Experimental study on end face grinding stability of thin-walled CFRP circular cell

ObjectivesCFRP circular cell honeycomb consists of thin-walled circular cells and are applied in the aerospace. It is difficult to machine the CFRP honeycomb due to its characteristics of thin walls, weak rigidity and non-continuous periodicity. During grinding, there are sharp noises and intense fluctuations of grinding force, reflecting the instability of the process. Considering the structural characteristics of thin-walled CFRP circular cells, this paper conducts end-face grinding experiments and explores the influence of the exit angle, grinding speed, feed rate, and grinding depth on grinding stability. MethodsThe machining of CFRP honeycomb is a repetition of machining thin-walled CFRP circular cells. Taking a single cell as the research object, the end-face grinding experiment is carried out by defining the exit angle and the interaction angle of grinding based on its structural characteristics. The influence of the exit angle on grinding stability is analyzed using the time-domain and frequency-domain characteristics of the axial force. The standard deviation of the resultant force in the horizontal plane is used to quantitatively describe the grinding stability of the thin-walled CFRP circular cell. Moreover, the influence of the exit angle on the interaction angle of grinding is analyzed based on the magnitudes of the tangential and the radial forces. The relationship between the interaction angle of grinding and the grinding stability is established to analyze the influence of grinding speed, feed rate and grinding depth on the interaction angle of grinding and the grinding stability. Furthermore, the influence of processing parameters on the radial, the tangential and the resultant forces in the horizontal plane is studied. ResultsIt is found that the exit angle is the main factor affecting the grinding stability. Compared with other exit angles, when the exit angle is 60° − 90°, the fluctuation range of the axial force in the time domain increases dramatically and a significant peak appears in the frequency domain. The standard deviation of the resultant force in the horizontal plane increases sharply. The interaction angle of grinding is small, and the direction of the resultant grinding force is close to the tangential direction of the thin-walled CFRP circular cell, resulting in poor grinding stability. The interaction angle of grinding increases linearly with the increase of the exit angle, which strengthens the grinding stability. With the increase of grinding speed, the interaction angle of grinding increases gradually, and grinding stability improves. With the increase of feed rate, the interaction angle of grinding shows no obvious change, and the grinding stability remains nearly unchanged after an initial decrease. With increasing grinding depth, the interaction angle of grinding decreases gradually, and the grinding stability declines. In terms of grinding force, with increasing exit angle, the radial force and the resultant force in the horizontal plane first decrease and then increase, while the tangential force decreases. With increasing grinding speed, the tangential force and resultant force in the horizontal plane gradually decrease, though the overall change range is small, and the radial force shows no obvious change. With increased feed rate and grinding depth, the radial force, tangential force, and resultant force in the horizontal plane increase approximately linearly. ConclusionsFor thin-walled and weakly rigid CFRP circular cell honeycomb, grinding stability is significantly affected by machining parameters. This paper investigates the influence of machining parameters on grinding stability through end-face grinding experiments of CFRP circular cells and reveals the relationship between the interaction angle of grinding and grinding stability. To enhance grinding stability of the CFRP circular cell honeycomb, the exit angle should avoid the range of 60° − 90°, and a larger grinding speed should be used with a smaller feed rate and grinding depth.