Laser polishing technology: development of engineering and scientific fundamentals

表面光洁度是制造部件最重要的质量特征之一。一般来说，在初级制造过程之后，需要光学/半光学表面质量的部件都是手工抛光的。然而，手工抛光过程需要先进的技术技能，并且加工速度慢，导致生产成本高。此外，通过铣削加工总是产生扇贝、脊和谷。无论刀具的切削轨迹变得多么狭窄和接近，最终的加工表面总是会表现出一定程度的形状误差、波浪形和表面粗糙度。**激光抛光（LP）是最近在德国和美国发展起来的一种表面处理技术。我们的团队正在开拓这一高度原创和创新的技术的发展，对加拿大和国外广泛的学术界和工业界具有重要影响。主要的挑战是在不破坏整体结构形式的情况下实现良好的表面处理。LP意味着表面平滑，通过表面张力在表面上熔化并重新分布一层薄薄的熔融材料，试图使表面能量最小化。由于没有材料去除，因此保留了给定几何特征的形式。LP作为一种颠覆性的、以知识为基础的技术，为具有复杂3D几何形状的增值部件的经济高效制造开辟了新的途径，消除了人工或其他类型的精加工操作。这种高度创新和原创技术的进一步发展有可能在制造业取得突破性进展。从科学的角度来看，LP是一个复杂的热物理过程，涉及几个多学科现象，伴随着快速加热、熔化、凝固、固态转变和冷却过程。然而，LP并没有完全发展的工程和科学基础，这限制了它作为常规技术的使用。主要的限制是：1)大量的工艺参数，没有系统化的可预测的使用，它们的选择和优化需要高技能的操作人员和大量的实验；2)作为材料熔化工具的激光束的不均匀和随时间变化的几何形状会导致表面几何形状的不良变化；3)没有可靠的预测模型；4) LP加工尚未采用CNC技术。在此背景下，拟议研究计划的主要目标是发展LP技术的基础知识，全面理解和工程基础。重点将放在理解和发展工程/科学基础，工艺规划和优化，其中将考虑激光材料相互作用区的几个热力学过程。将调查三个研究课题：A)熔融材料池的形成、快速凝固和表面几何形状变化的热力学建模和实验验证，b)熔化材料池沿着刀具轨迹移动时动态熔化凝固过程的建模和实验验证，以及c)工艺参数优化、系统识别和工艺规划，以实现具有所需质量的可再生表面。**开展这一协同开创性的研究将追求新的科学和技术理念，预计将对原创和战略技术的发展产生重要影响，通过开发创新的、以知识为基础的、具有成本效益的制造技术来制造高价值的部件和产品，从而增强加拿大公司的竞争优势。

Surface finish is one of the most important quality characteristics of fabricated components. In general, after the primary manufacturing process, components which require optical/semi-optical surface quality are polished manually. However, the manual polishing process requires advanced technical skills and is performed at slow processing rates resulting in high production costs. Also, finishing by milling always produces scallops, ridges, and valleys. No matter how narrow and close the tool's cutting-trajectory becomes, the resultant machined surface will always exhibit a degree of form error, waviness and surface roughness.**Laser polishing (LP) is one of the surface finishing techniques recently developed in Germany and USA. Our team is pioneering the development of this highly original and innovative technology influentially important to broad academic and industrial communities in Canada and abroad. The main challenge is to achieve good surface finishing without deteriorating the overall structural form. LP implies surface smoothing by melting and redistributing a thin layer of molten material over the surface through surface tension attempting to minimize surface energy. Since there is no material removal, the form of the given geometric feature is preserved.**LP as one of the disruptive, knowledge-based technologies opens new avenues in cost effective manufacturing of value-added components with complex 3D geometry eliminating manual or other types of finishing operations. Further development of this highly innovative and original technology has potential for groundbreaking advances in manufacturing. From a scientific point of view, LP is a complex thermo-physical process involving several multidisciplinary phenomena accompanying rapid heating, melting, solidification, solid-state transformations cooling processes. However, LP does not have fully developed engineering and scientific fundamentals this limits using it as a conventional technology. The main limitations are: 1) a large number of process parameters, which are not systemized for predictable use and their selection and optimization requiring a highly skilled operator and large number of experiments; 2) uneven and time-dependent geometry of the laser beam as a material melting tool contributes to undesirable changes in surface geometry; 3) no reliable predictive models exist; and 4) CNC technology has not been adopted for LP process yet.**In this context, the main objective of the proposed research program is to develop fundamental knowledge, thorough understanding, and engineering foundations of the LP technology. The emphasis will be on understanding and development of engineering/scientific fundamentals, process planning and optimization, where several thermo-dynamic processes in the laser-material interaction zone will be considered. Three research topics will be investigated: a) thermo-dynamic modelling and experimental verification of the formation of a pool of molten material and the rapid solidification and surface geometry change, b) modelling and experimental verification of the dynamic melting-solidification processes when a pool of molten material is moving along a tool path trajectory, and c) process parameter optimisation, system identification and process planning to achieve reproducible surfaces with desired quality.**Undertaking this synergetic groundbreaking research will pursue new scientific and technological ideas with expected influential significance in the development of an original and strategic technology that will enhance competitive advantage of Canadian companies through the development of innovative, knowledge-based, cost-efficient manufacturing technologies for fabrication of the high-value components and products.