船舶钢板激光弯曲成形的实验研究

在对船舶钢板激光弯曲成形过程进行实验研究中，采用CO2激光器研究了激光功率、扫描速度、扫描次数以及钢板厚度对船舶钢板激光弯曲成形的影响规律。实验中实时测量了船舶钢板激光弯曲成形过程钢板弯曲角度和温度的变化。结果表明：钢板弯曲角度随激光功率的增加而增加，随激光束扫描速度的增加而减小，而且随着钢板厚度的增加，弯曲角度减小；激光工艺参数和钢板厚度都对钢板激光多次扫描成形产生影响，钢板的弯曲角度随着激光扫描次数的增加而增加。对于较薄的船舶钢板，钢板弯曲角度随扫描次数增加近似呈线性增加，而较厚的钢板，随扫描次数的增加，钢板弯曲角度的增加逐渐减小。     

激光诱发热应力成形试验研究

利用2kW CO2激光器研究了低碳钢板料的激光弯曲情况,试验结果表明,对于多道扫描激光成形工艺,弯曲角度受到许多工艺参数的影响。其中,激光功率、光束直径、扫描速度、扫描次数、板料厚度等参数的效应尤其显著。对试验结果的定性分析,所得的结论可为激光弯曲成形技术的进一步理论研究和可能的工业应用提供依据。     

Some corrosion characteristics of stainless surface alloys laser processed on a mild steel

Preparation of corrosion-resistant ferritic and austenitic surface alloys on a mild steel was attempted by laser processing of chromium-plated mild steel and chromium and nickel-plated mild steel. The passivating ability increased with increasing number of laser irradiations due to an improvement of homogeneity of laser-processed surface layer with increasing number of meltings. However, there is an optimal number of irradiations, since further increase in number of laser irradiation meltings lowered both the passivating ability and pitting potential due to a decrease in chromium content in the laser-processed layer by evaporation.     

High Power Diode Laser Surface Treatment to Minimize Droplet Erosion of Low Pressure Steam Turbine Moving Blades

This article deals with the high power diode laser (HPDL) surface treatment to overcome water droplet erosion of Low Pressure Steam Turbine (LPST) moving blades used in high rating conventional, critical and super critical thermal power plants. The materials generally used in these steam turbines are titanium alloy (Ti6Al4V), precipitate hardened stainless steel (17Cr-4Ni PH), X20Cr13 and X10CrNiMoV1222 steels. During incubation period as well as under prolonged testing, the HPDL surface treatment of these materials except for 17Cr-4Ni PH steel has enhanced the droplet erosion resistance significantly. This is due to increased hardness and formation of fine-grained martensitic phase due to rapid heating and cooling rates associated with laser treatment. The droplet erosion results of HPDL laser surface treatment of all these materials and their analysis form the main part of the article.     

A laser-based technique for the coating of mild steel with a vitreous enamel

Marked changes in the wettability characteristics of EN8 mild steel were observed after high-power diode laser (HPDL) surface treatment of the metal. The morphological, microstructural and wetting characteristics of the steel were determined using optical microscopy, scanning electron microscopy (SEM), X-ray photoemission spectroscopy (XPS) and wetting experiments by the sessile drop technique. Improvements in the wetting action of the mild steel after HPDL surface treatment were identified as being the result of: HPDL-induced melting of the mild steel surface, which brought about a reduction of the surface roughness; and a small increase in the polar component of the surface energy and an increase in the surface O₂ content of the mild steel resulting from HPDL treatment. This work has demonstrated that the use of HPDL radiation to alter the wetting characteristics of mild steel in order to facilitate improved enamelling is a real possibility.     

Laser micro-bending process based on the characteristic of the laser polarization

The laser polarization is a basic characteristic of CO₂ and solid-state lasers. The material's absorptivity to laser is dependent upon the laser incident angle. Thus, the laser polarization can be utilized to control the bending angle by changing the laser incident angle during laser bending. The laser polarization is introduced into laser micro-bending, and an experimental system is established. Laser micro-bending process based on the characteristic of the laser polarization is realized. For uncoated stainless steel specimen, the bending angles acquired at bigger incident angles are bigger than those acquired at zero incident angles. The bending angles increase linearly with the increase of the incident angle when the incident angle changes from 60° to 80°. During laser multi-scan bending, the final bending angle no longer varies with the scanning number, and approximately equals to the complement angle of the incident angle when it approaches to the complement angle. By means of adjusting the laser incident angle and scanning velocity, unfinished and finishing laser bending can be realized to satisfy the forming efficiency and accuracy. The absolute error between the final bending angle and the expected angle is less than 0.1°.     

