Process study and control of electron beam melting technology using infrared thermography.

摘要

An IR camera was installed in an Arcam A2 system (Arcam AB, Molndal, Sweeden) and layer-by-layer image acquisition was achieved. The camera's capability to detect manufacturing defects was evaluated by implementing computer vision techniques using LabVIEW measurement and programming software (National Instruments, Austin, TX). Thermal maps acquired by the IR camera allowed layer-by-layer part temperature to be recorded. A core objective of this research was to study the impact of processing temperature on EBM-fabricated Ti-6Al-4V parts and achieve controlled mechanical properties. In this research, build variations were achieved by modifying parameters that change processing temperature from the standard processing temperature. Tensile testing, hardness testing, fracture analysis, and microstructural analysis were performed on the specimen from each build variation and the results were compared against a benchmark using standard EBM processing temperature parameters. The results of increased processing temperature, in general, were improved ultimate tensile strength, yield strength, and coarsened grains. Ultimate tensile strength measurements of up to 1032MPa (+/-5MPa) and yield strength of up to 993MPa (+/-8MPa) were achieved for parts fabricated under modified temperature conditions. Parts built with standard processing parameters produced an ultimate tensile strength of 988MPa (+/-2MPa) and yield strength of 878MPa (+/-7MPa). A closed-loop automatic control program was developed using LabVIEW that allows layer-by-layer image processing and on-demand processing parameter modifications from processing feedback. Image processing consisted of detecting differences in the thermal image and categorizing such differences into parts and defects such as porosity. Parameter modifications were achieved through a program developed that interfaces between LabVIEW and the EBM Control software (Arcam AB, Molndal, Sweden), which is the software that controls commands sent to the EBM system. The algorithm developed in this research was capable of changing processing parameters on-demand at user-defined points in a build to achieve microstructural variations. Microstructure analysis was performed on parts fabricated using the developed algorithm and the results show changes in grain size from sections where parameters were modified. The work presented here leads to recommendations of processing parameters that yield improved mechanical properties and an algorithm that allows closed-loop automatic control based on feedback acquired from an IR camera.