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Roughening of the free surface in micro-forming results in the local necking and subsequent fracture, which seriously affects the formability of sheet metals. In this work, laser pre-shocking (LPS) was introduced into microscale laser dynamic flexible bulging (μLDFB) to reduce surface roughening in terms of reducing the surface roughness and refining the internal grains. In LPS experiments, when the laser energy is 447 mJ, the rebound of the copper foils can be negligible. LPS can be expected to suppress the surface roughening by reducing the initial roughness R0, increasing the N value and decreasing the rate of surface roughening. The copper foils subjected by 447 mJ LPS were used for the μLDFB experiments. The 50 μm T2 copper foils with four different grain sizes were used in μLDFB under different laser pulse energies. When laser pulse energy ranges from 325 mJ to 575 mJ, compared with μLDFB without LPS, the surface roughness on the bottom surface of the bulging sample is decreased. And the nano-hardness, elastic modulus and forming uniformity are significantly improved. In μLDFB experiments without LPS, for fine-grained samples, the cracks initiate in the bulging transition zone under 725 mJ laser energy due to surface roughening. As laser energy increases to 1050 mJ, the cracks initiate in the mold entrance zone due to the strong stress concentration. For coarse-grained samples, cracks initiate under 575 mJ laser energy, and the propagations of the cracks are difficult to predict due to non-uniform distribution of grain size and the difference of grain orientation. The experimental results suggest that LPS can reduce the possibility of the premature fracture caused by the local necking, and alleviate the uncertainty in the fracture mode.

Based on the advantages of laser shock forming, such as high-speed dynamic loading, good filling ability of die cavity, and improving material formability along with its other advantages of warm forming to improve forming discreteness and further develop formability, a warm laser shock micro-heading forming (WLSMHF) method was investigated, and an experimental system was established. Combining ALE method in ABAQUS with experiment, the feasibility was studied with T2 copper. The propagation of stress wave, deformation process, and material flow law was studied. The influence of laser energy, temperature, and grain size on the deformation of upsetting head was studied. The influence of forming temperature and grain size on forming discreteness was analyzed. Results show that the phenomenon of the anti-Taylor anvil impact test first appears in the whole rod. When the inside of the die is filled with material, the deformation of the material outside the die is similar to that of micro-upsetting. The upper end of the upsetting head is slightly larger than the lower end because of the propagation of stress wave, inertia effect, and the restraint of the die to the material. The flow speed of the metal material in the die is fast, the die is filled well, and the filling property of the die is good. The deformation of upsetting head increases with the laser energy and temperature, which improves the formability of the material. The deformation of the upsetting head increases with the grain size, and the effect of grain size on forming can be reduced by increasing the forming temperature simultaneously. The increase in the forming temperature and decrease in the grain size can improve the discreteness of the forming size and forming accuracy, respectively.

Laser dynamic flexible forming (LDFF) is a novel high velocity forming (HVF) technology, in which the foil metal is loaded by laser shock wave. Strain localization is readily to occur around the bulge edge, which will result in the ultimate dynamic failure. In this work, the microstructures before and after dynamic fracture are characterized by transmission electron microscopy (TEM) to investigate the dynamic failure mechanism. The plastic deformation regions of copper foil are composed of shock compression, strain localization and bulge. Microstructure refinement was observed in three different plastic deformation regions, particularly, dynamic recrystallization (DRX) occurs in the strain localization and bulge regions. In bulge region, extremely thin secondary twins in the twin/matrix (T/M) lamellae are formed. The microstructure features in the strain localization region show that superplastic flow of material exists until fracture, which may be due to DRX and subsequent grain boundary sliding (GBS) of the recrystallized grains. The grain coarsening in strain localization region may degrade the material flowing ability which results in the dynamic fracture.

