Dry die-sinking EDM with mouldable graphite–polymer electrode investigation of process parameters and pulse identification methods

In this paper, a new dry die-sinking EDM polishing method using a mouldable polymer composite electrode as tool is presented. This EDM method involves two new concepts, namely: dry die sinking and the polymer composite tool. An experimental investigation was performed on the dry die-sinking EDM process to assess the feasibility of finishing down to 0.2–0.3 μm Sa, and polishing from 0.2 to 0.3 μm Sa down to the finest achievable surface finish. To simplify sample preparation, the methodology involved a reversal of the polishing process. Hence, the surface finish of a 13-mm diameter P20 tool steel disk was taken from a lapped 0.01-μm Sa surface finish up to a rougher steady-state surface finish value, assuming comparable results with conventional rough-to-fine polishing procedures. Several process parameters were evaluated such as: pulse current level I _EP, open-circuit voltage V _OC, pulse time on T _ON, pulse time off T _OFF, number of polishing cycles N _C and three pulse identification methods, for their effect on sample surface finish micrometre Sa, material removal rate MRR [cubic millimetre per hour] and electrode relative wear rate ERWR.     

Thermomechanical modeling and transient analysis of sliding contacts between an elastic–plastic asperity and a rigid isothermal flat

To investigate thermomechanical contacts between an elastic–plastic sphere and a rigid flat, simulations with slip rates ranging from 0.1 m/s to 10 m/s were performed. As interfaces with strong interfacial bonding but weak substrate were specifically targeted, slip initiation was treated as shear failure of the softer material in numerical simulations. The simulations show that both sliding friction coefficient and friction stress are significantly dependent on slip rate while the maximum static friction coefficient is independent of that. Moreover, the energy release during the transition from full stick to full slip is comparable to the shear fracture energy of the material.     

Improving Dynamic and Tribological Behaviours by Means of a Mn–Cu Damping Alloy with Grooved Surface Features

In this work, the effect of the damping component with/without individual grooved surface features on the friction-induced vibration and noise (FIVN) and surface wear performance is studied experimentally and numerically. The experimental results show that introducing a grooved damping component in the system has a significantly improved capability in suppressing the generation of FIVN. In addition, it is observed that the friction system with a grooved damping component suffers slighter wear. Numerical results show good agreement with the FIVN events observed in the experimental test. Through analysing the deformation behaviour of damping component and the contact behaviour of the friction system during friction process, it is speculated that the deformation behaviour of damping component plays a significant role in affecting the contact pressure and FIVN behaviour. In addition, linking the vibration performance and wear evolution, the connection between damping, and vibration and wear behaviour is discovered, which can further explain why the friction system with a grooved damping component shows improved capability in suppressing the FIVN of friction system.     

Finite element analysis of the head–neck taper interface of modular hip prostheses

The purpose of this paper was to identify which parameters influence the micromotion at the head–neck taper interface of modular hip prostheses. Finite element analysis was performed where 3D models of the head–neck taper interface were subjected to an assembly force, 3300 N of compression, and 100 N of tension. The micromotion increased as the head size, assembly force, and taper size increased. The micromotion also increased when a mixed alloy material combination (CoCr head and Ti6Al4V neck) was used instead of all CoCr alloy prosthesis and when the center of the femoral head was in a more superior position relative to the center of the neck taper.     

Surface roughness modeling and optimization of tungsten–copper alloys in micro-milling processes

Nowadays, the micrometric and nanometric dimensional precision of industrial components is a common feature of micro-milling manufacturing processes. Hence, great importance is given to such aspects as online metrology and real-time monitoring systems for accurate control of surface roughness and dimensional quality. A real-time monitoring system is proposed here to predict surface roughness with an estimation error of 9.5%, by using the vibration signal that is emitted during the milling process. In the experimental setup, the z-axis component vibration is measured using two different diameters under several cutting conditions. Then, an adaptive neuro-fuzzy inference system model is implemented for modeling surface roughness, yielding a high goodness of fit indices and a good generalization capability. Finally, the optimization process is carried out by considering two contradictory objectives: unit machining time and surface roughness. A multi-objective genetic algorithm is used to solve the optimization problem, obtaining a set of non-dominated solutions. Pareto front representation is a useful decision-making tool for operators and technicians in the micro-milling process. An example of the Pareto front utility-based approach that selects two points close to both extreme ends of the frontier is described in the paper. In the first case (point 1), machine time is of greater importance, and in the second case (point 2), importance is attached to surface roughness. In general terms, users can select different combinations, at all times moving along the Pareto front.     

