New Methodology for Inspecting Ruled and Free-Form Surface in Metrology

A new method is proposed to find the cutter contact (CC) points for both 3- and 5-axis CNC machining, and use this to determine measurement points using CMM. The first part of this research focuses on deriving a mathematical formulation to determine the CC points while using ball nose end mills and standard end mills to machine a given ruled surface, with a focus on surface finish operation. Then, the freeform surface is measured, using the Gaussian curvature and mean curvature at each grid point. These measurements at each grid point on the free-form surface are classified then into concave, convex, or saddle point surface. This way boundary surfaces are allowed to vary. This allows for a more accurate way to measure free form surfaces by distributing sample points within each boundary patch (rather than rectangular or square patches as is conventional). This will help the determination of upper and lower boundary for each patch, so that the free form surface is accurately measured. Simple experimental verification was done to demonstrate the validity of methods developed

Efficiency, manufacturability, and modeling challenges in structural design optimization

This thesis presents new developments in structural design optimization on three topics: semi-analytical sensitivity analysis, design of composite structures fabricated via additive manufacturing, and topology optimization of structures under contact boundary conditions. We first give a general overview and some new developments of the analytical and semi-analytical sensitivity analyses for nonlinear steady state, transient and dynamic problems. We discuss the restrictive assumptions, accuracy, and consistency of these methods. Both adjoint and direct differentiation methods are studied. In the second topic, we demonstrate a practical method for the optimization of fiber reinforced composite structures fabricated by additive manufacturing, that accommodate the manufacturability constraints of the direct ink writing process. To accomplish this, the toolpaths of each layer are defined by contours of a level-set function. With this representation, we can define the manufacturing constraints and the material model. We obtain optimal manufacturable toolpaths and maintain computational efficiency. We also propose to minimize manufacturing cost by solving a traveling salesman problem to obtain the linking sequence of these toolpaths. Finally, we apply topology optimization to design systems with multiple deformable three-dimensional bodies in contact. We formulate and resolve the design simulation problem using large deformation continuum mechanics and the finite element method. The contact conditions are discretized via the mortar segment-to-segment approach which provides smooth force variations over the contact surfaces. Since the contact problem is computationally expensive to solve, we solve the optimization problem using efficient nonlinear programming algorithms which require the sensitivities of the cost and constraint functions. To this end, we formulate analytical adjoint sensitivity expressions to compute the gradients of general functionals. Additionally, we use a B-spline design parameterization to reduce the number of design variables compared to element-wise parameterizations and regularize the topology optimization problem

Influence of machining strategies and thermochemical treatments on semi-spherical surfaces of hot stamping punches

