加工方法对基于CAD/CAM数控曲面加工质量与效率的影响

对基于CAD／CAM的三坐标数控曲面加工的参数线加工方法、截面线加工方法和投影加工方法的加工表面质量、加工效率、编程的方便性及零件加工程序规模进行了理论分析和实验研究,为合理选用三坐标数控曲面加工方法提供了参考依据。研究结果表明：在相同加工曲面和工艺条件下,参数线加工的加工表面质量较高,截面线加工的加工效率较高,投影加工编程方便且具有较大的综合优势。文中给出了在相同加工曲面和工艺条件下,参数线加工、截面线加工和投影加工方法的零件加工表面粗糙度、加工时间、零件加工程序规模的实验数据,并据此提出了它们的适用范围。最后,提出了提高三坐标数控曲面加工质量和效率的措施。     

聚晶金刚石加工技术进展

介绍了国内外正在研究和已经应用的聚晶金刚石的主要加工方法,即磨削加工、研磨加工、电火花加工、激光加工、化学加工、超声加工和复合加工,并对这些加工方法的特点、机理及影响因素、适用范围进行了分析。     

基于模具的高速切削加工技术

叙述了在模具加工中为实现高速加工所必需的一些关键技术及高速加工技术在模具制造中应用的意义,并通过与电火花加工方式的对比,描述了高速加工的优越性和局限性,最后以加工实例说明高速加工能有效缩短加工时间,提高加工精度。     

书讯

《第14届全国特种加工学术会议论文集》本书收录了第14届全国特种加工学术会议交流论文129篇,由综述、电火花成形加工技术、电火花微小孔加工技术、电火花线切割加工技术、其他电火花加工技术、电化学加工技术、激光加工及快速成形技术、复合加工技术、其他特种加工技术等9个部分组成,全面展示了近年来我国特种加工领域学术理论研究和自主技术创新的成果,可供特种加工领域     

电火花加工寻找最优电极加工时间的算法研究

根据电火花加工中电极加工时间对加工效率的影响规律,提出了寻找一定加工深度下最优电极加工时间的算法。通过电火花加工实验,利用算法分别寻找不同加工深度下的最优电极加工时间,与手动调整电极加工时间的寻找结果对比,发现二者相近,证明算法能准确快速地找到当前加工深度下的最优电极加工时间。     

基于特种加工的微细制造技术

通过例证概括介绍了特种加工方法在微细加工方面所取得的成就，这些加工技术包括：电火花加工、电化学加工、超声加工、激光加工、精密电铸等。阐述了特种加工技术在微细制造方面的特点：擅长加工复杂的三维微机械结构，且投资小，适于中小批量生产。     

工艺参数对TC4钛合金电解加工速率及加工质量的影响

目的 研究工艺参数对TC4钛合金电解加工速率及加工质量的影响。方法 采用三因素三水平的正交试验方法,通过实验研究了频率、占空比及加工间隙对加工速度及加工质量的影响规律,对正交试验结果进行了F检验,对加工参数的显著性进行了分析。采用激光共聚焦显微镜表征工件表面形貌及测量工件表面粗糙度。建立了电解液内流场数值仿真模型,获得了电解加工过程中加工区域电解液流动的规律。结果 本研究中电解加工频率及加工间隙对电解加工材料去除量的影响显著,占空比对材料去除量的影响不显著,在加工间隙为0.2 mm、加工频率为100 Hz的条件下,材料去除量最大,为0.261 g,表面粗糙度最低,为0.484 μm。降低加工间隙或提高加工频率,均有利于提高材料去除量,降低工件表面粗糙度。电解加工区域内的电解液流速分布规律与电解加工区域加工深度具有较好的一致性。结论 电解加工频率及加工间隙对电解加工速率及电解加工质量均有较大的影响,在实际加工过程中,应减小加工间隙,提高加工频率,以提高电解加工速率,降低加工表面粗糙度。加工区域内,电解液流速分布的均匀性对工件加工表面的均一性有一定影响,应合理设计夹具,以提高加工区域内电解液流速均匀性,从而提升加工表面均一性。     

深小孔加工方法综述

深小孔在各个领域中有着广泛的应用。深小孔加工方法主要分为传统加工方法和非传统加工方法两大类。文中主要对钻削加工、电火花加工、电解加工、电解-电火花复合加工以及其他加工方法进行了详细的分析,并总结了各加工方法的优缺点。     

第18届国际电加工会议综述

对第18届国际电加工会议论文进行了综述,介绍了近年来国际特种加工领域的最新研究进展。主要内容包括电火花成形加工、电火花线切割加工、电化学加工、超声加工、激光加工、增材制造、微细特种加工及相关复合加工工艺的研究成果。     

精密微小孔加工技术进展

介绍了国内外精密微小孔加工技术的现状、应用和发展方向,并列举了多种加工方法,包括传统机械加工、特种加工和复合加工。重点介绍了特种加工技术在精密微小孔加工中的应用,由于其加工精度高、生产成本低、应用范围广,特别适合于加工硬脆等难加工材料,因而是精密微小孔加工的发展方向。同时,还针对不同微小孔加工方法中的不足,介绍了相应的解决办法。     

