Geng Zhi

Experimental study of time-dependent performance in superalloy high-speed grinding with cBN wheels

ABSTRACT The time-dependent performance of grinding is expressed as the change of process output measures as a function of time during grinding. Although the wheel capability will be restored by dressing, the time-dependent performance of grinding during one dressing skip is the determinant on the grinding quality variation in terms of surface integrity and workpiece geometric accuracy. Therefore, understanding of grinding time-dependent performance in relation with the wheel–workpiece microscopic interaction is critical for wheel and process development to achieve stable grinding processes. In this article, the grinding of superalloy with cubic boron nitride (cBN) grinding wheels is performed. The time-dependent performance is recorded to represent the characteristic features, and the microscopic wheel topography is measured under scanning electron microscope (SEM) throughout the grinding process, so as to reveal the root cause for the time-dependent performance and its impact on the workpiece quality variation. The experiment results indicate that during the grinding process, there exist three characteristic stages, namely, initial wheel wear stage, severe wheel wear stage, and wheel resharpening stage. Moreover, the change trend of spindle power consumption, workpiece quality on surface hardness and roughness, wheel wear condition, and G ratio are consistent with the wheel topography evolution reflected by SEM photos, which can be used to present the three grinding stages. The wear and replacement of the efficient grain cutting edges result in the time-dependent performance during superalloy high-speed grinding with cBN wheels.

IM (Indentation Method) Based Impact Fracture Characteristics of cBN Crystal and Their Influence on High Speed Wheel Performance

Cubic Boron Nitride (cBN) is considered a superabrasive due to its excellent material behavior, and is commonly used in the manufacturing of high end grinding tools, in particular for machining hard-to-machine materials, in order to achieve high productivity in combination with high precision. During the actual grinding process, the performance of grinding tools is significantly affected by the fracture response of employed cBN crystals to the external impact load related to the grinding speed. Therefore, two types of cBN crystals are selected in this paper and their fracture resisting behaviors are measured under various impact loading rates through the Indentation Method (IM). In order to establish the fracture behavior of cBN crystals and the overall grinding performance of cBN wheels, high speed surface grinding experiments are conducted and grinding performances are evaluated regarding the evolution of grinding force and power consumption, wheel wear and grinding efficiency, as well as the chemical stability of cBN materials on affinity. The experimental results show a good agreement of cBN crystal’s impact fracture properties on the cBN grinding wheel performance, which helps to understand cBN crystal’s high speed grinding characteristics.

Time Dependent Behavior Analysis of Inconel 718 in High Speed Grinding Process

The time dependent behavior of grinding is expressed as the change of process output measures as a function of time during grinding. Although the wheel capability will be restored by dressing, the time dependent behavior of grinding during one dressing skip is determinant on the grinding quality variation in terms of surface integrity and workpiece geometric accuracy. Therefore, understanding of grinding time dependent behavior in relation with the wheel-workpiece microscopic interaction is critical for wheel and process development to achieve stable grinding processes. In this paper, the high speed grinding of inconel 718 with cBN grinding wheels is carried out. The time dependent behavior is recorded to represent the characteristic features. And the microscopic wheel topography is measured under SEM throughout the whole grinding process so as to reveal the root cause for the time dependent behavior and its impact on the workpiece quality variation.

The Modelling and Analysis of Topographical Properties with the ‘through-the-Process’ Grinding Wheel Model

The single layer superabrasive wheels are made by joining all abrasive grains onto the wheel hub by electroplating or brazing. Recently, the attention has risen to acquire better grinding quality through more stringent grain size control. For the size grain control process, the abrasive grains are re-meshed for smaller dimensional derivation after outsourced from external grain manufacturers. Therefore, the understanding of correlation between the grain dimensional deviations with the wheel performances will be critical for the wheel design and optimization. In this paper, the ‘through the process’ grinding wheel model is developed for single layer CBN wheels by simulating each wheel fabrication procedure numerically. The effectiveness of the wheel model is verified by comparing with the experimental measurement, which proves the efficacy of the wheel model and could further provide the quantitative basis for grinding wheel quality control and process design.