Integrated ANN-LWPA for cutting parameter optimization in WEDM

In this paper, we present a new approach to determinate cutting parameters in wire electrical discharge machining (WEDM), integrated artificial neuron network (ANN), and wolf pack algorithm based on the strategy of the leader (LWPA). The cutting parameters considered in this paper are pulse-on, current, water pressure, and cutting feed rate. Models of the effects of the four parameters on machining time (T_p), machining cost (C_p), and surface roughness (Ra) are mathematically constructed. An ANN-LWPA integration system with multiple fitness functions is proposed to solve the modelling problem. By using the proposed approach, this study demonstrates that T_p, C_p, and Ra can be estimated at 164.1852 min, 239.5442 RMB, and 1.0223 μm in single objective optimization, respectively. For example, as for Ra, integrated ANN-LWPA has optimized the Ra value by the reduction of 0.1337 μm (11.6 %), 0.3377 μm (24.8 %), and 0.105 μm (10.3 %) compared to experimental data, regression model, and ANN model, respectively. Consequently, the ANN-LWPA integration system boasts some advantages over decreasing the value of fitness functions by comparison with the experimental regression model, ANN model, and conventional LWPA result. Moreover, the proposed integration system can be also utilized to obtain multiple solutions by uniform design-based exploration. Therefore, in order to solve complex machining optimization problems, an intelligent process scheme could be integrated into the numeric control system of WEDM.     

Calculation of negative-pressure chip in suction-type internal chip removal system and analysis of influencing factors

Compacted graphite iron (CGI) is considered as the ideal material to make modern fuel-efficient diesel engine. Due to the vermicular or worm-like graphite distributed among the ferrite/pearlite matrix, CGI behaves better physical and mechanical properties in comparison with gray cast iron (GCI) and spherical graphite spheroidal cast iron (SGI). However, these good properties bring about the machining challenges. So it is important to appropriately select cutting parameters to machine this material with economy and efficiency. The present study investigated the influence of cutting parameters, such as cutting speed V, feed rate f, and exit angle Ψ, on workpiece material removal volume Q and cutting burr height on the entrance side H₁ and on the exit side H₂ during high-speed milling of CGI by the coated carbide tools_. On this basis, the relatively optimum high-speed cutting parameters were selected under the research condition. Cutting tool failure mechanism was also investigated with the aid of scanning electronic microscope (SEM) and energy-dispersive system (EDS) (SUPRA55, Germany) analysis. The results showed that Q, H₁, H₂, and the type of cutting burr on the exit side of the machined surface could be influenced by the cutting parameters. And the relatively optimum cutting parameters are V = 800 m/min, f = 0.25 mm/rev, and Ψ = 60°. Adhesive wear and thermal cracks which were perpendicular to the cutting edge were common wear mechanisms during the cutting process. However, with an increase in feed rate, mechanical cracks which were parallel to the cutting edge could be found on the flank face of the cutting tool.     

Sustainability analyses of cutting edge radius on specific cutting energy and surface finish in side milling processes

The aim of this work is to determine the influence of cutting edge radius on the specific cutting energy and surface finish in a mechanical machining process. This was achieved by assessing the direct electrical energy demand during side milling of aluminium AW6082-T6 alloy and AISI 1018 steel in a dry cutting environment using three different cutting tool inserts. The specific energy coefficient was evaluated as an index of the sustainable milling process. The surface finish of the machined parts was also investigated after machining. It was observed that machining with the 48.50-μm cutting edge radius insert resulted in lower specific cutting energy requirements when compared with the 68.50 and 98.72-μm cutting edge radii inserts, respectively. However, as the ratio of the undeformed chip thickness to cutting edge radius is less than 1, the surface roughness increases. The surface roughness values gradually decrease as the ratio of undeformed chip thickness to cutting edge radius (h/r _e) tends to be 1 and at minimum surface roughness values when the ratio of h/r _e equalled to 1. However, the surface roughness values increased as h/r _e becomes higher than 1. This machining strategy further elucidates the black box and trade-offs of ploughing and rubbing characteristics of micro machining and optimization strategy for minimum energy and sustainable manufacture.     

