Laser micro/nano remelting and redistribution for surface quality improvement and functionalization

表面光洁度是制造部件最重要的质量特征之一。随着增材制造（AM）技术的引入，生产具有复杂自由几何形状的功能部件和组件变得更加重要。然而，目前的增材制造工艺导致表面粗糙度差（通常从~5到15um Sa），阶梯结构表面，液滴，不利的残余应力以及低尺寸精度和精度。因此，AMed组件需要进行精加工以满足所需的表面特性。然而，手工抛光需要先进的技术技能，并且加工速度慢，导致生产成本高。铣削加工总是产生扇形、脊状和谷状，并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）是近年来发展起来的一种先进的制造表面处理技术，它通过熔化和重新分布一层薄的熔融材料来光滑表面，从而在不破坏整体结构形式的情况下提高表面质量。我们的团队能够从最初的1.2 nm Sa中获得72 nm Sa。LP为具有成本效益的增值零件、组件和工具的制造开辟了新的途径，显著降低了整体工具成本（高达40%）和制造时间（高达30%）。提出的研究计划的主要目标是进一步推进LP技术的基础知识，全面理解和工程基础，同时专注于提高AMed零件的表面质量及其表面功能化。重点将是研究如何通过激光材料重熔和再分配产生新的和/或增强现有表面功能的微/纳米级表面特征。这将需要理解和发展工程/科学基础，工艺规划和优化，其中激光材料相互作用区的热力学过程将作为微/纳米尺度进行研究。将研究三个研究课题：a)微/纳米重熔和再分配过程的热力学建模和实验验证；b)功能表面几何形状的过程建模、实际实施和实验验证；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/功能的可再生表面。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、具有成本效益的先进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. It becomes even more critical with introduction of additive manufacturing (AM) technologies for producing functional parts and components with complex free-form geometries. However, current AM processes result in poor surface roughness (typically from ~5 to 15 um Sa), stair-step structured surfaces, droplets, adverse residual stresses, and low dimensional precision and accuracy. Therefore, AMed components critically require finishing operation to meet required surface characteristics. Still, the manual polishing requires advanced technical skills and is performed at slow processing rates resulting in high production costs. Finishing by milling always produces scallops, ridges, and valleys and exhibits a degree of form error, waviness and surface roughness. Laser polishing (LP) is one of the advanced manufacturing surface finishing techniques that has been recently developed and successfully employed for improving surface quality without deteriorating the overall structural form through surface smoothing by melting and redistributing a thin layer of molten material. Our team was able to achieve 72 nm Sa from original 1.2 um Sa. LP opens new avenues in cost effective manufacturing of value-added parts, components and tooling significantly reducing overall tooling cost (up to 40%) and manufacturing time (up to 30%).    The main objective of the proposed research program is to advance further fundamental knowledge, thorough understanding, and engineering foundations of the LP technology while focusing novelty on improving surface quality of AMed parts and their surface functionalization. The emphasis will be on studies how micro/nano-scale surface features enabling new and/or enhancing existing surface functionalities can be produced by laser material remelting and redistribution. This will require understanding and development of engineering/scientific fundamentals, process planning and optimization, where thermodynamic processes in the laser-material interaction zone will be studied as a micro/nano-scale. Three research topics will be investigated: a) thermodynamic modelling and experimental verification of the micro/nano remelting and redistribution process, b) process modelling, practical implementation and experimental verification of the functional surface geometry formation, and c) process parameter optimization, system identification and process planning to achieve reproducible surfaces with desired quality/functionality.    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 advanced manufacturing technologies for fabrication of the high-value components and products.