No description available.

Titanium alloys have outstanding mechanical properties such as high hardness, a good strength-to-weight ratio and high corrosion resistance. However, their low thermal conductivity and high chemical affinity to tool materials severely impairs their machinability with conventional techniques. Conventional machining of Ti-based alloys is typically characterized by low depth of cuts and relatively low feed rates, thus adversely affecting the material removal rates (MRR) during the machining process. Ultrasonically assisted turning (UAT) is an advanced machining technique, in which ultrasonic vibration is superimposed on a cutting tool. UAT was shown to improve machinability of difficult-to-machine materials, such as ceramics, glass or hard metals. UAT employment in the industry is, however, currently lacking due to imperfect comprehensive knowledge on materials' response and difficulties in obtaining consistent results. In this work, significant improvements in the design of a UAT system were performed to increase dynamic and static stiffness of the cutting head. Concurrent improvements on depth-of-cut controls allowed precise and accurate machining operations that were not possible before. Effects of depth of cut and cutting speed were investigated and their influence on the ultrasonic cutting process evaluated. Different cutting conditions -from low turning speeds to higher recommended levelwere analysed. Thermal evolution of cutting process was assessed, and the obtained results compared with FE simulations to gain knowledge on the temperatures reached in the cutting zone. The developed process appeared to improve dry turning of Ti-15-3-3-3 with significant reduction of average cutting forces. Improved surface quality of the finished work-piece was also observed. Comparative analyses with a conventional turning (CT) process at a cutting speed of 10 m/min showed that UAT reduced the average cutting forces by 60-65% for all levels of ap considered. Temperature profiles were obtained for CT and UAT of the studied alloy. A comparative study of surface and sub-surface layers was performed for CT- and UAT-processed work-pieces with notable improvements for the UAT-machined ones. Two- to three-fold reductions of surface roughness and improvements of other surface parameters were observed for the UAT- machined surfaces. Surface hardness for both the CT- and UAT-machined surfaces was investigated by microindentation. The intermittent cutting of the UAT-process resulted in reduction of hardening of the sub-surface layers. Optical and electronic metallographic analyses of cross-sectioned work-pieces investigated the effect of UAT on the grain structure in material's sub-surface layers. Backscatter electron microscopy was also used to evaluate the formation of α-Ti during the UAT cutting process. No grain changes or α-precipitation were observed in both the CT- and UAT-machined work-pieces.

No description available.

No description available.

A tendência da fabricação de moldes e matrizes é utilizar a tecnologia de usinagem HSM (High Speed Machining), pois esta pode produzir superfícies com melhor qualidade. Isto é possível, pois pode-se aumentar o número de passes laterais de um molde, sem que haja perdas de tempo de ciclo de usinagem, melhorando assim a qualidade do produto. No entanto, com a crescente utilização desta tecnologia, o perfil gerado de uma superfície usinada com uma fresa de ponta esférica, é alterado. Isto ocorre porque, normalmente, é possível medir-se a rugosidade em duas direções, obtendo-se em cada uma delas um valor de rugosidade máxima: um é o pico (crista) entre passes laterais e o outro é a altura de crista entre avanços por dente sucessivos. Cada um deles tem maior importância em função dos parâmetros utilizados. Estudar os fatores que alteram o perfil de rugosidade se faz, portanto, necessário. O objetivo deste trabalho é verificar experimentalmente como os parâmetros de usinagem: avanço por dente, passe lateral, diâmetro da ferramenta, ângulo de inclinação do eixo axial da ferramenta de corte e direção de corte (unidirecional ou bidirecional) influenciam o perfil de rugosidade e a rugosidade máxima, além de criar um modelo matemático que possa prever estas alterações. Foi mostrado neste trabalho que o perfil de rugosidade para corte unidirecional é diferente do corte bidirecional, e que, à medida que a relação entre avanço por aresta e passe lateral cresce, a rugosidade máxima também aumenta. Mas, ao se inclinar o eixo axial da ferramenta e aumentar o diâmetro da fresa esférica a rugosidade máxima diminui. Em resumo, este trabalho visa mostrar quais são os fatores que influenciam o acabamento de superfícies usinadas com fresas de topo esférico em condições, cuja relação entre o passe lateral e avanço por dente são típicas da HSM. / The trend in molds and dies manufacturing is the use of the HSM (High Speed Machining) technology, since it is able to produce surfaces with a better quality. This is possible because the number of radial passes, can be increased without lossing in the machining cycle times, enhancing the product quality. But with the arising utilization of this technology, the generated profile in a surface machined with a ball nose end milling cutter is changed. This happens because, it is usually possible to measure the surface roughness in two directions, getting in each of them a maximum surface roughness value: one of them is the peak to valley height between radial passes and the other one is the same parameter between successive feed per tooth. Each of them has major importance depending on the used cutting parameters. To study the factors that change the surface roughness profile is, therefore, necessary. The goal of this work is experimentally verify how the cutting parameters: feed per tooth, radial pass, tool diameter, spindle inclination angle and cutting direction (unidirectional or bidirectional) influences the surface roughness profile and the peak to valley roughness, besides of creating a mathematical model able to predict these changes. It was showed in this work that the surface roughness profile generated in a unidirectional cut is different of the profile generated in a bidirectional cut and that, as the ratio between feed per tooth and radial pass increases the same happens with the peak to valley surface roughness. But when the spindle is tilt and the ball nose cutting tool diameter is bigger the surface roughness decreases. This work aims to show which are the factors that influences the finishing of surfaces milled with ball nose end milling cutters using conditions whose ratio between the radial pass and feed per tooth are typical of HSM.

