CO2 laser welding of zinc-coated steel sheets

Welding of zinc-coated steel sheets for the automotive industry has been investigated experimentally and theoretically, using a continuous wave 2 kW CO₂ laser. The specimens of 0.8, 1.0 and 1.2 mm thickness were welded as butt joint and lap joint. Argon gas was shielded co-axially to reduce the plasma and to protect the molten, pool from atmosphere. The mechanical tests of specimens were carried out to investigate the ductility of welds in butt joint and lap joint, using the Erichsen test, ball punch test and tensile shear test. The value of transverse weld pattern is higher than others. The fatigue life of longitudinal weld is superior, but that of circular weld pattern is inferior due to the high tensile residual stresses in the weld. The maximum Erichsen value was obtained as 96% and the deformability of zinc coated steel butt-welded was found to be 80% in the ball punch test. The high pressure formed by vaporization of zinc with the low boiling temperature during laser lap-joint welding splattered the molten pool and created porosities in the weld. The optimum gap was calculated to be 0.1 mm in the lap joint welding of zinc-coated steel sheet which was a good agreement with the experimental result.     

Optimization of pulsed GTA welding process parameters for the welding of AISI 304L stainless steel sheets

Optimization of pulsed gas tungsten arc welding (pulsed GTAW) process parameters was carried out to obtain optimum weld bead geometry with full penetration in welding of stainless steel (304L) sheets of 3 mm thickness. Autogenuous welding with square butt joint was employed. Design of experiments based on central composite rotatable design was employed for the development of a mathematical model correlating the important controllable pulsed GTAW process parameters like pulse current (I _p), pulse current duration (T _p), and welding speed (S) with weld bead parameters such as penetration, bead width (W), aspect ratio (AR), and weld bead area of the weld. The developed models were checked for adequacy based on ANOVA analysis and accuracy of prediction by conducting a confirmation test. Weld bead parameters predicted by the models were found to confirm observed values with high accuracy. Using these models, the main and interaction effects of pulsed GTAW process parameters on weld bead parameters were studied and discussed. Optimization of pulsed GTAW process parameters was carried out to obtain optimum bead geometry using the developed models. A quasi-Newton numerical optimization technique was used to solve the optimization problem and the results of the optimization are presented.     

CO2 laser welding of interstitial free galvanized steel sheets used in tailor welded blanks

Recently, laser welding technologies have been widely utilized to weld different automobile panels. In this research, the laser beam welding (LBW) process of interstitial free (IF) steel sheets used in the manufacturing of the car body was investigated on the basis of mathematical models. The quality indexes of LBW joints were estimated from Erichsen Cupping Test results including strength and Erichsen Cupping Index. Furthermore, three process parameters, namely laser power (P), welding speed (S), and focal position (F) were considered as the factors influencing the quality indexes. A 2.2-kW CO₂-laser beam was utilized to weld 1.2- and 0.8-mm-thick IF steel sheets. The modeling is done using experimental data which were gathered using design of experiments approach based on central composite face centered design matrix. The final regression models can be used to predict the quality indexes of laser beam-welded IF steel sheets joints at 95% confidence level. Optical metallography was utilized to characterize the weld profile and microstructures. In the second phase of this research, multi-objective genetic algorithm with the fitness function based on regression models was employed as an optimization procedure; as a result, the best quality indexes were obtained. Optimization results showed high compatibility with the actual experimental data.     

压力电阻点焊机焊接316(Ti)不锈钢板状件的工艺研究

用压力电阻点焊机作为焊接设备,对316(Ti)不锈钢板状结构件进行点焊试验,研究了压力电阻点焊工艺参数对焊缝质量的影响。试验结果表明,焊接电流、焊接压力以及电极形状是影响压力电阻点焊模式的主要因素,在小焊接压力和低焊接电流以及不理想电极形状的条件下,焊点容易产生飞溅且焊缝熔核较小,导致焊点外观和焊缝金相等性能均不满足要求,而过大焊接压力以及较高的焊接电流也会导致熔核尺寸降低以及产生飞溅等缺陷。压力电阻点焊的焊接参数需要合理匹配,才能获得好的稳定的焊缝质量。     

Drawability of stainless steel sheets

Stainless steels can be classified into two categories, i.e. austenitic and ferritic. These materials are different in crystalline structure: where austenitic stainless steel is face-centered cubic, ferritic stainless steel is body-centered cubic.In general, the quality of stainless steel tends to be assessed by its magnetic properties: it is believed that austentic stainless steel is better than ferritic stainless steel, because it is non-magnetic, but, in fact, the drawability of — magnetic — ferritic stainless steel is somewhat better than that of austenitic stainless steel. Press forming, however, consists of both drawing and stretch forming, and thus in the press forming of stainless steel sheets, it is necessary to have a good knowledge of the metallographic factors governing stretch forming and deep drawing.In this paper, the differences between austenitic and ferritic stainless steel of the metallographic factors which control press forming, are discussed.     

