Multi-objective optimization of process parameters for the helical gear precision forging by using Taguchi method

Precision forging of the helical gear is a complex metal forming process under coupled effects with multi-factors. The various process parameters such as deformation temperature, punch velocity and friction conditions affect the forming process differently, thus the optimization design of process parameters is necessary to obtain a good product. In this paper, an optimization method for the helical gear precision forging is proposed based on the finite element method (FEM) and Taguchi method with multi-objective design. The maximum forging force and the die-fill quality are considered as the optimal objectives. The optimal parameters combination is obtained through S/N analysis and the analysis of variance (ANOVA). It is shown that, for helical gears precision forging, the most significant parameters affecting the maximum forging force and the die-fill quality are deformation temperature and friction coefficient. The verified experimental result agrees with the predictive value well, which demonstrates the effectiveness of the proposed optimization method.     

汽车发电机磁极精锻成形三维有限元模拟和工艺优化

简述了汽车发电机磁极几种典型成形工艺。基于Abaqus通用有限元软件,应用三维刚粘塑性有限元显式算法对磁极精锻成形过程进行了模拟分析,得出了变形中材料的流动状态和等效塑性应变分布规律。根据有限元模拟分析结果对磁极精锻成形工艺参数、模具结构进行了优化设计,并进行了磁极精锻成形工艺试验。试验验证了有限元模拟分析结果,并精锻成形出合格的汽车发电机磁极产品。     

Development of an intelligent process model for EDM

This paper reports the development of an intelligent model for the electric discharge machining (EDM) process using finite-element method (FEM) and artificial neural network (ANN). A two-dimensional axisymmetric thermal (FEM) model of single-spark EDM process has been developed based on more realistic assumptions such as Gaussian distribution of heat flux, time- and energy-dependent spark radius, etc. to predict the shape of crater cavity, material removal rate, and tool wear rate. The model is validated using the reported analytical and experimental results. A neural-network-based process model is proposed to establish relation between input process conditions (discharge power, spark on time, and duty factor) and the process responses (crater geometry, material removal rate, and tool wear rate) for various work—tool work materials. The ANN model was trained, tested, and tuned using the data generated from the numerical (FEM) simulations. The ANN model was found to accurately predict EDM process responses for chosen process conditions. It can be used for the selection of optimum process conditions for EDM process.     

Prediction of deformation behavior and microstructure evolution in heavy forging by FEM

A numerical simulation of multi-stage heavy forging process using the finite element method (FEM) is presented in this study. The process of heavy forging is highly non-linear, where both microstructure and boundary conditions are altered by plastic deformation during forming. Therefore, it is necessary to understand the problem of plastic deformation in heavy forging. In order to investigate deformation behavior and microstructure evolution in heavy forging, a constitutive equation considering the effects of strain hardening and dynamic softening of the IN718 alloy is built. The constitutive equation and microstructure models are implemented into the finite element code to simulate deformation behavior and microstructure evolution in the rotary forging of heavy container head. As a result, variations of flow stress, effective strain, temperature, damage, and grain size in every stage are predicted.     

基于有限元的大型模锻压力机钢丝缠绕动梁预应力测试

预应力检测对重型压机钢丝缠绕工艺来说至关重要。钢丝缠绕压机动梁结构复杂,缠绕时表面应力场分布无明显规律,测试难度大,目前动梁缠绕工艺的应力测试尚属空白,给工艺质量评价及工艺控制带来不便。应用有限元法对400 MN航空模锻压机动梁缠绕进行模拟,研究动梁缠绕时端面的应力场分布特征,确定动梁端面存在环形的径向、周向单向应力区,据此制定应变测量贴片方案,解决了重型压机动梁缠绕过程中预应力测试的难题。有限元计算结果与试验结果基本吻合,确保动梁缠绕工艺质量达到设计要求,也证实了这种基于有限元的应力测试方法的可行性。该方法对于其他复杂工程结构的应力测试具有借鉴意义。     

基于数值模拟的叶片毛坯径向锻造成型分析

基于Simufact.Forming径向锻造模块对某叶片毛坯锻造成形过程进行数值模拟分析,研究了径向锻坯到叶片模锻的成型过程,获得了叶片锻坯在径向锻造过程中等效应变以及锻流线分布规律。深入分析锻坯锻透性,并对径锻成形过程进行理论计算和试验验证。结果表明:适当提高相对压下率能使锻坯变形均匀,采用拉打径向锻造方式能够有效保证锻坯成型的尺寸精度,得到的叶片锻坯模锻充型效果较好,飞边分布均匀,锻坯心部等效应力在锻打时有规律地发生波动,旋转锻打使金属材料沿周向流动,锻流线的扭转角与旋转角相一致,锻坯质量较好,无明显缺陷。     

