CAMX 2016 kicked off with pre-conference tutorials on Monday. Early birds could choose from one of six in-depth presentations covering everything gel coat application technology to composite test methods.
The morning tutorial on resin infusion and liquid molding technologies was led by Dirk Heider, associate professor in the College of Engineering at the University of Delaware and assistant director for technology at the Center for Composite Materials. His comprehensive presentation covered the basics of liquid composite molding, analytical and finite element infusion simulation, sensors and control, preform technology and more.
“There are a lot of variations in liquid molding processes, but why do we want to go the liquid molding route?” asked Heider. He cited a few reasons:
- To get a high fiber volume fraction, typically ranging from 40 to 60 percent.
- To reduce cycle time compared to the injection molding process.
- To utilize low viscosity polymers.
Heider then discussed several types of liquid molding processes, highlighting their benefits:
Compression Resin Transfer Molding – C-RTM is rapid because channel resistance to flow is minimal and infusion distances are governed by part thickness. In addition, two- to three-minute cycle times are possible, including the cure of fast-acting resins.
Wet Pressing – This process has the same benefits as C-RTM, but the infusion process is simplified as the resin is already applied on the preform surface. You can use fiber mats made from recycled fiber pieces. In addition, because there is no cavity pressure, wet pressing requires a less sophisticated tool design and less press force.
Vacuum-assisted RTM – Low-cost, one-sided tooling can be used in many applications. A high fiber volume fraction (approximately 45 to 55 percent) is adequate for many applications. Another benefit is low void content (typically below 2 percent). Also, unique structures can be fabricated, such as large-scale applications and complex geometries. It also offers reduced emissions compared to hand lay-up.
Liquid composite molding is utilized in many industries, including marine, wind energy and aerospace. Infusion technology was adopted by marine as far back as the late 1980s because of its repeatable quality, low VOC emissions, corrosion resistance, increased stiffness and minimum weight for top-side structures. The technology is now used for commercial boats up to 100 feet long and naval hull structures measuring more than 200 feet.
Most wind turbines have used infusion technology since the late 1990s because of the high fiber volume fraction, relatively low cost and faster production times compared to prepreg. Blade sizes range from several feet to 200-feet long for offshore applications.