Papers by Author: Jian Zhong Zhou

Abstract: Considering the efficiency and microscale requirement of melting polymer in micro-injection process, we present an experimental analysis of the CO2 laser irradiating Polyamide 12 (PA12) based on the photo-thermal effect of laser-materials interaction. The orthogonal experiments of laser plasticizing were designed by Taguchi method of Minitab software, the influence of process parameters on PA12 plasticization was investigated, and the effect sequence rule of the experiment parameters to melting depth was analyzed. Accordingly，the optimal process parameters combination on PA12 plasticization were obtained，i.e. laser power 3 W, beam diameter 2 mm, scanning velocity 200 mm/min, scanning distance 0.5 mm and environment temperature 20°C.

Abstract: A silicone mould fabrication technique based on vacuum casting was developed and its reproducibility was demonstrated. Orthogonal DOE method was adopted to analyze the effects of vacuum casting process parameters, and the process parameters that had an influence on the quality of the micro-mould cavities were identified and optimized. Micro-casting experiments were carried out using the optimized process parameters and the replicated micro-gears were obtained, these silicone copies were subjected to thorough analysis for dimensional accuracy against the master pattern. The results showed that the fabricated micro-mould was capable of producing functional micro-parts that were able to replicate micro-features, and micro-gears were successfully transferred from the silicone rubber moulds into PU resin pieces under vacuum conditions.

Abstract: Laser peen forming is an emerging novel process of metal plate bending, which uses laser-induced shock wave pressure to generate an unbalanced residual stress field in the target, the moment of the residual stress causes metal plate to develop plastic bending deformation. The mechanism of laser shock induced residual stress was introduced firstly, then the deforming process of metal plate induced by residual stresses was discussed and the depth of the residual compressive stress was proposed. Effects of processing parameters on the residual stress distribution and plate bending deformation were numerical analyzed. The results indicated that the bending deformation of sheet was relative to laser peening numbers, peening coverage and thickness of plate, the magnitude and distribution of residual stresses could be precisely controlled by adjusting laser processing parameters.

Abstract: Micro-scale laser shock peening (μLSP) is a flexible and precise process that can potentially be applied to metallic structures in micro devices to improve strength and reliability performance. In order to understand the mechanism of μLSP process, a typical experiment was carried out for copper foils specimen with various process parameters. Surface morphology, deformation and hardness of the specimens were observed and characterized by 3D microscope system and situ nano-mechanical test system respectively. It was found that overlapping rate of laser spot has a little effect on microscopic deformation depth which increases slowly with the increasing of laser energy, and micro-hardness of the laser treated specimens was improved significantly.

Abstract: Residual stress field induced by laser shot peening (LSP) was simulated using Box-Behnken experimental design. Compressive residual stress field intensity (S) was introduced to estimate the effect of compressive residual stress field on fatigue performance. The effect of laser process parameters (such as laser shock wave peak pressure, spot diameter and peening number) on S was analyzed by response surface analysis (RSA), quadratic regression predicting model for S was established, and the rationality of that was verified. Finally, the optimal combination of laser process parameters oriented to anti-fatigue manufacture was optimized. The results indicated statistical analysis results agreed well with those of simulation, RSA for parameter optimization of LSP is feasible.

Abstract: In order to enhance mechanical property and restrain crack growth of 6061-T6 aluminum alloy, laser shot peening (LSP) was employed to induce compressive residual stress and plastic deformation on the surface of metal. The FEA code ABAQUS and MSC. Fatigue were used to simulate crack growth of Compact tension (CT) specimens treated by LSP. The numerical simulation results showed that LSP can effectively inhibit the crack growth, decrease the crack growth rate as well as increase the final crack size, and as a consequence, fatigue life was extended. Adding peening times could get deeper compressive residual stress field which strengthen material surface and restrain crack growth, but the fatigue stress intensity factor threshold decreases.

Abstract: Microscale laser shock peening (μLSP) can generate beneficial compressive stress distribution in the targets, as the used beam diameter in μLSP is at the order of micron equivalent with grain size, the treated material must be considered as anisotropic and inhomogeneous, this causes an asymmetrical distribution of residual stress. In this paper, shape factor σSF was introduced and defined to characterize the asymmetrical distribution of stress, optimum conditions of factors and the influence degree were explored based on Taguchi design with the optimal object of stress characterization values. The results show that shape factor is a significant characteristic of residual stress induced by μLSP, crystal orientation is the most important influence factor, but laser energy and peening number have significant influence on stress characterization values.

Abstract: . Progressive dies are widely used for the mass production of sheet metal components due to the high productivity, high precision and low cost, but the design of progressive die is a complex and highly specialized procedure. In this paper, a design method of progressive die based on component was presented. Based on the technology of component object module, a number of key techniques in the design of progressive die design were addressed, the knowledge-based design frame system was developed, and the assembling model under UG environment was established. Finally, a practical design process for progressive die of complex panel was demonstrated, and the 3D integrated mould was realized.

Abstract: After the mechanisms of laser peen forming (LPF) were analyzed, the effect of sheet metal’s thickness on LPF was discussed in theory. The analysis model that residual stresses brought sheet bending was established, and the relationship between thickness and arc height of sheet metal was obtained. The process of laser shock wave loading during LPF was modeled, and then the residual stresses and deformation of the peened sheet were simulated by ABAQUS software. The results indicated that LPF use bending moments caused by residual stress to induce deformation, which was agreed with the theory analysis. The curvature of sheet metal induced by LPF decreased as the thickness increased, the arc height formed by bending was inversely proportional to thickness square of sheet metal on the whole. This research also has significance for the control of LPF and the investigation of further experiment

Abstract: As a new fabrication technique based on rapid prototyping, vacuum casting process can be especially used in the stage of products development. In this paper, a self-designed and made silicone mould was used to study process of vacuum casting panel part. ProCAST software was adopted to analyze the melt flowing behavior and effects of processing parameters. The key vacuum casting parameters, such as mould temperature, melt temperature, degree of vacuum and coefficient of heat transfer, on the effects of the filling rate of polymer melt were emphasized to be numerical studied. The results indicate that mould temperature and coefficient of heat transfer have the most important influence on quality of the formed panel.