Custom Extrusions for FRP Panels

[Alloy]

Because you can get them in 90 deg angles but if you want something different, you have them custom made.

Formable aluminum: Press brake bending 6061 with the 20% rule

Areas to consider for formable aluminum are formability, thickness and bend radius, tensile, yield, and elongation, and how to deal with bending tempered materials. Learn more here.

www.thefabricator.com

"6061 is the most versatile series within the heat-treatable family of alloys. In its annealed state, 6061 can be formed since the elongation is up to 18 percent and the difference between yield and tensile strengths is 10 KSI. However, as you move down the list of tempers, from annealed to T4 or T6, formability changes. This aluminum series’ ability to bend tends to decrease with temper. Bending these tempered alloys is not impossible, but it is very difficult and will most likely require larger bending radii to avoid cracking on the outside of the bend or completely fracturing at the bend line."

You can make a sharp bend in annealed and weak aluminum. For high strength aluminum you need a large radius which isn't ideal for panels that have sharp corners.

Stainless steel is much better in this application... custom angles for edge protection.

There's no need for 6061.

Custom shapes can be made from 5052 or 5086 alum. easier than stainless.

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[rruff]

Though not in the high strength category, those alloys are fairly strong and would be a good choice for forming.

 

[The Artisan]

Though not in the high strength category, those alloys are fairly strong and would be a good choice for forming.

Only downside on the 14ga angle is it added another 375lbs to my 455lb pod being 12.4 x 7.4 x 7 is not bad. If I hand lay 12k cf then total weight is less than 500lbs
Kevin

 

[rruff]

Ya, steel angle that thick is a bit much...

I'm kinda liking the idea of building a custom fiberglass and epoxy exoskeleton and gluing panels into it. Considering all the problems I have using Sketchup, that would probably be an exercise in frustration, though...

View attachment 699831

I thought you had PU foam core on your panels? That shows plastic honeycomb...

 

[Peter_n_Margaret]

I thought you had PU foam core on your panels? That shows plastic honeycomb...

Well spotted.
I did have some polypropylene honeycomb in the first batch of panels 17 years ago. It was a tad cheaper. A big mistake. Heavier and lousy insulation.
The new build has all PU, all except for the floor which is a PET foam chosen for its higher crush resistance.

There is sandwich panel and there is sandwich panel.
All of the current build panels are made wet-on-wet. In other words, the gel coat goes down on the table first, followed by the glass and resin, followed by the foam, followed by glass and resin and it is all vacuum bagged wet together.
Makes for much better panels than gluing pre made skins to foam. The only down side it the top skin is not nice and smooth gel coat, but that is a small price to pay.
Vanglass in Queensland can make panels over 2.5m wide and up to 11m long in one piece like this, then CNC cut it so it is like an IKEA flat pack to assemble. Or you can cut it yourself.
Cheers,
Peter
OKA196 motorhome

 

[Peter_n_Margaret]

An example of how strong these glue joints with sandwich panels can be .....
I mentioned earlier that the vehicle had a major prang a couple of years back. It rolled down a steep hill with no one on board. Took out a 200mm diameter tree, then launched itself to become air borne across a creek and hit the bank on the other side hard enough to smash the front axle housing (including the axle inside) and bend the chassis.


The ovehead cupboards inside were simply butt glued to the walls and ceiling (with Sikaflex 252). No rebates and no aluminium or other reinforcing supports of any kind. They were all full of "stuff".

Not a single glue joint failed anywhere on the vehicle. Not one.
There was cracked paint that was evidence of movement, but no failures of any kind.
I have since glued in aluminium angles to those joins, but I think they are well proven.
Cheers,
Peter
OKA196 motorhome

 

[rruff]

All of the current build panels are made wet-on-wet. In other words, the gel coat goes down on the table first, followed by the glass and resin, followed by the foam, followed by glass and resin and it is all vacuum bagged wet together.
Makes for much better panels than gluing pre made skins to foam. The only down side it the top skin is not nice and smooth gel coat, but that is a small price to pay.

I used PVC foam with epoxy and either fiberglass or carbon... and no vacuum bagging. I guess you needed to overlap cloth so that will always make ridges (as did mine).

How do you join the pieces? A big downside to wet layup is all the sanding... at least the way I'm doing it!

 

[simple]

Well spotted.
I did have some polypropylene honeycomb in the first batch of panels 17 years ago. It was a tad cheaper. A big mistake. Heavier and lousy insulation.
The new build has all PU, all except for the floor which is a PET foam chosen for its higher crush resistance.

