Papers by Author: Di Zhu

Abstract: Electrochemical discharge machining (ECDM), based on electrochemical machining (ECM) and electrodischarge machining (EDM), is an unconventional micro-machining technology. In this paper, with the use of water, the process of micro hole on ANSI 304 stainless steel machined by micro-ECDM with high speed rotating cathode is studied. The effects of machining conditions such as the cathode rotating speed and cathode diameter on the surface quality and accuracy of the shape are investigated. The results indicate that a relatively higher electrode rotating speed can improve the machining accuracy of the micro-holes and reduce the electrodes wear.

Abstract: In order to remove the reaction products generated from the interelectrode gap of the electrochemical micro-machining, an angle adjustable electrochemical micro-machining equipment has been developed, which consists of angle adjustment unit, feed system unit, etc. Small holes have been drilled on thin stainless steel 304 by using our developed equipment. The experimental results show that the adjusted cathode working angle and high speed of cathode rotation improves micro-ECM performance characteristics.

Abstract: . Electrochemical drilling (ECD) is a versatile process for drilling meso/micro size holes in hard-to-machine metals. Electrode insulation plays a significant part in improving ECD localization and accuracy. Electric field simulation of the side gap shows the current distribution varies remarkably with the size of insulation layer shape. Experiments are carried out to study the influence of insulation thickness (IT) on the machined hole characteristics. Poor hole was observed and identified as most likely to occur with a combination of low tool feed rate and low IT. Electrodes with the relatively thick insulating layer leads to a significant improvement in bored hole precision.

Abstract: A novel abrasion-assisted electroforming technique with the orbital motion of cathode is developed. The related theories are studied and experiments of nickel electroforming are carried out. It is confirmed that the hard particles can effectively remove the hydrogen bubbles and nodules by polishing the mandrel surface. A bright, smooth and compact deposit with the average surface roughness of about 0.12m is produced on a polyhedral mandrel.

Abstract: High frequency acoustic agitation is known to improve mass transport in conventional electroplating and electroforming. To better understand the effect of ultrasonic agitation on microelectroforms with high height-to-width aspect recessed microstructure features, electroforming of Ni from a nickel sulfamate type electrolyte under the influence of high frequency ultrasound (33KHz) at different level of power intensity from 2W/cm2 to 16W/cm2 was investigated experimentally in this paper, and then optimum operating parameters were determined basing on surface topography. A number of microelectroforming experiments assisted with acoustic agitation were further carried out to demonstrate and revise the optimum process parameters and further some metal microdevices were produced. Experimental results showed that fewer drawbacks in the microelectroforms, such as nubbles, pits, blunt-edges, and collapses were observed in the microcomponents when sonication power 12W/cm2~14W/cm2 was drawn on. Microelectroforming with ultrasonic irradiation at appropriate power intensity was characterized by better surface morphology and better uniform filling behavior.

Abstract: In this paper, the measurements of microhardness and tensile properties are performed to the electroformed Ni-Mn alloys which the mean grain size is near to or less than 100nm. It is studied that the effect of average deposition current density on microhardness and tensile properties of the alloys and the effect of post-electroforming annealing on microhardness of the alloys. The results show that with the increment of average current density, microhardness and strength of the alloys increase and elongation decreases because of the increment of Mn content and the decrement of grain size of the alloys. Microhardness of the alloys are slightly improved after annealing.

Abstract: The electro discharge machining (EDM) process is widely applied to produces surfaces of difficult-to-machine materials that require some form of grinding or finishing operation. This is conducted so as to improve the surface texture and appearance of the component’s surface. However, it is also desirable to remove the white uppermost recast layer or damaged surface layer (produced by the EDM process) in order to improve the functional performance of the surface. The finishing of the surface by traditional manual methods, especially in the operation of small and long internal cylinder surface, is both tedious and time-consuming. A novel electrically conductive diamond mounted point electrochemical grinding (DMP-ECG) process is being developed for hard passive alloys unclosed internal cylinder surface grinding. The process mechanism of DMP-ECG is introduced; the influence parameters of the surface roughness, machining accuracy, and diamond tool wear are investigated experimentally for nickel-based super alloys materials. An application of the DMP-ECG to aircraft engine component is verified in term of the optimized process parameters.

Abstract: With the development of high performance of gas turbine engine, there is a tendency to design the ribs in the cooling hole in order to improve the heat transfer and cooling efficiency in a cooling passage. This paper focuses on a machining method of the burbulated cooling hole. The cooling hole is formed by electrochemical machining (ECM) process using a shaped electrode. The ribs on the hole wall form using ECM after the shaped electrode is lowed into the bottom of the straight hole machined in advance. The experimental results indicate that machining efficiency increases obviously. Various parameters affecting the forming of the cooling hole, such as voltages, electrolyte concentrations, and the material of the workpiece, are discussed in detail. Furthermore, the flow field and temperature field of the different type of cooling hole are analyzed using computational fluid dynamics (CFD) model and finite element method. Result shows that the heat transfer coefficient in rib channels could enhances significantly

Abstract: Nickel deposits were electroformed by a novel technique, in which the mandrel rotated in hard particles (such as ceramic beads) filling between the electrodes. The microstructure and microhardness of the deposit were studied by means of SEM, XRD analysis in contrast with the traditional method. The effects of current densities on the surface morphology and microhardness of the deposit were also studied. The results showed that the polishing, impacting and disturbing of hard particles during electrodepositing could affect the microstructure and performance of the deposits. The grains were substantially refined, the preferred orientation of (200) face weakened and the microhardness significantly increased. Moreover, the presented technique could use higher current density and produce bright and smooth deposits.