Micro-scale laser dynamic forming (μLDF) is a kind of high velocity forming processes, which uses laser shock wave to load the sheet metal. The surface degradation of micro-mold in μLDF and its effects on workpiece are first investigated in this work. The surface degradation is the gradual failure of micro-mold due to the regular repeated laser shock loadings, and some micro-channel defects with the dimensions of several micrometers are observed on the mold surface. During μLDF process, the material of workpiece flows into the cavities of micro-defects on mold surface when the laser power density increases to 6.46 GW/cm2, and the more obvious defect-like features are formed on the rear surface of workpiece as laser power density increases. This type of single-side forming is very interesting, and similar to coining. In order to investigate the surface degradation evolution process, laser shock target experiments are performed. The surfaces of the nodular cast iron targets were irradiated by different numbers of laser pulses, and the corresponding surface morphologies were observed to investigate the surface degradation evolution process. The experimental results show that, surface degradation of micro-mold is formed by void nucleation, growth, and coalescence under the repeated shock loadings. Numerical simulations considering micro-defect on mold surface are performed to investigate the effect of micro-defect on workpiece. Numerical results also show that laser shock wave can be used to replicate micro-coining feature on metal surface.

A novel laser shock forming process called micro-laser shock hydraulic forming (MLSHF) was proposed to fabricate a micro-bowl with miniature concave at the apex of the bottom. Liquid water, used as a soft punch, can generate pressure waves under the action of laser shock to deform a 30-μm-thick copper foil. The influence of laser energy on morphology, forming accuracy, thickness distribution, and surface quality under MLSHF process was discussed through experimental means. Experimental results showed that the miniature concave was fabricated at 1050 mJ, and the whole micro-bowl was formed at 1550 mJ. With the increase of laser energy, the fittability improved and rebound became increasingly severe. Serious thinning occurred at the fillet of the miniature concave. Moreover, the die with great surface quality reduced the surface roughness of the workpiece surface that contacted with the die. A numerical finite element analysis (FEA) model was established by Hypermesh/LS-DANA. The FEA model was firstly verified through an experiment, and then it was used to investigate the deformation behavior including dynamic forming process and strain distribution.

In this study, a novel micro-forming process called laser shock micro hydraulic bulging was proposed to fabricate micro feature on copper foil. In this process, liquid medium water was used as a soft punch, rubber layer with thickness of 200 μm was used to squeeze liquid medium, and laser shock wave was used as driving force. Forming depth, surface quality, thickness thinning ratio, and cross section micro hardness were investigated under different laser energies. Experimental results showed that the forming depth and surface roughness increased with the laser energy. However, the surface roughness increased slightly with the increase of laser energy, and no thermal response area was found at forming area. Maximum thickness thinning occurred at the fillet when laser energies were 565, 835 and 1200 mJ, while fracture occurred at the bottom area (not the apex) when the laser energy increased to 1380 mJ. Hardness test indicated that, when the material was in cold-rolled, the hardness along the cross-section of the formed area showed an irregular trend. When the material was changed with copper foil annealed at 450 °C, the hardness improved remarkably.

Micro-scale laser dynamic flexible forming (μLDFF) is a new kind of high velocity forming (HVF) process, which uses laser shock wave pressure to realize thin metal sheets micro-forming. Rebound effect usually occurs when forming deep complex micro-features, which has a significant effect on the forming precision. This work firstly investigates the impact and rebound behaviors of workpiece in μLDFF with rubber medium to probe the main affecting factors of rebound effect, then proposes a new μLDFF with plasticine medium to reduce the rebound effect. With the increase of laser energy, the average surface roughness of impact-affected zone (IAZ) reduces firstly by flattening behavior, and then increases afterward due to coining-like operation. The 3D deviation analyses between workpieces and micro-die are performed to characterize the fitability. When laser energy is 675 mJ, bottom region of workpiece fits well with the micro-die. When laser energy is increased to 1020 mJ, bottom region of workpiece separates from the micro-die due to rebound effect. A finite element model considering the machining marks on micro-die surface is built, and the predicted results are validated by experimental results. Coefficient of restitution (COR) and the rebound ratio (α) are used to investigate the impact and rebound process. The results show that rebound effect is dominated by laser energy, surface morphology of micro-die, and loading duration. To effectively reduce the rebound effect, the plasticine layer is first introduced as pressure-carrying medium in this work. The deformation behavior of plasticine medium is like a Reiner-Rivlin fluid. So the plasticine medium closely contacts with the sample during forming, this is equivalent to indirectly increasing the stiffness of sample and prolonging the loading duration. In addition, the plasticine layer can absorb impact-induced reflection wave. So plasticine medium can effectively improve the forming precision.

