【作者】 杨志波；

【导师】 徐九华；

【作者基本信息】 南京航空航天大学 ， 机械制造及其自动化， 2007， 博士

【摘要】 具有优化地貌的高温钎焊单层金刚石工具具有磨粒出露高、容屑空间大、基体对金刚石磨粒把持强度高以及高的锋利度、高的磨削效率和磨料利用率等特点,在难加工材料高效、重负荷加工中已显示出传统金刚石工具无法比拟的优异性能。它们各有自己的优势和适用范围,同时,也各有自己的不足和工艺局限性。从长远看,在钎焊工具的制作领域,它们都还有自己进一步完善和发展的空间。本文在借鉴炉中钎焊和高频感应钎焊已取得的研究成果的基础上,通过对激光与材料相互作用的原理和特点的深入分析,提出采用CO2激光作为热源,高温钎焊金刚石工具的设想,试图为金刚石钎焊开辟一条新的途径。本文完成的研究工作主要包括:(1)与试验用激光加工设备配套,设计、研制成功了专用的工艺试验平台(装置),该平台可在激光头与工件配合移动的条件下,在提供完善的氩气保护氛围的同时,实施对工具基体表面金刚石磨粒的选择性扫描钎焊。配置在该试验平台上的热电测温系统具有对基体表面温度的瞬时响应能力,可跟踪记录激光钎焊时试样表面温度的动态变化。此项工作为激光钎焊金刚石磨粒的工艺研究奠定了基础。(2)利用已研制成功的工艺试验平台和在若干简化假设条件下建立起来的数学模型,完成了激光钎焊时试样表面(层)温度的实验测试与仿真研究。此项研究的结果对优化确定激光钎焊的用量组合条件有重要的意义。(3)按照优化获得的用量参数范围选择一组用量组合条件,在国内外率先采用Ni-Cr钎料激光钎焊金刚石磨粒取得了成功。采用三维体视显微镜、扫描电镜、EDS能谱仪和X射线衍射仪对钎焊金刚石试样进行形貌观察和理化分析。结果证明:Ni-Cr合金钎料对金刚石磨粒的浸润爬升效果良好,钎焊过程中钎料中的活性元素Cr向金刚石表面扩散、富集,生成了层片状碳化物Cr3C2;在钎料与钢基体结合界面上Ni-Cr合金和钢基体中的元素相互扩散形成化学冶金结合,从而实现了金刚石磨粒与基体的牢固连接。运用激光拉曼光谱和扫描电镜对热应力、石墨化和化学侵蚀等热损伤现象进行了深入研究,结果表明,只要采用合适的钎焊工艺,可在磨料不受热损伤的前提下确保其界面获得理想的高性能结合把持强度。(4)成功制备出国内外第一块激光钎焊的金刚石固结磨料砂轮,加工性能试验表明:金刚石磨粒在磨削过程中基本上为正常磨损,无磨粒脱落现象。更多还原

【Abstract】 Single-layer brazed diamond abrasive tools with optimum grit distribution have some distinguished advantages, such as high grit exposure, large storage space, strong grit retention, high grinding efficiency and high utilization rate of grits. Consequently, the brazed diamond tools show remarkable merits over the conventional electroplated diamond tools in the high efficiency and heavy load machining process of the difficult-to-cut materials. On the other hand, the different diamond tools have their unique advantages and working field. Additionally, they also have some inevitably disadvantageous. From a long-run viewpoint, the brazed tools have an improving and developing space. Based on the former research on the fabrication technology of the diamond tools, including vacuum furnace brazing and induction brazing, and the analysis of the interaction behavior between the laser and the materials as well, the way to develop diamond tools by laser brazing was put forward in this investigation. It could provide a new means to braze diamond grits.The main contents in this paper are as follows:1. Experiment platform for laser brazing has been established to match the laser machining equipment, including inert gas protecting device, temperature measuring and controlling system. Through the platform, the temperature measuring and controlling system for instant response could trace the transient surface temperature of the samples, and laser scan brazing was conducted under the cooperation of the laser equipment and the work pieces. The preparative work is essential to the subsequent brazing experiments.2. The instantaneous temperature on the specimen surface was measured successfully by the experiment platform. Furthermore, depending on the model derived from some simple calculations and conditions, the 3D dynamic simulation on the temperature field of laser brazing was completed satisfactorily. It is very important to optimize the working parameters in the laser brazing.3. By choosing the process parameter according to the optimized scope of parameters acquired previously, laser brazing experiments were carried out with Ni-Cr filler alloy and the brazed diamond tool was accomplished. The new-formed reaction products and the interfacial microstructure under the different conditions have been detected by three-dimensional stereomicroscope, scanning electron microscope (SEM), energy dispersion spectrometer (EDS), and X-ray diffraction (XRD). The results show that Ni-Cr alloy has good soakage to diamond grits, and the grits were held firmly by the chemical bonding. During brazing, Cr atoms segregated to the interface area and reacted with C ones to form carbide Cr3C2, which distributed as flake around the diamond. The special filler alloy realized the wetting and joining of both the diamond grits and steel substrate. Laser Raman spectroscopy (LRS) and SEM were used to detect the heat residual stress, the graphitization effects and the chemical soakage. The result indicates that high bond strength between the filler alloy and the grits without the thermal damage could be reached by applying the optimum induction brazing technique.4. In this work, the diamond grinding wheels with segment structure were firstly prepared successfully by laser brazing at home and abroad. Meanwhile, the machining performance of the brazed diamond tools was evaluated. The result shows that the main wear of the diamond grits was normal. None of the grits in the connecting layer was pulled out from the tools.更多还原