Laser Shock Forming Research Articles

Microstructure and corrosion behaviour of metal copper parts formed by laser shock

The effects of laser shock forming (LSF) on material microstructure evolution and its electrochemical corrosion behaviour were investigated. Results show that high-density dislocations and stacking faults are formed on the laser-irradiated surface layer of parts. The laser-irradiated surface of the parts subjected to two-shot LSF exhibited better corrosion resistance, with a 2-fold decrease in the passive current density, 3.5-fold increase in the charge resistance, and ∼12-fold thicker passive film compared with the undeformed sheet. The formation of nano-grains, compressive residual stresses, and a dense Cu2O oxidation film during LSF contributed to the improved corrosion resistance of the LSF-fabricated copper parts.

Microstructure evolution and strengthening mechanism of pure copper sheet induced by laser shock forming

laser shock forming (LSF) is a high strain rate forming process, which can significantly improve the formability of materials. Nevertheless, there is a lack of research on the microstructure evolution and improving mechanical properties of parts deformed by LSF. In this paper, pure copper sheet are formed into flat bottom parts under one- and two-shot LSF. The deformation topography, surface morphology and thickness distribution of the deformed parts are tested. The surface micro morphology of the mould can be additionally printed in the formed parts, and the sheet forming accuracy improved continuously and lower thickness thinning with the increase of the shock number. Transmission electron microscopy (TEM) showed that the microstructure on the surface of the formed specimens was composed of nanocrystalline arrays elongated in the direction of the transverse flow of the workpiece material. The dislocation density decreased and the twinned structures gradually disappeared with an increasing depth from the treated surface. More laser shocking can refine the metal material grain and improve material mechanical property of the formed part further. Eventually, the underlying improvement mechanism of mechanical properties induced by LSF-induced microstructure evolution on pure copper was systematically revealed.

Application of Python-Based Abaqus Secondary Development in Laser Shock Forming of Aluminum Alloy 6082-T6.

Aluminum alloy 6082-T6 is an important material for manufacturing the outer skin of high-speed trains, and laser shock forming can realize the rapid forming of complex-shaped plates. In order to improve the efficiency of the simulation modeling of laser shock forming for aluminum alloy 6082-T6, Python scripting language was used for the secondary development of Abaqus. A plugin was utilized to simulate and analyze the laser shock forming process of aluminum alloy 6082-T6. The coordinates of the plate after laser impact molding were measured using a coordinate measuring machine to calculate the arc bow height of the plate. The accuracy of the simulation model was verified by comparing with the simulation results. The deformation characteristics of plastic strain and arc height of aluminum alloy 6082-T6 under different laser process parameters were analyzed. The simulation plugin has a concise interface, high operability, and accurate results with the other parameters unchanged. When the laser energy is 5 J, 6 J, and 7 J, the corresponding arc heights are 5.9 mm, 6.6 mm, and 7.2 mm, respectively. As the thickness of the sheet increases, the deformation changes from concave at 1 mm to convex at 2 mm, 3 mm, 4 mm, and 5 mm. As the spot size increases from 1 mm to 5 mm, the transmission mode of the shock wave gradually changes from spherical wave to planar wave, and the arc height of the sheet increases from 4.6 mm to 8.2 mm. With the increase in the spot overlap rate, the impact area accumulates residual stress, and the arc height of the sheet is 5.7 mm, 6.6 mm, 7.3 mm, and 8.5 mm, respectively. The secondary development of ABAQUS 2021 using Python 3.6 scripting language has improved the efficiency of simulation modeling and provided reference for rapidly predicting the deformation characteristics of aluminum alloy 6082-T6 under different laser process parameters.

