Iam very new to the whole world of carbon fibre. I might be asking a question that will invite some differences of opinion but here go’s…
What advantages of using prepreg rather than resin infusion ??
I know costs fall on the side of resin infusion but is it the case that prepreg is lighter and stronger ???
advantages… a few off the top of my head (in my opinion)
easier to work with pre preg for difficult layups than dry layup
Easier to cut and kit on CNC fabric cutter with pre preg (allows for very intricate and detailed kits)
Better control of resin content in a part
Can make parts from unidirectional, thus a much higher fiber volume
Less wasted resin
Ability to use high temp resins
cleaner and easier to work with than dry fabrics
Potential for different curing methods including bladder molding, thermo expansion molds, RTM, press parts, oven cure, autoclave cure, etc.
Being a temperature cure, potential for parts that don’t need post cure.
price… Can be good if purchased in quantities.
No ‘setup’ of the feed system you’d use in VARTM
More even laminate thickness
Ability to use automated layup ATL
wide selections in resin systems
These are just off the top of my head… Each process has it’s advantages and disadvantages. (which listed none here) If I could, I would only use prepreg for personal projects. I would obviously use whatever process was best for the part, price, experience level, or other requirements of the job. Since working with prepreg, I really appreciate the versatility in what geometry can be used and the ease of layup on complex shapes. Having to store in a freezer and use the oven, are however a pain… especially when working on projects at home.
Thats really helpful Sammy thanks, if you were selling a part made from prepreg that has a equivalent made from resin infusion from somebody else , how would you sell your part over the resin infused one ?
It’s horses for courses, it really is. Pre-preg isn’t necessarily better than infusion, it’s just a different process.
The advantages of it really come down to the component you are making. If I was making a vehicle bonnet for example, that’s big and relatively flat and needs a fair bit of thickness, there’s really no advantages to making it in pre-preg what-so-ever. However if I was making a much more complex shape, something that absolutely couldn’t be done without creating templates etc. then pre-preg wins all day long.
It’s more about which process is going to make your job easier. Pre-preg can definitely be much quicker to cycle, you can fully cure a part in 8 hours or even 2-4 hours if you can use that much heat. There’s no consumables to remove afterwards, so demoulding is literally a 2 minute process (something I have really come to appreciate). Also if you need a high Tg, pre-pregs are generally going to handle at least 120 degrees whilst a high Tg infusion epoxy is much harder to find and very expensive.
On the other hand, with infusion you can throw your whole laminate stack onto the mould in 5 minutes, get it roughly into shape and then pull a vacuum to get it completely down. You don’t have to spend the time creating templates and laying up each individual piece (which is definitely an advantage if you don’t need to do it). You have the ability to use literally any material that you like, from carbon to fibreglass to Kevlar to flax and jute and diolen and Alufibre - hell you could infuse a pair of denim jeans and a handful of leaves if you wanted to. This makes the process a hell of a lot more versatile.
Simply put, don’t buy into one process being better than another. If someone tried to sell me a pre-preg part over a resin infused one then I would likely walk away from them. The process used to make the part doesn’t necessarily make it a better part, far from it.
I’d sell them the same way… they could potentially be pretty much identical. The fabrics and resin system could be the same or very similar. Like Hanaldo says, it’s a process. The difference in selling one over the other is really just cost. Cost from time, materials, tools. If you’re setup for pre preg, then you’d use that and vice versa for infusion. Some times you might have to step out of your comfort area and expertise, and use a new process when the one you like and are used to doesn’t work or if it would be too expensive. A well designed part should be able to do the job required regardless of which process you choose. I personally have access to pre pregs and tools and what not, so I would go with pre preg most of the time. Even on the car bonnet, pre preg would be very easy to make a simple shape with.
Like any job, you would figure out what the costs are for you and decide which process would make the most sense. There are many factors to deciding a process. Time, cost, expertise, facilities, etc. If you had a cutting machine, freezers, ovens, etc, you’d be using prepreg. But then you’d also need high temp molds, design experience with higher temp materials, and ovens with good temperature controls. These are the things that would keep most people out of prepregs. That and the cloth is pretty pricey if you’re buying by the yard… could be $100/yd for prepreg cloth. If you had a supply of materials, it would be cheaper. In that respect infusion might win out in cost for a one off or small production run. If you needed 100+ parts, then investing in prepreg process tools/facilities might be worth your while.
I mean wet layup is not a bad process either, you use what you have initially… trial and error is a good expensive teacher lol!