Zongbao Shen

Micromold-Based Laser Shock Embossing of Metallic Foil: Fabrication of Large-Area Three-Dimensional Microchannel Networks

Micromold-based laser shock embossing is a new three-dimensional (3D) forming technique, which utilizes laser-generated shock wave to shape the workpiece. In this article, the microchannel networks mold was produced by micro-wire electrical discharge machining (Micro-WEDM). Large-area three-dimensional microchannel networks were successfully fabricated on metallic foil surface using laser-generated shock wave. The investigation reveals that 3D microchannel networks have a high spatial resolution at the micron level. The fracture in the forming experiment was also detected. The fabrication cost is independent of the microstructures complexity. Therefore, micromold-based laser shock embossing holds promise for achieving precise, well-controlled, low-cost, high efficiency of 3D metallic microstructures.

Numerical simulation and experimentation of a novel laser indirect shock forming

A novel laser indirect shock forming is presented, which uses laser-driven flyer to load the workpiece. Experiments were performed by allowing the laser-driven flyer to impact a stationary workpiece. The flyer can protect the workpiece from thermal effects so that pure mechanical effects are induced. The experimental results show that laser indirect shock forming is possible and the workpiece have a high spatial resolution at the micron level. In addition, the forming technology can effectively prevent wrinkling. The effect of laser energies on the deformation mechanism was investigated experimentally, and experimental data obtained were then used to validate the corresponding simulation model. The results show that the finite element analysis can predict the final shape of workpiece properly.

Experimental and Numerical Simulation Research on Micro-Gears Fabrication by Laser Shock Punching Process

The aim of this paper is to fabricate micro-gears via laser shock punching with Spitlight 2000 Nd-YAG Laser, and to discuss effects of process parameters namely laser energy, soft punch properties and blank-holder on the quality of micro-gears deeply. Results show that dimensional accuracy is the best shocked at 1690 mJ. Tensile fracture instead of shear fracture is the main fracture mode under low laser energy. The soft punch might cause damage to punching quality when too high energy is employed. Appropriate thickness and hardness of soft punch is necessary. Silica gel with 200 µm in thickness is beneficial to not only homogenize energy but also propagate the shock wave. Polyurethane films need more energy than silica gel with the same thickness. In addition, blank-holders with different weight levels are used. A heavier blank-holder is more beneficial to improve the cutting quality. Furthermore, the simulation is conducted to reveal typical stages and the different deformation behavior under high and low pulse energy. The simulation results show that the fracture mode changes under lower energy.

Forming Properties of a Microscale Laser Dynamic Flexible Forming Technique

Microscale laser dynamic flexible forming (µLDFF) is a novel micro-forming process. Laser-induced shockwaves act on the soft punch to deform the metal foils. In this article, the forming properties of the µLDFF process are studied from four angles, namely, the maximum deformation depth, accuracy, thickness thinning ratio, and surface quality. The maximum deformation depth of the samples formed under different laser energies was measured. The 2D profiles of the workpieces were measured to study the accuracy. The results show that the deformed samples replicated the mold features well. The cold-mounted technique was used to measure the thickness of the deformed metal foils along the cross section and to discuss the thickness thinning ratio. The results show that µLDFF can reduce localized necking and stress concentrations effectively. The surface roughness was characterized to study the surface quality of the workpieces, and the results indicated that the deterioration of the formed surface was weakened during µLDFF. The advantages of the ultrahigh strain rate and soft punch are both presented in the µLDFF process, which is favorable for fabricating micro components.

Fabrication of Dish-Shaped Micro Parts by Laser Indirect Shocking Compound Process

Compound process technology has been investigated for many years on a macro scale, but only a few studies can be found on a micro scale due to the difficulties in tool manufacturing, parts transporting and punch-die alignment. In this paper, a novel technology of combining the laser shock wave and soft punch was introduced to fabricate the dish-shaped micro-parts on copper to solve these difficulties. This compound process includes deep drawing, punching and blanking and these processes can be completed almost at the same time because the duration time of laser is quite short, so the precision of the micro-parts can be ensured. A reasonable laser energy of 1550 mJ made the morphology, depth of deformation, dimensional accuracy and surface roughness achieve their best results when the thickness of the soft punches was 200 μm. In addition, thicker soft punches may hinder the compound process due to the action of unloading waves based on the elastic wave theory. So, the greatest thickness of the soft punches was 200 μm.

