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Machining process of glass fiber composites usually induces delamination damage. The presence of delamination may cause changes in the mechanical characteristics of the composite structures. In this research, a comprehensive experimental study is performed to analyze the influence of different parameters such as thermal fatigue, lay-up arrangement, resin type, feed rate and cutting velocity on the delamination of glass fiber composites under different drilling processes. Besides, influence of ultrasonic vibration exerting on the tool as a new and high-tech process is investigated. To follow this aim, different composite specimens with various resin types and lay-up arrangements are fabricated and a thermal fatigue condition is provided. Additionally, the Taguchi method is employed to obtain the optimized damage reduction condition in terms of mentioned parameters. The results indicated that thermal fatigue and unsymmetrical lay-up arrangement result in more delamination damage. It was also established that the influence of mentioned parameters is more considerable in higher cutting velocities. Moreover, ultrasonic vibration application is suggested to have the least delamination damage. [ABSTRACT FROM AUTHOR]

During machining of thin material, workpiece endures deflection due to cutting forces that negatively influence dimensional tolerances and machined surface quality. An applicable method for the restriction of such problems is machining in the presence of ultrasonic vibration. However, understanding of how this improvement is caused by this type of vibration needs extensive studies. This paper presents a workpiece deflection model for conventional drilling and ultrasonic-assisted drilling of 1 mm thickness aluminum 7075. The workpiece considered was a thin beam and the deflection was determined by the use of beam vibration theory in continuous system. The deflection of workpiece during both the conventional and ultrasonic-assisted drilling processes were determined by means of developed model and compared with those derived from experiments. It was found that the average prediction error in worst case was less than 20%. Also, it is observed from both the experimental and theoretical approaches that applying ultrasonic vibration to drilling tool significantly reduces the workpiece deflection. Furthermore, from both approaches, it is identified that increase in vibration amplitude causes a decrease in beam deflection. Restriction of beam deflection by exerting high-amplitude ultrasonic vibration causes elimination of cap burr in the exit hole due to enhancement in the rigidity of workpiece. [ABSTRACT FROM AUTHOR]

In this study, ultrasonic assisted drilling (UAD) is performed to investigate the effect of ultrasonic vibrations on common difficulties existed in conventional drilling (CD). UAD is a promising and advanced technique by which a harmonic movement with high frequency and low amplitude is superimposed on the movement of work material or cutting tool. The study is conducted both experimentally and numerically; at first, a UAD system is designed, manufactured, and carried out on a milling machine and then experimental tests are accomplished. In the following, experimental results are supported by the help of three-dimensional (3D) finite element simulation. Finally, the dependent parameters such as the burr height and cylindricity of the ultrasonically and conventionally drilled workpiece are measured and compared. Briefly, it was proved that the intermittent movement of drill bit in the direction of feed rate results in broken and discontinuous chips by which built-up-edge (BUE) is reduced and hole quality is improved. In addition, the burr height, which is known as unwanted projection of material at the exit surface of pieces, can notably decrease, if UAD is considered. [ABSTRACT FROM AUTHOR]

Conventional drilling (CD) which is known by two rotary and linear motions is considerably used in material removal processes; however, this method cannot satisfy the new demands of modern industry anymore, encountering with some serious technological constraints such as fast tool wear, high thrust force, and so on. A new and promising method which has been used recently as an alternative technique to cope or at least diminish common difficulties in CD is imposing ultrasonic vibrations to the cutting process, where vibrations usually with high frequency and low amplitude are superimposed in the movements of cutting tool. This study is a new exercise which considers the effects of one and two directional ultrasonic vibrations in drilling of AISI 1045 compared to CD. In one directional technique known as longitudinal ultrasonic assisted drilling (L UAD), ultrasonic vibrations are added to the feed motion and in two directional vibrations; ultrasonic vibrations are simultaneously applied to both feed and rotary motions known as longitudinal-torsional ultrasonic assisted drilling (L-T UAD). The study which is performed both experimentally and numerically does its best to evaluate and compare the obtained results in CD, L UAD, and L-T UAD. In experimental part, a system including two vibratory tools and a rotary mechanism is designed, fabricated, and then assembled with other equipment on a milling machine to accomplish drilling tests. In numerical part, a FE model is also developed with the aim of further understanding of experimental results, by which drilling operations either conventional or vibratory in different forms can be conducted and studied. As a brief conclusion, it was found that ultrasonic vibrations can be used as an effective tool for enhancement of drilling process and longitudinal-torsional vibrations reveal better results than longitudinal vibrations. [ABSTRACT FROM AUTHOR]

