Springback prediction of the vee bending process for high-strength steel sheets

The precise prediction of springback is a key to assessing the accuracy of part geometry in sheet bending. A simplified approach is developed by considering the thickness ratio, normal anisotropy, and the strain-hardening exponent to estimate the springback of vee bending based on elementary bending theory. Accordingly, a series of experiments is performed to verify the numerical simulation. The calculation of the springback angle agrees well with the experiment, which reflects the reliability of the proposed model. The effects of process parameters such as punch radius, material strength, and sheet thickness on the springback angle are experimentally tested to determine the dominant parameters for reducing the springback angle in the sheet bending process for high-strength steel sheets. Moreover, the effects of the thickness ratio, normal anisotropy, and the strain-hardening exponent on the springback angle in the vee bending process for high-strength steel sheets are theoretically studied. Therefore, improving understanding on and control of the springback reduction of the vee bending process in practical applications is possible.     

Predictions of the optimized friction stir spot welding process parameters for joining AA2024 aluminum alloy using RSM

The friction stir spot welding process (FSSW) is a variant of the linear friction stir welding process in which the material is being welded without bulk melting. The FSSW parameters such as tool rotational speed, plunge rate, plunge depth, and dwell time play a major role in determining the strength of the joints. A central composite rotatable design with four factors and five levels was chosen to minimize the number of experimental conditions. An empirical relationship was established to predict the tensile shear fracture load of friction stir spot-welded AA2024 aluminum alloy by incorporating independently controllable FSSW process parameters. Response surface methodology (RSM) was applied to optimize the FSSW parameters to attain maximum lap shear strength of the spot weld.     

Effect of powder thixoforging process on microstructural and mechanical properties of recycled 520 aluminum alloy

In this paper, reusing Al alloy chips via novel recycling process of powder thixoforging (PTF) is presented. PTF is a direct machining chips conversion method with partial melting into high quality final products with improved mechanical properties compared to parent alloy. 520.0 Al alloy powders from milling chips were produced via mechanical alloying (MA). The PTF product exhibited remarkable combination of mechanical properties of 168 HV hardness, compression yield strength (CYS) of 515 MPa, ultimate compression strength (UCS) of 1121MPa, and substantial fracture plastic strain of 45 %. Additionally, the PTF product showed relative weight reduction of 55.7 %. As a consequence, the microstructure refinement and modification during PTF have significant effects on dramatic improvement of mechanical properties, leading to considerable combination of superior strength and ductility.     

微细铣削铝合金表面粗糙度的实验研究

利用直径为2 mm的立铣刀对铝合金进行铣槽实验,研究分析切削速度与每齿进给量交互作用对加工槽底表面粗糙度的影响.实验结果表明:每齿进给量小于4μm时,随着切削速度的提高表面粗糙度值呈先减小后增大的变化趋势;而每齿进给量大于6μm时,随切削速度的提高表面粗糙度值先增大后减小.切削速度较低时,表面粗糙度值随每齿进给量的增大先减小后增大;但切削速度大于30 m/min时,随着每齿进给量的增大,表面粗糙度值呈现逐渐增大的趋势.     

Effects of thickness and surface roughness on mechanical properties of aluminum sheets

The effect of thickness on the mechanical properties of Al 6K21-T4 sheet specimens under uniaxial tension was investigated. In order to reduce the thickness of the specimens without changing the microstructure and grain size, chemical etching was carried out, resulting in Al sheets ranging from 0.40 mm to 1.58 mm in thickness. Additionally, the effect of surface roughness was determined by finite element (FE) calculations performed using FE code MARC 2007. Tensile specimens of varying surface roughness were modeled and simulated. An analysis of the combined effects of the thickness and surface roughness revealed that the yield and tensile strengths decreased when the number of grains over the thickness was decreased. The ductility also decreased when reducing the thickness. An FE simulation showed that both the surface roughness and thickness affected the flow-curve shape. Moreover, the effect of the surface roughness tended to increase when decreasing the sheet thickness of specimens having the same roughness.     

Predictions of the optimized friction stir welding process parameters for joining AA7075-T6 aluminum alloy using preheating system

The scope of this investigation is to evaluate the effect of welding parameters on the mechanical properties and microstructural features of 3-mm-thick AA7075-T6 aluminum alloy subjected to gas heating system as a preheating source during friction stir welding. Toward this end, a gas heating system was designed to heat up the weld seam just ahead of rotating tool to soften the material before being stirred. Three welding parameters, five levels, and a central composite design (CCD) have been used to minimize the number of experimental conditions. The joining parameters such as tool rotational speed, welding speed, and shoulder diameter have a significant influence on determining the mechanical properties of the welded joints. It was found that using preheating system mostly can result in higher total heat input into the weld joint and effectively reduces the formation of defects when unsuitable process parameters were used. Also, an attempt has been made to establish the mathematical model to predict the tensile strength and microhardness of the joints. The optimal welding conditions to maximize the final responses were investigated and reported. The results show that the joint fabricated at a rotational speed of 1,050 rpm, welding speed of 100 mm/min, and shoulder diameter of 14 mm exhibited higher mechanical properties compared to other joints.     

Effect of pinless tool shoulder diameter on dieless friction stir extrusion joining of AA 5052-H32 and AA 6061-T6 aluminum alloy sheets

Journal of Mechanical Science and Technology - A new spot joining process called dieless friction stir extrusion is proposed, in which simultaneous mechanical interlocking (collar formation) and...     

