  Cross-docking is a logistics strategy that minimizes the storage and picking
functions of conventional warehouses. The objective is to unload the cargo from
inbound trucks and directly load it into outbound trucks, with little or no
storage. The success of the strategy depends on an efficient transshipment
operation. This work undertakes a study of truck scheduling in a cross-docking
center. The problem is modeled as a two-machine flow shop scheduling problem
with precedence constraints, with the objective of minimizing the makespan. The
proposed method is based on a Lagrangean relaxation solved by a Volume
algorithm over a time-indexed formulation. We use polynomial time heuristics
for generating efficient upper and lower bounds in a computationally efficient
time, outperforming current results in the literature for small and large size
instances.
