Key Engineering Materials Vols. 359-360

Abstract: An investigation was reported of the injection of thermoplastic polyurethane (TPU) to fix diamond beads on wire saws. Effects of injection material hardness, injection temperature and dwell pressure on the mechanical properties of three types of TPU plastics were studied and the results showed that with the increase of material hardness, both the 100% Modulus and the tensile strength of TPU were improved, but the rupture extensibility reduced. With the increase of injection temperature, the tensile strength increased but the rupture elongation decreased. To every type of TPU, a minimum injection temperature can be found for an ideal density of TPU.

Abstract: The research and manufacture of endless diamond wire saws have been reported in this paper. The matrix of saws was 65Mn steel wire whose diameter was o.8mm, and was welded as a ring by argon arc welding. The endless diamond wire saws were made by setting diamond abrasives on endless steel matrixes using nickel-plating method. The cutting experiments were carried out using the diamond wire saws on the homemade test equipment. The characteristics of the saws are narrow slot, high cutting speed, low noises and good surface quality. The surface cut could be finishing grinding or polishing directly, so the productivity could be improved greatly. Endless diamond wire saws can cut not only rock, but also valuable hard and brittle materials such as ceramic, boulder, and silicon etc.

Abstract: The physical model of fixed-abrasive diamond wire-sawing monocrystalline silicon was founded to analyze the elastic deformation of the wire, supposing that every grit was connected to the surface of the wire by a spring. Ignoring lateral vibration of the wire, the geometrical model of wire-sawing was founded; the average cut depth of single grit was calculated theoretically. Based the indentation fracture mechanics and investigations on brittle-ductile transition of machining monocrystalline silicon, the removal mechanism and surface formation was studied theoretically. It shows that in the case of wire-sawing velocity of 10m/s or higher, infeed velocity of 0.20mm/s and diamond grain size of 64μm or smaller, the chip formation and material removal is in a brittle regime mainly, but the silicon wafer surface formation is sawed in a ductile regime. The size of the abrasives, the wire-saw velocity and infeed velocity can influence the sawing process obviously.

Abstract: Free abrasive wiresaw technology is the main method in slicing monocrystalline silicon wafers. The mathematical model of hydrodynamic action in the process of the free abrasive wiresaw slicing was founded, displacement caused under distributed radial load of every node on the wire is embodimented through self-compliance influence coefficient, which is beneficial to found the film thickness equation. The distributions of hydrodynamic pressure and film thickness in the free abrasive wiresaw slicing process are yielded by using the finite difference numerical methods to solve the two-dimension Reynolds equation. The results show that the minimum film thickness increases with the increase of wire speed, and slurry viscosity, while decreases with the increase of wire bow angle. The film thickness is greater than the average abrasive size so that the abrasives float in the slurry when the size of abrasive is small enough.

Abstract: Grinding, characterized by its high specific energy consumption, may generate high grinding zone temperature. These can cause thermal damage to the ground surface and poor surface integrity, especially in the grinding of difficult-to-machine materials. Conventional cooling methods based on large amounts of water-oil emulsions can be both ineffective and environmentally unacceptable. Here a new high efficiency cooling technology—cryogenic pneumatic mist jet impinging cooling technology is offered. It utilizes the high penetrative power of fast cryogenic air jet combined with a little quantity of 0°C water to greatly improve heat transfer effects in the machining zone. The experimental results indicated that CPMJI could offer better machining effects compared to cold air jet and traditional flood cooling method in the grinding of titanium alloy.

Abstract: Simulation on velocity field of gas-solid flow in the abrasive air jet nozzle was studied by the computed fluid dynamics(CFD) software. The velocity field of the two-phase flow in the abrasive air jet nozzle can be obtained by means of simulation. The effect of the nozzle diameter on the velocity field shows that the velocity field in the nozzle with a smaller diameter is more well-distributed. The velocity distribution along the nozzle axis and the radial direction of the nozzle outlet was also simulated.

Abstract: Simulation of the flow field of the gas-liquid-solid three-phase flow outside the abrasive water jet rectangle nozzle and ellipse nozzle is studied by the computed fluid dynamic software-fluent, and the velocity field of the three-phase flow is obtained. The simulation result expresses that the flow is expanded when it is out of the nozzle; the velocity of the flow is the highest at the axis, which comes down by its side, the velocity of the flow is high at the beginning then it is decreased because the flow is resisted by the air; the shape of the jet at the start is closed to the geometry of the nozzle, then it is rounded in the external area; the velocity field outside the ellipse nozzle is distributed evenly around the center. By plotting the velocity field of the rectangle nozzle and the ellipse nozzle in the Y-Z section, it is expressed that the changing range of velocity is enlarged with the increasing of distance offset the nozzle.

Abstract: It is innovative to combine abrasive jet machining and conventional grinding together in this thesis. And it realizes a new sort of grinding wheel restricted with abrasive jet processing. The three-dimensional mathematical model of hydrodynamic pressure of wedge-like grinding zone between grinding wheel and workpiece on abrasive jet finishing with wheel as restraint was established, and the finite elements simulation analysis for the hydrodynamic pressure was implemented. This paper investigated the liquid hydrodynamic pressure, the regularities of distributing of velocity, influencing factors and the affection for processing technique.

Abstract: This paper deals with an application to automatic compensation of grinding wheel wear by an image processing based real-time measurement method in dry curve grinding. An online image measurement system was schemed out and its principle was introduced in detail. Real time image of workpiece and grinding wheel is grabbed by CCD camera during grinding process. For the purpose of increasing the measurement precision, a new sub-pixel level accuracy edge detection approach combining Zernike moments operator with Sobel operator is proposed for locating the edge of the machined workpiece, which has advantages of fast processing speed and high edge locating accuracy. The wear amount of the grinding wheel is calculated by the image processing software, and is compensated automatically by NC controller. Finally, this method is applied to a new type CNC curve grinding machine MD9040. The experimental results show that the measurement and compensation method proposed in this paper is effective, and the contour error of the workpiece with real-time compensation is less than the feeding resolution for a compensation of 2μm.

Abstract: This paper presents a reasonable method for generating the tool-path of free-form surface polishing using the fractal curves. Free-form surface polishing processes as a finishing process are used to reduce the roughness of surfaces and smooth the surface form by eliminating the surface waviness left by tool marks, EDM spark erosion and so on. In the interest of realizing this aim without introducing undesirable surface waviness and time efficiency, a tool-path should provide even coverage of free-form surface during polishing. A fractal curve is suitable to cover the free-form surface uniformly at any complexity due to its plane-filling and self-similar characteristics. A method of generating the fractal path for free-form surface polishing is presented, and also an automatic polishing system is installed to confirm the path planning method’s validity.