A hybrid algorithm for predicting chip form/chip breakability in machining

Prediction of chip breakability for a wide range of machining conditions is a difficult task. Currently available predictive machining theories are not suitable for use in the shop floor environment. The methodology presented in this paper provides a new and viable means to predict chip breakability and chip shapes/sizes in machining process planning systems. Due to the extreme difficulty involved in developing a numerical model for predicting chip breakability for a wide range of machining conditions, including work materials, tool geometry, chip-breakers and cutting conditions, this paper presents a hybrid algorithm-based model to characterize various chip shapes and sizes, and to quantify the chip form/chip breakability based on a chip control reference database developed through a set of systematic machining experiments. The chip form and chip breakability could then be predicted with reasonable accuracy for a given set of machining conditions using this new algorithm in conjunction with the chip control reference database.     

Machining Ti–6Al–4V alloy with cryogenic compressed air cooling

A new cooling approach with cryogenic compressed air has been developed in order to cool the cutting tool edge during turning of Ti–6Al–4V alloy. The cutting forces, chip morphology and chip temperature were measured and compared with those measured during machining with compressed air cooling and dry cutting conditions. The chip temperature is lower with cryogenic compressed air cooling than those with compressed air cooling and dry machining. The combined effects of reduced friction and chip bending away from the cutting zone as a result of the high-speed air produce a thinner chip with cryogenic compressed air cooling and a thicker chip with compressed air cooling compared to dry machining alone. The marginally higher cutting force associated with the application of cryogenic compressed air compared with dry machining is the result of lower chip temperatures and a higher shear plane angle. The tendency to form a segmented chip is higher when machining with cryogenic compressed air than that with compressed air and dry machining only within the ranges of cutting speed and feed when chip transitions from continuous to the segmented. The effect of cryogenic compressed air on the cutting force and chip formation diminishes with increase in cutting speed and feed rate. The application of both compressed air and cryogenic compressed air reduced flank wear and the tendency to form the chip built-up edge. This resulted in a smaller increase in cutting forces (more significantly in the feed force) after cutting long distance compared with that observed in dry machining.     

A three-dimensional model of clip flow, chip curl and chip breaking for oblique cutting

In recent years, many publications have appeared dealing with chip breaking in orthogonal cutting of metals. However, in industry, oblique cutting and not orthogonal cutting is encountered in almost all actual machining operations. This paper deals with a model of chip flow, chip curl and chip breaking for oblique cutting. To simplify the analysis, a set of equivalent parameters are introduced. The relationship between the machining parameters and their corresponding equivalent parameters is developed theoretically and experimentally. To assess the level of chip breaking, a criterion of chiplbreaking is suggested under the concept of these equivalent parameters. The agreement of the experimental results with the predictive data of the model verifies that the definition of these equivalent parameters is reasonable. The influences of various machining parameters are discussed, in relation to their corresponding parameters. One significant finding is that the effect of each of the machining parameters on chip breaking is not totally inpdependent of one another. This implies that careful attention must be paid to the relationship between various machining parameters in three-dimensional parameters.     

Effect of micro-textured tools on machining of Ti–6Al–4V alloy: An experimental and numerical approach

In this work, an attempt is made to reduce the detrimental effects that occurred during machining of Ti–6Al–4V by employing surface textures on the rake faces of the cutting tools. Numerical simulation of machining of Ti–6Al–4V alloy with surface textured tools was employed, taking the work piece as elasto-plastic material and the tool as rigid body. Deform 3D software with updated Lagrangian formulation was used for numerical simulation of machining process. Coupled thermo-mechanical analysis was carried out using Johnson-cook material model to predict the temperature distribution, machining forces, tool wear and chip morphology during machining. Turning experiments on Ti–6Al–4V alloy were carried out using surface textured tungsten carbide tools with micro-scaled grooves in preferred orientation such as, parallel, perpendicular and cross pattern to that of chip flow. A mixture of molybdenum disulfide with SAE 40 oil (80:20) was used as semi-solid lubricant during machining process. Temperature distribution at tool–chip interface was measured using an infrared thermal imager camera. Feed, thrust and cutting forces were measured by a three component-dynamometer. Tool wear and chip morphology were captured and analyzed using optical microscopic images. Experimental results such as cutting temperature, machining forces and chip morphology were used for validating numerical simulation results. Cutting tools with surface textures produced in a direction perpendicular to that of chip flow exhibit a larger reduction in cutting force, temperature generation and reduced tool wear.     

