Mode Machining Research Articles

Ultrafast laser pump X-ray probe experiments by means of asynchronous sampling

A high time resolution in the picosecond range is required for the time-domain investigation of phonon dynamics in crystalline systems. Following a recently developed scheme in the visible spectrum, this resolution can be achieved by a method called asynchronous optical x-ray sampling (ASOXS). A pulsed femtosecond laser with high repetition rate is synchronized to the electron bunches in a storage ring. A slight frequency detuning changes the mutual delay continuously, resulting in a time-domain x-ray sampling of the laser-excited system. At the synchrotron radiation source ANKA a machine mode with low momentum compaction factor αc is available, which delivers ultra-short x-ray pulses in the picosecond range.

Special features of laser processing of layered materials

This article deals with the problems concerning the quality of laser machining of workpieces of laminates of natural and artificial origin (mica, thermoplastics and thermosetting plastics, foil sheets, and composite materials). The basic disadvantages of the laser machining operations (contour cutting and drilling of holes) are the material’s delamination at the edges of the processed workpieces, its melting, and destruction. These disadvantages arise because the irradiation conditions and the machining modes are not optimal; the selected mechanism of the workpiece material’s damage in the applied technological patterns of operations is not suitable. Theoretical and experimental studies of the machining process of various laminates allowed us to formulate and realize high-quality machining principles. The modes and results of the precision machining of workpieces of mica, foiled fiberglass laminate, and hybrid composites are presented.

Effect of machining parameters on surface integrity of silicon carbide ceramic using end electric discharge milling and mechanical grinding hybrid machining

A novel hybrid process that integrates end electric discharge (ED) milling and mechanical grinding is proposed. The process is able to effectively machine a large surface area on SiC ceramic with good surface quality and fine working environmental practice. The polarity, pulse on-time, and peak current are varied to explore their effects on the surface integrity, such as surface morphology, surface roughness, micro-cracks, and composition on the machined surface. The results show that positive tool polarity, short pulse on-time, and low peak current cause a fine surface finish. During the hybrid machining of SiC ceramic, the material is mainly removed by end ED milling at rough machining mode, whereas it is mainly removed by mechanical grinding at finish machining mode. Moreover, the material from the tool can transfer to the workpiece, and a combination reaction takes place during machining.

Statistical Modeling and Optimization of Process Parameters in Electro-Discharge Machining of Cobalt-Bonded Tungsten Carbide Composite (WC/6%Co)

In this paper, attempts have been made to model and optimize process parameters in Electro-Discharge Machining (EDM) of tungsten carbide-cobalt composite (Iso grade: K10) using cylindrical copper tool electrodes in planing machining mode based on statistical techniques. Four independent input parameters, viz., discharge current (A: Amp), pulse-on time (B: μs), duty cycle (C: %), and gap voltage (D: Volt) were selected to assess the EDM process performance in terms of material removal rate (MRR: mm3/min), tool wear rate (TWR: mm3/min), and average surface roughness (Ra: μm). Response surface methodology (RSM), employing a rotatable central composite design scheme, has been used to plan and analyze the experiments. For each process response, a suitable second order regression equation was obtained applying analysis of variance (ANOVA) and student t-test procedure to check modeling goodness of fit and select proper forms of influentially significant process variables (main, two-way interaction, and pure quadratic terms) within 90% of confidence interval (p-value≤0.1) It has been mainly revealed that all the responses are affected by the rate and extent of discharge energy but in a controversial manner. The MRR increases by selecting both higher discharge current and duty cycle which means providing greater amounts of discharge energy inside gap region. The TWR can be diminished applying longer pulse on-times with lower current intensities while smoother work surfaces are attainable with small pulse durations while allotting relatively higher levels to discharge currents to assure more effective discharges as well as better plasma flushing efficiency. Having established the process response models, a multi-objective optimization technique based on the use of desirability function (DF) concept has been applied to the response regression equations to simultaneously find a set of optimal input parameters yielding the highest accessible MRR along with the lowest possible TWR and Ra within the process inputs domain. The obtained predicted optimal results were also verified experimentally and the values of confirmation errors were computed, all found to be satisfactory, being less than 10%. The outcomes of present research prove the feasibility and effectiveness of adopted approach as it can provide a useful platform to model and multi-criteria optimize MRR, Ra, and TWR during EDMing WC/6%Co material.

