变速箱输出轴失效分析

通过宏观断口、化学成分、硬度和金相检测、输出轴校正、过渡角及表面粗糙度测试等,对变速箱输出轴断裂原因进行了研究。结果表明,输出轴断裂的主要原因是花键处过渡角较小,表面粗糙度较大,造成输出轴花键过渡角处在运行中产生了较大的应力集中,并且人工校正时下压力难以控制,容易在零件表面产生微裂纹。     

汽车车身冲压零件开裂、暗裂预防控制

<正>汽车冲压外覆盖零件本身尺寸较内部加强零件要大,而且形状更复杂。受零件在成形过程中拉延深度较大,型面复杂等因素影响,在前期调试期间产品容易出现开裂或者暗裂,不仅提高了制造成本、造成材料浪费,而且生产的不良品容易流入到后面的生产工序造成更大的质量事故。所以汽车冲压零件的开、暗裂缺陷必须在发生源进行控制,避免制造过程的品质不良风险。     

高光洁度注射模零件制造工艺研究

从加工设备、刀具、夹具、编程软件选用以及编程策略等方面进行了较深入的研究。试验件为一套高光洁度照相机模具零件,材料为POLMAX不锈钢。实际检测零件表面质量表明:零件表面粗糙度值最大处仅为0.57μm,其余大部分表面粗糙度值均在0.4μm左右,零件完全能够满足使用要求。     

一种用于大型套筒类零件加工的自定心专用夹具

套筒类零件一般由孔、外圆、端面和沟槽组成,其主要工作表面为内圆表面和外圆表面,形状精度和位置精度要求较高,表面粗糙度值较小,孔壁较薄且在加工过程中因受夹紧力、切削力、切削热等作用后易变形。因此,保证主要表面的相互位置精度和防止变形,是加工套筒类零件的关键。针对大直径的套筒类零件加工,设计制造了一种自定心专用夹具,解决了套筒类零件的装夹、定位问题,保证了零件的加工精度,提高了生产效率。     

形状复杂且不对称零件的拉伸

１前言对于轮廓尺寸大，结构形状复杂深度不均匀又不对称的拉伸件，在拉伸时，毛坯在模内变形较复杂，在工艺安排上，一般要经过多道拉伸工序才能完成，要求在拉伸过程中材料各部位都受到均匀的拉伸应力，拉伸应力大小要超过材料屈服极限（σs），而低于材料的强度极限（σb），使零件不产生弹性畸变且不破裂。所以能否满足上述要求，是决定拉伸工序成败的关键。对于形状复杂且不对称零件拉伸要比一般拉伸考虑的问题要复杂许多。能否设计制造这类零件的成形模具，拉出合格零件，也是衡量该企业制模水平的标准。由于零件形状复杂且不对称（图…     

大吨位水平镦锻液压机

高铁动车车辆上的扭杆轴和大跨距斜拉桥梁钢索张紧力调节用的拉杆轴等锻件尺寸大、形状比较特殊，用普通设备无法生产。为了解决此类零件的预镦成形，徐州开元世纪重型锻压有限公司设计了针对性很强的镦锻设备。本文对该设备的构造、性能参数及棒料类零件毛坯聚料制坯工艺过程进行了详细介绍。     

轴类零件渗碳淬火工艺硬化层深度与残留跳动变形量的关系及计算

通过对轴类零件渗碳淬火后的径向跳动变形与后续磨削加工情况综合分析，得出了轴类零件渗碳淬火工艺硬化层深度的计算公式。利用该公式的计算结果对轴类零件渗碳淬火工艺硬化层深度进行控制．可消除轴类渗碳零件硬化层深度不均的隐形质量隐患。     

30CrMnSiA支臂零件裂纹产生原因分析

30CrMnSiA支臂零件在机加工和热处理后,经无损探伤检验发现在零件轴线多处有裂纹存在。为明确支臂零件裂纹产生的原因,通过宏观观察、金相组织分析、微观观察和能谱分析、力学性能测试、化学成分分析等试验手段进行分析,并与原材料进行对比。结果表明：该零件材料的微观组织不均匀,容易产生较大的组织应力,异常的带状组织分布方向与裂纹扩展方向一致;裂纹主要位于零件截面尺寸变化处,因筋条的尺寸变化而造成的淬火冷速不一致,导致裂纹处存在较大热应力。经分析可知,零件裂纹均为淬火裂纹,零件原材料带状组织不均匀和零件形状尺寸变化较大等综合因素导致该零件淬火时容易产生淬火裂纹。     

基于曲率的曲面等效磁性研磨策略研究

在现有三坐标磁性研磨设备上进行曲面类零件加工时,由于曲面法矢与磁极轴矢的变化,使磨削量不均匀,导致零件表面粗糙度不一致,影响了研磨效果。解决这一问题的有效方法是优化研磨算法,根据曲面曲率的变化调整磨头方向,使磁极的轴线始终与曲面法矢重合或保持固定角度,以此来保证曲面零件表面磨量均匀,提高磨削效率,改善研磨质量。实践表明,该方法是可行的、有效的。     

