Simulation of low rigidity part machining applied to thin-walled structures

The aim of this study is to evaluate the modelling of machining vibrations of thin-walled aluminium workpieces at high productivity rate. The use of numerical simulation is generally aimed at giving optimal cutting conditions for the precision and the surface finish needed. The proposed modelling includes all the ingredients needed for real productive machining of thin-walled parts. It has been tested with a specially designed machining test with high cutting engagement and taking into account all the phenomena involved in the dynamics of cutting. The system has been modelled using several simulation techniques. On the one hand, the milling process was modelled using a dynamic mechanistic model, with time domain simulation. On the other hand, the dynamic parameters of the system were obtained step by step by finite element analysis; thus the variation due to metal removal and the cutting edge position has been accurately taken into account. The results of the simulations were compared to those of the experiments; the discussion is based on the analysis of the cutting forces, the amplitude and the frequency of the vibrations evaluating the presence of chatter. The specific difficulties to perfect simulation of thin-walled workpiece chatter have been finely analysed.     

Prediction of pressure drop and minimum spouting velocity in draft tube conical spouted beds using genetic programming approach

The smart method of genetic programming (GP) is used to predict the operating pressure drop (ΔP_s) and the minimum spouting velocity u_ms for conical spouted beds (CSBs) equipped with nonporous draft tubes. Accordingly, six dimensionless variables have been taken as model inputs, including crucial parameters associated with the bed and tube geometric and operating conditions. Two general correlations comprising almost all constitutive and operating variables have been derived for the first time by the GP approach. Both ΔP_s and u_ms values predicted by the GP technique are in a fair agreement with the values corresponding to the experiments, with average absolute relative errors (AARE) of 18.9 and 19.9 %, respectively. The results of the proposed correlations show that the GP method is a powerful tool to make reasonable estimates.     

Waterborne hybrid polyurethane coatings functionalized with (3-aminopropyl)triethoxysilane: Adhesion properties

Waterborne polyurethanes based on isophorone diisocyanate and two different soft segments, poly(1,4-butylene adipate) and poly(propylene glycol), were end-capped with (3-aminopropyl) triethoxysilane to impart them the ability to crosslink at room temperature. Polyurethanes were synthesized by means of acetone process and stabilized in aqueous medium using dimethylolpropionic acid (DMTA) as internal emulsifier. ¹³C NMR experiments confirmed the insertion of the alkoxysilane. The adhesion properties of the room temperature cured films as a function of alkoxysilane concentration were evaluated. The optimum film formation time and adhesion temperatures were established using the design of experiments (DOE) methodology. The Lap Shear adhesion increased as a function of the alkoxysilane content up to a point, 9.7 wt.% of alkoxysilane, where the adhesion capacity disappeared totally due to the rigidity of the material. Furthermore, both polyester and polyether based systems presented an optimum window, between 5 and 15 wt.% of alkoxysilane, where the synthesized systems promoted good adhesion at high temperatures above 200 °C for more than 24 h.     

Silicon and carbon substrates induced arrangement changes in poly(styrene-b-isoprene-b-styrene) block copolymer thin films

Poly(styrene-b-isoprene-b-styrene) (SIS) block copolymer ordering in thin films was studied using two selective substrates as carbon and silicon. Atomic force microscopy (AFM) and contact angle measurements were employed to examine the affinities between domains and surrounding interfaces. The surface morphology was examined by AFM using different amplitude ratios. Results showed polyisoprene (PI) domain layer formation in the outermost film layer. On the other hand, the layer close to substrate adopted different arrangements on silicon and carbon substrates. Topographical and phase images revealed that in both substrates with the thickest films, the interactions between substrate and block domains were not enough to induce surface ordering being the morphology independent of employed substrate. However, decreasing film thickness, SIS thin films displayed a variety of arrangements such as perforated lamellae and cylindrical morphologies. Depending on substrate, these morphologies were achieved in different film thicknesses. Finally, the thinnest film did not adjust to characteristic domain spacing commensurability and terraces formation was observed. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Tactile sensors based on conductive polymers