Laser dynamic flexible forming (LDFF) is a novel high velocity forming (HVF) technology, in which the high-energy laser shock waves act on the workpiece via a flexible medium. Dynamic bulge tests of copper sheet are performed to investigate the deformation and fracture behaviors in LDFF in this paper. The laser ablation states on K9 glass surfaces under different laser energies were characterized. The samples after LDFF were characterized by optical microscopy and scanning electron microscopy. For laser energy ranging from 1020 mJ to1380 mJ, as laser energy increases, the average surface roughness (Ra) in bulge region rapidly increases due to surface free forming. However, the Ra in laser shock compression region slowly decreases due to shock flattening. Strain localization occurs around the bulge edge, and the composition of oxygen element in this region is increased with laser energy. When laser energy is equal to or greater than 1690 mJ, localized deformation evolved into the dynamic failure. Apart from the elongated micro-voids, three interesting phenomena were observed: the melting marks, the serrated fracture boundaries and filaments. As the laser energy increases, the fracture mode varies from a tensile fracture mode to a shear fracture mode, then to a filament fracture mode. The filament fracture mode indicates that superplastic flow of material may exist until fracture, and oxidation behaviors make a great contribution to the superplastic flow.

Currently, the forming processes employed on formation of laminated composite metal sheets belong to quasi-static loading either in macroscale or microscale. Innovative forming processes are requested to meet the challenges in manufacturing of micro components produced by new materials. A new process that employing microscale laser flexible dynamic forming (MLFDF) on formation of laminated composite metal sheets was adopted in this paper. The feasibility of this new process was verified firstly. The research results showed that, the forming depth of Cu/Ni laminated composite metal sheets under MLFDF increased with laser energy increasing, number of laser pulse increasing and thickness of soft punch decreasing. Surface roughening happened in formed parts and the roughness increased with laser energy increasing. Deformation of Cu/Ni laminated composite metal sheets was dominant by external layer. Unlike conventional forming processes, it was found stacking sequence didn’t have considerable effect on forming behavior of Cu/Ni laminated composite metal sheets under MLFDF. Another advantage of MLFDF was discovered that Cu/Ni laminated composite metal sheets were formed without any delamination till fracture under this forming process. The experiment revealed that MLFDF could be a promising alternative of conventional microscale forming processes for formation of laminated composite metal sheets.

The influences of ablative layer, soft punch, die depth, and laser energy on novel micro clinching of Al/Cu were investigated. Ablative layer thickness notably influenced metal flow including neck and interlock; the relationship between reasonable ablative layer thickness and certain laser energy range was summarized. Soft punch with 100 μm was more suitable than with other thickness for the process. In the joinable laser energy range, with increase of laser energy, interlock thickness gradually increased, whereas the neck and bottom thicknesses gradually decreased. The process window of Al/Cu combination was acquired, and a certain thickness difference which was at least 40 μm inevitably existed between the upper and lower metal foils. For every joinable combination, matching function of optimum die depth are derived based on Al and Cu foil thickness when the thickness of each metal foil was less than 200 μm. The single lap shearing test showed that the tensile strength and failure model of the joint both depended on neck and interlock thicknesses; only the joint that simultaneously formed a large interlock and large neck can attain a high joining strength.

The inverse kinematics problem (IKP) is at the center of computer control algorithms for general serial manipulator. The exact number of feasible solutions of the IKP is highly dependent on the manipulator structure as well as the desired end-effector pose, and the existing inverse kinematics methods have difficulties to solve all feasible solutions of a general serial manipulator. In this work, a multiple solutions approach is applied to the IKP. Then, three numerical examples are used to validate the effectiveness of the multiple solutions approach, and the numerical results demonstrate that the multiple solutions approach is effective and practicable. Finally, an infinite solutions example is presented to show that the proposed approach could also provide limited number of numerical solutions in singularity.

