There is an ongoing drive to reduce the operating costs of aero-engines and this may be achieved partially via an increase in engine efficiency. To achieve this, industry needs to utilise new materials that can withstand higher operating temperatures and stresses. Many of the nickel-based alloys suitable for these applications, eg MAR-M-002, are difficult to join using conventional welding techniques. This paper describes a technique used to successfully weld 2.5 mm thick plates of cast MAR-M-002. The technique used FEA modelling to analyse stresses during welding and multiple axis electron beam deflection to alter the temperature and stress distribution around the fusion zone to prevent the initiation or propagation of cracks. FEA modelling of the process has been used to reduce the total number of practical tests, and hence, to conserve the limited material supply. This technique has made it possible to produce crack free welds in what is usually classed as an 'impossible to weld' alloy.