Min Jie Wang

Calculating of the Temperature Distribution of Primary Shear Zone in Orthogonal High Speed Cutting Based on the Non-uniform Volume Moving Heat Source

A method was presented for calculating the temperature distribution of primary shear zone in orthogonal high speed cutting based on the non-uniform volume moving heat source. The temperature distribution of primary shear zone in orthogonal high speed cutting was calculated by the dynamic plastic constitutive relationship and the distribution of strain and strain rate of primary shear zone. The results show that the temperature distribution of primary shear zone is uneven, from the original plane to the cutoff plane, the cutting temperature increases continuously. In the middle of primary shear zone, the change of cutting temperature is larger, at the position near to original plant and cutoff plane, the change of cutting temperature is smaller. The cutting temperature increases with the increase of cutting speed and cutting depth, but decreases with the increase of rake angle. The comparison with existing method shows that the method presented in this paper is not only available, but also simple, convenient and more accord with the fact of orthogonal high speed cutting.

White Layer and Surface Roughness in High Speed Milling of P20 Steel

Using solid carbide straight end mills with TiAlN coating, A P20 steel at 41HRC is machined in the cutting speed range of 301 to 754m/min. The workpiece subsurface are examined using scanning electron microscope (SEM) and surface roughness tester. The results show that the white layer is produced in all of the cutting conditions tested, and the white layer thickness and surface roughness are dependent on the cutting conditions. The result obtained by analysis of variance analysis shows that feed rate and cutting speed are the most significant effects on the white layer thickness and surface roughness. Furthermore, the mathematical models for the white layer thickness and the surface roughness in high speed side milling of hardened P20 steel are proposed, respectively.

Numerical Simulation of the Cooling Process of Extruded Plastic Profiles within Vacuum Calibrators

Plastic profiles produced by extrusion die are cooled down and calibrated by calibrators, so it is an important basis to solve design problems of calibrators that how to obtain the transient temperature field of cooling process of hot plastic profiles. Based on the analysis of heat transfer ways during the cooling process, computation model, initial and boundary conditions are studied deeply, and then ANSYS is applied to simulate the cooling process of plastic profiles. Lastly, the transient temperature field of the cooling process is gain. Results of the numerical simulation show that the temperature drops of functional blocks, main-walls and inner-ribs are reduced in order of priority. Based on the results, the cooling water channels can be adjusted in order to improve the distributing uniformity of temperature field. All this is effective to the calibrators’ design.

Quality Defects and Analysis of the Microfluidic Chip Injection Molding

Compared with hot embossing, microfluidic chips injection molding is higher efficiency process and more suitable for mass production, but the quality control for injection molding is much more complex. Experiments indicate that the incomplete replication of the micro-channel and the sink mark for microfluidic chips are the chief defects to the molding. Simulation and theoretical analysis show that the stagnant flow of the melt in micro-channel and the shrinkage difference of the chips in different directions are the main reasons for molding defect. A set of new methods that how to control process parameter, design mold, and select polymer material is proposed to reduce or avoid the defects.

Microscopic Examination of Primary Shear Zone in High Speed Machining of Hardened High Strength Steel

The microstructure observation and microhardness measurement were performed on the adiabatic shear bands in primary shear zone in the serrated chips formed during high speed machining of two tempering hardness of hardened high strength steel under different cutting speeds by optical microscope, SEM, TEM and microhardness tester. The investigation results show that two types of adiabatic shear bands are formed as cutting speed increases. One is deformed band with heavy elongated microstructures generated under lower cutting speed, another is transformed band with fine grains under higher cutting speed. The increase of the cutting speed little influences on the microhardness in the transformed bands, and the microhardness in deformed band results from strain hardening, whereas transformation hardening leads to very high microhardness in transformed band.