Thermal–mechanical analysis on the transient deformation during pulsed laser forming

The transient deformation of thin grade 304 stainless steel metal sheets heated by a single pulse of a CO₂ laser beam is simulated in this paper. The laser beam is assumed to be Gaussian mode and the coupled thermo-elastoplastic problem is treated as three-dimensional. The temperature field, deformation pattern, stress–strain states, and the residual stress distribution of the specimens have been calculated numerically and the transient response of the bending angle has been validated by experiments. Good agreement has been obtained between the numerical simulation and the experiments under various operating conditions. The numerical study reveals that a high temperature gradient exists for a positive bending angle and a low one for a negative angle. It transpires that the mechanisms of pulsed laser forming are dependent mainly upon the laser power, the heating time, the clamping arrangement, as well as the geometry, the thermal properties, and the original stress states of the specimen.     

Experimental investigation on high strength steel (HSS) tailor-welded blanks (TWBs)

This paper aims to investigate mechanical characteristics of the new tailor-welded blank (TWB) components made of high strength steel (HSS). A series of HSS-TWB thin plates with different orientations of weld line are studied through three-point bending tests to evaluate the effects of different design parameters, such as weld line locations and material combinations, on the deformation behaviors. The experimental results exhibit good repeatability of tests. And the relative shift phenomenon between indenter and specimen is observed and analyzed for the TWB steel sheets with different weld line orientations at parallel and 45° to the bending moment, respectively. The results from the experiment include the force versus displacement curves and some detailed photographical images throughout the loading process. It is found that the discrepancy of different combinations is quite noteworthy. In this paper, the peak force, absorbed energy and bending strength are presented to evaluate the mechanical characteristics of HSS-TWB thin plates with different weld line orientations and material combinations. The comparison demonstrates that the TWB structures with the weld orientation at 45° angle to the bending moment have the greatest advantages of different TWB steel sheets.     

Effects of laser beam energy and incident angle on the pulse laser welding of stainless steel thin sheet

This paper reports an experimental study of laser spot welding on stainless steel sheets. A pulsed Nd:YAG laser was used to weld the stainless steel specimen in the range of laser energy 0.6–1.2 J and incident angle 30–75° (the angle of the laser beam incident direction to the sheet surface). Metallography was applied to measure the cross-sectional size and shape of the welded spot. From the experimental results, it is found that as the laser energy increases, the penetration depth, bead length, and bead width of the welded spot increase. As the laser incident angle increases, the penetration depth and the bead width increase while the bead length decreases. The results illustrate that the shape and size of the welded spot depend not only on the laser energy, but also on the incident angle of laser beam.     

Computer simulation and experimental investigation of sheet metal bending using laser beam scanning

Computer simulation and experimental investigation of the sheet metal bending into a V-shape by the laser beam scanning without an external force exerted onto it have been performed. A 3-D FEM simulation has been carried out, which includes a non-linear transient indirect coupled thermal-structural analysis accounting for the temperature dependency of the thermal and mechanical properties of the materials. The bending angle, distribution of stress–strain, temperature and residual stresses have been obtained from the simulations. The sheet metal bending had been performed for different materials, thicknesses, scanning speeds and laser powers. The measurement of real-time temperature and bending angle was carried out. The bending angle is affected by the mechanical and thermal properties of the sheet metal material, the process parameters, and the output of laser energy. The bending angle is increased with the number of laser beam scanning passes and is the function of the laser power and the laser beam scanning speed. The simulation results are in agreement with the experimental results.     

