Advanced Materials Research Vol. 797

Abstract: There is a vitrified bond CBN point grinding wheel with coarse grinding area slope angle θ. This new grinding wheel has higher removing rate and better machining accuracy than conventional wheels. The design and manufacture principle of the new grinding wheels are studied in this paper. These wheels with different coarse grinding area slope angle θ are used to grind the stepped shaft of QT700 with a series of grinding parameters.VHX-1000E microscopic system and Micromeasure system are used to measure the surface quality of workpiece. In the same group of grinding parameters, compare the effect of these different wheels on surface roughness. The effect of deflection angle α on surface roughness is generalized.

Abstract: In the low-speed grinding process, the force generated when the wheel grinding the workpiece is the result of sliding friction, plough and cutting. While in the actual study, the cutting process has attracted extensive attention. Impact effect to the entire grinding process on the contact is ignored so that the error exists between the calculation grinding force and the measured grinding force. Basing on the shock effect to the grinding process, the paper divides the contact area into impact area and cutting area. And the model of impact load generated from single grit is built. Moreover, the grinding force theoretical calculation model and total grinding force mathematical model is also constructed by analyzing the impact load affecting on the grinding force mechanism. Finally experimental study verifies the correctness of theoretical analysis.

Abstract: Zirconia ceramic widely applied in the fields of electronics, instrumentations and mechanical manufacture for its good physical and chemical properties. The ultraprecision lapping technology for the Zirconia ceramic is studied in this paper, and the influence of the different lapping parameters such as slurry, load and lapping velocity on the surface roughness of Zirconia ceramic is discussed. The evolution of surface construction is observed with the microscope to analysis the material removal mechanism. An extremely smooth surface with roughness 6.55nm Ra is obtained in the ultraprecision process. It is also found that the gap in the material will limit improvement of surface roughness and a better surface roughness of 4.72nm Ra was observed when using more compactly material lapped by same method.

Abstract: The Quartz substrates are widely used in various fields, and the requirement for the surface quality of quartz substrate is higher than ever before. This paper focuses on the ultra-precision polishing technology for the quartz substrates, and the material removal mechanism in the process of ultra-precision polishing is discussed. The results showed that an extremely smooth surface of quartz substrate was obtained in the ultra-precision polishing process, and the best surface roughness reached Ra 0.82nm. Meanwhile, the thickness can be controlled very well.

Abstract: The hydrostatic seal rings are one of the most important components used in reactor coolant pumps. They are generally made of hard materials such as silicon nitride, alumina, silicon carbide and tungsten carbide. Meanwhile, the form error should be within the length of one to two helium light bands and the surface roughness should be in the scale of nanometers, which make them difficult to machining. In order to solve this problem, a high accuracy grinding method using a large cup wheel had been proposed and the tilt angle of the cup wheel spindle become a crucial factor affecting the ground form errors. This paper addresses a novel method for high-accuracy calibrating the tilt angle of the cup wheel spindle to fit the extremely shallow taper angle of the seal ring conical surface, and the mathematical model is established incorporating a standard optical flat with a high-accuracy laser displacement sensor. The practicability of this method is verified by grinding a seal ring sample with the outer diameter is 200 mm and the taper angle is 700 μrad. It is found that the taper angle error is only 1.72 μrad and the radical profile error of the conical surface is about 0.22 μm.

Abstract: With the development of the coating technology, coated tools have been widely used in processing industries. Thread turning is one of its applications. The performance of coated thread inserts varies with the change of coating material, coating thickness, matrix material and tool structure. Two tungsten-cobalt type alloy matrix, TiAlN coated thread inserts with different coating thickness, rake face type had been employed to conduct the thread turning experiments. By analyzing the cutting forces, chip formation and tool wear, it was found that insert with coating thickness of 4.35 μm would result in less tool wear under MQL condition, smaller cutting force, better chip morphology under dry condition compared with insert with coating thickness of 2.38 μm.

Abstract: High-strength carbon fiber reinforced plastic (CFRP) T800S/250F is used as the large commercial aircraft material for manufacturing the main load-bearing structural components. Drilling is the mostly used in final machining process of CFRP laminates, while the delamination and burrs occur frequently at the drill exit in the CFRP laminate. In this paper, the machinability of T800S/250F was investigated in term of drilling force and hole quality by using a twist drill and a dagger drill. The experimental results indicated that high spindle speed and low feed rate favor the reduction of thrust force for both drill bits. High spindle speed is a preference to gain the good hole quality at drill exit especially for the dagger drill, which also shows excellent drilling performance than the twist drill and was more suitable for drilling of T800S/250F CFRP laminate.

Abstract: Face milling is the most common milling operation and can be performed using a wide range of different tools. Tool life is an important indicator of the milling operation in manufacturing process. In high speed machining, there are two forms of security lapse including cutter body rupture and flying out to effect face-milling cutter life. This study investigates the influence of cutting tool body material on the distribution of stress field by utilizing finite element simulations (FEM). Two kind of cutting tool body materials including Al alloys and 40CrMo tool steels were used for simulation. The cutting tool was set to be idling under different rotation speed including 5000r/min, 10000r/min, 15000r/min, 20000r/min and 30000r/min, respectively. Results show that for the two kinds of materials, the security cutting speed is 15000r/min to Al alloys and 20000r/min to 40CrMo tool steels respectively. Under the same cutting condition, 40CrMo tool steels have higher shear stress than that of Al alloys, in hence they have higher security rotation speed.

Abstract: The paper investigates the effects of cutting conditions on the machinability of stainless steel coatings manufactured onto AISI 1045 steel by laser cladding technology. Two kinds of CBN (cubic boron nitride) tools with different corner radius and two different depths of cut were adopted in the experiments. Cutting force during machining, surface roughness and microhardness of machined surface were measured and analyzed. The results show that both the cutting force and surface roughness increase with the increase of depth of cut. When the other cutting parameters are identical, the surface roughness decreases with the increase of tools corner radius while the variations of different cutting force components present different tendencies. The microhardness of the machined surface and its varied gradient in the direction of depth of cut increase with the increase of tools corner radius. The experiment results will provide valuable suggestions for optimization of cutting performance for laser cladding coatings in order to obtain excellent surface quality.

Abstract: Three kinds of in-situ growth TaC whiskers toughening Al₂O₃ matrix ceramic cutting tool materials were prepared by two steps, which were in-situ synthesis of TaC whiskers in Al₂O₃ matrix powder by carbothermal reduction process and hot pressing of the composites respectively. The preparation process, microstructure, mechanical properties and toughening mechanisms of the composites were investigated. The in-situ synthesized TaC whiskers had a diameter of 0.1-0.5μm and an aspect ratio of 10-30. The composite containing 20vol.% TaC had the optimal comprehensive mechanical properties with flexural strength of 638MPa, fracture toughness of 6.5MPa·m^1/2 and hardness of 17.4GPa. The improvement of the mechanical properties was attributed to the TaC particles and whiskers which induced the toughening and strengthening effects such as crack deflection, crack branching, grain and whisker fracture, interface debonding and whisker pullout. The fracture mode of the composites was the combination of intergranular and transgranular fracture which also improved the mechanical properties of the composites.