机用等离子切割新技术

探讨了机用等离子切割技术的最新发展以及目前所采用的各种等离子系统．并了解新技术如何改变品质、速度、生产力及易耗件的使用寿命。此外,介绍了在采购新的机用等离子系统时应注意的主要功能与特点。     

Experimental determination of the critical welding speed in high speed MAG welding

In high speed MAG welding process, some weld formation defects may be encountered. To get good weld quality, the critical welding speed beyond which humping or undercutting weld bead can occur must be known for different conditions. In this research, high speed MAG welding tests were carried out to check out the effects of different factors on the critical welding speed. Through observing the weld bead profiles and the macrographs of the transverse sections of MAG welds, the occurrence tendency of humping weld was analyzed, and the values of critical welding speed were determined under different levels of welding current or voltage, and the effect of shielding gas compositions on the critical welding speed was also investigated.     

交流变频容积调速回路的特性与速度控制

分析了交流变频容积调速回路的调速特性, 并采取模糊控制策略提高了液压马达的响应速度及转速稳定性。     

一种新型的无速度传感器感应电机转速与定子电阻辨识方案

在Matlab/Simulink环境下搭建了基于自适应观测器的感应电机无速度传感器直接转矩控制系统仿真平台,应用Popov超稳定性理论,建立了基于自适应观测器的速度和定子电阻辨识率,并采用改进的空间矢鼍涮制技术取代传统直接转矩控制的开关表方案.仿真结果表明该模型具有很好的速度响应,并具有良好的鲁棒性.     

Critical cutting speed for onset of serrated chip flow in high speed machining

The transition of continuously smooth chip flow to periodically serrated chip flow as the cutting speed increasing is one of the most fundamental and challenging problems in high speed machining. Here, an explicit expression of the critical cutting speed for the onset of serrated chip flow, which is given in terms of material properties, uncut chip thickness and tool rake angle, is achieved based on dimensional analysis and numerical simulations. It could give reasonable predictions of the critical cutting speeds at which chips change from continuous to serrated for various metallic materials over wide ranges of uncut chip thickness and tool rake angle. More interestingly, it is found that, as the turbulent flow is controlled by the Reynolds number, the transition of the serrated chip flow mode is dominated by a Reynolds thermal number. Furthermore, the influences of material properties on the emergence of serrated chip flow are systematically investigated, the trends of which show good agreement with Recht’s classical model.     

同周速飞剪与异周速飞剪力能参数对比研究

介绍了断裂理论及断裂准则(Normalized CockcroftLatham),同时运用有限元软件DE-FORM-2D对异周速滚筒式飞剪动态剪切过程进行模拟,对比了同周速飞剪和异周速飞剪剪切力、剪切功、侧推力及剪切扭矩等力能参数的差异,对比分析了两种剪切方式下剪切断面质量,为滚筒式飞剪剪切理论研究提供了一定的依据。     

Nitriding of high speed steel

Abstract

Current practice when nitriding high speed steel (HSS) cutting tools is to avoid embrittlement of the cutting edge by limiting the depth of the diffusion zone. This is accomplished by reducing the nitriding time and temperature and eliminating any compound layer formation. However, in many applications there is an argument for generating a compound layer with beneficial tribological properties. In this investigation, results are presented of a metallographic, X-ray diffraction and X-ray photoelectron spectroscopy analysis of nitrided HSS surface layers generated using active screen plasma nitriding and reactive vapour deposition using cathodic arc. These results are discussed in the context HSS cutting tool performance when machining under built-up edge conditions.     

