Weixing Xu

Effect of tool vibration on chip formation and cutting forces in the machining of fiber-reinforced polymer composites

ABSTRACT This article investigates the chip formation mechanism and its influence on cutting forces during the elliptic vibration-assisted (EVA) cutting of fiber-reinforced polymer composites. To clarify the effect of the vibration, systematic finite element and experimental studies were performed on both the EVA and the traditional cutting of unidirectional fiber-reinforced polymers with various fiber orientations. The key factors that govern the cutting forces have been taken into account, such as the depth of cut, feed rate, tool vibration frequency and amplitude. The study found that fiber orientation significantly affects the chip formation and cutting forces. Fiber fracture can happen either above or below the trimming path, but that above the path dominates chip formation. When a fiber orientation is less than 90°, chipping is mainly through bending-induced fracture of fibers; when it is beyond 90°, however, chipping is mostly by crushing the fracture of fibers. Compared with a traditional cutting process, the EVA cutting can minimize the fiber orientation effect through localized fiber fracture. A dimensional analysis was then performed to provide a quantitative prediction of the cutting forces.

Micromechanical Modelling of Elliptic Vibration-Assisted Cutting of Unidirectional FRP Composites

Fibre-reinforced polymer (FRP) composites have been widely used in industry. However, the machining of FRP products is difficult, because of very different properties of the fibres and matrix. This paper discusses the development and implementation of a microstructure-based three-dimensional finite element model for the elliptic vibration-assisted (EVA) cutting of unidirectional FRP composites. The results showed that the EVA cutting has a good potential to the machining of FRP composites, featured a much reduced cutting force, better surface integrity and controllable chip size.

Nano-milling on monocrystalline copper: A molecular dynamics simulation

ABSTRACT Nano-milling is a promising technique for making miniaturized ultraprecision components. However, its underlying material removal mechanism is unclear and the accurate prediction of its performance is lacking. This study performs a systematic molecular dynamics analysis to reveal the material removal in the nano-milling of monocrystalline copper. It was found that the grooves by nano-milling, regardless of the machining parameters used, have two common features: (i) the groove top edge distortion is due to the effects of surface energy and high strain rate and (ii) the groove profile at the outlet side of the tool rotation aligns more closely with the designed geometry as a result of the atom flow variation and residual stress distribution. A dimensional analysis showed that the cutting speed factor and groove dimension factor significantly influence the specific energy and material removal rate in nano-milling. The groove quality can be improved by increasing the groove dimension factor or by decreasing the cutting speed factor. Finally, a machinability chart was developed for quality nano-milling processes.

A Two-Dimensional Ultrasonically Assisted Grinding Technique for High Efficiency Machining of Sapphire Substrate

This paper discusses the feasibility of improving machining efficiency of sapphire substrate by using two-dimensional (2D) ultrasonic vibration assisted grinding. An elliptic ultrasonic vibrator is designed and produced by bonding a piezoelectric ceramic device (PZT) on a metal elastic body (stainless steel, SUS304). The sapphire substrate is fixed onto the top face of the vibrator and ultrasonically vibrates in 2D vibration mode when the PZT is excited by two alternating current voltages with a phase difference. A grinding apparatus mainly composed of the ultrasonic vibrator is constructed, and experiments are performed with lateral modulation of elliptic ultrasonic vibration vertical to the grinding direction. Both the grinding forces and the ground work surface are measured and examined. Experimental results show that the grinding force decreases significantly and the resulted surface is improved in certain degree with the ultrasonic vibration compared to those of conventional grinding without ultrasonication. This indicates that the high efficiency grinding for sapphire substrate can be performed with the two-dimensional vibration grinding technique presented in this paper.

Laser Bending of Silicon Sheet: Absorption Factor and Mechanisms

Laser bending of silicon sheet is a process to form three-dimensional microstructural silicon elements in an ambient environment. This study aims to investigate the process mechanism with the aid of both experimental and numerical analyses. To this end, a thin-film thermocouple was prepared to capture the temperature field within the heating zone of the laser beam. A new method was then developed to precisely determine the absorption factor by coupling numerical simulation of the laser bending results with the experimental results. It was found that each laser pulse causes a cycle of sharp temperature risedrop in a silicon sheet. When the temperature in the heating zone is low, the sheet deforms elastically. When it is beyond the brittle‐ductile transition temperature of silicon, however, plastic deformation in the sheet takes place and bending occurs. The bending angle becomes larger with increasing the number of laser beam scanning, once the temperature gradient in the scanning area is large enough. [DOI: 10.1115/1.4025579]

