GRINDING TEMPERATURE AND COOLING RATE DURING GRIND-HARDENING OF 40Cr STEEL

The mathematical model of the grinding temperature is established. The grinding temperature and the cooling rate are measured in the grind-hardening process of 40Cr steel under different conditions. Moreover, the grind-hardening effects are investigated. Experimental results show that the calculated temperatures are comparatively close to the measured ones, and the required temperature and cooling rate can be achieved. Furthermore, the microstructure of the hardened zone is similar to that obtained through the high-frequency induction technique. The average hardness of the entirely hardened zone is HV670 and the thickness of the hardened layer is adjacent to 1.3 mm. It indicates that the hardening mechanism induced by the grinding heat and high-frequency heating is identical. Finally, the fine needlelike martensite is obtained.

Research into Grinding Hardening of Microalloyed Non-quenched and Tempered Steel

Grinding hardening is a new technology of hardening steel piece surfaces with grinding heat generated in the grinding process instead of with a high or medium frequency induction heating method,which can effectively integrate grinding and surface hardening. Experimental studies were carried out on grinding hardening of non-quenched and tempered steel. Through grinding experiments with variable depths of cut and feeding rate,the variation in the depth of the hardening layer was studied and the microstructure of the hardening zone of the test pieces was subsequently ana-lyzed. In the end,the hardening effect of non-quenched and tempered steel was compared with that of 40Cr steel,which revealed the superiority of non-quenched and tempered steel in grinding hardening technology.

External grind-hardening experiments and its grinding force

The grind-hardening method suitable for external grinding is proposed in this paper and the experiments are carried out on M1432B grinding machine. The hardened layer of the workpiece with cut depth 0.3 mm and speed 0.2 m/min is analyzed. The result indicates the metallurgical structure of the hardened layer is martensite and the top hardness value is 754 HV （about 62.3 HRC）. At the same time, the grinding force, one of the most important factors of external grind-hardening process is modeled, and the measurement method is provided with elastic core clampers. The measurement result shows that the values of both the tangential force and the normal force increase when the cut depth increases, and the top value is 146 N and 656 N with the cut depth value of 0.4 mm. The increment speed and the value of the normal force are larger than the tangential force.

Grinding-Hardening of Face Gears Under Minimum Quantity Lubrication with Disc Wheels

To shorten the process of face gears,the grinding-hardening effect experiment of face gears under minimum quantity lubrication(MQL)was carried out.Firstly,the grinding method of face gears was analyzed based on the envelope principle,and the control equation of grinding movement was constructed.Secondly,the distribution ratio equation of heat flux density was established,and the theoretical calculation formula of triangle heat source was derived.Thirdly,since a MATLAB calculation program was compiled,the temperature change law under MQL grinding was analyzed.In the end,the influence of grinding parameters on the grinding-hardening layer depth was analyzed.The results demonstrate that MQL grinding achieves the grinding-hardening effect.

Study on Surface Engineering of Normalized Steels Subjected To Machine Hardening

Engineering the surfaces of components to improve the life and performance of parts used in automotive and aerospace engineering is the active area of research. Suitable Thermal/ Mechanical/Thermo mechanical surface engineering treatments will produce extensive rearrangement of atoms in metals and alloys and corresponding marked variations in Physical, Chemical and Mechanical properties. Among the more important of these treatments are heat treatment processes such as hardening by Quenching, Induction hardening and Case Carburizing which rely on phase transformations to produce desired changes in mechanical properties. Other processes where phase transformation occur are casting, welding and machining etc. [1] Phase transformation may be homogeneous or heterogeneous. Homogeneous involves rearrangements in the structure of the material taking place simultaneously in all parts of the solid, while the heterogeneous transformation involves structural changes which are more localized. Alternatively they could be called as Isothermal and Nonisothermal transformation. But irrespective of the classification, these transformations alter the structure of the material giving rise to changes in the mechanical and physical properties of the processed material. It is of interest to review some consequences of surface modification in isothermal (Normalizing) and nonisothermal transformations (Machining) of low carbon steels.

