Effect of Types of Grinding Fluid on Grinding Characteristics of CMSX4

Nickel-based heat-resistant alloys are widely used for fabricating the turbine blades in gas turbine engines. An increase in the number of such engines operated by air carriers will increase the demand for high-efficiency machining of nickel-based heat-resistant alloys. However, the high-efficiency grinding of nickel-based heat-resistant alloys is challenging because of their low thermal conductivity and thermal diffusivity, high chemical activity, large work-hardening properties, and high-temperature strength. In this work, the authors propose a high-efficiency grinding technique that uses speed-stroke grinding of nickel-based heat-resistant alloys, and aim to clarify the optimum grinding conditions for the proposed grinding method. The workpiece material is CMSX4 used for the turbine blades. A Cubitron + WA grinding wheel and WA grinding wheel mounted on a linear motor-driven surface grind machines are used for grinding, and the grinding force, surface roughness, and grinding ratio are investigated with the removal rate maintained constant. Two types of grinding fluid are prepared: solution and soluble. From the experiments, it is found that wet grinding features a lower grinding force, smaller surface roughness, and higher grinding ratio when compared to dry-cut grinding. The improvement in the grinding ratio at high table speeds is significant, and it is found to be greater for the soluble-type fluid than for the solution-type fluid.

A Novel Particle-Based Approach for Modeling a Wet Vertical Stirred Media Mill

Modeling of wet stirred media mill processes is challenging since it requires the simultaneous modeling of the complex multiphysics in the interactions between grinding media, the moving internal agitator elements, and the grinding fluid. In the present study, a multiphysics model of an HIG5 pilot vertical stirred media mill with a nominal power of 7.5 kW is developed. The model is based on a particle-based coupled solver approach, where the grinding fluid is modeled with the particle finite element method (PFEM), the grinding media are modeled with the discrete element method (DEM), and the mill structure is modeled with the finite element method (FEM). The interactions between the different constituents are treated by loose (or weak) two-way couplings between the PFEM, DEM, and FEM models. Both water and a mineral slurry are used as grinding fluids, and they are modeled as Newtonian and non-Newtonian fluids, respectively. In the present work, a novel approach for transferring forces between grinding fluid and grinding media based on the Reynolds number is implemented. This force transfer is realized by specifying the drag coefficient as a function of the Reynolds number. The stirred media mill model is used to predict the mill power consumption, dynamics of both grinding fluid and grinding media, interparticle contacts of the grinding media, and the wear development on the mill structure. The numerical results obtained within the present study show good agreement with experimental measurements.

Measurements of Non-Grinding Forces and Power

Grinding forces and power are important parameters for evaluating grinding process performance, and they are typically measured in grinding experiments. Forces are typically measured using a load cell or a dynamometer, whereas power is measured using an electrical power sensor to monitor the power of the spindle motor. Direct readings of the measurements include the net grinding force and power components for material removal and non-grinding components such as the impingement of a grinding fluid. Therefore, the net components must be extracted from the direct readings. An approach to extracting the net grinding forces and power is to perform additional spark-out grinding passes with no down feed. The forces and power recorded in a complete spark-out pass are used as the non-grinding components. Subsequently, the net grinding components are obtained by subtracting the non-grinding components from the corresponding totals for actual grinding passes. The approach becomes less accurate when large depths of cut, particularly large depths of cut and short grinding lengths, are involved. A new experimental approach is developed in this study to measure the non-grinding force and power components and to extract the net components. Compared with the existing approach, the new approach is more accurate for grinding with large depths of cut or short grinding lengths. In this approach, two additional grinding passes on an easy-to-grind material, one with and the other without a grinding fluid, are conducted using the same setup and condition as those in the actual test material to measure the forces and power for obtaining the non-grinding components. Subsequently, these non-grinding components are used as the non-grinding components of the actual material and subtracted from the total force and power components of the actual material to obtain the net values. To illustrate the application of the approach, surface grinding experiments are conducted to collect the forces and power. The extracted net power is consistent with the power predicted with the extracted net forces.

Optimization of Wet Grinding Conditions of Sheets Made of Stainless Steel

This study addresses the wet grinding of large stainless steel sheets, because it is difficult to subject them to dry grinding. Because stainless steel has a low thermal conductivity and a high coefficient of thermal expansion, it easily causes grinding burn and thermal deformation while dry grinding on the wheel without applying a cooling effect. Therefore, wet grinding is a better alternative. In this study, we made several types of grinding wheels, performed the wet grinding of stainless steel sheets, and identified the wheels most suitable for the process. As such, this study developed a special accessory that could be attached to a wet grinding workpiece. The attachment can maintain constant pressure, rotational speed, and supply grinding fluid during work. A set of experiments was conducted to see how some grinding wheels subjected to some grinding conditions affected the surface roughness of a workpiece made of a stainless steel sheet (SUS 304, according to Japanese Industrial Standards: JIS). It was found that the roughness of the sheet could be minimized when a polyvinyl alcohol (PVA) grinding wheel was used as the grinding wheel and tap water was used as the grinding fluid at an attachment pressure of 0.2 MPa and a rotational speed of 150 rpm. It was shown that a surface roughness of up to 0.3 μm in terms of the arithmetic average height could be achieved if the above conditions were satisfied during wet grinding. The final surface roughness was 0.03 μm after finish polishing by buffing. Since the wet grinding of steel has yet to be studied in detail, this article will serve as a valuable reference.