I am having trouble with aluminum bonded panels warping during the adhesive cure process. Parts are aluminum thin skins with aluminum honeycomb core and are eventually assembled into lightweight aircraft interior doors. I remember hearing about issues due the temperature difference between the top and bottom skins during curing. Anyone know anything about this ??
This is a common problem in ski building. The industry answer is typically “ramp the heat slow and pull the part hot (ish…140F typically)”. Point is, ramping slow reduces the temperature gradient and pulling the part hot allows it to cool more evenly. Insulating the unheated platen is great whenever possible. If time isn’t an issue, allowing the resin to cure longer (or entirely) at room temp is an obvious choice.
Had problems with this using an autoclave. Insulated the top side and problem was reduced.
It’s more a problem of difference in coefficients of thermal expansion. The aluminium is 23.1 (x10^-6 m/m K) and carbon is 1.1 to 2.1. When heated the aluminium expands, the carbon adhere to it, it cools, the carbon stays put and the Ally shrinks back pulling a bow into the part. If you can prevent the Ally from getting to much heat, thus not expanding, you should be ok.
I once had a customer bring us a part to cook. When I opened the autoclave the part had bowed about 300mm over the 3m length. They blamed me until they went to demould it and found that they didn’t mould release the Ally.
Are the panels Aluminum skins on Aluminum core? No composites?
How are you bonding the skins to the core? Film adhesive and pressure?
Make sure they are the same thickness, and the ramp is slow for heat up and cooldown. Odd that you would get warping with aluminum and adhesive bonding, unless the temp difference between top and bottom is WAY off.