Peiyi Zhao

Bio: Peiyi Zhao is an academic researcher from Harbin Institute of Technology. The author has contributed to research in topics: Vibration & Flank. The author has an hindex of 2, co-authored 2 publications receiving 34 citations.

Prediction of critical cutting depth for ductile-brittle transition in ultrasonic vibration assisted grinding of optical glasses

Abstract: The modes of material removal in machining of brittle materials consist of ductile mode and brittle mode. It is believed that there is an obvious distinction between the energy expenditures in these two modes. In this paper, the specific energies expended in ductile and brittle modes removal are modeled as a function of ultrasonic vibration parameters, grinding parameters, and work-material intrinsic properties. An approach to predict the critical cutting depth for ductile-brittle transition in ultrasonic vibration assisted grinding of glasses is proposed based on the analytical expressions for the specific cutting energies consumed in ductile and brittle modes of machining. The critical cutting depth is identified at the point where both curves of specific energies expended in ductile and brittle modes intersect. Scratching tests of BK7 and JGS1 optical glasses are conducted to verify the validity of the proposed model. Experimental results are found to correspond well with the predicted data.

Sub-surface crack formation in ultrasonic vibration-assisted grinding of BK7 optical glass

Abstract: Due to the inherent properties of high brittleness and low fracture toughness of optical glass materials, sub-surface cracks would be inevitably induced into the ultrasonic vibration assisted grinding process. Knowledge of the formation mechanisms of sub-surface cracks plays a key role in implementing high efficiency and precision machining of this kind of materials. In this work, the ultrasonic vibration assisted grinding experiments of BK7 optical glass were carried out. Processed by cross-sectional polishing and assisted by HF acid etching, quite a few sub-surface cracks with different shapes were observed beneath the machined surfaces. Categorized by the shapes and formation mechanisms, four kinds of sub-surface cracks (i.e., straight median sub-surface crack, arc median sub-surface crack, lateral sub-surface crack, and bifurcated sub-surface crack) and their corresponding formation mechanisms were both clarified. Experimental and analytical results suggest that the arc sub-surface cracks were formed by the relative shear stresses parallel to the plane of median crack frontiers, which are generated by nonsymmetric contacting between abrasive grains and glass specimen in ultrasonic vibration grinding. The bifurcation cracks were formed by the distortion in frontier fields caused by the impact effect provided by ultrasonic vibration as the abrasive grains vibrate down to the glass material. Effects of grinding and ultrasonic vibration parameters on the maximum depth of sub-surface cracks were also investigated in this work. The value of the maximum depth of sub-surface cracks showed a great dependence on the processing parameters.

A Model for Energy Consumption of Main Cutting Force of High Energy Efficiency Milling Cutter under Vibration

Abstract: Understanding the influence of the main cutting force energy consumption of the milling cutter is the basis for prediction and control of energy and machining efficiency. The existing models of cutting force energy consumption lack variables related to milling vibration and cutter teeth errors. According to the instantaneous bias of the main profile of the milling cutter under vibration, the instantaneous cutting boundary of the cutter teeth was investigated. The energy consumption distribution of the instantaneous main cutting force of the cutter tooth was studied. The model for the energy consumption of the instantaneous main cutting force of the cutter tooth and the milling cutter were both developed. The formation of energy consumption of the dynamic main cutting force of a high energy efficiency milling cutter was researched. A method for identifying the time–frequency characteristics of the energy consumption of the main cutting force under vibration was proposed and verified by experiments.

Identification of Friction Behavior Variation in the Minor Flank of Square Shoulder Milling Cutters under Vibration

Abstract: In the milling process, the friction and wear of the tooth minor flank of the square shoulder milling cutter directly affects the machined surface quality and the cutter’s life. The friction of the minor flank of the cutter tooth presents a nonlinear distribution, and its variation cannot be revealed by using a single parameter. It is difficult to identify the dynamic characteristics of the friction of the minor flank of the cutter tooth. In this work, the friction velocity model for the cutter tooth minor flank was developed by using the relative motion relationship between the flank area element and the workpiece transition surface. In accordance with the atomic excitation theory developed under the potential energy field at the friction interface of the cutter, the model for friction energy consumption under the friction velocity and thermal-stress coupling field on the minor flank of the cutter tooth was developed. Based on the mechanism of the interfacial atomic thermal vibration, the model for the friction coefficient under thermal-stress mechanical coupling was developed. Using the instantaneous friction coefficient and normal stress, the instantaneous friction distribution function of the flank was obtained. Finally, an identification method for the friction dynamic characteristics of the shoulder milling cutter tooth flank under vibration was proposed and verified by experiments.

