A Material Removal Model for Nonconstant-contact Flexible Grinding

Contact calculation is of great importance in predicting the material removal (MR) of flexible grinding process (FGP). The contact is mostly considered approximately constant in the existing MR models, while the situations that contact varies a lot after FGP are ignored. Therefore, a novel model is proposed in this paper to take those situations into consideration. Firstly, the nonconstant-contact situation is introduced. Then an equivalent method is developed to convert the nonconstant-contact grinding process into the accumulation of several quasi-constant-contact grinding processes. Based on the equivalent method, a MR model is established, and the procedure to obtain the model parameters by the finite element analysis (FEA) is introduced. In the end, the equivalent method and the MR model are tested by a series experiments of different process parameters. Results show that the proposed MR model can predict the material removal effectively for the nonconstant-contact situations.

Thermodynamic Simulation Modeling Analysis and Experimental Research of Vertical Ultrasonic Vibration Assisted EDM

Compared with traditional EDM, ultrasonic vibration assisted EDM ((UEDM)) shows better performance in machining efficiency and surface quality. But the material removal process of UEDM is complex, and there are many influencing factors, so it is difficult to describe the material removal process accurately. In this study, based on the voltage variation during UEDM processing and combined with the heat transfer theory, the material removal model of TC4 titanium alloy under the condition of single pulse vertical ultrasonic vibration UEDM was established, and the material removal process of UEDM under different amplitudes was analyzed. The machining efficiency and surface quality of UEDM with different ultrasonic energy under the condition of vertical ultrasonic vibration are obtained verified by UEDM experiments. The best ultrasonic energy under different current can be obtained by adjusting the current and ultrasonic vibration energy, which can improve the efficiency of UEDM.

Material Removal Model for Lapping Process Based on Spiral Groove Density

The increasing demand for single-crystal wafers combined with the increase in diameter of semiconductor wafers has warranted further improvements in thickness variation and material removal rate during lapping to ensure price competitiveness of wafers; consequently, the lapping process has gained the attention of researchers. However, there is insufficient research on the effect of platen grooves on the lapping process. In this study, the parameters to describe grooves were defined in order to understand their influence on the lapping process, and a material removal model was suggested based on indentation theory and subsequently experimentally validated. The results indicate that changes in groove density affect the lubrication condition at the contact interface as well as the probability of abrasive participation by varying the oil film thickness. When fabricating the groove for a lapping platen, a groove density at the critical groove density (CGD) or higher should be selected. The higher the groove density, the easier it is to avoid the CGD, and the higher is the material removal rate. The results of this study will enable engineers to design lapping platen grooves that are suitable for the production of modern semiconductor wafers.

Study on Material Removal Model by Reciprocating Magnetorheological Polishing

In this study, a new reciprocating magnetorheological polishing (RMRP) method for a flat workpiece was proposed. Based on the RMRP principle and Preston equation, the material removal rate (MRR) model of the RMRP as well as its normal polishing pressure model was established. On this basis, the effects of different technological parameters including workpiece rotation speed, eccentric wheel rotation speed and eccentricity on the MRR of the workpiece were investigated. The K9 optical flat glass was polished with the RMRP setup to verify the MRR model. The experimental results showed that the effect of workpiece rotation speed on the MRR was much greater than that of eccentric wheel rotation speed and eccentricity, and the MRR increased from 0.0115 ± 0.0012 to 0.0443 ± 0.0015 μm/min as workpiece rotation speed rose. The optimum surface roughness reduced to Ra 50.8 ± 1.2 from initial Ra 330.3 ± 1.6 nm when the technical parameters of the workpiece rotation speed of 300 rpm, the eccentric wheel rotation speed of 20 rpm and the eccentricity of 0.02 m were applied. The average relative errors between the theoretical and experimental values were 16.77%, 10.59% and 7.38%, respectively, according to the effects of workpiece rotation speed, eccentric wheel rotation speed and eccentricity on MRR.

