The Research On The Mechanism Of Finish Dry Hard Turning The Harden Tool Steel

Dry hard cutting (DHC) is a process which has been developed since1980s, in which materials in the hardened state (50-70HRC) are machined with the single point cutting tools without using cutting fluids or using the least lubricating fluids to attain the well finish surface integrity. It is the best advanced technology with shorter cycle time, lower production cost as well as the elimination of environmentally hazardous cutting fluids. However, the new process has not been studied thoroughly in the theory at present, which restricts its generalization and application in the production to a great extent.Mechanism of finish dry hard turning (FDHT) hardened steel with the PCBN cutting tool, including the mechanical properties of turning the hardened tool steel in the different hardened states, the serrated chips, the cutting heat and temperature fields, the surface roughness of the machined workpiece, the micrographs and the white layer within the machined workpiece surface, was investigated systematically, by utilizing the test system which was made up of the digital control lathe, instrument of infrared measuring temperature, scanning electron microscopy (SEM),3D surface profilometer, and so on. The main investigation contents and contribution are listed as following:(1) The compressive and tensile mechanical properties, the friction and wear properties of the hardened tool steel were obtained in this paper.(2) Based on the geometric model in FDHT the hardened steel, the calculational models for cutting forces per unit area of cutting lay and material removal rate (MRR) were exploided under the condition of the smaller depth of cut-larger nose radius-oblique turning (SDOC-LNR-OT). The influences of the cutting parameters, the rake angle of the tool, the hardeness of the hardened steel and the nose radius on the cutting forces during FDHT the hardened tool steel Cr12MoV were analyzed by the experimental method of the single factor. The effects of the main factors which includ the cutting parameters, the rake angle of the tool, the hardeness of the hardened steel and the nose radius, and their interaction effects on the3-D components of cutting forces, such as the main cutting force Fz, the radial thrust force FY and feed force FX were investigated, based on the orthogonal experiment by using range analysis (RAAN) and analysis of variance (ANOVA). And the process parameters of FDHT were optimized. Meanwhile, the exponential and quadratic polynomial predictive model of the main cutting force Fz, the radial thrust force FY and feed force Fx by employing the factors, such as the cutting parameters, the hardeness of hardened steel and the nose radius, were developed by utilizing the orthogonal regression methodology (ORM) and response surface methodology (RSM). (3) The macroscopical and microscopical forms of the serrated chips, the mechanism of forming the serrated chip were analyzed during FDHT the hardened tool steel in various hardeness under various turning conditions. The geometry model for forming the serrated chip was developed; the calculational models of shear strain in the serrated chip, shear strain and shear strain rate within shear band in the serrated chip were perfected.(4) The calculational model of the mechanical energy transforming into thermal energy was exploided under the condition of the SDOC-LNR-OT. Based on the experiments and finite element modeling, the temperature of the cutting tool tip was simulated with the inverse simulation method utilizing the ANSYS software. Then, the AbaqusTM software were utilized to propose the FEM in finish dry hard orthogonal cutting (DHOC) the hardened AISI D2tool steel (62±1HRC) and validated by the experimental results. And this FEM was utilized to predict temperature fields within workpiece, cutting tool edge temperature, et al. The exponential and quadratic polynomial predictive models for temperater of workpiece surface were developed by utilizing the ORM and RSM, and the effects of the two predictive models were analyzed with the ANOVA.(5) The influence laws of the cutting parameters, the rake angle of the tool, the hardeness in the hardened steel and the nose radius on surface roughness during FDHT were analyzed by mean of utilizing various experimental ways and analysis methods. The effects of the main factors, including the cutting parameters, the rake angle of the tool, the hardeness in the hardened steel and the nose radius, and their interaction effects on surface roughness were investigated, based on the orthogonal experiment by using the RAAN and ANOVA. And the process parameters of FDHT were optimized. Then, the exponential and quadratic polynomial predictive models for surface roughness were developed by utilizing the ORM and RSM, and predicted accuracy of the two predictive models for surface roughness were compared. At the same time, the surface roughness was predicted by using Elman recurrent network. Such phenomene as the morphology, side flow and white layer within the machined surface and reasons leading to these phenomene were analyzed by mean of utilizing3D surface profilometer and SEM.These experimental conclusions are of great significance and reference value in understanding the mechanism of FDHT the hardened tool steel in various hardeness, further developing the theory of foundations of DHC and accelerating generalization and application of the technologe in the production.