Hi there,

I Have a large 6 Piece split mould for the main shell of a car body (1 Piece front end moulds and door moulds separate). Problem is that it doesn't have any wide flanges around the perimeter of the mould for the vacuum spiral or any sort of resin break. Instead of adding flanges could I envelop bag and run the vacuum spiral on the back side of the mould? Also by waxing the back of the mould I could run the peel ply around the edge on to the back side of the mould about 75mm to create a large enough resin break?  Or am I better to add wider flanges to the perimeter of the mould? Whatever I do I will be Envelop bagging. 

Thanks

You are always going to be better off adding flanges. For one, they will add a lot of stiffness to the mould, which may be important when envelope bagging as those forces can cause a bit of twisting. Depends how solid the current moulds are.

Second problem is that envelope bagging and infusion will lead to a lot of resin bleeding on to the back of the mould. For one this wastes a bit of resin, but more importantly it will cause lots of razor sharp ridges that will need to be ground off before you can use the mould again. Obviously if you only need to use the moulds once then no problem, but it's quite a lot of work when you do need to use the moulds again, especially on moulds that size. Given you are planning on envelope bagging regardless this may still be an issue for you, however with flanges you can at least run bagging tape around the flanges and seal that resin in to the correct side of the mould.

Thirdly, you don't have anywhere to place your resin inlets and outlets. If you place them directly on to the reinforcement, you will end up with this printing through on to the surface of the part unless the parts are quite thick. You can try placing them on the underside of the mould, but this will certainly lead to a lot more of the aforementioned razor sharp ridges, and possibly flow issues.

And finally, making parts without having a flange to allow excess material to extend past the edges of your part can cause issues. If you try to trim your reinforcement flush with the edges, it will inevitably dip below that when you apply vacuum and leave your part short of where it should be. If you try to leave the reinforcement oversize it will likely wrap on to the back of the mould and bond. You can then grind this off, but it's a bit of work again and might make a mess of the mould.

All of that said, what you are suggesting will work. It just isn't as good as having flanges. Having used flangeless moulds for infusion before, I don't recommend it - least of all for moulds of that size. But if time/budget doesn't allow for adding flanges, then you can still make it work.

+x

 

Hanaldo - 5/25/2019 1:35:31 PM

You are always going to be better off adding flanges. For one, they will add a lot of stiffness to the mould, which may be important when envelope bagging as those forces can cause a bit of twisting. Depends how solid the current moulds are.

Second problem is that envelope bagging and infusion will lead to a lot of resin bleeding on to the back of the mould. For one this wastes a bit of resin, but more importantly it will cause lots of razor sharp ridges that will need to be ground off before you can use the mould again. Obviously if you only need to use the moulds once then no problem, but it's quite a lot of work when you do need to use the moulds again, especially on moulds that size. Given you are planning on envelope bagging regardless this may still be an issue for you, however with flanges you can at least run bagging tape around the flanges and seal that resin in to the correct side of the mould.

Thirdly, you don't have anywhere to place your resin inlets and outlets. If you place them directly on to the reinforcement, you will end up with this printing through on to the surface of the part unless the parts are quite thick. You can try placing them on the underside of the mould, but this will certainly lead to a lot more of the aforementioned razor sharp ridges, and possibly flow issues.

And finally, making parts without having a flange to allow excess material to extend past the edges of your part can cause issues. If you try to trim your reinforcement flush with the edges, it will inevitably dip below that when you apply vacuum and leave your part short of where it should be. If you try to leave the reinforcement oversize it will likely wrap on to the back of the mould and bond. You can then grind this off, but it's a bit of work again and might make a mess of the mould.

All of that said, what you are suggesting will work. It just isn't as good as having flanges. Having used flangeless moulds for infusion before, I don't recommend it - least of all for moulds of that size. But if time/budget doesn't allow for adding flanges, then you can still make it work.

Thanks for the reply Hanaldo.  Other option may be to use MTI hose which may make life easier.