Les travaux de recherche menés dans cette thèse représentent une méthodologie de travail pour contribuer à l’étude du comportement dynamique non linéaire du système M – O – P en fraisage. Cette méthodologie est orientée selon les objectifs principaux relatifs à cette thèse. En effet, la recherche bibliographique réalisée a permis de donner un aperçu sur les travaux existants dans ce cadre et d’identifier les phénomènes vibratoires générés par la dynamique de coupe et les mécanismes d’instabilité mis enjeu. En fait, le processus de coupe génère, selon le cas, deux formes de vibrations : les vibrations forcées et les vibrations auto – entretenues. Dans une première approche, nous avons développé un modèle masse – ressort (à deux degrés de liberté) du système O – P pour étudier et analyser le comportement dynamique de la cellule élémentaire en fraisage. Ce modèle a permis d’examiner l’influence de la profondeur de passe sur la stabilité de la coupe. Cependant, ce modèle semble être insuffisant pour quantifier avec précision les vibrations en fraisage car les sources vibratoires générées par la dynamique de la machine ne peuvent être négligées. Dans une deuxième approche, nous avons modélisé le système globale Machine - Outil - Pièce. En effet, un modèle numérique basé sur la méthode de sous-structuration par éléments finis de l’ensemble M – O – P a été développé. Cette modélisation permet de tenir compte de l’effet de l’inertie des différents éléments tournants de la fraiseuse, de la structure de la machine et de la forme de l’outil. Nous avons ainsi réalisé des simulations du comportement dynamique global de l’opération du fraisage. L’influence de différents paramètres sur l’effort de coupe tels que l’avance, la profondeur de passe, les réponses dynamiques suivant les trois axes a été étudié. Cette étude a permis de conclure que ces paramètres sont fortement affectés par l’usinage. Pour compléter cette étude numérique, une étude expérimentale a été menée afin d’étudier l’influence de différents paramètres de coupe. En effet, la méthodologie expérimentale développée a mis en évidence les paramètres les plus importants qui influent sur le comportement dynamique globale du système M – O – P. Cette étude expérimentale a nécessité le développement d’un plan d’expérience complet pour pouvoir définir les paramètres d’entrées/sorties et organiser les essais à effectuer. L’analyse des résultats a permis de détecter l’influence de l’avance et de la profondeur de passe sur le niveau des vibrations générées. Le bilan de ces résultats a mis le point sur les niveaux extrêmes des variables provoquant le niveau vibratoire le plus élevé. De plus une confrontation entre les résultats expérimentaux et numériques a été effectuée et a montré une bonne concordance. / The research led in this thesis represents a methodology to contribute to the study of nonlinear dynamic behavior of the system M - O - P in milling. This methodology is directed according to the main objectives relative to this thesis. Indeed, the literature allows giving an overview of the existing work in this context and identifies the vibration phenomena generated by the dynamics of cutting mechanisms and the instability of the involved set cut. In fact, the cutting process generates, as applicable, two types of vibration: forced vibration and self – excited vibration. In a first approach, we developed a model mass - spring (with two degrees of freedom) of the system O - P to study and analyze the dynamic behavior of the elementary machining cell in milling. This model was used to examine the influence of the depth of cut on the stability of the cut. However, this model appears to be insufficient to accurately quantify the vibrations in milling because the sources vibration generated by the dynamics of the machine cannot be neglected. In a second approach, we modeled the overall system Machine - Tool - Part; indeed, a numerical model based on the substructure method by finite element of the M - O - P was developed. This modeling takes into account the effect of inertia of the various rotating elements of the milling machine, the machine structure and shape of the tool. We have conducted simulations of the dynamic behavior of the overall operation of milling. The influence of different parameters on the cutting force such as advance, the depth of cut, and the dynamic responses along the three axes was investigated. This study concluded that these parameters are strongly affected by machining. To complement this numerical study, an experimental study was conducted to study the influence of different cutting parameters. Indeed, the experimental methodology developed has highlighted the most important parameters that influence the overall dynamic behavior of the system M - O - P. This experimental study required the development of an experimental complete to define the parameters of Input / Output and arrange to be tested. The analysis of the results allowed detecting the influence of feed and depth of cut on the level of vibration generated. The outcome of these results put the item on the extreme levels of variables causing the vibration level is higher. Over a confrontation between the experimental and numerical results was performed and showed a good agreement.

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.