The case of fabricating micro-channel on copper foil using micro-scale laser dynamic flexible forming (μLDFF) is investigated in this work. To study the deformation and fracture behaviors, the copper foils are subjected to increasing laser power density until the occurrence of fracture. When laser power density ranges from 0.110 GW/cm2 to 0.441 GW/cm2, smooth micro-channel features are formed on copper foils, and the depth of the micro-channel gradually increases. Melting marks are observed at the micro-die entrance of the sample with 0.441 GW/cm2 laser power density. When laser power density is 0.544 GW/cm2, partial fractures are observed. The surface of fracture region is rougher than that of micro-cracks and no micro-cracks regions, which is caused by the higher strain in fracture region. And the fracture edge is irregular, which is caused by the soft effect of material. Complete fracture occurs when laser power density is 0.691 GW/cm2.

Laser high speed flexible micro-forming (LHSFF) process has been applied to the formation of metal sheets due to its unique advantages compared to conventional micro forming processes. The materials investigated in LHSFF were all single-layer metal sheets so far. However, new materials have been developed to replace single-layer metal sheets in some industry occasions because of their superior properties. This paper investigated a new process that employed LHSFF on the formation of multilayer metal sheets. The feasibility of this new process for three-layer Ni/Cu/Ni metal sheets was verified firstly. Some results could be obtained from the experiments. Surface roughening happened in formed components, and surface quality became worse with laser energy increasing. As thickness of soft punch increased, the forming depth of Ni/Cu/Ni metal sheets decreased under LHSFF. The thickness reduction and the amplification of micro-hardness of the external layer were larger than those of the middle layer, and those of the middle layer were larger than in the internal layer. Unlike conventional forming processes, the formation of Ni/Cu/Ni metal sheets did not suffer from delamination failure any more under LHSFF.

A forming process called the mask and flexible pad laser shock forming was proposed to fabricate the micro-features on the copper foil. In this process, the mask and laser beam were used as rigid punches. Shock waves induced by plasma were used as the source of loading and plasticine was used as a flexible pad. This was a micro scale and high strain rate forming process and the traditional forming method with micro-mold was changed. In the experiment, surface morphology of formed parts was represented and it was found that the mask played a significant role in the forming process. In order to understand the forming process in the experiment, process parameters, including laser pulse energy, numbers of laser pulse and grain size, were analyzed. The experimental results showed that different parameters had different effects on formed parts. The surface quality and the thickness distribution of formed parts were investigated. It was found that formed parts could keep good surface quality after laser shocking and the reasons were explored. The thickness distribution was measured and the thickness thinning rate was calculated. There was no local tightening or rupture in the forming area. In this paper, the micro-features could be obtained on metallic foils and the method of mold-free was proved to be feasible.

Overlapping laser shock imprinting (LSI) is proposed to alter the surface wettability of copper sheet. By using a micro-die with rough concave texture, under the action of laser shock waves, multiscale surface microstructures can be accurately fabricated. The homogeneity of the micro-pattern array under different overlap rates were investigated. The radial expansion effect can reduce the inhomogeneity, but the shock pressure induced by the radial expansion effect in the non-irradiated area is weaker than that in laser irradiated area. Observed contact angle result is in accord with theoretical Cassie-Baxter mode, and it increases first and then tends to be stable when the number of laser pulse ranges from 2 to 6. Multiscale surface microstructures can be observed in 4 and 6 laser pulses cases. LSI can reduce the surface free energy by decreasing its polar component, and it sharply decreases first and then tends to be stable when the number of laser pulse ranges from 2 to 6. The grain size of protruding feature decreases with laser pulse numbers. And nano-scale grains are observed on the surface layer, which is caused by the material flowing on the rough surface of micro-die. The nano-indentation tests indicated that mechanical properties are enhanced.