Glass fiber reinforced plastics are used in variety of industrial and constructional applications for their superb mechanical and physical properties. Delamination is one of the most important and prevalent damages in machining of glass fiber reinforced plastics. Diamond core drills have the capability of simultaneously drilling and grinding of fiber reinforced plastics, which results in hole quality improvement. Rotary ultrasonic-assisted drilling is the new machining process to drill holes on fiber reinforced plastics and has attracted increasing attention in recent years. In this paper, thrust force and delamination in rotary ultrasonic-assisted drilling of glass fiber reinforced plastics using diamond core drill have been investigated. A proper ultrasonic system for a core drill in ABAQUS was designed and fabricated. Influence of ultrasonic vibration and then tool grain size, fiber-volume fraction and machining parameters including spindle speed and feed rate on thrust force and delamination was investigated. Higher thrust force induces more delamination. As a result of the study, less delamination was achieved in ultrasonic-assisted mode by using a tool with larger grain size onto lower fiber-volume fraction composites. Additionally, experiments showed that lower spindle speed and higher feed rate induce more delamination. [ABSTRACT FROM AUTHOR]

In general, drilling of aeronautical materials is faced with some difficulties. To improve this process, a variety of methods have been presented by researchers. One of these methods is ultrasonic-assisted drilling (UAD). In this study, performance of longitudinal-torsional (L-T) vibration in UAD of Al 7075-T6 with HSS tool is investigated. Accordingly, a vibration tool with ability of producing L-T vibration was designed. After modal analysis and achievement of desired resonance frequency, it was fabricated and some experimental tests were conducted. A dynamometer with six degrees of freedom was utilized to measure torque and thrust force during the cutting process. As a result, it was revealed that this kind of vibration significantly reduces cutting forces compared with the conventional drilling (CD). Furthermore, this reduction was clarified by investigation of generated chips and tool rake angle. Moreover, effect of ultrasonic vibration on drill skidding and surface quality has been studied. [ABSTRACT FROM AUTHOR]

In this study, a combined drilling method consists of ultrasonic-assisted drilling (UAD) under the presence of minimum quantity lubrication (MQL), is evaluated. Effect of this method on machinability factors is investigated by implementation of a dynamometer and a vision-measuring microscope. Then the results are compared with the values obtained in conventional drilling, and separately UAD and MQL-drilling. As a result, it was revealed that the output parameters were significantly improved when combined MQL- UAD method was exerted. In particular, built-up edge and drill skidding have almost been eliminated. Moreover, it was shown that increase of tool rake angle and producing broken chips caused thrust force and surface roughness to be reduced in UAD and UAD-MQL. In the combined strategy, burr-less hole has been achieved due to the formation of solid burr at the exit surface of drilled hole. [ABSTRACT FROM AUTHOR]

In this study, 3D finite element simulation of ultrasonically-assisted drilling is carried out to analyze the effect of ultrasonic vibrations on common difficulties existed in conventional drilling. Influence of harmonic movement of drill bit on the formation of built-up edge is experimentally evaluated and also discussed by investigation of heat generation on the tool faces in simulation. At the end, it was revealed that intermittent movement of drill bit in vibration method causes the total time of heat transfer between workpiece and drill bit to be reduced resulting lower built-up edge formation compared to conventional drilling. Moreover, linear motion of cutting tool in the feed direction results in the increase of chip strain and consequently damage value which causes to generation of broken chips. [ABSTRACT FROM AUTHOR]