CompositesWorld
Issue link: https://cw.epubxp.com/i/450689
39 CompositesWorld.com NEWS N E W S N S N E W S E N W S W CFRP Camera Boom already knew what insulation we needed to reach the temperatures required for full cure," explains Dietsch. "It only took us a half day to build all of the insulated boxes. We couldn't have found an oven big enough to cure the parts in the time we had, nor did we have time for a long oven cure cycle." As part of the cure regime and quality control (QC) process, part tempera- tures were monitored by thermocouples installed across the part. All parts had to meet a minimum temperature require- ment yet remain under a maximum allow- able peak temperature, but Dietsch claims that the resin chemistry's design is such that "you don't need the temperature- control software used with traditional epoxy processing." Te user can determine when the peak exotherm will occur based on the part thickness and type of tooling used. "You don't have to adjust any cata- lysts or accelerators," he points out. For this project, the laminates reached peak temperature within two hours, followed by a cool-down period of four hours. Despite the resin predictability and the simplicity of the insulation-box tech- nique, Dietsch concedes, "We could still have had issues with temperature consis- tency across the part. But the past fve years have helped us to understand the heat and energy balance." Te team, there- fore, achieved a part yield of more than 90% (less than 10% scrap) over the whole project and recorded the fastest timeline, to date, for NONA Composites-built parts. Ensuring accurate assembly All of the composite parts were laminated within a couple of weeks. It took roughly two more weeks for postmold processing of the demolded parts and then assembly of the box beam sections (Step 5, p. 37). Trimming and machining were partly done in-house and partly subcontracted. "Waterjet cutting of the fat panels was so much faster than machining in-house," Dietsch recalls. "We could do one run per day for a couple of days and it was all done." Te channel trimming, however, took more setup. So, the team did that in-house using custom-built jigs. Te C-channel and side-plate surfaces were then prepared for bonding. Lord Corp.'s (Cary, NC, US) 7545 acrylic adhesive was flled with glass microbeads to help maintain a constant bondline thickness. "We chose this because it had a short setup time — specif- cally, within a couple of hours vs. 24 hours for other systems," recalls Dietsch. "We couldn't handle that much delay in the overall timeline." Te completed box beam sections were assembled using a joint system that incorpo- rated steel connection plates and high-tolerance shear pins and rivets, for which holes had to be machined (Step 6, p. 37). "We had to create a fairly complicated assembly jig that could mate two bonded beam sections simultaneously in order to make sure each