DD5缓进磨削表面粗糙度和硬化率对疲劳性能影响研究

为研究DD5镍基单晶高温合金缓进磨削表面粗糙度和硬化率对疲劳性能的影响规律及机理,设计实验并进行了试件磨削与疲劳性能测试。结果表明:表面粗糙度的增大引起应力集中加剧,导致疲劳性能降低,不同磨削工艺下表面粗糙度由0.347μm增大到0.687μm,其疲劳寿命由5.51×10^(5)降至3.38×10^(5),下降率约38.66%;表面粗糙度小于0.4μm时表面硬化可提高试件疲劳寿命,表面粗糙度超过0.4μm时表面硬化对疲劳性能的影响不显著;形貌测试结果表明,随着表面粗糙度的提高,磨削表面耕犁产生的沟壑数量和深度均增大,疲劳载荷作用下磨削表面裂纹源数量增加、应力集中加剧,从而导致疲劳寿命降低。较小的表面粗糙度与较大的表面硬化率均可提高DD5缓进磨削疲劳性能。

凸轮轴异常磨损分析及工艺优化

失效分析得出,凸轮轴感应淬火质量及凸轮轴精磨工艺引起的磨削烧伤是凸轮轴异常磨损的主要原因。通过砂轮修型、优化磨削工艺参数即采取更优磨削烧伤检测手段,增大磨削烧伤检测频次等措施彻底消除磨削烧伤。优化感应器尺寸、感应淬火参数及完善感应淬火后的检测方法,使感应淬火质量得到显著提升。同时工艺优化措施已经固化应用于实际生产中,凸轮轴短里程的异常磨损问题已基本解决。

YC31125 Hardened Gear Hobbing Machine

The YC 31125 hardened gear hobbingmachine was developed by theChongqing Machine Tools Works. Itworks according to the principle of continuousscale division: it can cut spur and helicalgears, and chain and worm wheels. Thanksto its rigidness, it can semi-finish or finishhardened gears by the hobbing method usinga carbide hob. In this way, hardened gearscan be efficiently finished by hobbingoperation instead of the grinding method,with higher precision and productionefficiency. When hobbing spur gears,

合金淬硬钢20Cr2Ni4A小直径CBN砂轮磨削研究

针对合金淬硬钢20Cr2Ni4A在小直径砂轮磨削过程中,存在磨削力大、排屑难且磨损快的问题,考虑实际砂轮形貌特征,建立了砂轮磨削轨迹与磨屑厚度模型,揭示了砂轮尺寸及磨料参数对磨粒运动轨迹与磨屑厚度的影响规律。进一步建立了磨削表面线轮廓模型,并通过开展小直径CBN砂轮磨削合金淬硬钢20Cr2Ni4A实验,验证了模型的准确性。探究了磨削比能随磨削厚度的变化规律,结果表明当磨屑厚度小于0.02μm时,受尺寸效应影响,随着磨屑厚度增大,磨削比能由75 J/mm3降低至40 J/mm3。当未变形磨屑厚度大于0.02μm时,磨削比能随磨屑厚度变化不大。对比分析了进给速度对不同粒度小直径砂轮磨削力的影响规律,结果表明,当进给速度在400 mm/min以下时,粒度#200砂轮的磨削力与粒度#120砂轮的磨削力相差不大,选用粒度#200的砂轮可获得更好的磨削质量。开展不同粒度的小直径砂轮磨损对比试验,结果表明,粒度#120砂轮磨损类型主要为磨粒破碎,粒度#200砂轮磨损类型包括镀层划擦与磨料破碎,揭示了不同粒度的小直径砂轮磨损机制。

