Zhongde Shi

Grinding characteristics of a nickel-based alloy using vitrified CBN wheels

An experimental study is reported on the grinding of a nickel-based alloy using vitrified CBN wheels. This work was motivated by switching the grinding of fir-tree root forms of jet engine blades from creep-feed grinding with conventional abrasive wheels to vitrified CBN wheels. The objective is to explore process limits and practical grinding parameters for judging the switch in terms of overall costs and productivity. Straight surface grinding experiments were conducted with water-based fluid on rectangular blocks at a fixed wheel speed vs = 45 m/s, various depths of cut a = 0.05–1.0 mm, and workspeeds vw = 2–40 mm/s. Grinding and dressing power, forces, surface roughness, and radial wheel wear were measured. Specific material removal rate of 8 mm3/(mm.s) was reached in rough grinding using a wheel dressed for achieving surface roughness Ra = 0.8 μm in finish grinding. It was found that shallow depths of cut combined with fast workspeeds, or less creep-feed modes, are more suitable for achieving high ma...

EXPERIMENTAL INVESTIGATIONS OF THE FORCE DISTRIBUTIONS IN THE GRINDING CONTACT ZONE

This paper is concerned with the experimental investigations for the prediction of the grinding force distribution in the grinding wheel and workpiece contact zone. A new approach was developed to predict the force distribution using the horizontal and vertical forces measured while grinding a workpiece with a shorter length along the grinding pass. Straight surface grinding experiments were conducted using straight oil as grinding fluid on a nickel-based alloy (IN718) with a 60-grit 150 mm diameter electroplated CBN wheel to implement this approach and to investigate the effects of wheel speeds and workspeeds on the distributions. Grinding power and forces were measured. It was found that the distribution along contact arc increases with a decreasing rate from bottom to top. Wheel speeds have a significant effect on the normal force distribution at the higher removal rate. The grinding power was estimated to verify the predicted force distribution and it was found to be in a good agreement with the measured power.

Exploration of a New Approach for Calibrating Grinding Power Model

This paper is concerned with the reliable calibration of the grinding power model. The power model used in the present paper is expressed by formulae with grinding parameters as input arguments, and a number of model constants representing a given wheel, workpiece, and grinding fluid combination. The model constants are calibrated using measured grinding forces and power, taking into consideration of the chip formation, sliding, and plowing components of the power. These correspond to the constants of specific chip formation energy uch, the coefficient of friction μ and average contact pressure pa, and the plowing force per unit width F′pl, respectively. A new generalized experimental approach was developed in this study to reflect the physical meaning of the model. Compared with other approaches, this approach does not require a pre-knowledge of the wheel wear flat area value and the regime of the average contact pressure. The proposed approach includes measurements of forces and power from surface grinding tests with a fixed set of grinding parameters conducted at different wheel dullness levels for calibrating the constant μ, as well as tests with variable workspeeds at each of the wheel dullness level for calibrating the other constants. As an application example, it was applied to calibrating the power model for grinding of a nickel-based alloy with oil as grinding fluid and electroplated CBN wheels. The calibrated model was then validated through tests under different grinding conditions.Copyright

Numerical simulation of force distributions in the grinding contact zone

Numerical simulation using finite element (FE) software (DEFORM) was performed for creep-feed grinding of Inconel (IN718) with a 60-grit 150 mm diameter electroplated CBN wheel to predict the normal and tangential force distributions in the grinding zone. The objective was to obtain the force distributions for predicting the maximum forces acting on individual grains and to explore the feasibility to simulate grinding processes with multiple cutting grains. The workpiece and wheel geometries were modelled first using 3D CAD modeller and then imported to DEFORM for simulation. Random distributions of the heights and spatial positions of abrasive grains on the wheel surface were considered in the wheel model. Material properties from material constitutive equations established by conventional cutting tests were used in the simulation. The simulated nodal forces were further processed to obtain the grinding zone force distributions. The simulated results were found to be in good agreement with experimental results.

High removal rate grinding of titanium alloys with electroplated CBN wheels

This paper is concerned with an experimental study on the grinding of a titanium alloy using electroplated CBN wheels with water-based grinding fluid and wheel surface cleaning fluid applied at high pressures. The objective is to explore the approaches and conditions to grind titanium alloys with enhanced material removal rates. Straight surface grinding experiments were conducted on titanium alloy blocks in both shallow depth of cut and creep-feed modes. Grinding power, forces, surface roughness, and radial wheel wear were measured. Specific material removal rates of 8 mm2/s in shallow cut mode and 3 mm2/s at a depth of cut as high as 3 mm in creep-feed mode were achieved without burning and smearing of ground surfaces. An average G-ratio of about 155 was obtained with a shallow depth of cut grinding condition. It was showed that it is feasible to grind titanium alloys with electroplated CBN wheels at enhanced removal rates by applying grinding and wheel cleaning fluid at high pressures.

Grinding of Chromium Carbide Coatings Using Electroplated Diamond Wheels

This paper reports an experimental study on grinding of chromium carbide coatings using electroplated diamond wheels. The work was motivated by machining carbide coatings in gas turbine engine applications. The objective is to explore the process conditions and parameters satisfying the ground surface quality requirements. Surface grinding experiments were conducted with water based grinding fluid on chromium carbide coated on flat surfaces of aluminum blocks for rough grinding at a fixed wheel speed vs = 30 m/s, and finish grinding at vs = 30, 60 m/s. The effects of depth of cut and workspeed on grinding power, forces, and surface roughness were investigated for each of the wheel speeds. Material removal rate Q = 20 mm3/s for rough grinding at a grinding width b = 101.6 mm was achieved. It was found that the maximum material removal rate achievable in rough grinding was restricted by chatters, which was mainly due to the large grinding width. The specific energy ranged from 27 to 59 J/mm3 under the tested conditions. Surface roughness Ra = 3.5- 3.8 µm were obtained for rough grinding, while Ra = 0.6 - 1.5 µm were achieved for finish grinding. Surface roughness was not sensitive to grinding parameters under the tested conditions, but was strongly dependent on the diamond grain sizes. Imposing axial wheel oscillations to the grinding motions reduced surface roughness by about 60% under the tested condition. It was proved that it is feasible to grind the chromium carbide coating with electroplated diamond wheels.

Assessment of an experimental setup for high speed grinding using vitrified CBN wheels

This paper is concerned with the assessment of an experimental setup for grinding experiments with a top wheel speed of 250 m/s. Among other considerations, high speed grinding is widely considered as a way for enhancing material removal rates by utilising large depths of cut and/or high workspeeds. Performing high speed grinding operations, however, presents challenges to the setup due to the high wheel speeds involved. An experimental setup was established in this study for high speed grinding of hardened nodular cast iron and steel using vitrified CBN wheels. This setup was assessed prior to grinding for wheel balancing and guarding, wheel core expansion and temperature rise, grinding fluid delivery, and idle power consumptions. It was found that high speed wheel rotations caused wheel expansion and temperature rise. A significant portion of the total power was consumed on actions other than material removals. The preliminary grinding tests indicated that the setup met the requirements for high speed grinding in general.