光学薄膜淀积的计算机仿真

介绍了利用计算机对光学薄膜淀积过程进行仿真 ,编写了基于 Matlab的计算机仿真程序。对采用反射率极值法监控的镀膜系统的薄膜淀积结果以及薄膜淀积过程中监控片透射率的实时变化进行了模拟 ,根据模拟结果所计算的薄膜的光学特性曲线与成膜的实测结果一致。     

MECHANISM OF CHIP FORMATION IN HIGH-SPEED TURNING OF INCONEL 718

The mechanism of serrated chip formation during high-speed turning of Inconel 718 using PCBN cutting tools has been investigated with the aid of scanning electron microscopy and optical microscopy. A conceptual model of chip formation has been developed knowing the chip morphology. It is followed by the analysis of chip segmentation frequency and the chip forms. Further, the chip segment forms and geometry were quantitatively characterized as a function of machining parameters and the cutting edge geometry using statistical methods. The chip morphology has been correlated with the cutting forces, specific shearing energy and the resultant roughness of the machined surfaces.     

Friction modelling in metal cutting

This paper reviews the experimental evidence for what is the nature of the friction contact between chip and tool during continuous chip formation and the historical development of friction models. It considers three separate circumstances of turning: at low speeds when lubricants can reduce friction by partial penetration of the chip-tool contact; at high speeds when thermal softening can provide self-lubrication; and at intermediate speeds when in some cases solid-lubricating inclusions from the work material can segregate in the chip-tool contact. It demonstrates, through numerical simulation of the turning process, shortcomings in a commonly used friction model and proposes an improved formulation.     

Simulation of Chip Formation and Fracture in the Design of Complex Turning Inserts

Theoretical principles are outlined for the design of complex cutting inserts in conditions of three-dimensional chip formation. Simulation of the formation and fracture of continuous chip provides the basis for developing a system of complex turning inserts with improved performance. Production experience with the new cutting tool is satisfactory.     

Efficient Chip Breaker Design by Predicting the Chip Breaking Performance

As machining technology develops toward the unmanned and automated system, the need for chip control is considered increasingly important, especially in continuous machining such as in the turning operation. In this study, a systematic chip breaking prediction method is proposed using a 3D cutting model with the equivalent parameter concept. To verify the model, four inserts with different chip breaker parameters were tested and their chip breaking areas were compared with those obtained from the model. Finally, a new type insert (MF1) for medium-finish operations with variable parameters was designed by modifying the commercial one. The chip breaking region predicted by using the modified 3D cutting model for the above insert agrees with the one obtained experimentally. The newly designed insert showed better chip breaking ability than the base model, and other performance tests such as surface roughness, cutting force and tool wear also showed good results.     

2D FEM estimate of tool wear in turning operation

Finite element method (FEM) is a powerful tool to predict cutting process variables, which are difficult to obtain with experimental methods. In this paper, modelling techniques on continuous chip formation by using the commercial FEM code ABAQUS are discussed. A combination of three chip formation analysis steps including initial chip formation, chip growth and steady-state chip formation, is used to simulate the continuous chip formation process. Steady chip shape, cutting force, and heat flux at tool/chip and tool/work interface are obtained. Further, after introducing a heat transfer analysis, temperature distribution in the cutting insert at steady state is obtained. In this way, cutting process variables e.g. contact pressure (normal stress) at tool/chip and tool/work interface, relative sliding velocity and cutting temperature distribution at steady state are predicted. Many researches show that tool wear rate is dependent on these cutting process variables and their relationship is described by some wear rate models. Through implementing a Python-based tool wear estimate program, which launches chip formation analysis, reads predicted cutting process variables, calculates tool wear based on wear rate model and then updates tool geometry, tool wear progress in turning operation is estimated. In addition, the predicted crater wear and flank wear are verified with experimental results.     

Study of cutting speed on surface roughness and chip formation when machining nickel-based alloy

Nickel-based alloy is difficult-to-machine because of its low thermal diffusive property and high strength at higher temperature. The machinability of nickel- based Hastelloy C-276 in turning operations has been carried out using different types of inserts under dry conditions on a computer numerical control (CNC) turning machine at different stages of cutting speed. The effects of cutting speed on surface roughness have been investigated. This study explores the types of wear caused by the effect of cutting speed on coated and uncoated carbide inserts. In addition, the effect of burr formation is investigated. The chip burr is found to have different shapes at lower speeds. Triangles and squares have been noticed for both coated and uncoated tips as well. The conclusion from this study is that the transition from thick continuous chip to wider discontinuous chip is caused by different types of inserts. The chip burr has a significant effect on tool damage starting in the line of depth-of-cut. For the coated insert tips, the burr disappears when the speed increases to above 150 m/min with the improvement of surface roughness; increasing the speed above the same limit for uncoated insert tips increases the chip burr size. The results of this study showed that the surface finish of nickel-based alloy is highly affected by the insert type with respect to cutting speed changes and its effect on chip burr formation and tool failure.     

