Thin-walled Inconel aerospace engine casing prototype made by additive manufacturing in hours

The laser metal deposition process took 7.5 hours to manufacture the circular Inconel 718 component, 300 mm diameter and 90 mm tall, which includes an overhang, but did not require supporting material. The final prototype has a surface finish of 15 microns RA and average dimensional variance from CAD of 0.2 mm across the part radius. As part of the European Community research project MERLIN (www.merlin-project.eu), TWI has devised laser metal deposition (LMD) CAD-to-part software, taking in two years of development and six months of demonstration. The software maps a 5-axis vector toolpath, along with deposition parameters, to guide a 3-axis coaxial LMD nozzle across a moving substrate manipulated by a 2-axis CNC rotary table. Another innovation was to use an adaptive slicing algorithm that varies the nozzle lead distance according to the substrate tilt angle. 'The part, a helicopter combustion casing intended for engine R&D (and not for flying), can be removed from the stainless steel substrate without distortion, although it would need heat treatment to reduce residual stresses built up during manufacture,' TWI says. Helicopter turbine engine manufacturer Turbomeca of France is assessing its suitability for prototype part manufacture in support of engine performance testing. If approved, the process could remove months from the prototyping development stages, which include development of tooling, according to Carl Hauser, TWI principal project leader, joining technology group. In LMD, a weld track is formed using metal powder as a filler material that is fed through a coaxial nozzle to a melt pool created by a focused high-power laser beam. With precise synchronisation of the movements of rotation and tilt of the substrate with incremental movements of the coaxial nozzle (predominantly in the +Z direction), a continuous spiralling weld track can be deposited. The process used 1.2 kg of powder to produce the 700 g prototype.