Estimation of Maximum Allowable Step Length for Five-Axis Cylindrical Machining

Five-axis cylindrical machining is the only way to machine some complicated sculptured surfaces, such as the wheel surfaces of turbo compressors. Current computer-aided manufacturing (CAM) algorithms for five-axis cylindrical machining only consider the surfaces’ geometric information when generating cutter contact points (CC points). Hence, the step length, which is the distance between two CC points, is determined only by the surface parameters for these CAM algorithms. Because of tool-axis rotation, the actual cut trajectory within each step is no longer a straight line passing through two consecutive CC points for five-axis machining. Thus the cut error and the maximum allowable step length should depend on the structural parameters of NC machines as well as the surface's geometry. This paper develops a new algorithm to estimate the maximum allowable step length based on the cut error of five-axis cylindrical machining, and shows that this algorithm provides better estimation than traditional algorithms.     

Ruled Surface Machining on Five-Axis CNC Machine Tools

To achieve high precision and high productivity in machining sculptured surfaces, a new architecture for a five-axis CNC interpolator for machining ruled surfaces was developed and demonstrated on a milling machine. The objective of the five-axis interpolator is to continuously maintain the milling cutter axis in parallel with the straight lines of the ruled surface. The cutter position and orientation are calculated at each sampling period of the interpolator, and corresponding axial position commands are generated by an inverse kinematics algorithm. This real-time approach produces precise surfaces and requires substantially less machining time compared to the conventional off-line approach. Two new g-codes are also given in this paper for the new interpolator to produce part surfaces in CNC milling machines.     

Cryogenic Machining of Tantalum

A new approach for the machining of tantalum is presented. The new approach is a combination of traditional turning and cryogenically enhanced machining (CEM). In the tests, CEM was used to reduce the temperature at the cutting tool/workpiece interface, and thus reduce the temperature-dependent tool wear to prolong cutting tool life. The new method resulted in a reduction of surface roughness of the tantalum workpiece by 200% and a decrease of cutting forces by approximately 60% in experiments. Moreover, cutting tool life was extended up to 300% over that in the conventional machining.     

Parallel Kinematic Machine Positioning Accuracy Assessment and Improvement

Although parallel kinematic machines potentially offer high force/torque capacity, structural rigidity, speeds, and dexterity, characterization of the first generation of hexapods has proven the need for improving the positioning accuracy before these new machines will be accepted for manufacturing applications. This paper proposes a systematic approach to assess the accuracy of a parallel kinematic machine subject to structural errors and then to effectively compensate for them. Analytical models were constructed for both the nominal and actual structures. Sensitivity analysis was performed, and it was determined-that of the 33 sources of error, only the six due to strut length deviations are significant. Simulations indicate that the accuracy of strut length calculations shows a discrepancy of at most ±4 micrometers. In summary, the simulation and preliminary experimental results show that the performance of parallel kinematic machines can be enhanced through error modeling and compensation.     

Comparison of Parallel Structure Concepts for Five-Axis Machining

Parallel structures are characterized by closed kinematics chains. Compared with conventional structures, which have serially arranged axes and are thus characterized by open kinematics chains, parallel structures have a variety of advantages. These primarily include lower moved mass, high dynamics, the high number of possible repeating parts, and the advantageous integration of measures in the control system that are relevant to accuracy. The following presentation classifies parallel structures with six degrees of freedom according to the type of drive used. Based on free-form surface machining in die and mold making, kinematics requirements will be explained and various concepts regarding kinematics, structure. loading, and stiffness will also be discussed. Finally, a preferable solution will be provided in the summary.     

车装焊复合加工装备的服役可靠性评估

目的评估某型航天用车装焊复合加工装备在服役过程中的服役可靠性。方法首先分析装备常见的故障模式,统计装备在使用过程中的故障数据,由于装备故障数据样本量较少,所以提出基于贝叶斯理论的小样本车装焊复合加工装备可靠性评估方法,其中通过马尔科夫链蒙特卡罗(MCMC)法抽样解决贝叶斯理论中后验积分复杂的问题。结果确定了车装焊复合加工装备的寿命威布尔分布模型,并运用贝叶斯方法,计算出该车装焊复合加工装备的平均无故障工作时间(MTBF)。结论评估结果略低于设计要求,原因是目前该装备处于服役初期,服役初期故障数据较多。待进入稳定服役期时,故障率会有一定程度的降低后趋于稳定,MTBF会有一定幅度的增加,所以该车装焊复合加工装备MTBF基本满足设计要求。     

