In the present study, electron beam welding bead-on-plate of electrolytic pitched copper (ETP-Cu) plate was carried out to study the behavior of different defects formed in the weld by varying the beam oscillation amplitudes. The defects like spattering, spiking and porosity were considered in this study. Spattering and spiking phenomena were determined with visual inspection and image analysis software, respectively. Porosity measurement was conducted with X-ray tomography. Spattering was found to decrease with the oscillation amplitude up to the optimized value and then, it showed an increasing effect with it. Spatters in the weld also contributed to the pore formation in the weld by the inside pores available in it. Spiking was found to be more dynamic, and not directly related to the oscillation amplitude. But, in general, it was increasing with the increase of amplitude. Spiking was found to have a linear relationship with mean diameter of pores, which implied that a weld with the sharper spikes was more prone to large size root pores in the weld. Mean diameter and volume fraction of the pores were tending to increase with oscillation amplitude; however, there were discontinuities in the trend at the optimized amplitude value. An optimized value of oscillation amplitude was found to be useful for suppressing these defects in the weld. However, a random oscillation amplitude could be more detrimental to the quality of the weld joint.

In this paper an inverse method is presented to evaluate the inner workpiece temperature distribution during cryogenic turning of metastable austenitic steel AISI 347 utilizing a FE representation of the process. Temperature data during the experiments is provided by thermocouples and a commercial thermo-graphy system. A constant cutting speed at two varying feeds are investigated. Inverse parameter verification by aligning simulated and experimental data in a least squares sense is achieved. A heat flux from tool to workpiece as well as heat transfer coefficients for forced convection by air and by carbon dioxide as cryogenic coolant are identified for each set of cutting parameters. Rigid body rotation in the model is considered applying convective time derivatives of the temperature field. Unphysical oscillations occurring in regions of high Péclet numbers are suppressed utilizing a streamline-upwind/Petrov-Galerkin scheme.

3D additive manufacturing, namely 3D printing, has been increasingly needed in the fabrication of biological materials and devices. Compared to traditional fabrication, direct 3D digital transformation simplifies the manufacturing process and enhances capability in geometric fabrication. In this paper, we demonstrated a rapid and low-cost 3D printing approach for “lego” assembly of micro-structured parts as an electro-transfection device. Electro-transfection is an essential equipment for engineering and regulating cell biological functions. Nevertheless, existing platforms are mainly employed to monolayer cell suspensions in vitro , which showed more failures for translating into tissues and in vivo systems constituted by 3D cells. The knowledge regarding the three-dimensional electric transport and distribution in a tissue microenvironment is lacking. In order to bridge the gap, we assembled PDMS parts molded from 3D-printed molds as the 3D-cell culture chamber, which connects arrays of perfusion channels and electrodes. Such design allows spatial and temporal control of electric field uniformly across a large volume of 3D cells (10 5 ∼10 6 cells). Most importantly, multi-dimensional electric frequency scanning creates local oscillation, which can enhance mass transport and electroporation for improving transfection efficiency. The COMSOL electrostatic simulation was employed for proof of concept of 3D electric field distribution and transport in this “lego” assembled electro-transfection device, which builds the foundation for engineering 3D-cultured cells and tissues.

Modulation assisted machining (MAM) superimposes a low-frequency oscillation onto the cutting process. The otherwise continuous cutting is transformed into a series of discrete, intermittent cutting events. A primary benefit of this process is to form discrete chips of small sizes and hence to improve chip evacuation. For applications in drilling the ability to control the chip size offers a direct route to improving process efficiency and stability. In this paper, the MAM process is evaluated for drilling applications via systematic experiments in drilling copper and Ti6Al4V with a two-flute twist drill and a single-flute gun drill. Based on the measurement of thrust force and examination of chip morphology, the continuous cutting and intermittent cutting regimes of MAM are determined experimentally in the normalized frequency and amplitude parameter space. The results are compared with those predicted by the kinematic model of MAM. Furthermore, the results clearly demonstrate the effect of chip morphology control on chip evacuation and process stability in drilling. The modulation conditions leading to the best performance in chip evacuation are discussed. The study shows that MAM is a promising process for enhancing the efficiency and stability in drilling difficult-to-cut materials and/or holes with high length-to-diameter ratio.