A microscale laser shock flexible drawing (µLSFD) is a novel ultrahigh strain rate manufacturing technology that provides an effective means for fabricating complicated microparts shapes in foil. However, the size effect phenomenon in ultrahigh strain rate microforming is still largely unknown. In this work, the micro-mold and process parameters were designed to investigate the size effects based on the similarity theory. The parts were formed using annealed copper foils with four different grain sizes to study the grain size effect. The parts were fabricated by use of different micro-molds and copper foils with varying thicknesses but with the same annealing temperature to investigate the effect of feature size. The experimental results indicated that the depth of the formed parts increased with an increase in the grain size; the forming depth decreased significantly when the feature dimension was smaller than a critical value. The surface roughness and the thickness thinning ratio of the formed parts increased when the grain size and feature dimension increased. The maximum thinning ratio appeared at the bottom of the formed parts. The regression analysis revealed that the material deformation was more homogeneous with a decrease in the grain size and an increase in the feature dimensions when the µLSFD process was employed. This study provides a theoretical basis for the investigation of size effects in laser shock flexible forming.

A novel laser shock synchronous welding and forming method is introduced, which utilizes laser-induced shock waves to accelerate the flyer plate towards the base plate to achieve the joining of dissimilar metals and forming in a specific shape of mold. The samples were obtained with different laser energies and standoff distances. The surface morphology and roughness of the samples were greatly affected by the laser energy and standoff distances. Fittability was investigated to examine the forming accuracy. The results showed that the samples replicate the mold features well. Straight and wavy interfaces with un-bonded regions in the center were observed through metallographic analysis. Moreover, Energy Disperse Spectroscopy analysis was conducted on the welding interface, and the results indicated that a short-distance elemental diffusion emerged in the welding interface. The nanoindentation hardness of the welding regions was measured to evaluate the welding interface. In addition, the Smoothed Particle Hydrodynamics method was employed to simulate the welding and forming process. It was shown that different standoff distances significantly affected the size of the welding regions and interface waveform characteristics. The numerical analysis results indicated that the opposite shear stress direction and effective plastic strain above a certain threshold are essential to successfully obtain welding and forming workpiece.

A novel laser dynamic flexible punching process is employed to fabricate micro-gears to address the difficulties in punch-to-die alignment in the conventional micro-punching process. In this process, induced shockwaves act as micro-punches and soft punch acts as the media to transmit pressure. The influences of laser intensity, foil thickness and grain size on dimensional accuracy and rollover diameter have been investigated experimentally. In addition, the changes in the hardness and elastic modulus of the workpiece after the laser shock effect are characterized by nano-indentation experiments. It is revealed that the dimensional accuracy is optimal when the laser intensity is 5.6 GW/cm2, but the laser intensity has little effect on the rollover diameter. Punched gears of thicker foils result in worse dimensional accuracy and larger rollover diameter. Foils annealed at 350 °C achieve the best punching accuracy but compromise with regard to the maximum rollover diameter. Furthermore, both the nano-hardness (9.92%) and elastic modulus (14.37%) are improved after the laser shock effect, as the evidence of an increase of surface strength and material stiffness. The proposed method, laser dynamic flexible punching, will potentially lead to new methods for micro-gears fabrication in the future.

Laser dynamic forming (LDF) is a novel high velocity forming technique, which employs laser-generated shock wave to load the sample. The forming velocity induced by the high energy laser pulse may exceed the critical forming velocity, resulting in the occurrence of premature fracture. To avoid the above premature fracture, rubber is introduced in LDF as a forming medium to prolong the loading duration in this paper. Laser induced shock wave energy is transferred to the sample in different forming stages, so the forming velocity can be kept below the critical forming velocity when the initial laser energy is high for fracture. Bulge forming experiments with and without rubber were performed to study the effect of rubber on loading duration. The experimental results show that, the shock wave energy attenuates during the propagation through the rubber layer, the rubber can avoid the premature fracture. So the plastic deformation can continue, the forming capability of LDF is improved. Due to the severe plastic deformation under rubber compression, adiabatic shear bands (ASB) occur in LDF with rubber. The material softening in ASB leads to the irregular fracture, which is different from the premature fracture pattern (regular fracture) in LDF without rubber. To better understand this deformation behavior, Johnson–Cook model is used to simulate the dynamic response and the evolution of ASB of copper sample. The simulation results also indicate the rubber can prolong the loading duration.