This paper presents results from a selection of tactile sensors that have been designed and fabricated. These sensors are based on a common approach that consists in placing a sheet of piezoresistive material on the top of a set of electrodes. We use a thin film of conductive polymer as the piezoresistive material. Specifically, a conductive water-based ink of this polymer is deposited by spin-coating on a flexible plastic sheet, giving it a smooth, homogeneous and conducting thin film. The main interest in this procedure is that it is cheap and it allows the fabrication of flexible and low cost tactile sensors. In this work, we present results from sensors made using two technologies. Firstly, we have used a flexible printed circuit board (PCB) technology to fabricate the set of electrodes and addressing tracks. The result is a simple, flexible tactile sensor. In addition to these sensors on PCB, we have proposed, designed and fabricated sensors with screen-printing technology. In this case, the set of electrodes and addressing tracks are made by printing an ink based on silver nanoparticles. The exhaustive characterization provides us insights into the design of these tactile sensors.     

Polymer/silica nanohybrids by means of tetraethoxysilane sol–gel condensation onto waterborne polyurethane particles

Stable waterborne polyurethane/silica hybrid dispersions were obtained by sol–gel reaction of tetraethoxysilane added to previously synthesized waterborne polyurethane nanodispersions. Two series of polyurethane/silica nanostructures with different silica contents were synthesized using pure polyurethane particles and polyurethane particles previously functionalized with (3-aminopropyl)triethoxysilane (APTES) as colloidal templates. The optimum experimental conditions for tetraethoxysilane sol–gel reaction (T = 75 °C and semi batch polymerization conditions) leading to the formation of silica/polyurethane aqueous nanodispersions were established. The presence of silica was confirmed using TGA, FTIR, ²⁹Si NMR and TEM. TEM images showed an excellent final dispersion of the silica nanoparticles in the polymer matrix when silane functionalized polyurethane nanoparticles were used.     

Modelling batch drying of sand in a draft-tube conical spouted bed

A model has been built to predict the evolution of sand drying in a conical spouted bed with a non-porous draft tube. Three regions have been considered in the model, i.e., spout, annulus and fountain, and unsteady-state mass balances have been written for water in the solid and gaseous phases. The model has been validated by comparing its results with the experimental ones obtained in a previous study and it allows predicting the moisture content evolution of both the air and the sand during the drying process.     

A method for the identification of the specific force coefficients for mechanistic milling simulation

This paper presents a new method to obtain the specific cutting coefficients needed to predict the milling forces using a mechanistic model of the process. The specific coefficients depend on the tool–material couple, the cutting conditions and the geometry of the tool, being usually calculated applying the force model in an inverse way. The most used inverse method is based on the calculation of the average cutting force per revolution values measured in a series of slot machining tests at different feed rates. In this research work, the inverse method is applied using the instantaneous cutting force values, solving the equations system by a constrained least squares fitting method. Furthermore, the cutting force and specific cutting coefficients relation with rake angle and chip thickness is analysed. The results are validated by the comparison of the simulations and experiments in orthogonal cutting test, showing the advantages of using the new method.     

Waterborne polyurethane dispersions obtained by the acetone process: A study of colloidal features

Waterborne polyurethane (PU) dispersions were prepared from isophorone diisocyanate (IPDI), 2‐bis(hydroxymethyl) propionic acid (DMPA), 1,4‐butane diol (BD), poly(propylene glycol) (PPG), and triethylamine (TEA) by means of phase inversion through the acetone process. Changes in DMPA content, initial PU content in acetone, phase‐inversion temperature, evaporation conditions, and solvent nature were found to have a great impact on dispersion properties. Using a DMPA concentration of 0.30 mmol/g_pol, stable PU dispersions could only be obtained when the initial PU content in acetone was at least 60 wt %, and phase‐inversion temperature was lower than 30°C. However, when increasing the PU content to 75 wt %, stable dispersions were obtained using DMPA concentrations three times lower. Finally, viscosity curves during the water addition step as well as a phase diagram were determined to understand the particle formation mechanism. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011