Vacuum Bagging Process vs. Vacuum Infusion
This article is about the pros and cons of the vacuum bagging process and the resaons to switch over to the vacuum infusion process. The vacuum bagging process utilizes a flexible and transparent film (ie: fabric, nylon, rubberized sheet or plastic) in order to fully enclose and compacting the wet laminate by using atmospheric pressure. This process is also called vacuum bagging for short as it uses a vacuum and pump to extract the air from inside the vacuum bag and compress the part under atmospheric pressure in order for the compacting and hardening process to take place. Vacuum bagging is an upgrade of the wet lay-up process and is widely spread in the composite industry because of its clear benefits over this method. You will most often see the use of fiberglass, carbon fiber and resin materials being laminated together using the vacuum bag technique. The outer atmospheric pressure caused through the vacuum within the closed system will compress the laminate and excess resin is sucked out of the wet laminate into the bleeder cloth and resin catch pot.
Parts and moulds placed inside the bag will undergo a pressure rating of up to 29.92 inHG, which then results in an equivalent of 10to./m2. The bag may come in a flat sheet or tube and custom applications can also be created for specific and unique parts for your needs. One area of caution is to pay particularly close attention to the tightness of the bag on the part. The accurateness of bagging the part is crucial for proper results. Too tight and the vacuum film will bridge over various complexities of the part. In order to ensure full pressure on the part, the bag should be large enough and loose enough to conform to its entirety without voids once pressure and the vacuum is applied for compacting the laminate. When done properly, atmospheric pressure is applied uniformly and the parts inside the bag are held tightly together during curing with the vacuum being present throughout the entire process.
Benefits of the Vacuum Bagging Process
There are advantages for using vacuum bagging over conventional lay-up methods. The first is that the finished product will yield a better strength rating and be lighter. Parts that are stronger yet lighter can have a serious competitive advantage over others, especially since they are more durable and use less resources and material. This is most evident when comparing the ratio of glass to resin which is better accomplished under the vacuum bag molding process. Another benefit is that the process is relatively easy to switch to and materials for basic parts are inexpensive and easily obtained.
Disadvantages of the Vacuum Bagging Process
But there are also some apparent disadvantages to vacuum bagging as well, particularly if we compare the Vacuum Bag Process with the state of the art production processes, including the Vacuum Infusion Process with the MTI hose.
- The process of vacuum bagging begins with the production of an oversaturated laminate. Applied vacuum pressure then removes excess resin; however the amount removed will depend on multiple different and critical variables that may be hard to control.
- Removing excess resin, which was first brought in, is a clear waste of money and resources.
- In larger projects, it is also necessary to apply the vacuum bagging process a couple of times since the resin pot-life is the limiting factor.
- The amount of resin that is removed from part to part can also vary substantially depending on the timing of the vacuum pressure being applied.
- The process of bagging can become rushed opening up the opportunity for error if a leak in the vacuum seal occurs and cannot be immediately located.
- Producing hand- lay-ups means bringing in a sizeable amount of air bubbles which become entrapped in the reinforcement fabric during the production process. It is a myth that embedded air can be sucked out through the application of a vacuum. Instead, using the vacuum bagging technique afterwards will lead to the growth of those air bubbles, causing voids in the laminate and surface.
- Unfortunately with bagging, the fiber to volume ratio cannot be successfully calculated as it can with other processes, and over-bleeding or dry laminates can be a large concern.
- Bigger and more complex lay-ups also require additional helpers, increasing labor needs and support.
- Another imminent disadvantage with hand-lay-up and bagging is that the process must be completed once started, with no option to pause or take a step back.
- There is a clear time and forgiveness disadvantage in wetting-out and squeegee processes with a race against the resin pot-life and getting all of the materials in place.
The composite industry welcomed the vacuum bagging process 20 years ago because of its ability to offer a more consistent, thinner, lighter and stronger product in comparison to wet lay-up. But the Vacuum Resin Infusion Process particularly if the MTI hose is applied is the latest cutting edge technology for today’s most competitive needs.