What is Vacuum Infusion?

Vacuum Infusion is the process which we use to create all of our custom composite plates here at Composite Envisions. It is also a topic we get a lot of questions on as composites aficionados try their hand at infusing their own parts or are just curious about it.

To help provide some more information on what Vacuum Infusion is we asked our friend Chris Rogers from Explore Composites to provide an overview of what this process is as well as the benefits & drawbacks to it.

What is Vacuum Infusion?

Vacuum infusion (or “Resin Infusion”) is a process of combining fiber and resin that uses atmospheric pressure to drive resin through a stack of dry reinforcement materials that are under vacuum. It’s pretty neat to watch – resin just flows into and through the stack of fiber wetting it out as it goes. The fiber is under a vacuum bag and so everything is already well compacted and pressed against the mold. When the resin has completely filled the part, you clamp off the feed lines and let it cure. The resulting part is well compacted and should have a very low void content – no air bubbles – and a nice pinhole-free surface. When all goes well it’s a beautiful thing, but the learning curve is steep, and even small mistakes can result in scrapping the whole part!

For the last thirty years, vacuum infusion has steadily become a more standard composite process. It fits in the middle between pre-preg on the higher end and hand layup on the lower. Infusion has been steadily stealing ground from both as more fabricators grow comfortable with the process and part quality and efficiency continue to improve. Even aircraft components – long the domain of pre-pregs and autoclaves – are increasingly infused as large manufacturers look for ways to decrease costs and shorten the overall build time.

Let’s have a look at the trade-offs:

The big benefits of vacuum infusion are:

  • Layup is done with dry fiber and tailoring and ply layout is not constrained by resin gel time. So you can make it nice!
  • No autoclave or oven! (except to post-cure)
  • High quality laminates with low void content and excellent core-bonding.
  • Clean, worker-friendly layup process. Only mix resin once and don’t get it on you.
  • Consistent part-to-part quality and repeatable weight. Not as good as pre-preg but better than hand layup.
  • Ability to laminate both skins and core, and potentially stringers and other structures in one shot.
  • Production-friendly for moderate volumes. Easy to control once you have a system. It is very trainable, and continuously- improve-able!

At the same time, there are a few drawbacks:

  • Mistakes can be catastrophic – easy to lose parts if the infusion goes off the rails.
  • Requires some fussy bagging work with lots of details.
  • Not suitable for high-volume production.
  • Not compatible with honeycomb cores.
  • Can be heavier than bagged wet-layup, but only because a wet-bagged core uses lighter filled resin (or air) to bond core.
  • Heavy unidirectional reinforcements can be problematic to infuse.
  • Lots of waste! Holy crap what a lot of trash – but not much worse than other similar processes.

Overall, vacuum infusion is a desirable way to build composite parts. It has a lot of the benefits of pre-preg in terms of detailed layups and thick laminates, but it’s cheaper and faster and doesn’t require an oven or  autoclave. Compared to open molded or vacuum bagged wet layup, it is much cleaner and more consistent – and the resulting laminates have a much lower void content. After decades of steady development, vacuum infusion is a mature technology with well-established processes, support products and equipment.

You can read more of Chris’ insights and tips at  https://ExploreComposites.com/ . We will also be featuring more of Chris’ advice and information here at Composite Envisions on an ongoing basis.