Influences of lubrication conditions and blank holder force on micro deep drawing of C1100 micro conical–cylindrical cup

Lubrication conditions and blank holder force (BHF) are two key processing parameters in deep drawing. This is more obvious in micro forming because of the miniaturization of the specimen size. Micro conical–cylindrical cups with internal conical bottom diameter of only 0.4 mm were well formed. The influences of lubrication conditions and BHF on micro deep drawing of micro conical–cylindrical cups were investigated using a micro blanking–deep drawing compound mold. Pure copper C1100 with a thickness of 50 μm, which was annealed at 450 °C for 2 h in vacuum condition, was chosen as the specimen material. The experiments were conducted on a universal testing machine with a forming velocity of 0.05 mm/s under 4 kinds of lubrication conditions and BHF. The experimental results showed that a micro conical–cylindrical cup with internal conical bottom diameter of only 0.4 mm was well formed, and the limiting drawing ratio (LDR) reached 2.1. The polyethylene (PE) film, which decreased the drawing force and increased the drawing ratio (DR), was superior to castor oil, petroleum jelly and dry friction, and can be chosen as a proper lubricant for micro deep drawing. The rim of the micro cup seriously wrinkled when BHF was less than 4.2 N. The bottom of the micro cup cracked when the BHF was larger than 5.6 N.     

Kinematic and Dynamic Analysis of a 3-■US Spatial Parallel Manipulator

Parallel Kinematic Machines(PKMs) are being widely used for precise applications to achieve complex motions and variable poses for the end effector tool. PKMs are found in medical, assembly and manufacturing industries where accuracy is necessary. It is often desired to have a compact and simple architecture for the robotic mechanism. In this paper, the kinematic and dynamic analysis of a novel 3-PRUS(P: prismatic joint, R: revolute joint, U: universal joint, S: spherical joint) parallel manipul...     

Multi-variable measurements and optimization of GMAW parameters for API-X42 steel alloy using a hybrid BPNN–PSO approach

This research addresses multi criteria modeling and optimization procedure for Gas Metal Arc Welding (GMAW) process of API-X42 alloy. Experimental data needed for modeling are gathered as per L₃₆ Taguchi matrix. Model inputs include work piece groove angle as well as the five main GMAW process parameters. The proposed back propagation neural network (BPNN) simultaneously predicts weld bead geometry (WBG) and heat affected zone (HAZ). Image processing technique along with Bridge Cam and AWS gauges are used to take accurate measurements of WBGs and HAZs. The adequacy of the developed BPNN is established through comparisons against measured process outputs. Measurements indicate that the BPNN model simulates GMAW process with average errors of 0.33 to 0.82%. Next, the BPNN model is implanted into a particle swarm optimization (PSO) algorithm to simultaneously optimize HAZ and WBG characteristics. The hybrid BPNN–PSO determines process parameters values and groove angle so as a desired WBG is achieved while HAZ is minimized. Verification tests demonstrate that the proposed BPNN–PSO is quite efficient for in multi-criteria modeling and optimization of GMAW.     

Research on soft sensing modeling method of gas turbine’s difficult-to-measure parameters

During the operation of a gas turbine, there are many key parameters that are difficult to directly measure or to ensure measurement accuracy, which can only be measured by offline analysis methods. However, the data obtained by offline analysis has a large time lag, and it is difficult to realize real-time monitoring, control and optimization of gas turbines. In recent years, with the widespread application of data-driven methods, data-driven soft sensing technology has become a breakthrough method for online prediction of difficult-to-measure variables. Due to the time-varying nature of the gas turbine operation process, the predictive performance of the offline modeling method will inevitably degrade over time. Therefore, an adaptive soft-sensing multi-level modeling method based on the combination of the just in time learning and the ensemble learning is proposed in this paper. Taking compressor inlet air flow and turbine inlet temperature as examples, the research is carried out and verified by actual operating data. The results verify the effectiveness of the method.

     

Surface Characterization and Erosion–Corrosion Behavior of Q235 Steel in Dynamic Flow

The study aims at investigating the surface evolution and erosion–corrosion behavior of Q235 steel during erosion–corrosion process in various dynamic flows. For the purpose, true flow fields with the average flow velocities of 0.4 and 0.8 m/s and impact angles of 0°, 30° and 90° to the sample surface were successfully measured by particle image velocimetry. The topography of erosion–corrosion surface was observed by laser scanning confocal microscopy. The evolution of localized corrosion pattern is found to be determined by impact angle, i.e., round or elliptical corrosion pit corresponds to impact angle of 90° and ribbon-like corrosion pit corresponds to 0°. The deeper corrosion pits were observed at impact angle of 30° than those at the other two impact angles owing to combined effects of shear and normal stresses. Electrochemical impedance spectroscopy of samples shows smaller radiuses of capacitive loops at velocity of 0.8 m/s than those at 0.4 m/s. Equivalent circuit analysis implies unstable surface state of sample in dynamic flow. Above results indicate that the flow velocity and impact angle play the key role in the erosion–corrosion behavior of Q235 steel.     

