Hong Hua Su

The Influence of Grinding Parameters on the Superficial Hardening Effect of 48MnV Microalloyed Steel

The current surface strengthening process of microalloyed unquenched and tempered steel components is usually induction or laser quenching treatment. Subsequent to heat treatment, these structural parts are subjected to grinding, during which impairment of hardened materials can be caused by thermo-mechanical influence of the grinding process. This paper studies a new method of surface heat treatment by making use of grinding heat and stress to create favorable microstructures and promote high wear and fatigue resistance. This work outlines the influence of grinding parameters on the superficial hardening effect of 48MnV microalloyed steel. It was found that the thickness and hardness of the treated surface layer could be up to 1.6mm and HV750 respectively. The beneficial microstructure of the layer was created by an enhanced martensite transformation. It is highly possible that the method can be used to incorporate grinding and surface hardening into a single grinding operation to develop a cost-effective production method.

Microstructure and Performance of Porous Ni-Cr Alloy Bonded Diamond Grinding Wheel

Although the porous metal bonded diamond grinding wheel, which has recently been developed, had an excellent grinding performance for hard-brittle materials, its applications were only in precision grinding in past study. A new method for fabricating the new porous metal bonded diamond grinding wheel by Ni-Cr alloy as bond and vacuum loose powder sintering was proposed in this paper. The morphology of cross section of the segments and microstructure of interface between diamond grits and bond were analyzed. The wetting mechanism between Ni-Cr alloy bond and diamond is reacting wetting. Machining performance experiments about grinding ratio and surface roughness have been carried out. The testing results show that the porous Ni-Cr alloy bonded diamond grinding wheel has certainly fine machining performance in high grinding force occasion, and the maximal grinding ratio and best surface roughness were 6660 and 1.08 m, respectively.

Machining Performance of Brazed Diamond Wire Saw with Optimum Grain Distribution

A kind of new monolayer brazed diamond wire saw with both chemical bonding at the interface between diamond grits and brazing alloy and optimum grits distribution was made. And a machining performance comparative experiment was carried out between the sintered diamond saw from Italy and the brazed one mentioned above. The sawn material is marble with middle hardness. The testing results show that the wire saw with a brazed bonding diamond grid can achieve two to three times the working efficiency of conventional sintered diamond saw, and the corresponding service life can do 3~4 times. Furthermore, the grits of the brazed diamond wire fail mainly in micro fracture modes other than pull-out ones of the sintered diamond saw grits, indicating the strong retention of brazing alloy to the diamond grits. Almost no grits pulling out for brazed diamond wire saw is the key factor of its longer service life, and the optimum distribution and micro fracture of the brazed diamond wire grits raise the machining efficiency.

Finite Element Analysis of Residual Stress in Diamond/Steel Brazed Joint

In the application of brazed diamond tools, residual stress caused by differences in materials properties is an important factor in obtaining good brazing quality. The residual stress in diamond/steel brazed joint is studied by means of finite element method and Raman spectroscopy in this paper. The comparison between the results from the simulations and the measurements shows that a good agreement has been reached. Tensile stress concentration at the diamond edge near interface was observed. High residual stress concentration may cause cracks in diamond. Actually, cracks in diamond caused by brazing residual stress after were observed. The stress concentration of the joint must be reduced to obtain good brazed joint. The change of brazing atmosphere or to adopt the soft brazing alloy will reduce the stress concentration.

Experimental Study on Ultrasonic Assisted Grinding of C/SiC Composites

In the present work, ultrasonic assisted grinding (UAG) and conventional grinding (CG, without ultrasonic) tests of Carbon fiber reinforced silicon carbide matrix (C/SiC) composites were conducted. In addition, analysis was done by comparing the machining quality, grinding force, and specific grinding energy between the two processes. The results showed that material removal mode of carbon fiber both in CG and UAG were brittle fracture, and fracture size had no obvious difference. Compared with CG, brittle fracture area of SiC increased during UAG. In comparison with CG, the normal grinding force and tangential grinding force for UAG were reduced maximally by 45%, 39% respectively of those for CG. Accordingly, specific grinding energy was also reduced by UAG. Therefore, UAG can improve the grinding performance of C/SiC composites significantly.

Experimental Study on Performance of Monolayer Brazed Diamond Wheel through Chemical-Mechanical Dressing

The dressing methods of monolayer diamond tool have recently been developed increasingly because a substantial improvement of the ground surface roughness could be achieved with the dressed monolayer diamond tools. In this paper, a new dressing method was proposed, namely chemical-mechanical dressing of the diamond grits. Dressing experiments were carried out on the monolayer brazed diamond grinding wheel. The grit-tip distances from the base of wheel substrate were measured before and after dressing. Grinding experiments were conducted on K9 optical glass after each dressing interval. The roughness parameters of the ground surfaces were measured. The outcome of this attempt appeared highly encouraging, and the dressing of monolayer brazed diamond grinding wheel is effective with the chemical-mechanical dressing.

Effect of Ti Addition on Shear Strength of Brazing Diamond and Ag Based Filler Alloy

The shear strength samples of brazed single crystal diamond with the (72Ag–28Cu)–xTi (x=2, 4, 7wt.%) active filler metal were prepared, using vacuum brazing methods. Microstructure evolution of interfacial reaction product and shear strength of the brazed diamond and Ag based filler alloy were studied. The results show that there exits a layer of TiC on the surface diamond in different Ti additions, and the thickness of TiC layer increases with the increase of Ti addition. With the increase of Ti addition, the shear strength of the brazed joint decreases due to the increase of TiC layer thickness and amount of intermetallics. From the results, it was seen that mutual diffusion of C and Ti was effective on the morphology of the interface zone that affected the shear strength of the bonds. To achieve a reliable brazed joint, the Ti content must be controlled under 4wt.%.

Investigation on Simulation for Grind-Hardening Temperature Field of Non-Quenched and Tempered Steel

This paper studies the grinding temperature field of non-quenched and tempered steels grind-hardening technology using experiments and finite simulation. A mathematical model of grind-hardening temperature field is established to investigate steel 48MnV which is used for making crankshaft. The grinding temperature field is simulated and the hardened depth is forecasted by finite-element method with the triangular shape of the heat source model based on the ANSYS software. The experimental results show that the simulative temperature and estimating hardened depth are comparatively close to the measuring ones. The model could be utilized to forecast the distribution and variation characteristics of the grinding temperature field and the hardened layer depth.

Turning of Cast Inconel 718 with Coated Carbide and Whisker Reinforced Ceramic Tools

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.

Interfacial Microstructure of Ultra-High Frequency Induction Brazed CBN Grains Using Ag-Based Alloy

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.