Ti6Al4V零件铣削加工表面等效残余应力与作用深度的测量及其有限元分析

金属零件在切削加工后,其被加工表面会形成一残余应力层,其所引起零件的变形是影响精密弱刚性零件精度的重要的因素。为了预测Ti6Al4V零件因铣削加工表面残余应力而引起的变形,本文介绍一种测量表面等效残余应力及其作用深度的方法而达到此目的。通过对被加工面的对面进行两次腐蚀去除材料的操作使得零件的厚度和中性层的位置发生变化,测量此过程中零件挠度和表面应变的变化,进而计算得铣削加工引起的零件表面等效残余应力及其作用深度值。通过有限元分析验证该方法得到的结果,发现有限元计算得到的零件挠度和应变的变化与实际测量值非常吻合,因此可以断定该方法得到的结果是正确的,其可以正确评估铣削加工引起的表面残余应力性质和大小并能准确预测零件铣削加工后因表面残余应力而引起的工件的变形量,从而可以预测零件是否满足精度要求。     

Process simulation using finite element method — prediction of cutting forces, tool stresses and temperatures in high-speed flat end milling

End milling of die/mold steels is a highly demanding operation because of the temperatures and stresses generated on the cutting tool due to high workpiece hardness. Modeling and simulation of cutting processes have the potential for improving cutting tool designs and selecting optimum conditions, especially in advanced applications such as high-speed milling. The main objective of this study was to develop a methodology for simulating the cutting process in flat end milling operation and predicting chip flow, cutting forces, tool stresses and temperatures using finite element analysis (FEA). As an application, machining of P-20 mold steel at 30 HRC hardness using uncoated carbide tooling was investigated. Using the commercially available software DEFORM-2D™, previously developed flow stress data of the workpiece material and friction at the chip–tool contact at high deformation rates and temperatures were used. A modular representation of undeformed chip geometry was used by utilizing plane strain and axisymmetric workpiece deformation models in order to predict chip formation at the primary and secondary cutting edges of the flat end milling insert. Dry machining experiments for slot milling were conducted using single insert flat end mills with a straight cutting edge (i.e. null helix angle). Comparisons of predicted cutting forces with the measured forces showed reasonable agreement and indicate that the tool stresses and temperatures are also predicted with acceptable accuracy. The highest tool temperatures were predicted at the primary cutting edge of the flat end mill insert regardless of cutting conditions. These temperatures increase wear development at the primary cutting edge. However, the highest tool stresses were predicted at the secondary (around corner radius) cutting edge.     

Tool wear-dependent process analysis by means of a statistical online monitoring system

Simulating milling processes can provide numerous optimization possibilities regarding process stability and surface quality. In tool and die manufacturing often long-running processes are necessary. In contrast to very time-consuming Finite-Element-based approaches, geometric physically-based simulation systems allow predictions for such processes because of their relatively short runtime. The machining of hardened material and varying engagement conditions between the tool and the workpiece provoke a gradually increasing influence of tool wear on the cutting edges. To consider these alterations while simulating milling processes, different approaches can be used. Because of the complex characteristics of tool wear, methods, which result in an increased simulation runtime, have to be used for the geometric modeling of tool wear. In this paper, a novel approach for monitoring a milling process is presented, which utilizes an online-selection of pre-calculated simulation data to predict the process stability for different states of tool wear. To achieve this, measured data are compared to simulated data, which result from offline simulation conductions for each defined state of tool wear. As tool wear changes when the process is progressing, different simulation data for different states of tool wear have to be selected to ensure a valid stability prediction.     

某井油管脱扣原因分析

针对某井用Φ88.9mm×6.45mm P110钢级NU油管脱扣事故进行深入调查研究,对脱扣的油管进行了宏观和微观形貌分析,对油管材质进行了理化性能试验,对该批次未使用的油管接头试样进行了参数测量。通过试验分析和研究,认为油管接头材质及螺纹参数符合标准要求,油管脱扣属于低载荷滑脱失效,滑脱失效的主要原因是由于粘扣和上扣不到位导致接头的连接强度大幅度降低造成,而粘扣和上扣不到位的主要原因是上扣过程中发生了错扣。     

