Well, yeah, I can't see him, like, blasting at a pile of metal and melting it to slag, but if he had to, say, melt through a metal door or something, I suspect he could generate a lot of heat just by angling a repulsor beam to skim right over the edge of it, so the friction heat goes into the metal, and keeping the beam going for several minutes or so, without even having to jigger the electronics.

(If you need him to be able to melt a pile of metal into slag just by aiming the repulsors at it, I would go for some kind of interference effect between two different repulsor beams, where they are pushing against each other and the extra energy gets dumped as heat. Crossing the streams, as it were.)