The infusion is nice but you have to eliminate any leakage in both the mold and the vacuum bag. A leak will ruin the part because air will become entrained in the laminate. Leaks are the biggest problem with vacuum bagging. You also have to position the feed lines properly. It is not hard to figure that out but it takes practice and some trail & error before you get the positioning right for your particular project. Positioning is determined by how fast the resin flows through the laminate and how far it has to travel.
Speed of flow is determined by resin viscosity and the laminate stack and whether there is a core in the laminate (sliced and perforated) or an interlaminar flow medium or a surface flow medium.
You have to make a lot of test samples to get the technique down and to learn how to eliminate leaks in the hose connections and bag. The through bag aluminum twist lock caps work a bit better then those suction cup types and they can be purchased for 18 bucks here.
http://www.fiberglasssupply.com/Product_Catalog/Vacuum_Bagging/vacuum_bagging.html
Here are some other methods of vacuum bagging to discus.
Infusion is a method of transferring or introducing resin into the reinforcing layer. To transfer you need pressure or create a difference of pressure from the atmosphere to the part.
Resin Transfer Method (RTM) is a method wherein the resin is transferred or infused to the reinforcing fibers by a pressure pump, no vacuum. This requires a heavy inner and outer mold.
RTM- VAT is resin transfer using both pressure and vacuum assist to pull the resin in. A closed mold or vacuum bag is used. This technology was the common term when it was slowly being adapted in the U.S.
RTM VIP- Resin Transfer Molding Vacuum Infusion Process is now the most widely used term by the composite industry.
VARTM- Vacuum Assist Resin Transfer Method is purely vacuum to transfer the resin under a closed mold or vacuum bagged mold.
LRTM- Light Resin Transfer Molding came into development in Belgium about 20 years ago. It is a process where pressure pump was used to transfer resin and vacuum was used to assist. Vacuum was low, about 20 in.
Another variation of this is VARTM- UV curing, vacuum bagged process.
Vacuum bagging- prepreg molding is a process where there is no resin transfer because the resin is already impregnated into the reinforcing material and you have to cook it in an oven.
As with all of the process described, not ordinary off the shelf material will work. Resins and fabric works hand in hand to make the process work as well as the correct vacuum pressure profile over a period of time. When overdone, another problem creeps in. The laminate becomes thinner due to reduced resin content than was originally designed for. A thin laminate flexes more and stiffness is a function of thickness. Care must be exercised that there is no major deviation from design.