螺纹铣削的数控加工工艺研究

传统的螺纹加工方法不能满足高效率、高质量的生产要求。该文从螺纹铣刀的类型、螺纹铣削的刀具轨迹和切削参数以及螺纹铣削的编程等方面,分析了螺纹加工的工艺性。通过合理规划生产中一个实例的加工工艺,并在加工中心上加工出该产品且满足了产品的技术要求。由于一次装夹成形,工作效率大大提高。     

Process and microstructure simulation in thermal spraying

Thermally sprayed coatings are widely used to improve wear and corrosion behavior of mechanical parts. To develop new coating processes and applications - a detailed knowledge of process-material interaction is necessary. According to the progress in computing and commercial software today simulation can be used to understand the interaction of process parameters with the material behavior like solidification, microstructure and residual stresses within the coating. Under commercial aspects the process parameters can be optimized to increase the deposition rate and minimize the residual stresses simultaneously. For plasma spraying the simulation of the coating process from plasma generation, particle injection, heating and acceleration to particle impact on the substrate, solidification and residual stresses and the influence of different parameters will be demonstrated and correlated to the experimental results.     

An integrated macroscopic model for simulating SLM and milling processes

Due to their flexibility to also build up highly complex geometries, Additive Manufacturing (AM) processes are increasingly applied. Although near net-shape components can be manufactured using, for example, the Selective Laser Melting (SLM) process, the required surface quality can often not be achieved. In order to manufacture contact areas or functional surfaces, subsequent machining processes can be used to achieve the required accuracy in shape and dimension as well as the desired surface quality. In order to reduce the experimental effort during process design and optimization, simulation systems that are able to efficiently model both processes are required. In this paper, an empirical geometry-based model for SLM and milling processes will be presented. Due to the usage of an empirical model, based on the analysis of a set of reference structures, the simulation of macroscopic geometries can be achieved and used in subsequent milling simulations. Furthermore, an experimental validation of the combination of the two simulation models will be presented.     

An interactive process planning system for prismatic parts (ICAPP)

This paper presents an interactive automatic process planning system ICAPP (Interactive Computer Aided Process Planning) for non-rotational prismatic parts produced on machining centres and conventional milling, drilling and boring machines. The ICAPP system is feature-oriented and is capable of processing eight basic machining processes, i.e. face milling, peripheral milling, drilling, boring, reaming, tapping, counterboring and countersinking, using both variant planning, via the part family concept, and generative planning. Machining operations can be planned interactively so that appropriate tasks can be shared by the computer and the planner to improve the overall system performance.     

Analysis of form threads using fluteless taps in cast magnesium alloy (AM60)

Threads are used in the most assemblies of industrial products. Commonly, mechanical components need to have threaded parts allowing fast and accurate assemblies and disassemblies. Internal tapping is one of the most demanded machining operations, and threads obtained by forming have been a good alternative. This work investigates the effect of the factors the hole diameter, the forming speed and types of tool on the responses: torque, hardness, fill rate, and thrust force of the form tapping process. The experiments were carried out with three diameters, three forming speeds, and two coatings. The material used was the AM60 alloy due to its high ductility and wide application as head engine. The results revealed torque is more affected by the hole diameter than thrust force, and little hardening occurred using high forming speed with a small diameter. The fill rate of the thread profile was not significantly affected by the intermediate and large diameters. Finally, it can be stated that the recommended hole diameter provided by the tool's supplier can be modified to achieve more accurate thread profiles.     

中厚板矫直过程的有限元研究

采用弹塑性有限元法建立中厚板矫直过程的二维动态有限元分析模型,并针对某厂11辊矫直机不同厚度板材、不同矫直方案的矫直过程进行了模拟计算.给出了矫直过程板材应力场、应变场和各矫直辊矫直力的分布.     

Investigations on residual stresses and deformations in selective laser melting

For establishing Selective Laser Melting (SLM) in production technology, an extensive knowledge about the transient physical effects during the manufacturing process is mandatory. In this regard, a high process stability for various alloys, e.g. tool steel 1.2709 (X3NiCoMoTi 18-9-5), is realisable, if approaches for the virtual qualification of adequate process parameters by means of a numerical simulation based on the finite element analysis (FEA) are developed. Furthermore, specific methods to evaluate and quantify the resulting residual stresses and deformations due to the temperature gradient mechanism (TGM) are required. Hence, the presented work contains particular approaches using the FEA for the simulation of transient physical effects within the additive layer manufacturing (ALM) process. The investigations focus on coupled thermo-mechanical models incorporating specific boundary conditions and temperature dependant material properties to identify the heat impact on residual stresses and deformations. In order to evaluate the structural effects and simultaneously validate the simulation, analysis on residual stresses based on the neutron diffractometry as well as considerations concerning part deformations are presented.     