Orientador: Anselmo Eduardo DinizTese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia MecânicaResumo: A obtenção de boa qualidade superficial das ferramentas de processos de conformação mecânica é importante para que os produtos conformados apresentem bom acabamento e para que a vida em serviço das ferramentas de conformação seja longa. Assim, os processos de obtenção das ferramentas de conformação necessitam gerar superfícies com valores de parâmetros de análise de qualidade superficial satisfatórios. Para aumentar a resistência ao desgaste e às avarias, além de adoção de estratégias que geram superfícies mais resistentes, podem-se utilizar tratamentos termoquímicos que aumentam a dureza superficial e que podem tornar a superfície mais ou menos eficiente quanto ao desempenho do lubrificante. Neste trabalho, avaliaram-se a influência das estratégias de usinagem e a influência de tratamentos termoquímicos sobre punções, de material AISI H13, temperados e revenidos, com dureza de 48 HRC. Utilizaram-se seis estratégias de fresamento em processo do tipo high speed machining e duas estratégias de torneamento com inserto de cerâmica para a redução do raio da semiesfera do punção. As estratégias de fresamento utilizadas foram circular ascendente, circular descendente, radial ascendente, radial descendente, contornos paralelos e espiral ascendente. Já as estratégias de torneamento foram torneamento ascendente e torneamento descendente. Após a usinagem, os punções foram divididos em três grupos de acordo com a realização de tratamentos termoquímicos, de modo que os punções do grupo ST foram mantidos como controle, sem tratamento termoquímico, os punções do grupo NP foram nitretados a plasma e os punções do grupo NC foram nitrocarbonetados pelo processo conhecido como Tenifer®. As peças usinadas com cada estratégia apresentaram resultados de rugosidade diferentes de acordo com a região medida, indicando influência de vibração e flexão da ferramenta de usinagem na proximidade da base da semiesfera e de ocorrência de deformações plásticas na proximidade do topo da semiesfera. A aplicação da nitretação a plasma resultou em tendência a reduzir os valores dos parâmetros de rugosidade e apresentar valores positivos de parâmetro Ssk e valor aproximadamente 3 para o parâmetro Sku. A aplicação da nitrocarbonetação apresentou a tendência de aumento dos valores de parâmetros de rugosidade, valores negativos de parâmetro Ssk e valores altos de parâmetro Sku. A região a 45° a partir da base apresentou os melhores resultados para os três grupos de punções. Os punções foram submetidos à estampagem a quente de arruelas de aço AISI 1020 aquecidas a 1.000 °C, em duas etapas, em processo que acelerou a evolução do desgaste na região a 45° da base da semiesfera. As estratégias de torneamento e a estratégia de contornos paralelos apresentaram maior resistência à deterioração que as demais estratégias para o grupo ST. Os punções tratados termoquimicamente apresentaram-se mais resistentes à deterioração que os punções do grupo ST. A estratégia de usinagem utilizada mostrou-se influente também para os punções tratados termoquimicamente. Os punções nitretados a plasma apresentaram maior resistência à deterioração que os punções nitrocarbonetadosAbstract: The search for good surface quality of mechanical forming tools is important to obtain good surface finish in the conformed products and to extend the life of these tools. Thus, the processes to obtain the mechanical forming tools need to generate surfaces with suitable values of surface quality parameters, which mean more efficient surfaces to lubricant action during mechanical forming process and also resistant to wear and damages to which mechanical forming tools are exposed. Aiming the increase of the resistance to wear and to damages, thermochemical processes may be applied to increase surface hardness, but they may modify lubrication efficiency during mechanical conformation process. In this work, the influence of machining strategies and the influence of thermochemical treatments were evaluated of punches type samples made of AISI H13, quenched and tempered to 48 HRC. They were machined by six milling strategies, in a high speed machining process, and two turning strategies with ceramic insert to reduce the radius of a semi spherical punch. Milling strategies were circular upward, circular downward, radial upward, radial downward, parallel contours and spiral upward. Turning strategies were turning upward and turning downward. After machining, the punches were divided in three groups, one group, ST, presented punches without thermochemical treatment as a control group. Punches from group NP were submitted to plasma nitriding process and punches from group NC were submitted to nitrocarburizing by process Tenifer®. Machining strategies presented different results of surface parameters values according to the measured region, indicating the occurrence of machining tool bending vibration in vicinity of semi sphere base and indicating the occurrence of plastic deformation in the vicinity of semi sphere top. Plasma nitriding application tended to reduce values of roughness parameters, to present positive values of parameter Ssk and values around 3 of parameter Sku. Nitrocarburizing application tended to increase values of roughness parameters, to present negative values of parameter Ssk and high values of parameter Sku. The region at 45° from semi sphere base presented the best results of surface quality parameters from measured regions. Punches were submitted to hot stamping process. Washers made of AISI 1020 heated to 1000 °C were stamped in a process to accelerate wear evolution at punches region 45° from semi sphere base in two steps. From group ST, turning strategies and parallel contours strategy presented higher resistance to wear and damages. Machining strategies influenced the resistance to surface deterioration even in thermochemically treated punches. Thermochemical treated punches presented higher wear and damage resistance than not treated punches. Nitrided punches presented higher surface deterioration resistance than nitrocarburized punchesDoutoradoMateriais e Processos de FabricaçãoDoutora em Engenharia Mecânica2013/00551-7FAPES