In machining complex dies, molds, aerospace and automotive parts, or biomedical components, it is crucial to minimize the cycle time, which reduces costs, while preserving the quality and tolerance integrity of the part being produced. To meet the demands for high quality finishes and low production costs in machining parts with complex geometry, computer numerical control (CNC) machine tools must be equipped with spline interpolation, feedrate modulation, and feedrate optimization capabilities. This thesis presents the development of novel trajectory generation algorithms for Non Uniform Rational B-Spline (NURBS) toolpaths that can be implemented on new low-cost CNC's, as well as, in conjunction with existing CNC's. In order to minimize feedrate fluctuations during the interpolation of NURBS toolpaths, the concept of the feed correction polynomial is applied. Feedrate fluctuations are reduced from around 40 % for natural interpolation to 0.1 % for interpolation with feed correction. Excessive acceleration and jerk in the axes are also avoided. To generate jerk-limited feed motion profiles for long segmented toolpaths, a generalized framework for feedrate modulation, based on the S-curve function, is presented. Kinematic compatibility conditions are derived to ensure that the position, velocity, and acceleration profiles are continuous and that the jerk is limited in all axes. This framework serves as the foundation for the proposed heuristic feedrate optimization strategy in this thesis. Using analytically derived kinematic compatibility equations and an efficient bisection search algorithm, the command feedrate for each segment is maximized. Feasible solutions must satisfy the optimization constraints on the velocity, control signal (i.e. actuation torque), and jerk in each axis throughout the trajectory. The maximized feedrates are used to generate near-optimal feed profiles that have shorter cycle times, approximately 13-26% faster than the feed profiles obtained using the worst-case curvature approach, which is widely used in industrial CNC interpolators. The effectiveness of the NURBS interpolation, feedrate modulation and feedrate optimization techniques has been verified in 3-axis machining experiments of a biomedical implant.

In machining complex dies, molds, aerospace and automotive parts, or biomedical components, it is crucial to minimize the cycle time, which reduces costs, while preserving the quality and tolerance integrity of the part being produced. To meet the demands for high quality finishes and low production costs in machining parts with complex geometry, computer numerical control (CNC) machine tools must be equipped with spline interpolation, feedrate modulation, and feedrate optimization capabilities. This thesis presents the development of novel trajectory generation algorithms for Non Uniform Rational B-Spline (NURBS) toolpaths that can be implemented on new low-cost CNC's, as well as, in conjunction with existing CNC's. In order to minimize feedrate fluctuations during the interpolation of NURBS toolpaths, the concept of the feed correction polynomial is applied. Feedrate fluctuations are reduced from around 40 % for natural interpolation to 0.1 % for interpolation with feed correction. Excessive acceleration and jerk in the axes are also avoided. To generate jerk-limited feed motion profiles for long segmented toolpaths, a generalized framework for feedrate modulation, based on the S-curve function, is presented. Kinematic compatibility conditions are derived to ensure that the position, velocity, and acceleration profiles are continuous and that the jerk is limited in all axes. This framework serves as the foundation for the proposed heuristic feedrate optimization strategy in this thesis. Using analytically derived kinematic compatibility equations and an efficient bisection search algorithm, the command feedrate for each segment is maximized. Feasible solutions must satisfy the optimization constraints on the velocity, control signal (i.e. actuation torque), and jerk in each axis throughout the trajectory. The maximized feedrates are used to generate near-optimal feed profiles that have shorter cycle times, approximately 13-26% faster than the feed profiles obtained using the worst-case curvature approach, which is widely used in industrial CNC interpolators. The effectiveness of the NURBS interpolation, feedrate modulation and feedrate optimization techniques has been verified in 3-axis machining experiments of a biomedical implant.

Nowadays almost all products used in our daily life are made in pursuit of streamline and good look, including mobiles, motorcycles, aerospace and 3C industry; therefore, how to shorten process time and enhance the smoothness of the product¡¦s surface has become one of the important issues. However, the process method of traditional CNC machines only can support line and circular interpolations but cannot accept motion along curve and circular paths. Therefore, the traditional CNC machines have to rely on CAM, a method to generate the NC code called G-code and M-code by approximating many tiny linear or circular segments, to plan the cutter paths. But this approximating method requires higher transmission speed; it also occupies huge memory capacity and makes the velocity of machine tool discontinuous, in order to difficultly meet the requirement of high speed and better precision. In order to solve the above problems, this thesis adopts the NC code created by CAD/CAM¡¦s NURBS curve which called NURBS-code, making CNC machines have the function of processing NURBS curve interpolations to improve the defect of the traditional processing and thus reach the goal of high speed and better precision. Furthermore, due to NURBS interpolators are always implemented by the controller. This always makes CNC machine become very expensive; meanwhile, adjusting parameters is very troublesome. Therefore this thesis also provides the intergrated method of NURBS and DDA real-time interpolator to make the application in the easy way without the consideration of controller design for AC driver.

