INDUCTION-HEATED TOOL MACHINING OF ELASTOMERS—PART 1: FINITE DIFFERENCE THERMAL MODELING AND EXPERIMENTAL VALIDATION

ABSTRACT

Experiments and finite difference thermal modeling of the induction-heated tool for end milling of elastomers are investigated. Three sets of experiments are designed to calibrate the contact thermocouple for the tool tip temperature measurement, study the effect of tool rotational speed on induction heat generation and convective heat transfer, and measure the tool temperature distribution for finite difference inverse heat transfer solution and validation of modeling results. Experimental results indicate that effects of tool rotation on induction heat generation and convective heat transfer are negligible when the spindle speed is below 2000 rpm. A finite difference thermal model of the tool and insulator is developed to predict the distribution of tool temperature. The thermal model of a stationary tool can be expanded to predict the temperature distribution of an induction-heated rotary tool within a specific spindle speed range. Experimental measurements validate that the thermal model can accurately predict tool tip peak temperature.     

DIRECT INTERPOLATION AND ADAPTIVE MACHINING OF COMPOUND SURFACES

ＤＩＲＥＣＴＩＮＴＥＲＰＯＬＡＴＩＯＮＡＮＤＡＤＡＰＴＩＶＥＭＡＣＨＩＮＩＮＧＯＦＣＯＭＰＯＵＮＤＳＵＲＦＡＣＥＳＺｈｏｕＹｕｎｆｅｉ，ＧａｏＳａｎｄｅ，ＺｈｏｕＪｉＨｕａｚｈｏｎｇＵｎｉｖｅｒｓｉｔｙｏｆＳｃｉｅｎｃｅａｎｄＴｅｃｈｎｏｌｏｇｙＡｂ...     

COMBINED EFFECTS OF FLANK AND CRATER WEAR ON CUTTING FORCE MODELING IN ORTHOGONAL MACHINING—PART II: BAYESIAN APPROACH-BASED MODEL VALIDATION

Flank and crater wear are the primary tool wear patterns during the progressive tool wear in metal cutting. Cutting forces may increase or decrease, depending on the combined contribution from the flank and/or crater wear. A two-dimensional (2D) slip-line field based analytical model has been proposed to model the force contributions from both the flank and crater wear. To validate the proposed force model, the Bayesian linear regression is implemented with credible intervals to evaluate the force model performance in orthogonal cutting of CK45 steels. In this study, the proposed analytical worn tool force model-based predictions fall well within the 75% credible intervals determined by the Bayesian approach, implying a satisfactory modeling capability of the proposed model. Based on the parametric study using the proposed force model, it is found that cutting forces decrease with the increasing crater wear depth but increase with the increasing flank wear length. Also, the predicted cutting forces are affected noticeably by the friction coefficients along the rake and flank faces and the ratio of crater sticking region to sliding region, and better knowledge of such friction coefficients and ratio is expected to further improve worn tool force modeling accuracy. Compared with the finite element approach, the proposed analytical approach is efficient and easy to extend to three-dimensional worn tool cutting configurations.     

SEMI-ACTIVE CONTROL OF VEHICLE SUSPENSION WITH MAGNETO- RHEOLOGICAL DAMPERS: PART Ⅰ-CONTROLLER SYNTHESIS AND EVALUATION

A modified skyhook-based semi-active controller is proposed for implementing an asymmetric control suspension design with symmetric magneto-rheological (MR) dampers. The controller is formulated in current form, which is modulated by integrating a continuous modulation and an asymmetric damping force generation algorithms, so as to effectively minimize switching and hysteretic effects from the MR-damper. The proposed controller is implemented with a quarter-vehicle MR-suspension model, and its relative response characteristics are thus evaluated in terms of defined performance measures under varying amplitude harmonic, rounded pulse and random excitations. The sensitivity of the semi-active suspension performance to variations in controller parameters is thoroughly evaluated. The results illustrate that the proposed skyhook-based asymmetric semi-active MR-suspension controller has superior robustness on the system parameter variations, and can achieve desirable multi-objective suspension performance.     

INVESTIGATING THE EFFECTS OF EDM PARAMETERS ON SURFACE INTEGRITY,MRR AND TWR IN MACHINING OF Ti–6Al–4V

Ti–6Al–4V is a kind of difficult-to-cut material with poor machinability by traditional machining methods, while electrical discharge machining (EDM) is suitable for machining titanium alloys. In this paper, three input machining parameters including pulse current, pulse on time and open circuit voltage were changed during EDM tests. To investigate the output characteristics; material removal rate (MRR), tool wear ratio (TWR) and different aspects of surface integrity for Ti–6Al–4V samples such as topography of machined surface, crack formation, white layer (recast layer) thickness and microhardness were considered as performance criteria. The variations of MRR and TWR versus input machining parameters were investigated by means of main and interaction effect plots and also verified by ANOVA results. The effect of pulse energy based on pulse on time and pulse current variations against recast layer thickness and microhardness was studied. The possibility of forming different chemical elements and compounds on the work surface after EDM process was investigated by EDS and XRD analyses. The experimental results revealed that general aspects of surface integrity for machined samples are mostly affected by pulse current and pulse on time. The approximate density of cracks, micro holes and pits on the work surface is intensively dependent on pulse energy variations. Although increase of pulse energy improves the material removal efficiency but leads to increase of average thickness and microhardness of recast layer.     