Soft computing models and intelligent optimization system in electro-discharge machining of SiC/Al composites

In this paper, a multi-variable regression model, a back propagation neural network (BPNN) and a radial basis neural network (RBNN) have been utilized to correlate the cutting parameters and the performance while electro-discharge machining (EDM) of SiC/Al composites. The four cutting parameters are peak current (I_p), pulse-on time (T_on), pulse-off time (T_off), and servo voltage (S_v); the performance measures are material remove rate (MRR) and surface roughness (Ra). By testing a large number of BPNN architectures, 4-5-1 and 4-7-1 have been found to be the optimal one for MRR and Ra, respectively; and it can predict them with 10.61 % overall mean prediction error. As for RBNN architectures, it can predict them with 12.77 % overall mean prediction error. The multivariable regression model yields an overall mean prediction error of 13.93 %. All of these three models have been used to study the effect of input parameters on the material remove rate and surface roughness, and finally to optimize them with genetic algorithm (GA) and desirability function. Then, an intelligent optimization system with graphical user interface (GUI) has been built based on these multi-optimization techniques, in which users can obtain the optimized cutting parameters under the desired surface roughness (Ra).     

Parametric optimization of CNC turning process for hybrid metal matrix composite

Machining of hybrid metal matrix composite is difficult as the particulates are abrasive in nature and they behave like a cutting edge during machining resulting in quick tool wear and induces vibration. An attempt was made in this experimental study to evaluate the machining characteristics of hybrid metal matrix composite, and a mathematical model was developed to predict the responses, namely surface finish, intensity of vibration and work-tool interface temperature for known cutting condition while machining was performed in computer numerical control lathe. Design of experiments approach was used to conduct the trials; response surface methodology was employed to formulate a mathematical model. The experimental study inferred that the vibration in V _x, V _y, and V _z were 41.59, 45.17, and 26.45 m/s², respectively, and surface finish R _a, R _q, and R _z were 1.76, 3.01, and 11.94 μm, respectively, with work-tool interface temperature ‘T’ of 51.74 °C for optimal machining parameters, say, cutting speed at 175 m/min, depth of cut at 0.25 mm and feed rate at 0.1 mm/rev during machining. Experimental results were in close conformity with response surface method overlay plot for responses.     

Investigate on milling force of cryogenic cooling processing aluminum honeycomb treated by ice fixation

Aerospace metal honeycomb materials with low stiffness had often the deformation, burr, collapse, and other defects in the mechanical processing. They were attributed to poor fixation method and inapposite cutting force. This paper presented the improvement of fixation way. The hexagonal aluminum honeycomb core material was treated by ice fixation, and the NC milling machine was used for a series of cryogenic machining. Considering the similar structure of fiber-reinforced composite materials, the milling force prediction model of ice fixation aluminum honeycomb was established, considering tool geometry parameters and cutting parameters. Meanwhile, the influence rule on milling force was deduced. The results show that compared with the conventional fixation milling method, the honeycomb processing effect is improved greatly. The machining parameters affect order on milling forces: the cutting depth is the most important, followed by the cutting width, then the spindle speed and the feed. Moreover, too small cutting depth (a_p?=?0.5 mm) will cause insufficient cutting force, while a_p?>?2 mm with higher force will reduce the processing quality of honeycomb. Simultaneously, the honeycomb orientation (θ) has a great influence on processing quality. Using the model, the predicted and measured error values of the feed and main cutting force are all small in θ?<?90°. But, the rate is 33 and 26% for the main cutting force and feed force error in θ?>?90°, respectively, while they all exhibit the smallest error in θ?=?60°. This bigger error mainly is due to unstable cutting force with obtuse angle. In addition, the tool rake angle has little influence on cutting quality in θ?<?90°, but bigger on that in θ?>?90°. Furthermore, the calculation model successfully conforms to the main deformation mechanism and influences parameters of the cutting force in the milling process, and it can accurately predict the cutting force in θ?<?90° and guide the milling process.     