Research on dynamic deformation behaviors of laser driving metal sheet precision forming

Laser shock forming (LSF) is an advanced sheet forming technology. With the aid of forming die, it can realize sheet precise forming, and has extensive application prospects in aeronautic and electronics industries. In the paper, a two-dimensional axial symmetric numerical model of SUS304 stainless steel is established. Finite element method is utilized to explore the dynamic deformation behaviors of the laser-driving sheet impacted by the forming die. The results show that the node velocity of metal sheet increases in an oscillatory manner during initial stage and then it starts to bulge. After collision with die cavity bottom, the central region of metal sheet jumps up reversely, and experiences repeating damped vibration. The metal sheet gradually exhausts the obtained kinetic energy from the shock wave, and the flat sheet is finally shaped into the geometrical shape of die cavity. The sheet forming precision can be improved by way of increasing laser shock pressure. The corresponding experiments are also carried out to verify the predicted results. The applied method and gained results can provide a reference for theoretical research and parameters optimization in LSF.

Effect of Sheet Thickness on Forming Precision in Single Laser Shock Forming with Mold

Laser shock forming (LSF) is one of the sheet metal dynamic forming techniques that employ laser-induced shock waves to form sheet metal into complex three-dimensional parts rapidly. This work investigates the effect of sheet thickness on the forming precision in laser shock forming with mold. ABAQUS/Explicit analysis software is adopted to study the effect of sheet metal thickness on forming accuracy. The corresponding forming experiments with sheet thickness arranged from 0.1mm to 0.4 mm are conducted to validate those numerical values. The numerical and experimental results indicate that the sheet thickness plays an important role in the precision of the formed parts, with the increase of sheet thickness, the forming precision is decreased.

The saturated convex bending curvature of 7075 aluminum panel bent by orthogonal laser shock forming

Laser shock forming is an innovative and flexible forming technology that induces bending deformation in thin panel by the action of laser shock wave. In the convex deformation, laser shock forming lacks the ability to continuously enhance the bending curvature for one panel, especially for thick panel. This paper explores the saturated convex bending curvature by increasing overlapping ratio, the number of repeated shock and laser power intensity sequentially in orthogonal laser shock forming. The induced bending moment and bending curvature are calculated by the average induced stress obtained from representative cell model, and this method improves the efficiency of evaluating the saturated bending curvature. 50% overlapping ratio can improve the bending curvature, and ensure the processing efficiency and quality of laser shock forming. The induced stress gradually tends to be saturated in the repeated shocks. Based on 50% overlapping ratio and 5 repeated shocks, when the laser power intensity exceeds 6.37GW/cm2, the bending curvature cannot be significantly improved by increasing laser power intensity for the saturation effect and the bending moment reduction. The curvature prediction method can effectively predict the saturated bending behavior of one panel in laser shock forming, and the method can avoid the invalid forming process design, which is a guidance for laser shock forming and the selection in forming methods.

Improving mechanical property and microstucture evolution of 7075 aluminum panel formed by unequal alternate double-sided laser shock forming

With thrust weight ratio increasing, integral panel is an important component to reduce the aircraft weight, and it is a great challenge to ensure the forming accuracy and mechanical property in the large-scale panel. Laser shock forming has a great development prospect in realizing integral panel forming and improving its mechanical properties. This work investigated unequal alternate double-sided laser shock forming, which can make 7075 aluminum panel form and induce the hardened layers in both panel sides. The improvements were analyzed in mechanical properties and microstructure evolution of 7075 aluminum panels after unequal alternate double-sided laser shock forming. In the surface and subsurface layer, the residual stress and microhardness were verified to be enhanced by the laser shock wave. The results of XRD and EBSD provided the evidence of grain refinement. The strengthening mechanism of unequal alternate double-sided laser shock forming was analyzed in this work. The grains are distorted and refined during high strain rate plastic deformation due to dislocation slip and accumulation. The mechanical properties were enhanced by unequal alternate double-sided laser shock forming due to the hardened layers in both panel sides. The hardened layers and grain refinement have a great significance in inhibiting the crack generation and growth.

