Formability evaluation of a pure titanium sheet in the cold incremental forming process

Owing to its ability to deform a sheet metal locally, the single point incremental forming (SPIF) process produces larger deformations as compared to the conventional forming processes. In the present study, we investigated the effect of some process parameters – pitch, tool diameter, feed rate and friction at the interface between the tool and blank – on the formability of a commercially-pure titanium sheet. Trends between the process parameters and formability are presented in this paper.     

Microstructural and mechanical properties of dissimilar friction stir welds between AA6082-T6 and AA7075-T651

In the present work, similar and dissimilar friction stir welds have been produced on 6-mm-thick plates of AA6082-T6 and AA7075-T651. The microstructural characteristics and the mechanical response of both similar and dissimilar welds were investigated aiming to determine the major differences between them. Material mixing of the dissimilar weld nugget, which was created after the welding process, was studied in order to determine the produced different areas and their dominant alloying elements in this zone. Microstructural investigation was made in the welding zones of similar and dissimilar friction stir welds and indications of partial dynamic recrystallization were observed in the thermomechanically affected zone of the similar welds. Transverse and longitudinal microhardness distributions determined the heat affected zone as the weaker area in the welded specimen. After tensile testing, the fracture of the similar and the dissimilar welds at heat affected zone demonstrated the good bonding and weld quality of the similar and dissimilar weld nuggets.     

Efficient force prediction for incremental sheet forming and experimental validation

Incremental sheet forming (ISF) has been attractive during the last decades because of its greater flexibility, increased formability and reduced forming forces. However, traditional finite element simulation used for force prediction is significantly time consuming. This study aims to provide an efficient analytical model for tangential force prediction. In the present work, forces during the cone-forming process with different wall angles and step-down sizes are recorded experimentally. Different force trends are identified and discussed with reference to different deformation mechanisms. An efficient model is proposed based on the energy method to study the deformation zone in a cone-forming process. The effects of deformation modes from shear, bending and stretching are taken into account separately by two sub-models. The final predicted tangential forces are compared with the experimental results which show an average error of 6 and 11 % in respect to the variation of step-down size and wall angle in the explored limits, respectively. The proposed model would greatly improve the prediction efficiency of forming force and benefit both the design and forming process.     

On the FSW of AA2024-T4 and AA7075-T6 T-joints: an industrial case study

The paper presents an artificial neural network-optimization hybrid model to predict and optimize penetration depth of CO₂ LASER-MIG hybrid welding used for 5005 Al–Mg alloy. The input welding parameters are power, focal distance from the work piece surface, torch angle, and the distance between the laser and the welding torch. The model combines single hidden layer back propagation artificial neural networks (ANN) with Bayesian regularization for prediction and quasi-Newton search algorithm for optimization. In this method, training and prediction performance of different ANN architectures are initially tested, and the architecture with the best performance is further used for optimization. Finally, the best ANN architecture is found to show much better prediction capability compared to a regression model developed from the experimental data.     

Thermography in incremental forming processes at elevated temperatures

Temperature measurement is essential for several forming processes at elevated temperatures. It serves to determine and control the workpiece temperature. Thermography as a non-contact-based technology offers the possibility to capture thermograms of complete workpieces without any time-offset. However, the application of thermography requires the knowledge of the fundamentals of radiation thermometry, in particular the emissivity. This paper presents the results of the application of thermography in incremental sheet forming (ISF) with Joule heating and radial–axial ring rolling as a bulk forming process. Using thermography for the determination of the temperature of the forming zone allows for a real-time closed loop control in ISF with Joule heating. Additionally, the results of the temperature measurement of the surface temperature of radial–axial rolled rings are presented, which can be used as a starting point to make a forecast of the rings’ dimensions in cold state.     

Investigation on the forming force and surface quality during ultrasonic-assisted incremental sheet forming process

The integration of ultrasonic vibration into the incremental sheet forming (ISF) process can significantly reduce the forming force and bring other benefit     

Electromagnetic superposed forming of large-scale one-dimensional curved AA2524-T3 sheet specimen

This study proposes a methodology for helical mill-grinding of tiny internal threads made of hard brittle materials such as SiCp/Al composites. The methodology uses the helical mill-grinding method incorporating with a diamond form-grinding wheel. A mathematical model is established to predict thread form errors and provide a rational range of wheel parameters, such as variation of tool profile angle Δα and ratio of the wheel diameter to the thread major diameter η. Based on the methodology, a grinding wheel is developed for processing the M2 internal threads in a validation experiment. The study demonstrates that an M2 internal thread made of the SiCp/Al composite of 45% SiC volume fraction is successfully machined in 5 min with pitch error <0.08% and angle error <0.3%. The thread profile on the pitch diameter is within the axial equivalent tolerance zone (0–0.016 mm), which indicates that the thread precision reaches the H4 level.     

