Investigation on the functionality of thermoresponsive origami structures

Additive manufacturing (AM) has recently been introduced as a reliable technique for the fabrication of highly complex geometries that were not possible before. Due to the flexibility in the organization of material properties such as responsive elements in space, AM is now a capable technology for the production of smart structures that can transform their geometry, for example, from a compact state to a deployed configuration. Among others, fused deposition modeling (FDM) can reliably be used to manufacture polymeric constructs with high resolution. Polylactide (PLA), the most popular polymer in FDM printing is a shape-memory polymer. Therefore, the manufacturing of shape-transforming constructs can be simplified to the construction of foldable products that can be programmed simply by applying mechanical forces. Origami can then be used as a simple platform in which the shape-transforming of a programmed construct is via the folding of material through the thinner sections (hinges). Herein, PLA and FDM are used to fabricate foldable structures. The effects of different parameters namely total thickness, layer height, nozzle temperature, and activation temperature on the shape recovery of the manually programmed origami structures are then investigated

Development of smooth finishes in electrostatic fluidized bed (EFB) coating process of high-performance thermoplastic powders (PPA 571 H)

This paper deals with the analysis of the evolution of the surface morphology of metal substrates coated with high-performance thermoplastic powders, namely PPA 571 H, by using electrostatic fluidized bed (EFB) process. Attention has been particularly focused on the relationship between baking time and temperature of EFB coated substrates and the morphological characteristics of the resulting polymeric films. First, thermal behaviour of PPA 571 H polymeric powders was characterized by using standard calorimetric techniques. Accordingly, PPA 571 H melting kinetic was experimentally deduced. Based upon experimental findings, predictive analytical model was also developed and employed to trace 'iso-conversion' curves out. Second, metal substrates, made from low carbon steel (AISI 1040), were EFB coated and baked at several baking time and temperatures. Combined analyses of scanning electron and confocal microscopes were led to measure the evolution of the films surface morphology under different baking conditions. Accordingly, a relationship between film morphologies and melting degree was sought. Consistent trends of roughness parameters versus baking parameters were found, with smoother finishes of the polymeric films being achieved for higher degrees of melting, that is, for higher baking temperature and time. Full maps and related analytical models of the finishing levels according to baking parameters were also built up, hence providing first useful indications to powder coaters on how to best deal with their settings. © 2006 Elsevier B.V. All rights reserved

The prediction model for additively manufacturing of NiTiHf high-temperature shape memory alloy

NiTi-based alloys are one of the most well-known alloys among shape memory alloys having a wide range of applications from biomedical to aerospace areas. Adding a third element to the binary alloys of NiTi changes the thermomechanical properties of the material remarkably. Two unique features of stability and high transformation temperature have turned NiTiHf as a suitable ternary shape memory alloys in various applications. Selective laser melting (SLM) as a layer-based fabrication method addresses the difficulties and limitations of conventional methods. Process parameters of SLM play a prominent role in the properties of the final parts so that by using the different sets of process parameters, different thermomechanical responses can be achieved. In this study, different sets of process parameters (PPs) including laser power, hatch space, and scanning speed were defined to fabricate the NiTiHf samples. Changing the PPs is a powerful tool for tailoring the thermomechanical response of the fabricated parts such as transformation temperature (TTs), density, and mechanical response. In this work, an artificial neural network (ANN) was developed to achieve a prediction tool for finding the effect of the PPs on the TTs and the size deviation of the printed parts

Investigation the effect of pulsed laser parameters on the temperature distribution and joint interface properties in dissimilar laser joining of austenitic stainless steel 304 and Acrylonitrile Butadiene Styrene

Direct laser joining of metal to plastic materials is one of the cost effective methods of joining. The demand for laser welding of stainless steels and thermoplastics is going on increase because of having many applications such as automotive, aerospace and aviation industries. This paper presents the experimental investigation of direct laser joining of stainless steel 304 and Acrylonitrile Butadiene Styrene (ABS). The effects of pulsed laser parameters including laser welding speed, focal length, frequency and power on the themperature field and tensile shear load was investigated. The results showed that excessive increase of the joint interface temperature mainly induced by high laser power density results in exiting of the more volume of the molten ABS from the stainless steel melt pool. Also, increasing the laser power density through decreasing the focal length or increasing the laser power led to an increase in the surface temperature, higher beam penetration and high volume of molten ABS. Decreasing the focal length from 5 to 2 mm significantly rose the temperature from 150 to 300 °C. By increasing the laser pulse frequency, the number of bobbles at the ABS interface surface remarkably increased where the temperature increased from 120 to 180 °C. The X-ray spectroscopy results showed the existence of the polymer elements on the metal surface at the joint interface zone. The tensile shear load clearly increased from 280 to 460 N with augmentation of laser average power from 180 W to 215 W. Applying higher levels of laser power has clearly decreased the tensile shear load due to creating bigger bobbles and more cavities at the adhesive zone

