Papers by Author: Hong Hua Su

Abstract: As a new type of material, Ti₂AlNb based alloy has a broad application prospects in aerospace field due to its excellent properties such as low density, high specific strength at elevated temperature, excellent oxide and creep resistance. Many studies involving its material composition and structural properties have been published. However, there are relatively few literatures available on the machinability of Ti₂AlNb based alloy. In this work, the turning experiment of Ti₂AlNb based alloy was carried out with coated cemented carbide tools. The machinability of Ti₂AlNb based alloy was investigated through the cutting force, cutting temperature, tool wear and surface roughness. The result shows that the cutting force is lower and surface quality is better under condition of higher cutting velocity, lower feed rate and smaller depth of cut. The life of tool is longer when they were cutting under the high cutting velocity, low feed rate and small depth of cut. The research could provide some instructive information and basic data for the turning process parameters optimization of Ti₂AlNb based alloy.

Abstract: A monolayer brazed diamond grinding wheel was dressed 23 times with a plate wheel. The grinding forces were measured during the grinding experiments which carried out on SiC ceramics after each dressing interval. The surface roughness of SiC ceramics was also measured. In this study, the dullness of the grinding wheel during the dressing procedure is mainly discussed. The results showed that the surface roughness of SiC ceramics reduced a lot after dressing which means the dressed grinding wheel can meet the requirements of precision machining. On the premise of this, there was no obvious dullness occurred on the grits of the grinding wheel during dressing because new cutting edges had emerged.

Abstract: Nickel-based alloy is known as one of the most difficult–to-machine materials and the milling process is one of the most common metal removal operations. Modeling and simulation of milling process have the potential for understanding the milling mechanism, improving cutting tool designs and selecting optimum conditions, especially in advanced applications such as high-speed milling. This paper presents a 3D coupled thermo-mechanical finite element model based on ABAQUS\Explicit for the simulation of Inconel 718 chip formation in metal cutting. In the simulations, a Lagrangian formulation with an explicit solution scheme and a penalty contact algorithm has been used. The material behavior is modeled with classical Johnson-cook plasticity constitutive model and dynamic failure criteria for element removal, coupled with adaptive meshing and mass scaling technology for limiting the calculation time. The milling tool is modeled in UG software according to the real tool geometry, and meshed as a rigid tool. In order to verify the accuracy of 3D simulation, results (cutting forces and cutting temperature) were compared with the experimental results under the same cutting conditions as the simulations. The results obtained indicate that the simulation methodology is capable of predicting the cutting forces and cutting temperature. It suggests that 3D finite element simulation model of cutting processes can be truly trusted.

Abstract: Titanium matrix composites (TMCs) possess many outstanding properties and have increasing and potential application in aerospace, automobile and other industries. However, TMCs are typical difficult-to-machining material due to the rapid tool wear rate and excessive machining induced defects. In this paper, tool wear, cutting forces, cutting temperature and surface roughness were investigated when milling TMCs with Polycrystalline Diamond (PCD) and carbide tools. The results showed that the values of surface roughness obtained by carbide tools were higher than that of PCD tools under the same cutting conditions. The value of cutting temperature for PCD tool was about 75% of the carbide tools, and the main cutting force value of PCD tool was about 85% of the carbide tool. Abrasive and adhesive wear were the main wear mechanisms of PCD and carbide tools. In all, PCD tools had a better cutting performance than carbide tools during finishing milling titanium matrix composites.

Abstract: A numerical investigation was conducted to apply cold expansion methods on composites structures under the guidance of cold expansion techniques of metal materials and interference-fit techniques of composites structures. Finite element expansion models with sleeves or without sleeves are established to study the stress distributions and failure conditions around cold expanded holes with different expansion values (0.5%, 1% and 1.5%). Results show that no damage occurs with expansion value 0.5% and using a sleeve in the expansion process can cause uniform stress distributions.

Abstract: Nickel-based alloy is known as one of the most difficult-to-machine materials. During the machining process, the high temperature coupled with high strength and work hardening leads to excessive tool wear, short tool life, low productivity, etc. Tool life and material removal rate are the two targets of rough machining. In this paper, some turning tests are conducted to investigate the tool lives and material removal rate of coated carbide tools and whisker reinforced ceramic tools. The results show that notch wear is the dominant failure mode for whisker reinforced ceramic tools while severe flank wear and micro-chipping for coated carbide tools. The whisker reinforced ceramic tools are more effective in machining nickel-based alloys than the coated carbide tools both in tool life and material removal rate.

Abstract: Continuous induction brazing with ultra-high frequency was proposed to braze the monocrystalline CBN grains using Ag-based filler alloy. The interfacial microstructure of the brazed specimen and the resultant morphology on the CBN surface was investigated and analogized by scanning electron microscopy (SEM) and energy diffraction X-ray (EDX). The experimental results showed that the bonding among CBN grains, filler alloy and steel matrix was achieved. The CBN grains were well wetted by the filler alloy and formed a massive support profile. Moreover, the active element Ti of the filler diffused markedly and gathered in the interfacial of matrix/filler and filler/grain respectively. Due to the short dwell time in brazing, the newly formed resultants grew in a short time. The resultants layer did not entirely covered the CBN grain, and discretely distributed on the surface of CBN grain. The size of the resultants was less than 200nm.

Abstract: Localized ultra-high frequency induction brazing is proposed to deal with the thermal deformation problem of brazed diamond tools. In order to investigate the temperature field distribution, the simulation model of induction brazing for solving the temperature field is described through the FLUX 2D software. The experiment is carried out to verify the numerical simulation result. Good agreement is observed between experimental value and simulation result. The influence factors on temperature field are investigated by the simulation software. Ultra-high frequency induction brazing with diamond grits is carried out based on the conditions given by simulation results. Good bonding between the diamond grits and the filler alloy is observed and the width of the brazed region is less than 3 mm.

Abstract: Titanium Matrix Composites (TMCs) parts usually requires high mechanical performance. The good workpiece surface quality and long tool life is the two target of finishing machining. In this paper, finishing turning tests are performed to investigate the workpiece surface roughness and tool life of machining TMCs with Polycrystalline Diamond (PCD) tools at the cutting speed range 60m/min to 120m/min. The results show that the workpiece surface roughness is obtained range Ra 0.44 to Ra 0.53m. tool life reaches about 10.6min, 7.9min, 7min and 5.5min at the cutting speed of 60m/min, 80m/min, 100m/min and 120m/min, respectively.

Abstract: It is essential to control the heat generated in the cutting zone in order to ensure the workpiece quality after grinding. This article deals with an investigation in using graphite and hexagonal boron nitride as solid lubricants to reduce friction and thereby improve the surface integrity of Ti-6Al-4V alloy. The polymer-based solid lubricant coating wheels have been prepared. Grinding experiments have been conducted to study the effect of the graphite and hexagonal boron nitride lubricants on the grinding temperature and the surface quality of the workpiece while grinding Ti-6Al-4V. Results indicate that there is a considerable improvement in the performance of grinding Ti-6Al-4V using graphite and hexagonal boron nitride as solid lubricants in dry grinding in terms of grinding temperature and surface quality of the work piece. The indigenous polymer-based solid lubricant coatings are effective in dry grinding.