The task of cleaning surfaces where foreign particles are removed by mechanical scrubbing requires oscillatory motions of the cleaning tool. Selecting the optimal operation parameters is important to automate this task with robots. The operation parameters can be the tool speed, force applied to the surface, frequency and amplitude of tool oscillation, stiffness offered by the robot, etc. The optimal set of parameters will be different for different surface/stain profiles and physical limitations of the robot. A large number of cleaning experiments need to be done if we try to find the optimal parameters exhaustively in a high dimensional space. It will also take a significant number of experiments to find the right model for the cleaning function and predict the optimal cleaning parameters under supervised learning settings. Conducting large number of experiments is often not feasible. We describe a semi-supervised learning approach to reduce the number of cleaning experiments to automate the process of finding the optimal cleaning parameters for arbitrary surface/stain profiles. This generalized method is also applicable for the tasks of grinding and polishing. Results from experiments with two Kuka robots performing cleaning tasks show the validity of our approach.

The understanding of the rock-cutter interaction is essential for efficient rock cutting/drilling performed with polycrystalline diamond compact (PDC) cutters in petroleum engineering and gas exploration. Finite element modeling of the rock cutting process still remains a challenge due to the complex material properties of rock, rock fracture and chip formation phenomena and large force oscillations during the dominant brittle cutting mode. A finite element study was conducted to investigate the chip formation and force responses in two-dimensional orthogonal cutting of rock. The Drucker-Prager model that incorporates a simple shear strain failure criterion was exploited to simulate the interactions between the rock and the cutter. A fully instrumented rock cutting testbed was developed to enable the measurements of the three orthogonal force components and of the uni-axial acceleration in the cutting direction along rectilinear tool-paths to evaluate the simulation results. The chip formation phenomena and force response predictions derived by the FEM simulations were in good agreement with the experimental tests.

In cylindrical plunge grinding with conventional grinding wheels, self-excited vibrations are one of the most limiting factors in terms of productivity and process stability. Initial vibration related to the dynamic behavior of the workpiece and machine copy on the grinding wheel, causing an increasing waviness due to uneven wear and therefore, an increasing vibration of the workpiece. These self-excited oscillations lead to many expensive true-running cycles in order to ensure high workpiece quality and process stability. In this context, we present an abrasion manipulation system for active vibration control using a self-built magnetic actuator to influence the tool wear and prevent the development of wheel-sided chatter. Estimation of the grinding wheel’s surface waviness has been achieved using a surface model, which parameters are estimated by a recursive-least-square-algorithm (rls), exclusively using data of workpiece movement. Using the estimated tool-surface-signal to predict forces onto the workpiece, it is possible to compensate them by the actuator and impend the development of waves on the wheel’s surface. The concept has been applied to a standardized plunge grinding process demonstrating successful chatter suppression at a former instable process.

Past work at UNC Charlotte has demonstrated that the use of oscillating CNC toolpaths provides a reliable chip breaking alternative to conventional methods such as the use of cutting inserts with special geometries and/or adjusting machining parameters. The specific toolpath geometry and the selection of the oscillating parameters is an important step to reliably and constantly create broken chips using this new method. This paper builds on the past work and discusses the proper selection of oscillation amplitude and its effect on the ability to break chips and to achieve desired chip lengths.

A lumped parameter dynamical model is developed to describe the metal transfer for gas metal arc welding (GMAW) in the globular mode. The oscillations of molten drop are modeled using a mass-spring-damper system with variable mass and spring coefficient. An analytical solution is developed for the variable coefficient system to better understand the effect of various model parameters on the drop oscillations. The effect of welding drop motion on the observed current and voltage signals is investigated and the model agrees well with the experimental results. Furthermore, the effect of wire feeding rate (or welding current) on the metal transfer cycle time is studied and the model successfully estimates the cycle times for different wire feeding rates.