机械加工振动公害控制

根据多年从事机械、环保科研设计及工厂的实践 ,仔细分析了机械加工振动污染源对操作者及周围居民的危害。并提出了对其所造成的公害进行适应控制的基本措施。     

浸河水环境对某小口径步枪的动力学影响分析

目的 研究浸河水环境对某小口径步枪自动机运动特性的影响规律。方法 采用摩擦系数仪测得在浸河水后自动机枪机框与枪机、导轨之间的摩擦系数,获得浸河水浓度对2个摩擦系数的影响规律。根据某小口径步枪的三维模型,在ADAMS平台中,建立其虚拟样机模型,并进行模型验证。在上述基础上,将不同浸河水后运动副间的摩擦系数加载到模型中,经仿真分析获得不同浸河水浓度对自动机运动特性的影响规律。结果 某小口径步枪的枪机、导轨与枪机框之间的摩擦系数随着浸河水浓度的增加而有所增大,而自动机的后坐到位速度、复进开始速度、复进到位速度以及射频都会随着浸河水浓度的增加而下降,其中,后坐到位速度在不同浸河水浓度环境下的降低幅度最小,其降低幅度小于10%,复进到位速度的降低幅度最大,为16.9%,但自动机后坐最大速度与浸河水浓度无关。结论 浸河水环境会增大运动副间的摩擦系数,增加自动机运动过程中的能量损耗,且当浸河水的质量浓度增大到20 kg/m³时,出现后坐不到位故障,运动副之间的摩擦系数对自动机的复进到位无影响。     

A Postprocessor Based on the Kinematics Model for General Five-Axis Machine Tools

This paper presents a novel concept to describe the three types of five-axis machine tools by a generalized kinematic structure. A generic postprocessor capable of converting the cutter location (CL) data to machine control data was developed based on the generalized kinematics model of five-axis machine tools. The machine tool's form-shaping function matrix is derived according to the homogeneous coordinate transformation matrix and the kinematic parameters characterizing the configuration of general five-axis machine tools. The analytical equations for NC data are determined by equating the CL data matrix and the form-shaping function matrix. A trial-cut experiment on a typical five-axis machine tool and the verification on the coordinate measurement machine demonstrates the effectiveness of the proposed scheme. The algorithm proposed here can facilitate determination of the postprocessors for various five-axis machine tools more systematically.     

Laser tempering based turning process for efficient machining of hardened AISI 52100 steel

Cost-effective machining of hardened steel components such as a large wind turbine bearing has traditionally posed a significant challenge. This paper presents an approach to machine hardened steel parts efficiently at higher material removal rates and lower tooling cost. The approach involves a two-step process consisting of laser tempering of the hardened workpiece surface followed by conventional machining at higher material removal rates with lower cost ceramic tools to efficiently remove the tempered material. The laser scanning parameters that yield the highest depth of tempered layer are obtained from a kinetic phase change model. Machining experiments are performed to demonstrate the possibility of higher material removal rates and improved tool wear behavior compared to the conventional hard turning process. Tool wear performance, cutting forces, and surface finish of Cubic Boron Nitride (CBN) tools as well as low cost ceramic tools are compared in machining of hardened AISI 52100 steel (~63 HRC). In addition, cutting forces and surface finish are compared for the laser tempering based turning and conventional hard turning processes. Experimental results show the potential benefits of the laser tempering based turning process over the conventional hard turning process.     

机器学习在碳基环境功能材料领域的应用研究进展

随着环境功能材料领域产生的数据量及其数据复杂性急剧增加,高成本、长周期的传统实验手段已无法迎合目前功能材料的发展趋势。近年来迅速发展的机器学习能对数据进行深入挖掘和解析,有望为此类问题提供有效的解决方案。机器学习具备效率高、精度高等优势,有效弥补了传统"试错"方式的不足。介绍了机器学习的基本工作原理和算法,从预测理化性质、辅助微观表征和指导新型材料合成3个方面简述了机器学习在环境碳基功能材料领域中的应用研究进展,分析了机器学习在该领域的问题与挑战,展望了机器学习方法在环境碳基功能材料领域的前景与发展趋势。     

Robust prediction of chatter stability in milling based on the analytical chatter stability

A major obstacle that limits the productivity in machining operations is the presence of machine tool chatter. Machining is a dynamic process and chatter behavior depends upon a number of different aspects including spindle speeds, material properties, tool geometry, and even the location of tool respect to the rest of machine. Many of the traditional models used to predict chatter stability lobes assume that parameters such as natural frequency, stiffness, and cutting coefficients remain constant. In reality, these parameters vary and they affect the chatter stability. The uncertainty in these parameters can be taken into consideration by employing the robust stability theory into a two degree of freedom milling model. Utilizing the Edge theorem and the Zero Exclusion condition, a robust chatter stability model, based on the analytical chatter stability milling model, is developed. This improves the reliability compared to the projected pseudo single degree of freedom model. The method is verified experimentally for milling operations while considering a changing natural frequency and cutting coefficient.     

