Thermal monitoring instrumentation for metal additive manufacturing - PYRAM

本提案的目的是开发一种用于线材增材制造（AM）工艺的温度测量仪器。该仪器将使用一根带透镜的光纤电缆，将其馈送到一个基于相机的设计中，使其能够在不同的沉积环境中工作，并将与各种金属兼容。该系统将提供增材制造熔池的实时温度图像，从而提高增材制造工艺的效率。反过来，这将导致高质量的增材制造零件，并通过加强质量控制提高生产率。大型部件的金属增材制造将对专业部件的生产产生重大影响，因为它固有的成本和材料节约，以及提供了一种轻松改变设计和允许组件定制的途径。金属部件是通过将导线放入焊接电弧或激光中形成的，然后将熔融金属沉积在预定位置，并通过重复层来构建结构。使用这种技术建造的结构可以具有优异的材料性能，但由于熔池温度的变化，内部金属结构有时可能是不规则的，这导致组件的最终机械性能发生变化。熔池表面的温度测量通过确保生产来解决这些变化；恒定的材料内部结构，可重复的层尺寸和组件温度加热/冷却循环，从而确保良好的组件质量控制。如果金属表面温度可以被指定、测量和控制，那么这就保证了部件的机械性能在要求的规格范围内。热像仪对熔池的测量具有挑战性，因为温度可能超过2400度。此外，电弧产生的强光会使相机失明或降低测量精度。用于增材制造过程的商用热像仪往往具有较大的固定镜头，这使得在典型增材制造火炬周围有限的空间中安装有镜头的相机变得困难，因为它们需要与熔池保持视线，以便清晰地观察它。为了克服这些挑战，将开发一种新型光纤双波长相机仪器，该仪器专为在800-2400℃范围内工作的基于线的AM工艺量身定制，该仪器不会被强弧光遮挡，并且具有紧凑而灵活的成像光学器件。这使得相机头可以在有限的空间内使用，但相机仪器本身可以位于距离AM处理工具几米远的机械臂上。该仪器也可以有效地用于其他增材制造焊接工艺，并进行一些调整，以及物理访问非常有限的应用，例如燃气轮机发动机。这种双波长的设计使用了一束光纤和一个照相机以及特殊的滤光片来阻挡不需要的光，同时传输两种图像“颜色”。然后，这两种颜色分别在同一个相机传感器上成像。图像的温度由两个光信号的比值决定。这确保了较宽的工作温度范围，而不需要对熔池本身的热特性有专门的了解。该仪器的设计克服了强光和进出受限带来的挑战。定制软件将生成熔池的实时温度图，并允许仪器随后与控制AM机器的过程软件一起使用。这将允许对焊接电弧进行功率反馈控制，从而限制熔池温度的显著变化。该研究将开发一种最先进的仪器，解决金属增材制造工艺面临的主要挑战之一，并为制造可复制和符合规格的组件提供途径。

The aim of this proposal is to develop a temperature measurement instrument for use in a wire based additive manufacturing (AM) processes. The instrument will use a lensed fibre-optic cable fed to a camera-based design, allowing it to operate in different deposition environments and will be compatible with a variety of metals. The system will provide real-time temperature images of the AM melt pool that will improve the effectiveness of the additive manufacturing processes. In turn, this will result in high-quality AM parts and improved productivity via quality control enhancement. Metal AM of large components will have a major impact on the production of specialist components due to its inherent cost and material savings as well as offering a route to easily changing the design and allowing component customisation. Metal components are formed by feeding a wire into a welding arc, or laser, which is then moved to deposit molten metal in predetermined positions and a structure is built by doing this in repeating layers. Structures built using this technique can have excellent material properties, but due to variations in the temperature of the melt pool, the internal metal structure can sometimes be irregular, which causes variations in the final mechanical properties of the component. Temperature measurement of the melt pool surface addresses these variations by ensuring the production of; a constant material internal structure, repeatable layer dimensions and component temperature heating/ cooling cycles, thereby ensuring good component quality control. If the metal surface temperature can be specified, measured and controlled, then this guarantees the mechanical properties of the component are within the required specifications.Thermal camera measurements of melt pools is challenging as the temperatures can be in excess of 2400 deg. C. Also, the intense light from the arc can blind the camera or degrade measurement accuracy. Commercial thermal cameras used for AM processes tend to have large, fixed lenses which makes installation of the lensed camera difficult in the limited space around typical AM torches as they need to be line-of-sight with the melt pool, to view it clearly. To overcome these challenges, a novel optical fibre two-wavelength camera instrument, tailored for the wire-based AM process operating over the range 800-2400 deg. C, will be developed, which is not blinded by the intense arc light and has compact and flexible imaging optics. This allows the camera head to be used in restricted spaces but the camera instrumentation itself can be located some metres away from the AM processing tool, on the robot arm. This instrument could also be usefully used with other AM welding processes with some adaption, and applications where physical access is very restricted e.g. gas turbine engines. The two-wavelength design uses an optical-fibre bundle and a camera together with special filters to block the unwanted light but transmit two image "colours". These two colours are then imaged on the same camera sensor separately. The temperature of the images is determined by the ratio of the two light signals. This ensures a wide operating temperature range, without requiring special knowledge of the thermal properties of the melt pool itself. The instrument design overcomes the challenges presented by the intense light and restricted access. Custom software will produce a real-time temperature map of the melt-pool, and allow the instrument to be then used with the process software controlling the AM machine. This will allow power feedback control of the welding arc and hence limit significant variations in the melt pool temperatures. The research will develop a state-of-the-art instrument addressing one of the major challenges facing metal AM processes and provides a route to fabricating reproducible and specification compliant components.