Experimental determination of the tool–chip thermal contact conductance in machining process

Tool–chip contact is still a challenging issue that affects the accuracy in numerical analysis of machining processes. The tool–chip contact phenomenon can be considered from two points of view: mechanical and thermal contacts. Although, there is extensive published literature which addresses the friction modeling of the tool–chip interface, the thermal aspects of the tool–chip contact have not been investigated adequately. In this paper, an experimental procedure is adopted to determine the average thermal contact conductance (TCC) in the tool–chip contact area in the machining operation. The tool temperature and the heat flux in tool–chip contact area were determined by inverse thermal solution. Infra-red thermography was also used to measure the average chip temperature near the tool–chip interface. To investigate the effects of the work piece material properties on the tool–chip TCC, AISI 1045, AISI 304 and Titanium materials were considered in the machining experiments. Effects of the cutting parameters such as cutting velocity and feed rate on TCC were also investigated. Evaluating the tool–chip thermal contact conductance for the tested materials shows that TCC is directly proportional to the thermal conductivity and inversely proportional to the mechanical strength of the work piece. The thermal contact conductance presented in this paper can be used in the future numerical and analytical modeling of the machining process to achieve more accurate simulations of the temperature distribution in the cutting zone and better understanding of the tool–chip contact phenomena.     

Quantification of the chip segmentation in metal machining: Application to machining the aeronautical aluminium alloy AA2024-T351 with cemented carbide tools WC-Co

The chip segmentation process has a significant effect on the cutting force fluctuation during machining which could affect tool vibration and tool wear. This paper deals with a quantitative analysis of the chip segmentation phenomenon in metal machining. The notion of intensity of the phenomenon has been introduced. Various parameters have been proposed for this purpose. These parameters are based on dimensional characteristics of the segmented chip and the strain distribution within the chip. A Finite Element based modelling has been developed to simulate the chip formation process in the case of machining aeronautical aluminium alloy AA2024-T351 with WC-Co based cutting tools. From the simulated chip morphologies, introduced chip segmentation parameters are assessed. The impact of the cutting speed and tool geometry on the chip segmentation intensity is clearly highlighted. The relevance of each parameter is discussed. Cutting force and contact length fluctuations with respect to the cutting speed variation when segmentation occurs are discussed and deeply analysed. A correlation between average cutting force reduction and segmentation intensity when the cutting speed increases as well as between chip formation process and cutting force oscillation has been established thanks to the introduced parameters, showing thus their usefulness.     

The prediction of dimensional error for sculptured surface productions using the ball-end milling process. Part 1: Chip geometry analysis and cutting force prediction

The study of machining errors caused by tool deflection in the balkend milling process involves four issues, namely the chip geometry, the cutting force, the tool deflection and the deflection sensitivity of the surface geometry. In this paper, chip geometry and cutting force are investigated. The study on chip geometry includes the undeformed radial chip thickness, the chip engagement surface and the relationship between feed boundary and feed angle. For cutting force prediction, a rigid force model and a flexible force model are developed. Instantaneous cutting forces of a machining experiment for two 2D sculptured surfaces produced by the ball-end milling process are simulated using these force models and are verified by force measurements. This information is used in Part 2 of this paper, together with a tool deflection model and the deflection sensitivity of the surface geometry, to predict the machining errors of the machined sculptured surfaces.     

铝合金高速铣削过程切屑成形机制研究

高速铣削加工中,切削力、切削热和机床振动等被广泛研究,而对切屑的研究相对较少.本文针对立铣刀高速铣削的特点,对切屑的成形进行了研究.根据理论分析,在UG环境下对切屑进行了绘制,其形状与实际切屑基本吻合,证明了研究方法的可靠性.通过切屑的研究反馈设计过程,对立铣刀的结构设计提供支持.     

Energy dissipation in modulation assisted machining

The specific energy in modulation assisted machining (MAM) – machining with superimposed low frequency (<1000 Hz) modulation in the feed direction – is estimated from direct measurements of cutting forces. Reductions of up to 70% in the energy are observed relative to that in conventional machining, when cutting ductile metals such as copper and Al 6061T6. Evidence based on chip structures and strains, stored energy of cold work, recrystallization, and finite element simulation of chip formation, is presented to show that this reduction is due to smaller strain levels in chips created by MAM. A simple geometric ratio of the length to thickness of the ‘undeformed chip’, which can be estimated a priori from MAM and machining parameters, is shown to be a predictor of the transient chip formation conditions that result in the reduction in specific energy and deformation levels.     

Chip formation and modeling of dynamic force behavior in machining polycrystalline iron–aluminum

Intermetallic iron–aluminum (FeAl) has an excellent resistance against corrosion and abrasion, a low density as well as high specific strength compared to conventional steel. In addition, the raw materials and manufacturing costs of FeAl-alloys are relatively low. The machinability is challenging. Economical machining of FeAl-alloys is currently not possible because of high tool wear. The chip formation mechanisms in machining FeAl-alloys are currently unknown. This study focuses on the influence of the material grain size on the thermomechanical processes during chip formation. A simultaneous measuring system for the determination of process forces, temperatures and chip formation in planing and orthogonal turning is presented. The chip formation mechanisms change with the grain transition and grain size. Decreasing grain sizes lead to the higher ductility in material separation by favorable thermomechanical loads and reduced crack initiation. By using force data from monocrystalline machining a model is introduced, which predicts the force dynamics in machining of polycrystals.