锅炉钢架大板梁的焊接技术及应用

通过多年制造锅炉钢架的实践,修正原对称X型坡口并利用焊接反变形控制,减少大板梁对接的翻面次数,达到图纸平面度要求,提高了生产效率.     

The effect of welding parameters on fracture toughness of resistance spot-welded galvanized DP600 automotive steel sheets

The aim of this study was to evaluate the fracture toughness of resistance spot welded (RSW) lap joints of galvanized DP600 steels. RSW lap joints galvanized DP600 steel sheets were performed on spot welded in a pneumatic, phase-shift-controlled, and 0–9?kA effective weld current capable AC spot welding machine. Defect-free RSW lap joints were produced on galvanized DP600 steel sheets. Fracture toughness of RSW lap joints were calculated from the results of shearing tensile tests: the dependence of fracture toughness to welding current, welding time, and hardness of welding zone for galvanized DP600 steel sheets. According to the experimental data, the fracture toughness increases as welding current and welding time increase up to a certain value, then the fracture toughness starts to decrease. Also, it was seen that the fracture toughness varies with the hardness of the welding zone. This variation is related to welding current.     

Energy absorption mechanism of Al–steel bilayer sheets produced by cold roll welding during wedge tearing

The behavior of Al–steel bilayer sheets produced by cold roll welding is investigated through the wedge tearing process. It is observed that through tearing the energy absorbed by cold roll welded bilayer sheets is larger than that of non-welded ones, even though all parameters are identical. Also bilayer sheets with low bond strength have the same energy absorbed by non-welded bilayer sheets. By investigating all contributing mechanisms in tearing and mechanical properties of composite layers and developing theoretical equations, it is concluded that bending of sheets through wedge tearing plays a major role in difference of energy absorbed by welded and non-welded bilayer sheets. Moreover, there is a good correlation between experimental data and theoretical equations developed for predicting the load–displacement curves of tearing and energy absorption of Al–steel bilayer sheets.     

阀座不锈钢喷焊层厚度的电磁法检测

介绍了一种新的检测不锈钢喷焊层厚度的方法,论述了其在实际应用中的可靠性和高效率。     

薄板点焊热过程的有限元分析

基于ANSYS有限元分析系统,建立用于点焊瞬态热过程分析的电热耦合有限元模型,考虑随温度变化的材料特 性参数、相变以及对流边界条件等,对点焊过程中的接触问题进行适当简化。通过对低碳钢薄板点焊过程的分析,得到 点焊接头的温度场及各部位的热历程,模拟了焊核形成过程,求得焊核及热影响区的形状和尺寸。     

Friction stir butt welding thin aluminum alloy sheets

0.8-mm-thick alclad 2024-T4 aluminum alloy sheets were friction stir butt welded. A 15-mm diameter shoulder tool was used to guarantee sufficient heat input during welding. A 0.08-mm shoulder plunge depth was adopted to reduce sheet thickness reduction. Sound joints were obtained at rotating speeds from 400 to 1000 rpm and welding speeds from 50 to 150 mm/min. A thickness reduction of 6% was achieved at 1000 rpm and 50 mm/min. Secondary phases firstly precipitated at the black lines in the stir zone (SZ). The hardness of the SZ showed a decrease about 6% compared with the base metal. A maximum tensile strength of 399.5 MPa and an elongation of 5.6% were achieved at 1000 rpm and 150 mm/min. The fracture morphologies showed typical ductile fracture mode.     

Review on electromagnetic welding of dissimilar materials

Electromagnetic welding (EMW) is a high-speed joining technique that is used to join similar or dissimilar metals, as well as metals to non-metals. This technique uses electromagnetic force to mainly join conductive materials. Unlike conventional joining processes, the weld interface does not melt, thus keeping the material properties intact. Extremely high velocity and strain rate involved in the process facilitate extending the EMW technique for joining several materials. In this paper, the research and progress in electromagnetic welding are reviewed from various perspectives to provide a basis for further research.     