Cell damage due to the mechanical impact during laser-assisted cell direct writing has been observed and is a possible hurdle for broad applications of fragile cell direct writing. The objective of this study is to numerically investigate the bubble expansion-induced cell mechanical loading profile in laser-assisted cell direct writing. Some conclusions have been drawn as follows. The cell velocity oscillates initially and then smoothes out gradually with a constant ejection velocity. Both the cell acceleration and pressure can be very high at the beginning period of bubble expansion and then quickly approaches zero in an oscillation manner. A high viscosity can lead to an observable velocity increment at the initial stage, but the ejection velocity decreases. The pressure magnitude decreases when the distance is large, and a larger initial pressure induces a larger cell pressure as expected. This study serves as a foundation to further investigate the cell damage mechanism in laser-assisted cell direct writing to improve the effectiveness and efficiency of cell direct writing techniques.

An experimental study has been carried out to determine the effect of viscoelasticity in comparison to viscosity on micro-injection molded parts. In this study, two different polymeric materials — Polystyrene (PS) as a viscous material and High Density Poly-Ethylene (HDPE) as a viscoelastic material — have been selected to observe the effect of melt elasticity on the filling phase of micro molding based on cavity pressure of molded part. All process parameters except temperature are the same for both polymers. Process temperatures have been selected in order to match the viscosity for both polymers used. Polymer viscosity was characterized at different shear rate and temperature. Viscoelasticity of both polymers were investigated using rotational rheometry in the oscillation mode. The mold geometry with high aspect ratio has been used and the effect of viscoelasticity on cavity pressure has been discussed. It was observed that there is retardation on the response of pressure because of elastic response of material during filling. Despite the differences in slope, peak value, area, and cycle time between two curves, they share similar trends. The only difference is their response during solidifying because of material property.

To achieve the required performance of a Micro Machining Center, the control system must issue position commands with nanometer resolution, while holding the axis position with oscillations down to sub-micron level. The requirements call for a highly flexible CNC platform with unconventionally high-bandwidth servo controller. In this paper, we present a system-wide design based on an open CNC architecture with integrated digital servo drives. The proposed design incorporates customization of the digital protocol between CNC and drives, ultra-fine interpolation of the encoder signal, and novel approaches to increase the servo-loop bandwidth. A three-axis Micro Machining Center was successfully built with the proposed design, which was then proven to meet the stringent requirements with extensive dry-run and cutting experiments.

In order to improve efficiency of high-performance drilling processes while preserving tool life, the current study focuses on the design and implementation of an optimal fuzzy-control system for drilling force. The main topic of this study is the design and implementation of a networked fuzzy controller. The control algorithm is connected to the process through a multipoint interface (MPI) bus, a proprietary programming and communication interface for peer-to-peer networking that resembles the PROFIBUS protocol. The output (i.e., feed-rate) signal is transmitted through the MPI; therefore, network-induced delay is unavoidable. The optimal tuning of the fuzzy controller using a maximum known delay is based on the integral time absolute error (ITAE) criterion. In this study, a step in the force reference signal is considered a disturbance, and the goal is to assess how well the system follows set-point changes using the ITAE criterion. The main advantage of the approach presented herein is the design of an optimal fuzzy controller using a known maximum allowable delay to deal with uncertainties and nonlinearities in the drilling process and delays in the network-based application. In order to suppress the cutting-force increase, the feed rate is decreased gradually as the drilling depth increases, and the cutting force is quite well regulated at the given setpoint. The good transient response is verified by improvements in the integral time absolute error (11.77), integral time square error (2.912) and integral of absolute error (12.81) performance indices. Moreover, the experimental results without oscillations and overshoot corroborate that increases and fluctuations in force drilling can be suppressed despite an increase in drilling depth. Thus, the drilling process can be stabilized and the risk of drill failure can be greatly reduced through a fuzzy-control system.