For stabilization of a robot manipulator upon collision with a stiff environment, a nonlinear bang-bang impact controller is developed. Under this control, a robot can successfully achieve contact tasks without changing control algorithm or controller gains throughout all three modes: free space, transition and constrained motion. It uses a robust hybrid impedance/time-delay control algorithm to absorb impact forces and stabilize the system. This control input alternates with zero when no environment force is sensed due to loss of contact. This alternation of control action repeats until the impact transient subsides and steady state is established. After impact transient, the hybrid impedance/time-delay control algorithm is utilized. This bang-bang control method provides stable interaction between a robot with severe nonlinear joint friction and a stiff environment and achieves rapid response while minimizing force overshoots. During contact transition, we employ one simple control algorithm with same gains that switches only to zero, while other controllers use more than one control algorithms or different control gains. It is shown via experiments that overall controlled performance is superior or comparable to existing impact force control techniques.