Key Engineering Materials Vols. 359-360

Abstract: In this paper, we emphasize that residual stresses in a ground surface are primarily generated due to grinding zone temperature effect, and discuss grinding zone temperature can be debased based on characteristics of the thin vitrified bond CBN wheel and quick-point grinding. Via experimental results of 5 group working procedures, we find that surface roughness Ra showed a tendency to reduce slightly with infeed rate reduced, cut depth increased, grinding wheel speed and grinding variable angle increased, the favorable residual compressive stress could obtained along with variables angle(α, β) increased, the sub-surface white etching layer and tempered martensite layer in size become thinner with α, β angle and grinding wheel speed increased when removal rate Z=0.06mm3/mm keep constant in quick-point grinding, by contraries, surface quality were decreased entirely when variables angle(α, β) equal to zero. The results indicate it is important that grinding variable angle were choice in quick-point grinding for to obtain favorable residual compressive stress.

Abstract: The surface integrity finished by abrasive jet with grinding wheel as restraint was experimentally investigated. Experiments were performed with plane grinder M7120 equiped with abrasive jet finishing device and harded workpiece material 45 steel which was ground with the surface roughness values of Ra=0.6μm.The machined surface morphology was studied using Scanning Electron Microscope (SEM) and microscope and microcosmic geometry parameters were measured with TALYSURF5 instrument. The surface hardness for ground and finished surface was measured with HVS-1000 instrument and the phase structure was analyzed by X-ray energy dispersive spectram and residual stresses were measured by PW3208 X-ray diffraction. The Results show that longitudinal geometry parameter values were diminished and ripple was obviously improved comparing with ground surface. Furthermore, the finished surface has condensible residual stresses and high surface hardness comparability compared to grinding machining surface. As a result, life and precision consistency of finished workpiece were improved.

Abstract: Molecular dynamics is a rapidly developing field of science and has become an established tool for studying the dynamic behavior of material machining. A three-dimensional molecular dynamics (MD) model about the atoms of the diamond cutting tools and the diamond grits is built by using the molecular dynamics. The Tersoff potential function is used to calculate the force and potential energy among the atoms of the diamond tools and the atoms of the diamond grits. The lapping processes at a special cutting depth are simulated. The variety of the specimen potential energy in the lapping process is observed. The mechanism of the diamond micro machining and the form of the surface formation are given by comparing the distribution maps of atoms in initial and cutting states. This study will give a strong support to the diamond cutting tools’ lapping.

Abstract: Right getting hold of the contact form between the wafer and the pad is the precondition of fully understanding the material removal mechanism in wafer chemical mechanical polishing (CMP) process. In this paper, according to friction and abrasion theory, the differentiating method of contact form between the wafer and the pad has been obtained firstly. Then, the material removal rate (MRR) produced by mechanical action, chemical action and their interaction has been achieved by test results of MRR. According to analysis on test results of MRR, it is concluded that the mechanical action produced by abrasives is the main mechanical action, the MRR produced by the interaction between the mechanical action of abrasives and chemical action of slurry is the main MRR and the contact form between the wafer and the pad is solid-solid contact in wafer CMP. These results will provide theoretical guide to further understand the material removal mechanism of in wafer CMP.

Abstract: In order to elevate the efficiency of the surface finish to reach the fast improvement of the surface roughness of the workpiece, so as to reduce the residual stress on the surface efficiently. The present study discusses the surface after traditional machining, of which the plane surface used a design of finish tool includes an electrode and a nonconductive grinding wheel to execute the synchronous process of grinding and electrochemical finishing. The electrode form and the machining process are obviously different from electrochemical grinding (ECG). In the experiment, the design electrode is used with continuous and pulsed direct current. The controlled factors include die material, and chemical composition and concentration of the electrolyte. The experimental parameters are flow rate of electrolytes, position of plate electrode, electrode thickness, electrode rotational speed, electrical current rating, feed rate of workpiece, and pulsed period. The experimental results show that the supply of current rating is near concern with the position and thickness of the plate electrode. The use of large electrolytic flow rate and thick electrode is advantageous to the finish effect. High rotational speed of finish tool produces better polishing. The finishing effect is better with longer off-time because discharge of polishing dregs becomes easier. Higher current rating with quicker workpiece feed rate effectively reaches the fast improvement of the surface roughness of the workpiece is recommend in current study.

