Papers by Author: Ming Chen

Abstract: The two phase (α+β) titanium alloys are extensively applied in aerospace, automotive, and biomedical industries owing to their excellent comprehensive performance combining of high strength-to-density ratio, good corrosion resistance, and high strength at elevated temperature. However, the poor machinability of these alloys restricts the improvement of manufacturing productivity and cost savings. In this paper, machinability of three α+β titanium alloys was studied at the finish hard turning conditions.

Abstract: The α+2βtype Ti-5Al-4.75Mo-4.75V-1Cr-1Fe (TC18) is a very difficult machine material for its low thermal conductivity, low elastic modulus, and high chemical activity. So how to improve the machining efficiency and prolong the tool life have got more and more attentions. In this paper, wear mechanism and wear types of coated (TiN+TiAlN) carbide tool and uncoated carbide tool are presented when face milling the Ti-18 alloy under the same machining condition. The results showed that wear types of PVD coated tool are mainly adhesive, diffusion and crater wear, while the mainly failure mode of uncoated carbide tool is tipping. So it is more appropriate to select the PVD coated tool than uncoated tool in the milling TC18 alloy process.

Abstract: Aluminum alloy, as a kind of large-scaled structures, have been widely used in modern aerospace industry. In order to reduce its machining deformation, cutting parameter optimization is absolutely necessarily. By fuzzy synthetic evaluation, cutting parameters are optimized based on factors: surface roughness, residual stress, radial milling force and milling temperature. By maximal grade of membership rule, optimized values are obtained by different two methods. And by BP network with Bayesian regularization method the corresponding milling parameters are obtained too.

Abstract: With the development of aerospace, biomedical and chemical industries, titanium alloy Ti-5Al-5Mo-5V-1Cr-1Fe (TC18) is becoming widespread used. TC18 has even better mechanical property than Ti-6Al-4V (TC4). For better cutting TC18, simulation model was set up. PVD and CVD coated carbide inserts were used to machine titanium alloy TC18. The cutting forces were measured. Milling model was set up for the extraction of the cutting force coefficients and chip flow angle. Results were compared. All the coefficients of CVD coated carbide insert were found to be larger than those of PVD coated carbide insert. The model was proved to be reasonable after validation.

Abstract: Microcrystalline diamond (MCD) and fine-grained diamond (FGD) films are deposited on silicon nitride (Si3N4) inserts using the hot filament chemical vapor deposition (HFCVD) method. Scanning electron microscope (SEM), X –ray diffraction (XRD) and Raman spectrum are employed to characterize these as-deposited diamond films. Cutting performance of as-fabricated CVD diamond coated Si3N4 inserts is examined in dry turning glass fiber reinforced plastics (GFRP) material, comparing with the uncoated Si3N4 inserts. The results indicate that the tool failure is mainly attributed to its severe flank wear, which is caused by continuous friction and impact brought by many hard SiO2 particles distributed in the GFPR work piece. The lifetime of Si3N4 inserts can be prolonged by depositing MCD or FGD films on them and the FGD coated insert shows better wear resistance than the MCD coated one.

Abstract: The diamond and diamond-like carbon (DLC) films were deposited on the cobalt cemented tungsten carbide (WC-Co) cutting tools respectively adopting the hot filament chemical vapor deposition (HFCVD) technique and the vacuum arc discharge with a graphite cathode. The scanning electron microscope (SEM), X-ray diffraction spectroscopy (XRD) and Raman spectroscopy were used to characterize the as-deposited diamond and DLC films. To evaluate their cutting performance, comparative turning tests were conducted using the uncoated WC-Co and as-fabricated CVD diamond and DLC coated inserts, with glass fiber reinforced plastics (GFRP) composite materials as the workpiece. The research results exhibited that diamond and DLC coated inserts had great advantages in cutting tests compared to uncoated insert. The flank wear of the CVD diamond coated insert maintained a very low value about 50μm before the cutting tool failure occurred. For the DLC coated insert, its flank wear always maintained a nearly constant value of 70~200μm during whole 45 minutes turning process. The flank wear of CVD diamond coated insert was lower than that of DLC coated insert before diamond films peeling off.

Abstract: Centerless grinding is a widely used manufacturing process in the mass production of precision parts. However, its productivity and precision is largely determined by the grinder set-up conditions, process stability and workpiece surface integrity. Grinding titanium alloys encounters difficulties due to its low thermal conductivity, high shear strength and extreme chemical reactivity. Therefore, the grindability of titanium alloy should be improved in order to increase the productivity for the sake of workpiece quality. In this paper, centerless grinding process was introduced initially and the research of impact factors on centerless grinding performance was reviewed. The problems occurred in the centerless grinding of titanium alloy were studied and optimum guidelines were proposed.

Abstract: The nickel-based superalloy GH80A has been widely used in kinds of aeronautical key structures because of its high yield stress and anti-fatigue performance at high temperature. However, it is also a typical difficult-to-cut material. In order to improve cutting process, kinds of methods have been applied to study cutting process including experimental approach and finite element method (FEM). In this paper, a comparison of chip formation is carried out between traditional Johnson-Cook (JC) model and Isotropic model. Besides, effects of tool rake angle and friction coefficient on chip formation are investigated by Isotropic model. FEM predicated results such as stress and cutting temperature are also analyzed. Relative turning tests are performed and comparison of chip morphology between FEM and experiment is carried out.

Abstract: Titanium alloys are extensively applied in aerospace, automotive, biomedical, and chemical industries owing to their excellent performance combining high strength-to-density ratio, good corrosion resistance, and high strength at elevated temperature. Ti-6.5Al-3.5Mo-1.5Zr-0.3Si (TC11) alloys are used to replace the most common Ti-6Al-4V in some important applications such as some parts in aerospace engine. The purpose of this paper is to evaluate the machinability of TC11 alloys in the finish hard turning conditions. The paper presents the machinability results of TC11 alloys compared with Ti-6Al-4V, and analyzes the variables such as cutting force, surface integrity, and tool wear mechanism in the experiments.

Abstract: The confine of ductile-mode cutting and brittle-mode cutting seems to be a crucial step for designing a brittle material removal process. However, the existing transition from ductile-mode to brittle-mode for BK7 material makes the confine of different mode very difficult. Through a series of micro/nano-machining tests, measurements of cutting forces and morphological appearance of cutting groove as well as the cross section at the certain depth of cut, the confirmation of ductile-mode cutting, transition-mode cutting and brittle-mode cutting has been clearly described in the paper. This lays a foundation for the fundamental understanding of cutting physics concerning of material characteristics and cutting tools, and thereafter for the development of optimal process technology.