Grindability and Surface Integrity of Cast Nickel-based Superalloy in Creep Feed Grinding with Brazed CBN Abrasive Wheels

AbstractThe technique of creep feed grinding is most suitable for geometrical shaping, and therefore has been expected to improve effectively material removal rate and surface quality of components with complex profile. This article studies experimentally the effects of process parameters (i.e. wheel speed, workpiece speed and depth of cut) on the grindability and surface integrity of cast nickel-based superalloys, i.e. K424, during creep feed grinding with brazed cubic boron nitride (CBN) abrasive wheels. Some important factors, such as grinding force and temperature, specific grinding energy, size stability, surface topography, microhardness and microstructure alteration of the sub-surface, residual stresses, are investigated in detail. The results show that during creep feed grinding with brazed CBN wheels, low grinding temperature at about 100 °C is obtained though the specific grinding energy of nickel-based superalloys is high up to 200-300 J/mm3. A combination of wheel speed 22.5 m/s, workpiece speed 0.1 m/min, depth of cut 0.2 mm accomplishes the straight grooves with the expected dimensional accuracy. Moreover, the compressive residual stresses are formed in the burn-free and crack-free ground surface

Heat transport capacity of an axial-rotating single- loop oscillating heat pipe for abrasive-milling tools

In order to enhance heat transfer in the abrasive-milling processes to reduce thermal damage, the concept of employing oscillating heat pipes (OHPs) in an abrasive-milling tool is proposed. A single-loop OHP (SLOHP) is positioned on the plane parallel to the rotational axis of the tool. In this case, centrifugal accelerations do not segregate the fluid between the evaporator and condenser. The experimental investigation is conducted to study the effects of centrifugal acceleration (0–738 m/s2), heat flux (9100–31,850 W/m2) and working fluids (methanol, acetone and water) on the thermal performance. Results show that the centrifugal acceleration has a positive influence on the thermal performance of the axial-rotating SLOHP when filled with acetone or methanol. As for water, with the increase of centrifugal acceleration, the heat transfer performance first increases and then decreases. The thermal performance enhances for higher heat flux rises for all the fluids. The flow inside the axial-rotating SLOHP is analyzed by a slow-motion visualization supported by the theoretical analysis. Based on the theoretical analysis, the rotation will increase the resistance for the vapor to penetrate through the liquid slugs to form an annular flow, which is verified by the visualization

Ultrasonic vibration assisted grinding of CFRP composites: Effect of fiber orientation and vibration velocity on grinding forces and surface quality

Ultrasonic vibration assisted grinding (UVAG) of carbon fiber reinforced plastic (CFRP) composites was carried out using a monolayer brazed diamond tool. Effects of the fiber orientation and vibration velocity on grinding forces and surface quality were analyzed. The maximum vibration velocity was varied by adjusting the grinding tool length. The results reveals that the grinding force is decreased with the increase of vibration velocity. The maximal grinding force is obtained with the fiber orientation at 135°, while the minimum grinding force is produced when the fiber orientation is 45°. Surface damages, such as groove scratch, fiber breakage are reduced with the increase of vibration velocity. Additionally, the fiber orientation plays a critical role in the surface morphology. Keywords: Vibration velocity, Fiber orientation, Grinding force, Surface quality, Carbon fiber reinforced plastic composites, Ultrasonic vibration assisted grindin

Tool wear investigation in high-pressure jet coolant assisted machining Ti2AlNb intermetallic alloys based on FEM

The excellent mechanical properties of Ti2AlNb intermetallic compounds are beneficial to improve the performance of aero-engine. However, because of their high strength ratio especially at high temperature along with the low thermal conductivity of Ti2AlNb, the machinability of this material is poor. In this paper, high-pressure jet cooling technology is applied for the machining of Ti2AlNb intermetallic alloys to investigate the effects of high pressure jet cooling on the machinability of Ti2AlNb. The performance associated with the cutting force, the cutting temperature, the chip morphology and the tool wear have been discussed. The results showed that the high pressure jet cooling can enhance the heat dissipation by weakening the phenomenon of bubble adsorption in the cutting area based on the FEM simulations. The high pressure jet cooling can break the chip into C-type chip and improve the chip breakage capability. It also demonstrates that the crater wear and adhesive wear near the cutting edge can be significantly reduced with the high pressure jet cooling technology. When the jet pressure reaches 10 MPa, the cutting temperature reduced 22% and the tool life improved by 89%. Keywords: Intermetallic alloys, High pressure jet coolant, Tool wear, FEM, Chip breakage, Tool lif

Grinding performance evaluation of porous composite-bonded CBN wheels for Inconel 718

For high-efficiency grinding of difficult-to-cut materials such as titanium and nickel alloys, a high porosity is expected and also a sufficient mechanical strength to satisfy the function. However, the porosity increase is a disadvantage to the mechanical strength. As a promising pore forming agent, alumina bubbles are firstly induced into the abrasive layer to fabricate porous cubic boron nitride (CBN) wheels. When the wheel porosity reaches 45%, the bending strength is still high up to 50 MPa with modified orderly pore distribution. A porous CBN wheel was fabricated with a total porosity around 30%. The grinding performance of the porous composite-bonded CBN wheel was evaluated in terms of specific force, specific grinding energy, and grinding temperature, which were better than those of the vitrified one under the same grinding conditions. Compared to the vitrified CBN wheel, clear straight cutting grooves and less chip adhesion are observed on the ground surface and there is also no extensive loading on the wheel surface after grinding