A Novel Monitoring Method for Belt Wear State Based on Machine Vision and Image-processing Under Varying Grinding Parameters

The wear state of abrasive belt is one of the important factors affecting the grinding precision of belt grinding processes. Accurate monitoring of abrasive belt wear can not only provide the basis for accurate material removal model to improve grinding accuracy, but also can replace the belt to avoid surface burn in time. However, most of the existing abrasive belt wear monitoring methods are only suitable for monitoring the belt wear state under specific grinding parameters, are not universal. This paper introduces a method of belt wear state monitoring based on machine vision and image-processing. All the surface images of the belt were obtained from the new belt to the worn-out of the belt by a non-contact electron microscope. The features of abrasive belt surface images are extracted from RGB color space and wavelet texture. By analyzing the trendency of the extracted features in the whole grinding process, the wear state is divided into three categories. Three image features related to the wear state are selected: the first order distance of color component R, the entropy of horizontal subgraph, and vertical subgraph of texture feature. Based on the selected features and the random forest classification algorithm, the wear state classifier of abrasive belt is established. The performance of the classifier is verified and evaluated by using the data subset of different images. The results show that the proposed method has high recognition accuracy for the belt wear state, and the accuracy can reach 99% in the accelerated wear stage. The proposed method is suitable for the monitoring of the belt wear state by the surface images of the abrasive belt measured under different grinding parameters and different measurement parameters.

Research on the Mechanism of Micro-Water Jet-Guided Laser Precision Drilling in Metal Sheet

As the microporous structure has been widely used in the field of precision machining, at the same time, the requirements for the quality of microporous machining are continuously increasing. Water jet-guide laser processing technology (WJGL) has been gradually applied for its high machining precision. However, there are a few researches on the heat conduction process of WJGL processing metal materials. Therefore, it is of great significance to study the transient thermal effect of metal materials and the mechanism of material removal to improve the processing quality. In order to explore the heat conduction model of WJGL processing metal materials, this paper is based on the “element birth and death” technique in the finite element method, and the three-dimensional transient temperature field of four typical metal materials (titanium alloy, stainless steel, aluminum alloy, copper) and material removal model are established. Under this model, the removal mechanism of different metal materials and the influence of different process parameters on the temperature field distribution of the material are studied, and the influence of fixed-position drilling and helix drilling on the microporous morphology is compared. The results show that copper and aluminum alloys can obtain a larger depth-to-diameter ratio and a smaller hole taper. Titanium alloy and stainless steel have better hole roundness, lower hole edge temperature, and smaller thermal deformation. Hole roundness error and hole taper decrease with the increase of laser power. The roundness error of each material is reduced to within 10 μm when the laser power is 10 W, and the average hole taper is 8.73°.

Modeling and Analysis of the Material Removal Rate for Ultrasonic Vibration-assisted Polishing of Optical Glass BK7

The emergence of ultrasonic vibration-assisted polishing technology has effectively improved the machining accuracy and efficiency of hard and brittle materials in modern optical industry, however, the material removal mechanism of ultrasonic vibration-assisted polishing (UVAP) still needs to be further revealed. This paper focuses on the material removal mechanism of ultrasonic vibration-assisted polishing of optical glass (BK7), the application of ultrasonic vibration to axial vibration and the atomization of polishing slurry, the material removal model was established. Based on the analysis of the relationship between the nominal distance d of the polishing pad and the actual contact area distribution, the prediction of the material removal profile is realized. In addition, the effects of different parameters on the material removal rate (MRR) were analyzed, including polishing force, spindle speed, abrasive particle size, ultrasonic amplitude, feed rate, and flow-rate of polishing slurry. Based on the motion equation of abrasive particles, the trajectory of abrasive particles in the polishing slurry was simulated, and the simulation results show that the introduction of the ultrasonic vibration field changes the motion state and trajectory of embedded and free abrasive particles. The new model can not only qualitatively analyze the influence of different process parameters on MRR, but also predict the material removal depth and MRR, providing a possibility for deterministic material removal and a theoretical basis for subsequent polishing of complex curved surfaces of optical glass.

Mechanism of Debris Ejection in Atomized Dielectric-Based Electrical Discharge Machining

Atomized dielectric-based electrical discharge machining (EDM) is a novel machining process in which a thin film of moving fluid resulting from a spray acts as the dielectric in the interelectrode gap. In addition to acting as the dielectric, the thin film also helps to flush the debris away from EDM crater features and requires very small quantity of fluid in doing so. This results in significantly less dielectric consumption compared to the conventional EDM while yielding higher material removal rates and better debris flushing. This paper presents a model-based investigation of the mechanism of debris flushing in atomized dielectric-based EDM. A material removal model is used to predict the amount of debris removed in terms of number of particles ejected during a single EDM discharge. The dielectric material properties and atomization spray parameters are varied in order to produce different ejection conditions and crater geometries, respectively. Particles are ejected from the bottom of crater geometries. The model captures the asymmetry in particle motion caused by the dielectric film flow and predicts the percentage of debris flushed away from the crater center. It is also observed that crater shape and size of debris particles play a role in the amount of debris flushed away.