Ze Sheng Lu

High Speed Wire Electrical Discharge Machining (HS-WEDM) Phenomena of Insulating Si3N4 Ceramics with Assisting Electrode

Advanced engineering ceramics are more and more widely employed in modern industries because of their excellent mechanical properties such as high hardness, high compressive strength, high chemical and abrasive resistance. This paper investigates the high speed wire electrical discharge machining (HS-WEDM) of Si3N4-based ceramics by assisting electrode method. The theory of assisting electrode method is introduced. The machining phenomena under different electrical parameters were studied and the optimized machine pulse width was got. The material removal mechanisms change with the increase in the power of single pulse.

Electrical Discharge Machining (EDM) Phenomena of Insulating ZrO2 Ceramics with Assisting Electrode

Advanced engineering ceramics are more and more widely employed in modern industries because of their excellent mechanical properties such as high hardness, high compressive strength, high chemical and abrasive resistance. These properties limited the machining to the insulated ceramics. This paper investigates the electrical discharge machining (EDM) of ZrO2-based ceramics by assisting electrode method. The theory of assisting electrode method is introduced. The machining phenomena under different electrical parameters were studied. The material removal mechanisms change with the increase in the power of single pulse. Some work-pieces have been machined successful through the assisting electrode method.

Study on Non-Burr & Sharp-Edge Protecting Grinding Method of Functional Edge

This paper researches on the formation mechanism of functional edge (e.g. throttle edge of servo valve’s valve core) during grinding process, and presents due to plastic deformation which is extruded by grinding wheel, burrs are appeared on the edge, and furthermore the edge becomes not sharp. This paper provides a non-burr & sharp-edge protecting grinding method which is named protection part method, used a protection part to protect the edge out of burrs and be sharp. Experimental data prove that utilizing protection part which is the same hardness with the processed part and an appropriate magnitude of interference parameter, this method can assure non-burr & sharp-edge protecting grinding of functional edge.

Simulation Research on Effect of Diametral Clearance of Spool Valve to Valve Orifice Discharge Characteristic

This paper studies the effect of spool valve diametral clearance of electro-hydraulic servo valve on orifice discharge characteristic. To ensure that the freely sliding between spool and sleeve, there must be given diametral clearance between spool and sleeve, which will have an impact on valve orifice discharge characteristic, this paper first individually sets up a 3D models of clearance from 0 to 5 μm, opening value from 0 to 40 μm, then calculates each model’s discharge on the condition that valve orifice’s inlet and outlet differential pressure is constant, finally according to the result of the discharge plots the diametral clearance curve of spool valve. The quantitative numerical relationship of diametral clearance and spool valve characteristic index is given after doing the analysis, Finally, an experimental verification of the simulation results is to be done to prove the simulation results are correct and reliable. The research of this paper provides the basic guidelines for spool valve designing and testing.

The Prediction Model of Cutting Forces Based on Johnson-Cook’s Flow Stress Model

Thin-walled parts with complex configurations are extensively used in aerospace and precise instrument industry. However, because of low stiffness, cutting forces, clamping forces and residual stresses in cutting have been the main factors influenced on machining accuracy of thin-walled parts. Furthermore, biggish deviation exists between practical finished surface and theoretical value as a result of machining deformation caused by cutting force namely “cutter relieving” phenomenon; besides, direct relation exists between determination of clamping force and generation of machining residual stress and cutting force, so it is necessary to build up accurate cutting force prediction model to improve the machining accuracy of thin-walled parts. Therefore, cutting force prediction model based on Johnson-Cook’s flow stress model and Oxley’s shear angle model has been developed, which takes the property of high strain, high strain ratio in area of cut and high cutting temperature into account fully and determines shear angle more accurately on the basis of force balance principle; with different cutting and tool geometric parameters existing, perform simulation and experiment studies on cutting force prediction model, verify the validity of prediction model and obtain the response rules resulted from cutting force prediction model acting on cutting and tool geometric parameters.

Study on Brittle-Ductile Transition Mechanism of Ultra-Precision Turning of Single Crystal Silicon

According to the size effect theory established on the concept of geometrically necessary dislocations and results of nano-indentation experiments, a novel brittle-ductile mechanism of ultra-precision turning of single crystal silicon is proposed. The accurate critical chip thickness is firstly calculated on the basis of theoritical analysis. A macro-micro cutting model is created based on the brittle-ductile transition mechanism. Finally, the results of study are testified through experiments.

Research of Temperature Field Simulation on Electrode Wire Wear for WEDM

The wire electrical discharge machining (WEDM) technology is widely used in the field of mold industry, aerospace, automobile and so on. However, in the discharge machining, the electrode wire wear will affect the machining accuracy and machining efficiency. There are many factors that affect the electrode wire wear, and cutting many work-piece and precise surveying are needed in the wear experiment, so the whole experiment is complex. This article analyzed the wear mechanism and found the main reason of affect the electrode wire wear by using the ANSYS software to do the temperature field simulation. The simulation parameters and simulation results were verified through experiments. The experiment showed that appropriate ratio of peak current and pulse width and the slow current rise slope can reduce the electrode wire wear significantly.

Simulation on the Wear of Micro Mill Cutter in Micro Milling

In this paper, the prediction model of micro-milling cutters in milling process is established to simulate the wear depth in the software DEFORM-3D, the chips growing up an forming process. The paper studies the wear level during the cutting process of micro milling amount of feed per tooth and spindle speed. In this paper the cutting force, cutting heat flow and the contact situation between cutting tool and workpiece are considered in the simulation model. The paper uses abrasion mathematical model related to contact stress and temperature, etc. and studies the influence of the wear depth of milling cutter through the analysis of milling temperature and metal sliding characteristics. Finally, the FEA micro –soft ware is used to verify the change of amount of feed per tooth and the spindle speed with wear depth. The paper provides reasonable parameters for using the micro milling cutter better.

Study on Fluid Process Measurement Technology

Process Measurement is a measuring method which is accompanied with process of the manufacture of work piece. This paper puts forward a new concept of fluid process measurement, and provides four types of fluid process measurements, which are, pressure pneumatic process measurement, flow pneumatic process measurement, pressure hydraulic process measurement, and flow hydraulic process measurement, and establishes the mathematical and physical modal for them. This paper also provides an example of the application of this measurement method. This measurement has a good prospect, because it can deal with the work pieces with high-precision, complex shape and which are hard to be measured in the machining process.

The Theoretical Study on the Mechanism of BDT in Machined Si Single Crystal

The mechanism of brittle-ductile transition (BDT) in machined Si single crystal is investigated by simulating dislocations emission from crack tip along (111) and (111) slip plane under mixed-mode loading. One kind of compression-shear crack is taken into account and the law of strain-energy-density-factor is applied as fracture criteria. The total number of the emitted dislocations and the number of dislocations in each slip plane at the onset of cleavage are calculated. It is found that the ratio of stress intensity factor kII to kI that the crack tip is subjected has significant effect on the BDT in machined Si single crystal. Then the results are applied to study the action of negative rake angle and edge radius of diamond tool in the ultra-precision turning.