There is sandwich panel and there is sandwich panel.
All of the current build panels are made wet-on-wet. In other words, the gel coat goes down on the table first, followed by the glass and resin, followed by the foam, followed by glass and resin and it is all vacuum bagged wet together.
Makes for much better panels than gluing pre made skins to foam. The only down side it the top skin is not nice and smooth gel coat, but that is a small price to pay.
Vanglass in Queensland can make panels over 2.5m wide and up to 11m long in one piece like this, then CNC cut it so it is like an IKEA flat pack to assemble. Or you can cut it yourself.
Cheers,
Peter
OKA196 motorhome

Makes sense that adding a thicker glass layer to both sides of the sandwich would be more impact resistant but I imagine it doesn't necessarily make it a lot more rigid than an FRP skin. Do you use glass mat or woven? How thick is the glass that you use? Would an equivalent thickness FRP skin have the same impact strength characteristics?

 

[rruff]

The answer to your last question is no... but it should be lighter for the same thickness because there is more resin and less glass.

I don't know what Peter's skins are, but on most of mine I used a layer of 17oz 45/45 biax, 10oz 0/90 biax, and 6oz plain weave, so 33oz of fiberglass per side... and a core of 1.5" 4 lb'ft^3 PVC. Each weighs about 0.5 lb/ft^2 for 1.5 lb/ft^2 total.

The FRP skins I've seen have higher resin content (and are polyester not epoxy) making them less stiff and strong but also a little lighter (for the same thickness) vs what I made. I measured a bunch of my samples for stiffness and they were stiffer than FRP data I found ... spent way too much time playing with samples! Peter is vacuum bagging so he should have a low resin and high glass content.

In the grand scheme of things I don't think it matters much, because it doesn't take anything fancy to make these boxes stiff and strong *enough* in bending. Impact resistance or resistance to pulling the skin off the foam (ripping the foam apart) are probably more important. Strong foam certainly helps there. No idea if a thinner but stronger skin would be better or worse at resisting impact than a thicker but equivalent weight, weaker one. But I did notice that fiberglass was better than carbon at taking impact in my testing.

All of the current build panels are made wet-on-wet. In other words, the gel coat goes down on the table first, followed by the glass and resin, followed by the foam, followed by glass and resin and it is all vacuum bagged wet together.

How do you get that all put together before the resin cures?

 

[Peter_n_Margaret]

I am not making these panels, this is how my supplier makes them. Too hard for me, although a friend made his own by vacuum bagging them in his shed.

Cheers,
Peter
OKA196 motorhome

 

[WanderingBison]

I suspect there was “a bit” of sanding on this one - beautiful habitat.


Sent from my iPhone using Tapatalk Pro

 

[Victorian]

I have worked at a semi trailer factory in Germany where we wet lay the FRP/Foam panels. What a mess! The factory did it because of cost and speed. With heated moulds (up to 40' long) we could make several panels per 8 hour shift. If you vacuum bag it needs to sit for pretty much a full day. That is why we run 8 tables at 40' length in a climate controlled room.
Down side between wet layup and the way we make our panels is weight. You will be hard pressed creating an insulated FRP/Foam/FRP panel that is as lighter with the same strength as with a Skin lay up. If you need additional strength in crucial spots (like the floor or alcove) you can embed internal members to help increase the stiffness and tensile strength.

Basically, both systems have valid points but both come with compromises . (weight/cost)

 

[PacificNorthWestJeeper]

All good ideas, thank you... Any others?

 

[PathNotTaken]

Some great info in this thread. Thought I should chime in as I’m currently ordering the aluminum for my panel framing. I personally think aluminum is a great option for the DIY box here. As @Victorian pointed out, custom fiberglass extrusions isn’t really an option for the DIY’er, so you’d have to glass them yourselves. As I’ve learned, at a certain point you can’t learn to make everything as your build will take you a decade!

Anyways, deciding the thickness has been my primary concern. I had been planning .125 for the longest time but am now considering .100 for slight weight savings. at the end of the day it really shouldn’t matter since this thickness isn’t where the box strength is coming from. Atleast that’s what I’m trying to convince myself.

 

[OldGreen]

I made DIY composite panels with mitered edges. I used aluminum angle on the outside and 80/20 on the inside. The inside framing provides the base for all of the inside structure. So, it essentially is an internal roll cage. Anywhere that the framing is connected to the walls is 3M VHB tape. In fact, I used VHB to connect the box to the frame. It has been in HARD service for almost 3 years. No issues. Everything is integrated. Build thread: https://forum.expeditionportal.com/...verland-trailer-to-be-towed-by-a-jeep.223957/