Joining similar and dissimilar material combinations by laser shock forming

Abstract This paper verified the feasibility of joining similar and dissimilar material combinations by laser shock forming. Typical joining defects and failure modes during the deformation process were also discussed. Neck fracture often takes place in the lower foil, which was subjected to serious joint shearing effect from laser-induced shock wave and hole edge of perforated sheet. Meanwhile, bottom fracture was more likely to occur in the upper foil, in which the direct laser shock pressure was quite large. Process windows of Cu/Cu/Ss combination and Cu/Al/Ss combination were acquired after conducting an array of experiments. The influences of laser energy and material properties on interlocking structure were investigated by analyzing cross-sectional material flow and measuring key structural dimensions. With the increase of laser energy, interlocks gradually increased while neck thicknesses gradually decreased. Under the same processing conditions, interlocks of Cu/Al/Ss combination were larger than that in Cu/Cu/Ss combination, while both neck thicknesses showed an opposite trend. Single lap shearing tests showed that mechanical strength and failure modes of joints were notably influenced by interlocking structure, a high joining strength can only be obtained under larger interlocks and larger neck thicknesses.

Experimental research on plastic deformation of metal foil through ns laser-induced mechanical effects underwater

Laser shock forming (LSF) is an effective method to induce plastic deformation of metal foil, but the need for a solid-state energy absorbent layer during LSF limits its engineering application. Strong shockwave can also be launched by laser-induced breakdown in water because of the nonlinear absorption of water. So through this method, underwater laser-induced mechanical forming (LMF) without specialized absorbent layer can be achieved. In this paper, nanosecond laser was used to induce the breakdown of water. The feasibility of inducing metal foil plastic deformation through LMF with water as the absorbent layer was validated. The surface morphology of the obtained micro pit on the metal foil was observed and measured by a topography measuring instrument and a scanning electron microscope. The laser-induced shockwave and the process of forming bubbles were recorded by a high speed camera. It is found that there are three possible mechanisms responsible for the plastic deformation of metal foil underwater: water-breakdown-induced shockwave, bubble-pulsation-induced shockwave and bubble-collapse-induced micro jet. The dominant forming mechanism and the forming result can be controlled by changing the distance between the laser focus and the foil surface.

Experimental investigation of sheet metal forming of Aluminum 2024 using nanosecond pulsed Nd: YAG laser

Laser-induced shockwaves can modify the mechanical properties and plastically deform sheet metal in a process called Laser Shock Forming. This process has proven to be a viable forming method for both micro and macro scale fabrication of metal parts with complex geometry. In this research, the effects of laser intensity, sample thickness and overlapping ratio on the amount of deformation of Aluminum 2024 using Q-switched Nd: YAG laser operating at its fundamental wavelength of 1064 nm and pulse repetition rate of 1 – 5 Hz has been investigated. Through the experiments carried out, we observed that laser intensity and overlapping ratio had a positive effect on the size of the deformation whereby increasing any one of these parameters significantly increased the deformation observed as opposed to the sample thickness which had an inverse effect. By varying the sample thickness from 1 to 3 mm and laser energy from 2 to 6 J, we observed a transition from concave to the convex forming mechanism with a critical threshold or transition interval of 1.2–1.6 mm. We employed multiple regression analysis techniques to establish a relationship between the process parameters studied to the forming depth for the convex forming mechanism.

Researches on the curvature adjustment of metal sheet induced by laser shock forming through experiments and simulations

Laser shock forming (LSF) is an emerging method for metal sheet forming, and it can also be used to adjust the curvature of the curved metal. A series of laser shock adjustment experiments were conducted on 1-mm-thick curved aluminum 6061-T6 sheets using pulsed Nd3+:YAG laser operating at 1064-nm wavelength. The effects of various factors on the curvature adjustment were studied, including laser energy, impacted area, coverage rate of laser spots, and initial sheet shape. The mechanisms of curvature adjustment by LSF were studied by FEM simulation. The results have shown that the stress gradient mechanism and the shock bending mechanism were responsible for the two different kinds of deformation. The characteristic difference between the two mechanisms lies in whether the plastic deformation is directly induced on the bottom surface when the laser-induced shock wave is transmitted to the bottom surface. The curvature of the metal sheet can be adjusted conveniently within a certain range by changing the laser processing parameters, which is very useful for the engineering application.

The New Technologies Developed from Laser Shock Processing.

