A Thermal Model to Predict Tool Temperature in Machining of Ti-6Al-4V Alloy With an Atomization-Based Cutting Fluid Spray System

In this study a heat transfer model of machining of Ti-6Al-4V under the application of atomization-based cutting fluid spray coolant is developed to predict the temperature of the cutting tool. Owing to high tool temperature involved in machining of Ti-6Al-4V, the model considers film boiling as the major heat transfer phenomenon. In addition, the design parameters of the spray for effective cooling during machining are derived based on droplet-surface interaction model. Machining experiments are conducted and the temperatures are recorded using the inserted thermocouple technique. The experimental data are compared with the model predictions. The temperature field obtained is comparable to the experimental results, confirming that the model predicts tool temperature during machining with ACF spray cooling satisfactorily.

Effects of Tool Deflection in Accumulated Double-Sided Incremental Forming Regarding Part Geometry

Incremental forming is a flexible dieless forming process. In incremental forming, the metal sheet is clamped around its periphery. One or multiple generic stylus-type tools move along a predefined toolpath, incrementally deforming the sheet metal into a final, freeform shape. Compared with the traditional sheet metal forming process, the incremental forming process is more flexible, energy efficient and cost effective due to lower capital investment related to tooling. However, maintaining tight geometric tolerances in incremental formed parts can be a challenge. Specifically, undesired global bending is usually induced near the region between the tools and fixture resulting in a compromise in geometric accuracy. To address this issue, Accumulated Double-Sided Incremental Forming (ADSIF) is proposed, which utilizes two tools on both sides of the metal to better achieve localized deformation while simultaneously constraining global bending outside the forming area. Moreover, in ADSIF, the two tools are moving from inward to outward, and thus the tools are always forming virgin material and so as to limit forces on the already-formed part. Thus, ADSIF has a higher potential to achieve the desired geometry. Nevertheless, tool deflection due to machine compliance is still an issue that can have a considerable effect on geometric accuracy. In this work, the effect of tool deflection related to part geometry is studied for the ADSIF process. The nature of using two tools, rather than one, in ADSIF inherently implies that relative tool position is a critical process parameter. It is the region near these two tools where local squeezing and bending of the sheet occurs, the primary modes of deformation found in ADSIF. The change of relative tool positions (i.e., tool gap and relative position angle) are studied in detail by first developing an analytical model. It is concluded that the tool gap will be enlarged under the influence of tool compliance while the relative position angle is less affected. Additionally, a finite element simulation capable of modeling tool deflection is established. The comparison between the simulation results using rigid tools and deformable ones clearly demonstrated the significant influence of tool compliance on part geometry. Lastly, an axisymmetric part with varying wall angles was formed, and it was confirmed that ADSIF demonstrates improved geometry accuracy compared with conventional Double-Sided Incremental Forming.

A Method to Manufacture Repeatible Graphene-Based NEMS Devices at the Wafer-Scale