A Comparative Study of High-Power Diode Laser and CO2 Laser Surface Hardening of AISI 1045 Steel

The study investigates laser surface hardening in the AISI 1045 steel using two different types of industrial laser: a high-power diode laser (HPDL) and a CO₂ laser, respectively. The effect of process parameters such as beam power, travel speed on structure, case depth, and microhardness was examined. In most cases, a heat-affected zone (HAZ) formed below the surface; a substantial increase in surface hardness was achieved. In addition, big differences were found between the hardened specimens after HPDL surface hardening and CO₂ laser surface hardening. For HPDL, depths of the HAZ were almost equal in total HAZ o, without surface melting. For CO₂ laser, the depths changed a lot in the HAZ, with surface melting in the center. To better understand the difference of laser hardening results when use these two types of laser, numerical (ANSYS) analysis of the heat conduction involved in the process was also studied. For HPDL method, a rectangular beam spot and uniform energy distribution across the spot were assumed, while for CO₂ laser, a circular beam spot and Gaussian energy distribution were assumed. The results showed that the energy distribution variety altered the thermal cycles of the HAZ dramatically. The rectangular HPDL laser beam spot with uniform energy distribution is much more feasible for laser surface hardening.     

温度梯度机理下激光参数对激光成形的影响

以纯铝板和低碳钢板为主要研究对象，对温度梯度机理下激光输入功率、扫描速度、离焦量以及扫描次数等参数与成形弯曲角之间的关系进行了试验研究，深入分析了温度梯度机理下影响成形的主要因素。     

Über den Einfluß des aufgenommenen Wasserstoffs auf die Wechselbiegefähigkeit von Kohlenstoffstahl bei der Beizung in Schwefelsäure

Influence of hydrogen pick-up on the alternating bending strength of carbon steel during sulfuric acid pickling Steel coupons (St 3 GBKL) were acid-pickled in 1 M sulfuric acid at 50° C. The dissolution rate (by weight), the hydrogen uptake (by high temperature vacuum extraction and gaschromatographic determination) and the alternating bending strength (by alternating bending at 25 Hz and deflection angle ± 5°) were measured as a function of pickling time. The linear corrosion rate was 21 · 10^?6 · kg · m^?2 · sec^?1, the saturation concentration of hydrogen in steel was 8,76 ppm and the diffusion coefficient of hydrogen in steel was calculated as 8,74 · 10^?7 cm² · sec^?1. The number of bendings until fracture is not only a function of the integral hydrogen concentration, but is strongly influenced by the concentration profile of hydrogen in the sample; a hypothesis is given to explain this experimental finding.     

Enhanced Droplet Erosion Resistance of Laser Treated Nano Structured TWAS and Plasma Ion Nitro-Carburized Coatings for High Rating Steam Turbine Components

This article deals with surface modification of twin wire arc sprayed (TWAS) and plasma ion nitro-carburized X10CrNiMoV1222 steel using high power diode laser (HPDL) to overcome water droplet erosion occurring in low pressure steam turbine (LPST) bypass valves and LPST moving blades used in high rating conventional, critical, and super critical thermal power plants. The materials commonly used for high rating steam turbines blading are X10CrNiMoV1222 steel and Ti6Al4V titanium alloy. The HPDL surface treatment on TWAS coated X10CrNiMoV1222 steel as well as on plasma ion nitro-carburized steel has improved water droplet resistance manifolds. This may be due to combination of increased hardness and toughness as well as the formation of fine grained structure due to rapid heating and cooling rates associated with the laser surface treatment. The water droplet erosion test results along with their damage mechanism are reported in this article.     

中厚船舶钢板激光弯曲成形几何效应的数值模拟

建立板材激光弯曲的三维非线性准静态弹塑性热力耦合有限元模型。使用有限元软件 MSC Marc对中厚船舶钢板的激光弯曲成形过程进行数值模拟。计算了船舶钢板激光弯曲成形过程的温度场和变形场, 并进行相应的实验验证。模拟结果与实验结果吻合较好。用建立的模型对中厚船舶钢板的激光弯曲成形过程中钢板的几何效应进行数值模拟, 讨论了一定工艺条件下钢板几何参数与弯曲角度之间的关系, 为在将来实际生产中制定和优化钢板激光弯曲成形的工艺参数提供理论依据。     

