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Corte por indentação de películas poliméricas – caso de estudo
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O tema explorado nesta tese advém de um equipamento desenvolvido em ambiente em-
presarial, que apresentou resultados insatisfatórios, já depois da fase de produção. Trata-se
de uma prensa de ação pneumática que tem como função cortar película de LDPE (com um
tratamento superficial que lhe confere dureza acrescida), através do processo de corte com
matriz.
Desenvolveu-se uma investigação sobre o processo de corte com matriz, e do mecanismo
de corte envolvido - corte por indentação - no sentido de identificar as causas (e possíveis
soluções) dos resultados indesejados, produzidos pelo equipamento. Essa investigação in-
cluiu, para além de uma pesquisa aprofundada sobre o tema, uma série de testes preliminares,
com o intuito de despistagem de possíveis causas e soluções teorizadas até esse momento.
Nesses testes, avaliaram-se os resultados obtidos no corte com substratos de diferentes dure-
zas e também com diferentes modos de aplicação de força - constante ou por impacto.
Como complemento à investigação realizada, conduziu-se uma série de ensaios em la-
boratório com o objetivo de investigar a influência da geometria do contorno de corte, na força
envolvida no corte com matriz. Os ensaios foram realizados numa prensa do Laboratório
DEMI, na FCT-UNL. De forma a permitir a montagem das lâminas com diferentes geometrias
à prensa, projetaram-se suportes capazes de acomodar um lâmina em três geometrias diferen-
tes - retilínea, circular e em "S".
Concluiu-se que o equipamento estudado teve falhas de projeto. O dimensionamento
inicial de 100 kgf foi incorreto e insuficiente. Para além disso, a escolha do substrato e dos
cortantes foi também inadequada. O substrato escolhido apresenta uma dureza demasiado
próxima do material cortado, pelo que promove a ocorrência de dents, impossibilitando o corte
da película. No caso dos cortantes, a espessura do gume de corte dos mesmos é demasiado
elevada para a espessura da película de LDPE, o que torna impossível a ocorrência de separa-
ção do material.
Em relação à influência da geometria do cortante na força necessária para o corte de
película poliméricas, observou-se que no caso da geometria em "S", a força de corte obtida
experimentalmente apresentaa um valor cerca de 25% superior àquela calculada teoricamente,
para o mesmo perímetro. No entanto, apenas foi possível contabilizar um ensaio nesta geome-
tria. Para além disso os ensaios realizados indicaram que, no caso de geometrias simples (neste caso, retilínea), a fórmula utilizada se mostra adequada e produz resultados concordantes com
os que se observaram experimentalmente.
The subject explored in this thesis arise from an equipment, developed in a business environment, which presented unsatisfactory results, after the production phase. This equip- ment is a pneumatically actuated press whose function is the cutting of LDPE film (with a surface treatment that increases its hardness), through the die cutting process. An investigation was carried out on the die cutting process, and the cutting mechanism involved in that process – indentation cutting – in order to identify the causes (and possible solutions) for the undesired results produced by the equipment. This investigation included, in addition to an in-depth research on the subject, a series of preliminary tests, in order to ex- clude possible causes and solution theorized up to that moment. In these tests, the results ob- tained in cutting substrates of different hardness and also with different modes of force ap- plication – constant or impact – were evaluated. As a complement to the investigation, a series of laboratory tests were carried out, in order to investigate the influence of the geometry of the cutting contour on the force needed for the die cutting process. The tests were carried out in a press existent in the DEMI Labora- tory, at FCT-UNL. In order to allow the assembly of blades with different geometries to the press, holders were designed, capable of accommodating the blade in three different geome- tries: rectilinear, circular and “S”. It was concluded that the equipment studied had design flaws. The initial sizing of 100 kgf was incorrect and insufficient. Furthermore, the substrate and cutters chosen were also inadequate. The substrate had an hardness too close to the target material, which promotes the occurrence of dents, making it impossible to cut the film. Regarding the cutters, the thick- ness of the cutting edge is too high, when compared to the thickness of the LDPE film, which makes material separation impossible. Regarding the influence of the geometry of the cutter on the force required for the cut- ting of polymeric films, it was observed that in the particular case of the “S” geometry, the cutting force obtained experimentally presented a value about 25% higher than that calcu- lated theoretically, for the same perimeter. However, it was only possible to count one test in this geometry. Also, the tests carried out indicated that, in the case of simple geometries (rec- tilinear), the formula used is adequate and produces results in agreement with those ob- served experimentally.
The subject explored in this thesis arise from an equipment, developed in a business environment, which presented unsatisfactory results, after the production phase. This equip- ment is a pneumatically actuated press whose function is the cutting of LDPE film (with a surface treatment that increases its hardness), through the die cutting process. An investigation was carried out on the die cutting process, and the cutting mechanism involved in that process – indentation cutting – in order to identify the causes (and possible solutions) for the undesired results produced by the equipment. This investigation included, in addition to an in-depth research on the subject, a series of preliminary tests, in order to ex- clude possible causes and solution theorized up to that moment. In these tests, the results ob- tained in cutting substrates of different hardness and also with different modes of force ap- plication – constant or impact – were evaluated. As a complement to the investigation, a series of laboratory tests were carried out, in order to investigate the influence of the geometry of the cutting contour on the force needed for the die cutting process. The tests were carried out in a press existent in the DEMI Labora- tory, at FCT-UNL. In order to allow the assembly of blades with different geometries to the press, holders were designed, capable of accommodating the blade in three different geome- tries: rectilinear, circular and “S”. It was concluded that the equipment studied had design flaws. The initial sizing of 100 kgf was incorrect and insufficient. Furthermore, the substrate and cutters chosen were also inadequate. The substrate had an hardness too close to the target material, which promotes the occurrence of dents, making it impossible to cut the film. Regarding the cutters, the thick- ness of the cutting edge is too high, when compared to the thickness of the LDPE film, which makes material separation impossible. Regarding the influence of the geometry of the cutter on the force required for the cut- ting of polymeric films, it was observed that in the particular case of the “S” geometry, the cutting force obtained experimentally presented a value about 25% higher than that calcu- lated theoretically, for the same perimeter. However, it was only possible to count one test in this geometry. Also, the tests carried out indicated that, in the case of simple geometries (rec- tilinear), the formula used is adequate and produces results in agreement with those ob- served experimentally.
Descrição
Palavras-chave
Corte com matriz corte por indentação contorno de corte geometria projeto prensa