One of the major challenges in producing highly accurate graphene-based nanoelectromechanical (NEMS) resonators is the poor fabrication repeatability of graphene-based NEMS devices due to small variations in the residual stress and initial tension of the graphene film. This has meant that graphene-based nanoelectromechanical resonators tend to have large variations in natural frequency and quality factor from device to device. This poor repeatability makes it impossible to use these resonators to make accurate, high-precision force and displacement sensors or electromechanical filters. However, by actively controlling the tension on the graphene resonator it is possible both to increase repeatability between devices and to increase the force/mass sensitivity of the nanoelectromechanical resonators produced. Such tension control makes it possible to produce electrometrical filters that can be precisely tuned over a frequency range of up to several orders-of-magnitude. In order to controllably strain the graphene resonator, a microelectromechanical system (MEMS) is be used to apply tension to the graphene. The MEMS device consists of a graphene resonator connected between a set of gold electrodes. Each gold electrode is located on a different MEMS stage. Each stage is connected to a set of flexural bearings which are used to guide the motion of the stage. The displacement stage is actuated using a thermal actuator that allows a uniform and constant tension to be applied to the graphene resonator. The displacement of the actuator and the tension applied to the graphene are measured using a pair of differential capacitive actuators. The resonator is actuated electrostatically using the electrical back gate, and the resonant frequency is measured from the change in conductance of the graphene as it approaches resonance. Using this setup, it is possible to tune the natural frequency of the graphene resonator with high precision and accuracy. In addition to designing devices that can compensate for manufacturing errors in nanomanufactured devices, this paper will present several methods that can greatly expand the scope and rate at which nanomaterials-based devices can be fabricated. For example, this paper will present a transfer-free, wafer-scale manufacturing process that can be used to produce suspended graphene-based devices such as the graphene-based NEMS resonators. This new method involves the growth of graphene directly on the device wafer and release of the graphene-based device through etching of the copper catalyst layer. This method replaces traditional graphene fabrication methods, such as mechanical exfoliation, electron beam lithography, or transfer from copper foils, which are slow and require a transfer step that is the source of much of inconsistency in suspended graphene-based devices. Therefore, these new transfer-free, wafer-scale fabrication methods offer the potential to increase the throughput, yield, and repeatability of manufacturing processes for graphene resonators while reducing manufacturing costs and complexity.

Laser Cladding of Alumina Material Coating: Effects on Deposition Quality

Alumina ceramic is a high performance engineering material with excellent properties, including high melting point, high hardness and brittle nature make the alumina ceramic difficult to machine and needing high cost by using conventional manufacturing methods. Coating is an important method for alumina fabrication. The excellent properties of coatings can be used for special surface protection and ceramic parts repairing. Comparing with other coating methods, laser cladding method has many good properties to overcome the drawbacks. The reported investigations on laser cladding provide little information about alumina materials for ceramic coating. In this paper, effects of different input variables of laser cladding of alumina materials for ceramic coating were studied. And this paper for the first time reported the relationship between the properties (including surface roughness, flatness and powder efficiency) and input variables such as laser power, powder feeding rate and laser head moving rate. The obtained results will be helpful to establish efficient and effective processes for ceramics coating.

Springback Evaluation of 304 Stainless Steel in an Electrically Assisted Air Bending Operation

Driven by the automotive industry’s drive towards lightweighting, electrically assisted forming (EAF) is one of the most rapidly growing research fields in bulk deformation, and is classified under the general term “Electrically-Assisted Manufacturing (EAM)”. In EAF electric current (continuous or intermittent) is applied to a metallic sheet during the forming process, leading to numerous advantageous effects that have been studied and proven by several research groups and for different structural metals, such as reduced forming load and flow stress, increased formability, and reduction (or even elimination) of springback. Electrically-assisted bending (EAB) is a recent evolution of EAF technique, with the aim of capitalizing on the aforementioned advantages of EAF technique. In this work the effects of the EAB process on the final springback in an air bending test are identified, with the metal sheet being bent under different electrical field conditions. In addition, a comparison between the effects of applying the current during forming versus post forming are investigated. It was found that in general, higher current density (amount of current through cross sectional area of specimen (A/mm2), more frequent pulse period, and longer pulse duration all resulted in a greater degree of springback reduction. A microstructural evaluation showed no change in grain size in the presence of electric current.

Direct Printing of Capacitive Touch Sensors on Flexible Substrates by Additive E-Jet Printing With Silver Nanoinks

In this paper, techniques of direct printing of capacitive touch sensors on flexible substrates are presented. Capacitive touch sensors were fabricated by using electrohydrodynamic inkjet (E-jet) printing onto flexible substrates. Touch pad sensors can be achieved with optimized design of silver nanoink tracks. An analytical model was developed to predict touch pad capacitance, and experiments were conducted to study the effects of sensor design (e.g. number of electrodes, electrode length, and electrode distance) on the capacitance of printed coplanar capacitance touch sensors. Details of the fabrication techniques were developed to enable rapid prototype flexible sensors with simple structure and good sensitivity. The presented techniques can be used for the on-demand fabrication of different conductive patterns for flexible electronics with high-resolution and good transparency.