Thesis (Masters Diploma (Food Technology))--Cape Technikon, Cape Town,1993 / This study is based on the Hazard Analysis in the Wet Milling of maize for the production of starch at the Bellville plant of African Products. Wet milling of maize is a highly specific and completely integrated system developed to separate the major components of the kernel as completely as possible. Many microbiological problems existed in the process at this plant which could not be solved over the years. Microbial analyses were done throughout the plant and high microbial counts were obtained at various sampling points. In applying HACCP, the following major hazards were identified: The presence of Faecal Streptococci, Sraphylococcus aureus, Bacillus cereus, Faecal coliforms, Fusarium, Dip/odia, Aspergillus, Penicillium and various Yeast strains. The follOWing Critical Control Points (CCP's) were identified in the wet milling process: Maize trucks, in-process water, steeping, storage tanks, Reineveld, wet mlxmg boxes, Laidlaw, drying and bagging off point. The follOWing were done as part of the HACCP plan: i) modifications of the plant were suggested, ii) different sanitation programmes were evaluated, iii) monitoring of cep's, and iv) training of personnel. In general, a regular sanitation programme need to be exercised in the wet-milling plant to prevent a build up of microbial populations at various sampling points. High S02 levels can be maintained throughout the plant to achieve this. The final starch will then be used for Industrial starch. Criteria to monitor the CCP's were suggested. Hazard Analysis is an effective method to improve the quality of the final product.

Digitized by Kansas Correctional Industries

Typescript (photocopy). / Digitized by Kansas Correctional Industries

Typescript (photocopy). / Digitized by Kansas Correctional Industries

Minimizing cost and optimization of nonlinear problems are important for industries in order to be competitive. The need of optimization strategies provides significant benefits for companies when providing quotes for products. Accurate and easily attained estimates allow for less waste, tighter tolerances, and better productivity. The Nelder-Mead Simplex method with exterior penalty functions was employed to solve optimum machining parameters. Two case studies were presented for optimizing cost and time for a multiple tools scenario. In this study, the optimum machining parameters for milling operations were investigated. Cutting speed and feed rate are considered as the most impactful design variables across each operation. Single tool process and scalable multiple tool milling operations were studied. Various optimization methods were discussed. The Nelder-Mead Simplex method showed to be simple and fast.

No description available.

Machinists often simulate a part program to verify its correctness, since mistakes can cause damage to the part, machine, oneself, or others. A popular approach for part program simulation involves representing the stock (the material the part is being carved from) as a heightmap. Although this approach is computationally fast and memory efficient, only objects that are representable as functional surfaces (e.g., z = f(x, y)) can be machined. This thesis presents a new heightmap-based data structure, called a multidirectional heightmap, that does not have this limitation. A multidirectional heightmap, in response to an overhang, recursively subdivides itself until each piece can be represented by an axis-aligned heightmap. More precisely, a multidirectional heightmap is a kD-tree with the property that all cells are functional: each cell contains a heightmap that represents a functional portion of the stock. To improve accuracy, each regular heightmap can be replaced by a 3-Way Heightmap, a new type of heightmap that samples the tool along all three stock axis directions (three ways) rather than just one. The experimental results herein suggest that the multidirectional heightmap data structure achieves a good level of performance with respect to memory usage, CPU usage, and approximation error.

The main objective of this thesis is to further reduce the machining cycle time for producing Calcium Polyphosphate (CPP) implant constructs. To achieve this, the impregnation of the CPP lattice with various polymers is investigated, with the aim of improving the toughness of the material. By applying Taguchi’s orthogonal array method it was determined that CPP infiltrated with an ionic bonding polymer produces the best material for generating high quality machined surfaces and features. While there is some loss in surface porosity, in comparison to cutting uninfiltrated CPP, the porosity loss was deemed acceptable for the clinical purpose of the implant, and in many cases, would be trimmed off during a consecutive finish machining operation. The 2 fluted 4 mm diameter flat end mill at a cutting speed of 30 m/min and ¾ immersion up-milling, 0.1 mm chip load and 3 mm depth of cut were determined to be highly suitable for achieving both high productivity as well as excellent surface integrity. These conditions produced a material removal rate of 4,302 mm3/min, which was 14 times higher than the material removal rate achieved in machining pure CPP in earlier studies. The constructed machining model was highly successful in predicting the cutting forces, and therefore can be used in process planning and optimization in the production of tissue engineered implant constructs out of CPP. The Finite Element analyses predicted that the implant would not chip or break during the roughing operation, as validated experimentally. This allowed the roughing cycle time to be reduced from 159 min to 19 min, effectively achieving a productivity improvement of 8 times over the earlier work done in this area.