AA7075板材热处理的增塑机制及成形性能

结合生产工艺过程，研究了成形所需固溶处理、工序衔接所需自然时效、性能恢复所需人工时效对板材力学性能和成形性能的影响；通过金相显微镜、扫描电子显微镜和能谱分析等手段，探索热处理对板材显微组织与宏观力学性能的影响。结果表明：AA7075板材经固溶(480 ℃,0.5 h)水淬且自然时效处理后，最大力总伸长率提高85%、屈服强度降低60%，后经人工时效(120 ℃,12 h)处理，板材可完全恢复力学性能；固溶后,板材成形极限大幅提高，回弹比率显著减小；后继时效处理对弯曲角变化影响微弱。     

Effects of sheet thickness and anisotropy on forming limit curves of AA2024-T4

In this study, the effects of sheet thickness and anisotropy of AA2024-T4 on forming limit curve (FLC) are experimentally investigated according to ISO 12004-2 standard. A new limit strain measurement method is proposed by using the grid analysis method so as to determine limit strains conveniently and reliably. In addition to the regular test specimens, various widths are added to enhance the FLC’s accuracy at the plane strain condition (PSC). The accuracy and reliability of the proposed method are verified for different materials. Results illustrate that an increase in the sheet thickness increases the FLC level. The additional experiments for additional widths improve the accuracy of the FLC at the PSC, and the position of the lowest major strain value differs from the literature. However, the effect of anisotropy on the FLC is found to be insignificant. Finally, experimental and numerical case studies are carried out for conventional deep drawing, stretch drawing, and hydraulic bulge processes. Results reveal that different FLCs are necessary for different thicknesses for accurate predictions.     

Force-based failure criterion in incremental sheet forming

In incremental sheet forming, a hemispherical tool deforms a sheet moving along a predefined path. The process, useful for making prototypes or small series, is characterized by high flexibility and development times and costs reduction. The part feasibility is strongly influenced by the adopted tool path and, in particular, tool path corrections are requested to obtain the final geometry and to prevent the sheet rupture. To save time and costs, sheet failure criteria are therefore essential. In this paper, a real time force-based sheet rupture criterion is presented and tested on steel, aluminum, and titanium alloys. In particular, it will be shown that the sheet rupture can be related with the tangential forming force, the geometry of the component to be realized, and the sheet material characteristics.     

Incremental forming of Mg alloy sheet at elevated temperatures

In the present study, incremental forming of Mg alloy sheet at elevated temperatures was attempted with local heating apparatus. The device is composed of several halogen lamps and designed to move with forming tool for local heating in deformation zone. In order to investigate the influences of process parameters to incremental formability of AZ31 alloy sheet, a series of incremental forming tests of AZ31 for cone and pyramid type of simple models were carried out under various process conditions. Experiments were performed under various temperatures, feeding depth per cycle and inclination angles and the results were analysed.     

Surface integrity in broaching of AA 7075-T651 aluminum alloys

Special features as noncircular hole shapes are manufactured by the broaching process. The rise per tooth varies in different zones of the broaching tool. In this article, the effects of the two main process parameters (cutting speed and rise per tooth) on surface integrity (surface roughness, micro-hardness) and chip morphology will be studied. The experiments have been done on AA7075-T651 aluminum alloy. To investigate the effect of rise per tooth, one of the cutting edges of broaching tool is separated and the broaching process is implemented for nine samples. The samples are broached with three different cutting speeds (6, 12 and 18 m/min) and three rise per tooth (0.02, 0.05 and 0.1?mm). Also, the effect of cutting speed is investigated with a broaching needle (rise per tooth 0.1?mm). The results show that best surface roughness is obtained at cutting speed 12 m/min. The surface roughness will be improved by decreasing the rise per tooth. Also, the surface hardness decreases by increasing the cutting speed. The surface integrity (surface roughness and surface hardness) is comparable for single edge cutting tool and broaching needle. Continuous chips are formed during the broaching process and decreasing the cutting speed cause more compression of the chips.     