Status of the CMS Detector Control System

The Compact Muon Solenoid (CMS) is a CERN multi-purpose experiment that exploits the physics of the Large Hadron Collider (LHC). The Detector Control System (DCS) is responsible for ensuring the safe, correct and efficient operation of the experiment, and has contributed to the recording of high quality physics data. The DCS is programmed to automatically react to the LHC operational mode. CMS sub-detectors’ bias voltages are set depending on the machine mode and particle beam conditions. An operator provided with a small set of screens supervises the system status summarized from the approximately 6M monitored parameters. Using the experience of nearly two years of operation with beam the DCS automation software has been enhanced to increase the system efficiency by minimizing the time required by sub-detectors to prepare for physics data taking. From the infrastructure point of view the DCS will be subject to extensive modifications in 2012. The current rack mounted control PCs will be replaced by a redundant pair of DELL Blade systems. These blade servers are a high-density modular solution that incorporates servers and networking into a single chassis that provides shared power, cooling and management. This infrastructure modification associated with the migration to blade servers will challenge the DCS software and hardware factorization capabilities. The on-going studies for this migration together with the latest modifications are discussed in the paper.

A New Experimental Approach to Determination of Critical Depth in High Speed Machining of Soda-Lime Glass

Soda-Lime glass is a very hard and brittle material which is commonly used as window panels and many other common applications. Due to its low fracture toughness it is very difficult to machine and obtain good surface finish under nornal cutting conditions. Hence, machining has to be done in ways to avoid brittle fracture on the finished machined surface. Such machining is only possible under ductile mode machining conditions when the removal of material is performed in the plastic state. However, ductile mode machining requires that during machining the temperature generated in the cutting zone in the working temperature range of glass to avoid crack formation during machining. This makes all types of machining of glass an extremely challenging affair, given the current state and mode of mechanical machining. This research paper elucidates the results of an experimental study for determination of critical depth of cut as a function of cutting parameters in high speed end milling of soda-lime glass. The critical depth is defined as the depth of cut at which crack formation the material is initiated for a given high speed attachment. In determining the critical depth as well as the ductile brittle transition depth, machining was performed on a tapered surface. Vibration signals from an accelerometer in time domain (amplitude vs. time display) and the surface characteristics were used in identifying the critical depth of cut. The new method has been found to be useful in online determination of the critical depth, as well as the brittle-ductile transition depth, for generating crack-free surfaces with good surface finish in high speed end milling of soda lime glass.

A predictive model of the critical undeformed chip thickness for ductile–brittle transition in nano-machining of brittle materials

There is a distinct transition in the mode of material removal in machining of brittle materials if the undeformed chip thickness is below a critical threshold of submicron scale. It is believed that at such small scale of material removal, the energy required to extend pre-existing flaws in the microstructure of brittle material exceeds the energy required to mobilize the micro-structural dislocations and hence plastic deformation serves as the dominant mode of material removal. It is postulated that a transition in the mode of material removal in machining of brittle materials is accompanied by a corresponding shift in the representative mode of energy expenditure. Hence, machining energy is a viable parameter to characterize the modes of material removal in machining of a brittle material. This paper presents a specific cutting-energy based model to predict the ductile–brittle transition point in ultra-precision machining of brittle materials. The energy expended in brittle and ductile modes of machining is modeled as a function of work-material intrinsic properties, tool geometry and process parameters. The transition point is identified in terms of undeformed chip thickness at which the mode of energy undergoes a transition from the plastic deformation based one to the fracture based one. The validity of the proposed model is verified by single-edge cutting tests on single-crystal silicon and BK7 glass. The experimental results are found in good agreement with model results.

Modélisation forward-backward des machines synchrones à pôles saillants en régime stationnaire

This paper presents a diphase analytical modelling of salient pole synchronous machines aiming at studying 'accurately' the operating of these structures. Based on the Park transformation and the concept of forward and backward currents, the proposed model differs from usual approaches by the fact it introduces the e.m.f. into the different relations. This model is then used to study different motor and generator operating modes of salient pole synchronous machines and buried permanent magnet synchronous machines. The results confirm known practical results and also show a certain number of non trivial features.