Tool chatter in longitudinal turning is addressed with a new perspective using a complex machining model describing the coupled tool-workpiece dynamics subject to nonlinear regenerative cutting forces, instantaneous depth-of-cut (DOC) and workpiece whirling due to material imbalance. The workpiece is modeled as a system of three rotors: unmachined, being machined and machined, connected by a flexible shaft. The model enables workpiece motions relative to the tool and tool motions relative to the machining surface to be three-dimensionally established as functions of spindle speed, instantaneous DOC, rate of material removal and whirling. Excluding workpiece vibrations from the cutting model is found improper. A rich set of nonlinear behaviors of both the tool and the workpiece including period-doubling bifurcation and chaos signifying the extent of machining instability at various DOCs is observed. Presented numerical results agree favorably with physical experiments reported in the literature. It is found that whirling is non-negligible if the fundamental characteristics of machining dynamics are to be fully understood. The 3D model is explored along with its 1D counterpart, which considers only tool motions and disregards workpiece vibrations. Numerical simulations reveal diverse behaviors for the 3D coupled and 1D uncoupled equations of motion for the tool. Most notably, observations made with regard to the inconsistency in describing stability limits raise the concern for using 1D models to obtain stability charts. The nonlinear 3D model is linearized to investigate the implications of applying linear models to the understanding of machining dynamics. Taylor series expansion about the operating point where optimal machining conditions are desired is applied to linearize the model equations of motion. Modifications are also made to the nonlinear tool stiffness term to minimize linearization errors. Numerical experiments demonstrate inadmissible results for the linear model and good agreement with available physical data in describing machining stability and chatter for the nonlinear model. Effects of tool geometry, feed rate, and spindle speed on cutting dynamics are also explored. It is observed that critical DOC increases with increasing spindle speed and small DOCs can induce cutting instability -- two of the results that agree qualitatively well with published experimental data.

In this study, an electrolytic micro-machining tester is employed to investigate the effects of the supply voltage, the immerse depth of tungsten rod, and the machining time on the current waveform, the material removal rate, and the geometry of the tungsten needle. The tungsten rod to be electrolyzed is dipped in an aqueous electrolyte of 10 wt% sodium hydroxide as the anode, and the stainless steel ring as the cathode. The spindle rotating speed and the stirring rotating speed are set to be 100 rpm and 200rpm, respectively. According to analyze the topography of the tungsten needle, four machined regimes have been identified as:¡]1¡^non-machined regime,¡]2¡^incomplete machined regime,¡]3¡^complete machined regime,¡]4¡^over machined regime. In order to obtain the perfect tungsten needle, the experiments are conducted in the complete machined regime. Results show that the tungsten rod becomes a short cone for the immerse depth of 5 mm, and a long cone for the depth of 10mm. When the immerse depth of 10 mm and the supply voltage of 3V, the surface of tungsten needle becomes rough slightly and the tip radius of tungsten needle is about 2£gm. With increasing the supply voltage to 4.5 V, the surface of tungsten needle is uniform with a downward trend in material removal rate, and the tip radius can achieve a submicron. For the supply voltage of 6V, because the material removal rate varies violently, it becomes very difficult to control the diameter of tungsten needle. During the machining time between 0 to 10 min for the supply voltage of 4.5V, the diameter of tungsten rod is decreased from 1000 to 200£gm, but during the machining time between 10 to 12.5 min, the tungsten rod gradually transforms into the needle due to a downward trend in current, and the tip radius is decreased from 200£gm to submicron. Hence, the machining time must be controlled accurately to manufacture the needle in a submicron radius.

Metal Matrix Composites (MMC) offer several thermo-mechanical advantages over standard materials and alloys which make them better candidates in different applications. Their light weight, high stiffness, and strength have attracted several industries such as automotive, aerospace, and defence for their wide range of products. However, the wide spread application of Meal Matrix Composites is still a challenge for industry. The hard and abrasive nature of the reinforcement particles is responsible for rapid tool wear and high machining costs. Fracture and debonding of the abrasive reinforcement particles are the considerable damage modes that directly influence the tool performance. It is very important to find highly effective way to machine MMCs. So, it is important to predict forces when machining Metal Matrix Composites because this will help to choose perfect tools for machining and ultimately save both money and time. This research presents an analytical force model for predicting the forces generated during machining of Metal Matrix Composites. In estimating the generated forces, several aspects of cutting mechanics were considered including: shearing force, ploughing force, and particle fracture force. Chip formation force was obtained by classical orthogonal metal cutting mechanics and the Johnson-Cook Equation. The ploughing force was formulated while the fracture force was calculated from the slip line field theory and the Griffith theory of failure. The predicted results were compared with previously measured data. The results showed very good agreement between the theoretically predicted and experimentally measured cutting forces. / UOIT

The field of numerically controlled (NC) machining has long been interested with predicting and measuring the errors in machining. Creating a simulation of NC machining is one way of achieving this. This thesis presents one such implementation of an NC simulation. It also runs a number of numerical and physical tests to verify the simulation?s correctness. The numerical tests show that the simulator work correctly as well as providing guide lines for appropriate simulation parameters. The physical tests show that the results of the simulation match the results of real NC machines. It is hoped that this thesis can provide a guide for the creation of machining simulators and their verification.

The field of numerically controlled (NC) machining has long been interested with predicting and measuring the errors in machining. Creating a simulation of NC machining is one way of achieving this. This thesis presents one such implementation of an NC simulation. It also runs a number of numerical and physical tests to verify the simulation?s correctness. The numerical tests show that the simulator work correctly as well as providing guide lines for appropriate simulation parameters. The physical tests show that the results of the simulation match the results of real NC machines. It is hoped that this thesis can provide a guide for the creation of machining simulators and their verification.