Materials Science Forum Vols. 626-627

Abstract: In this paper, a novel Pulsed-Width-Modulated (PWM) half-bridge High Speed Drilling Electrical Discharge Machining (HSDEDM) power supply has been developed. This power supply has excellent features that include minimal component count and inherent protection. This topology has an energy conservation feature and eliminates the output bulk capacitors and current limiting resistances. Energy used in the erosion process will be controlled by the switched Insulated Gate Bipolar Transistors (IGBTs) in the half-bridge network and be transferred to the gap between the tool and work-piece. The relative tool wear and machining speed of our proposed topology have been compared with that of a normal power supply with current limiting resistances.

Abstract: In Wire Electro Discharge Machine (WEDM), as the big randomicity of electro discharge, single discharge energy is various. In this paper a resistor-less and half-bridge power supply is investigated based on pulse width modulation(PWM), whose single discharge energy is equal , adopting discharge control strategy of breakdown waiting. And the experiment shows the cutting speed and surface roughness of this isopluse power supply is superior to that of traditional isofrequency power supply.

Abstract: Water-jet guided laser micromachining is the new development of laser machining. This paper analysis the action mechanism of the plasma shock wave and hollow erode effects in water-jet guided laser machining processing, on the base of the thermal effects of the laser and water-jet. And the numerical model on the action effects between the water-jet guided laser and the material was founded. Using the software ANSYS, the processing of the water-jet guided laser micromachining was simulated. This paper gave the investigation on the distributing of temperature field in processing of water-jet guided laser micromachining. And the results of the correlative experiment correspond with the simulation results.

Abstract: Using diamond saw wire could cut the seabed oil compound pipes. There are different advancing velocities according to the material of pipes; it makes the cutting and advancing velocities under the condition of harmony at the time of cutting the compound pipes underwater. First of all, the experiment system of diamond saw wire was set up by test cistern, equipment of diamond wire saw underwater, hydraulic pressure system, measuring and controlling system, diamond saw wire and single layer seabed oil compound pipes so on. Next, the cutting parameters, which include pipe sizing, working pressure, tensioning force of diamond saw wire, cutting velocity and advancing velocity were initialized and the first experimentation was done. Then, after adjusting the cutting parameters according to the analysis of cutting test, the next cutting experimentation underwater was done. In the end, the wearing capacity of diamond beads was measured and got the optimal advancing velocity which can minish the wearing capacity and prolong the cutting time of diamond beads. So, using these cutting parameters to cut the seabed oil compound pipes validated the feasibility of engineering application.

Abstract: The surface quality of components has the important influence on the components’ operational performance, characteristic of the geometry topography and statistical Characteristic is the important aspect of the surface quality. This study takes the arithmetic mean deviation of the assessed profile (Ra) to reflect the altitude characteristic of the surface profile, takes the mean width of the profile elements (Sm) to reflect the width characteristic of the surface profile, takes the material ratio of the profile (tp) to reflect the shape characteristic of the surface profile and takes the altitude density function φ(z) and autocorrelation function R(l) to reflect the statistical characteristic. Four groups of experiments are carried out in which 1Cr18Ni9Ti is taken as the material object of the test piece and test pieces with different initial surface roughness are polished. By experiment, the changing rules of the value of Ra, Sm, tp, φ(z) and R(l) after different polishing time are obtained. By analyzing the changing rules of Ra, Sm, tp, φ(z) and R(l), the influence of the Electrochemical Polishing (ECP) process on the surface geometry and statistical characteristic is obtained.

Abstract: A three-layer FEM model, based on the characteristics along the thickness direction of laminated composite metal sheets (LCMS), was developed to study the variation rules of transient deformation in the flexible forming of LCMS using plasma arc. Besides, the comparisons of the typical LCMS Q235A/1Cr13 and single layer metal sheet (SLMS) Q235A were performed. It indicates that the displacement of end point of SLMS is 0.076 mm larger than that of LCMS with the same process parameters. Moreover, the differences of X-axis plastic strain, Z-axis plastic strain along the thickness direction of LCMS decide the bending direction, the occurrence of the edge effect of LCMS during linear heating, respectively. Furthermore, Y-axis stresses of LCMS different layers undergo three dramatic changes with the maximum stress difference of 1.420×107 Pa, and the possible failure of interface delamination occurs in the bonding interface of Q235A and transition layer.

Abstract: In order to obtain micro holes with high aspect ratio, a new technique of machining deep micro holes by combining EDM (Electrical Discharge Machining) with USM (Ultrasonic Machining) in inversion installing is researched. The workpiece is over the electrode. The ultrasonic vibration is affixed to the electrode. The workpiece and electrode are all immersed in working liquid. The debris generated by EDM is dropped out the hole from the gap between the electrode and the hole wall by the gravity and the pumping effect of ultrasonic vibration, so as to increasing the machining velocity and machined depth. The structural features of the machining device are described, and the exploratory experiment is carried out. The corresponding process relations are found out, which can provide references for further study of this technique. The micro holes with larger than 25 in aspect ratio are machined.

Abstract: This study investigates the dry wire electrical discharge machining (WEDM) in multiple cut. To improve surface quality with high-speed WEDM (HS-WEDM), a new procedure as Gas-liquid Combined Multiple Cut (roughing is processed in dielectric liquid, and semi-finishing is in liquid or gas, while the finishing is in gas) is presented. Effects of pulse duration, pulse interval, peak current, offset, wire winding speed and wire length on roughness, straightness and removal rate had been studied in dry and wet conditions. Experiment results show that multiple cut with dry WEDM in semi-finishing and finishing can improve surface roughness significantly.

Abstract: ECM micro drilling with tool electrode jump motion in cycles is introduced in this work. A linear motor is employed to carry tool to jump with high acceleration in cycles. Due to the high accelerating motion of tool electrode, the electrolyte within machining gap is able to be refreshed. The Z-axis feeding motor, linear motor and DC supplier are coupled in the experimental setup and a series of micro-holes are drilled on stainless steel (1Cr18Ni9Ti) plate with thickness of 0.5mm to investigate the presented process. Experimental results shows, cycle jump motion of tool electrode, higher jump acceleration, longer jump height and shorter cycle machining time lead to better machining accuracy.

Abstract: It is becoming general that the contour of part is defined with free-form curves for abrasive waterjet cutting. In this paper, the effect of the traverse speed on cut surface quality is discussed. After that, the free-form Pythagorean Hodographs (PH) curve is defined and its main characteristics are discussed. A new CNC interpolator capable of driving the nozzle along the PH curves at the feedrate adaptable of the curvature of the contour is presented. The taper shape or jet lag can be minimized with it through the variation of the traverse speed. Experimental data indicate that a decrease of about 58 per cent in kerf taper angle can be obtained under a given condition.