Laser pre-shocking (LPS) was introduced into the laser dynamic flexible micropunching process to refine the grain size of a workpiece to improve the forming quality of punched parts. T2 copper foils with five different grain sizes and seven different laser power densities with and without LPS were used for the experiment. The results showed that the grains are refined and the average surface roughness decreases after LPS. For copper foils annealed at 650 &deg, C, the value of decreases from 0.430 to 0.363 &micro, m. The increase in laser energy density and grain size leads to the deterioration of the fracture surface. LPS can improve the quality of the fracture surface. Compared with punched holes without LPS, the dimensional accuracy and shape accuracy of punched holes can be improved by LPS. When grain size is close to the thickness of the copper foil, the forming quality of the punched parts becomes uncertain, owing to the difference in the orientation of the initial grains. The instability of laser dynamic flexible micropunching can be reduced by LPS. Especially, the improvement of forming quality of the punched part brought by LPS is significant for the copper foils with coarse grains.

A finite element model of the flexible micro-bending process based on various grain sizes of pure copper is developed. The geometrical model of grain structure is established with Voronoi tessellation, which is employed to describe the polycrystalline aggregation. A model based on dislocation density is adopted to describe the flow stress of grain interior (GI) and grain boundary (GB) quantitatively. In this paper, silicon rubber is used as the flexible punch and four annealing conditions of pure copper as the workpieces, respectively. The influence of grain structure and grain size is discussed. It is observed that as the ratio of workpiece thickness (t) to grain size (d) decreases, the forming depth increases. The inhomogeneous deformation occurs in the coarse-grained micro-parts. Furthermore, the results indicate that the surface asperity increases with grain size. The numerical simulation results agree well with the tendency of experimental results. During the micro-bending process, the phenomenon of stress concentration occurs at the grain boundary of the micro-parts. The maximum von mises stress appears at the grain boundary located at the fillet position. The maximum von mises plastic strain primarily concentrates on the junction of the grain interior and grain boundary in the fine-grained parts, while it concentrates at the surface of the grain interior in the coarse-grained parts.

Unlike quasistatic loading of traditional microforming technology, microscale laser dynamic forming (μLDF) provides an efficient approach to fabricate microparts with enhanced mechanical properties. However, the size effects phenomenon is still inevitable in high strain rate microforming. It is thus necessary to investigate the size effects and dynamic deformation behaviour in μLDF. In this work, four different microchannels using annealed copper foils with four different grain sizes are manufactured simultaneously to investigate the size effects on formability in μLDF. The ratio of sheet thickness to grain size ( N = t / d ) is used to represent the interactive effects of grain size and specimen size, whereas the ratio of channel width to sheet thickness ( M = W / t ) is employed to characterize the feature size effect. Experimental results show that the N value and M value have an interactive effect on the normalized forming depth and the surface roughness value. When the M value decreases to the critical point of 4.5, the normalized forming depth is dramatically decreased and greatly influenced by the N value. Furthermore, the formability characterized by surface quality, thickness reduction and forming accuracy declines with the decrease of N value. The irregular thickness distribution and the inhomogeneous material flow of coarse-grained microchannel are attributed to the anisotropy and uneven grain distribution of microstructure. Despite the decreased formability, the coarse-grained microchannel with high necking ratio is still fabricated without failure and experiences more enhanced hardening effect than the fine-grained specimen, presenting the superplastic deformation behaviour in μLDF. When laser energy increases, the surface quality of the formed parts is improved by the intensive high speed sliding of asperities on the micro-die. The surface roughness value of the coarse-grained specimen is significantly reduced and therefore, the localized necking can be suppressed.

