Different Aero Manufacturing Processes

Owned by Tommy Tran
Last updated: Jan 21, 2021 by Maciek Pajak (Deactivated)
4 min read

The method we will be using for MSXIV will be Prepreg, although resin infusion is a viable option, it is a nightmare to set up and we have been advised against using it.

 

For more information on prepreg, visit this confluence page: Basic Composites Knowledge.

 

Although prepreg is the optimal method, we must take the following things into account for making a perfect part:

  • The cost as a lot of the equipment needed for this method is specialized and can be quite expensive

  • Being able to control temperature and pressure since they’re paramount for prepreg components

  • Temperature and pressure can be easily controlled by an autoclave but, campus autoclaves most likely won’t be large enough and those machines come at a very high cost

The following research I have conducted aims to combat these issues and find cheaper ways to do prepreg that we could easily emulate for MSXIV.

 

Ovens

The first method I found was the use of an oven in place of an autoclave. Although an oven can’t directly control the pressure of a part, there are two ways we can go about this. The first is by vacuum bagging our carbon fiber panel and putting it into the oven without an active vacuum connection and the other is by doing the same thing but, with an active vacuum connection.

The following information was summarized from this Beginner's Guide to Out-of-Autoclave Prepreg Carbon Fibre.

 

Process:

  • Perform a normal prepreg setup

  • Perform a vacuum leak drop-test

    • After we’re done setting up our prepreg part, we switch off the vacuum pump and close the vacuum valve on the bag and wait 30 minutes

    • After 30 minutes we should see how the bag feels and it should feel perfectly tight

    • Then switch the vacuum pump on with the vacuum valve on the bag closed, familiarize yourself with the tone of the pump and then open the valve on the bag. If the tone of the pump changes that means you have a leak, if not then you have a perfect and can go straight to curing.

  • If you aren’t using a vacuum connection while curing, preheat the oven to 80 degrees C and place the part into the oven for 8-10 hours.

  • If using a vacuum connection, run a silicone hose through a hole in the oven and connect it to the vacuum bag and run it throughout the curing process

    • During this process, it is also advised to attach a vacuum leak-flow indicator in-line with the silicone hose to serve as a useful visual indication of any problems occurring inside the oven, if it starts spinning, there is a problem whether there is a leak developing or the bag bursts.

    • The following is a picture of this small device attached to the hose:

 

  • Once the curing process is done, let it sit for a couple of hours to cool down to room temperature before de-molding.

  • The final step is finishing the part if the panel doesn’t come out with a high gloss finish.

No vacuum connection:

This method involves the normal setup for a prepreg part but then we just put it in an oven.

Pros:

  • Relatively easy on paper

  • Need less specialized equipment

Cons:

  • Need to be perfect while sealing our vacuum bag as one leak could ruin the part

  • Overall could be riskier than just using a vacuum connection

 

With a vacuum connection:

This method is identical to the method without a vacuum connection but, during the curing process, we have a hole in the oven that we feed a vacuum silicone hose into that can compensate for small leaks in the vacuum bag.

The reason we use the silicon hose is that with a standard PVC hose, at 100 degrees celsius, the hose will soften and collapse at elevated temperatures whereas a silicone hose will not.

Pros:

  • Much safer than the other method

  • We don’t need to be as meticulous with sealing our vacuum bag

Cons:

  • Need to make a hole in an oven

  • Needs more equipment than the previous method

 

Conclusion

Although this process is simple enough, there is one problem that arises, finding an oven that would compensate for our task. Unless we buy our own oven, we will have to outsource and I doubt that a company would make a hole in their oven just for us so, we’d have to do the process without a vacuum connection. If we can somehow get a vacuum connection into a regular industrial oven, great but it may be unsafe without the proper setup.