A portable hemming apparatus includes a support structure, a plurality of modular self-contained hemmers disposed about the support structure and at least one pneumatic drive mounted on the support structure. Each modular hemmer includes a hem die holder, a hem die fixed to the hem die holder and a movable hem punch. A hem operator is operatively connected to each modular hemmer. Each hem operator is a lever arm assembly. Actuation of the drive moves the hem operators and causes the hem punches to close and open on the hem die, allowing for the hemming of a metal panel located within the modular hemmers. The support structure of die hemming apparatus can be adapted to be mounted on a robot arm, mounted on a pedestal stand, or hung from a tool balancer. These arrangements allow for various uses of the hemming apparatus. Further, the modular design of the hemmers allows the apparatus to be used for the hemming of various sizes and shapes of panels.