Defect assessment of welded specimen considering weld induced residual stresses using SINTAP procedure and FEA

The defect assessment in butt-welded joint of ASTM A36 steel plates and 7075-T7351 aluminum alloy plates containing transverse through thickness crack was analyzed using SINTAP procedure and FEA incorporating weld induced residual stresses. Weld induced longitudinal residual stress profile can be obtained through SINTAP procedure, FEA or experimental analysis. This residual stress profile can be fitted with the trapezoidal residual stress profile available in SINTAP. For three different cases, crack length and residual stress intensity factor (SIF) are calculated and its comparison with the results obtained through FEA is plotted with respect to crack length. The stress intensity factor for mechanical loading is also plotted in the same graph. Using this graphical plot, the total SIF, including residual stress and mechanical loading, can be calculated for any particular crack size. The total SIF can be compared with the fracture toughness of the material for damage tolerance analysis. Also a failure assessment diagram is drawn for welded 7075-T7351 aluminum alloy plates with different crack sizes for as-welded (only residual stress) and mechanical loading along with the existing weld induced residual stresses to show the safety level for a particular crack size and mechanical loading.     

Analytical and experimental investigations on thread milling forces in titanium alloy

This study deals with the thread milling process that is considered a complex machining technique due to its elaborated tool geometry and its tridimensional tool trajectory. It needed advanced research on the threading process which has not been much studied. Previous studies focused on geometrical modeling or mechanistic modeling of the thread milling process. There is a need for a better understanding of parameter effects to accomplish a model that tends to be more realistic and includes local parameters. This investigation does the analysis of thread milling parameters: thread geometry, cutting conditions and tool angles, which can be applied to the tool optimization. The cutting forces and torque were measured and representative values of its variation were calculated and analyzed as response of the experiments. A geometrical analysis and an analysis of variance were employed for determining the influence of the factors and based on the results, it is proposed a physical understanding of the process.     

筒形件磁脉冲辅助冲压成形数值模拟

针对磁脉冲辅助冲压成形过程,提出了基于ANSYS平台的有限元分析程式,通过编制用户子程序,采用重启动分析法,建立了冲压预成形过程显式求解和瞬态磁脉冲成形"松散"耦合分析之间的动态连接,并用于5052-O铝合金圆筒形拉深件磁脉冲辅助冲压成形过程的有限元仿真研究。结果表明,所建立的有限元分析方案,能实现圆筒形件磁脉冲辅助冲压成形连续变形过程的模拟,板坯变形信息体现了准静态冲压变形和高速率磁脉冲成形之间的耦合。有限元模拟结果与实验吻合较好。     

Fuzzy control of spindle torque for industrial CNC machining

Developing a dedicated control system for each and every machining process or machine is costly and time-consuming. Such a practice has obviously undermined the usefulness of many current systems. This paper presents a fuzzy control system that can be used for different machining processes. This system consists of a basic fuzzy logic controller, a fuzzy rule base, and a tuning mechanism used to enhance the adaptability of the system. Industrial tests have been carried out for both end milling and turning processes. The control signal is spindle torque, readily available on many CNC machines. The test results show that the system performs well on both end milling and turning operations and can easily adapt to tool changes as well as workpiece material changes.     

Finite Element Simulation of Residual Stress Development in Thermally Sprayed Coatings

The coating buildup process of Al₂O₃/TiO₂ ceramic powder deposited on stainless-steel substrate by atmospheric plasma spraying has been simulated by creating thermomechanical finite element models that utilize element death and birth techniques in ANSYS commercial software and self-developed codes. The simulation process starts with side-by-side deposition of coarse subparts of the ceramic layer until the entire coating is created. Simultaneously, the heat flow into the material, thermal deformation, and initial quenching stress are computed. The aim is to be able to predict—for the considered spray powder and substrate material—the development of residual stresses and to assess the risk of coating failure. The model allows the prediction of the heat flow, temperature profile, and residual stress development over time and position in the coating and substrate. The proposed models were successfully run and the results compared with actual residual stresses measured by the hole drilling method.     