Experimental Study of Tangential-feed Centerless Grinding Process Performed on Surface Grinder

In our previous study, a new centerless grinding method using surface grinder was proposed. In this method, a compact unit consisting mainly of an ultrasonic elliptic-vibration shoe, a blade, and their respective holders is installed on the worktable of a multipurpose surface grinder to conduct tangential-feed centerless grinding operations. For the complete establishment of this new method, firstly in this paper workpiece rotational speed control tests were carried out to make sure that the workpiece rotational speed is exactly controlled by the elliptic vibration of shoe to achieve high-precision centerless grinding. Then, the effects of the process parameters such as the worktable feed rate, the stock removal and the workpiece rotational speed on the workpiece roundness were clarified experimentally. The obtained results showed that (1) The workpiece rotational speed can be controlled exactly by the shoe ultrasonic vibration, (2) The roundness is improved with the increases in the voltage applied and the stock removal, but the decrease in the worktable feed rate; The best roundness obtained was 0.84m.

A micromechanics analysis of the material removal mechanisms in the cutting of ceramic particle reinforced metal matrix composites

ABSTRACT In previous investigations on the cutting of ceramic particle reinforced metal matrix composites using the finite element (FE) method, the particles are usually considered to be rigid. This is inconsistent with the actual situation and thus makes the FE predictions less practical. This paper proposes a micromechanics model to investigate the material removal mechanisms by considering the elasticity and fracture of the particles. It was found that the interaction position of a particle relative to the cutting edge greatly influences the particle and matrix fracture, particle-matrix debonding, surface integrity and cutting forces. There are two particle cracking mechanisms. One is caused by the direct contact of the cutting edge with the particle, and the other is due to the indirect tool-particle interaction through matrix. When the cutting path is below a particle, a smooth surface without subsurface damage can be achieved. When it is passing through a particle, particle fracture mostly occurs. If it is above a particle, subsurface damage is dominated by particle-matrix debonding. Cutting force peaks once the cutting edge is in contact with a particle and the cutting edge is easier to be damaged when the tool is passing through the upper part of the particle.

Ceramic Balls Machining by Centerless Grinding Using a Surface Grinder

This paper proposes a novel method for machining ceramic balls by centerless grinding technique performed on a surface grinder. In this method, a compact unit consisting mainly of an ultrasonic shoe, an ultrasonic regulator, a relay controller, a blade, a stopper and their respective holders is installed on the worktable of a surface grinder to conduct centerless grinding operations of ceramic balls. The ultrasonic shoe and regulator are produced by bonding a piezoelectric ceramic device (PZT) onto a metal elastic body, and when two phases of AC voltage are applied to the PZT an elliptic motion occurs on their end-faces which can be used to control the ball rotational motion in the radial and axial direction of the wheel, respectively. The function of the relay controller is to regulate the alternating current “on” and “off” time which is applied on the regulator for achieving the whole spherical surface grinding process. A grinding unit was actually constructed and it was experimentally confirmed that the ball rotational speed can be controlled well by the shoe or regulator. Grinding tests were subsequently carried out and the obtained results indicated that the constructed grinding unit performed well on actual ball centerless grinding operations.

Performing in‐feed type centerless grinding process on a surface grinder

In our previous study, a new centerless grinding method using surface grinder was proposed. In this method, centerless grinding operations are performed by installing a compact centerless grinding unit, consisting mainly of an ultrasonic elliptic‐vibration shoe, a blade and their respective holders, on the worktable of a surface grinder. During grinding, the cylindrical workpiece is held on the ultrasonic shoe and the blade, and its rotational motion is controlled by the elliptic motion of the shoe end‐face. An actual unit had been produced and its performance in tangential‐feed type centerless grinding using a surface grinder had been confirmed in the previous workd. In this paper, the performance of the grinding unit in in‐feed centerless grinding operation was confirmed, and the effects of the main process parameter, i.e., eccentric angle, on the workpiece roundness was investigated experimentally. The obtained results showed that: (1) the centerless grinding unit performed well in in‐feed type centerl...

Simulation Investigation of Tangential-Feed Centerless Grinding Process Performed on Surface Grinder

In our previous study, a new centerless grinding method using surface grinder was proposed. This paper describes a simulation method for investigating the workpiece rounding process in which a model taking the elastic deformation of the machine into consideration is created, and revealing how the process parameters affect the machining accuracy in the new grinding technique. In addition, a practice way to determine the machining-elasticity parameter showing the elastic deformation is developed. The simulation results are compared to show the effect of process parameters on the machining accuracy.