Holes In Brittle Materials Research Articles

Comparative Analysis of Movements of Curved Ultrasonic Instruments

The paper presents a theoretical analysis of vibrations of a curvilinear rod in the form of a loop of low rigidity formed from a quarter of a circle with a constant radius, limited by an angle π/2 < γ < π and two rectilinear rods. It is indicated that in the practice of ultrasonic technology, some types of structures are known in which elastic elements are used as resonators, waveguides, oscillation transformers and instruments for influencing the processed materials. Their use makes it possible to obtain an additional impulse of force in the working area by using the potential energy caused by the action of the elastic properties of such elements. However, insufficient attention has been paid to the theoretical justification of the use of elastic elements in ultrasonic systems. In this regard, the present work is devoted to the theoretical substantiation of the use of an elastic tool made of a thin rod having the shape of a loop. The diagram and calculation of displacements of the free end of a curved rod under the action of forces directed along the longitudinal axis are given in the paper. It is shown that elastic displacements are caused by a curved shape in the form of an arc of a circle of a curved rod. For comparison, calculation schemes of two types of curved rod with an attached rod are given. In the first case, the free ends of the rectilinear rods, directed vertically downwards, make elastic movements along two coordinates. In the second case, the ends of rectilinear rods directed at a certain angle to the vertical axis and converging at the bottom point due to the symmetry of their location, make vertical movements only along one coordinate. The considered shape of the curved rod can be successfully used as a tool for performing technological tasks in the ultrasonic method of processing holes in brittle materials, spot welding, etc. Such a scheme, in contrast to the traditional ultrasonic treatment scheme based on the use of rectilinear rods, makes it possible to increase the magnitude of the vibration amplitude of the instrument due to elastic displacements of the curved section of the rod of low rigidity. The proposed form will increase the intensity of tool vibrations and increase process productivity and processing accuracy. The resulting calculation formula shows that the amount of elastic displacements of curved rods is affected by the cross-sectional stiffness and the radius of curvature of the curved part, as well as the angle of inclination of the rectilinear rod. The theoretical calculation is supplemented by a comparative experimental study of the Chladni forms for both schemes obtained on the sheet surface using abrasive particles.

Laser forming of holes in brittle materials assisted by stress reduction through heating

A laser method for forming holes in brittle materials, such as glass and glass-ceramics, and the effect of heat treatment applied prior to and during hole formation on laser-induced transient and residual stresses, sample strength and hole quality are reported. We have shown, for the first time to our knowledge, that developed CO2 laser-based hole forming technique utilizing pulse burst mode operation enables quick formation of the holes of various diameters in substrates of different thickness in the range from about 0.03mm up to 3mm without cracking or shattering of the material, mitigating a negative effect of an ablation process.

Investigations on the critical feed rate guaranteeing the effectiveness of rotary ultrasonic machining

Rotary ultrasonic machining (RUM) is a well-known and efficient method for manufacturing holes in brittle materials. RUM is characterized by improved material removal rates, reduced cutting forces and reduced edge chipping sizes at the hole exit. The aim of this study is to investigate the critical feed rate to guarantee the effectiveness of RUM. Experimental results on quartz glass and sapphire specimens show that when the feed rate exceeds a critical value, the cutting force increases abruptly, accompanied by a significant decrease of ultrasonic amplitude. An analytical model for the prediction of critical feed rates is presented, based on indentation fracture mechanic and the theory of impact of vibrating systems. This model establishes the theoretical relationships between the critical feed rate, idling resonant ultrasonic amplitude and spindle speed. The results predicted by the analytical model were in good agreement with the experimental results.

Investigations on the edge-chipping reduction in rotary ultrasonic machining using a conical drill

The edge chipping of holes, which is induced by mechanical machining, restricts the applications of brittle materials. Rotary ultrasonic machining is considered a suitable approach to machine holes in brittle materials with a smaller edge-chipping size. However, obvious edge chipping at the hole exit in rotary ultrasonic machining remains observable. In this study, conical diamond core drills with various characteristic angles ( θ) were designed to further reduce the edge-chipping size for rotary ultrasonic machining. Machining tests on quartz glass were conducted to evaluate the effectiveness of this new type of drill. Experimental results show that the conical drill can obviously reduce the edge-chipping size only when certain conditions are satisfied. The mechanism of edge-chipping reduction using a conical drill was revealed by the theoretical analysis and detailed observation of the thrust force and obtained cylinder. To guarantee the feasibility of the conical drill, its characteristic angle should exceed a critical value at a certain feed rate. A higher feed rate requires a higher critical characteristic angle. The other advantage of the conical drill is its ability to suppress the bad effects of increasing the feed rate on the stability of ultrasonic vibration.

On the mechanism of edge chipping reduction in rotary ultrasonic drilling: A novel experimental method

Edge chipping induced by the mechanical machining of holes in brittle materials restricts the applications of the brittle materials. Rotary ultrasonic drilling is a suitable approach for the machining of holes in brittle materials with a smaller size of edge chipping. A good understanding of the mechanism of edge chipping reduction when employing rotary ultrasonic drilling is helpful to the application and optimization of the drilling technique. In this study, a novel edge chipping mechanism for the machining of holes considering machining-induced cracks was proposed and verified by experiments on quartz glass. The size of the machining-induced crack was evaluated experimentally. Experimental results indicate that the initiation of edge chipping is determined by both the magnitude of the driving force and the size of the machining-induced crack. However, the size of edge chipping strongly depends on the undrilled thickness following a directly proportional relation. Moreover, the geometric similarity of edge chipping is evidence for the consistency of the crack propagation direction when edge chipping begins. Finally, experiments conducted under various machining conditions demonstrate that the reduction of the size of machining-induced cracks in rotary ultrasonic drilling is another important factor contributing to the reduction of the size of edge chipping in rotary ultrasonic drilling, comparing with conventional diamond drilling.

