高温合金GH4169的切削加工性评价方法和本构模型研究

发布时间：2018-08-23 07:51

【摘要】：高温合金GH4169是典型的难加工材料,改善其切削加工性、提高表面加工质量是降低其应用成本,提高工件服役能力的重要途径。本文研究了面铣加工GH4169时的刀具寿命和刀具失效机理,提出了新的切削加工性评价方法；研究了面铣加工GH4169时的切削参数对加工表面完整性和工件表面三点弯曲疲劳寿命的影响；建立了考虑热力耦合作用的GH4169材料本构模型,进行了有限元切削仿真研究；研究了干切削、湿切削和低温切削GH4169时的刀具寿命、刀具失效机理和加工表面完整性。研究了在较大切削速度范围内铣削高温合金时的刀具寿命和刀具失效机理,提出了切削加工性评价新方法。在高温合金GH4169的铣削加工中,刀具寿命随切削速度的增加而急剧降低。当切削速度较低时,刀具失效形式是后刀面磨损,磨损机理为典型的磨粒磨损。随着切削速度的增加,刀具失效形式转变为刀尖破损。在中等切削速度下,刀具在机械冲击和热冲击共同作用下产生裂纹、导致崩刃。在较高切削速度时,热冲击是刀具产生裂纹、导致崩刃的主要原因。提出了采用刀具寿命对切削速度的敏感系数和刀具失效形式由磨损转变为破损的临界切削速度两个指标评价工件材料切削加工性的新方法。刀具寿命对切削速度敏感系数越大,表明该材料的切削加工性越差；刀具失效形式由磨损转变为破损的临界切削速度越低,表明该材料的切削加工性越差。采用此方法评价了四种高温合金的切削加工性,其切削加工性由难至易排序为GH605 GH4169 GH4033 GH2132。研究了面铣加工GH4169时的切削参数对加工表面完整性和工件表面三点弯曲疲劳寿命的影响。在所选切削参数范围内,切削速度对表面粗糙度影响较小,随着切削速度的增加,表面粗糙度先减小后增大；随着每齿进给量的增加,表面粗糙度增大。工件表面加工硬化层厚度小于20gm,随着切削速度和每齿进给量的增加,工件表面硬度略有增加。加工表面存在残余拉应力,切削速度对残余应力的影响规律不明显,残余拉应力随着每齿进给量的增加而增大。在三点弯曲疲劳寿命实验中,试样发生了多源疲劳断裂,疲劳裂纹萌生于加工表面。在所选切削参数范围内,切削速度对工件表面疲劳寿命的影响较小。每齿进给量对工件表面疲劳寿命的影响较显著,随着每齿进给量的增加,工件表面粗糙度增大,因此表面应力集中系数增大,导致工件表面疲劳寿命降低；加工硬化无明显变化,对加工表面疲劳寿命的影响可以忽略；残余拉应力增大,工件表面疲劳寿命降低,但残余拉应力在疲劳过程中发生了松弛,降低了残余应力对疲劳寿命的影响程度。建立了考虑热力耦合作用的GH4169材料本构模型,并进行了有限元切削仿真研究。通过霍普金森压杆实验,在500-800℃温度范围和5000～11000s-1应变率范围内研究了GH4169的动态力学性能。结果表明,材料动态变形中存在应变率强化效应和应变率软化效应。在不同温度下,应变率强化效应和应变率软化效应的临界温度不同,应变率对力学性能影响的规律性不强。不同应变率对应的温度热软化作用规律保持不变。建立了高温高应变率下的GH4169材料本构模型,通过切削仿真和实验验证,证明了该本构模型的适用性,其仿真精度高于现有模型。采用本文建立的材料本构模型进行了正交车削GH4169仿真,研究了刀具刃口半径对切削力、切削变形区温度场和应变率场的影响。随着刀具刃口半径的增大,刀具对工件材料的剪切去除作用降低,犁耕作用增强,切削力增大；第一变形区和第三变形区在刀具刃口附近扩展,导致温度场中高温区域扩大。研究了干切削、湿切削和低温切削GH4169时的刀具寿命、刀具失效机理和加工表面完整性。在端面车削GH4169中,与干切削相比,湿切削和低温切削能显著提高刀具寿命。干切削和湿切削时刀具失效机理为磨粒磨损和粘结磨损,低温切削时,切屑流向的改变和切屑上毛刺的产生是导致边界磨损的主要原因。在面铣削GH4169中,与干切削相比,湿切削和低温切削能显著提高刀具寿命,湿切削和低温切削抑制了扩散磨损和氧化磨损,但在低温切削时,较大的热冲击仍导致热裂纹。在端面车削GH4169中,与干切削相比,在较低的切削速度下,湿切削和低温切削得到的加工表面粗糙度较大；在较高的切削速度下,湿切削和低温切削得到的加工表面粗糙度较小。在于切削、湿切削和低温切削条件下,工件表面都出现了加工软化现象,低温切削得到的工件表面软化程度低；随着切削速度的增加,工件表面软化程度增强。随着切削速度的增加,干切削的加工表面残余拉应力增大；湿切削的加工表面残余压应力转变为残余拉应力；低温切削的加工表面在较高速度下仍保持残余压应力。
[Abstract]:Superalloy GH4169 is a typical hard-to-machine material. Improving its machinability and surface quality is an important way to reduce its application cost and improve the service ability of workpiece. The influence of cutting parameters on machining surface integrity and three-point bending fatigue life of workpiece surface at GH4169 is studied; the constitutive model of GH4169 considering thermo-mechanical coupling is established, and the finite element cutting simulation is carried out; the tool life, tool failure mechanism and machining table of GH4169 under dry cutting, wet cutting and low temperature cutting are studied. In the milling of superalloy GH4169, the tool life decreases sharply with the increase of cutting speed. When the cutting speed is low, the tool failure mode is the rear tool face. The wear mechanism is typical abrasive wear. With the increase of cutting speed, the failure mode of the tool changes into tool tip breakage. At moderate cutting speed, the tool cracks under the combined action of mechanical impact and thermal shock, resulting in edge collapse. A new method for evaluating the machinability of workpiece materials by using the sensitivity coefficient of tool life to cutting speed and the critical cutting speed from wear to breakage is proposed. In order to reduce the critical cutting speed, the worse the machinability of the material is indicated. The machinability of four superalloys is evaluated by this method. The machinability of the superalloys is in the order of GH605 GH4169 GH4033 GH2132. The