Effect of tilted plate vibration on solidification and microstructural and mechanical properties of semisolid cast and heat-treated A356 Al alloy

To optimize the machining process, finding the minimum uncut chip thickness is of paramount importance in micro-scale machining. However, strong dependency of the minimum uncut chip thickness to the tool geometry, workpiece material, tool-work friction, and process condition makes its evaluation complicated. The paper focuses on determination of the minimum uncut chip thickness experimentally during micro-end milling of titanium alloy Ti-6Al-4V with respect to influences of cutting parameters and lubricating systems. Experiments were carried out on a CNC machining center Kern Evo with two flute end mills of 0.8 and 2 mm diameters being used in the tests for micro- and macro-milling, respectively. It was found that the micro-milling caused more size effect than macro-milling due to higher surface micro-hardness and specific cutting forces. The specific cutting force depended strongly on feed rate (f _z) and lubricating system, followed by depth of cut (a _p) and cutting speed (v _c), mainly in the micro-scale. All output parameters were inversely proportional to the specific cutting force. Finally, depending on different process parameters during micro-milling of Ti-6Al-4V, the minimum uncut chip thickness was found to vary between 0.15 and 0.49 of the tool edge radius.     

Improvement of AA5052 sheet properties by electromagnetic twin-roll casting

Although servo scanning 3D micro electro discharge machining (SS-3D MEDM) can achieve a high discharge ratio, the processing efficiency is still lower than expected because the discharge area at micro-electrode tip is much smaller than the area to machine. In particular, for 3D micro cavities, the processing efficiency and the machining accuracy inherently contradict each other. In this paper, an on-machine process of rough-and-finishing SS-3D MEDM is proposed with consideration that most cavity material cannot affect the dimensional accuracy. In the rough machining process, technological measures such as high discharge energy and large-diameter tool electrodes are applied to maximize processing efficiency. In the finishing machining process, a small amount of material is removed for dimensional accuracy, smooth surface, and clear edges-and-corners by changing multi-factors of machining parameters. The research is concentrated on two key techniques: rough-and-finishing border strategy and micro tool-electrode precision measurement for the process transformation from rough to finishing. Moreover, an online measurement method is proposed by the point electric contact between a micro electrode and a standard thin-rod, and the measurement accuracy was up to ±1 µm in our experimental system. Machining experiments of 3D micro cavities < 800 µm verified the proposed methods and the processes including 3D model design, rough-machining, micro-electrode measurement and fabrication, and finishing machining. The experimental results were successfully achieved as follows: the dimensional accuracy < 5 µm, surface roughness Sa0.38 µm, and the processing efficiency being improved to 2.4 times.     

Numerical and experimental investigation on the diffuser optimization of a reactor coolant pump with orthogonal test approach

The diffuser of a reactor coolant pump was optimized using an orthogonal approach with numerical simulation to improve the pump hydraulic performance. Steady simulation was conducted by solving Reynolds-averaged Naiver-Stokes equations with the SST k-ω turbulence model using CFX code. The influence of the diffuser geometric parameters, namely, S, φ, α ₄, b ₄, δ ₂, R _t and R ₄, on the pump performance were determined. L₁₈ (3⁷) orthogonal table was chosen for the optimization process. Best indicators were determined, and range analysis of energy losses, head, and efficiency at the rated condition was performed. Optimal parameters of the diffuser were S = 490 mm, φ = 36°, α ₄ = 30°, b ₄ = 200 mm, δ ₂ = 20 mm, R _t = 5 mm and R ₄ = 565 mm. The final design was experimentally tested. Simulation results showed more remarkable performance than the experimental result. However, the numerical predictions and experimental results were consistent, validating the design procedure. Loading of the impeller and diffuser blades was analyzed to investigate the direct impact on the hydrodynamic flow field. The head was 14.74 m, efficiency was 79.6 %, and efficiency of the prototype pump was 83.3 % when the model pump functioned at the rated conditions. Optimization results showed that efficiency and head were improved at the design condition.     

