Composite materials are amazing, but they have some serious downsides – especially when used in the wrong application. There are a lot of other materials that do a better job at certain things and you should look at the other options.
Make sure there isn’t a cheaper, faster, stronger, less fussy, less wasteful alternative.
Most of your alternatives will be single-material choices manufactured using well-established production methods. There are a lot of great choices that can meet similar needs to composites – and often a lot faster or cheaper – here are some examples:
- machined aluminum
- injection-molded ABS plastic
- machined high-density urethane foam
- thermoformed HDPE
- 3D printed Ultem
- fabricated titanium
- RIM molded DCPD
- cast urethane
- wood!
All these (and thousands more) processes and materials are used every day and produce the vast majority of products and components. Here are some examples where something else might be better that a fiber/resin composite – and why.
Industrial Housings
You are building body panels for a piece of industrial equipment that will be used outside. The panels are non-structural and attach over a welded steel frame and protect the equipment housed inside from dirt and impact – and they make the machine look nice. You could totally make these out of gelcoated fiberglass – the surface would be shiny and they’d be strong and stiff. But maybe too shiny… and all those molds and that need laminating. You’re going to be making a few hundred of these a year – hopefully more! Here’d I’d suggest looking into thermoformed plastic. Thermoforming requires tooling just like fiberglass, but it is simpler and the cosmetics are derived from the flat sheet feedstock, rather than from a perfect mold. It’s not perfect and the thickness of the panels is not controlled – but wow is it fast! For simple geometry, heavy gauge thermoforming makes compound curves fast and cheap and uses tough (and recyclable) plastics.
High Performance Bracket
For another example, lets say you’re building the brackets to support a piece of equipment inside the frame of a high performance vehicle. Weight is an issue. You only need one and it may need to be modified. To make this in composites (carbon of course – probably pre-preg) you will need a mold and because there are some angles and a cutout for hoses, it will not be the most simple mold ever. Here it might be good to look into machined aluminum (if it’s small) or 3D printed Ultem (or something else awesome and strong) or fabricated titanium. A machinist/welder with a waterjet and a brake could knock out a very strong and easily-modifiable bracket in a few hours – and it would be done – no curing or trimming or anything. The 3D printer could have it done tomorrow morning and nobody would have to actually DO anything except load the model and program the parameters for the print. You’ve got options – in this case maybe composites aren’t the best choice.
Ribbed Variable-Thickness Solid
Your last example is a part that has variable thickness and some holes. There are some thin areas and a flange with some ribs to stiffen it. You could mold this in a one-sided mold and then bond in composite plate ribs to support the flange and laminate over. Or if there are going to be a bunch of these, you could cast them in a two part mold using a bulk molding compound. You might want to see what the actual weight savings would be over machined aluminum. If strength is less of an issue, maybe 3D printing would do. For a whole bunch, a molded – and maybe filled – resin (RIM molding or urethane casting) method could handle the variable thickness and provide a reasonable cost per part.
Composites are Usually NOT The Best Material!
What I’m getting at here is that composites are not a universal answer. In fact they are very often NOT the best solution – so please check your assumptions. Trying to use composite materials when they aren’t the right choice is frustrating, expensive and time consuming – and it will make you crazy. But when none of the other materials can do the job and tick all the boxes, you might find that fibers and resins and cores and in-mold surface coatings are the magic mix that makes your project a success!