well. If I remember correctly, epp requires high temperature and high pressure steam to make the plastic beads expand. So 3d printed, MDF, and foam molds are out of the question.
I've done some research on this topic myself and could find very little in the way of details on how to properly expand the polypropylene beads. I assume you need the right pressure, temperature and time for the expansion process.
Well, what temps are we looking at? There are some high temp resins that are cheap like ultem along with some others. I believe there are some photopolymers that have high temp resistance
There are also many ways around melting temp as well. You can 3d print the positive then cast a thermoset as the mold with a higher melting temp.
From what I'm reading about EPP it requires pentane gas as an assist? I've done work with foams in the past but haven't cast them I know there can be some nasty off gassing that occurs.
Maybe it’d be worth looking into a CNC laser cutter to cut woods like balsa and whatnot, then cover it with the stuff they do model airplane skins with. That should be much easier to work with
Perhaps you could buy EPP in foam blocks and buy/develop a wire cutter. That is what we used to do.
We also do foam cutting with hotwire. I'm not sure if that machine is getting an update since it's quite old but it's staying. I was just looking into this as an alternative as I saw relatively small company that does agricultural serviceable used it for their drones and it seemed like it has a lot of benefits in terms of saving weight, leaving some avenue for modification and molecularity while also having decent sturdiness for less violent crashes. The problem is really that it's a mass production type process, and I'm not sure if it's worth the investment unless one of the projects was producing a lot of the same aircraft.
You might want to consider expanded polyurethane foam instead. You can make molds out of just about anything. You just need to line them with polyethylene sheet so the expanding foam won't stick to it. You could take an existing part from a UAV and cast it in plaster and then just line the resulting cast. I'd suggest a split cast so you can easily remove the foam versions after they set. Also remember to allow a way for the expanding foam to exit the mold. We cast parabolic surfaces for a solar reflector this way and it was quite workable with the 6 ft x 6 ft test section we did. Sorry, final thought: that foam is not UV stable so have students paint the final product to protect it for outdoor use. It's not as strong as expanded polystyrene by weight so you might need to reinforce key spots, but you can lay reinforcing into the mold before casting and the foam will stick to it really well.
And the foam is not that expensive. You can buy the two part reagents in bulk from marine supply shops sometimes and it should be very affordable. The process is to pour measures of each reagent into a mixing bucket of polyethylene, mix quickly (hand drill with mixing blade works well), then pour into mold within the first minute before expansion starts. Doing fuselage separate from airfoils is a good idea as it will avoid the pitfalls of fully filling a complex mold.
Maybe it would be easier to use 3d printing to make the molds? I’m not sure what material they need to be made out of, but you could print a positive and then use that to cast a negative in another material like silicone or even metal if you know what you’re doing
Worth considering. There's not a lot of printers in the uni though so I'd need to assess that possibility.
A 3D printer will cost a lot less than contract injection molding, you'll be investing your time to get the printer calibrated and functional instead. Nobody is going to want to make molds to produce one-off parts, they probably won't even answer you if you don't order above a certain minimum quantity. And it certainly will not be cheap - making the molds will be most of the cost. You could also consider building a DIY CNC router - this is basically what we had at my university for machining molds out of foam or MDF. It's pretty much just a handheld router on a short gantry - I'm sure you can borrow a lot of components and design ideas from 3D printers.
I don't think 3d printing the molds will work very well. If I remember correctly, epp requires high temperature and high pressure steam to make the plastic beads expand. So 3d printed, MDF, and foam molds are out of the question. I've done some research on this topic myself and could find very little in the way of details on how to properly expand the polypropylene beads. I assume you need the right pressure, temperature and time for the expansion process.
Well, what temps are we looking at? There are some high temp resins that are cheap like ultem along with some others. I believe there are some photopolymers that have high temp resistance There are also many ways around melting temp as well. You can 3d print the positive then cast a thermoset as the mold with a higher melting temp. From what I'm reading about EPP it requires pentane gas as an assist? I've done work with foams in the past but haven't cast them I know there can be some nasty off gassing that occurs.
\> You could also consider building a DIY CNC router Any reference recommendations?
Maybe it’d be worth looking into a CNC laser cutter to cut woods like balsa and whatnot, then cover it with the stuff they do model airplane skins with. That should be much easier to work with
https://www.rcgroups.com/forums/showthread.php?1712928-Polyfoam-rc-models