Infusion molding is one way to make large composite structures such as turbine blades. Briefly, fiber plies and other
The Turbo Auto Sprue, a pneumatically controlled injection valve, lets mixed resin pass into a mold cavity. When it fills, the valve closes and gets a flush of acetone from the mixing machine and a blast of air to dry it, leaving it clean for later production.
materials are laid in a mold, covered and sealed with a flexible film, subjected to a vacuum, and infused with catalyzed resin. The method allows pulling air-free resin throughout the material. But the method has relied on conventional valves and a lot of manual skilled monitoring.
U.K. manufacturer MVP says it has improved the method with “fIRST”, ( Film Infusion of Reinforcement Systems Technology) a composite molding method that improves resin handling and delivery for infusion molding. “Improvements focus on the direct feed of the infusion mold from a high output, meter-mix machine and brings precise control to infusion molding,” says MVP’s Alan Harper.
The conventional process often uses a resin feed from a pre-mixed bulk holding tank and from which a mold is fed through many disposable large-bore pipes and flow controlled at each entry point by experienced operators. To provide sufficient open-gel time, workers catalyze resin in batches and refill a holding tank so fresh resin is used as the infusion proceeds. A first concern is that the holding tank never runs out between each refill. Another concern is to exclude air when refilling because it may enter the closed infusion mold and remain as void contamination.
But why place mixed resin in a holding tank in the first place to feed an infusion mold when a meter-mix machine can eliminate the need and directly supply the mold without involving consumables? “Such a delivery system can be thought of as an infinite volume holding tank of mixed resin,” says Harper. The problem has been that some meter-mix machinery delivers pressures too great for an infusion process. “This concern, however, is no longer an issue because fIRST provides precision inlet pressure control at the mold face monitored from directly under the film,” adds Harper.
Using the Turbo Auto Sprue (TAS) injection valve at each injection port, the machine delivers the resin at up to 8 bar pressure and flow rates from 0.5 to 50 l/min. (1 lb/min to 110 lb/min). “Signals from properly placed pressure sensors tell when to open or close each valve. Sensors are directly connected to each local inlet control valve at the mold face and need no lengthy and complex control lines,” he adds.
Resin is mixed on demand and catalyzed as needed by remote control through an all-pneumatic operation including, when needed, programmed changes on the fly. Harper says many previous approaches to the problem attempted to control the machine output to internal pressures measured under the infusion film. However these pressures vary greatly depending on location, fiber loading, and infusion stage. Hence, signals from multiple sensors are needed to assist controlling many injection points.
“The new equipment makes this complex operation more practical,” says Harper. A more cost effective and simpler approach is now offered with new rugged and locally powered pneumatic sensors for direct feed infusion.
He adds it would be hard to say when the breakeven cost point is reached compared to filling a mold by conventional tanks, pipes, and manual feeding and control. On a large infusion job, labor rates, consumables, and waste are built-in costs for every cycle, so breakeven would not be more than 5 to 10 cycles or sooner, before a fIRST system pays for itself. Also, the equipment provides a higher degree of optimised, and repeatable infusion control with lower risk of mishap. WPE
A basic three-inlet infusion resin mold shows its simplicity over other schemes. In operation, resin is fed to each inlet Turbo Auto Sprue valve. The pressure sensed under the mold film lets controls open or close the valves. As pressure builds to near atmospheric, the valve closes until the mold fills. The set up repeats for many infusion points on the structure all fed from one machine and all cleaned the same way leaving no disposable pipes or resin containers.
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