A current generator of the artificial lightning for full-scale tests of engineering objects

A powerful lightning current generator, which forms both individually its pulse (A), intermediate (B), long (C or C*), and repeated pulse (D) components of the negative (positive) polarity and their joint combinations in various unions, is described. Circuit and structural solutions are described that ensure (across a common active-inductive load) component A with an amplitude of no less than 200 kA and duration of up to 500 μs, component B with an average current of no less than 2 kA and duration of up to 5 ms, component C with an amplitude of no less than 800 A and duration of up to 1000 ms, component C* with an average current of 400 A and duration of up to 50 ms, and component D with an amplitude of no less than 100 kA and duration of up to 0.5 ms.     

Experimental and numerical research on magnetic pulse forming of DP600 high-strength steel with driver sheet

This study aims to investigate the effect of the three cutting parameters (rotation, feed rate, and number of tool strokes) on the values of roughness (Rk, Rpk, Rvk, Mr1, Mr2, Rp/Rt ratio, and Vo) in flexible honed crankcase cylinder of hermetic compressors. The study was based on a full factorial design 2 × 2 × 3, where the rotation and the feed rate were investigated in two levels and the number of tool strokes in three levels. The cylinders were initially honed using a multi-spindle honing machine, Gehring model. A set of three honing tools was used each with two strokes, the first for roughing (120 mesh), the second for semi-finishing (270 mesh), and the third for finishing (600 mesh). For conventional honing (CH), the depth of the cut and the feed rate were kept constant. The flexible honing process was carried out after conventional honing (C+FH) in a CNC milling machine using a Silicon Carbide flex hone tool 800 mesh and 24.2 mm nominal diameter considering 12 different cutting conditions. An electromechanical surface roughness tester was used to carry out roughness measurements. The measurement uncertainty was assessed following the recommendations of the GUM-JCGM 101. The analysis of variance (ANOVA) technique was applied, and it was observed that the number of the tool strokes was the factor that contributed the most to the improvement of the surface finish of the cylinders.     

Experimental investigations on effects of tool flank wear on surface integrity during orthogonal dry cutting of Ti-6Al-4V

Machining titanium alloy Ti-6Al-4V is a challenging task since tool flank wear adversely affects surface integrity. Quantitative effects of predetermined tool flank wear values (VB) on the surface integrity were investigated through the orthogonal dry cutting of Ti-6Al-4V. Experimental results indicated that three-dimensional (3D) average surface roughness increased with the VB ranging from 0 to 0.2 mm but decreased at VB = 0.3 mm. Given the effects of rubbing and ironing enhanced, surface material burning and plastic flows emerged on the machined surface at VB = 0.3 mm. Not only the plastic deformation layer became deeper but also the grains were greatly distorted with the increase of tool flank wear. When machined by using the tool at VB = 0.3 mm, the β phase of Ti-6Al-4V decreased near the machined surface layer than that of using the fresh tool. Besides, the depth of work-harden layer increased from 20 to 60 μm with the VB increasing from 0 to 0.3 mm. The softened layer was generated near the machined surface by using the tool at VB = 0.3 mm. In addition, the residual compressive stresses of the machined surface had the trend of decreasing. Experimental results indicated that the VB less than 0.2 mm was the most suitable condition for better surface integrity during orthogonal dry cutting of Ti-6Al-4V. This study aims at providing experimental data for optimizing the processing parameters and improving the surface integrity of Ti-6Al-4V.     

