Advanced Materials Research Vol. 1027

Abstract: Titanium alloy has been widely used in aeronautics and astronautics industry owing to its unique combinations of properties. The unique physical and chemical properties of titanium alloy make it a typical difficult-to-machine material. The elevated temperatures at the machining zones may cause thermal damage, residual stress and micro-structural changes in the surface layer of titanium alloy during grinding. In this study, grinding experiments were performed on the titanium alloy, and the grinding temperature was experimentally tested with the grindable thermocouples. The effects of the grinding parameters on the grinding temperature were analyzed. The grinding temperature rises with the increase of grinding speed and grinding depth.

Abstract: Longitudinal-bending complex vibration can be realized by opening chute on the amplitude amplifier pole. Different longitudinal and bending amplitudes can be obtained under different angles and the number of the chutes. Based on the theory of two-dimensional ultrasonic cutting, the effects of the two dimensional amplitude on the cutting characteristics were analyzed experimentally in the paper. Research results show that the amplitudes of longitudinal and bending vibration have a great effect on cutting force and machining quality in two-dimensional ultrasonic vibration cutting of hard and brittle materials. When keeping constant longitudinal amplitude and increasing bending amplitude in a certain extent, the cutting force could be reduced and the machining quality of workpiece could be improved effectively. The research provides relevant basis for designing two-dimensional longitudinal bending vibration cutting system.

Abstract: The adoption of conformal optics system can evidently improve the synthetical performance of infrared missiles. Hot-pressing poly-crystal magnesium fluoride (MgF₂) is an ideal material for conformal optics dome. But many problems about machining and surface test of deep aspheric surface have not been solved at present, and there is not much research about the machining characteristics of MgF₂ material. In this paper, in-situ measurement system is designed, so positional errors that introduced by repeating installation can be avoided. Then, machining process of MgF₂ material by single point diamond turning is studied, and optimized diamond turning process is proposed by experiments in order to obtain low surface roughness. Furthermore, surface accuracy is tested by on-machine measurement system. Based on the result, error compensation process of conformal dome is carried out. Finally, the shape error of the dome is less than 0.8μm PV.

Abstract: A series of grinding experiments were carried out with CBN wheel to focus on the surface integrity of titanium alloy TC4-DT in high speed grinding . In order to get the proper process parameters to control the surface integrity of the TC4-DT, surface roughness, subsurface morphology and microhardness variations have been studied. In addition to the use of CBN wheel, scanning electron microscopy (SEM), 3-d contour instrument and microhardness tester was applied. The results show that the surface roughness is decreased obviously when grinding wheel linear velocity rises from 60m/s to 80m/s. While the grinding speed rises from 80m/s to 100m/s, the surface roughness value increases slightly. Moreover, the surface roughness value increases with the grinding depth and the increasing trend is obvious in the process of machining. The microstructure analysis shows that during high speed grinding with CBN wheels, good quality surface with 10μm grinding depth can be obtained. Table feed rate has weak influence on the grinding surface topography. The microhardness analysis indicates that surface microhardness increases sharply with the increasing of grinding wheel linear velocity in high speed grinding.

Abstract: Silicon carbide ceramics with its excellent physical and mechanical properties have become the preferred material for space large diameter mirror. Diamond wheel grinding is the main way of SiC ceramics forming processing. Subsurface cracks is generated due to the high hardness and brittleness of the material after grinding. In order to remove the impact of cracks, poishing processing with very low efficiency is applied, so it is significant to control the depth of silicon carbide ceramic grinding subsurface cracks and shorten the processing cycle.In this paper grinding experiment of SiC ceramic is conducted. The method of cross-section polishing combined with scanning electron microscope observation is used to research grinding subsurface cracks. The depth of broken surface layer and the maximum depth of sub-surface cracks were proposed to evaluate the grinding subsurface cracks. The result show broken surface layer depth and the maximum depth of sub-surface cracks increase with the decreasement of spindle speed, and increasement of feed rate and grinding depth.

Abstract: Based on the principle of disc slitting process, a 3D model of the disc slitting process for galvanized sheet was established by using DEFORM-3D software, and the deformation, fracture and material effective stress of galvanized sheet were analyzed. The surface morphology of numerical simulation is in good agreement with the actual result. The curve of shearing force was obtained and well matched with the change rule of slitting process. Compared with the theoretical calculation result, the simulation result is reliable and can provide a reference for the calculation of shearing force.

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: In the process of HFCVD diamond film growth on the multitudinous micro end mills, the uniformity and stability of the temperature distribution have a vital importance on the quality of film. So a new method by using the finite volume is proposed to analyze the importance of different disposition parameters on the uniformity of substrate temperature field. These parameters are filament diameter (d), filament-substrate distance (H), filament separation (S) and filament length (L). The mono-factor method are used to optimize the best parameter combination. The simulation results show that the optimized parameters are d=0.65mm, H=10mm, S=27mm and L=160mm.

Abstract: In chemical mechanical polishing (CMP) of ultra-thin stainless steel, the oxidant of polishing slurry determines the material removal rate (MRR). In this paper, the influences of oxidant in slurry on MRR and surface roughness have been studied in CMP of ultra-thin 304 stainless steel based on alumina (Al₂O₃) abrasive. The research results show that, in the same conditions, the MRR increases with the increase of the oxidant C and the oxidant B, the MRR decreases with the increase of the oxidant A and the MRR is max with the oxidant C. It indicated that the oxidant C has a large effect on MRR in CMP of the 304 stainless steel. The research results can provide the reference for studying the slurry in CMP of ultra-thin stainless steel.

Abstract: Chemical reaction rate of SiC wafer surface usually determines the material removal rate (MRR) in chemical mechanical polishing (CMP). In this paper, systemic experiments are carried out to discover the relationship between Fe catalyst with different forms or valence and chemical reaction rate based on Fenton reaction. Experimental results show that the MRR changes little using Fe powder or hydrogen peroxide (H₂O₂) alone, but the MRR of SiC will increase largely by adding them both that will produce Fenton reaction. The MRR continues to increase slightly when Fe²⁺ ions is employ as catalyst, but that is much lower when utilizing Fe³⁺ ions. Moreover, SiC wafer with a smaller surface roughness and better quality can be obtained when using Fe powder as catalyst in Fenton reaction. The results indicate that the Fenton reaction can effectively improve the polishing efficiency of SiC substrate and Fe powder is more suitable for polishing of SiC than ferrous or ferric salt in CMP based on Fenton reaction.