In-situ monitoring of component integrity during additive manufacturing using optical coherence tomography

增材制造被誉为最新工业革命的代表，并吸引了专家用户和普通大众的想象力。新的制造能力使我们能够探索新的设计自由度，并根据用户的需求生产优化的产品。随着技术能力的提高和可信度的提高，这些趋势将进一步增强。目前市场上有一系列机床可以直接从数字化中实现零件。这些利用各种能源（例如激光，电子束，IR灯，加热喷嘴等）和材料原料（例如金属/聚合物粉末，光固化树脂，塑料线）来实现设计意图。与更成熟的机床不同，在这些系统中明显缺乏过程监控和关键过程变量的反馈控制。这带来了一个重大的问题，因为没有任何方法可以确保构建过程中的一切都很好。因此，在许多情况下，只有在工艺完成后才能识别缺陷，假设它们在表面可见。当零件的完整性至关重要时，组件主体内的缺陷值得关注。这些只能通过横截面或X射线计算机断层扫描（CT）等过程观察。因此，真实的需要新的方法来提供关于预熔化材料层的质量和熔化后的质量的“过程中”信息。显然，需要对零件进行一定程度的渗透，以创建完整的图片，该图片可以以逐层的方式重构，以在完成时创建零件的完整性图。这可用于识别表现出分层、孔隙、破裂和密度变化的掩埋区域。此外，对预熔化的沉积材料的分析应该能够识别空隙，并给出关于表面粗糙度和理想材料特性的一些信息。光学相干断层扫描（OCT）是一种成像技术，如果能够根据塑料成像的特定要求进行调整，并在AM工具中进行原位应用，则可以用来应对这一挑战。该项目将通过基于新型非接触式光学技术的精密、原位、实时过程控制，实现高价值增材制造的成熟。OCT是一种非侵入性成像技术，有可能彻底改变增材制造技术。它将使增材制造在产品完整性方面符合既定的生产工艺，同时还提供显著的成本和资源效率，以支持增材制造工具在整个制造业的广泛部署，并开发新的和未开发的应用。目前还没有专门用于区分增材制造中使用的聚合物的适当高速OCT配置。这样的系统将被构建，将新型中红外组件集成在外腔激光器配置中，允许对一系列单一和多聚合物部件进行振动独立成像。该项目的一个成功成果将是实现一种OCT系统，该系统能够快速分析由多种塑料组成的增材制造部件的亚表面微观结构（例如空隙和成分），以及将其纳入增材工艺的方案，从而实现对工艺完整性的原位监测。除此之外，还将收集数据集并进行后处理，以评估和证明这项新技术对增材制造的适用性

Additive manufacturing has been hailed as representing the latest industrial revolution and has captured the imagination of expert users and the general public alike. New manufacturing capabilities have permitted us to explore new design freedoms and produce optimised products which are customised to the needs of the user. These trends are set to increase as the technology grows in capability and gathers credibility.There are an array of machine tools available on the market at the moment that can realise parts direct from digital. These make use of various energy sources (e.g Lasers, electron beams, IR lamps, heated nozzles etc) and material feedstocks (e.g metal/polymer powders, photocurable resins, plastic wires) to realise the design intent. Unlike more established machine tools there is a marked lack of process monitoring and feedback control of key process variables in these systems. This presents a significant problem since there is no method for ensuring that all is well within the build process. Therefore, in many cases it is only possible to identify defects after the process is complete assuming they are visible at the surface. Of significant concern, when integrity of parts is critical, are defects within the body of components. These can only be observed through cross sectioning or processes such as X-Ray Computed Tomography (CT). Naturally this comes at some considerable cost and only provides information once a part has been produced.Therefore, there is a real need for new methods to provide 'in process' information about the quality of the pre-fused material layer and the quality post melting. Clearly some penetration into the part is required to create a full picture which can be reconstituted in a layerwise manner to create an integrity map of parts upon completion. This can be used to identify buried regions which exhibit de-lamination, pores, cracking and density variations. Furthermore analysis of the deposition material pre melting should be able to identify voids and give some information about surface roughness and ideally material properties. Optical Coherence Tomography (OCT) is an imaging technique which, if tuned to the specific requirements of plastic imaging and applied in-situ within the AM tool, could be used to meet this challenge.This project will enable high-value additive manufacturing to come of age through implementation of sophisticated, in-situ, real-time process control based on novel non-contact optical techniques. OCT is a non-invasive imaging technique, which has the potential to revolutionise additive manufacturing technologies. It will bring additive manufacturing in line with established production processes with respect to product integrity, whilst also offering significant cost and resource efficiencies to support the widespread deployment of additive manufacturing tools throughout the manufacturing sector and to develop new and untapped applications.Appropriate high-speed OCT configurations aimed specifically at distinguishing between polymers of use in additive manufacturing are not currently available. Such a system will be built, integrating novel mid-IR components within an external cavity laser configuration, allowing vibration independent imaging of a range of single and multi-polymer parts. A successful outcome of this project will be the realization of an OCT system capable of rapid analysis of the sub-surface microstructure (e.g. voids and composition) of additively manufactured parts composed of multiple plastics, and a scheme for its incorporation into the additive process whereby in-situ monitoring of process integrity is enabled. Beyond this data sets will be gathered and post processed to evaluate and demonstrate the applicability of this new technology to additive manufacturing