Experimental Investigation of Rotary Ultrasonic Machining of Fiber Reinforced Polymer Composites

Abstract

Composite materials have been exercised and utilized in the fields of engineering since late1960s. These materials extended to progress at a great footstep in line with the emergence in other materials like metals, ceramic, and polymeric materials. Consequently, more than fifty thousand composite materials have found immense acceptance in wide variety of industries. Composite materials developed with polymer as matrix and carbon fiber reinforcement are called carbon fiber reinforced polymer composite (CFRP). newlinePolyetherimide composite is one of the most inflexible and lightest composite material having wide applications in aviation, aerospace and automobile sectors. Conventional machining of Polyetherimide composite demonstrate problems of drill jamming, introduction of cracks, delamination of composite and poor surface topography of components. Therefore, it becomes impetrative to explore the effectiveness of rotary ultrasonic drilling in drilling of Polyetherimide composite. No previous research studies have attempted drilling of Polyetherimide composite by rotary ultrasonic drilling process so far. Hence, present study intended to explore the potential of rotary ultrasonic drilling in drilling of Polyetherimide composite. newlineSince, there is no availability of commercial rotary ultrasonic drilling machine; in this study, attempt is made to fabricate the rotary ultrasonic drilling set up by modification of an existing vertical milling machine by incorporation of ultrasonic generator, tool and horn assembly, slip rings, and carbon brushes etc. Provision is also made for precise control of impingement of ultrasonics on the workpiece. Hollow diamond tools as recommended by literature are also designed and fabricated for drilling of Polyetherimide composite. newlinePolyetherimide composite is developed by hand laying technique and subsequent use of power press. The composite is fabricated by using 24 layers of carbon fibers in a Polyetherimide matrix. Various types of testing involving hardness test, wear volume and coefficient of friction tests are carried out to check the suitability of Polyetherimide composite in industrial applications. newlineIn the present study, an attempt is made to compare the performance of normal drilling, rotary drilling and rotary ultrasonic drilling in terms of output performance measures of force, torque, surface roughness, material removal rate and cutting temperature. It has been observed that rotary ultrasonic drilling exerts less force and torque on workpiece as compared to normal newlinevi newlinedrilling and rotary drilling. Force, torque, surface roughness and material removal rate reduced with increase in abrasive grit size. A better surface morphology is obtained after carrying out rotary ultrasonic drilling than normal drilling and rotary drilling in drilling of Polyetherimide composite. newlineThe present study also carried out detailed parametric analysis of rotary ultrasonic drilling in drilling of Polyetherimide composite. The effect of grit size, ultrasonic power, feed rate and rotational speed on performance measures of force, torque, surface roughness, material removal rate and cutting temperature are ascertained by carrying out statistically designed experiments planned by central composite design. A number of experiments are conducted to access the main effects as well as interaction effects of parameters on aforesaid performance measures. Results of this phase revealed that cutting force and torque predominantly decided by abrasive grit size followed by feed rate and tool rotational speed. Surface roughness and temperature are most significantly affected by tool rotational speed. newlineMultivariate regression models have been developed for force, torque, surface roughness, material removal rate and cutting temperature, which are capable of predicting the value of performance measures at any desirable parameter settings and these models have been successfully validated. newlineStudy also presented optimal set of parameters by carrying out single objective optimization and multi-objective optimization of performance measures. These optimal sets of control factors serve as drilling guidelines for manufacturing planners for subsequent use of these findings in industrial applications. newlineStudy also explored the possibility of repeated use of same drill tool in normal drilling and rotary ultrasonic drilling. The study revealed that hollow diamond tool can be used repeatedly up to 100 times without serious effect on the performance measures. Whereas, a continuous decline in performance measures is observed in normal drilling after the repeated use of drill. newlineKeywords: Polyetherimide composite, rotary ultrasonic drilling, normal drilling, rotary drilling, central composite design, force, torque, surface roughness, material removal rate and cutting temperature.