Ultrasonic-vibration-assisted micromachining of composite materials

Recently, the use of composite materials like CFRP (carbon fiber reinforced plastic) has become widespread in industrial fields because of their remarkable characteristics. However, CFRP is one of difficult to machine materials. The conventional machining of CFRP generally leads to tool wear and low quality of the machined surface. In particular, micromachining techniques such as micro-drilling processes have the problem of low rigidity of cutting tools. In order to overcome these problems, the ultrasonic-vibration-assisted machining of CFRP is proposed in this study. The cutting force is expected to decrease when axial- directional ultrasonic vibration is applied to the tool as a result of the intermittent cutting process with a large acceleration over a short period, which shown by H. Isobe [1]. The reduction in the culling force results in an improvement in the machining accuracy and the suppression of the delamination. The culling chips which adhere to the cutting edge and plug up to the drilled hole sometimes cause tool breakage. In order to remove the chips from the culling area, the application of cavitation's cleaning effect to the culling process, which proposed by H. Ogawa [2], is also proposed in this study. The ultrasonic vibration is applied to the culling fluid using a specially designed ultrasonic vibration horn. The cavitation generated around the culling point prevents the chips from adhering to the tool and drilled hole, so it is expected to ensure higher machining efficiency and better machining accuracy. This paper discusses small hole drilling tests on CFRP to verify the effect of toolvibration drilling, cavitation-aided drilling, and their combination (hybrid drilling). The delamination, easily occured at the outlet of a machined hole, can be reduced by applying ultrasonic vibration. With respect to the culling force, hybrid method can reduce the thrust force by 30% compared to conventional drilling. The experimental results show that the proposed method is useful for the efficient and accurate drilling. reduce the thrust force by 30% compared to conventional drilling.