Optical tomography from industrial 3D printers
Even the smallest deviations in components, such as undesirable cavities or pores, can pose a risk to aviation safety in an emergency. Every component must therefore be thoroughly checked. To avoid having to destroy the parts, the inspection is carried out using ultrasound or X-ray methods.
Components from industrial 3D printers cannot be inspected as thoroughly using these processes. One example is selective laser melting: In the 3D printing process, metal powder is melted and applied in wafer-thin layers until the desired component is finished. MTU Aero Engines has been manufacturing borescope eyepieces for the A320neo geared turbofan engines in this way for more than five years. The part, a few centimeters in size, which is located on the housing of a low-pressure turbine and allows the insertion of a borescope, is made applying more than 1,000 layers. The problem: due to the layered structure produced with selective laser melting, any deviations are usually very small or extremely flat. The geometry of additively manufactured components is sometimes considerably more complex than that of cast or milled components. Conventional inspection techniques such as ultrasound or X-rays are often not sufficient to detect deviations.
The layer-by-layer buildup principle of additive manufacturing processes requires a completely new solution for quality assurance. MTU Aero Engines has developed a new inspection procedure for the particularities of this manufacturing process: The system, called EOSTATE Exposure OT, is distributed by EOS and works on the basis of optical tomography (OT) – an imaging method used in medicine, for example, to examine tissues. During the manufacturing process, a high-resolution camera documents the entire manufacturing process from the first to the last layer – a completely new quality inspection offering maximum efficiency.
The inspection during the manufacturing process eliminates the need for subsequent quality controls for volume testing. This reduces time and costs considerably. In addition, the system collects valuable data that can be used for later optimization of components and manufacturing processes.
During development, MTU collaborated with EOS, the world's leading technology provider for industrial 3D printing of metals and polymers. EOS has been distributing the joint development since June, so that OT can also be used by other companies. The development work is also continuing. The aim is to provide a monitoring system that can also be used for sequential control of the welding process. In the final stage, the monitoring system is to be further developed into a fully automated quality assurance and control system to eliminate defects while having it approved as an inspection procedure at the same time.