端面齿形的切削加工与冷锻成形

对端面齿齿形的各种加工原理作了详细的介绍,分析了切削加工及冷锻成形工艺对端面齿齿形的影响.     

Evaluating the use phase energy requirements of a machine tool system

This paper has an energy consumption reduction perspective by considering alternative machining strategies and system components interactions translated into variable and constant power flows with respect to various use phase regimes of a machine tool system. The methodology is able to estimate the mechanical energy requirements of the spindle and feed axes with respect to 2.5D machining strategies by taking into account steady-state and transient regimes. In addition, the specific amount of fixed energy drawn by a machine was determined based on a careful monitoring of the energy share amongst the auxiliary equipment that supports the accomplishment of the machining tasks. The numerical results were experimentally validated and the good agreement between them led to the conclusion that the proposed methodology can be used effectively for the calculation of the total energy required by a machine tool system for the milling of a part. This enables a straightforward comparison of different milling part programs with respect to their energy consumption levels.     

加工回转体零件的柔性制造系统

概述了柔性制造系统的组成、各部分功能以及维护等方面的内容 ,为了解认识FMS提供了背景知识 ,旨在推广FMS的应用范围。     

浅谈锌合金冲裁模制造工艺

介绍了应用锌合金技术制造冲裁模具的工艺方法和注意事项及在生产实际中所达到的效果     

An experimental investigation into micro ball end-milling of silicon

Silicon is a representative operational material for semiconductor and micro-electronics. In certain MEMS applications, it is required to fabricate three dimensional channels and complex pattern on silicon substrate. Such features are typically fabricated by photolithography and chemical etching. These processes have low productivity and have certain other limitations. Therefore, a viable switch-over from non-traditional fabrication processes to traditional machining is highly desired for improved productivity in high-mix low-volume production. However, machining of silicon by traditional process is extremely difficult due to its high brittleness. Even very small forces produced during machining can cause brittle fracture on silicon surface resulting in deteriorated surface quality. The fundamental principle in machining of a brittle material such as silicon is to achieve material removal through plastic deformation rather than crack propagation. This paper presents the experimental results of ductile-mode machining of silicon by micro ball end-milling. The workpiece surface was inclined to the rotational axes of the cutter to improve the surface finish. It was established experimentally that 15-μm deep, fracture-free slots can be machined on silicon wafer by micro ball end-milling if the feed rate is below a certain threshold. The influence of several machining parameters on the roughness of machined-surface was also investigated. Cubic boron nitride (CBN) is presented as much economical alternative tool-material to single-crystal diamond for machining silicon in ductile-mode.     

Machining assessment of nano-crystalline hydroxyapatite bio-ceramic

Hydroxyapatite (HAP) is a widely used bio-ceramic in the fields of orthopedics and dentistry. This study investigates the machinability of nano-crystalline HAP (nHAP) bio-ceramic in end milling operations, using uncoated carbide tool under dry cutting conditions. Efforts are focused on the effects of various machining conditions on surface integrity. A first order surface roughness model for the end milling of nHAP was developed using response surface methodology (RSM), relating surface roughness to the cutting parameters: cutting speed, feed, and depth of cut. Model analysis showed that all three cutting parameters have significant effect on surface roughness. However, the current model has limited statistical predictive power and a higher order model is desired. Furthermore, tool wear and chip morphology was studied. Machined surface analysis showed that the surface integrity was good, and material removal was caused by brittle fracture without plastic flow.     

Parametric glass milling with simultaneous control

Parametric glass milling is presented to machine periodical circular channels on the glass plates for manufacturing micro testing devices. An end mill traverses in the linear motion during the workpiece rotation, which are synchronized by simultaneous control. The glass milling is controlled by 4 parameters in a mathematical model without NC program. Based on the principle of the parametric machining and the effect of the cutter axis inclination on the cutting process, a milling machine was developed to perform the parametric glass milling with an inclined ball end mill. The cutter axis inclination and the actual feed rate are associated with the critical feed rate, the maximum feed rate at which a crack-free surface is finished. As a machining example, a periodical circular channel was machined with a transparent surface by the simultaneous control.     

硅钢片冲孔模具的镶块修补技术

电机硅钢片冲孔模具在制造及使用中常因各种原因使某个槽孔损坏而需要修补.此文介绍了该类模具的修补技术.实践证明:该技术可延长硅钢片冲孔模具的使用寿命.