车削Inconel 625锯齿形切屑形成对颤振影响的试验研究

为研究高温合金Inconel 625车削过程中锯齿形切屑的产生对颤振的影响,本文通过有限元软件对车削刀具、机床主轴等部件进行模态仿真,获取对应的模态频率;进行不同切削参数的车削试验,采集加速度信号并进行频域分析以获取其FFT功率谱。通过超景深显微镜观察切屑形态,并计算不同切削参数下的切屑锯齿化频率。对比仿真和试验结果发现:当切屑锯齿化频率接近于车床某部件的主振频率时,产生了较大的颤振峰值,这说明锯齿形切屑的产生会诱导切削颤振发生,对切削过程稳定性产生了不利的影响。     

基于AdvantEdge的斜角车削仿真实验确定刀屑摩擦因数的方法

当使用AdvantEdge软件进行切削仿真实验时,刀屑摩擦因数对仿真结果的影响明显,但现有有限元软件未提供刀屑摩擦因数数据库。为建立一种基于AdvantEdge的斜角车削仿真实验的刀屑摩擦因数确定方法,首先提出基于斜角车削的摩擦力计算方法,然后建立AdvantEdge三维斜角车削仿真模型,设定不同切削速度、切削深度、进给量及摩擦因数,通过AdvantEdge 仿真正交试验,获得刀屑摩擦因数的经验计算公式。为验证刀屑摩擦因数经验计算公式的正确性,设定不同切削速度和切削深度及进给量的斜角车削正交试验,获得切削力数据,并基于摩擦因数经验计算公式求得对应刀屑摩擦因数。利用求得的摩擦因数数据修改AdvantEdge中刀屑摩擦因数参数,进行残余应力切削仿真实验。仿真实验获得的残余应力与实际切削实验获得的残余应力相比,误差在10%以内,证明提出的刀屑摩擦因数确定方法是正确的。     

Tool life and wear mechanism of coated and uncoated Al2O3/TiCN mixed ceramic tools in turning hardened alloy steel

The focus of this paper is the continuous turning of hardened AISI 52100 (～63HRc) using coated and uncoated ceramic Al₂O₃–TiCN mixed inserts, which are cheaper than cubic boron nitride (CBN) or polycrystalline cubic boron nitride (PCBN). The machinability of hardened steel was evaluated by measurements of tool wear, tool life, and surface finish of the workpiece. Wear mechanisms and patterns of ceramic inserts in hard turning of hardened AISI 52100 are discussed. According to the results obtained, fracture and chipping type damages occur more frequently in uncoated tools, whereas crater wear is the more common type of damage in TiN coated tools. Most important result obtained from the study is that TiN coating and crater wear affect chip flow direction. In uncoated ceramic tool, the crater formation results in decrease of chip up-curl radius. Besides, uncoated cutting tool results in an increase in the temperature at the tool chip interface. This causes a thermal bi-metallic effect between the upper and lower sides of the chip that forces the chip to curl a smaller radius. Chips accumulate in front of the tool and stick to the workpiece depending on the length of the cutting time. This causes the surface quality to deteriorate. TiN coating not only ensures that the cutting tool is tougher, but also ensures that the surface quality is maintained during cutting processes.     

Tool wear, chip formation and workpiece surface issues in CBN hard turning: A review

Steel parts that carry critical loads in everything from automotive drive trains and jet engines to industrial bearings and metal-forming machinery are normally produced by a series of processes, including time-consuming and costly grinding and polishing operations. Due to the advent of super-hard materials such as polycrystalline cubic boron nitride (PCBN) cutting tools and improved machine tool designs, hard turning has become an attractive alternative to grinding for steel parts. The potential of hard turning to eliminate the costs associated with additional finishing processes in conventional machining is appealing to industry. The objective of this paper, is to survey the recent research progress in hard turning with CBN tools in regard of tool wear, surface issues and chip formation. A significant pool of CBN turning studies has been surveyed in an attempt to achieve better understanding of tool wear, chip formation, surface finish, white layer formation, micro-hardness variation and residual stress on the basis of varying CBN content, binder, tool edge geometry, cooling methods and cutting parameters. Further important modeling techniques based on finite element, soft computing and other mathematical approaches used in CBN turning are reviewed. In conclusion, a summary of the CBN turning and modeling techniques is outlined and the scope of future work is presented.     

Observations of the tool–chip boundary conditions in turning of aluminum alloys

Interface boundary conditions are critical to the determination of the tool temperatures and stresses which in turn are needed to design better tools and select better cutting conditions. Friction at the interface has been studied for 60 years and yet the accurate modeling of friction has presented a formidable challenge, especially in operations such as turning where the interface is inaccessible due to the continuous contact between chip and tool. A historical perspective of friction in machining is provided to better evaluate the purpose of this article. The contradictions arising in the assumptions regarding friction are analyzed. This is substantiated by experimental observations regarding seizure and sliding and their domains of validity at the interface. This paper concentrates on turning operations in the machining of aluminum workpieces using carbide cutting tools, at a range of speeds common to conventional practice.     