Analysis of ductile mode and brittle transition of AFM nanomachining of silicon

The goal of this research is to investigate/monitor the machining characteristics and mode transitions during AFM nanoscratching of a brittle material such as Si (100) using acoustic emission (AE). By utilizing a specially designed AFM/nano stage setup, nano experiments were performed for various AFM tip engaging depths. With the aid of AFM and FE-SEM images, not only the typical features of each mode, such as pile-ups, chip formations, and crack propagations, but major mode changes including elastic/plastic and ductile brittle/transitions are observed and analyzed. To estimate mode transition depths, such as the yielding depth, the cutting initiating depth and the crack starting depth, theoretical models are employed and compared with the experimental results. Regarding in-process AE monitoring, various AE parameters such as AE RMS, AE count rate and AE frequency contents are generated from the monitoring signals and utilized to detect the mode states and transitions. Our results, which shows reasonably close theoretical estimations and appropriate sensitivity in AE monitoring, indicate that the proposed scheme can be used to characterize machining states and to differentiate various mode transitions from plastic deformation to the brittle crack generations during nano-scale machining.

Analytical model to determine the critical conditions for the modes of material removal in the milling process of brittle material

Brittle materials are prone to cleavage-based fracture during machining. In conventional scale machining of brittle material, crack-propagation is the dominant mechanism of material removal which results in a degraded machined surface. The challenge is to perform machining of brittle material such that the material removal occurs predominantly by chip formation rather than the characteristic brittle fracture. In this case, a high quality finish is achieved on the machined surface. Ductile-mode machining has emerged as a promising technique to finish a crack-free machined surface on macroscopically brittle materials. In the past, ductile-mode machining has mostly been performed by single-edge cutting process. This paper outlines an analytical model to determine the critical conditions for finishing a crack-free surface on brittle material by milling process. Four distinct modes of machining have been identified in the milling process of brittle material. In this model, the critical conditions for different modes of machining have been determined with respect to the relationship between the radial depth of cut and the depth of subsurface damage caused by the brittle fracture during machining. Verification tests were performed on tungsten carbide workpiece and the experimental results have validated the proposed machining model. It has been established that if the radial depth of cut is greater than the subsurface-damage depth in the milling process of brittle material, it is possible to finish a crack-free machined surface by removal of material through a combination of plastic deformation and brittle fracture. However, if the radial depth of cut is less than the subsurface damage depth, brittle fracture must be prevented in ductile-mode milling to finish a crack-free machined surface.

Evaluation of shaping accuracy upon electrochemical machining of metals

Electrochemical dimensional machining (ECDM) is based on the local high rate anodic dissolution of metals [1–5]. Upon ECDM of metals and alloys, the following results are achieved: the provision of high rates of anodic dissolution, the quality of the machined surface, and shaping accuracy both in terms of the shape and dimensions. High rates of anodic dis� solution of the majority of metals and alloys, as well as the quality of the formed surface, are implemented by way of the selection of the appropriate electrolyte solutions and modes of electrochemical machining [6]. At the same time, the achievement of satisfactory accuracy of electrochemical shaping is a far more complicated problem. The complicity of its solution is related to the fact that, for simultaneous provision of, for instance, productivity and accuracy, it is necessary to meet mutually exclusive conditions. For example, electrolytes with sufficient electric conductance and

고투과율 광학유리(SF57HHT) 초정밀절삭의 실험적 연구

Heavy flint optical glass(SF57HHT) is new material that has extremely high transmittance. Due to brittleness and high hardness, optical glass is one of the most difficult to materials for ultra-precision turning. According to the hypothesis of ductile machining, all materials, regardless of their hardness and brittleness, will undergo transition from brittle to ductile machining region below critical undefromed chip thickness. In this study, cutting test was carried out to evaluate cutting performance of heavy flint glass using ultra-precision machine with single crystal diamond bite. The machined workpiece surface topography, tool wear and surface roughness were examined using AFM and SEM. The experimental results indicate that the machining mode become the brittle mode to ductile mode, when the maximum undeformed chip thinkness is large than critical value. Tool wear mainly occurs on the flank face and its wear mechanism is dominated by abrasion. This study demonstrates the feasibility of SF57HHT by diamond turning.

Fractal multidimensional scale for controlling of the mode of dimensional electrochemical machining and evaluation of its output data

The article proposes an updated and expanded version of the previously proposed fractal multidimensional scale, allowing through the fractal dimension to regulate the mode of the dimensional electrochemical machining and evaluate the structural and dynamic characteristics of the processed surface.

A finite element model of electric machine with flux switching-over for studying the dynamic operation modes

The article is devoted to modeling the dynamic modes of a flux switching machine using the finite element method. The proposed model allows one to study highly dynamic transient processes in an electric machine under arbitrary control algorithms and take into account the geometric features of the machine in detail, the saturation, and the energy dissipation in magnets and steel.