Electrostatic spray painting of carbon fibre-reinforced epoxy composites

Electrostatic spray deposition (ESD) of aesthetic and protective low curable transparent powder coatings onto carbon fibre-reinforced epoxy composites (i.e., carbon laminates) is the matter of the present investigation. An original environment friendly pretreatment of the substrate, based on fluidized bed peening of glass beads followed by a moderate temperature oven baking, has been proposed. Then, the influence of ESD operational parameters on coating performance has been looked into. Design of experiments (DOE) was used to schedule the experimental trials. Coating thickness and its uniformity over the coated substrates upon curing was systematically evaluated. Further, visual appearance of the coatings was analyzed by both optical and stereoscopic microscopy. Finally, analysis of variance (ANOVA) was performed to model the available experimental data. Detailed examinations of the experimental results allowed to define the best settings of ESD process as well as the maximum deposition time before the occurrence of severe electrical breakdown in the powder layer and/or the increase in the incidence of massive back-ionization phenomena. Accordingly, 3D process maps of the coating thickness versus the operational parameters, applied voltage, feeding and auxiliary pressure, were developed, thus supporting the practitioners in their choices and in the identification of processing windows wide enough for practical purposes. © 2008 Elsevier B.V. All rights reserved

Laser sealing of compostable packaging solutions: Experimental approach and adhesion mechanisms

This work aims to demonstrate the possibility of using laser technology to seal compostable coffee capsules in engineered, poly(lactic acid) (PLA) based, bioplastic material with thermoplastic starch (TPS) toplids. The welded joints were characterized by peel-off tests to evaluate the adhesion energy of the toplid to the capsule body as the laser process parameters vary, i.e. the power of the laser beam and scan speed. The results of the peel-off test made it possible to optimize the choice of laser process parameters for the various scenarios under investigation. 3D process maps were then constructed in which the adhesion index between toplid and capsule body was reported as the laser process parameters changed, allowing to identify the intervals of greatest practical relevance. In particular, the procedure allowed to define an adhesion index, a measure of the total adhesion energy between capsule body and toplid. Adhesion between conventional aluminum toplids and compostable capsules were also studied for comparative purposes. Based on the experimental findings, mechanisms of adhesion varying the material used for the toplid and capsule body were also discussed

Laser sealing of PLA-based compostable coffee capsules

The aim of the present work is to examine the possibility of using laser technology to make welded joints to hermetically seal bioplastic containers with aluminum or bioplastic foils. Specifically, the focus is on the laser sealing process of compostable coffee capsules with toplids in aluminum and in paper coated with compostable plastic (mainly based on polylactic acid, PLA). The aluminum toplid does not allow obtaining a compostable package, but represents the currently most used standard on the coffee capsule market. The welded joints made with laser technology were characterized by peel-off tests to evaluate the adhesion strength of the toplid to the capsule with the laser operational parameters, namely processing and pre-heating laser power, scanning speed of the laser beam. The results of the peel-off test allowed optimizing the choice of the operational parameters of the laser sealing process for the various scenarios examined. Based on the experimental findings, 3D process maps have therefore been built in which the adhesion strength between the toplid and the capsule has been plotted by varying the laser operational parameters process, making it possible to identify the optimal processing windows

Hybrid forming process of AA 6108 T4 thin sheets: Modelling by neural network solutions

The highly non-linear deformation processes occurring in most dynamic sheet metal forming operations cause large amounts of elastic strain energy to be stored in the formed material and massive related springback phenomena. Therefore, this paper investigates how effective a laser source is in reducing the extent of springback in mechanical contact forming operations. The hybrid forming process investigated was composed of using a high-power diode laser to induce local heating of mechanically bent AA 6108 T4 thin sheets in order to minimize the extent of the springback. In particular, experiments were carried out to assess the influence of the leading process parameters such as laser source power, scan speed, and starting elastic deformation of the mechanically bent sheets. It was found that the trends in the experimental response of residual deflection were always consistent with the operating parameters. Artificial intelligence techniques were then used to model the hybrid forming process. The extent of the springback in the hybrid forming process of AA 6108 T4 thin sheets was predicted by using different neural network models and training algorithms. Lastly, the reliability of the best neural network solutions was checked by comparing these solutions with experimental results and by developing an ad hoc first approximation technical model. © IMechE 2009