PROCESS CONTROL FOR MELT OVERFLOW RAPID SOLIDIFICATION TECHNOLOGY

A PROMISING NEW TECHNIQUE FOR DIRECT CASTING RAPIDLY SOLIDIFIED TITANIUM ALLOY RIBBONS FOR AIRFRAME HONEY COMB STRUCTURES WAS DEVELOPED BY RIBBON TECHNOLOGY CORPORATION (RIBTEC) WITH NASA SUPPORT. THE PLASMA MELT OVERFLOW PROCESS COMBINES TRANSFERRED PLASMA ARC SKULL MELTING TECHNIQUES AND MELT OVERFLOW RAPID SOLIDIFICATION TECHNOLOGY TO DIRECT CAST RIBBONS AND STRIP THAT ARE AMENABLE TO PROCESSING TO FOIL GAUGES. WE PROPOSE TO CONTROL THE AS-CAST STRIP'S PHYSICAL DIMENSIONS AND INCREASETHE MELT SIZE THROUGH FOUR INNOVATIVE TECHNIQUES: REDESIGN OF THE WATER-COOLED COPPER HEARTH USED TO CONTAIN THE LIQUID TITANIUM; CONTROL OF THE HEARTH POURING RATE; MONITOR AND CONTROL OF THE HEARTH WATER-COOLING SYSTEM; AND USE METALLIC INSULATING MATS BETWEEN THE TITANIUM SKULL AND HEARTH AS A BARRIER TO HEAT TRANSFER. IF SUCCESSFUL, THESE FOUR TECHNIQUES WILL BOTH INCREASE THE AMOUNT OF LIQUID TITANIUM THAT CAN BE MELTED BY THE PLASMA ARC SKULL MELTING PROCESS AND IMPROVE THE DIMENSIONAL UNIFORMITY OF THE TITANIUM ALLOY RIBBONS CAST BY THE MELT OVERFLOW RAPID SOLIDIFICATION PROCESS.