Papers by Author: Qin He Zhang

Abstract: In this paper, experiments were conducted to investigate the effects of cylindrical electrode and helical electrode on the micro electrical discharge machining (EDM) performances during micro-hole machining of titanium alloy. The results show that the material removal rate (MRR) and the tool wear rate (TWR) increase with open circuit voltage, regardless of electrode shapes. Compared to the cylindrical electrode, helical electrode can result in higher MRR and lower relative tool wear ratio (RTWR). It can be concluded that the helical electrode is more suitable than cylindrical electrode for machining micro parts.

Abstract: As a kind of commonly used tools, junior hacksaw plays an important role in our daily life. A new kind of bimetal band saw taken low carbon medium alloy steel X32 as the backing material and the high-speed steel M42 as the saw tooth material is developed. In this paper, a new method to machine the bimetal band saw with wire electrical discharge machining (WEDM) is introduced. The processing route for common tooth profile is calculated. The fixture with specific angles is designed with CAD software (proe5.0) and machined with 3D printing technology. The experiments show that bimetal band saw machined with WEDM method has better surface quality compared with that machined through the traditional grinding process. Without any burrs, the new bimetal band saw is more resistant to wear and has a longer service life.

Abstract: Biopsy is a common medical procedure to treat and diagnose prostate cancer and breast cancer. Needle insertion is a critical step in biopsy, but the inserting force has a big effect on precision of needle insertion. A new method is presented to reduce the penetration force, and then improve the precision of needle insertion in this paper. Preloaded piezo actuator was introduced to provide biomimetic vibration for needle during needle insertion into a pork liver, just as a fascicle insertion into the skin by a mosquito. The experimental results showed that the penetration force was reduced 26.7% compared with the force without biomimetic vibration.

Abstract: The paper addresses a modelling procedure to automatically generate 2D finite element meshes of tires, together with the assignment of material property. A program is developed based on the secondary development of HyperMesh with TCL/TK language, thus achieving the automatic FE modelling starting from the AutoCAD tire cross-section profile. The model created as input file can be exported into ABAQUS directly. By automatizing the modeling process, the program can significantly reduce the modeling time and improve modeling efficiency.

Abstract: Micro EDM is used to machine micro features which are of the same size order as material microstructure of workpiece. Due to the difference of the thermal properties between the crystal grain and grain boundary, the machining performance of micro EDM varies with the crystal grain sizes of workpiece. This paper investigated on the influence of grain size and grain boundary on the machining performance of micro EDM. By drilling micro holes on two pieces of stainless steel 304 (SUS 304) which are different in grain sizes, test results revealed that the characteristics of micro EDM is influenced by grain sizes of workpiece materials significantly.

Abstract: In micro-EDM machining process, the debris of materials is difficult to be removed form the discharging gap. This problem leads the instability of discharge state, and reduces the efficiency of discharge machining. A new method of PZT incentive synchronous compression discharge channel micro-EDM is developed based on the inverse piezoelectric effect of PZT ceramics, driving by a spark discharge and PZT sync pulse power. The composition of the system is described and many experiments have been done and the effects of parameters on electrode wear ratio (EWR) have been analyzed in this paper. The results indicated that increasing the voltage and width of pulse can lower the rate of electrode wear, increase the efficiency of electric-machining, while increasing the frequency of discharge pulse can lead the increasing of EWR.

Abstract: In order to improve the accuracy of biopsy, an accurate FEM model is quite essential. To get the coefficients of the puncture target material which will be used in the Abaqus FEM analysis, the paper performed indentation test on gelatin phantom which is more stable than normal biological tissue. The Neo-Hookean and the improved Kelvin constitutive model were used to describe the mechanical properties of gelatin phantom demonstrated in the tests, including the hyperelastic and viscoelastic characteristics, then least squares method was used to fit the experimental data, finally the parameters of each constitutive model were achieved, which will be used to establish the material model in the further Abaqus FEM simulation.

Abstract: Electro-arc machining is similar with traditional electrical discharge machining (EDM) while the pulse duration of electro-arc machining is longer than that of EDM. The longer discharge was named arcing, and the arcing could lead to high material remove rate (MRR) and low tool wear ratio (TWR). Processing factors including discharge medium, tool polarity, tool material, voltage and rotational speed were chosen as input parameters on MRR and TWR. Taguchis method was used to evaluate their effects. All of the five processing factors had effects on MRR and TWR. The effects and the mechanism are also discussed.

Abstract: Micro Electrical discharge machining (Micro-EDM) is a non-traditional concept of machining. It is very suitable for machining micro parts of Micro-electromechanical Systems (MEMS). However, the application of micro-EDM is restricted for its own shortcomings such as poor material removal rate and high electrode wear ratio etc. In order to overcome this shortcoming, a new piezoelectric self-adaptive micro-EDM (PSMEDM) is developed based on inverse piezoelectric effect of piezoelectric ceramics and its working mechanism and characteristics have been analyzed in this paper. This machining method can realize the self-tuning regulation of discharge gap depending on the discharging conditions, facilitate removing the debris in the machining gap, reduce the occurrence of arcing and shorting and can realize the self-elimination of short circuits, thus the machining efficiency can be improved drastically. The tool electrode wear ratio (EWR) in machining is studied in this paper. Many experiments have been done and the effects of parameters on electrode wear ratio have been analyzed. Experimental results indicate that: 1) The EWR will rise with the increase of open-circuit voltage and main capacitance in circuit because the increase of open-circuit voltage and capacitance result in increase of single discharge energy. 2) The effect of resistance R1 on EWR is light. With the increase of resistance R1, the EWR will decrease slightly. 3) With the increase of resistance R2, the EWR will decrease firstly and then becomes to increase.

Abstract: RC-pulse generator has a simple structure and it is easy to be made and repaired. Especially RC-pulse generator can provide high frequency and low energy discharges. Therefore RC-pulse generators are used in micro-EDM field. But its high tool wear ratio and low efficiency restrict its applications. Ringing effect is considered to have effect on the defects. This research was done to study the ringing effect in electrical discharge. Taguchi method was used and discharge curves of voltage and current were recorded and analyzed. Ringing effect plays a key role in discharges and reversed current. A waveform model established with ringing effect theory is almost the same as the waveforms recorded in the experiment. Reversed current exists in almost a half time of discharge period which is the representation of ringing effect. Suitable process parameters can reduce reversed current and proper improvements could eliminate reversed current which will reduce the tool wear ratio and increase the efficiency in RC-pulse generator.