Heat bending foam possibilities ...

[GPW]

We all Love those nice rounded surfaces, but hate the mess and complexity of kerfing cuts to get the foam to bend... Laminating thinner foams together is work , and lots of glue . Plus the fact that kerfing weakens the foam unless the kerfs are close fitting and glued together... and the usual laminating glues might take forever to dry on the inside ... The answer is Heat bending ... easily accomplished with thinner foam , but bending the thicker (up to 2” thick) has been somewhat more difficult to figure out .. So after much thinking about this , we came up with another drawing to possibly show how it can be done ... This is just a table sized variation on our smaller bendFoam jig ( used elsewhere) ... The secret to this is you’re NOT heating the whole sheet at a time , just two narrow areas ( top and bottom ) which bends the foam in stages, You heat and bend a little bit at a time , advancing the foam as more is to be bent ... The pivoting Bending board just keeps the foam even as it's bent ... Heating would be by two people one on top heating the Tension side of the bend , the other underneath heating the compression side ... Narrow heating like this could be easily done with a couple HF cheap heat guns...
A “stop" could even be added to the “bending board" to achieve a uniform bend and repeatability ...

This is just an Idea , but JMHO , I think it could really work well , adding an easy method to get curves into foam sheets ... best thing , once it’s cooled in that shape , it STAYS in that shape ( no springback ) , so is actually stronger... We’ve proven this on thinner foams in the past .

The table sized jig could be make from leftoverwood scraps and just screwed together for disassembly after the job ...
See what you think ...

I offer this only as an idea for further development ... Nothing is written in stone... yet ...

[Pmullen503]

Heat bending foam seems to be the holy grail. Having done a lot of this for RC planes let me share my experience. First, the temperature that foam becomes bendable is very close to the temperature it melts and the structure collapses. That makes it hard to do with a heat gun, even on a small scale. Second, the heat must "soak" into the foam so that the center is warm enough to form. That takes about 10 minutes for 1/4" foam in my oven with the temp. PID controlled at 98'C.

The biggest problem I see is that the foam will expand when it gets warm enough to form. I solve this with thin foam by molding over a plug and covering the whole thing with PVC tape. The tape also shrinks as it warms forming the female part of the mold. Some expansion might be OK, just sand it straight again.

I would suggest you try a wallpaper steamer, the kind you can rent. The wet steam automatically limits the temperature to around 200F so you don't melt the foam. Plus the wet steam will be much more effective than dry air at heating the foam. Maybe you could build a box around the area to bend, pump steam into it (just like they do when they steam bend wood), then wrap it around a bending form.

[KCStudly]

They use steam in manufacturing the foam. I live within a shot of Dow's Allyn's Point plant where the blue foam is made.

One time I was startled in my house by what literally sounded like a 747 landing on my roof. I called the police and they informed me that it was the plant's steam relief valve going off during a maintenance cycle. Yeah, right, let's not scare the locals. This was not any event that had been planned, I can guarantee you that! It was ferocious even a half mile away!

So, my guess as to why nobody has tried this (perhaps even including you, GPW) is because it would be more work and material invested than just using the kerfing method that works perfectly well.

GPW hit it on the head; if for multiple unit production it might be justified to build a steam box or buy a heat blanket, but for us little guys it would be more of a science project than a practical method.

I've tried many different methods on my build, making fixtures and jigs, and sometimes it was the best way to get what I wanted done accurately and expediently. Other times, if I had it to do over (like my formed laminated galley wall hard edges) I would pick a simpler method.

I guess it all depends on what one is trying to achieve. If you want a free form shape or something that is best formed over a mold, making a large heat box might be the best way to go.

[Camp4Life]

Could you use aluminum or tin sheets and sandwich the foam? Heat the sheet and bend a little at a time. Once you have the curve you want, try prying apart to see if it stays. If not, sandwich again and apply more heat until it keeps its shape on its own.

[KCStudly]

While aluminum transfers heat well, anytime you have two materials meeting, even if in intimate contact, there is a thermal barrier formed, so that could be problematic. The fact that the insulation is an insulator even unto itself, means that it is already hard to get the heat to soak into the middle, especially when the thickness is scaled up. A shiny aluminum surface might actually reflect more heat than it transfers into the foam, depending on the type of heat source.

1/4 inch foam used in RC model building is a very different animal from 2 inch thick, or even 1-1/2 inch thick foam. Just saying.

[Camp4Life]

Good point KC. So is there really a good way to warm up foam all the way through other than letting it sit in an oven then? Hard to do with large pieces. Soak in a large tub of boiling water? There must be a way!

[GPW]

The bending jig only requires you heat a thin strip of the foam , and is bent in segments ...much easier than heating a whole sheet ... It works on the thinner foam as we’ve made many airfoiled wings like that ...
It may seem slow and tedious , but I believe it would be the easiest method (cheapest too) for at home ... Couple cheap HF heat guns , some scrap wood , piece of pipe or round closet bar ... Not much of an investment ...

[ghcoe]

I have found 1" foam that was laying over a edge bent from heat from the sun. Never did follow up on it, but thought I would mention it here to give others ideas.

[daveesl77]

Oh boy, now you guys have me thinking, which can be dangerous! Instead of just a straight bend, what about a bubble-ite, in other words a multi-directional curve for say a nose area. It would require a mould of some sorts and using the concept of steam, to literally lay a sheet big enough over the entire curve, then perhaps it can form into the curve. I might try it this week on a small scale, could be interesting.


dave

[KCStudly]

Where is rowerwet when we need him? Perfect if this could be made to work for a foamie boat. Wax your kayak, cook your foam, drop said foam on said kayak; instant boat core! (Just scaled up slightly.)

[Tempest]

The wheels are turning but no light bulbs lite yet so I have nothing to contribute! Do plan on 2" and for the moment toying with a 50" radius for a roof profile. I believe it can be done. I really do not want to kerf the bends! 2" 25 psi EXP service temp spec is 165f. Degradation begins around 392f.

[aggie79]

I guess you could use spray foam and a female mold like is done for fiberglass and carbon fiber. Build the mold, use a light webbing of headliner adhesive to temporarily adhere canvas, add battens for depth measurements and hard points for attachments, and spray way. After curing, use a hot wire knife to trim to depth along the battens. Add canvas or whatever interior finish it to be used. And then unmold the "spray in place" foamie shell.

[Tempest]

So I was checking out the 2" foam today at the HD. Has anyone experienced any problems with the factory cut kerfs in the 2" foam? I was easily able to flex it back and forth at the kerf cut. Was wondering if anyone glued inside these kerfs before using them on their builds. These factory kerfs could definitely cause issues in the bending of the foam if used with the bend instead of against the bend.

[ghcoe]

So I was checking out the 2" foam today at the HD. Has anyone experienced any problems with the factory cut kerfs in the 2" foam? I was easily able to flex it back and forth at the kerf cut. Was wondering if anyone glued inside these kerfs before using them on their builds. These factory kerfs could definitely cause issues in the bending of the foam if used with the bend instead of against the bend.

Those kerfs are break points for construction use. Set it on a straight edge, apply a bit of pressure and it will snap in a clean cut. So yeah, probably could be a issue.

[rowerwet]

Once you skin the foam with PMF the scores in the foam don't really matter.