Gear hot forging process robust design based on finite element method

During the hot forging process, the shaping property and forging quality will fluctuate because of die wear, manufacturing tolerance, dimensional variation caused by temperature and the different friction conditions, etc. In order to control this variation in performance and to optimize the process parameters, a robust design method is proposed in this paper, based on the finite element method for the hot forging process. During the robust design process, the Taguchi method is the basic robust theory. The finite element analysis is incorporated in order to simulate the hot forging process. In addition, in order to calculate the objective function value, an orthogonal design method is selected to arrange experiments and collect sample points. The ANOVA method is employed to analyze the relationships of the design parameters and design objectives and to find the best parameters. Finally, a case study for the gear hot forging process is conducted. With the objective to reduce the forging force and its variation, the robust design mathematical model is established. The optimal design parameters obtained from this study indicate that the forging force has been reduced and its variation has been controlled.     

Application of finite element method and artificial neural network to the die design of radial forging processes

This investigation adopts the finite element method (FEM) and the artificial neural network (ANN) to plan the radial forging of work-hardened materials to yield the optimal designed die. The process parameters considered herein are die corner radius (R), ring gap height (H), friction factor (m), work-hardening coefficient (n), gap between the billet and die (c) and the punch load (f). The accuracy of the FEM model constructed herein is established. Fifty sets of processing parameters are simulated by the FEM, and the results, together with the outer rims of the flange after forming, are taken as the learning file in ANN. Then, based on the range that is set by the learning file, another 20 sets of flange with different shapes than those in the test file are selected to obtain a combination of parameters of the die, materials and lubricants and other factors. During the design of the die, many tests are conducted, and flanges of similar shapes are found to be obtained with various combinations of processing parameters. This result indicate that the learning pattern presented herein meets the needs of all types of parameter combinations. Finally, based on the required specification of the shape of the outer rim of the flange, this work uses ANN to obtain all the specified processing parameters. Finite-element analysis is then used to confirm the accuracy of the results and further investigate the effect of the related parameters on the flange shape. The following conclusion is drawn: The design of the die can yield finished flange products with similar shapes using different parameter combinations. During the forming process, a suitable range of parameters is selected for the die, the materials and the lubricant. Then, according to the strength of their effects, their inputs and output values are appropriately adjusted and the most suitable combination of processing parameters identified according to the similarities in the flange shapes they produce.     

Influence of process parameters on impact toughness and hardness of dissimilar AISI 4140 and AISI 304 continuous drive friction welds

Dissimilar joints between austenitic stainless steel and low alloy steel are extensively used in many high temperature applications in the energy conversion systems. In the present investigation, emphasis is made on the influence of process parameters on the impact toughness and hardness of the friction welded joints between these two materials. The important process parameters in friction welding such as friction force, forge force, and burn-off lengths are considered for optimization by Taguchi method using L₈ 2⁷ orthogonal array. It is found that under low friction force, forging force, and burn-off conditions, the impact toughness is high due to the observed acicular martensite. Low impact toughness is reported for the welds made at higher levels of the parameters. Carbon depletion is also observed close to interface in low alloy steel side. Microhardness at the weld center is less than the microhardness on either side at the interface of low alloy steel and austenitic stainless steel close to weld center. The contribution of each parameter and significance of interactions of these parameters is determined by Taguchi method. Among these parameters, friction force has significant influence and forging force has negligible influence on microhardness. The burn-off has maximum influence while forge force has minimum effect on toughness of the welds. Statistical analysis of variance is carried out, optimum process parameters are evaluated, and regression equations are obtained.     

径向锻造工艺参数对锻透性的影响

将轴类锻件径向锻造过程的锤迹投影到单位圆柱面上,分析了径向压下率、轴向送进率等工艺参数应满足的约束条件,推导了判断径向锻造锻透性的经验三角形法则与锻造工艺参数的关系,分析了锻造工艺参数对锻透率的影响;为了验证经验法则的有效性,对轴类锻件径向锻造过程进行了数值模拟,以等效应变应大于临界值以及不出现轴向拉应力作为锻透性的判断准则,分析了工艺参数对锻透率的影响。经验准则计算结果与数值模拟结果的比较表明:采用经验准则能够有效地判断轴类锻件径向锻造过程中的锻透性,其结果偏于安全。     

Multi-objective optimization of forming parameters for tube hydroforming process based on the Taguchi method

