Prediction of Microstructural Changes and Residual Stresses in Hard Machining

这笔赠款为开发一种计算工具提供资金，用于分析和预测在使用单点刀具切割硬化钢时产生的微观结构变化和残余应力。该计算工具将用于确定最佳的切割速度、进给量、切割深度和刀具几何形状的参数值，以便在二维切割硬化钢材料时产生有利的残余应力和无不良组织变化(如白层形成)的工件表面。为了实现这一目标，将建立钢淬火过程中冶金相变的分析模型，并将其与使用ABAQUS标准有限元程序开发的二维切割过程的热力耦合更新拉格朗日有限元模型相结合。为了验证完整的模型，将使用由模型确定的切削参数，以轴承钢(例如，AISI 52100)为工件材料，以PCBN刀具材料为例，进行正交切削试验。现有的材料性能数据和/或高温高应变率试验将被用来建立用于模拟的材料流动-应力模型。用光学显微镜和扫描电子显微镜对加工后的试件的微观结构进行表征，用X射线衍射仪测量残余应力。如果成功，这项研究的结果将能够准确地模拟淬火钢加工中的表面生成，并确定最佳的切割条件窗口，以产生提高淬火钢部件使用寿命的表面特征。这将反过来有助于降低成本，提高零件质量，并促进硬加工技术的工业应用。在根本层面上，拟议的研究将促进当前对硬加工中材料和切割过程相互作用的物理理解，特别是从工件微观结构变化(例如，白层形成)和残余应力的角度。拟议的研究还将为未来开发用于模拟车削和铣削等硬加工过程的三维模型提供坚实的框架。

This grant provides funding for the development of a computational tool for analysis and prediction of microstructure changes and residual stresses generated in cutting of hardened steels using single-point tools. The computational tool will be used to establish the optimal parameter values for cutting speed, feed, depth of cut and tool geometry that yield favorable residual stresses and a workpiece surface free of undesirable microstructure changes (e.g., white layer formation) in two-dimensional cutting of a hardened steel material. To achieve this goal, analytical models of the metallurgical phase transformation occurring in quenching of steels will be developed and combined with a coupled thermo-mechanical updated Lagrangian finite element model of the two-dimensional cutting process developed using the ABAQUS Standard finite element code. In order to validate the complete model, orthogonal cutting experiments will be performed with bearing steel (e.g., AISI 52100) as the workpiece material and PCBN tool material using cutting parameters determined from the model. Existing material property data and/or elevated temperature high strain-rate tests will be used to establish the material flow-stress models to be used in the simulations. The microstructure of the machined workpiece samples will be characterized using optical and scanning electron microscopy while residual stresses will be measured using X-ray diffraction. If successful, the results of this research will provide the capability of accurately simulating surface generation in machining of hardened steels and determining an optimal window of cutting conditions to produce surface characteristics that enhance the service-life of hardened steel components. This will in turn help to reduce cost, improve part quality, and promote the industrial use of hard machining technology. On a fundamental level, the proposed research will advance current physical understanding of material and cutting process interactions in hard machining, particularly from a standpoint of workpiece microstructure changes (e.g., white layer formation) and residual stresses. The proposed research will also provide a solid framework for future development of a three-dimensional model for simulating hard machining processes such as turning and milling.