Six-DoF haptic rendering is useful for interactive applications in virtual assembly and maintenance of complex machinery, such as, for example, car engines and landing gears. Because mechanical components are often geometrically complex, such applications require efficient interactive simulation, involving collision detection and rigid and deformable object simulation. I will give recent advances on virtual assembly for haptic force-feedback rendering in my group at the University of Southern California. I will discuss signed distance field generation, continuous collision detection, adaptive stiffness and friction. I will also discuss how to augment 6-DoF haptic rendering of contact to maximize virtual assembly training efficiency, by employing carefully selected visual and haptic guidance strategies.