Study of tribological properties of moulds obtained by stereolithography

Stereolithography (SL) is a process that allows the rapid manufacturing of high-accuracy rapid tools using an ultraviolet laser beam to polymerize a liquid resin, layer-by-layer. In this work, the friction properties of commercial SL resins in contact with several thermoplastics were assessed. Friction experiments were done with plastics overmoulded onto moulding blocks made from SL resins. It was observed that polymers with Hildebrand solubility parameters close to the resins showed adhesion characteristics that were not observed in polymers with values of this parameter further apart.EU Programme ALFA (project Plastinet-master

Caracteristicas desejaveis para a implantação e o emprego de sistemas CAE/CAD/CAM no setor de moldes de injeção de plasticos

Tese (doutorado) - Universidade Federal de Santa Catarina, Centro TecnologicoNeste trabalho é feita uma abordagem sobre o estado-da-arte com relação à utilização de sistemas CAE/CAD/CAM no setor de moldes de injeção para peças de plástico. Através da elaboração de um Manual de Orientação sobre o assunto, são apresentados conceitos básicos, referentes a tecnologia CAx, detalhando as fases do processo de desenvolvimento de um molde onde já é possível obter o auxílio destas tecnologias. Além disso, são apresentadas considerações visando orientar a implantação de sistemas CAx, bem como é feita uma abordagem sobre problemas e dificuldades inerentes ao emprego de sistemas CAE/CAD/CAM em empresas de moldes de injeção, baseada na análise de estudos de casos, análise de artigos especializados e projetos da comunidade européia, bem como relatos de experiências industriais. Concluindo, são apresentadas as características básicas que devem estar presentes em um sistema CAx tipicamente voltado ao referido setor

Fabricação assistida por computador aplicada à produção de matrizes de injeção para solados de calçados

Dissertação (mestrado) - Universidade Federal de Santa Catarina, Centro Tecnológico. Programa de Pós-Graduação em Engenharia Mecânica

Thermal effects on stereolithography tools during injection moulding

In this work the changes to stereolithography (SL) resin mechanical properties during the injection moulding process were evaluated. A multi-impression SL mould was built and used to inject a series of small flat mouldings. The fixed half SL tool insert included recesses to accommodate tensile test specimens. Tensile test specimens made from SL resin were positioned in these recesses and plastic parts were injected. After injecting a predetermined number of mouldings, tensile tests were performed using the tensile test specimens. The results from the tensile tests showed that the thermal cycling encountered during the injection moulding process did not significantly affect the mechanical properties of the resin. Observations indicated that reducing the temperatures encountered in the tool may lead to longer tool life

Ergonomic development of plastic products aided by rapid prototypes

O objetivo deste artigo é discorrer acerca do desenvolvimento ergonômico de produtos de plástico, mostrando a importância de aplicar a ergonomia desde o início do processo de projeto e como a utilização de protótipos rápidos pode auxiliar na inclusão de características ergonômicas nos produtos. Ao final é apresentado um estudo de caso para demonstrar as idéias principais do artigo

Virtual versus Real Nuclear Compton Scattering in the Delta(1232) Region

In this paper we calculate the cross section for Virtual Compton Scattering off nuclei in the delta resonance region. We also calculate the background for the process from Coherent Bremsstrahlung in nuclei and explore the regions where the Virtual Compton Scattering cross section dominates. The study also shows that it is possible to extract the cross section for Real Compton Scattering from the Virtual Compton one in a wide range of scattering angles.Comment: latex , 11 pages, ps.gz file, 16 figure

Evaluating the use of functionally graded materials inserts produced by selective laser melting on the injection moulding of plastics parts

