激光熔覆粉末不锈钢的切削机理与工艺基础研究

Laser cladding has been considered as a strategic technique to repair engineering components. However, laser cladding deposit results in granulated surfaces, and dimensional control is poor. It is necessary to machine the deposits in a finishing operation to achieve the tight geometric, dimensional, and roughness tolerances required. Machining of laser cladding powder metals is quite different to machining of traditional metals because of their specific properties. Material removal mechanism for machining of powder metallurgical stainless steel by laser cladding is proposed in this project. The microstructures and composition analysis for cladding layer are evaluated. The depth of cut for machining of powder metallurgical stainless steel is optimized based on the research of influence of laser cladding process parameters on heat-affected zone. The maximum feed rate will be determined through analyzing the kinematics of the wiper insert turning operations. In view of the laminar structure and of discontinuities, the effects in the form of pores and hard particles on PCBN tool life are investigated. Quantitative correlation between chip morphologies and cutting speeds is developed. Cutting conditions to produce complete broken chips with equivalent spherical diameters of up to 300-700 micrometer are explored. The optimized cutting speeds are then determined to reconstitute generated broken chips into a usable solid structure. Simulated results with discrete element models and experimental results are presented to illustrate the efficacy of the developed machining processes of laser cladding powder metals. The comparison of the technical and ecological performances between proposed machining process and previous grinding process surface milling is described. The research results of this proposal will establish a firm theoretical foundation to optimize the laser cladding processes. It is recommended that the generated chips with appropriate shape and size can be collected and reused a second time to form additional laser cladding layers. The reduction of processing time and material consumption will be realized in the applications for repair and remanufacture of engineering components using laser cladding.

为满足激光熔覆零件修复加工的环保、节能要求，提出激光熔覆粉末不锈钢以车代磨干切削修复加工技术，实现熔覆层材料的回收再利用。基于激光熔覆工艺参数对熔覆层结合强度和热影响区影响的研究，探索熔覆层材料组织及力学物理性能参数的梯度分布规律，确定最优切削深度；揭示Wiper刀具切削加工表面形成和强化机理，确定最大进给量，在保证加工质量的同时获得最高切削加工效率；通过层叠材料与粉末冶金材料切削机理的研究，探索发现激光熔覆粉末不锈钢切削加工单元节状切屑（等效直径300-700微米）形成的热力学条件，确定激光熔覆粉末不锈钢最佳切削速度；诠释孔隙率和粉末硬质点对激光熔覆层切削加工性影响的细观力学机理。进行切削试验及离散元仿真验证理论研究成果，形成激光熔覆粉末不锈钢干车削修复加工工艺。项目取得研究成果可为优化激光熔覆工艺奠定理论基础，同时，通过切屑形态控制实现激光熔覆材料的回收再利用，带来巨大社会和经济效益。

后续机械加工决定了激光熔覆层表面的最终几何形状、表面粗糙度和应力状态等，进而影响其服役性能。以液压立柱为研究对象，在45#钢基体表面制备Cr/Ni合金激光熔覆层，开发液压立柱的修复加工技术，在报废液压立柱表面重新获得具有良好耐腐蚀性的高性能熔覆层。首先，利用激光熔覆在45#钢表面制备了厚度不小于1.5 mm、组织致密、无裂纹、低孔隙率、高结合强度、高硬度、高力学强度并具有良好耐腐蚀性的Cr/Ni基合金熔覆层。其次，基于直角切削应力模型提出了切削激光熔覆分层材料的应变连续条件下的未变形切屑厚度临界条件。再次，建立了熔覆层后续切削加工的表面完整性评价图谱，对传统刀片和wiper刀片车削以及滚压加工的表面完整性进行对比分析，开发了wiper刀片大进给车削和滚压的复合加工工艺。并针对wiper刀片在不同进给量下的表面残留和三维表面形貌进行建模，揭示了wiper刀片大进给车削表面的形成过程。最后，建立了车削与滚压复合加工熔覆层表面完整性与耐腐蚀性的关联关系。