【作者】 乔玉鹏；

【导师】 康仁科；

【作者基本信息】 大连理工大学 ， 机械电子工程， 2010， 博士

【摘要】 作为最常用的低膨胀材料,Invar 36合金在精密仪器、精密模具、精密加工设备和武器装备等领域具有无可替代的应用价值,例如可用于制造光刻机的精密结构件和激光器反射镜基板等关键零件。然而,Invar 36合金在物理特性、机械性能等方面与普通合金差异较大,对Invar 36合金的加工性、加工表面完整性以及加工残余应力引起的变形等重要方面认识的不足限制了该合金的应用。本文比较系统地研究了Invar 36合金切削加工性、磨削加工性、磨削加工表面完整性及低应力加工工艺,在此基础上提出了Invar 36合金低应力加工的工艺路线和工艺参数。本文的主要研究工作及结论如下：通过车削试验,从切削力、断屑性能、表面粗糙度、加工变质层以及刀具寿命等方面研究了Invar 36合金切削加工性。与C45钢和1Cr18Ni9Ti不锈钢相比较,Invar 36合金加工表面粗粗糙度较好,加工变质层厚度较小,刀具寿命较长,但是切削力大,并且易生成连续带状切屑,切屑内表面纤维化也比较明显,滞流层厚度是C45钢和1Cr18Ni9Ti不锈钢的10～12倍,因此,断屑性能差。综合评价,Invar 36合金的切削加工性优于1Cr18Ni9Ti不锈钢,但是比C45钢差。从磨削力、磨削温度、磨削表面粗糙度和表面变质层深度、成屑形态、磨削比等方面分析了Invar 36合金磨削加工性。Invar 36合金的磨削力高于1Cr18Ni9Ti不锈钢和C45钢,磨削温度介于C45钢和1Cr18Ni9Ti不锈钢之间,磨削比明显低于C45钢但略高于1Cr18Ni9Ti不锈钢。Invar 36合金正常磨屑呈弯曲的纤维状。当磨削深度超过20μm时,砂轮粘附和堵塞比较严重,砂轮过早钝化,并导致磨削温度升高、工件表面质量下降。综合比较认为,Invar 36合金的磨削加工性介于C45钢与1Cr18Ni9Ti不锈钢之间。从表面粗糙度、表层残余应力、加工硬化及变质层等方面研究了Invar 36合金的磨削表面完整性,着重研究了Invar 36合金磨削残余应力。在本文试验条件下,Invar 36合金表面有较大的残余拉应力,峰值残余应力位于表面以下40～50μm,表面80μm以下为较小的残余压应力,磨削表面残余应力层深度小于180μm。磨削温度是磨削残余拉应力生成的主要原因。Invar 36合金的磨削温度对工艺参数比较敏感,其中磨削深度的影响最为显著。当磨削深度减小时,磨削温度降低,表面层残余拉应力减小；当磨削深度小于20pm时,磨削表面层温度约降低到300℃以下,材料热膨胀系数急剧减小,磨削表面层残余拉应力显著减小。为降低磨削残余应力,磨削深度不宜超过20μm。通过总结Invar 36合金已有的热处理工艺和本文加工工艺试验结果,以控制加工变形和减小残余应力为目标,提出了低应力加工工艺路线,即在粗加工、半精加工和精加工之间分别引入去应力及稳定化处理,并在精加工中采用低应力加工工艺参数。在此基础上,进行了精加工工艺参数的选择。切削加工Invar 36合金时,YG8硬质合金刀片切削力较小,适宜于Invar 36合金精加工。提高切削速度、增大刀具前角、减小切削深度均可减小切削力,并减小加工硬化程度和表面变质层厚度。铬钢玉砂轮磨削Invar 36合金时磨削力小,磨削温度低,磨削表面粗糙度好,适宜于Invar 36合金低应力磨削。更多还原