Laser shock processing (LSP) is an advanced material surface hardening technology that can significantly improve mechanical properties and extend service life by using the stress effect generated by laser-induced plasma shock waves, which has been increasingly applied in the processing fields of metallic materials and alloys. With the rapidly development of modern industry, many new technologies developed from LSP have emerged, which broadens the application of LSP and enriches its technical theory. In this work, the technical theory of LSP was summarized, which consists of the fundamental principle of LSP and the laser-induced plasma shock wave. The new technologies, developed from LSP, are introduced in detail from the aspect of laser shock forming (LSF), warm laser shock processing (WLSP), laser shock marking (LSM) and laser shock imprinting (LSI). The common feature of LSP and these new technologies developed from LSP is the utilization of the laser-generated stress effects rather than the laser thermal effect. LSF is utilized to modify the curvature of metal sheet through the laser-induced high dynamic loading. The material strength and the stability of residual stress and micro-structures by WLSP treatment are higher than that by LSP treatment, due to WLSP combining the advantages of LSP, dynamic strain aging (DSA) and dynamic precipitation (DP). LSM is an effective method to obtain the visualized marks on the surface of metallic materials or alloys, and its critical aspect is the preparation of the absorbing layer with a designed shape and suitable thickness. At the high strain rates induced by LSP, LSI has the ability to complete the direct imprinting over the large-scale ultrasmooth complex 3D nanostructures arrays on the surface of crystalline metals. This work has important reference value and guiding significance for researchers to further understand the LSP theory and the new technologies developed from LSP.

Characteristics of stress distribution within the metal sheet bent by laser shock forming

Laser shock forming(LSF) is an emerging method for metal sheet forming. Besides dimension accuracy, the stress distributions on the surface and within the target material are also important for the actual engineering applications. In this paper, the stress distributions along the sheet depth direction and parallel to the target surface have been made clear through simulations. The deformation mechanisms of two typical deformation modes, convex and concave, were directly verified and further explained by the temporal and spatial residual strain/stress distribution. For the convex deformation, the stress distribution along the thickness direction is roughly divided into three regions: the near surface layer, the intermediate layer and the bottom layer. Among these, both the top and bottom surface layers are mainly subjected to compressive residual stresses. For this case, the stress wave effect does not ‘penetrate’ the sheet material, and a stress gradient is induced along the depth direction of the sheet, which is responsible for final convex deformation. For the concave deformation, the stress distribution along the thickness direction is divided into two regions: the surface tensile stress zone and the lower compressive stress zone. The stress wave effect penetrates the sheet material, directly causing the overall tensile deformation of the sheet material, and finally causes the sheet material to undergo deep plastic deformation. The stress distribution characteristics of the two deformation modes can provide useful references for the practical application.

Making Line Undercut Structure by Incremental Laser Shock Forming

A novel technology to plastically deform line undercut structures by pulsed laser, named as incremental laser shock forming (ILSF) of sheet metal, is presented in this paper and is investigated by experiments and numerical simulations. The deformation of a line undercut structure can be considered as the accumulation of several point undercuts, the shape evolution during ILSF of copper foils was observed, and the thickness distribution on a cross-section was measured. The influences of laser energy E, forming height H, and laser spot overlap rate η on the process were studied and a process window was established to avoid deformation failure. The results show that the plastic deformation at η = 0% is less uniform and more vulnerable than that at η = 50%. Three typical failure modes were concluded and discussed. Finite element method simulation was conducted to verify the feasibility of forming line undercut structure by ILSF, and to analyze its deformation mechanism.

A study on failure mechanisms and formability of aluminum alloy sheets under laser shock forming

In the process of laser shock forming, fracture and failure are tend to occur at the center of deformation in metal sheets, which seriously affect the formability of metal sheets under laser shock forming. This paper adopts different process parameters and carries out a series of experiments on the laser shock forming for aluminum alloy 3003H16, investigates failure behaviors in the process of forming, and studies and analyzes the mechanisms of such failures as well as their relationships with limit forming depths. This study reveals three primary failure mechanisms for 3003H16 fracturing under laser shocks, including spallation failure, thinning failure, and mixed failure. The limit forming depths of sheets under different failure mechanisms are different. The spallation failure has the least depth, and the thinning failure has the largest one. It is necessary to select appropriate process parameters for the forming to avoid spallation and improve the formability of sheets under laser shocks.