An internal cooling grinding wheel:From design to application

The cooling and lubrication conditions during the grinding process significantly impact the nickel-based superalloy’s final service performance.The existing jet cooling and heat pipe technology can solve the heat conduction problem in the grinding process of superalloy.Still,managing cooling,lubrication,and chip removal are difficult.This paper describes the design and fabrication of a novel central fluid-through internal cooling slotted grinding wheel with an ordered grain pattern to improve the grinding machinability of a nickel-based superalloy.The pressurized grinding fluid was ejected into the grinding zone via the pipe and tool holder from the lower-end face of the inner cooling wheel.The structure of the grinding wheel was optimized using computational fluid dynamics(CFD).The flow field in the grinding area achieved the highest overall flow rate,distribution homogeneity,and effective exit flow when the internal flow channel had four throughholes.The exit for the inner runner is located at the abrasive edge and diamond staggered pattern.Single-layer brazing was used to create cubic boron nitride(CBN)abrasive rings with various abrasive patterns.The internal cooling wheel matrix and various components were prepared according to the optimized grinding wheel geometry model.A grinding test bench was built to conduct an experimental study of grinding the nickel-based alloy GH4169.The results show that,under the same conditions,a diamond-shaped staggered pattern obtains lower grinding temperature,lower surface roughness,better surface morphology,and more significant residual compressive stress distribution than an abrasive cluster diagonal circular staggered pattern or disordered pattern.The average effective flow rate calculated by CFD is increased by 42.3%when compared to the disordered pattern.In the experiment,compared to the disordered arrangement,with the increase of grinding wheel’s rotating speed and coolant pressure,the average grinding temperature of abrasive grain with diamond-interleaved arrangement decreases by 58.2%and 51.7%respectively,and its surface hardening degree decreases by 11.1%and 11.7%respectively.

磨削淬硬加工技术的研究现状及展望

磨削淬硬加工是一种利用磨削加工直接对零件表面淬火的绿色复合加工技术。阐述了磨削淬硬技术的研究进展,指出表面完整性三要素的影响,即从表层质量、表面质量和棱边质量三方面进行了总结。通过分析磨削淬硬技术目前存在的问题,展望了磨削淬硬技术的未来发展趋势。提出构建磨削淬硬表面完整性评价和质量控制体系是实现磨削淬硬加工从理论研究到实际应用的基础。

表面硬度对PSHG零件滚动接触性能影响分析

为研究表面硬度对预应力淬硬磨削复合加工(PSHG)零件滚动接触疲劳性能的影响,设计滚动接触疲劳试验,加工3组表面硬度递增的PSHG复合加工45钢试件,对比试件表面接触区的疲劳损伤,分析其影响规律。通过ABAQUS软件仿真,对比不同表面硬度PSHG试件滚动接触时的应力、应变。结果表明,在HV_(0.5)为561到787硬度范围内,PSHG复合加工45钢试件的滚动接触疲劳性能随硬度增大而提高,表面疲劳损伤区域比例降低32.6%;其原因为表面硬度越大,试件在滚动接触中产生的塑性应变累积越小。通过控制PSHG加工参数获得合理的表面硬度,满足实际的抗疲劳使用要求,可以为PSHG复合加工新工艺开发提供参考。

Residual stress model of pre-stressed dry grinding considering coupling of thermal, stress, and phase transformation

Pre-stressed dry grinding can result in a hardened layer on the part surface while the surface residual stress is controlled.Considering the factors of the thermal field,pre-stress,and microstructural transformation,a proximate model of surface residual stress for pre-stressed dry grinding is established using the ANSYS finite element simulation method and verified through experiment.The variation laws and mechanisms of the residual stress along with the grinding parameters are revealed.Under the comprehensive effect of pre-stress and phase transformation,the residual stress of pre-stressed dry grinding is revealed mainly as compressive stress.This increases as the pre・stress and grinding depth increase.Under the coupling effect,pre-stress has larger influence on the residual stress than the grinding depth.The model can analyze and predict the residual stress of pre-stressed dry grinding in general.