固溶温度对新型高强变形铝合金组织和力学性能的影响

通过研究一种高强变形铝合金固溶处理温度对其组织和性能的影响规律,探讨了在固溶处理过程中温度对合金组织及性能影响的机理。结果表明:在相同的时效处理工艺下,550～560℃的固溶处理温度可使合金达到较高的力学性能,相对于未经形变处理的合金材料,固溶温度可以提高5～10℃。     

Effect of thermal ageing on mechanical properties of a high-strength ODS alloy

A new high-strength ODS alloy, ARROS, was recently developed for the application as the cladding material of a Sodium-cooled fast reactor (SFR). To assess the long-term integrity under thermal ageing, ARROS was thermally aged in air at 650°C for 1000 h. The degree of thermal ageing was assessed by mechanical tests such as uniaxial tensile, hardness, and small punch tests at from room temperature to 650°C. Tensile strength was slightly decreased but elongation, hardness, and small punch energy were hardly changed at all test temperatures for the specimen aged at 650°C for 1000 h. However, the variation in mechanical properties such as hardness and small punch energy increased after thermal ageing. Using the test results, the correlation between tensile strength and maximum small punch load was established.     

Vibrational tests in study of the mechanical properties of aluminum alloy samples

The results of vibrational tests of aluminum alloy samples with different filler content are reported. The resonance frequency, the frequency and transmission characteristics, and the dissipation parameters were determined for identifying and certifying the samples. A specialized vibration stand was designed. The influence of the excitation amplitude on the amplitude-frequency and phase-frequency characteristics of the harmonically and resonantly excited samples was analyzed. It is shown that various methods exist for estimating the damping characteristics and the nonlinear effects in test samples.     

铝合金活塞铸造工艺数值模拟研究

针对铝合金活塞铸造成型过程中存在缩松、缩孔、晶粒尺寸不均匀等缺陷问题,利用Procast专业铸造有限元分析软件,进行了ZL108铝合金活塞铸造工艺的数值模拟研究,利用正交试验法考察了浇注温度、浇注速度、模具温度3个工艺参数,对数值模拟结果进行了晶粒尺寸、缩松缩孔分布、充型率等几个方面的综合评分.研究结果表明:最优的工艺参数组合为700℃的浇注温度、0.3 kg/s的浇注速度和150℃的模具温度.ZL108铝合金活塞铸造工艺数值模拟研究结果为壁厚不均匀的重要复杂零件铸造成型提供了理论指导,节省零件工艺优化设计的成本和时间.     

高速铣削AF1410高强度钢的实验研究

高强度钢具有优异的机械性能和广阔的应用,但切削加工较为困难,存在加工效率低,加工表面质量差等问题.以AF1410高强度钢为研究对象,应用高速铣削的加工方法,使用涂层硬质合金刀片,对AF1410高强度钢进行了高速铣削实验,研究分析了在高速切削条件下刀具磨损、切削力、切削温度以及已加工表面粗糙度的变化规律.研究发现以TiC...     

钢和LY12铝合金的非共线非线性特性

本文基于非共线波束混叠技术,建立了一种非共线非线性超声检测实验系统,分别观察了钢和LY12铝合金的非共线非线性响应.实验结果表明:①利用非共线波束混叠技术的空间可达、波型转换及频率方向可控等性质,可以达到有效抑制系统非线性干扰的效果;②钢和LY12铝合金试块内部均存在波型转换与波束混叠现象,LY12铝合金比钢具有更强烈的非共线非线性响应,测量结果更明显;③从实验上证明了该技术具有检测材料内部均匀性的能力.     

螺栓用钢ML35CrMoV最佳热处理制度的选择

通过实验,确定了钢ML35CrMoV最佳热处理工艺,使之达到12.9级高强度螺栓用钢的要求.     

Modeling and computation of the three-roller bending process of steel sheets

Sheet metal bending processes are some of the most commonly used industrial manufacturing operations. The development and optimization of these processes are time consuming and costly. Therefore, finite element simulations may aid the design and quality assurance of sheet metal products. In the present study, a commercial finite element package was used to analyze the three-roller bending of a steel sheet. A two-dimensional finite element model of this process was built under the ABAQUS/Explicit environment based on the solution of several key techniques, such as contact boundary condition treatment, material property definition, meshing technique, and so on. Maps with desired curvature radii were established by varying the distance between the two bottom rollers and the position of the upper one. The developed maps made the rolling process easier and less time consuming. An industrial experiment using optimized numerical results was carried out to validate the numerical model. Residual stress and equivalent plastic strain distributions were also studied. The numerical spring back phenomenon was compared with analytical results.     

铝合金铸件机箱四孔定位加工工艺方法研究

铸造铝合金材料因其良好的抗腐蚀性、流动性和切削加工性能,适合铸造薄壁、形状复杂和强度高的机箱等各类零件。根据实际生产过程中某薄壁类铸件机箱加工中易变形的问题,进行工艺流程改进,总结出铸件机箱的典型加工工艺方法,提高了产品质量和生产效率。     

Application of laser joining process for elimination of stair steps in steel laminate tooling

Laminate tooling is a relatively fast and simple method of making large metal tools directly for various moulding processes in the rapid prototyping and manufacturing field. Metal sheets are usually cut, stacked, aligned and joined. In most cases, lasers are used only for the cutting of steel sheets in laminate tooling, but in this study, the use of the laser was expanded for improved laminate tooling. First, the laser was applied to eliminate the stair steps of steel laminates by filling them with molten filler metals. Then application of hard particles to molten filler metals for improved surface hardness of laminate tools was investigated. To achieve this goal, a CO₂ laser system composed of a CO₂ laser, a five-axis CNC table, an automatic feeding equipment of filler metal and flux and a personal computer was developed. Various experiments on filling stair steps and hardening were performed and the results were verified and estimated.