Electric hot incremental forming of Ti-6Al-4V titanium sheet

Electric hot incremental forming of metal sheet is a new technique that is feasible and easy to control to form hard-to-form sheet metals. In the present study, Ti-6Al-4V titanium sheet was studied because it was wildly used in the aeronautics and astronautics industries. Although Ti-6Al-4V titanium can be well-formed in high temperature, the surface quality is a problem. In order to enhance the surface quality, it is very important to select the proper lubricant. At the same time, because Ti-6Al-4V titanium has a lively chemical property, it is very important to choose a processing temperature range in order to acquire excellent plastic property and to prevent oxidation. Various lubricants were selected in processing to compare the effect, and some workpieces were formed at different temperatures to find the best forming temperature. The results show that using the lubricant film of nickel matrix with MoS₂ self-lubricating material, Ti-6Al-4V titanium workpiece was formed with high surface quality, and the optimum thickness of composite coating is 20 μm for Ti-6Al-4V titanium sheet of 1.0-mm thickness. In fact, the lubricant film also does help to prevent oxidation of Ti-6Al-4V titanium sheet. The appropriate temperature range of Ti-6Al-4V forming with slightly oxidized is 500–600°C in processing, and the maximum draw angle formed in this range was 72°.     

Fretting fatigue behavior of Al7075-T6 at sub-zero temperature

In some fretting fatigue applications, such as aero industry, the temperature may drop well below −50 °C Fretting fatigue behavior of aluminum alloy Al7075-T6 is investigated at temperatures of 24, 0, −25 and −50 °C in this work. The results show that (i) normal fatigue life increases considerably at sub-zero temperatures up to around 85% for low working stresses and reduces to about 40% for higher working stresses; (ii) fretting fatigue life at sub-zero temperatures rises significantly up to around 220% for low working stresses and reduces to about 50% for higher working stresses; (iii) ultimate strength of material changes from −15% to 15% under the fretting fatigue test conditions; and finally (iv) some parameters such as mechanical properties and fatigue behavior of material at low temperatures, contact load relaxation, crack closure, oxidation and some unknown sources can be thought to be responsible for fretting fatigue behavior of Al7075-T6 at sub-zero temperatures.     

Improving industrial suitability of incremental sheet forming process

Although in the last years a large amount of research work has been spent on incremental sheet forming process, industrial applications are not spreading accordingly. This is due to process characteristics such as slowness and limited accuracy. In the paper, the authors investigated the suitability of incremental sheet forming at very high feed rates to strongly reduce processing time. What is more, a simple strategy to reduce the part inaccuracy was implemented. The investigation concerned a simple conical shape but the obtained results are quite general.     

AA7075-T6圆筒形零件热态颗粒介质压力成形过程的力学分析

基于颗粒介质传压性能试验和AA7075-T6板材材料性能试验,对采用热态颗粒介质压力成形(HGMF)工艺拉深成形圆筒形件的法兰区、传力区和自由变形区进行了塑性力学分析,求解得到内压非均匀分布条件下成形压力的函数关系式,并与实测数据进行比对。分析结果表明,在成形中后期产生较大的偏差,理论求解最大成形力低于实测值24.6%。工艺试验研究表明,在成形温度为250℃条件下,采用HGMF工艺可一道次成形AA7075-T6圆筒形零件(底部为自由变形区)的极限拉伸比(LDR)为1.71。HGMF工艺操作便捷,装置简单,可在通用压力设备上实现轻合金板材件热成形,适用于航空、航天和军工等领域中小批量产品。     

Effects of forming parameters on temperature in frictional stir incremental sheet forming

Frictional stir Incremental sheet forming (ISF) is a new technology used to fabricate parts of hard-to-form materials without using heating equipment. Thus far, limited information is known about the effects of main forming parameters, except spindle speed of the tool, on the temperature of formed sheet in friction-stir ISF. The effects of six forming parameters, namely, sheet thickness, tool vertical step, tool diameter, spindle speed, feed rate, and wall angle of the formed part, were identified using the design of experiment of orthogonal array, analysis of response tables and graphs, and analysis of variance. Results show that spindle speed, feed rate, sheet thickness, and tool vertical step significantly affect the temperature of the sheet. In addition, the temperature of the sheet is significantly increased by increasing sheet thickness, tool vertical step, and spindle speed but significantly decreased with increasing tool feed rate.