The influence of speed on material removal mechanism in high speed grinding with single grit

In this paper, the effect of speed on material removal was investigated by single grit grinding of the GH4169 super alloy which is difficult to machine, with a new test method. During the tests the whole material removal process, was observed and then the critical thickness of chip formation was quantitatively analyzed. In order to provide insight into the speed effect, the grinding forces, chip formation and pile-up ratio were investigated. It was found that the stages of material removal process changed with the grinding speed, and the graphical relationships between grinding speed and the critical thickness of chip formation, grinding forces and the pile-up ratio were found to have a common characteristic, namely a common turnover point which was about 100 m/s. This trend in the results is attributed to alternating predominance between the strain hardening and thermal softening effects. The results of this study demonstrated that the grinding speed has a significant impact on material removal mechanism, and also provide a basis for sound understanding of the high speed grinding process of difficult to cut materials.     

转速对电磁离心铸造高碳高速钢碳化物的影响

用自制的电磁离心铸造机在磁场强度为0.10T,离心转速分别为600、960、1370 r/min条件下制备了高碳高速钢,利用光学显微镜(OM)、扫描电子显微镜(SEM)、能谱分析(EDS)对不同转速下制备的高碳高速钢的一次碳化物和二次碳化物进行了实验研究.结果表明,随着离心转速的提高,铸态组织块状碳化物颗粒逐渐变细小、分布变均匀,弥散;共晶组织中碳化物板条逐渐变短、变细,间距变小;热处理组织中细小的颗粒状碳化物逐渐增多,分布趋于均匀、弥散,且粒度呈现减小的趋势.     

一种用于永磁同步电机无速度传感器控制系统的转速辨识复合算法

本文针对永磁同步电机控制系统,提出了一种将模型参考自适应(MARS)转速辨识算法与直接估算转速算法相结合的转速辨识复合算法,并构建了复合仿真模型。结果表明,采用复合算法的系统性能优于只采用单一的MARS转速辨识算法的系统性能。     

Chatter suppression by adaptive speed modulation

In this paper a PD fuzzy logic controller is designed and implemented to suppress chatter in peripheral milling. The controller selects combinations of the amplitude and frequency of spindle speed modulation, online, to keep a chatter indicator, the R-value, close to a prescribed set point. The controller was successful in suppressing chatter at certain operating points. The effect of the control action delay time and the degree of process instability on the controller performance were addressed through simulations and experiments. At some operating points the controller resulted in an oscillatory behaviour of the process and the R-value fluctuated significantly. Stability lobes were used to explain this phenomenon. Strategies for enhancing the performance of the controller were proposed.     

Effect of roll speed ratio on deformation characteristics of IF steel subjected to differential speed rolling

The paper investigates the effect of the roll speed ratio on the deformation characteristics of interstitial free (IF) steel processed by the differential speed rolling (DSR) technique. An intense plastic strain induced by a single DSR with various roll speed ratios ranging from 1:1 to 1:4 for the lower and upper rolls was successfully imparted to the samples, resulting in the formation of fine elongated ferrite grains as the roll speed ratio increased. Observations of the preferred orientation using electron back-scattered diffraction and transmission electron microscopy revealed that the {110} slip was readily activated as the dominant deformation mode in order to accommodate the intense plastic strain imposed by the DSR. In addition, the microhardness values of the IF steel sample deformed via DSR under a roll speed ratio of 1:4 increased, and this is discussed on basis of the frictional force between the roll and the sample during DSR deformation.     

High speed measurement of engineering surfaces

This paper considers the case for on line gaging of surface texture. Some systems for the logical implementation of gaging and the traceability of the necessary standards are discussed.The introduction of some well known statistical functions such as auto and cross correlation, via optical techniques are cited, along with methods for using coherent scattering (speckle) and specular reflection to gage finish.The use of unthinking routines based upon simple logic and patterned on the compound eye of lower crustations can give the speed along with low cost, that may be required in the production environments of the future.     