Abstract: The average Reynolds equation and average clearance equation of circular translational polishing (CTP) under the quasi-stable mixed lubrication state are set up in polar coordinates. The distributions of fluid pressure and contact pressure during polishing are numerically analyzed by solving simultaneously these equations along with the contact pressure equation. The effects of various process parameters on hydrodynamic performance of CTP are analyzed. By comparing the distributions of periodic average pressure along radial direction under fully and partially lubricated states, we conclude that carefully controlled CTP under mixed lubrication is beneficial to improving the surface quality and planarity of the wafer.

Abstract: Nanomachining tests have been conducted on single-crystal Al using atomic force microscope to simulate single-blade machining process of single gain. The influences of nanomachining experimental parameters (lateral feed and velocity) on the properties of engineering surface, material removal and chip formation were studied. Results indicated that the cutting depth of nanomachined surface increased as the lateral feed decreased. Insensitivity of cutting depth to velocity at same normal load was revealed. The different chip behaviors of nanomachined surface were investigated through scanning electron microscope (SEM). Results indicated that different lateral feeds caused different chip behaviors. Three typical chip behaviors were characterized as the lateral feed increased. In addition, the chip behavior and the volume of material removed were observed having no evident linear transformation with the evolution of the velocity by SEM graphics. Furthermore, it was concluded from the chip behaviors in nanomachining process that the material at high loads was removed by plastic deformation with no fracture or crack happened.

Abstract: The application of hard and brittle materials become wider and wider because its self-characteristics. It is used widely in finish machining of products, such as memory record device, information products, precision instrument, etc. Traditional grinding-polishing methods have not suited for precision machining requirements of hard and brittle materials. Carbide and ceramic are chosen as workpiece. Diamond polishing film is chosen as polishing tool. Polishing experiments are done by using self-made film polishing machine with high speed and cooling inside. Polishing mechanism and polishing technology of what polishing film polishes hard and brittle materials will be studied by changing polishing speed and diamond grain size and so on. The experimental study of wear shape of gringding grain, desquamation process of grain and surface quality of workpiece will be done in this paper so that the reasonable technology of polishing hard and brittle materials with high productivity is obtained. It enrich and perfect the ultra-precision machining theory. A new method of ultra-precision lapping and polishing of hard and brittle materials is provided.

Abstract: In this paper, a newly developed ultra-fine abrasive polishing pad by gel technology was adopted to polish silicon wafer on a nano-polishing machine. In order to evaluate the machining performances of the polishing pad, the influences of abrasive sizes, abrasive concentration and polishing parameters (pressure, rotating speed and machining time) on the silicon wafer were investigated respectively. Optical microscope and ZYGO 3D surface analyzer were applied to examine the surface morphologies and surface roughness of the polished silicon wafer respectively. The experimental results showed that the surface roughness of silicon wafer decreased with the decreasing of abrasive grits and the increasing of abrasive concentration and polishing parameters (pressure, rotating speed and polishing time) when polishing silicon wafer with the polishing pad containing Al2O3 abrasive. When abrasive concentration, polishing pressure and polishing time reached certain values, few changes would happen for the silicon wafer.

Abstract: In the present work, high power DC arc plasma jet chemical vapor deposition (CVD) is used to prepare diamond films with full width half magnitude (FWHM) less than 10 wave numbers at 1332 cm−1 Raman peak. During the polishing process, diamond film is hold against the stainless steel holder, which rotates and swings when the sample comes into contact with the cast-iron plate. Average surface roughness of the forming nucleus polished surface and growing polished surface is 560nm, 90nm respectively. And the materials removal rate is quite different. Fine crystal grain of the forming nucleus surface and the thick column crystal of growing surface are dominant in structure. In the meantime, effects of the size of the abrasive power, the applied force and polishing direction are also discussed. A profilometer, an Raman spectroscopy, X-ray diffraction and a scanning electron microscope have been used to evaluate the surface states of diamond films before and after polishing. This result reveals an. improvement of polishing efficiency and a great potential for commercial application.