The demand for productivity and shape complexity on the injection moulding industry necessitates new research to improve tool design, material, and manufacturing. A research field is the development of functionally graded materials (FGMs) to build injection moulds. For example, moulds built with the FGMs technique can have distinctive regions with higher heat conduction. Higher rates of heat transfers from thicker regions of the injected part can be useful to produce better and cheaper injection moulded polymer parts. It is possible to obtain moulds with differential conductivity by adding locally, during the fabrication of the mould, copper to the mould base material such as tool steel. In this work, an investigation into the effect of FGM copper (Cu)-tool steel mould insert over polymer injected parts is presented. The work is divided in two parts: a numerical thermal analysis comparison between Cu-tool steel graded and tool steel inserts and an injection moulding experiment with comparisons between mould surface temperature and degree of crystallinity of polypropylene parts. The numerical model was used to compare different behaviour of the mould heat transfer according to the mould insert material. Thereafter, a bolster was built to hold FGMs and tool steel inserts obtained by a selective laser fusion process. Polypropylene was injected over the inserts to compare with the numeric results. To observe the effect of the cooling rate in the polypropylene parts using the graded inserts, the degree of crystallinity of the parts was measured by differential scanning calorimetry (DSC) test. The temperature of the mould was also evaluated during the injection cycles. The results showed that the graded Cu-tool steel inserts tested had lower capacity to store heat energy. As Cu was added to the tool steel, the mixture proved to transfer heat more efficiently but it had less capacity to absorb heat

Scanning strategies and spacing effect on laser fusion of H13 tool steel powder using high power Nd : YAG pulsed laser

Layered manufacturing technologies have been used to produce complex parts of diversified materials through different physical/chemical manufacturing principles. Nevertheless only a few materials are commercially available to build parts suitable for engineering applications. In this paper, the powder fusion of H13 tool steel is investigated. A high power Nd:YAG pulsed laser source on a CNC machine was used to fuse the powder, layer by layer, building solid cubes for further analysis. Four different laser vector scanning strategies were evaluated by comparing the results of porosity and layer distortion. The complexity of the laser/powder interaction shows that a complex strategy must be used to avoid porosity and distortion

Wood/water relations of 15 south american lesser-used wood species

In the Amazonian forests of Perú a large variety of native wood species can be found, of which only a few are commercially exploited. Exploitation is focused on high density durable hardwoods for flooring applications. After selective logging of a few valuable trees the forests often are considered being “unproductive” because there is no market for most of the remaining trees. Having a long-term sustainable forest management and utilization plan in mind, a continuous extraction of more tree species is desirable. For opening out new markets for lesser-used species a concise knowledge of their physical and mechanical properties is essential. Fifteen lesser-used Peruvian wood species were investigated to characterize their wood/water relations. Density, shrinkage behavior, and sorption characteristics were determined. In addition, the functional relation between electrical resistance and moisture content was determined to provide a sound basis for non-destructive moisture content measurements

Evaluation of the total photoabsorption cross sections for actinides from photofission data and model calculations

We have calculated the fission probabilities for 237-Np, 233,235,238-U, 232-Th, and nat-Pb following the absorption of photons with energies from 68 MeV to 3.77 GeV using the RELDIS Monte-Carlo code. This code implements the cascade-evaporation-fission model of intermediate-energy photonuclear reactions. It includes multiparticle production in photoreactions on intranuclear nucleons, pre-equilibrium emission, and the statistical decay of excited residual nuclei via competition of evaporation, fission, and multifragmentation processes. The calculations show that in the GeV energy region the fission process is not solely responsible for the entire total photoabsorption cross section, even for the actinides: ~55-70% for 232-Th, \~70-80% for 238-U, and ~80-95% for 233-U, 235-U, and 237-Np. This is because certain residual nuclei that are created by deep photospallation at GeV photon energies have relatively low fission probabilities. Using the recent experimental data on photofission cross sections for 237-Np and 233,235,238-U from the Saskatchewan and Jefferson Laboratories and our calculated fission probabilities, we infer the total photoabsorption cross sections for these four nuclei. The resulting cross sections per nucleon agree in shape and in magnitude with each other. However, disagreement in magnitude with total-photoabsorption cross-section data from previous measurements for nuclei from C to Pb calls into question the concept of a ``Universal Curve'' for the photoabsorption cross section per nucleon for all nuclei.Comment: 39 pages including 11 figure