Optimisation of layer height control in direct laser deposition

Abstract

Direct Laser Deposition (DLD) is a blown-powder laser deposition process which can be used to quickly produce fully-dense metallic prototypes by a layered manufacturing method. DLD can also be used to repair or modify high-value components. In common with other laser deposition processes, variation in the process parameters (traverse speed, powder flow rates etc.) can cause height errors in the built part. Layer height control methods are therefore a continually investigated field. Research carried out at Liverpool University has resulted in a non-feedback layer height controlling process based on controlling the shape of the powder streams emitted from a four-port side feed nozzle. This method limits deposited layer height by causing a sharp reduction of catchment efficiency in the vertical plane at a fixed distance from the powder feed nozzle, and is therefore capable of depositing a consistent layer height in spite of power, powder flow or process velocity variation. This paper examines the effects of altering the configuration of a four port nozzle system on the shape of the emitted powder streams and demonstrates the benefits of using the derived ‘best’ configuration in the production of test samples. In addition, the effects upon microstructure of parts generated in this fashion are discussed.