Additive Manufacturing using Alloy 718 Powder : Influence of Laser Metal Deposition Process Parameters on Microstructural Characteristics

Sammanfattning: Additive manufacturing (AM) is a general name used for production methodswhich have the capabilities of producing components directly from 3D computeraided design (CAD) data by adding material layer-by-layer until a final component is achieved. Included here are powder bed technologies, laminated object manufacturing and deposition technologies. The latter technology is used in this study.Laser metal deposition using powder as an additive (LMD-p) is an AM processwhich uses a multi-axis computer numerical control (CNC) machine or robot toguide the laser beam and powder nozzle over the deposition surface. Thecomponent is built by depositing adjacent beads layer by layer until thecomponent is completed. LMD-p has lately gained attention as a manufacturing method which can add features to semi-finished components or as a repair method. LMD-p introduce a low heat input compared to arc welding methods and is therefore well suited in applications where a low heat input is of an essence. For instance, in repair of sensitive parts where too much heating compromises the integrity of the part.The main part of this study has been focused on correlating the main processparameters to effects found in the material which in this project is the superalloy Alloy 718. It has been found that the most influential process parameters are the laser power, scanning speed, powder feeding rate and powder standoff distance and that these parameters has a significant effect on the dimensionalcharacteristics of the material such as height and width of a single deposit as wellas the straightness of the top surface and the penetration depth.To further understand the effects found in the material, temperaturemeasurements has been conducted using a temperature measurement methoddeveloped and evaluated in this project. This method utilizes a thin stainless steel sheet to shield the thermocouple from the laser light. This has proved to reduce the influence of the emitted laser light on the thermocouples.