High speed fusion weld bead defects

Abstract

A comprehensive survey of high speed weld bead defects is presented with strong emphasis on the formation of humping and undercutting in autogenous and non-autogenous fusion welding processes. Blowhole and overlap weld defects are also discussed. Although experimental results from previous studies are informative, they do not always reveal the physical mechanisms responsible for the formation of these high speed weld bead defects. In addition, these experimental results do not reveal the complex relationships between welding process parameters and the onset of high speed weld bead defects. Various phenomenological models of humping and undercutting have been proposed that were based on observations of events in different regions within the weld pool or the final weld bead profile. The ability of these models to predict the onset of humping or undercutting has not been satisfactorily demonstrated. Furthermore, the proposed formation mechanisms of these high speed weld bead defects are still being questioned. Recent welding techniques and processes have, however, been shown to be very effective in suppressing humping and undercutting by slowing the backward flow of molten metal in the weld pool. This backward flow of molten weld metal may be the principal physical phenomenon responsible for the formation of humping and undercutting during high speed fusion welding.     

Tool optimization for high speed grinding

Vitrified bonded cBN grinding wheels catches on for batch production especially in the automotive industry for components of power trains. In pursuit of higher productivity with steady quality the optimization of manufacturing processes and tools are getting more relevant. In this contribution potentials and challenges of structured grinding tools for the optimization of grinding processes are discussed. Technological investigations with structured and non-structured vitrified bonded cBN grinding wheels were carried out and the results of varying setting parameters were analyzed. The main aspects of interest for these studies were the detection of possible coolant savings and phenomena of vibrations, the reduction of the thermal damage of the workpieces as well as the influence on the workpiece roughness and the grinding wheel radial wear. The experiments show the potentials of structured cBN grinding wheels for roughing and finishing in cylindrical plunge grinding processes. But there are some basic requirements for the geometry of the structures especially due to the vibrations of the grinding process. For the roughing tests the adequate structured abrasive layers show less grinding forces and thermal damage of the workpiece. For finishing processes the results show comparable values of roughness and waviness referring to non-structured grinding wheels. In addition, a limit for suitable grinding wheel structures in conjunction with the setting parameters could be identified that offers valuable clues for the dimensioning of structured abrasive layers even for non-circular grinding processes.     

高速切削加工中的刀具技术

高速切削加工切削速度、进给速度和加速度提高近一个数量级,对刀具技术提出新的要求并促进其不断发展.文章分析了由于旋转离心惯性力大幅度增大引起的刀具与夹紧装置机械故障及其预防保护措施,概括了高速切削常用的刀具材料、应用范围及制造新技术,归纳了加工中缓解刀具寿命下降的工艺措施,介绍了新型的激光刀具检测系统的性能、工作原理和优点,表明刀具技术的综合性、系统性.     

高速三丝熔化极气保护焊接工艺

针对造船企业平面分段生产流水线纵骨双丝角焊接最大焊接速度小于1.0m/min的问题,研究开发了高速三丝熔化极气保护焊接新工艺,即三根焊丝分别为引导焊丝、中间焊丝和跟随焊丝纵向排列。每根焊丝各接一套送丝系统、焊接电源和保护气,构成独立的电弧-电源系统,其焊接工艺参数分别可调,以满足各种焊接要求。结果表明,当采取引导焊丝(DCEP)/中间焊丝(DCEN)/跟随焊丝(DCEP)或引导焊丝(DCEN)/中间焊丝(DCEP)/跟随焊丝(DCEN)的极性组合时,焊接过程稳定,焊缝外观表面光洁、左右对称、起渣容易、飞溅小、无气孔,满足船舶焊接的要求。通过选用合适的焊接电流、电压组合,可以使焊接速度达到1.8m/min,焊脚长度达5～8mm。此焊接新工艺可广泛用于角焊缝的高速焊接应用场合。     

双稳态高速开关力矩马达浙

高速开关阀的开关特性在很大程度上取决于其电-机械转换元件的特性.本文提出了一种新型电-机械转换元件--双稳开关力矩马达,该马达由脉冲电流驱动,具有记忆功能.理论分析和测试结果表明,该力矩马达具有较高的开关速度.