I have been doing weld repair on alumium plates using straight helium, TIG process, DCEN, 4043 filler rod. Plates are used for injection mold prototypes. Using AC with a balled tungsten was not practical given size of plates. However, sometimes I am required to weld down inside a slot. The helium burns so hot that sides of slot melt before bottom. Have tried a mixture of 75% argon/25% helium. Mixture did not burn hot enough. Would a mixture of 75% helium/25% argon give me more control? Or perhaps some other idea? Thank-you!