Experimental Investigation on the Performance of Grinding Assisted Electrochemical Discharge Drilling of Glass

Grinding assisted electrochemical discharge drilling (G-ECDD) is a novel technique for producing micro and macro holes in brittle materials including advanced ceramics and glass, both efficiently and economically. G-ECDD involves the use of a rotating diamond core drill as the tool in a normal electrochemical discharge machine setup. The material removal happens by a combination of thermal melting due to electric discharges, followed by grinding action of diamond grits and chemical etching action. In this study, the effect of process parameters like voltage, duty cycle, cycle time and electrolyte concentration on material removed (MR) was investigated systematically using response surface methodology. Analysis of variance was performed to identify the significant factors and their percentage contribution. The most significant factor was found to be duty cycle followed by voltage, cycle time and concentration. A quadratic mathematical model was developed to predict MR. Tool wear was found for different frequencies and voltages. Higher tool wear was observed for high frequency above 5kHz pulsed DC supply at high voltage of 110V. Tool wear at the end face of the tool was found to be a significant problem affecting the tool life.

Characteristics of ultrasonic complex vibration for hole machining in brittle materials: Comparison of longitudinal and complex vibration sources

Ceramic materials have the advantage of abrasion resistance, heat resistance, and corrosion resistance compared with metal materials. The combination of ultrasonic vibration and polishing slurry has been shown to be an effective method for machining holes in brittle materials. However, conventional ultrasonic methods use only longitudinal vibration. Complex vibration sources with diagonal slits have been applied to ultrasonic motors and ultrasonic welding; in contrast, few studies have been conducted on ultrasonic machining using complex vibration and polishing slurry. Removal rates and machining accuracy are expected to be improved by using ultrasonic complex (longitudinal-torsional) vibration. Therefore, we have developed a new method using polishing slurry together with ultrasonic longitudinal and torsional vibration sources with diagonal slits for hole machining of brittle materials. Torsional vibration is considered to improve the processing of the hole side of ceramic materials such that the polishing slurry can circulate more easily. We assume improvement of removal rate and machining accuracy for that reason. In experiments, soda-lime glass is used as the processing material in ultrasonic complex vibration or ultrasonic longitudinal vibration, and machining time is measured to assess the hole machining characteristics.

Mathematical model for cutting force in rotary ultrasonic face milling of brittle materials

Rotary ultrasonic machining of brittle materials, such as glass, ceramics, silicon, and sapphire, has been ex- plored in a large number of experimental and theoretical investigations. Mechanistic models have been developed to predict the material removal rate or cutting force in the rotary ultrasonic machining of brittle materials. However, most merely describe the rotary ultrasonic machining process of drilling holes in brittle materials. There are no reports on the development of a cutting force model for flat surface rotary ultrasonic machining, i.e., rotary ultrasonic face milling. This paper presents a mathematical model for the cutting force in the rotary ultrasonic face milling of brittle materials under the assumptionthatbrittlefractureremovalistheprimarymodeof material removal. Verification experiments are conducted for the developed cutting force model and show that the trends of input variables for the cutting force agree well with the trends of the developed cutting force model. The developed cutting force model can be applied to evaluate the cutting force in the rotary ultrasonic face milling of brittle materials.

Material Removal Mechanisms Involved in Rotary Ultrasonic Machining of Brittle Materials

Rotary ultrasonic machining (RUM) is considered to be a very effective and relatively accurate way to drill deep holes in brittle materials. Although brittle fracture (micro chipping) is the dominant material removal mechanism utilized by the RUM process, poor surface roughness and deep penetrated cracks are the consequence if the machining parameters are not properly controlled. To ensure the quality of the generated surface and to improve the process efficiency, efforts have been made in this study to correlate the material removal mechanisms, surface integrity and tool wear involved in the RUM process. Diamond-impregnated tools were used in the experiment and the ultrasonic vibration frequency was kept at 20 kHz. Three major material removal modes namely, impact mode, grinding mode and erosion mode were found to be the dominant removal processes at the tool tip, around the diamond wheel and around the steel sleeve respectively. It was also found that, during the grinding/erosion processes, the bonding material of the wheel was first eroded away and left big part of diamond grits well-exposed. Pull-out and/or fracture are normally the consequence of these exposed diamond grits due to the lack of support and protection.

Formation of Holes in Engineering Ceramic Plates by Press-Working

The purpose of the present research is to establish a simple method of forming holes in brittle materials by a conventional press-working. By utilizing a specially designed blunted spherical punch, a small hole is formed at the center of the specimen at its first stage, and subsequently the hole is enlarged by a continuous punching operation. The present improved technique realizes a very low load for punching operation as well as a considerably low clamping stress for preventing serious radial cracks around the hole. Some punching works in engineering ceramic plates were performed by the method for various aspect ratios AR=3∼32(AR=D/t, D; the diameter of the hole and t; the plate thickness). As long as the AR value is larger than about 3, the present method proved to be very successful in forming holes in tough engineering ceramics such as alumina, silicon-nitride and toughend zirconia, as well as in making small holes less than 1 mm in diameter. The technique is also successful in forming many holes by a single operation.

Forming holes in brittle materials: An antique technique and its report by Charles Babbage, 1792–1871

In his biography, Passages from the Life of a Philosopher, Charles Babbage, an outstanding pioneer in computer technology, described a method of forming holes in brittle materials. This he had from one of his many “practical” friends, the originator of the method not being known. The technique is of great importance to-day in relation to the working of ceramics. Close similarities are often described in present-day papers and thus it is fitting that historical knowledge of the method be known.