This thesis presents a study into the enhancement of productivity in micromilling processes by considering a fundamental treatment of tool path trajectory generation techniques and process optimization strategies that account for the impact of scale effects present in high-speed, high-precision micromachining operations. Micromilling is increasingly applied to the production of a wide variety of micro components, due to its high precision and flexibility. However, the productivity of micromilling is limited by the low feedrates necessitated by the inherent high precision and small feature size. In this study, several scale effects present at the microscale are identified, in particular the increase of the ratio of tool size to feature size, and the corresponding impact on trajectory generation and process optimization is investigated. The scale effects are shown to cause increased geometric error when the standard method of VF-NURBS is applied to microscale feedrate optimization. The method of Enhanced Variable-Feedrate NURBS (EVF-NURBS) is proposed and shown to successfully compensate for the scale effects leading to reduced geometric error. A key contribution of this study is the construction and experimental validation of the Variable-Feedrate Intelligent Segmentation (VFIS) method for increased feedrates and improved stability. The VFIS method provides a cutting time reduction of more than 50% in some cases, while effectively constraining geometric error. Two tool size optimization schemes are presented for maximizing productivity and minimizing geometric error while accounting for dynamic effects uniquely present at the microscale. Finally, the development of a low-cost, high-precision micro-mesoscale machining center (mMC) is presented.

Systematic investigation of the Friction Stir Welding (FSW) process shows that a fixed rotational velocity and feed rate may not yield uniform mechanical properties along the length of a weldment. Nevertheless, correlations between process parameters and post-weld material properties have successfully demonstrated that peak temperature and cooling rate drive post-weld properties. There have been many reported methodologies for controlling friction stir welding, with varying degrees of cost to implement and effectiveness. However, comparing data from uncontrolled FSW of AA 6111-T4 sheet with controlled FSW at temperatures ranging from 375 °C to 450 °C demonstrates that a simplified methodology of a single-loop PID controlling with spindle speed may be used to effectively control temperature. This methodology can be simply used with any machine that already has the ability to actively control spindle speed, and has been previously shown to be able to be auto-tuned with a single weld. Additionally, implementation of this method compared to uncontrolled FSW in AA6111 at linear weld speeds of 1-2 meters per minute showed improved mechanical properties and greater consistency in properties along the length of the weld under temperature control. Further results indicate that a minimum spindle rpm may exist above which tensile specimens did not fracture within the weld centerline, regardless of temperature. This work demonstrates that a straight-forward, PID-based implementation of temperature control at high weld rates can produce high quality welds with auto-tuned gains. This method also shows promise in application to other processes in the Friction Stir family, and preliminary results in an application to the Additive Friction Stir Deposition (AFSD) process are also presented.

Made available in DSpace on 2015-05-08T14:59:55Z (GMT). No. of bitstreams: 1 arquivototal.pdf: 6398613 bytes, checksum: e09f8497ce0bd0c80029b3b1c6af2d9e (MD5) Previous issue date: 2014-03-27 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / In this paper, a control strategy is presented to control the position and feedrate of the table of a milling machine driven by three-phase induction motor for machining pieces consisting of different types of materials: steel, brass and nylon. In the development of the control strategy, it was applied the technique of vector control to drive three-phase induction machines. The motor electromagnetic torque estimation was used to determine the feedrate for the machining of each type of material. The speed control was developed using fuzzy logic model Takagi-Sugeno and the electromagnetic torque estimation using neural network type LMS algorithm. The induction motor was powered by a three-phase voltage inverter, driven by a digital signal processor (DSP). This processor was programmed to generate the pulse width modulation (PWM), perform signals acquisition of voltage, current and position, and implement the control strategy of the system. Simulated and experimental results are presented. / Neste trabalho, é apresentada uma estratégia de controle para controlar a posição e a velocidade de avanço da mesa de uma máquina fresadora acionada por motor de indução trifásico, na usinagem de peças constituídas por diferentes tipos de materiais: aço, latão e nylon. No desenvolvimento da estratégia de controle, aplicou-se a técnica de controle vetorial para o acionamento de máquinas de indução trifásicas. A estimação do conjugado eletromagnético do motor foi utilizada para a determinação da velocidade de avanço na usinagem de cada tipo de material. O controle de velocidade foi desenvolvido usando a lógica fuzzy modelo Takagi-Sugeno e a estimação do conjugado eletromagnético usandose a rede neural do tipo algoritmo LMS. O motor de indução foi alimentado por meio de um hardware inversor de tensão trifásica, acionado através de um processador digital de sinais. Esse processador foi programado para gerar a modulação por largura de pulso, realizar a aquisição dos sinais de tensão, corrente e posição, e implementar a estratégia de controle do sistema. Resultados simulados e experimentais são apresentados.

The diploma thesis is focused on solution of technology optimization of steam turbine rotor blades machining. Main goal is to evaluate machining cost accord-ing to change of tools feedrate speed and proposed production technology. During experimental production was monitored the tool wearing VBB of roughing and finishing mill cutter depending on machining time tA. Further, there was evaluated new technology time saving – two piece production and material consumption. The results of experiment are material cost saving and noticeable time reduction for machining of rotor blade, mainly reduction of non-machine working time.