Tube hydroforming is an attractive manufacturing technology which is now widely used in many industries, especially the automobile industry. The purpose of this study is to develop a method to analyze the effects of the forming parameters on the quality of part formability and determine the optimal combination of the forming parameters for the process. The effects of the forming parameters on the tube hydroforming process are studied by finite element analysis and the Taguchi method. The Taguchi method is applied to design an orthogonal experimental array, and the virtual experiments are analyzed by the use of the finite element method (FEM). The predicted results are then analyzed by the use of the Taguchi method from which the effect of each parameter on the hydroformed tube is given. In this work, a free bulging tube hydroforming process is employed to find the optimal forming parameters combination for the highest bulge ratio and the lowest thinning ratio. A multi-objective optimization approach is proposed by simultaneously maximizing the bulge ratio and minimizing the thinning ratio. The optimization problem is solved by using a goal attainment method. An example is given to illustrate the practicality of this approach and ease of use by the designers and process engineers.     

锻造模具的随机疲劳损伤分析

塑性应变控制的低周疲劳失效是锻造模具的主要失效形式，由于受到多种因素的影响，其损伤过程呈现随机性。应用有限元与BP神经网络，建立了一种基于损伤累积理论的锻造模具的随机疲劳损伤分析模型。首先用有限元对锻造过程中模具内的场变量进行分析，由计算结果找到模具的危险部位，认为危险部位失效时的寿命即为模具寿命，并计算出确定性损伤；再考虑模具材料及实际工况的随机性，应用BP神经网络对模具的损伤进行模拟；根据损伤的累积效应，得出考虑随机因素作用下的模具疲劳寿命。以锻造齿轮模作为分析对象，得到不同工况下模具疲劳寿命的频数分布，其分布规律基本服从Weiubull分布。另外，还分析了打击速度对模具寿命的均值和离差的影响及可靠性随使用次数的变化。该 模型可用来对模具进行寿命预测和可靠性分析。     

一种新型Al-Zn-Mg-Cu合金杯形件摆辗成形数值模拟及实验研究

为了研究摆辗成形工艺对一种新型Al-Zn-Mg-Cu合金杯形件力学性能的影响,对初始高径比分别为0.4、0.8和1.2的坯料摆辗成形进行数值模拟和实验研究。通过有限元法模拟摆辗成形过程中坯料的金属流动、等效应变分布和温度分布,并在此基础上进行摆辗成形实验,分别测试杯形件底盘弦向和径向的强度。有限元研究发现,与摆头接触的变形区域网格畸变量大,并且变形过程热效应明显。研究结果表明,当坯料高径比为0.8时,杯形件的底盘弦向强度可达到507MPa,比母材提高了64.4%;摆辗成形可以提高该新型Al-Zn-Mg-Cu合金杯形件的底盘强度,同时初始坯料的高径比对杯形件底盘的强度分布影响较大。     

Geometric optimization and performance analysis of radial MR valve using Taguchi orthogonal experiment method

Aiming at the problems of increasing external dimensions and deteriorating key performance indicators in the design process of magnetorheological (MR) valve by using structural optimization method, a geometric optimization design methodology for the optimal design of a MR valve structure under specific volume constraints is proposed in this article. The optimization methodology couples the finite element model (FEM) constructed in COMSOL software with the Taguchi orthogonal experiment and response surface technology to build an approximate response surface function for the identified independent variables. Suitable optimization algorithms are then utilized to determine the optimal geometry of the MR valve, thereby maximizing the valve performance. Firstly, a radial MR valve with a single excitation coil was presented, and its structure and working principle were also elaborated. A mathematical model of the pressure drop was derived on the basis of the Bingham-Papanastasiou non-Newtonian constitutive model of MR fluid and the magnetic circuit had been analyzed with the FE analysis methodology. Then, a second-order response surface model (RSM) had been fitted for the magnetic flux density in the radial flow channel and spool region of the radial MR valve based on the Taguchi orthogonal experimental design. The fitted model was a function of the four independent variables of the radial MR valve, and the accuracy of the developed response surface function over the entire design space had also been estimated. Meanwhile, predictions made by the RSM and FE models were evaluated by analysis of variance and it was exhibited that the RSM model’s results agree with FE result fairly. Subsequently, the geometric optimization problem had been formulated for the constructed RSM exploiting the genetic algorithm to find the global optimum geometrical parameters of the radial MR valve. Furthermore, the experimental test rig was setup to explore the pressure drop and the response time characteristics of the initial and optimal radial MR valve as well as the dynamic performance of the MR valve controlled cylinder system under different excitation conditions. The experimental results show that under the applied current of 2 A, the pressure drop and adjustable coefficient of the optimal radial MR valve observably increased with values of 3.15 MPa and 5.40, respectively, when compared to 2.11 MPa and 4.22 of their respective initial values. Also, at the applied current of 1.25 A, the damping force of the MR valve controlled cylinder system enlarged by 46 %, with its optimal value being 3.65 kN and initial value as 2.50 kN, which was an excellent verification of the correctness of the RSM and the effectiveness of the optimal design.