钛合金板料激光曲线弯曲及热辐射对其组织性能的影响

研究了激光能量密度、路径曲率和扫描次数对TC4（Ti－6Al-4V）板料弯曲变形的影响规律,同时,分析了热辐射对板料显微组织和表面硬度的影响。结果表明：（1）存在一个最的能量密度值使板料一次弯曲所获得的的弯曲角度达到峰值;（2）随路径曲率的增加,弯曲角度减小;（3）第一次扫描以后的扫描次数与弯曲角度呈准线性关系。（4）合适的工艺参数不会导致材料显微组织变化,且激光热辐射对材料表面有淬火效应,使加热区材料表面硬度均有所提高。     

Springback behaviour in bending of ultra-high-strength steel sheets using CNC servo press

The springback behaviour of ultra-high-strength steel sheets in bending was investigated under controlled conditions using a CNC servo press. Although the ultra-high-strength steel sheets are attractive in reducing weight of cars, the amount of springback of the ultra-high-strength steel sheets in the forming is very large due to high strength. The CNC servo press has the function of accurately controlling the motion by two servo motors. The effects of the material, the finishing reduction in thickness, the forming speed and the holding time at the bottom dead centre on the amount of springback in V-shaped bending were examined. The scatter of the springback for the ultra-high-strength steel sheets was improved by using real thickness and not nominal thickness of each individual sheet in the control of the punch stroke. The amount of springback for the ultra-high-strength steel sheet in the V-shaped bending was much larger than that for the mild steel sheet, and the amount was decreased by the finishing reduction in thickness direction because of uniform stress distribution. The effects of the forming speed and the holding time at the bottom dead centre were small. The amount of springback for the steel sheets was almost proportional to the ratio of the tensile strength to the elastic modulus.     

Study on static and fatigue strength of structural adhesive-bonded joints of steel sheets for automotive application

The static and fatigue strength of crush durable structural adhesive-bonded lap joints of steel sheets for automobiles was evaluated by tensile shear tests. The steel sheets used in this study were uncoated and galvannealed (GA) with tensile strength ranging from 270 MPa-grade to 980 MPa-grade and the thickness ranging from 0.7 to 1.8 mm. Also, the effects of the adhesive types were evaluated. The results are as follows: In the static tensile shear tests, when the steel sheets deformed during the tensile test, the tensile shear strength increased with the increase in the base metal properties, such as the yield strength and thickness; however, when the base metal properties were sufficiently high not to undergo plastic deformation, the tensile shear strength exhibited a constant value. On the other hand, the effect of base metal properties on the fatigue joint strength was relatively small. The static joint strength of the GA steel joints was slightly lower than that of the uncoated steel sheets; however, the fatigue strength of the GA steel joints was higher than that of the uncoated steel sheets. The coating failure of the GA was affected by the type of adhesive, base metal properties and type of test. Choosing the proper adhesive can reduce the failure of the GA coating, and the high strength steel showed fewer coating failures than the mild steel.     

管材激光弯曲工艺研究

管材激光弯曲是一种具有极高柔性的金属塑性加工方法,特别适合于薄壁管材的小曲率半径弯曲。文章依据塑性力学原理推导了管材激光弯曲的弯曲角度计算公式,并与试验结果进行了对比。理论计算与试验结果均表明,激光弯曲角度随激光扫描次数的增加而增大,但并不呈线性关系,同时还存在一个获得永久塑性弯曲的激光功率阈值。     

Square cup deep drawing and 2D-draw bending analysis of Hadfield steel

Hadfield steel is the dominant material in the production of bullet proof steel helmet for military uses. The conventional bullet proof steel helmets are extensively fabricated by cold forming (deep drawing) 1.2 mm Hadfield steel sheets at room temperature. This paper presents the experimental analysis of the square cup deep drawing and 2D-draw bending of Hadfield steel as a continuation of an international bench mark research program organized by NUMISHEET'93 organising committee in Japan. The draw-in values of the flange have been determined for various punch travels in the square cup operation. The principal strains were evaluated in three directions from grid measurments for those punch travels. Springback values and sidewall curls were also described in 2D-draw bending operation. The experimental results were compared with that of ones in mild steel.