A three-dimensional laser absorption model based on ray tracing was established to describe the coupled interaction of a laser beam with particles in the powder layers of pure tungsten(W)material processed by selectiv...A three-dimensional laser absorption model based on ray tracing was established to describe the coupled interaction of a laser beam with particles in the powder layers of pure tungsten(W)material processed by selective laser melting(SLM).The influence of particle size on the powder-to-laser absorptivity and underlying absorption behavior was investigated.An intrinsic relationship between the absorption,distribution of absorbed irradiance within the powder layers,and surface morphology and geometric characteristics(e.g.,contact angle,width and height of tracks,and remelted depth)of the laser scanning tracks is presented here.Simulation conclusions indicate that the absorptivity of the powder layers considerably exceeds the single powder particle value or the dense solid material value.With an increase in particle size,the powder layer absorbs less laser energy.The maximum absorptivity of theWpowder layers reached 0.6030 at the particle size of 5 lm.The distribution of laser irradiance on the particle surface was sensitive to particle size,azimuthal angle,and the position of the powder particles on the substrate.The maximum irradiance in the powder layers decreased from 1.117×10^–3 to 0.85×10^–3W·μm^-2 and the contour of the irradiance distribution in the center of the irradiated area gradually contracted when the particle size increased from 5 to 45 lm.An experimental study on the surface morphologies and cross-sectional geometric characteristics of SLM-fabricated W material was performed,and the experimental results validated the mechanisms of the powder-to-laser-absorption behavior that were obtained in simulations.This work provides a scientific basis for the application of the ray-tracing model to predict the wetting and spreading ability of melted tracks during SLM additive manufacturing in order to yield a sound laser processability.展开更多
【目的】为了适应中国牧场的移动通信环境,加强动物从饲养至屠宰的全程监管,实现对动物的追踪和溯源。【方法】组合"Alien H3"和"Mifare One S70"两种特性不同的芯片,制作一种复合型的RFID动物耳标。其中"H3&q...【目的】为了适应中国牧场的移动通信环境,加强动物从饲养至屠宰的全程监管,实现对动物的追踪和溯源。【方法】组合"Alien H3"和"Mifare One S70"两种特性不同的芯片,制作一种复合型的RFID动物耳标。其中"H3"芯片适宜远距离身份识别,需要应用抗碰撞数学模型实现识别概率的优化。"S70"芯片适宜存储动物饲养日志,为了避免日志被篡改,需要采用"位运算"方式计算适宜的权限控制码。【结果】复合型耳标支持在运动中远距离识别动物身份,算法优化后,单时隙识别概率从0.055 4提升至0.379 8,表现为识别效率提高7倍;耳标还支持近距离扫描更新饲养日志,控制码设置为"70FF0869",保护日志不被篡改的同时实现透明阅读。【结论】复合型耳标可以帮助牧场追踪动物的饲养过程,避免动物在活动中错漏重要的防疫流程,并加强了动物档案的管理;复合型耳标又能支持流通环节的NFC扫描,客户可以通过手机透明地阅读动物饲养日志,实现溯源。展开更多
文摘A three-dimensional laser absorption model based on ray tracing was established to describe the coupled interaction of a laser beam with particles in the powder layers of pure tungsten(W)material processed by selective laser melting(SLM).The influence of particle size on the powder-to-laser absorptivity and underlying absorption behavior was investigated.An intrinsic relationship between the absorption,distribution of absorbed irradiance within the powder layers,and surface morphology and geometric characteristics(e.g.,contact angle,width and height of tracks,and remelted depth)of the laser scanning tracks is presented here.Simulation conclusions indicate that the absorptivity of the powder layers considerably exceeds the single powder particle value or the dense solid material value.With an increase in particle size,the powder layer absorbs less laser energy.The maximum absorptivity of theWpowder layers reached 0.6030 at the particle size of 5 lm.The distribution of laser irradiance on the particle surface was sensitive to particle size,azimuthal angle,and the position of the powder particles on the substrate.The maximum irradiance in the powder layers decreased from 1.117×10^–3 to 0.85×10^–3W·μm^-2 and the contour of the irradiance distribution in the center of the irradiated area gradually contracted when the particle size increased from 5 to 45 lm.An experimental study on the surface morphologies and cross-sectional geometric characteristics of SLM-fabricated W material was performed,and the experimental results validated the mechanisms of the powder-to-laser-absorption behavior that were obtained in simulations.This work provides a scientific basis for the application of the ray-tracing model to predict the wetting and spreading ability of melted tracks during SLM additive manufacturing in order to yield a sound laser processability.