An Experimental Study on Micro Clinching of Metal Foils with Cutting by Laser Shock Forming

This paper describes a novel technique for joining similar and dissimilar metal foils, namely micro clinching with cutting by laser shock forming. A series of experiments were conducted to study the deformation behavior of single layer material, during which many important process parameters were determined. The process window of the 1060 pure aluminum foils and annealed copper foils produced by micro clinching with cutting was analyzed. Moreover, similar material combination (annealed copper foils) and dissimilar material combination (1060 pure aluminum foils and 304 stainless steel foils) were successfully achieved. The effect of laser energy on the interlock and minimum thickness of upper foils was investigated. In addition, the mechanical strength of different material combinations joined by micro clinching with cutting was measured in single lap shearing tests. According to the achieved results, this novel technique is more suitable for material combinations where the upper foil is thicker than lower foil. With the increase of laser energy, the interlock increased while the minimum thickness of upper foil decreased gradually. The shear strength of 1060 pure aluminum foils and 304 stainless steel foils combination was three times as large as that of 1060 pure aluminum foils and annealed copper foils combination.

Research on the Micro Sheet Stamping Process Using Plasticine as Soft Punch

Plasticine is widely used in the analysis of metal forming processes, due to its excellent material flow ability. In this study, plasticine is used as the soft punch to fabricate array micro-channels on metal sheet in the micro sheet stamping process. This is because plasticine can produce a large material flow after being subjected to force and through the material flow, the plasticine can cause the sheet to fill into the micro-channels of the rigid die, leading to the generation of micro-channels in the sheet. The distribution of array micro-channels was investigated as well as the influence of load forces on the sheet deformations. It was found that the depth of micro-channels increases as the load force increases. When the load force reaches a certain level, a crack can be observed. The micro sheet stamping process was also investigated by the method of numerical simulation. The obtained experimental and numerical results for the stamping process showed that they were in good agreement. Additionally, from the simulation results, it can be seen that the corner region of the micro-channel-shape work piece has a risk to crack due to the existence of maximum von Mises stress and significant thinning.

Investigation of Micro-Bending of Sheet Metal Laminates by Laser-Driven Soft Punch in Warm Conditions

Microscale laser dynamic flexible forming (µLDFF) is a novel ultrahigh strain rate manufacturing technology with high efficiency and low cost. However, the µLDFF is just confined to single-layer foil at present. In this work, sheet metal laminates (Cu/Ni) were selected as the experimental material for its excellent mechanical and functional properties, and a new micro-bending method of sheet metal laminates by laser-driven soft punch was proposed in warm conditions. The micro-mold and warm platform were designed to investigate the effects of temperature and energy on formability, which were characterized by forming accuracy, surface quality, element diffusion, and so on. The experimental results show that the forming accuracy and quality increased first and then decreased with laser energy, but the hardness increased consistently. In warm conditions, the fluidity of material was improved. The forming depth and accuracy increased for the relieved springback, and the surface quality increased first and then decreased. The tensile fracture disappeared with temperature for the decreased hardness and thinning ratio, and the element diffusion occurred. Overall, this study indicates that the formability can be improved in warm conditions and provides a basis for the investigation of micro-bending of sheet metal laminates by µLDFF in warm conditions.

Experiment and numerical simulation of laser shock micro dents

In order to overcome the deficiencies of the traditional laser surface texturing, a useful surface texturing method by generating micro dents based on the laser shock processing technology was investigated in this paper. A series of experiments focusing on the effects of pulse energies and shock numbers for laser shock micro dents were carried out. An analysis procedure including dynamic analysis performed by ANSYS/LS-DYNA and static analysis performed by ANSYS is presented in detail to establish a 3D finite element model. By establishing more reasonable and accurate model, the simulation results would have better correlation with the experimental results. The bulges around the dents are observed in the experiment and simulation results. Besides, the calculation formula of laser shock wave pressure can be revised by comparing simulation results with experimental results.

Formation of nanostructure and nano-hardness characterization on the meso-scale workpiece by a novel laser indirect shock forming method

The meso-scale workpiece with greatly enhanced mechanical properties is potential to be widely used in the electronics productions and micro-electro mechanical systems. In this study, it demonstrates that the meso-scale cup-shape workpiece with good geometry can be obtained by a novel laser indirect shock forming method. After the forming process, the mechanical properties and microstructures of the formed workpiece were characterized. By transmission electron microscope observation, it was found that a mixed refined microstructure consisting of nano-scale twins embedded in nano-sized grains was produced at the center of the formed sample. Formation of these nanograins could be mainly attributed to two mechanisms: twin-twin intersections and twin∕matrix lamellae fragmentation. By nanoindentation tests, it reveals that the hardness of the sample has increased greatly after laser shock forming and the hardness increases with the laser energy. The elevated hardness originates from a considerable number of nano-scale twins and nanograins, which possess a pretty high strength due to the significant effects of grain boundary strengthening and twin boundary strengthening.