Making interlock by laser shock forming

A novel processing technology for interlocking and joining three sheets of two copper foils and a perforated stainless steel sheet by laser shock forming is presented in this paper. In this forming process, two layers of ductile copper foils are positioned above a perforated stainless steel sheet, a shock pressure induced by pulsed laser is applied on the upper foil, both foils are indented downwards through the hole of the perforated sheet, and impact on the rigid bottom support, then spread radially to produce a double interlock, thus to join the three sheets together. Finite element analysis as well as practical experiments were conducted to verify the feasibility of making interlocks by laser shock forming. The numerical simulation reveals the deformation mechanism of interlocks based on the analysis of plastic flow and shape evolution during the process. These results point to the practicality of clinching and joining three sheets by laser induced plastic deformation, namely laser shock joining or laser shock clinching.

Properties of a Laser Shock Wave in Al-Cu Alloy under Elevated Temperatures: A Molecular Dynamics Simulation Study.

The laser shock wave (LSW) generated by the interaction between a laser and a material has been widely used in laser manufacturing, such as laser shock peening and laser shock forming. However, due to the high strain rate, the propagation of LSW in materials, especially LSW at elevated temperatures, is difficult to study through experimental methods. A molecular dynamics simulation was used in this study to investigate the propagation of LSW in an Al-Cu alloy. The Hugoniot relations of LSW were obtained at different temperatures and the effects of elevated temperatures on shock velocity and shock pressure were analyzed. Then the elastic and plastic wave of the LSW was researched. Finally, the evolution of dislocations induced by LSW and its mechanism under elevated temperatures was explored. The results indicate that the shock velocity and shock pressure induced by LSW both decrease with the increasing temperatures. Moreover, the velocity of elastic wave and plastic wave both decrease with the increasing treatment temperature, while their difference decreases as the temperature increases. Moreover, the dislocation atoms increases with the increasing temperatures before 2 ps, while it decreases with the increasing temperatures after 2 ps. The reason for the results is related to the formation and evolution of extended dislocations.

2024-T351铝合金薄板在橡胶支撑下的激光冲击成形

2024-T351铝合金薄板在橡胶支撑下的激光冲击成形

Numerical and experimental investigations of laser shock forming aluminum alloy sheet with mold

Laser shock forming (LSF) technology employs shock waves to form sheet metal into three-dimensional complex parts, and has application potential in manufacturing sheet metal parts. In this paper, the forming of 2024 aluminum alloy sheet with LSF was investigated through numerical and experimental methods. The numerical model was established with the commercial code ABAQUS/Explicit. The formed conical cup was obtained from the simulation, and validated by the experiment. With the verified numerical model, the deformation behaviors, including deformation velocity, sheet thickness variation and strain distribution, were studied. In addition, the influence of different shock wave pressures on the forming precision was also investigated. The experimental and numerical results show that the metal sheet loaded by shock wave can take the shape of the mold, and the non-uniform thickness is distributed in the formed cup. The investigations also display that there exists reverse deformation at the central region of deforming sheet owing to severe collision during LSF. In order to obtain formed part with better quality, an appropriate pressure of applied shock waves is required.

Simulation of the forming process of conical cup shaped by laser-induced shock waves

Laser shock forming (LSF) is a sheet plastic forming technology, which employs laser-induced shock waves to make sheet metal duplicate a desired shape of the mold. In this paper, a finite element analysis (FEA) model was developed to simulate dynamic forming process with the commercial finite element code ABAQUS/Explicit, and a series of dynamic deformation behaviors of the metal sheet shaped into conical cup at the end of different periods of time were displayed and discussed in detail. The springback of conical cup and the distribution of residual stress were analyzed with ABAQUS/Standard. All these investigations could provide insight into the physics process of the ultra-fast deformation. The LSF experiment was further conducted to verify the results predicted by FEA. The experiment results are well consistent with the numerical predicted data, which validates the FEA model. It indicates that FEA can be used to simulate the forming process and optimize its parameters.