Numerical and experimental study on the flow characteristics of abrasive slurry jet with polymer additives

Based on a refined mathematical model, the hydrodynamics of abrasive slurry jet (ASJ) was numerically investigated in consideration of the non-Newtonian rheological properties of the slurry. It is found that adding polymer has significant effects on the jet properties, such as axial velocity and abrasive volume fraction. The coherence length (L _c) is proposed to measure the initial region of jet, where external air acts insignificantly on the axial velocity magnitude and thus the averaged kinetic energy is large. In the ASJ flow field, L _c is increased after adding polymer additives, while reduced as the operating pressure (P ₀) goes up. The prediction to the L _c agrees well with the experimental results, with P ₀ ranging from 1 to 16 MPa. Accordingly, an empirical formula is presented to describe the relationship between L _c and P ₀. The distinct characteristics of ASJ with polymer additives together with the verified length model of coherence region provides a qualitative and quantitative basis for the optimization of ASJ machining process, for instance, improving cutting efficiency and precision.     

Geometry simulation and evaluation of the surface topography in five-axis ball-end milling

Limited by the factors such as dynamic vibrations, cutting heat, and the use of coolant, it is difficult to measure or evaluate the surface quality in real time. Geometry simulation of the surface topography became the main method used in engineering to estimate and control the quality of the surface machining. This paper proposed a new method for geometry simulation and evaluation of a milled surface. Allowing for the coherency in geometric variations management process, the proposed method is developed based on the skin model of a workpiece. To make the simulated surface topography more realistic, the effects of locating errors, spindle errors, geometrical errors of the machine tool, and cutting tool deflections are included. And a new method is adopted to evaluate the milled surface, in which the roughness of the surface is characterized by the modal coefficients, instead of the R _a , R _z , and R _q values. At the end of this paper, measurements and cutting tests are carried out to validate the proposed method.     

Generating efficient toolpath by cutter posture optimization in five-axis machining based on inverse feedback mechanism

This paper proposes a tool posture optimization method in five-axis machining using configuration space (C-Space) transformation according to the inverse feedback message. In conventional computer numerical control (CNC) manufacture process, the machining status information transmission is in single direction, and the CNC system interpolates the toolpaths without feedback. However, considering the drives’ acceleration and deceleration, the interpolation situation would greatly affect the machining efficiency and the trajectory should be adjusted in CNC. In this case, the toolpath efficiency is deteriorated and unable to be evaluated exactly by traditional c omputer-aided manufacturing (CAM) system, where the efficiency is approximately estimated by the length of toolpath. In this paper, an inverse feedback mechanism is proposed; the simulated information on CNC system interpolation can be feedback to CAM system to help evaluate the toolpath efficiency. An axis-based dynamic confined feedrate schedule model is used to find the feed sensitive zones of the toolpaths. A C-Space method is adopted to adjust the tool postures in the sensitive zones. Several examples are given to verify the method, and the machining efficiency is raised by 10% on the whole after feedback optimization.     

Cutting-force components in turning by tools with no cutting tip

Turning by tools that are characterized by a linear or curved cutting blade but have no cutting tip is studied experimentally. The influence of the depth and cutting speed, the supply, and the cutter inclination on the components P _z and P _y of the cutting force is investigated in inverse and direct cutting.     

Impact of aspect ratio and surface heating on pollutant transport in street canyons

This paper investigated the impacts of surface heating on pollutant transport and Air Exchange Rate (AER) in street canyons of different aspect ratios (building heightH to street widthW) using computational fluid dynamic (CFD) technique. Street canyons ofH/W varied from 0.1 to 2 were employed in the study. These street-canyon aspect ratios covered a range of basic flow regimes including skimming flow (H/W=1 and 2), wake interference flow (H/W=0.5), and isolated roughness flow (H/W=0.1). Different façade/surface heating imposed different influence on the flow field and pollutant transport in street canyons of differentH/W. The AER induced by vertical velocity fluctuationAER _w, and mean vertical velocityAER _w . AER of street canyon with differentH/W and different surface heating exhibited their unique characteristics.     