齿轮渗碳淬火变形与齿面磨削量的关系研究

齿轮渗碳淬火变形指标有很多,但最终都将体现在齿面实际磨削量上。通过理论分析并结合长期生产实践发现,齿顶圆胀缩对磨削量影响最大,螺旋角变化和轮缘周向翘曲影响次之,其他因素影响相对较小。给出了依据齿轮直径胀缩量和其他参数计算齿面最大、最小磨削量的经验公式。在设计、工艺编制及热后质检时利用这些公式,可更加合理地确定图纸有效硬化层深度(Case-Hardened Depth,CHD)、滚齿时齿面预留磨削量和渗碳淬火时的目标CHD;渗碳淬火后还可以按照经验公式提前计算预估最大磨削量、最小磨削量和磨后齿面实际CHD,为后续生产提供指导。

等温淬火球墨铸铁磨球的生产实践

介绍了含碳化物等温淬火球墨铸铁磨球的铸造生产工艺以及热处理工艺。球墨铸铁磨球经过等温淬火及回火工艺处理,HRC硬度达到50~55,冲击韧性为12.4 J/cm^(2).实践证明,奥铁体磨球获得优良的力学性能关键在于获得高球化率,铸造工艺的精心设计与优化以及生产过程的严格控制可以保证获得高球化率。系统全面、严格精细的工艺管理不仅保证了高质量CADI磨球质量的稳定性,同时增强了企业的核心竞争力。

砂轮特性对40Cr钢磨削淬硬层的影响

以平面磨削淬硬试验为基础,研究了不同砂轮特性条件下40Cr钢磨削淬硬层的组织与性能。结果表明,在磨削淬硬加工中的热、机械耦合作用下,砂轮特性对磨削淬硬层的马氏体组织形貌及其高硬度区硬度值无显著影响。随着砂轮粒度或砂轮硬度的提高,磨削淬硬层深度相应增加。与树脂结合剂砂轮相比,采用陶瓷结合剂砂轮可使淬硬层深度增加近40%。

非淬硬钢磨削表面硬化层的试验研究

在平面磨床上对非淬硬钢进行了磨削硬化处理,研究了磨削方式和冷却条件对表面硬化层的影响。结果表明:硬化层完全硬化区均由细小的孪晶马氏体和板条马氏体组成,且硬化层的组织形貌及显微硬度无显著变化,但硬化层略粗马氏体相的出现位置有所差异;在磨削用量恒定时,顺磨硬化层的深度以及最大残余压应力均大于逆磨硬化层;在磨削功率恒定时,采用逆磨方式可以获得更深的硬化层;与干磨相比,湿磨硬化层表面残余压应力有所提高,但其硬化层深度减少了约30%。

原始组织对40Cr钢磨削硬化层的影响研究

在平面磨床上 ,采用刚玉砂轮和干磨削方式对 4 0Cr钢进行了表面磨削硬化处理 ,研究了原始组织对磨削硬化层组织与性能的影响。结果表明 ,在磨削温度和应力的综合作用下 ,完全硬化区马氏体均呈现“细 -粗 -细”的变化规律 ,且相对粗大马氏体相出现在次表层 ,而过渡区组织的形成因原始组织而异。此外 ,原始组织对完全硬化区显微硬度无显著影响 ,硬度值均在 6 30～ 70 0HV之间 ,原始组织越均匀 。

45钢磨削硬化的试验研究

在平面磨床上,采用干磨削方式对45钢进行了磨削硬化处理,研究了磨削硬化层的组织与性能.结果表明,在磨削温度场和应变场的综合作用下,完全硬化区马氏体相呈现“细-粗-细”的变化规律,且相对粗大马氏体相出现在次表层;而过渡区组织的形成主要在于磨削热循环温度场的作用.磨削深度或原始组织对显微硬度无显著影响,硬度值均在700～750HV之间;但磨削硬化层深度随着磨削深度的增加或原始组织均匀性的提高,从0.9mm增大到1.4mm.

基于概率统计的磨削力研究

采用数理统计的方法对磨削弧区的粒子进行概率统计分析,在对单颗磨粒受力状态进行分析的基础上,建立了磨削力理论计算模型。通过试验研究对理论分析进行了验证,结果表明,试验结果与理论预测结果较为吻合,该计算模型能够准确预测磨削力。