Instantaneous friction energy consumption and its evolution of high energy efficiency milling cutter

Abstract: In the process of high-efficiency milling of titanium alloys, cutting vibration causes the frequent changes in the contact relationship between the flank face of the cutter tooth and the workpiece. The instantaneous friction speed, friction force and energy consumption of the milling cutter thus change continuously, resulting in the difficulty to precisely control the wear and life of milling cutter. This has become a bottleneck of restricting the further improvement of the cutting performance of high energy efficiency milling cutter. In this work, the model of instantaneous friction velocity and friction energy consumption of the flank face of the cutter tooth under vibration are developed. The distribution and evolution of instantaneous friction speed and friction energy consumption are studied. The proposed models are verified by high-efficiency milling experiments. The results show that the average relative error of the proposed model is 10.05%, by using this model, the influences of the cutting vibration on instantaneous friction energy consumption and friction wear boundaries could be effectively unveiled. The proposed model also could accurately describe the distribution and evolution of the above-mentioned parameters.

A model for grinding forces prediction in ultrasonic vibration assisted grinding of SiCp/Al composites

Abstract: Ultrasonic vibration assisted grinding is an advanced method for machining difficult-to-process materials such as SiCp/Al composites. This paper presents a mechanics model for predicting grinding forces in ultrasonic vibration assisted grinding of SiCp/Al composites. It consists of side grinding force model and end grinding force model. In side grinding force model, the major components are the normal force and tangential force in which the analytical expressions for the chip formation force based on Rayleigh’s probability density function, the frictional force, and the particle fracture force based on Griffith theory are established, respectively. In contrast, the axial force developed based on the indentation theory is the major component in end grinding force model. The coefficients in the proposed grinding force model were obtained through two groups of orthogonal experiments. Based on the mechanics prediction model, the relationship between grinding forces and process variables were predicted. At last, two groups of single factor experiments were conducted to verify the proposed grinding force model and experimental results were found to agree well with predicted results.

Rotary ultrasonic machining of carbon fiber reinforced plastic composites: a study on fiber material removal mechanism through single-grain scratching

Abstract: Rotary ultrasonic machining (RUM) has become an effective process for both hole making and surface grinding of carbon fiber reinforced plastic (CFRP) composites. Unlike other brittle materials such as ceramic, glass, silicon, etc., CFRP composites exhibit inhomogeneous and anisotropic properties, thereby resulting in different material removal mechanisms. However, the material removal mechanism in RUM of CFRP is still not clearly recognized in the literature. The lack of such knowledge would significantly limit the optimization and practical applications of RUM technique. In this work, single-grain diamond scratching tests without and with ultrasonic vibration are conducted to study the material removal mechanism in RUM of CFRP. Morphology of scratched groove, cross-sectional profiles, and scratching forces are analyzed. The results indicate that CFRP workpiece is extensively removed by the brittle removal mode, causing matrix damage, severe fiber pull-out, and macro-cracks in the conventional scratching test. Whereas, ultrasonic vibration-assisted scratching of CFRP leads to a larger ductile removal region before the successive brittle fractures and cracks. The fiber-matrix debonding and pullout phenomena are also remarkably reduced with only matrix buckling and fiber breakage occurring within the groove. The obtained results will enrich the understanding of the material removal mechanism in RUM of CFRP and contribute to the improvements of part quality during RUM of CFRP.

Estimation of Energy and Time Savings in Optical Glass Manufacturing When Using Ultrasonic Vibration-Assisted Grinding

Abstract: Energy and time savings are highly important aspects of green manufacturing. Ultrasonic vibration-assisted grinding (UVAG) is a high-efficiency, low-energy-consumption processing method for optical components made from hard and brittle materials. This work presents an experimental investigation of the specific grinding energy and the subsurface damage depth in UVAG of optical glasses to estimate the increased energy and time savings produced when using UVAG in optical glass manufacturing. The normal and tangential grinding forces of traditional grinding (TG) and axial UVAG processes on optical glasses were investigated for various machining parameters. The specific grinding energies during the TG and UVAG of the optical glasses were calculated and analyzed from the perspective of the energy consumption of the grinding process. The subsurface damage depths in optical glass during TG and UVAG were measured as an estimate of the machining quality, and the magnetorheological polishing spot method was used to analyze the time saved in subsequent polishing processes. The results show that UVAG can reduce energy consumption during the grinding of glass and produce significant time savings in subsequent polishing processes. The UVAG process therefore shows good potential for use in green manufacturing of optical components.