3D FEM Simulation of Milling Force in Corner Machining Process

To optimize milling force and machining accuracy quality in corner milling process, the changing law of milling force is revealed by Finite Element Method(FEM). Based on DEFORM software a serial of 3D FEM models for corner milling process are devloped. Tool curved trajectory is achieved by establishing accurate relationship of tool location with milling time. Adaptive remeshing technique and iterative algorithm are adopted to ensure convergence of FEM model. Component force characteristics are revealed by analyzing FEM simulation results. It indicates that the milling force in Y direction becomes negative comparing with forces in X and Z direction. Magnitude of forces in three directions decreases with increase of spindle speed, while it increases with increase of milling feedrate. The simulation results for cutting force are in good agreement with those obtained from experiment. The FEM simulation model is first successfully established for corner milling process in this study, and the results provide a guide for optimizing cutting parameters in cutting process.     

Improvement of grinding performance and investigation of cutting parameters using a grinding mechanism with secondary rotational axis

“Grinding Mechanism having Advanced Secondary Rotational Axis” (GMASRA) is one of the newer plane surface grinding methods that have an uncommon abrasion mechanism. Unlike conventional methods, in GMASRA, there are two rotations of a wheel. The first rotation is the same as in conventional grinding methods, which is the circumferential rotation. The other rotation is the newly developed axial rotation, where the wheel rotates around itself perpendicular to its radial axis. In this study, the effects of certain cutting parameters on arithmetical mean deviation of the assessed profile (the R_a parameter) were investigated. Particularly, the effects of cutting parameters on R_a in the GMASRA grinding process were examined. The selected cutting parameters were the depth of cut, the number of axial revolutions of the wheel, and the stepover distance of the wheel. Five wheels with different properties were chosen. Additionally, GMASRA was modeled using the Taguchi orthogonal test design. In this orthogonal design, the depth of cut, the spindle speed, and the type of grinding wheel were chosen as the control factors. The effect of the specified control factors on the surface roughness was demonstrated using an analysis of variance (ANOVA) test. Results show that GMASRA produced better R_a values than the conventional method. R_a values were very close to each other in every part of the ground workpieces. According to the modeling results, the spindle speed had the highest effect on R_a, followed by the depth of cut and the type of grinding wheel. GMASRA is also very cost effective and can be adapted to most milling machines and CNC milling machines.     

Experimental prediction of multi-nozzle spray characteristics for optimal design in a lead frame etching process

The objective of this paper is to provide quantitative information of uniform impact forces on the sprayed surface in order to optimize the multi-nozzle spray etching system. Spray characteristics obtained from optical non-intrusive measurements using particle image velocimetry (PIV) and particle motion analysis system (PMAS) are measured in single- and twin-nozzle sprays, and then the multi-nozzle spray characteristics is simulated based on those of measurement data. The influences of the multi-nozzle arrangement, nozzle pitch, and pipe pitch on the spray characteristics such as droplets’ velocity, diameter, number density, impact force and their uniformity are properly evaluated. The experimental cases E1 and E2 represent single-spray nozzle A and B, respectively. For twin-spray tests, three nozzle combinations, namely E3 (nozzle A-A), E4 (nozzle A-B) and E5 (nozzle B-B) are considered with different nozzle pitches. The multi-spray simulation cases S1 and S6 represent the multi-spray cases with a homo-nozzle arrays which is consisted in all nozzles of nozzle A or B. For cases from case S2 to S5, the multi-spray cases with a hybrid-nozzle arrays which is consisted in all nozzles of nozzle A and B. The results show that the impact force increases approximately twice as much for changing of experimental test cases from E1 to E5 owing to the differences in nozzle characteristics of single-sprays and the overlap region between two adjacent nozzles. For the multi-nozzle spray simulation, the uniformity of impact force (UI) is increased with increasing the number of nozzle B which has larger orifice diameter and a wider spray angle. The optimum multi-nozzle spray arrangement is case S4 with more than 90 % UI, based on the fact that the UI is quite stable with increasing the nozzle pitch ranging from 90 mm to 145 mm.