Study on orthogonal turning of titanium alloys with different coolant supply strategies

In this paper, the effects of different coolant supply strategies (using flood coolant, dry cutting, and minimum quantity of lubricant [MQL]) on cutting performance in continuous and interrupted turning process of Ti6Al4V are investigated. Based on the observation of the cutting forces with the different coolant supply strategies, the mean friction coefficient in the sliding region at the tool–chip interface has been obtained and used in a finite element method (FEM) to simulate the deformation process of Ti6Al4V during turning. From the FEM simulation and Oxley’s predictive machining theory, cutting forces have been estimated under different coolant supply strategies and verified experimentally.     

数控车削过程断屑不良的解决措施

以切屑形状为研究对象，介绍了切屑的控制、断屑以及切削用量对屑形的影响。通过比较不同屑形，分析了数控车削加工的理想屑形，并提出了在实际车削过程中的改进建议，实现在线调整，得到良好的断屑效果。     

Morphology evolution and micro-mechanism of chip formation during high-speed machining

In this paper, the morphology and micro-mechanism of chip formation during high-speed machining aluminum alloy 7050-T7451 is investigated based on the combination of dislocation theory and plastic deformation theory. Experiments of quick stop stoppage for turning and special method (Buda) for milling process were carried out in order to obtain shear angle in different cutting speeds. The results show that effective flow stress and temperature in front edge zone is higher and more concentrated than that in other deformation zones. The shear front-lamellar structure was observed and analyzed in the front edge zone which influences the chip formation directly. The influence of cutting speed on chip formation was analyzed by simulation and experiments. Cutting speed is an important factor affecting the morphology evolution and chip formation. When the cutting speed is below 1500 m/min, the concentration of shear stress and the shear front-lamella structure of cutting deformation are more remarkable and easier for forming continuous ribbon chips. With the cutting speed increase, the ribbon chip transforms into serrated chip when a critical cutting speed (2500 m/min) is reached. Finally, microscopic mechanism of chip formation has been revealed and critical condition of the shear front—the layer structure formation—has been determined.     

Correlation Between Cutting Data Selection and Chip Form in Stainless Steel Turning

This article presents investigations related to the turning of stainless steel as a representative of difficult-to-cut materials and the effectiveness of selected chip breakers working in the local machining environment. Martensitic steel AISI 416 was used to test two commercially available types of chip breaker. The efficiency of a chip breaker working in the range of cutting conditions recommended (by the tool manufacturers) was the aim of the turning tests. As a result of the investigations an algorithm of cutting condition selection, combining both the cutting tests and the simulation procedure for the efficiency of the chip breaker was created. The vision system, equipped with a high-speed camera was used for chip form estimation. Simultaneously, the cutting force components were measured to check if the simulation calculation was correct. The FEM simulation was applied to estimate the manner in which the chip groove was filled. The article presents certain recommendations for cutting condition correction in the local machining environment for the purpose of achieving an acceptable chip form.     

Prediction of chip flow angle in orthogonal turning of mild steel by neural network approach

Improvement of chip control is a necessity for automated machining. Chip control is closely related to chip flow and it plays also a predominant role in the effective control of chip formation and chip breaking for the easy and safe disposal of chips, as well as for protecting the surface-integrity of the workpiece. Although several ways to predict the chip flow angle (CFA) have been subjected in some researches, a good approximation has not been achieved yet. In this study, using different indexable inserts and cutting conditions for turning of mild steel, the chip flow angles were measured and some of the collected data from this experimental study were used for training with a two hidden layered backpropagation neural network algorithm. A group was formed from randomly selected data for testing. The chip flow angle values found from multiple regression, neural network (NN) and studies of previous researchers under the same turning conditions of the present study were compared. It has been seen that the best prediction was obtained by neural network approach.     

钛合金薄片零件车削工艺

通过对钛合金薄片零件车削方法的研究,解决了在普通车床上加工厚度小于0.6mm、环形面宽度在20mm以内、尺寸精度及形位精度在0.02mm内的高精度薄片零件的加工质量问题。阐述了利用普通车床加工钛合金薄片零件的工艺设计要领。该车削工艺方法简单、可靠,具有成本低、操作简便、高效的特点,形成了一种典型的加工工艺。     

Definition and determination of the minimum uncut chip thickness of microcutting

Uncut chip thickness is comparable to cutting edge radius in micromachining. If the uncut chip thickness is less than a critical value, there will be no chip formation. This critical value is termed as minimum uncut chip thickness (MUCT). Although minimum uncut chip thickness has been well defined in orthogonal cutting, it is often poorly understood in practical complex turning and milling processes. In this paper, a set of definitions of minimum uncut chip thickness for three-dimensional turning and milling processes are presented. This paper presents an analysis of the state-of-the-art research on minimum uncut chip thickness in precision micromachining. Numerical and experimental methods for determination of MUCT values and their effects on process mechanics and surface integrity in microcutting will be critically assessed in this paper. In addition, a detailed discussion on the characteristics of different methods to determine minimum uncut chip thickness and several unsolved problems are proposed for the future work.