Abrasive tools consist of abrasive grains, binder and pores. Binders are the matrix of the material and may be of the metallic, vitrified or resin type. The wide use of polymeric materials (resinoid) is due to their low cost and excellent mechanical properties. The grain has the function of roughing the material, the binder, on the other hand, has the characteristics of ensuring grain adhesion and the pores in the structure are responsible for cooling the abrasive tool. In this work, we report the preparation and evaluation of the mechanical characteristics of resin bond composite abrasives with different structures based on the porous concentration. The composite abrasives were made with phenolic resin and alumina grains. Four different structures were studied from 10 to 30% of porous volume fraction with 50% of grain volume fraction. The concentration of porous and bond in the structure composition were employed to compare the mechanical performance of the prepared composite abrasive. To evaluate the mechanical properties of composites, Impact strength, Young’s Modulus by impulse excitation and flexural strength were realized. It was observed that as the porosity is higher, the impact resistance (absorbed energy) is lower, which confirms the lower resistance produced by the surface area contact (grain/binder) and a greater accumulation of tension in the binder material, the higher porosity value, higher the flexural strength value until 20% of porosity. Samples with higher volumes level of porosity presented lower Young’s Modulus but the presence of pores produced by volatiles by-products (mainly water) should act as stress concentrators, thus favoring lower mechanical properties at the resin-grain interface.

ZnO nanoflakes with varying thickness (10–120 nm) and width (250–1600 nm) were synthesized on the tooltip (∅ ≤ 200 μm) by a novel route method called electrochemical spark deposition and growth method. The leaf-like nanostructures were found under varying pulsated DC voltage potentials (50–80V) at normal room temperature (25°C). Equimolar concentration (0.1M) of zinc nitrate hexahydrate (Zn(NO 3 ) 2 .6H 2 O) and methenamine ((CH 2 ) 6 N 4 ) HMTA) mixture was used as a growth (precursor) solution. The anodization time (deposition and growth time) was varying from 10 seconds to 25 seconds. Further, the consequence of pulse voltage on the growth morphology was examined critically. The structural evolution and elemental composition were investigated by field emission scanning electron microscopy (FESEM) and energy-dispersive X-ray spectroscopy (EDX) respectively. The size distribution (thickness and width) of ZnO nanoflakes were estimated by image processing software (Image J). Ultimately, the ultraviolet visible infrared spectroscopy (UV-Vis) analysis was carried out to determine the excitation energy of the zinc oxide nanoflakes. The estimated bandgap energy (via. Tauc plot) of the nanoflakes was found approximately 2.63 eV.

Excessive and unstable vibrations that are caused by the machining forces are among the most critical problems that limit the use of industrial robots instead of CNC machine tools. Reduction and control of robot’s vibrations during machining require accurate models of the robot’s vibration response to the dynamic forces exerted at the Tool Centre Point (TCP) where the cutting tool interacts with the workpiece material. The existing models of vibrations in robotic machining have been formed by assuming the linearity of the dynamic response at the TCP. In this paper, the accuracy of this assumption is investigated experimentally, and the results show that the dynamic response at the TCP is strongly nonlinear. An experimental procedure is presented to identify the nonlinearities by employing the first-order Frequency Response Functions (FRFs) measured using various input force excitations. Nonlinear Complex Mode Analysis is then used to extract the modal parameters of the system when its dynamics is linearized around a harmonic response with a constant amplitude. The extracted modal parameters strongly depend on the amplitude of the applied force and the resulting vibrations. This study highlights the need for considering the nonlinearities of the structural dynamics of industrial robots in modelling machining vibrations.

This paper investigates the impact on free abrasive machining (FAM) process using a vibrating wire with an oscillating boundary condition. The experimental results show that the vibration of wire in slurry with abrasive grits can result in material removal due to FAM on brittle material. We present a theoretical model of a wire moving axially at a constant speed, subject to an oscillating boundary condition with damping, and derive an analytical solution of the partial differential equation of motion. Based on the modeling and analysis, the frequency of vibration of wire corresponds to the frequency at the oscillating boundary at steady state. The damping factor suppresses the lateral movement of wire from the fixed boundary to moving boundary when it is increased. The change of axial wire speed or the oscillating frequency at boundary can counteract the suppression on the vibration response induced by increased damping factor. This study also presents an experimental study using an experimental setup of a slurry-fed wire with a periodic excitation to study the FAM process on silicon. The results of experiments show that vibration of wire can impart the silicon carbide abrasive grits in slurry to generate observable grooves and fractures on the surface of silicon in just a few minutes. The grooves and fractures are generated by the indentation of abrasive grits via loading and unloading on the silicon surface. When the vibrating wire is only fed with water without abrasives or under a dry condition, compressive deformation with shallow grooves on silicon is observed; however, the surface is found to be free of surface features of indentation and scratching. Furthermore, evidence of both wire compression and abrasive machining is more pronounced at the edges of silicon specimen, especially at the edge close to the periodic excitation, which is consistent to our modeling.

Additive manufacturing is driving major innovations in many areas such as biomedical engineering. Recent advances have enabled 3D printing of biocompatible materials and cells into complex 3D functional living tissues and organs using bioink. Inkjet-based bioprinting fabricates the tissue and organ constructs by ejecting droplets onto a substrate. Compared with microextrusion-based and laser-assisted bioprinting, it is very difficult to predict and control the droplet formation process (e.g., droplet velocity and size). To address this issue, this paper presents a new data-driven approach to predict droplet velocity and size in the inkjet-based bioprinting process. An imaging system was used to monitor the droplet formation process. To investigate the effects of excitation voltage, dwell time, and rise time on droplet velocity and droplet size, a full factorial design of experiments was conducted. Two predictive models were developed to predict droplet velocity and droplet size using random forests. The accuracy of the two predictive models was evaluated using the relative error. Experimental results have shown that the predictive models are capable of predicting droplet velocity and size with sufficient accuracy.

