The Influence of Surface Quality on Flow Length and Micro-Mechanical Properties of Polycarbonate

This study describes the influence of polymer flow length on mechanical properties of tested polymer, specifically polycarbonate. The flow length was examined in a spiral shaped mould. The mould cavity’s surface was machined by several methods, which led to differing roughness of the surface. The cavity was finished by milling, grinding and polishing. In order to thoroughly understand the influence of the mould surface quality on the flow length, varying processing parameters, specifically the pressure, were used. The polymer part was divided into several segments, in which the micro-mechanical properties, such as hardness and indentation modulus were measured. The results of this study provide interesting data concerning the flow length, which was up to 3% longer for rougher surfaces, but shorter in cavities with polished surface. These results are in disagreement with the commonly practiced theory, which states that better surface quality leads to greater flow length. Furthermore, evaluation of the micro-mechanical properties measured along the flow path demonstrated significant variance in researched properties, which increased by 35% (indentation hardness) and 86% by indentation modulus) in latter segments of the spiral in comparison with the gate.

Experimental and numerical investigation on draping behaviour of woven carbon fabric

In the liquid composite moulding (LCM) process, fabric is draped over the mould surface and a resin is injected under pressure to develop a composite laminate. Wrinkling is one of the most common flaws that occurs during the draping of the fabric. Wrinkling of the fabric within the composite could severely reduce the quality of the finished composite laminate. Thus, to develop a high-quality composite laminate, exact prediction of fabric wrinkling behaviour is necessary. The aim of the paper is to investigate the draping behaviour of carbon fabric. Carbon fabric with an areal density of 245 g/m2 is used in the study. Both experimental and numerical investigations were performed. An experimental setup was developed to predict the draping behaviour of the carbon fabric used in the study. LS-DYNA/Explicit solver is used to achieve macro level draping simulation. Material model MAT_REINFORCED_THERMOPLASTIC [MAT_249] offers the possibility to simulate the forming behaviour of a thermoplastic material. To simulate dry fabrics using MAT_249, a very low properties are used for the matrix in the material model. To capture the forming behaviour of fabric, an intensive material characterization has been performed. Tensile and shear properties of the fabrics were determined using uniaxial and picture frame tests, respectively. Influence of the position of the integration points from the mid surface on bending behaviour is studied and calibrated using a simple test.

Innovative fabrication of diffractive surfaces on plastic parts via textures micromilled on NiP injection moulds

Diffractive microstructured surfaces are nowadays increasingly applied to polymeric parts for aesthetic, security and optical functionalities. However, both the machining of the mould blaze-grating and its replication on plastic are still representing challenging issues, from both the technical and economical points of view. In this work, an innovative process chain based on carbide tools micromilling of mould gratings was developed for mass production of diffractive patterns on injection moulded parts. A micromilling experimental campaign was conducted on a nickel-phosphorus (NiP) thick coating to machine a blaze-grating on the mould surface, evaluating the influence of the cutting parameters on the diffractive surface quality. Subsequently, the microstructures were replicated on ABS, PC and PMMA by injection moulding. The roughness parameters Sk, Spk and Svk were added with the idea that their sum is representative of the polymer replication of regular diffraction grating pattern. Moreover, the effect of the moulded grating surface quality on the optical performance was preliminarily assessed. The obtained results show that the proposed process chain is suitable for low-cost mass production of polymeric parts with diffractive microstructures.