A new process fabricating micro parts of thin metal foils by laser shock waves with forming/blanking compound die is reported in this article, in which flexible rubber material was used as the soft punch to act on the thin metal sheet. Systematic studies were carried out experimentally on the process with different laser energies and materials. The formed parts were examined in terms of their morphology, surface roughness, forming depth and mechanical properties (including nanohardness, plasticity and elastic modulus) characterized by nanoindentation test. According to the results, the ablation states of confinement medium and the surface roughness of the different regions change with energies. Additionally, the proper energies are necessary to form complex parts and the forming process can be applied to manufacture parts with good surface quality. What׳s more, the nanoindentation test results showed that the nanohardness, plasticity and elastic modulus of material were increased after impact. The increase in nanohardness and plasticity can attribute to higher stiffness of the parts. The enhanced elastic modulus indicates an increased stiffness of the parts, providing an evidence for the reduced spring back of copper during laser shocking.

In this paper, a laser-generated shock wave was used to induce plastic deformation of metallic foils using Plasticine as a flexible support. In this new micro-drawing process, the laser-generated shock wave and the Plasticine are used to replace the conventional metal punch and mold. By undergoing large plastic deformation under the laser-generated shock wave, Plasticine accurately keeps the shape of the deformed workpiece, thereby improving the forming quality. Moreover, this is a damage-free forming process because the Plasticine is softer than metal foils. The feasibility of this new drawing process was conducted experimentally on aluminum, cooper, and titanium foils. The thickness distribution at the cross-section of the work piece was studied to evaluate the risk of crack. Meanwhile, the arrays of craters were fabricated on titanium foils. The results show that mold-free laser shock micro-drawing forming is an effective method to fabricate controlled micro-craters on metallic foils.

Multilayer metal composite sheets possess superior properties to monolithic metal sheets, and formability is different from monolithic metal sheets. In this research, the feature size effect on formability of multilayer metal composite sheets under microscale laser flexible forming was studied by experiment. Two-layer copper/nickel composite sheets were selected as experimental materials. Five types of micro molds with different diameters were utilized. The formability of materials was evaluated by forming depth, thickness thinning, surface quality, and micro-hardness distribution. The research results showed that the formability of two-layer copper/nickel composite sheets was strongly influenced by feature size. With feature size increasing, the effect of layer stacking sequence on forming depth, thickness thinning ratio, and surface roughness became increasingly larger. However, the normalized forming depth, thickness thinning ratio, surface roughness, and micro-hardness of the formed components under the same layer stacking sequence first increased and then decreased with increasing feature size. The deformation behavior of copper/nickel composite sheets was determined by the external layer. The deformation extent was larger when the copper layer was set as the external layer.

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.

Laser flexible shock micro-bulging (LFSB) is a novel micro fabrication technology, which combines laser dynamic forming and flexible die forming, which is a type of high strain rate micro-forming. The LFSB of 304 stainless steel foils was investigated in this paper. Experimental and simulated results indicated that the bulging depth and thickness thinning rate of bulging parts increased with an increase of laser energy and a decrease of workpiece thickness. Experimental results also showed the surface morphology of bulging parts. The hardness distribution in the cross section of bulging parts was revealed by nanoindentation experiments. The internal microstructure of micro bulging parts was observed by TEM. In addition, the equivalent stress and plastic strain distribution of bulging parts were shown in the numerical simulation under different workpiece thicknesses and laser energies.

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 dur...

Metal foil forming by laser-driven flyer (LDF) is a new micro-forming technology. The performance of the flyer is one of the main factors affecting the forming quality of workpiece. Considering the features of this technology, this paper presents a novel multi-layered flyer. Via magnetron sputtering, the absorption layer (titanium) and the ablation layer (aluminum) are produced on the confining medium. The impactor layer is manufactured by special cutting (a micro-punching method) and adhered to the center of the ablation layer by a gluing method. A pressure measurement system is conducted to measure the shockwave forming pressure of the laser-driven flyer, and a series of forming experiments are carried out to investigate the forming ability of the multi-layered flyer. Experimental results show that the multi-layered flyer can enhance the laser coupling efficiency to the flyer and achieve higher forming pressure than the single-layered flyer. Especially, the multi-layered flyer with the nonmetallic impactor layer of 100 µm polyurethane rubber has good forming quality in the laser-driven flyer micro-forming (LDFµF).

