Reducing Chemical Wear of Single Crystal Diamond Tools Cutting Alloys

下一代自由形状光学元件通常由金属模具制成，这些模具本身是在使用合成单晶钻石(SCD)的高质量机器上切割的。尽管钻石是已知最坚硬的工具材料，但由于化学作用，在切割一些金属时，钻石磨损得惊人地快。这项研究将调查这些相互作用的各个方面，例如，在钻石/工件相互作用的长度尺度上，极难测量的切割温度。可以使用带有一些嵌入假设的模型来预测温度；为微系统制造开发的方法将被用于在钻石工具表面沉积温度传感器并测量温度分布。这些测量将用于验证模型。化学磨损率作为金刚石取向的函数将使用专门制造的工具进行测量，并通过在可控气氛下加工来测量作为氧浓度的函数。对钻石磨损率的定量预测可以使在目前不被认为是可加工钻石的合金中生产寿命更长的光学模具具有成本效益。这种模具将使下一代结构化和自由形状光学表面的制造成为可能，应用范围从节能照明到虚拟现实、平视显示器和夜视的紧凑型成像系统。提高对钻石加工的科学认识可以对许多制造业产生积极影响，包括汽车、航空航天、消费电子和国防。技术传播将通过出版物、专业协会、行业联盟，如NSF I/UCRC自由形式光学中心，以及教育活动。北卡罗来纳大学夏洛特分校是一个为少数族裔服务的机构，因此，向代表不足的少数族裔提供本科生和研究生研究机会应该是富有成效的。结果将被整合到研究生和本科课程中。在二年级的制造业中，平视显示器和未来几代虚拟现实等“酷”应用会激发学生的兴趣，而最硬的材料无法切割最软的金属之一(铈)的例子则有助于保持学生的参与度。该项目将寻求对金属合金加工过程中导致单晶金刚石工具磨损的热、化学和机械条件的更好的基本了解，以实现工艺改进。金刚石刀尖温度是化学工具磨损的一个重要因素，但在切割过程中很难测量它们。需要经过验证的热模型。经过验证的温度将用于使用Arrhenius方程确定化学磨损反应的激活能，从而提供对不同条件下刀具磨损的预测性理解。钻石的高热导率显著影响所模拟的温度分布，因此应影响反应速度。现在正在生产的人造钻石的热导率比以前高出约30%。将使用来自不同供应商并通过不同方式生产的钻石来测试由测量出的不同热导率的钻石制成的工具的磨损情况。金刚石的晶体取向影响机械磨损和某些熔融金属对金刚石的刻蚀速率。为了确定金刚石取向对化学磨损的影响，将测试不同取向的SCD刀具在切割活性合金时的磨损率。一个围绕着用钻石工具进行车削作业的环境室将阐述氧气对钻石磨损的重要性。自由曲面光学是光学能力的下一次革命。它们在照明中的使用提高了能源效率，减少了光污染。更紧凑、更高性能的成像系统使从多光谱军事系统到立方体卫星任务的更小、更轻的系统成为可能。这里开发的对制造过程的科学理解将使具有成本效益的应用范围不断扩大。结果将通过美国光学学会、SPIE(国际光学和光子学学会)、美国精密工程学会和CIRP(国际生产工程学会)的行业互动和出版物/演示文稿传播。北卡罗来纳大学夏洛特分校致力于招聘和留住那些将在本科生(制造系统(核心ME)和计量与精密工程(选修课))和研究生课程(光学制造与测试导论，高级表面抛光)中遇到这一研究结果的未被充分代表的群体。

Next-generation freeform optical components are often made from metal molds which themselves are cut on high quality machines using synthetic single crystal diamonds (SCD). Despite being the hardest known tool material, diamond wears surprisingly quickly when cutting some metals due to chemical interactions. This research will investigate aspects of those interactions, such as temperatures in cutting which are extremely difficult to measure at the length scale of the diamond/workpiece interaction. The temperatures can be predicted, using models with some embedded assumptions; methods developed for microsystems manufacturing will be used to deposit temperature sensors on the diamond tool surfaces and measure temperature distributions. These measurements will be used to validate the models. Chemical wear rate as a function of diamond orientation will be measured using specially manufactured tools and as a function of oxygen concentration by machining in a controlled-atmosphere chamber. Quantitative prediction of diamond wear rates could enable cost effective production of longer life optical molds in alloys not currently considered "diamond machinable". Such molds will enable manufacturing of next generation structured and freeform optical surfaces for applications ranging from energy efficient illumination to compact imaging systems for virtual reality, heads-up displays, and night vision. Improvements in the scientific understanding of diamond machining can positively impact a number of manufacturing sectors, including automotive, aerospace, consumer electronics and defense. Technology dissemination will be through publications, professional societies, industry consortia such as the NSF I/UCRC Center for Freeform Optics, and through educational activities. UNC Charlotte is a minority serving institution, and therefore outreach to underrepresented minorities for undergraduate and graduate research opportunities should be fruitful. Results will be integrated into graduate and undergraduate courses. In sophomore manufacturing, "cool" applications such as heads-up displays and future generations of virtual reality spark interest, while the example that the hardest material cannot cut one of the softest metals (cerium) helps keep the students engaged. This project will seek an improved fundamental understanding of the thermal, chemical and mechanical conditions leading to single crystal diamond tool wear during metal alloy machining, with the goal of allowing process improvement. Diamond tool tip temperatures are a significant factor in chemical tool wear, but they are notoriously difficult to measure during cutting. Validated thermal models are required. Validated temperatures will be used to determine activation energies for the chemical wear reaction using the Arrhenius equation, providing predictive understanding of tool wear under different conditions. The high thermal conductivity of diamond significantly affects modelled temperature distributions and should therefore affect the reaction rates. Synthetic diamonds are now being produced with thermal conductivities around 30% higher than previously available. Wear of tools made from diamonds with measured, different thermal conductivities will be tested by using diamonds sourced from different suppliers and produced through different means. The crystallographic orientation of a diamond affects mechanical wear and diamond etching rates by some molten metals. To determine the effect of diamond orientation on chemical wear, the wear rates for SCD tools of varying orientation when cutting reactive alloys will be tested. An environmental chamber enclosing a turning operation with a diamond tool will address the importance of oxygen on diamond wear. Freeform optics are the next revolution in optical capabilities. Their use in illumination improves energy efficiency and reduces light pollution. More compact, higher performance imaging systems enable smaller, lighter systems ranging from multispectral military systems to CubeSat missions. The scientific understanding of the manufacturing process developed here will enable an ever broadening range of cost effective applications. The results will be disseminated through industry interactions and publications/presentations at the Optical Society of America, SPIE (the international society for optics and photonics), the American Society for precision Engineering, and CIRP (The International Academy for Production Engineering). UNC Charlotte is dedicated to recruitment and retention of under-represented groups who will encounter the results of this research in undergraduate (Manufacturing Systems (core ME) and Metrology and Precision Engineering (elective)) and graduate classes (Introduction to Optical Fabrication and Testing, Advanced Surface Finish).