Deformation and stress of a composite–metal assembly

Compliant structures, e.g. automobile body panel and airplane wing box are widely used. A compliant structure consists of one or more flexible parts, and these parts share the mating features among them. Because of process-induced deformation and part-to-part variations, external forces are applied during the assembly process and the parts are deformed. As a result, the final assembly is pre-stressed and its geometrical shape may deviate from the designed shape. Therefore, the assembly variation and residual stress need to be analysed in order to evaluate the structure performance. In this study, a new approach based on response surface methodology is developed. A number of organised virtual experiments are conducted with the aid of finite element analysis and regression models are fitted to the resulting data. These regression models relate part variations to assembly variation and residual stress. Monte Carlo simulation can be conveniently done using these simple regression models. The effectiveness of this method was illustrated using a composite–metal assembly. It is shown that the method presented in this paper provides a practical and reliable solution to the analysis of compliant structures.     

Measured Performance of a Highly Preloaded Three-Lobe Journal Bearing–-Part II: Dynamic Characteristics

The dynamic coefficients of a three-lobe bearing with a preload factor of 0.75 were determined. Principal and cross-coupled stiffness and damping coefficients were derived from measured responses to forced harmonic excitation. Three operating speeds were tested and, for each speed, the load was varied so that the Sommerfeld number ranged from 0.23 to 2.87. Three orbits were used for each test condition, which resulted in three data points for each condition. At each condition the nominal data points fell within the uncertainties of the data. Non-dimensionalized data at all three speeds were independent of any given Sommerfeld number; thus, the Reynolds number had little influence for the range of conditions tested. Data indicated that minimization of the uncertainties is possible with optimal orbit selection.     

Design,modeling, and control of a monolithic compliant x-y-θ microstage using a double-rocker mechanism

This paper reports the design, modeling, and control of a novel three-degrees-of-freedom piezoelectric compliant microstage by introducing a new double-rocker mechanism. The double-rocker mechanism combines a first (leverage) amplifier and a second (rocker) amplifier for double-stage displacement amplification and parasitic motion reduction. An analytical model is established to calculate the deformation behavior of the microstage, and the model is verified using finite-element analysis (FEA). An improved Prandtl-Ishlinskii (PI) model is proposed to describe piezoelectric hysteresis characteristics by optimizing the threshold selection. Then, a composite control strategy is designed to achieve precision trajectory control. The control strategy consists of a hysteresis-based feedforward controller and a proportional-integral feedback controller. A prototype of the microstage is manufactured, and an experimental system is established. Several open-loop and closed-loop experiments are conducted, and the experimental results validate the effectiveness of the proposed microstage and the designed control strategy.     

Effect of hybrid electrochemical smoothing–roller burnishing process parameters on roundness error and micro-hardness

In this paper, a novel finishing process, which integrates the merits of electrochemical smoothing (ECS) and roller burnishing (RB) for minimizing the roundness error and increasing surface micro-hardness of cylindrical parts, is proposed. Through simple equipment attachments, electrochemical smoothing–roller burnishing (ECS–RB) can follow the turning process on the same machine. To explore the optimum combinations of the ECS–RB process parameters in an efficient and quantitative manner, the experiments were designed on the basis of the response surface methodology technique. The effect of ECS–RB parameters, namely, burnishing force, applied voltage, inter-electrode gap, and workpiece rotational speed on the roundness error and surface micro-hardness was studied. From the multi-objective optimization, the optimal combination of parameter settings are burnishing force of 350 N, applied voltage of 8.2 V, inter-electrode gap of 2.75 mm, and rotational speed of 970 rpm for achieving the required lower roundness error and higher surface micro-hardness. Surface micro-hardness considerably increases about 31.5% compared to the initial surface micro-hardness, and about 2.32 μm roundness error can be achieved using the optimum combination of process parameters. Therefore, the combination of ECS and RB is a feasible process by which it potentially reduces roundness error and surface micro-hardness of axis-symmetric parts improving their reliability and wear resistance.     

Comparison of the Dynamic Behavior and Lubrication Characteristics of a Reciprocating Compressor Crankshaft in Both Finite and Short Bearing Models©

The compression force of refrigerant gas, the viscous and inertial force of the piston, and the centrifugal force of balancer weight induce rotating whirl of the crankshaft in a small reciprocating compressor. It is necessary to develop an analytical model for the accurate prediction of dynamic behavior of the compressor mechanism having coupled characteristics between the piston and crankshaft. The reciprocating compression mechanism is dynamically modeled by considering the viscous frictional force of a piston and the variation in the contact length of the piston-cylinder system, and then numerical analysis is performed for the coupled dynamic behavior of the piston and crankshaft. For the accurate predictions of the dynamic behavior and characteristics of lubrication of the crankshaft-journal bearing system, a finite bearing model is adopted. In addition, the dynamic trajectory and characteristics of lubrication of the crankshaft such as power consumption and oil leakage are compared between the finite bearing model and the short bearing approximation. The influences of the variation in the radial clearance of the journal bearings, lubricant viscosity, and mass and mass moment of inertia of the piston and connecting rod on the dynamic behavior and characteristics of lubrication such as power consumption and oil leakage are investigated.