In-situ high-speed X-ray imaging of piezo-driven directed energy deposition additive manufacturing.

Powder-blown laser additive manufacturing adds flexibility, in terms of locally varying powder materials, to the ability of building components with complex geometry. Although the process is promising, porosity is common in a built component, hence decreasing fatigue life and mechanical strength. The understanding of the physical phenomena during the interaction of a laser beam and powder-blown deposition is limited and requires in-situ monitoring to capture the influences of process parameters on powder flow, absorptivity of laser energy into the substrate, melt pool dynamics and porosity formation. This study introduces a piezo-driven powder deposition system that allows for imaging of individual powder particles that flow into a scanning melt pool. Here, in-situ high-speed X-ray imaging of the powder-blown additive manufacturing process of Ti-6Al-4V powder particles is the first of its kind and reveals how laser-matter interaction influences powder flow and porosity formation.

A novel piezoelectrically actuated 2-DoF compliant micro/nano-positioning stage with multi-level amplification.

This article presents a novel two-degrees-of-freedom (2-DoF) piezo-actuated parallel-kinematic micro/nano-positioning stage with multi-level amplification. The mirror symmetric stage consists of four leverage mechanisms, two Scott-Russell mechanisms, and a Z-shaped flexure hinge (ZFH) mechanism. Taking advantage of the ZFH mechanism, 2-DoF motions with final-level flexural amplification and decoupled motion guidance are achieved. Analytical models of the stage are developed and validated through finite element analysis to characterize its working performance. Practical testing of a prototype stage is conducted to demonstrate the design process and to quantify its response characteristics. Due to the utilized multi-level amplification, a practical amplification ratio of 13.0 is realized by the prototype. The decoupled output motion guidance feature of the stage makes it amenable for implementation in raster scanning type of measurements.

Effects of ultrasonic vibrations in micro-groove turning.

Ultrasonic vibration cutting is an efficient cutting process for mechanical micro-machining. This process can generate intricate surface textures with different geometric characteristics. Micro-grooves/micro-channels are among the most frequently encountered micro-structures and, as such, are the focus of this paper. The effectiveness of both the linear and ultrasonic elliptical vibration-assisted machining technique in micro-groove turning is analyzed and discussed in the paper. The paper first investigates the mechanisms of micro-groove generation induced by the linear and elliptical vibration modes. A simplified cutting force analysis method is given to compare the effectiveness of the two modes in micro-groove turning. The surface roughness of the generated micro-grooves is analyzed next and theoretical expressions are given for the two cases. Finally, micro-groove turning experiments are conducted to compare the influences of the two vibration modes on the cutting forces and the surface roughness. The experimental results show that linear vibration-assisted micro-groove turning leads to better surface roughness as compared to the elliptical vibration-assisted case, while elliptical vibration-assisted micro-groove turning shows advantages in terms of decreasing the cutting forces.