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Zhong S.-Y.,Northwestern Polytechnical University | Qi L.-H.,Northwestern Polytechnical University | Qi L.-H.,Key Laboratory of Contemporary Design and Integrated Manufacturing Technology | Luo J.,Northwestern Polytechnical University | And 3 more authors.
Journal of Materials Processing Technology | Year: 2014

Stable generation of copper droplets is a key issue in fabricating copper parts by drop-on-demand (DOD) technology. The process parameters such as supply pressure and electronic pulse width have significant effect on pressure variation and droplet formation. In the present work, a pressure acquisition system was first set up to measure the pressure variation in crucible. Then the measured pressure data were applied on a 2D axisymmetric model as inlet conditions to study the influence of process parameters on copper droplet formation. The results indicated that the peak pressure in crucible increased linearly with the increase of supply pressure. As supply pressure increased, the jet velocity and the limiting length increased to critical value and droplet could be generated. The peak width increased with the rise of electronic pulse width. By increasing the electronic pulse width, the time of pressure above threshold value increased and the jet limiting length grew to critical value for breakup. However, if supply pressure and electronic pulse width were too large, satellite droplets would be formed. Pure copper droplet generating experiments were conducted to obtain appropriate parameters. Single droplet was generated while supply pressure was between 60 kPa and 100 kPa and pulse width was between 550 μs and 1550 μs. Also the range of pulse width varied as the supply pressure increased for generating single droplet. The statistics of droplet diameter suggested that droplet diameter increased with the increase of supply pressure. Electronic pulse width had influence on the droplets size and the standard deviation increased with the increase of electronic pulse width. So small supply pressure and electronic pulse width should be used for generating uniform droplets. © 2014 Elsevier B.V. All rights reserved. Source


Yan X.,Key Laboratory of Contemporary Design and Integrated Manufacturing Technology
Advanced Materials Research | Year: 2011

A developed method to predict the cutting forces in end milling of generalized corners is proposed in this paper. The cornering milling process is divided into a series of cutting segments with different cutting states. The mathematical model of the geometric relationship between cutter and the corner profile is established for each segment. Cutting forces is predicted by introducing the classical cutting force model. The computational results of cutting forces are in good agreement with experimental data. Source


Qi L.-H.,Northwestern Polytechnical University | Qi L.-H.,Key Laboratory of Contemporary Design and Integrated Manufacturing Technology | Chao Y.-P.,Northwestern Polytechnical University | Luo J.,Northwestern Polytechnical University | And 3 more authors.
International Journal of Machine Tools and Manufacture | Year: 2012

Metal micro-droplet deposition manufacture technology has attracted wide interest for potential application in micro-structure fabrication. In order to fabricate functional metal components by sequentially depositing molten metal droplets on substrate layer by layer, the perfect overlapping and bonding strength among droplets have to be obtained. In this paper, the influence of scanning step on overlapping of droplets was investigated, and the critical overlapping condition of droplets was calculated by analyzing the relationship of the shape parameters of solidified droplet on the substrate. Four kinds overlapping states of adjacent droplets were predicted according to the change of scanning steps: no overlapping, partial overlapping, ideal overlapping and excessive overlapping. On this basis, two simple and effective models were proposed to calculate and predict the optimal scanning steps (W XP and W YL). The calculation results show that the W XP and W YL were only affected by droplet diameter (D) and solidification angle (θ). Based on this analysis, a pneumatic droplet generator was used to produce uniform molten Sn60Pb40 alloy droplets with specific diameters (256 μm, 400 μm and 700 μm), and a series of deposition experiments were carried out with different scanning steps on the condition of fixed droplet temperature (270 °C) and substrate temperature (90 °C). The experimental results show that good overlapping and bonding strength of adjacent droplets could be obtained in deposited lines and layers, and low porosity and high density three-dimensional metal component was fabricated with optimized experimental parameters (W XP and W YL) according to theoretical models. The work can provide useful theoretical and experimental guide for metal micro-droplet deposition manufacture. © 2011 Elsevier B.V. All rights reserved. Source


Qi L.-H.,Northwestern Polytechnical University | Qi L.-H.,Key Laboratory of Contemporary Design and Integrated Manufacturing Technology | Zhong S.-Y.,Northwestern Polytechnical University | Luo J.,Northwestern Polytechnical University | And 2 more authors.
International Journal of Machine Tools and Manufacture | Year: 2015

Metal micro-droplet deposition manufacture has potential applications and attracts increasing attention in wide areas. By quantitatively describing and predicting the surface topography, the influence of parameters on surface quality could be studied effectively. In present work, a new approach aimed to the characterization of part surface topography was proposed and the evaluation indexes such as arithmetic average height (Ra) and stratification angle (θ) were used to characterize the surface topography. Based on the surface geometrical profile, two prediction models were developed to calculate the evaluation indexes of part surface. Then experiments for fabricating thin wall parts were conducted and the evaluation indexes were measured experimentally. By comparing the experimental values with the predicted results, the mechanism of process parameters affecting surface topography was investigated. The results indicated that the top surface was mainly affected by scan step (Wd) which also could be represented by overlap ratio (μ). While overlap ratio was larger than 25.7%, excessive overlap resulting in poor surface topography occurred and the prediction model was invalid. In another hand, the side surface was mainly affected by offset distance (Wo) which also could be represented by offset ratio (τ). If offset ratio was too large, the ending side would collapse resulting in poor side surface topography and the prediction model would fail to calculate the side surface roughness. The experiment results indicated that collapse would occur while offset ratio was larger than 54.5%. In the last, the surface roughness of a cubic object was measured and the results demonstrated that the method proposed in present work was useful for evaluating surface quality of 3D object. © Elsevier Ltd. All rights reserved. Source


Chao Y.-P.,Northwestern Polytechnical University | Qi L.-H.,Northwestern Polytechnical University | Qi L.-H.,Key Laboratory of Contemporary Design and Integrated Manufacturing Technology | Zuo H.-S.,Northwestern Polytechnical University | And 3 more authors.
International Journal of Machine Tools and Manufacture | Year: 2013

Micro-void and cold lap are the most common defects of 3D components in aluminum alloy droplet deposition manufacture, which have been found to be associated with the poor remelting and metallurgical bonding between droplets under inappropriate droplet and substrate temperatures. To address this problem, the appropriate temperature condition for achieving good metallurgical bonding between droplets was analyzed and the relationships among surface temperature (Tsurf), substrate temperature (Tb), droplets temperature (Tdrop), droplets deposition frequency (f) and height of deposition layer (h) were estiblished by one-dimensional (1D) heat transfer analytical model. On this basis, a three-dimensional (3D) transient finite element mode was developed to simulate the thermal behavior during metal droplet deposition component using element birth and death technology. The distribution and variation of surface temperature of previously deposited droplets (T surf) were predicted and analyzed under different process parameters in fabricating aluminum alloy 3D components. And then, a series of deposition experiments were conducted with different droplet temperatures (T drop) and substrate temperatures (Tb). The experimental results show that the good remelting and metallurgical bonding between droplets were obtained with the appropriate combination of Tdrop (700 C) and Tb (450 C). The micro-void and cold laps were not observed in the interior of formed samples, indicating that experimental results basically agree with the theoretical analysis and simulation results. The work provides a useful theoretical and experimental guide for metal droplets deposition manufacture. © 2013 Elsevier Ltd. Source

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