旋转锻造成形技术研究现状

旋转锻造是一种用于棒料、管材或线材精密制造的渐进近净成形工艺,具有加工范围广、加工精度高、产品性能好、材料利用率高和生产灵活性大等优点,广泛应用于航空航天、汽车制造等领域。介绍了国内外旋转锻造设备的研制现状,对旋转锻造成形数值模拟技术的最新研究进行了概括,概述了空心轴类件、非回转类零件的旋转锻造成形技术,阐述了在焊接性能较差的材料以及不易结合界面的旋转锻造塑性连接技术,并介绍了旋锻工艺优化设计方面新的进展。     

五轴机床刀尖点频响特性及切削稳定域位置的演变

五轴机床在航空航天领域大型曲面零件加工中应用极其广泛,其高速、高精度和大材料去除率的加工特点对加工稳定性提出了很高要求,影响五轴机床铣削稳定性的主要问题是切削颤振。通过对一台转摆头五轴机床进行动力学性能测试,对比分析主轴系统在不同位置和转摆头在不同姿态下刀尖点的频响特性,得出刀尖点频响特性随位置的演变规律。以频域法构建切削稳定性叶瓣图,得到极限切深的位置演变规律。研究结果为五轴机床切削参数的优化提供了参考。     

The effect of machine stiffness on grinding of silicon nitride

This study investigates the effect of machine stiffness on normal forces, actual depth of cut, and workpiece strength in grinding of silicon nitride. To obtain a grinding system with an adjustable stiffness, a compliant workholder is added to a precision grinder. Single-pass and multi-pass grinding experiments are conducted to evaluate the effect of machine stiffness. Cup-type diamond wheels of two different bond types and three grit sizes are used in the grinding experiments. Static and dynamic simulation is carried out to correlate grinding forces and actual depth of cut with machine stiffness. Since the simulation uses a time-domain model, it can accommodate non-linearities caused by the effect of machine stiffness on grinding forces and actual wheel depth of cut, workpiece regeneration, wheel wear, as well as wheel bond type and grit size effects, etc. Particularly, the model allows simulating grinding instability and the interference phenomenon due to residual material removal in multi-pass grinding. The study concludes that both simulation and experimental results have a good agreement.     

现场动平衡技术在高线吐丝机上的应用

针对高线吐丝机吐丝盘修复后出现吐丝机运转振动和噪声异常现象,对振动故障特征进行了分析,得出振动异常是由吐丝盘动不平衡引起的,采用现场动平衡仪对吐丝机进行现场动平衡校正,校正后吐丝机振动明显下降。     

The material removal mechanism in mechanical lapping of diamond cutting tools

In order to reveal the surface layer removal nature and explain the anisotropy of material removal rate in mechanical lapping single crystal diamond cutting tools, a brittle-ductile transition lapping mechanism is proposed. And then, the dynamic critical depths of cut for brittle-ductile transition in different directions on different planes can be calculated. The lapped surface layer of diamond cutting tool will be removed in plastic mode as long as the embedding depth of diamond grit into the lapped surface is less than the corresponding critical depth of cut. Lapping experiments on the named (110) plane and (100) plane are carried out and the lapped surfaces are measured with atomic force microscope (AFM). The results show that all the lapped surfaces of diamond cutting tools consist of plastic grooves in nanometric scale and the maximal groove depths have prominent anisotropy in different orientations and on different planes, which are consistent with the critical depths of cut well. Therefore, the material removal rate anisotropy of lapped surface layer can be analyzed by comparing the critical depths of cut on different crystallographic planes and in different orientations of the identical plane quantitatively.     

Transitions of micro-EDM/SEDCM/micro-ECM milling in low-resistivity deionized water

Owing to its slight conductivity, deionized water has been used as a bi-characteristic fluid to combine micro-EDM and micro-ECM milling in a unique machining process which has been named as SEDCM milling. To attain both electrical discharge and electrochemical reaction during machining, selection of machining parameters such as feedrate and layer depth has been empirically observed to be of prime importance. This paper presents an analytical model to identify the critical conditions for transitions of material removal mechanisms in this hybrid machining process. The criteria for three distinct machining modes micro-EDM/SEDCM/micro-ECM milling are determined based on the thickness of material layer that electrochemical reaction could dissolve when the electrode scans over the surface. The critical feedrate for transitions of material removal mechanisms are then predicted using double layer theory, Butler–Volmer equation and Faraday's law of electrolysis. Experimental tests were also performed to validate the proposed model. It has been established that the SEDCM milling is only attained at moderate feedrate. For high feedrate, machining mode is changed to micro-EDM milling alone when the thickness of material layer that electrochemical reaction could dissolve is smaller than the roughness of micro-EDMed surface. On the contrary, for low feedrate, material removal mechanism is converted to pure micro-ECM when the thickness of layer dissolved by electrochemical reaction is higher than the preset layer depth. In addition, it is also found that lower feedrate is required for SEDCM milling when higher layer depth is used because more material needs to be removed by the sparks in every feed.     