Laser indirect shock micro-embossing is a novel micro-high velocity forming technique, which uses laser-driven flyer to load the workpiece. In this paper, laser indirect shock micro-embossing of commercially pure copper and titanium sheet are investigated using both experimental and numerical methods. A fully 3-D finite element mode is proposed to simulate the transient deformation behaviors. The effects of material and laser energy on the deformations are investigated experimentally. Thickness distribution at the cross-section of the micro-channel is analyzed experimentally. Strain states during micro-embossing are used to interpret the variation in thickness distribution. Fracture along the inner edges of the micro-mould occurs for 8 μm copper when the pulse energy is 1200 mJ, 1380 mJ and 1550 mJ. Moreover, the 13 μm titanium is completely sheared off along the inner edge of the micromould when the pulse energy is 1550 mJ. With further development, the laser-driven flyer technique can realize the blanking forming. And experimental data obtained are then used to validate the corresponding simulation model. The results show that the finite element analysis can predict the final shape of the work piece properly.

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.

Laser shock forming is a three-dimensional forming technique. It is promising for achieving precise, well-controlled, low-cost, high efficiency 3D metallic microstructures. In this research, a combined process of embossing and blanking is studied by experimental and simulation methods, in which the embossing and blanking of copper sheets are performed at the same time in only one operation. In order to obtain multi-workpieces in one process, overlapping laser spots were applied in the experiment. Moreover, the influence of laser energies on the work pieces were considered, and the results show that the micro features on the boss surface of the mold were successfully replicated on the blanking copper foil surface with the suitable energy. By evaluating the surface roughness data, it can imply that the work piece surface can fit the mold surface. Meanwhile, the process of the combined embossing and blanking was also studied by numerical simulation, the simulation results show that the finite element analysis can predict the final shape of work piece properly, verifying the feasibility of this process.

This work describes an advanced technique for metal welding and composite production, namely laser shock welding. A series of laser shock welding experiments were conducted to verify the welding ability of aluminum/aluminum and aluminum/copper plates. Two kinds of interface morphologies were observed by metallographic investigation on cross-sections of the joint areas, including the linear and wavy interfaces. Besides, micro-hardness testing results show the welded interface has a much greater hardness than the base metals. The lap shearing test was used to characterize the joint. According to the experimental results, it can be imply that this kind of technique shares the same bonding mechanism with explosive welding and magnetic welding.

Rigid pipeline assembly via welding has rich applications in mechanical engineering and civil engineering. The quality of assembly directly influences the reliability, performance, and lifecycle of products. In the assembly process, two ends of a rigid pipeline are required to be matched with another two ends of existing pipelines. Due to the installation errors, two ends of a rigid pipe may not match their corresponding targets. To mitigate the dismatch, the following two issues need to be addressed: (i) matching the axis lines of the ends of the moving pipe and the axis lines of the ends of the existing pipes; and (ii) maximizing the overlap areas of each end of the moving pipe and its corresponding target on an existing pipe. The mathematical model of rigid pipeline assembly problem is established and a method for computing a nice initial position of the moving pipeline with respect to installed pipes is proposed. An iterative optimization algorithm are elaborated to address the problems. Using a running example, it is shown that our proposed methods are efficient for solving the problems.

This work proposes a micro-shear clinching process by laser shock for joining similar and dissimilar metal foils. The joint appearance and cross-section were investigated to determine basic process parameters. The soft punch thickness was 100 μm. The numbers of laser pulses on the upper and lower foil sides were set as two and one, respectively. Joint deformation was divided into three stages and we investigated the deformation law of the joints. The process windows of the Al foil combinations were acquired to determine a reasonable range of process parameters for obtaining qualified joints. The mechanical properties and failure modes of different joints were analyzed to identify the process characteristics. Mechanical properties were related to shear test directions and were influenced by upper and lower foil thicknesses. One failure mode was observed in the parallel shear test, and four failure modes were observed in the perpendicular shear test. These modes were determined by the differences between upper and lower foil thicknesses. Results showed that the proposed process can be used to join Al and Cu foils successfully. The laws governing the mechanical properties and failure modes of dissimilar materials were similar to those governing the mechanical properties and failure modes of similar materials.