surface roughness decreases first and then increases with the increase of cutting speed. The surface roughness increases with the increase of feed per tooth. The thickness of hardened layer is less than 20gm, and with the increase of cutting speed and feed per tooth. In the three-point bending fatigue life test, multi-source fatigue fracture occurred and fatigue cracks initiated on the machined surface. Within the range of parameters, cutting speed has little effect on the surface fatigue life of the workpiece. The influence of feed per tooth on the surface fatigue life of the workpiece is more significant. With the increase of feed per tooth, the surface roughness of the workpiece increases, so the surface stress concentration coefficient increases, which results in the decrease of the surface fatigue life of the workpiece. The influence of the residual tensile stress on the fatigue life of the machined surface can be neglected; the fatigue life of the workpiece surface decreases with the increase of the residual tensile stress, but the residual tensile stress relaxes during the fatigue process, which reduces the influence of the residual stress on the fatigue life. The dynamic mechanical properties of GH4169 were studied by Hopkinson compression bar test in the temperature range of 500-800 C and strain rate range of 5000-11000s-1. The results show that strain rate hardening effect and strain rate softening effect exist in the dynamic deformation of GH4169. At different temperatures, strain rate hardening effect and critical temperature of strain rate softening effect are studied. The constitutive model of GH4169 at high temperature and high strain rate is established. The applicability of the constitutive model is proved by cutting simulation and experimental verification. The simulation accuracy is higher than the existing model. The material constitutive model is established and simulated by orthogonal turning GH4169. The effects of tool edge radius on cutting force, temperature field and strain rate field in cutting deformation zone are studied. The tool life, tool failure mechanism and surface integrity in dry cutting, wet cutting and low temperature cutting GH4169 were studied. In end face turning GH4169, wet cutting and low temperature cutting can significantly increase tool life compared with dry cutting. In face milling GH4169, wet cutting and low temperature cutting can significantly increase tool life compared with dry cutting, while wet cutting and low temperature cutting inhibit diffusion wear and oxygen. In GH4169, compared with dry cutting, the surface roughness of wet cutting and low-temperature cutting is higher at lower cutting speed, and that of wet cutting and low-temperature cutting is lower at higher cutting speed. Under cutting, wet cutting and low-temperature cutting conditions, the workpiece surface softening phenomenon appears, and the workpiece surface softening degree is low after low-temperature cutting; with the increase of cutting speed, the workpiece surface softening degree increases. With the increase of cutting speed, the residual tensile stress on the dry cutting surface increases; and the surface residual in wet cutting. The residual compressive stress is transformed into residual tensile stress, and the surface machined at low temperature remains residual compressive stress at higher speed.
【学位授予单位】：山东大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：TG506

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