Development of a thermal imaging feedback control system in electron beam melting
The Electron Beam Melting (EBM) process is a promising technology in the rapid manufacturing of metal components. EBM has the potential to reduce the cost of metal parts by minimizing the use of raw materials and machining time. The EBM technology has several advantages over other additive manufacturing (AM) technologies of metal, such as manufacturing speed and mechanical properties of the finished parts. For the process to be accepted in the aerospace industry as a flight-ready manufacturing technology, however, improved control and feedback must be implemented in the building process for better part quality and uniform production in manufacturing. As part of this research, an infrared (IR) imaging system was implemented in an Arcam A2 EBM (Arcam AB, Sweden) system providing another level of control for the EBM process that could lead to rapid certification of flight-ready parts. The scope of the project is to incorporate IR thermal imaging in the fabrication process of EBM to provide layer-by-layer feedback and ensure quality products are produced in the Arcam A2 (Arcam, Sweden) metal AM system. Layer-by-layer build surface temperature profiles were imaged and analyzed, providing information that was used to modify build parameters (i.e. beam current, beam speed, focus offset, heating times, etc.) for proceeding build layers. To acquire temperature data within an appropriate level of certainty, a calibration procedure was established. The operator must provide the camera with several input parameters necessary for the camera's internal measurement functions; most noteworthy is the target's emissivity. A step-by-step procedure was developed to obtain a solid metal's emissivity, the mean radiant temperature (reflected temperature), and external optics transmission. Other contributing parameters are discussed. The thermographs obtained from the images were analyzed to identify defects or cool temperature zones on the build's surface. An experimental setup was designed to analyze the effects of part placement on the start plate, and, in essence, providing insight to the heat transfer taking place inside the build chamber. Using the acquired surface temperature data, parameter build modifications were implemented manually to assess the impact of temperature feedback on product quality control. Finally, the thermal imaging system was also used as a tool to develop processing parameters for the fabrication of unique materials, such as copper, via EBM. Copper is a non-standard material in EBM technology, and due to its high thermal conductive nature, it was quite a challenge to maintain a constant temperature throughout the fabrication process for appropriate melting with the electron beam. Surface temperatures versus layer plots were attainable due to the infrared images acquired during the parameter exploration phase; the plots were found to be a big advantage in the time to successfully develop optimal processing conditions.
Rodriguez, Emmanuel, "Development of a thermal imaging feedback control system in electron beam melting" (2013). ETD Collection for University of Texas, El Paso. AAI1539992.