Back-Tension Drawing Process

Back-tension drawing, a novel drawing process and a manufacturing method capable of producing precise complex structural shapes, was successfully demonstrated. Rough extrusions of AISI 4340 steel were drawn to precise T sections with a web thickness of 40 mils. In Phase 1, a special hydraulic drawbench capable of independently exerting up to 25 tons of back-tension (back pull) force to a workpiece was designed, constructed, and operated. In Phase 2, comprehensive tests using AISI 1010 and AISI 4340 round steel bars were conducted to establish the relationship between the principal back-tension drawing variables. It was clearly demonstrated that back-tension is capable of greatly reducing the die stresses. In Phase 3, more than 200 drawing operations were performed on extruded AISI 4340 steel T sections. Steel T's having a height of 1 inch, a width of 2 inches, and section thicknesses varying between 0.080 and 0.090 inch were successfully drawn to 0.040 plus or minus .001 inch thickness. The as-drawn T's were straight with negligible bow, twist, or camber. In Phase 4, preliminary attempts were made to apply the process to 1-inch by 2-inch by 0.10-inch T shapes of the alloy Ti-6Al-4V. Back-tension stress levels of 70 to 80 percent of the material yield strength were required to control bow, twist, and camber in drawn sections. (Author) Errata sheet inserted.