     

Optimization of surface roughness,cutting force and tool wear of nitrogen alloyed duplex stainless steel in a dry turning process using Taguchi method

In this work, the dry turning parameters of two different grades of nitrogen alloyed duplex stainless steel are optimized by using Taguchi method. The turning operations were carried out with TiC and TiCN coated carbide cutting tool inserts. The experiments were conducted at three different cutting speeds (80, 100 and 120 m/min) with three different feed rates (0.04, 0.08 and 0.12 mm/rev) and a constant depth of cut (0.5 mm). The cutting parameters are optimized using signal to noise ratio and the analysis of variance. The effects of cutting speed and feed rate on surface roughness, cutting force and tool wear were analyzed. The results revealed that the feed rate is the more significant parameter influencing the surface roughness and cutting force. The cutting speed was identified as the more significant parameter influencing the tool wear. Tool wear was analyzed using scanning electron microscope image. The confirmation tests are carried out at optimum cutting conditions. The results at optimum cutting condition are predicted using estimated signal to noise ratio equation. The predicted results are found to be closer to experimental results within 8% deviations.     

Optimum process conditions on shrinkage of an injected-molded part of DVD-ROM cover using Taguchi robust method

Plastic injection molding is an important process to produce thin-shell parts. However, the difficulty in adjusting optimum process conditions may cause defects of the injected-molded parts such as shrinkage. This study investigates on the optimum combinations of process conditions on shrinkage of an injected-molded part of the DVD-ROM cover based on Taguchi method. In doing this, a series of Moldflow analyses have been performed as per L₂₇ orthogonal array design with each analysis by means of the process conditions of mold temperature, melt temperature, injection pressure, injection time, and cooling time. In the meantime, signal-to-noise (S/N) ratio is utilized to determine the optimum combinations of the process conditions for shrinkage through analysis of variance (ANOVA). ANOVA is further used to find which of the process conditions are statistically significant. Finally, confirmation tests at the optimum combinations of the process conditions were executed to verify the robustness and the effectiveness of Taguchi method within 95% confidence interval. From the findings, it can be stated that Taguchi method is a powerful tool for evaluating the defect of shrinkage in the plastic injection molding.     

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.     

单榫头叶片叶身精锻成形规律

利用自行开发的叶片锻造过程三维刚粘塑性有限元模拟系统对单榫头叶片精锻过程进行了模拟分析,揭示了其叶身精锻成形规律,并以塑泥为模拟材料,采用物理模拟的方法对其进行了试验验证。三维有限元数值模拟结果与物理模拟结果的良好吻合表明了单榫头叶片精锻过程三维数值模拟结果的可靠性。该研究对叶片精锻过程的预成形毛坯的优化设计具有重要的指导意义。     

A study on the cutting force and chip shrinkage coefficient in high-speed milling of A6061 aluminum alloy

In this paper, finite element (FE) simulation for high-speed milling of aluminum alloy was performed using a ductile fracture model with Mohr–Coulomb criterion proposed by Bai and Wierzbicki (BW). To verify the model, predicted cutting forces were compared to experimental results in the same cutting conditions. Then, further simulations were performed to estimate the cutting forces and chip shrinkage coefficients subjected to different cutting parameters such as cutting speeds, cutting depths, and clearance angles of a cutting tool. The obtained results were also used to determine optimal cutting parameters using the Taguchi method. The analysis of variance (ANOVA) was employed to investigate the influence percentage of each cutting parameter on cutting force and chip shrinkage coefficient. The simulation results showed that inclusion of strain rate in numerical model significantly improved the accuracy of estimated cutting force in comparison to experiment. The optimum values obtained for high-milling process were cutting speed 1000 m/min, cutting depth 1 mm, clearance angle 15°, and rake angle 4°.     

Analysis of the drop forging of a piston using Slip-Line Fields and FEM

The paper analyses the process of a forging piston-type product. The Finite Element Method (FEM) is used to determine the forging loads and the kinematics of metal flow during the press forming process analysed. The Slip-Line Field Method (SLFM) is used to obtain a simplified solution. This helps to determine the distribution of material-tool contact pressures which is the basis for computing the forging load. The results from both methods were verified experimentally and good agreement was obtained. In addition a comparison is made between the forging load values obtained in the present study and those given by selected equations from the literature.