为解决载气式、超声振动和惯性力等现有微输送方法在较宽输送速率范围内难以克服的角形金属粉体堵塞难题, 本文研究以超声驻波场声辐射力为驱动力, 通过悬浮分散微喷嘴内密集态粉末颗粒, 实现金属粉末的稳定微输送。以激光熔覆技术中常用且易堵塞的100目、200目和300目角形铬粉和200目角形钛合金粉为对象, 进行脉冲式和连续式两种模式的微输送精度和稳定性实验研究。实验显示, 300目角形铬粉单脉冲输送质量可控范围为0.4~16 mg且连续输送速率可控范围为6.0~65 mg/s; 脉冲微输送质量的变异系数随微喷嘴内径的增大而大幅降低(小于2%)、连续输送速率的变异系数均低于6%。实验结果表明, 声辐射力驱动微米级角形金属粉末具有较大的输送速率可控范围、输送精度、稳定性和多种角形金属粉末的普适性, 可从根本上解决角形粉末喷嘴微输送的堵塞问题。本文研究结果也可为其它尺度金属粉末和非金属粉末的微输送提供参考。

Stable micro-feeding of micron-size metal powder is one of the core issues in advanced metal parts manufacturing technology, including laser cladding deposition and 3D micro-printing. This study solves the difficult problem associated with the aggregation of irregular shape metal powder, which is unavoidable in existing methods when the feeding mass has a broad range. Such methods are based on the use of a gas-powder feeding system, ultrasonic vibration, pulse inertia force and etc. This study uses acoustic radiation force in an ultrasonic standing wave field as the driving force, so that the aggregating powder is suspended in a nozzle to realize a stable pulse dose in a continuous feed mode. The commonly used irregular shape chromium and titanium alloy powder, which can block the nozzle easily during laser cladding deposition, is adopted as the research object to conduct experiments on micro-feeding accuracy and stability. The particle sizes are 100-mesh, 200-mesh, and 300-mesh. The experimental results show that the pulse dose mass for the 300-mesh irregular shape chromium powder is in the range 0.4 to 16 mg and that the continuous feed rate is in the range 6.0 to 65 mg/s. The coefficient of variation for the pulse dose process decreases with an increase in the outlet diameter of the micro-nozzle, and the minimum value of the coefficient of variation is below 2%. All the coefficients of variation for the continuous feeding rate are below 6%. As a result, the proposed method for micro-feeding micron-size irregular shape metal powder, actuated by acoustic radiation force, has high accuracy, high stability, and good universality for different particles. Thus, this method can solve the problem of powder aggregation. The results proposed in this paper can also serve as reference for the micro-feeding of other kinds of powders based on different materials and with different shapes.