CRITICAL REVIEW ON THE ANALYTICAL METHODS FOR THE DETERMINATION OF ZWITTERIONIC ANTIEPILEPTIC DRUGS—VIGABATRIN,PREGABALIN, AND GABAPENTIN—IN BULK AND FORMULATIONS

Drugs with antiepileptic activity constitute a group of heterogeneous compounds and therefore their determination cannot follow a universal procedure. Among them, vigabatrin, pregabalin, and gabapentin are of similar nature, due to their zwitterionic structure. This structure enables similar approaches for their determination, including derivatization protocols. This article presents a thorough survey on published methods for the determination of this subgroup of antiepileptic compounds in bulk and pharmaceutical preparations. Spectrophotometric and spectrofluorimetric methods, with or without derivatization reagents, as thin-layer chromatography, high-performance liquid chromatography with various detectors, gas chromatography, capillary electrophoresis, infrared, and potentiometric methods, have been extensively applied for these compounds, providing reliable results. Additionally, the number of citations and purpose for each method were discussed with critical commentary.     

INVESTIGATION OF DOMINANT FREQUENCIES IN TRANSITION REYNOLDS NUMBER RANGE OF FLOW AROUND A CIRCULAR CYLINDER PARTⅡ: THEORETICAL DETERMINATION OF THE RELATIONSHIP BETWEEN VORTEX SHEDDING AND TRANSITION FREQUENCIES AT DIFFERENT REYNOLDS NUMBERS

An attempt has been made to explore whether the power relation can be obtained from theoretical considerations. The classical laminar and turbulent boundary layer concepts have been employed to determine appropriate values of the scaling lengths associated with vortex shedding and shear layer frequencies to predict the power law relationship with Reynolds number. The predicted results are in good agreement with experimental results. The findings will provide a greater insight into the overall phenomenon involved.     

HIGH-PERFORMANCE LIQUID CHROMATOGRAPHY AND GAS CHROMATOGRAPHY — MASS SPECTROMETRY METHODS FOR THE DETERMINATION OF IMIDACLOPRID,CHLORPYRIFOS, AND BIFENTHRIN RESIDUES IN TEA LEAVES

□ A sensitive, rapid, and reproducible high-performance liquid chromatography–diode array method and a gas chromatography/mass spectrometry method were developed to determine imidacloprid, chlorpyrifos, and bifenthrin in tea leaves. Solid-phase extraction (SPE) was employed for sample preparation. The extraction solvent used was acetonitrile:toluene (3:1, v/v). Linearity was observed in tea spiked with 0.4–6.0 µ g mL^?1 (n = 6) of imidacloprid, 0.8–15.0 µ g mL^?1 (n = 6) of chlorpyrifos, and 0.3–6.6 µ g mL^?1 (n = 6) for bifenthrin. The correlation coefficients obtained were higher than 0.99 for all pesticides. The limits of detection for imidacloprid, chlorpyrifos, and bifenthrin were 0.06, 0.12, and 0.05 mg kg^?1, respectively. The limits of quantification for imidacloprid, chlorpyrifos, and bifenthrin were 0.20, 0.40, and 0.17 mg kg^?1, respectively. Recoveries of the analytes were between 80% and 96% with RSDs <10% (intra-day and inter-day). The methods were applied to monitor pesticide residues in tea. The results obtained by both techniques indicated that their feasibility for practical applications.     

Design of a five-axis ultra-precision micro-milling machine—UltraMill. Part 2: integrated dynamic modelling, design optimisation and analysis

Using computer models to predict the dynamic performance of ultra-precision machine tools can help manufacturers to substantially reduce the lead time and cost of developing new machines. However, the use of electronic drives on such machines is becoming widespread, the machine dynamic performance depending not only on the mechanical structure and components but also on the control system and electronic drives. Bench-top ultra-precision machine tools are highly desirable for the micro-manufacturing of high-accuracy micro-mechanical components. However, the development is still at the nascent stage and hence lacks standardised guidelines. Part 2 of this two-part paper proposes an integrated approach, which permits analysis and optimisation of the entire machine dynamic performance at the early design stage. Based on the proposed approach, the modelling and simulation process of a novel five-axis bench-top ultra-precision micro-milling machine tool—UltraMill—is presented. The modelling and simulation cover the dynamics of the machine structure, the moving components, the control system and the machining process and are used to predict the entire machine performance of two typical configurations.