【Abstract】 As a kind of low-expansion materials, Invar 36 alloy is widely used in manufacturing of precision instruments, mould and machining equipments. For instance, it is used as precision components of lithography machine and the substrate of laser mirror. However, the physical and mechanical properties of Invar 36 alloy are very different from other alloys, and its machinability, machined surface integrity and deformation induced by the residual stress have not been well understood, which limited the application of Invar 36 alloy. In this thesis, the machinability, grindability, ground surface integrity and low-stress processing of Invar 36 alloy were studied systematically. On the basis of the above research, the low-stress process routes and the researsonable processing parameters are proposed.The main research contents and conclusions are as follows:The machinability of Invar 36 alloy was evaluated in terms of the cutting force, the chip-breaking performance, the surface roughness, the affected layer, the tool life, etc. by the turing tests. When turning Invar 36 alloy, in comparison with C45 steel and 1Cr18Ni9Ti stainless steel, the better surface roughness, thiner affected layer, the longer tool life, but the larger cutting force were obtained. The cutting chips are generally continuous in turning Invar 36 alloy. The stagnant layer is about 10～12 times thincker than that of C45 steel and 1Cr18Ni9Ti stainless steel. Therefore, the chip-breaking performance of Invar 36 alloy is poor. In conclusion, the machinability of Invar 36 alloy is better than that of 1Cr18Ni9Ti stainless steel, but worse than that of C45 Steel.The grindability of of Invar 36 alloy was estimated in respects of the grinding force, the grinding temperature, the chip characteristics, the affected layer, the grinding ratio, etc. The larger grinding force was detected when grinding Invar 36 alloy compared with that of C45 steel and 1Cr18Ni9Ti stainless steel. The grinding temperature of Invar 36 alloy is higher that of 1Cr18Ni9Ti stainless steel, but lower than that of C45 steel. The grinding ratio of Invar 36 alloy is much lower than that of C45 steel, but a little higher than that of 1Cr18Ni9Ti stainless steel. The grinding chips of Invar 36 alloy were normally curved with fibroid shape. When grinding depth is more than 20μm, the higher grinding temperature and worse surface quality were obtained owning to the grinding wheel dull resulted from the severe loading and adhesion, conclusively, the grindability of Invar 36 alloy is between C45 Steel and 1Cr18Ni9Ti stainless steel.The ground surface integrity, especially the grinding residual stress, of Invar 36 alloy was investigated by the surface roughness, the residual stress in the surface layer, the work-hardening and the metamorphic layer. Under current experimental conditions of this test, the apparent residual tensile stress were left in the grinding surface layer of Invar 36 alloy, the peak value of which located at about 40～50μm under the surface. In the subsurface deeper than 80μm , the residual stress is compressive stress, the value of which is lower than that of the residual tensile stress in the shallow surface layer. The total depth of residual stress layer is less than 180μm. The grinding temperature is one of the key reasons for the generation of the grinding residual tensile stress. The grinding temperature is sensitive to the processing parameters, especially to the grinding depth. As the decreasing of grinding depth, both the grinding temperature and the residual tensile stress in the surface layer decrease. When the grinding depth is lower than 20μm, the grinding temperature is no more than 300℃.The thermal expansion coefficient of the material drops distinctly from 300℃, resulting in the ovvious decreasing of the residual tensile stress in the surface layer. Therefore, the grindinig depth should be lower than 20μm to reduce the grinding residual stress.To control the workpiece deformation and reduce the residual stress in the machined surface,, a low-stress processing route for Invar 36 alloy was proposed based on the existing heat treatment process and the experimental results obtained from this work. The proposed processing route include the rough machining, semi finish machining and finish machining, The stress relief and the stabilization treatment are employed between the rough and semi finish maching, and between the semi finish and finishing machining. The low-stress processing parameters in the finish machining of Invar 36 alloy are determinted. In the finish turning of Invar 36 alloy, the YG8 carbide blade is suitable because the relative low cutting force could be obtained. The cutting force, the surface hardening and the affected layer decrease as the inceasing of the cutting speed and the tool rake angle, as well as the decreasing of the cutting depth. In the finish grinding of Invar 36 alloy, the chromium corundum wheel is suitable due to the low grinding force, grinding temperature and surface roughness.更多还原