Predicting the Force Needed to Create a Compression Seal in an Ultra-Thin Elastoviscoplastic Membrane

In this paper, a finite element model is developed, and experimentally validated, for predicting the force required to produce a compression seal between a polycarbonate sealing boss and a 25 μm thick elastoviscoplastic hemodialysis membrane. This work leverages previous efforts to determine the conditions for hermetic sealing in a microchannel hemodialyser fabricated using hot-embossed polycarbonate microchannel laminae containing sealing boss features. Methods are developed for mechanically characterizing the thin elastoviscoplastic hemodialysis membrane. Experimental data for assessing the depth of penetration into the membrane as a function of force show an R2 value of 0.85 showing good repeatability. The average percent error was found to be −8.0% with a range between −21.9% and 4.4% error in the strain region of interest.

Fabrication of Custom Pattern Reinforced AZ31 Multilayer Composite Using Ultrasonic Spray Deposition

Mimicking the unique hierarchical, multiscale structures of natural biological materials is a promising approach to create novel materials with outstanding properties. One of the challenges, however, is the lack of scalable fabrication methods capable of making such complex structures. In this study, a multilayer nanocomposite has been synthesized by incorporating an ultrasonic spray deposition technique. The spray deposition system was used to deposit nanoparticles on substrate foils, which were consolidated to synthesize the multilayer composite. A patterned mask was used to create micro-patterns with nanoscale structures. A magnesium alloy, AZ31, foils were used as the matrix material. A mixture of nano-silicon carbide (nano-SiC) and aluminum alloy, Al6061, particles was used as the reinforcement phase in the deposited patterns. A three point bend test and a small punch test were carried out to evaluate the mechanical properties. A multilayer composite consisting of circular micro-patterns with SiC nano-structure was successfully created. The patterned composite showed an enhancement in the flexural yield strength and the flexural ultimate strength of 43% and 30% respectively, compared with the uniform multilayer composite without the patterns.

Residual Stresses in Flow Drill Screwdriving of Aluminum Alloy Sheets

With an increase in fuel economy standards and the need for reducing emissions set for the automotive sector, has resulted in the increased demand for lightweight vehicles. It is well know that the single heaviest component of a passenger vehicle is the body structure, thus has the greatest potential for significantly reducing the vehicles mass. Therefore, transitioning from steel-based bodies to ones composed of lightweight materials, such as: aluminum, magnesium and advanced high strength steels are of great interest. However, with the introduction of these new materials comes with a new means of joining, where conventional methods do not work. Therefore, this work examines a novel joining technique, flow drill screwdriving which is a thermo-mechanical process for joining aluminum and dissimilar materials. The focus of this work is to examine the residual stress distribution in a joint, because mechanical behavior and joint quality are greatly affected by the residual stress. Neutron diffraction was used for the determination of the residual stress in two samples processed with low and high fastener force. The high penetration depth of neutron radiation allows for the determination of triaxial residual stress states inside the material without destruction of the sample. It was found that the stress field around the joint location is primarily in tension, which is problematic if external forces are applied near the joint. Therefore, additional stress measurements were conducted under applied load through a lap shear test. Two load levels were applied to determine the effects on stress concentrations around the proximity of the joint.

Rock Cutter Interactions in Linear Rock Cutting

Polycrystalline diamond compact (PDC) cutter, as a major cutting tool, has been widely applied in oil and gas drilling processes. The understanding of the complex interactions at the rock and cutter interfaces are essential for the advancement of future drilling technologies, yet, these interactions are still not fully understood. Linear cutting of rock, among all the testing methods, avoids the geometric and process complexities and offer the most straightforward way to reveal the intrinsic mechanisms of rock cutting. Therefore, this paper presents an experimental study of the cutter’s cutting performance and the rock’s failure behaviors on a newly developed linear rock cutting facility. A series of rock cutting tests were designed and performed. The acquired experimental data was analyzed to investigate the influences of process parameter and the rock’s mechanical properties on chip formation and force responses.