Many methods have been developed to perform the resin infusion in the aerospace industry, once the dry preforms are created manually or automatically. These processes are identified by different names and acronyms, which can lead to some confusion. Here is a description of some of the more widely known infusion methods.
SCRIMP (Seemann Composites Resin Infusion Molding Process) is one of the earliest patented infusion methods. It is used for many marine and Wind blade applications, but was also licensed by some aerospace firms. It relies upon the use of a flow or “distribution media” with high permeability between the layup and vacuum bag to rapidly and evenly distribute resin laterally across the part.
VARTM (Vacuum Assisted Resin Transfer Molding) is the name of the process used by Lockheed Martin that is similar to SCRIMP, but does not use a flow media. The entire fuselage of the AGM 159 JASSM missile is made using VARTM.
CAPRI (Controlled Atmospheric Pressure Resin Infusion) was patented by Boeing and is said to reduce thickness variation and result in fiber volumes and mechanical properties equivalent to prepreg/autoclave materials. First it uses vacuum debulking cycles on the dry preform to reduce compressed thickness prior to infusion. During infusion, the resin supply is held at partial vacuum, which assists in degassing the bulk resin but also reduces the pressure differential driving resin into the preform.
VAP (Vacuum Assisted Process) was patented by EADS and used in parts like the A380 Aft Pressure Bulkhead and the massive A400 Cargo Door. VAP features a gas permeable membrane placed over the infused layup, which helps to evacuate trapped air and volatiles in the infused layup prior to cure. By letting gases through the membrane (but not the resin) VAP is said to achieve lower voids and higher, more controlled fiber volume for better laminate quality.
RTI (Resin Transfer Infusion) is a Bombardier patented process used to produce the wing skins of its CSeries aircraft. Infusion of resin into the preform is performed with vacuum pressure only. However, the mold is located in an unpressurized autoclave during the infusion step. After the preform is fully infused, the autoclave is pressurized and heated to perform cure. This makes it easier to achieve high laminate quality because positive cure pressure (>14 psi) helps prevent void formation from entrapped air and volatiles. It has the drawback that a suitable size autoclave is still requited. All other methods cited above are true Out of Autoclave processes.
There are also other acronyms for similar processes, which can create a kind of “alphabet soup” confusion about infusion.
The important thing to remember is that many different users have had success making a wide range of parts (some very large and critical) using infusion processes.