Hi, 
I've having issues with bridging when trying to do a 5mm thick carbon/kevlar shell for a robot project of mine, im a machinist and have done fibreglass moulds for customers before but never a carbon fibre one, i think i rushed into machining the mould has i thought i would be able to wet lay carbon fibre sheet and resin like fiberglass, i've had 2 failed attempts trying to wet lay with struggling to get the fabric into all the contours with trying to get a quite thick wall thickness, i phoned easy and they said resin infusion is the way to go with using a tack spray to hold the fabric is place until the vacuum and resin is in, i purchased the kit and have tried the infusion but i think i haven't left enough flange around the base to have excess fabric pull its way down has i've had a better finish but still bridging/not taking the full shape, could this be the issue?, i can machine another mould with a 50mm flange around rather than the 25mm i have at the moment 



Thanks
Andy

What vacuum are you pulling? and if you are worried about the size of the flange you can always envelope bag it if the flange is too small. Do you have a picture of one of your infusions that went wrong? Might help in getting you the right answers.

I don't think pre-preg is necessary here, in-fact it would be a bit trickier than infusion would be for a beginner - all those grooves and deep recesses are very likely to catch one out. Not to mention Andy is using a carbon/Kevlar layup, so your conventional OOA pre-pregs aren't an option.

Stick with infusion Andy, there's nothing wrong with that. Your flanges are small, and if you are wanting to make 20 or 30 of these things then ideally I would remachine the mould with bigger flanges. But if this is a one off or less than 5 at the most, then stick with what you've got and envelope bag it as Drippy suggested. The important thing with infusion is to really take your time making sure that everything is completely down against the mould surface. You should be able to press down all areas of your reinforcement without feeling or seeing any movement at all, if anything moves then you need to keep positioning it. Spray tacks can help, but then can also work against you and hold the fabric where you don't want it to. Position the first layer of dry fabric loosely into the mould first, and then starting from the deepest area give the the mould a very light mist of adhesive and position that section of carbon. Once the deepest section is in position, move on to the the next deepest areas, and repeat this until everything is in place. Then repeat again with your next layers of reinforcement until you have all the layers firmly in place. Go over everything a dozen times, and if you suspect any bridging then continue working the material until you're sure it is tight to the mould.

Then position your peel ply. You can tack this into place, but it is often easier just to use a lot of excess and loosely position it for now. Do the same with your perforated release film if you're using one, and finally with your infusion mesh. I would suggest using a knitted infusion mesh on a part like this, but the regular stuff will work if you are patient and make sure you have a decent amount of excess. You can also place relief cuts in this, or even cut it into smaller pieces to make sure it can move around relative to itself - just make sure that you have sufficient material so that the entire piece is covered, you don't want gaps between your flow mesh. Position any spiral hose and infusion connectors and then you're ready to bag. Stick the whole lot in an envelope bag, and pull a partial vacuum so that you can still easily slide things around. Now is when you make sure you haven't got any bridging in your peel ply or other consumables. Take your time again going around, firmly pushing things into place. Pull a bit more vacuum to assist you, but if you haven't got everything in place then let the vacuum off again and keep trying to manipulate the consumables into where they are supposed to be. Be very patient and gentle, you need to make sure there is no bridging but you also don't want to be too aggressive and put a hole in the bag. You'll get there.

When you can pull a full vacuum, everything should be very tight to the mould. Have one last final check of everything making sure there is no movement or 'spongy' feeling when you press down on everything. Then proceed with your vacuum leak down test, and if all is good, proceed with the infusion. From here it is hopefully happy days! If things don't work out as planned, then as Drippy said, photos would let us help you.

OOA Aramid/Carbon mix :-)



Rarely use the wet stuff these days, so messy and time constrained unless using infusion (which is a bit of a faff IMO) There are even prepregs that don't need to be kept in a freezer!

However, each to his own :-)

Dont get me wrong, I'm all for pre-preg! I use it for most applications. I just dont think it's necessary for this job, and isn't really any more suitable than infusion is. Hes already bought the infusion kit, so for me there's no point investing more money in a different setup.

Thank you for the answers and suggestions 
I will have another go taking extra care and see how it turns out, will post a few pictures if theirs anymore issues

+x

 

Steve Broad - 8/6/2018 6:24:57 PM

+x

 

Andy - 8/6/2018 2:58:37 PM

Thank you for the answers and suggestions 
I will have another go taking extra care and see how it turns out, will post a few pictures if theirs anymore issues

Post photos of the finished item please, good or bad :-)