Tool Deflection Error Regularization and Compensation in End Milling of Contour Surfaces

This paper presents a new approach of tool deflection error regularization and compensation in end milling of contour surfaces. The material removal rate (MRR) is adopted as the dominant factor of surface dimensional error. A mathematics model of determining the MRR in generalized contour surfaces machining is proposed. Feedrate scheduling methodology is applied to regulate a constant MRR along curved tool path. The expectation with the constant MRR is that it will potentially produce a constant surface dimensional error. Thus, the compensation can be conveniently achieved by offsetting the nominal finishing path. The desired MRR and corresponding offsetting value of finishing tool path are determined by a peripheral milling test. Machining results obtained in this study reveal that the proposed approach can significantly reduce the surface dimensional error and the smooth variation of feedrate can get a few variation of surface dimensional error. Comparing to the existing methods, the time-consuming iterative process in error compensation is omitted.

Adiabatic Shear Localization in High Speed Cutting of Hardened Steel

The formation and development of adiabatic shear localization in serrated chips have great significance to study of mechanism of high speed cutting. This paper investigates the theory prediction and experimental verification of the critical cutting speed of adiabatic shear localization, distribution of adiabatic shear band in serrated chip and the geometry of adiabatic shear band during high speed cutting of hardened steel. The results indicated that the theoretical prediction of critical cutting speed is consistent with the experimental results.With the increase of cutting speed, the width and spacing of adiabatic shear bands in the serrated chips decrease linearly. There are two types of adiabatic shear bands during the formation and development of adiabatic shear localization, i.e. the deformation shear band and the transformed shear band.

Experimental Study on WEDM Machining of PCD and PCBN Compacts

Some typical kinds of PCD and PCBN compacts are selected to be machined by WEDM, and a series of processing tests are taken. After machining, the surface roughness of cutting section, the processing quality of cobalt-rich interface layer and the edge of superhard material layer are measured by surface profiler and 3D microscope. The results show that processing quality is affected by superhard particle size and concentration greatly, and better processing quality can be obtained after several cutting of WEDM. The minimum sharpening allowance of PCD cutting tools can be controlled within 4~15μm after WEDM, and within 10μm for PCBN BNX20, while BZN6000 needs larger follow-up workload of sharpening.

Microscopic Observation of White Band within Shear Zone of Chip Produced during High Speed Machining of AISI 1045 Hardness Steel

To study the microstructure of white band is helpful for revealing formation mechanism of serrated chip. This paper investigates the microstructural characteristics of white bands at primary and second deformation zone within the serrated chips produced during High Speed Machining (HSM) of AISI 1045 hardened steel usingoptical microscope, SEM, TEM, and electron microprobe, X-Ray diffraction. It was found that the white bands within primary and second deformation zone consist of small equiaxed grains which formed due to dynamic recrystallization during adiabatic shear, however, martensitic transformation just only taken place within the white band in second deformation zone. The re-distribution of chemical elements between the composition phases occurred due to the combined effect of adiabatic temperature rise and high speed deformation in formation process of white band. The former is result from adiabatic shear in primary deformation zone during formation of chip, while the latter is caused by the intense shear and friction between tool and chip.

Ductile Fracture due to Adiabatic Shear during the Serrated Chip Formation in High Speed Cutting: a Microscopic Investigation

A deep understanding of adiabatic shear fracture (ASF) during serrated chip formation is essential to explore the material removal mechanism of high speed cutting (HSC). This paper aims to reveal the microscopic details of ASF in serrated chips. The material to investigate was AISI 1045 steel of different hardness grades, and the micro-structural analysis was conducted using optical and scanning electronic microscopes. The investigation showed that at the hardness of HRC50, most fractured surfaces were covered by a large number of dimples elongated along the shear direction, indicating that the fundamental cause of the serrated chip generation is the deformation localization of the adiabatic shear followed by ductile damage fracture in primary shear zones. The higher the material hardness is, the easier the adiabatic shear and ductile fracture take place. A new model was then proposed to interpret the ductile fracture due to adiabatic shear governed by the nucleation, growth and coalescence of micro-voids during serrated chip formation.