基于轴承毛坯表面分析的磨削材料去除率模型与应用实验

目的 在轴承套圈磨削加工中,传统基于动力学模型建立的磨削材料去除率模型仅考虑了磨削工件-砂轮-机床三者的弹性变形,未考虑毛坯零件表面不规则变形对模型的影响,导致传统理论模型在实际磨削应用中的效果不佳。针对此问题,基于轴承套圈毛坯表面形状分析建立了新的磨削材料去除率模型,并进行了应用实验。方法 基于轴承套圈毛坯零件表面形状的工艺研究,针对粗磨阶段毛坯零件表面不规则形状和弹性变形对磨削加工及产品质量的影响,建立不同偏心圆数量的轴承套圈结构分析方法,并提出一种以分段函数形式的磨削材料去除率模型,该模型充分考虑了轴承套圈毛坯零件表面不规则变形和偏心圆形状对磨削材料去除的影响,可有效反映轴承套圈实际材料磨削去除过程。最后,通过大量实验对所建的分段函数形式的磨削材料去除率模型进行应用实验研究。结果 与传统磨削材料去除率模型GPSM相比,所建的以分段函数形式的磨削材料去除率模型MMRG的准确率提高了96%以上,该模型可有效在线量化分析毛坯表面不规则大小及偏心圆结构。结论 该模型对指导毛坯零件制造,保证磨削加工质量和磨削加工效率有着重要的理论指导意义。     

Effects of mixed abrasive grits in slurries on free abrasive machining (FAM) processes

Effects of mixed abrasive grits in slurries on free abrasive machining (FAM) processes are studied using a single-sided lapping machine. Impacts of mixing abrasives on various parameters such as amount of material removed, material removal rate, surface roughness, particle size distribution and relative angular velocity are studied. The material removed is monitored as a function of time. The experimental results suggest that (i) mixing abrasive grits can increase the amount of material removed, (ii) smaller abrasives can directly or indirectly affect the material removal process, (iii) slurries undergo severe grain size transition during lapping, and (iv) the surface roughness did not change significantly under different loading. The results of this study may have profound implication on the FAM processes that practitioners use today because the mixed abrasive grits increase material removal rate and reduce the grain size transition, while rendering similar surface roughness.     

Modeling and analysis of the material removal depth for stone polishing

In this paper, a model of predicting the material removal depth of the workpiece surface for the mould polishing by fixed abrasives is developed and an approach to achieve the material removal profile is presented. The effect of the grain size on material removal depth is considered. The distribution of the abrasive grain protrusion heights is taken to be Gaussian distribution. The relationship between the pressure and the depth of indentation is investigated by analyzing interaction of the abrasive grains and the workpiece. It is assumed that the pressure distribution is Hertzian at the contact between the tool and the workpiece surface. The theoretical model of linear removal intensity is presented by calculating the removal volumes of all abrasive grains participating in cutting. The depth of the material removal can be obtained by integrating the linear removal intensity along the polishing contact path formed by the polishing tool passing this position. The predicted results based on the current model are shown to be approximately consistent with the experimental results.     

基于内置传感器的数控机床动态加工误差测量方法

以HJ044双转台型五轴联动数控机床为例,以机床内置传感器信息和多体系统理论为基础,建立了刀具相对工件的运动学模型,提出了一种基于内置传感器信息的动态加工误差测量方法。该方法利用机床编码器或光栅尺等机床内置传感器信息获取机床各轴运动位移,并结合机床运动学模型,测量由机床的动态特性引起的加工误差。并通过实验表明该方法是一种简单有效的数控机床动态加工误差测量方法。     

Analytical model to determine the critical conditions for the modes of material removal in the milling process of brittle material

Brittle materials are prone to cleavage-based fracture during machining. In conventional scale machining of brittle material, crack-propagation is the dominant mechanism of material removal which results in a degraded machined surface. The challenge is to perform machining of brittle material such that the material removal occurs predominantly by chip formation rather than the characteristic brittle fracture. In this case, a high quality finish is achieved on the machined surface. Ductile-mode machining has emerged as a promising technique to finish a crack-free machined surface on macroscopically brittle materials. In the past, ductile-mode machining has mostly been performed by single-edge cutting process. This paper outlines an analytical model to determine the critical conditions for finishing a crack-free surface on brittle material by milling process. Four distinct modes of machining have been identified in the milling process of brittle material. In this model, the critical conditions for different modes of machining have been determined with respect to the relationship between the radial depth of cut and the depth of subsurface damage caused by the brittle fracture during machining. Verification tests were performed on tungsten carbide workpiece and the experimental results have validated the proposed machining model. It has been established that if the radial depth of cut is greater than the subsurface-damage depth in the milling process of brittle material, it is possible to finish a crack-free machined surface by removal of material through a combination of plastic deformation and brittle fracture. However, if the radial depth of cut is less than the subsurface damage depth, brittle fracture must be prevented in ductile-mode milling to finish a crack-free machined surface.