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Continuous feeding of powders is critical to ensure manufacturing quality in laser-based additive manufacturing processes. However, current powder delivery systems are either not capable of continuous feeding of powders or cannot guarantee that the powders achieve a certain motion velocity to assure their uninterrupted motion into the melt pool. Therefore, a new powder delivery system is developed which use the advantages of vibration and pneumatic feeders. In this powder delivery system, vibration is used to disperse agglomerated powders and control the powder federate while pneumatic pressure is used to increase powder velocity to guarantee that the powder enters the melt pool. Powder flow simulation has been conducted to reveal powder flow characteristics. To test the feasibility of the developed powder delivery system for powder delivery and verify the correctness of powder flow simulation results, powder delivery experiments have been conducted. Effects of argon gas flowrate and vibration parameters on powder flowrate have been investigated. Experimental results show that a stable and repeatable powder flowrate can be controlled by adjusting the vibration parameters and the argon gas flowrate with the developed delivery system.

•A new vibration-assisted cutting method is proposed to enable the efficiently machining micro images onto freeform surfaces on metal workpieces. Taking advantage of a non-resonant complaint cutting device used in a machining system, two vibration components can be used at the same time in the micro machining process. One vibration component is used to fabricate the freeform surface, while another is used to generate the grayscale images on the freeform surface.•A toolpath generation algorithm was developed by considering the toolpath components for both the grayscale image and the freeform surface.•The images have been successfully machined both on flat and saddle surfaces on metal workpiece, demonstrating the capability of the proposed method. This technology has potentially wide applications to machine master molds for mass production of patterned plastic components or drugs in anti-counterfeiting field.

•A flexible hinge mechanism is used in a non-resonant vibration generator to generate larger vibration amplitudes over a range of frequencies. Another advantage of this device is that it can use not only a single frequency but also multiple frequencies at the same time. Therefore, complex texture can be generated in one step.•The principles of this vibration assisted surface texturing process both on the cylindrical and face surfaces of a cylinder were detailed analyzed.•Surface generation models both for cylindrical and flat surfaces of a cylinder are established to serve as the vehicle for generating the desired surface topography. The predictive accuracy of the proposed surface generation models were ascertained by experimental results.•The uniform surface textures on face surface of a cylinder can be generated by proposed vibration controlling method.

Micro-end-milling is used for the fabrication of complex geometrical features with high precision on a wide variety of materials. One of the main challenges is related to chatter vibrations, which are detrimental to the productivity and overall quality of the manufactured parts. In this article, a novel chatter-detection method based on wavelet coherence functions is proposed to evaluate the stability of the micro-end-milling process. Then, the method is experimentally tested under different cutting conditions. The results show that the wavelet coherence functions of two orthogonal acceleration signals are sensitive enough and applicable for chatter detection. When chatter occurs, the two orthogonal acceleration signals are highly correlated at the chatter frequency, resulting in a sharp increase in the magnitude of the wavelet coherence functions to values approaching unity.

Textured surfaces have been widely applied in many fields due to their excellent functional performances. Although several micro-scale surface texturing techniques have been used to fabricate surface textures, most are either very expensive, have material limitations, or lack flexibility. In this study, a novel textured surface generation method using vibration-assisted ball-end milling with a non-resonant vibrator is proposed. Firstly, the configuration of the vibration-assisted ball-end milling system is introduced. Then, the trajectories of the cutting edges are modeled and analyzed. Furthermore, an analysis of a non-resonant vibrator is conducted. Finally, surface texture machining experiments are conducted, and the feasibility of the proposed vibration-assisted ball-end milling method for surface texture fabrication is verified.

This paper presented the effect of run out on the experimental characteristic of micro-milling brass using carbide micro-end mills. A method of calculation and measurement for the run out of tool-holder-spindle assembly in micro-end mill was developed. A series of micro-milling process experiments were carried out under varying cutting parameters. The effect of run out on cutting forces, effect of cutting parameters on surface roughness, and size effect were analyzed. It was seen that the cutting force signature was seriously affected by run out in the micro-milling process. When the feed per tooth is less than the run out, the cutting force signals showed that only one cutter flute engaged in cutting process due to the effect of run out. It was also seen that the cutting force signature showed erratic variations due to the effect of tool–workpiece and the run out of tool tip at higher spindle speed. Surface roughness was affected by both cutting speed and feed per tooth. For lower cutting speed, there was increase in the surface roughness with the decrease in the cutting speed due to the effect of built-up edge. For higher cutting speed, there was increase in the surface roughness with the increase in the cutting speed due to dominance of the shearing effects. When the feed per tooth was less than the minimum chip thickness, due to the indentation and ploughing-dominated process, nonlinear increase of specific shear energy can be obtained. At lower feed per tooth, the specific energy increases with increased cutting speed. These results are used to provide strategies to optimize cutting parameters and achieve better surface quality in micro-milling brass process.

Accurate modeling and prediction of cutting forces are important for process planning and optimization in micro end-milling process. In order to exactly predict the cutting forces, an innovative uncut chip thickness algorithm is proposed by considering the combination of the exact trochoidal trajectory of the tool tip and the cutting trajectory of all previously passing teeth, tool run-out, minimum chip thickness and the material’s elastic recovery. The proposed uncut chip thickness algorithm also considers the variation of the entry and exit angles caused by tool run-out. To determine the cutting force coefficients, a finite element model (FEM) of orthogonal micro-cutting that considers strain hardening, strain rate sensitivity, thermal softening behavior, and temperature-dependent flow has been established. Based on the results from FEM analysis, the cutting force coefficients are identified and represented by a nonlinear equation of the uncut chip thickness, cutting edge radius and cutting velocity. The identified cutting force coefficients are integrated into a mechanistic cutting force model and used to simulate micro end-milling forces. The simulation results show a very satisfactory agreement with the experimental results.

AbstractThis paper presents an experimental study of the effects of cutting parameters of micro-end-milling process on the machined surface roughness, in order to find the optimal operation conditions for improved surface finish. Three types of metals, namely 6160 aluminium alloy, brass, and AISI 1040 steel, are used as work materials. The effect of material property on the surface roughness is investigated. It is found that under the same machining condition, the machined surface quality of aluminium alloy is the worst, while that of brass is the best. A multiple regression model for the surface roughness is developed, which includes the effects of cutting speed, feedrate, and the interaction between them. Results based on analysis of variance (ANOVA) show that the cutting speed is the most significant factor on surface roughness. The residual analysis indicates that the multiple regression model is valid and agrees with the experimental results.

Abstract: The excited-state intramolecular charge transfer of four oxazolo[4,5-b]pyridine derivatives with different electron donating and electron withdrawing groups was investigated using the time-dependent density functional theory. The vertical excitation energies and the electronic structures were explored. Their distinct properties of absorption and fluorescence spectra in solvent phase were explained according to the electronic coupling matrix elements calculated by the Mulliken-Hush theory. The substituent on the oxazolo[4,5-b]pyridines will remarkably change their spectra properties and increase the first excited-state dipole moments. The effect of protonation on the absorption and fluorescence spectra was also investigated systematically. Our study suggests that the present method is feasible to explain charge transfer excitation and predict the properties of absorption and emission spectra in the studied systems.