Tapping of Al–Si alloys with diamond-like carbon coated tools and minimum quantity lubrication

The deep hole drilling and tapping of automotive powertrain components made of hypoeutectic Al–Si alloys are of considerable importance. This work investigates the dry and minimum quantity lubricated (MQL) tapping of Al–6.5%Si (319 Al) alloys as alternatives to conventional flooded tapping. Two types of tests were done in comparison with flooded tapping. In the first set dry tapping experiments were performed using diamond-like carbon (DLC) coated and uncoated HSS taps. HSS-dry tapping caused immediate tool failure within less than 20 holes due to aluminum adhesion, resulting in high forward and backward torques. DLC-dry tapping improved tool life considerably and exhibited small torques. The second set of tapping experiments used MQL and only uncoated HSS taps. The use of MQL at the rate of 80 ml/h produced similar average torques to flooded tapping, and a high thread quality was observed. DLC coatings’ low COFs against 319 Al limited the temperature increase during DLC-dry tapping to 75 °C. The low COF of DLC against aluminum was responsible for preventing built-up edge (BUE) formation and thus, instrumental in improving thread quality. The use of MQL reduced the tapping temperature to 55 °C. The mechanical properties of the material adjacent to tapped holes, evaluated using hardness measurements, revealed a notable softening in the case of HSS-dry tapping, but not for MQL tapping. The presence of sulphur and phosphorus-based additives in MQL fluids proved beneficial in preventing aluminum adhesion.     

Structural modeling of end mills for form error and stability analysis

Structural modeling of end mills is crucial for predicting deflections and vibrations in milling processes. End mill geometry is very complex which makes the use of simple beam models inaccurate. Stiffness and frequency response function (FRF) measurements need to be performed to identify the static and dynamic properties experimentally. This can be very time consuming considering the number of tool–tool holder combinations in a production facility. In this paper, methods for modeling structural properties of milling tools are presented. Static and dynamic analysis of tools with different geometry and material are carried out by finite element analysis (FEA). Some practical equations are developed to predict the static and dynamic properties of tools. Receptance coupling and substructuring analyses are used to combine the dynamics of individual component dynamics. In this analysis, experimental or analytic FRFs for the individual components are used to predict the final assembly’s dynamic response. Clamping parameters between the tool and the tool holder may effect the results significantly. These parameters are also identified from the measurements. The effects of changes in tool parameters and clamping conditions are evaluated. The predictions are verified by the measurements for different conditions.     

Model-based predictive force control in milling: determination of reference trajectory

Today, powerful process simulation tools allow an offline process planning and optimization of metal cutting processes. The quality of the optimization strongly depends on the model and its parameters. Real cutting processes are influenced by uncertainties such as tool wear status or material properties, which are both unknown. To overcome this limitation, sensors and process control systems are used. Model-based Predictive Control (MPC) was developed in the 1970s for the chemical process industry. This control method was found to be very suitable to control complex manufacturing processes such as milling processes. Using MPC in metal cutting processes allows considering technological boundary conditions explicitly. Adapting the feed velocity and thus the process force increases the productivity and process stability in milling. A core element of the MPC is the use of a reference trajectory representing the time-dependent set point value in the optimization procedure. The tool path information, however, is given position-based. Thus, calculating the reference trajectory is not trivial and strongly influences the control quality. This paper presents two methods for determining the reference trajectory. The first method is based on an adaptive signal filter. For the second method the MPC is extended to a two-layer MPC: the first layer calculates an optimal reference trajectory; the second layer controls the machine tool.     

某盒形件拉深成形计算机仿真研究

基于DYNAFORM动力显式有限元分析软件,将数值模拟技术应用于某盒形件的拉深成形过程,研究了该件的一次拉深成形,不同的毛坯形状、尺寸,以及不同的材料参数对该盒形件拉深的成形极限图、厚度分布、减薄率的影响。研究结果表明:一次拉深成形不能满足成形要求,必须采用多道次拉深;板料1由于尺寸较小而更利于拉深成形;厚向异性系数r值较大的材料,有利于拉深成形。