Inkjet printing as a viable technology has been widely adapted for various biomedical applications, such as 3D biofabrication which utilizes the droplets generated from inkjet printing of bioink to build 3D viable structures. One of the key challenges is cell distribution which is cell number embedded per droplet/microsphere. It significantly affects the post-printing cell viability and proliferation. This paper focuses on the effect of excitation voltage on the living cell distribution during drop-on-demand inkjet printing of bioink containing living cells. The cell distribution results are compared under two different excitation voltages of 40V and 50V. The normal distribution is used to fit the experimental results. It is found that 1) at both 40V and 50V, the mean cell number of the experimental results is always smaller than the theoretical value due to cell motion inside the nozzle; and 2) the mean cell number errors are 3% at 40V and 18% at 50V, which is due to different ligament flow near the nozzle orifice. The resulting knowledge benefits efficient and effective fabrication of 3D cellular constructs with uniform cell distribution.

Organ printing is an emerging technology for fabricating artificial tissues and organs, which are constructed layer by layer by precisely placing tissue spheroids or filaments as building blocks. These fabricated artificial organs offers a great potential as alternatives to replace the damaged human organs, providing a promising solution to solve organ donor shortage problem. Inkjetting, one of the key technologies in organ printing, has been widely developed for organ printing because of its moderate fabrication cost, good process controllability and scale-up potentials. Droplet formation process as the first step towards inkjetting 3D cellular structures needs to be studied and controlled precisely. This paper focuses on the ligament flow of exit-pinching during droplet formation process of inkjet printing. The ligament flow directions during pinch-off process of inkjet printing of a sodium alginate solution with a concentration of 0.5% (w/v) have been studied. It is found that two different types of flow directions inside a single ligament during pinch-off process may occur. At an excitation voltage of 30 V, the ligament flow has two different directions at the locations near the nozzle orifice and the jet front head: the negative z direction at the location near the nozzle orifice due to the dominant capillary effect, and the positive z direction at the location near the jet front head due to both the fluid inertial and capillary effects. On the contrary, at an excitation voltage of 70 V, the ligament flow directions are the same at the locations near the nozzle orifice and the jet front head: the positive z direction at the location near the nozzle orifice due to the sufficiently large fluid inertial effect, and the same positive z direction at the location near the jet front head due to both the fluid inertial and capillary effects. Two flow directions inside a single ligament benefit single droplet formation without satellite droplets, but the droplet trajectory will be easily affected by the airflow in the laboratory due to the small droplet velocity as well as the droplet deposition accuracy. Single flow direction inside a single ligament usually results in a long ligament due to the large fluid inertia which eventually breaks into several undesirable satellite droplets. The resulting knowledge will be beneficial for better understanding of the ligament pinch-off during droplet formation process of inkjet printing biological viscoelastic alginate bioink for 3D cellular structure fabrication as well as precise droplet controllability for good quality of fabricated 3D structures.

A multidisciplinary design optimization (MDO) process of a large scale hybrid composite wind turbine blade is developed. Multiple objectives are considered in this design optimization: maximize length of blade, minimize weight and manufacturing cost. A wind turbine blade is divided into regions and the layup sequences for each region are considered as design variables. Applied load due to extreme wind condition for rotor rotation and rotor stop condition are considered for finite element analysis (FEA) to evaluate the structural strength. The structural stiffness is designed and illustrated so that the natural frequency of the blade does not coincidence with the excitation frequency of the wind turbine. A process of obtaining an optimum hybrid composite laminate layup and an optimum length of wind turbine blade is developed in this research.

The two-degree of freedom oscillator is presented to model the dynamics of a machine tool system in the cutting process. The chip dynamics are presented through a discontinuous system with a velocity boundary (frictional force). The closed form solutions are presented for the normalized linear set of ordinary differential equations. The basic mappings are introduced to investigate the stick-slip motion in such a mechanical model. The mapping structures for the periodic motions will be developed. The numerical prediction of the phase trajectory, over a range of the excitation frequency is presented through the discontinuity. The predictions are verified by numerical illustrations of the phase trajectory, velocity and forces time histories. The main contributions are the forces and force product distribution at the switching points for this machine-tool.

Significant cost and quality metrics can be realized through the no-faults-forwards approach. This philosophy has put emphasis on early detection of defects through innovative signature analysis techniques within Powertrain Operations production lines. This paper captures the unique approach adopted on gear machining line for functionality testing of individual gears and detection of subtle gear profile anomalies leading to Noise, Vibration and Harshness (NVH) issues in fully assembled transmissions and vehicles. Gears are tested in a Vibration Based Gear Checker (VGC) in single flank engagement and operating under a torque load. The short cycle time enables feasibility for high volume measurements. The structure of Gear Checker is tuned for optimum gear profile anomaly detection**. The tuning is accomplished by structural modifications such that the Gear Checker structural natural frequencies and modes are shifted to enable a high level of excitation at harmonics of Gear Mesh Frequency (GMF) during operation. Impact testing was deployed to guide the structural adjustments for tuning. Gear checker vibration signatures for smooth and defective gears are provided; capability for detection of defective gears is demonstrated. The Gear checker frequency band vibration levels exhibit excellent correlation with the dimensional gear profile measurements by Analytical Gear Checker Coordinate Measuring Machines (CMM’s).