An apparatus and method for performing an ALM process is described. A first energy beam source (1) provides an energy beam (1b) which selectively melts a substrate powder (3) into a melt pool. A second energy beam source (2) provides an energy beam (2b) to heat condition substrate powder proximate to the melt pool. The path of the second energy beam (2b) is controlled by a controller (6) to oscillate independently of the path followed by the first energy beam (1b). The method may be applied to control and optimise heating and cooling rates of the sintered substrate during the ALM process enabling its microstructure to be controlled to suit the end use of the product and reduce the occurrence of residual stresses and consequent crack propagation.