This study reports on the numerical model development for the prediction of the material removal rate and surface roughness generated during electrical discharge machining (EDM). A simplified 2D numerical heat conduction equation along with additional assumptions, such as heat effect from previously generated crater on a subsequent crater and instantaneous evaporation of the workpiece, are considered. For the material removal rate, an axisymmetric rectangular domain was utilized, while for the surface roughness, a rectangular domain where every discharge resides at the end of previous crater was considered. Simulated results obtained by solving the heat equation based on a finite element scheme suggested that results are more realistic by considering instantaneous evaporation of the material from the workpiece and the effect of residual heat generated from each spark. Good agreement between our model and previously published data validated the newly proposed models and demonstrate that instantaneous evaporation, as well as residual heat, provide more realistic predictions of the EDM process. Machines 2019, 7, 47 2 of 17 model where the problem of heat conduction for both infinite and semi-infinite bodies with a constant heat source was solved. DiBitonto et al. [7] developed a point heat source cathode erosion model. Since spherical symmetry was considered in their model, the heat transfer equation in spherical coordinates was implemented. In their model, the constant cathode energy fraction of 0.183 was assumed. In their subsequent study [8], they developed an anode erosion model, by assuming a disk heat source. Beck et al.[9] developed a model to find the temperature distribution of a semi-infinite cylinder with a constant heat source and an insulated boundary. Since this model was not developed particularly for the EDM process, the heat fraction to the workpiece is not considered.Process performances of EDM have been investigated by many researchers. D'Urso et al.[10] defined a process index based on process parameters and material properties to analyze the process and geometric indexes of micro-EDM process. D'Urso and Ravasio [11], based on a material-technology index (MTI), studied the process performance of micro-EDM. Tsai and Masuzawa [12] analyzed the electrode wear of different electrode materials in a micro-EDM process. Based on experimental results, a new wear resistance index based on modified boiling and melting points for the evaluation of erosion performance was proposed. Marafona and Araujo [13] proposed an additive model to investigate the influence of hardness on the material removal rate and surface roughness. Alshemary et al. [14] studied effects of different process parameters on fabricating cylindrical holes by wire-EDM. Mandal et al. [15] investigated the surface integrity of wire-EDM. They reported that both grinding and etching-grinding techniques removed the recast layer, and hence improved the surface integrity. Prakash et al. [16] proposed altering the EDM process for coating TiO 2 -T...

A coupled surface response optimization method with a three-dimensional finite volume method is adopted in this study to identify five independent geometric variables of the die interior that provides a design with the lowest velocity variance at the exit of the coat-hanger extrusion die. Two of these five geometric variables represent the manifold dimension while the other three variables represent the die profile. In this method, B-spline fitting with four points was used to represent the die profile. A comparison of the optimized die obtained in our study and the die with a geometry derived by a previous theoretical work shows a 20.07% improvement in the velocity distribution at the exit of the die.

In the polymer sheet processing industry, the primary objective when designing a coat-hanger die is to achieve a uniform velocity distribution at the exit of the extrusion die outlet. This velocity distribution depends on the internal flow channels of the die, rheological parameters and extrusion process conditions. As a result, coat-hanger dies are often designed for each polymer based on its individual rheological data and other conditions. A multi-rheology method based on a flow network model and the Winter–Fritz equation is proposed and implemented for the calculation, design and optimization of flat sheeting polymer extrusion dies. This method provides a fast and accurate algorithm to obtain die design geometries with constant wall-shear rates and optimal outlet velocity distributions. The geometric design when complemented and validated with fluid flow simulations could be applied for multi-rheological fluid models such as the power-law, Carreau–Yasuda and Cross. This method is applied to sheet dies with both circular- and rectangular-shaped manifolds for several rheological fluids. The designed geometrical parameters are obtained, and the associated fluid simulations are performed to demonstrate its favorable applicability without being limited to only the power-law rheology. The two such designed dies exhibit 32.9 and 21.5 percent improvement in flow uniformity compared to the previous methods for dies with circular and rectangular manifolds, respectively.

We apply the non-equilibrium molecular dynamics approach (NEMD) to study thermal rectification in a hybrid graphene-carbon nitride system (G − C 3 N) under a series of positive and negative temperature gradients. In this study, the effects of temperature difference, between two baths (∆T), and sample size on thermal rectification are investigated. Our simulation results indicate positive correlation between thermal rectification and temperature difference for ∆T > 60 K, and high thermal rectification values, up to around 50% for ∆T = 100 K. Furthermore, this behavior remains practically consistent among different sample lengths. The underlying mechanism leading to a preferable direction for phonons is calculated using phonon density of states (DOS) on both sides of the G − C 3 N interface, and the contributions of in-plane and out-of-plane phonon modes in total thermal rectification are also explored.

In the design of coat hanger extrusion dies, the main objective is to provide a uniform flow rate at the die exit. Previously, a multi-rheology isothermal method model for coat hanger extrusion dies was developed to reach this objective. Polymer melts in extrusion dies commonly experience high shear rates. Viscous dissipation rooted by high shear rate may lead to significant temperature differences across the die. Due to temperature-dependency of viscosity, temperature differences may lead to nonuniform flow rates, which may significantly affect the flow rate at the die exit. As a result, a new design method is proposed to take into account the effects of temperature and viscous dissipation in the design of coat hanger dies. Although more non-Newtonian fluid rheology models can be adapted in the proposed study, as demonstration, temperature-dependent power-law and Carreau–Yasuda models are adapted in this study. Performances are compared with our isothermal method published earlier. In addition, the novel nonisothermal method is comprehensively examined where the effect of viscous dissipation is studied through Brinkman number of extrusion die. It is demonstrated that, for a low Brinkman number, both isothermal and nonisothermal design give similar flow uniformity level. However, for higher Brinkman numbers, the proposed nonisothermal method produces a design with more desirable velocity uniformity level along with a maximum improvement of 5.24% over the isothermal method. In addition, dependency of flow field on temperature, due to temperature-dependent viscosity, is studied, and it is demonstrated that fully-developed velocity profile changes as temperature increases along the flow channel. Moreover, the effect of the temperature sensitivity parameter in temperature-dependent non-Newtonian models is considered. It is demonstrated that the temperature boundary condition with the Biot number of 1.0 gives adequate results for lower values of the temperature sensitivity parameter.