Electrical Discharge Machining Technology and its Latest Application

Electrical Discharge Machining (EDM), as an emerging non-traditional machining technology, solves the machining problems which cannot be resolved by traditional machining methods. The working principle of EDM technology, as well as its machining features and modes are expounded, The applicable objects of EDM are analyzed, The latest application of EDM technology is analyzed. The developmental trends of EDM is forecasted finally.

A Manufacturing Model for Ball-End Mill Gashing Based on a CAM System

To facilitate the manufacturing of a ball-end mill, this paper presents an algorithm for ball-end mills gashing by using a five-axis computer numerical control (CNC) grinding machine. In this study, the normal helix models are proposed. Then, based on the cutting edge geometric model and the machining mode of the five-axis computer numerical control (CNC) grinding machine, the coordinate of the grinding point when the step of the gash out is grinded will be calculated. With the input data of ball-end mill geometry, wheels geometry, wheel setting and machine setting, the NC code for machining will be generated. Then the code will be used to simulate the ball-end mill machining in 3 Dimension. The 3D simulation system of the ball-end mill grinding is generated by VBA and AutoCAD2008. The algorithm of ball- end mill gashing can be verified by the 3D simulation system. Result shows that the algorithm presented in this paper provides a practical and efficient method for the manufacture of a ball-end mill gashing.

GaN-Based Light-Emitting Diode With Sputtered AlN Nucleation Layer

The crystal quality, electrical, and optical characteristics of GaN-based light-emitting diodes (LEDs) were improved using a sputtered AlN nucleation layer. Replacing the in situ AlN nucleation layer with the sputtered AlN nucleation layer reduced the (002) and (102) X-ray rocking curve widths of the GaN layer from 318.0 to 201.1 and 412.5 to 225.0 arcsec, respectively. The -20-V reverse leakage current of the LEDs with the sputtered AlN nucleation layer is about three orders less than that of the LEDs with the in situ AlN nucleation layer. In addition, the LEDs with sputtered AlN nucleation layer could sustain more than 60% passing yield on the ESD test of under a -600-V machine mode, whereas the LEDs with the in situ AlN nucleation layer sustained less than 40% passing yield. Moreover, the 20-mA output power of the LEDs with the sputtered AlN nucleation layer also improved by approximately 5.73% compared with that of the LEDs with the in situ AlN nucleation layer.

Comparison Study for Finished Accuracy of WEDM Process

WEDM wire-cutting processing is a special machining method using pulse discharge happenns between electrodes and workpieces. This paper have analyzed and compared the two working modes of high-speed wire-EDM machine and low-speed wire-EDM machine. For the holes or slots distributed in mould device should be machined by WEDM method and could meet technical regulation. If all the holes or slots with higher accuracy requirement are machined in one process, the form accuracy and positional accuracy mighty be achieved. The paper compared two machining methods for the special holes with experiment. The result indicates that the improved process can greatly improve the machining accuracy and this method can be used in WEDM-HS and WEDM-LS process.

Machining of shaped holes using focused laser radiation

The process of manufacturing shaped holes in rotating blank parts using focused laser radiation is investigated. It has been revealed that a hole with a specified shape and cross section can be obtained by varying the inclination angle of the blank’s rotation axis and the laser machining modes.

Compound machining of silicon carbide ceramics by high speed end electrical discharge milling and mechanical grinding

A compound process that integrates end electrical discharge (ED) milling and mechanical grinding to machine silicon carbide (SiC) ceramics is developed in this paper. The process employs a turntable with several uniformly-distributed cylindrical copper electrodes and abrasive sticks as the tool, and uses a water-based emulsion as the machining fluid. End electrical discharge milling and mechanical grinding happen alternately and are mutually beneficial, so the process is able to effectively machine a large surface area on SiC ceramic with a good surface quality. The machining principle and characteristics of the technique are introduced. The effects of polarity, pulse duration, pulse interval, open-circuit voltage, discharge current, diamond grit size, emulsion concentration, emulsion flux, milling depth and tool stick number on performance parameters such as the material removal rate, tool wear ratio, and surface roughness have been investigated. In addition, the microstructure of the machined surface under different machining conditions is examined with a scanning electron microscope and an energy dispersive spectrometer. The SiC ceramic was mainly removed by end ED milling during the initial rough machining mode, whereas it is mainly removed by mechanical grinding during the later finer machining mode; moreover, the tool material can transfer to the workpiece surface during the compound process.