Yeasts in different types of cheese

<abstract> <p>Yeasts constitute an important part of cheeses, and especially the artisanal ones. The current study reviews the occurrence of yeasts in different cheese varieties and the role of yeasts in cheesemaking process. The use of molecular methods for identification and strain typing has extended the knowledge for yeast diversity in cheeses. For the study of the occurrence of yeasts in different cheese types, seven categories are used, that is: 1) hard, 2) semi-hard, 3) soft, which includes soft pasta-filata and whey cheeses, 4) white brined cheeses, 5) mould surface ripened, 6) bacterial surface ripened cheeses, and 7) blue cheeses. For some cheese types, yeasts are the main microbial group, at least for some part of their ripening process, while for some other types, yeasts are absent. Differences between industrially manufactured cheeses and artisanal cheeses have specified. Artisanal cheeses possess a diverse assortment of yeast species, mainly belonging to the genera <italic>Candida</italic>, <italic>Clavisporalus</italic>, <italic>Cryptococcus</italic>, <italic>Debaryomyces</italic>, <italic>Geotrichum</italic>, <italic>Issatchenkia</italic>, <italic>Kazachstania</italic>, <italic>Kluyveromyces</italic>, <italic>Kodemaea</italic>, <italic>Pichia</italic>, <italic>Rhodotorula</italic>, <italic>Saccharomyces</italic>, <italic>Saturnispora</italic>, <italic>Torulaspora</italic>, <italic>Trichosporon</italic>, <italic>Yarrowia</italic> and <italic>ZygoSaccharomyces</italic>. The role of the yeasts for selected cheeses from the seven cheese categories is discussed.</p> </abstract>

Rapid prototyping method for 3D PDMS microfluidic devices using a red femtosecond laser

A rapid prototyping technique is demonstrated which uses a red femtosecond laser to produce a metallic mould which is then directly used for the replica moulding of PDMS. The manufacturing process can be completed in less than 6 h making it a viable technique for testing new designs quickly. The technique is validated by creating a microfluidic device with channels of height and depth of 300 µm, with a ramp test structure where the height and width of the channels reduces to 100 µm to demonstrate the techniques 3D capabilities. The resulting PDMS device was easily removed from the metallic mould and closely replicated the shape aside the expected shrinkage during thermal curing. As the technique uses a single replica process, the surface roughness at the base of the channels corresponds to the un-ablated polished metal mould, resulting in a very low surface roughness of 0.361 nm. The ablated metallic mould surface corresponds to the top of the PDMS device, which is bonded to glass and does not affect the flow within the channels, reducing the need for optimisation of laser parameters. Finally, the device is validated by demonstrating laminar flow with the no-slip condition.

Minimizing Warpage on Injection molding through Response Surface Methodology (RSM)

Cosmetic defects can occur in injection molding. The aim of this study is avoidance of warpage on an injection moulding parts. The selected parts is an aesthetics part in automotive industry This study is conducted on moulded parts on the plating jigs, where warpage cannot be compensated through the fixing of parts on jigs entering plating baths where the temperature of the etching baths is around 65deg.Analysis of variance is used to determine how inputs affect outputs. The inputs used are mould surface temperature, raw material melting temperature, filling pressure and filling time. These parameters are varied to get an optimal process parameters setting to avoid the warpage of the parts by using response surface methodology.It is very difficult to understand why the warpage on the parts happens.There is lots of factors which can contribute for warpage and to identify them is a huge task and this can be due to numerous things and to sequester the role of each parameters is an uphill task. One of the parameters is the holding pressure which decides how much the part is packed which, in turn, is the cause for the stress in the part. This induced stress when gets relieved over a period of time creates warpage in the part. Warpage can also be dependent on the sequence of filling the part with various gates. For example, if the part is filled from the centre & the end gates are opened last, it may cause over packing of the part at the end & cause more warpage only at the ends locally. However, usually parts are filled in this fashion only to avoid warpage in the centre.

Steel mould surface improvement by robot fluid jet polishing and robot pad polishing for polymer optic production

In order to improve the quality of injection-moulded polymer optic parts, it is necessary to improve the quality of the respective steel moulds. For this reason, it is not only necessary to improve the surface roughness of the mould, but also its geometrical shape. The material removal obtained from robot pad polishing is too low. This makes a shape correction after the milling step a very prolonged process. The aim of this work is to use a polishing chain to improve the surface quality of steel samples in terms of shape deviation and surface roughness. This correction polishing chain uses the robot fluid jet polishing for the geometrical shape correction and afterwards the robot pad polishing for the improvement of the surface roughness. Due to the high material removal rates of the fluid jet polishing, it is possible to correct the geometrical shape of steel moulds very fast up to a certain deviation. The pad polishing process improves the surface roughness of the steel samples. A correction of the shape deviation of more than 80% with a RMS of approximately 8 nm was obtained.