ARC welding method for bonding steel with aluminum

When welding steel with aluminum, the appearance of intermetallic compounds of Fe and Al will decrease tenacity and increase rigidity, which leads to bad joint performance. A new type of low energy input (LEI) welding technology is introduced which can be used to weld steel with aluminum. Using the technology, brazing was located on the steel side and arc fusion welding on the aluminum side. The less heat input reduces the thickness of intermetallic compounds to 3–4 μm. Tensile strength tests prove that the joint breaks at the heat-affected zone and the strength is higher than 70% of the aluminum’s. Thus, the method can lead to a good performance joint.     

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.     

Development of application technique of aluminum sandwich sheets for automotive hood

Objective of this study was to develop basic techniques in order to apply aluminum sandwich sheets for an automotive hood part. The aluminum sandwich sheet is the material fabricated by adhering two aluminum skins to one polypropylene core. When it has the same bending stiffness as a steel sheet, it is 65% lighter than the steel sheet and 30% lighter than an aluminum alloy sheet. Therefore, it is notified exclusively as good substitutive materials for a steel body to improve the fuel efficiency. Through aluminum sandwich sheet, however, it has relatively lower formability than that of the steel sheet for automotive application. In this study, we developed application techniques of the aluminum sandwich sheet for automotive hood. The various formability evaluations were carried out in order to secure the fundamental data for the measurement of sheet metal forming and the establishment of optimum application conditions of the sandwich sheet. From these results, it was found that the sandwich sheet could reduce the weight and maintain the flexural rigidity simultaneously comparing to the steel sheet.     

9%Ni钢用国产镍基焊丝的焊接试验研究

针对镍基焊丝的热裂纹敏感性试验,研制出FISCO热裂纹试验装置,利用该装置对研制的ERNiCrMo-3镍基焊丝进行焊接热裂纹敏感性试验,结果表明,研制焊丝的热裂纹敏感性与进口焊丝相当,均具有较低的热裂纹敏感性。采用研制焊丝焊接9%Ni钢的工艺试验结果表明,焊接接头各项力学性能优良,焊缝组织为纯奥氏体组织,析出相很少,可以满足大型LNG储罐的设计要求。     

钢轨接口的焊接

唐钢冷轧薄板厂的桥式起重机钢轨以前采用预留间隙的夹板连接方法,此连接方法将钢轨直接固定在梁上,当受到振动、热胀冷缩等因素的影响易发生夹板松动使接口处错位,造成行走轮磨损或毁坏,严重威胁安全生产。现采用在梁与钢轨间铺胶垫板,钢轨接口焊接的无间隙柔性处理后,经一段时间运行,收到良好的效果。为安全生产和经济效益提供了保障。     

The dependence of local deformations and internal stress fields on welding technique for grade VSt3sp structural steel: I. The influence of welding technique on the mechanical characteristics and acoustic emission parameters of grade VSt3sp steel

A staging analysis was carried out for deformation curves and the evolution of local deformation fields in defective and defect-free specimens of welded joints of grade VSt3sp steel that were made using manual arc and manual pulsed arc welding. Stages of elasticity, microplasticity, nucleation and motion of Chernov–Luder’s bands, and parabolic deformation strengthening were considered. The parameters of acoustic-emission signals during tension of specimens with a welded seam were analyzed.     

Seam gap bridging of laser based processes for the welding of aluminium sheets for industrial applications

Laser welding has a large potential for the production of tailor welded blanks in the automotive industry, due to the low heat input and deep penetration. However, due to the small laser spot and melt pool, laser-based welding processes in general have a low tolerance for seam gaps. In this paper, five laser-based welding techniques are compared for their gap bridging capabilities: single-spot laser welding, twin-spot laser welding, single-spot laser welding with cold wire feeding, twin-spot laser welding with cold wire feeding and laser/GMA hybrid welding. Welding experiments were performed on 1.1- and 2.1-mm-thick AA5182 aluminium sheets. The resulting welds were evaluated using visual inspection, cross sectional analysis with optical microscopy, tensile tests and Erichsen Cupping tests. The results show that the use of a filler wire is indispensable to increase the gap tolerance. A proper alignment of this wire with the laser spot(s) is crucial. With the single spot laser welding with cold wire feeding, a gap up to 0.6 mm could be bridged as opposed to a maximum allowable gap width of 0.2 mm for single-spot laser welding without filler wire. For 2.1-mm-thick sheets, the laser/GMA hybrid welding process can bridge even gaps up to 1.0 mm. Most welds had a high tensile strength. However, during Erichsen Cupping tests, the deformation of the welds is significantly lower as compared to the base material.