Mario D. Monzón

Anisotropy of Photopolymer Parts Made by Digital Light Processing

Digital light processing (DLP) is an accurate additive manufacturing (AM) technology suitable for producing micro-parts by photopolymerization. As most AM technologies, anisotropy of parts made by DLP is a key issue to deal with, taking into account that several operational factors modify this characteristic. Design for this technology and photopolymers becomes a challenge because the manufacturing process and post-processing strongly influence the mechanical properties of the part. This paper shows experimental work to demonstrate the particular behavior of parts made using DLP. Being different to any other AM technology, rules for design need to be adapted. Influence of build direction and post-curing process on final mechanical properties and anisotropy are reported and justified based on experimental data and theoretical simulation of bi-material parts formed by fully-cured resin and partially-cured resin. Three photopolymers were tested under different working conditions, concluding that post-curing can, in some cases, correct the anisotropy, mainly depending on the nature of photopolymer.

Predictability of Plastic Parts Behaviour Made from Rapid Manufacturing

One of the most important issues to resolve in parts manufactured from rapid manufacturing (RM) technologies is to know their behavior working under real conditions. Total quality manufacturing (TQM) is only possible if mechanical properties are well known in the design stage depending on the processing parameters. This work is mainly focused on testing of several samples made with different selective laser sintering (SLS) parameters and technologies. This procedure is the starting point to establish a basis for designing for RM and the standardization of RM testing. The experiments and the analysis of variance (ANOVA) analyzed the effects of several factors on mechanical properties. The SLS technologies were 3DSystem and EOS. The results show which factor has a large effect on the variables and the interaction between them. The conclusions are very useful for developing rules for designing (designing for RM) and creating new standard rules (ISO, AISI, and DIN) for RM materials and parts testing. The ANOVA gives a better knowledge of the effects of these factors and eliminates unimportant parameters.

Banana and Abaca Fiber-Reinforced Plastic Composites Obtained by Rotational Molding Process

Natural fibers can be used in rotational molding process to obtain parts with improved mechanical properties. Different approaches have been followed in order to produce formulations containing banana or abaca fiber at 5% weight, in two- and three-layer constructions. Chemically treated abaca fiber has also been studied, causing some problems in processability. Fibers used have been characterized by Fourier transform infrared (FTIR) spectroscopy, thermogravimetric analysis (TGA), optical microscopy, and single-fiber mechanical tests. Rotomolded parts have been tested for tensile, flexural, and impact properties, demonstrating that important increases in elastic modulus are achieved with these fibers, although impact properties are reduced.

Lightweight parametric design optimization for 4D printed parts

4D printing is a technology that combines the capabilities of 3D printing with materials that can transform its geometry after being produced (e.g. Shape Memory Polymers). These advanced materials allow shape change by applying different stimulus such as heating. A 4D printed part will usually have 2 different shapes: a programmed shape (before the stimulus is applied), and the original shape (which is recovered once the stimulus has been applied). Lightweight parametric optimization techniques are used to find the best combination of design variables to reduce weight and lower manufacturing costs. However, current optimization techniques available in commercial 3D CAD software are not prepared for optimization of multiple shapes. The fundamental research question is how to optimize a design that will have different shapes with different boundary conditions and requirements. This paper presents a new lightweight parametric optimization method to solve this limitation. The method combines the Latin Hypercube design of experiments, Kriging metamodel and specifically designed genetic algorithms. The optimization strategy was implemented and automated using a CAD software. This method recognizes both shapes of the part as a single design and allows the lightweight parametric optimization to retain the minimum mechanical properties

Production of banana fiber yarns for technical textile reinforced composites

Natural fibers have been used as an alternative to synthetic ones for their greener character; banana fibers have the advantage of coming from an agricultural residue. Fibers have been extracted by mechanical means from banana tree pseudostems, as a strategy to valorize banana crops residues. To increase the mechanical properties of the composite, technical textiles can be used as reinforcement, instead of short fibers. To do so, fibers must be spun and woven. The aim of this paper is to show the viability of using banana fibers to obtain a yarn suitable to be woven, after an enzymatic treatment, which is more environmentally friendly. Extracted long fibers are cut to 50 mm length and then immersed into an enzymatic bath for their refining. Conditions of enzymatic treatment have been optimized to produce a textile grade of banana fibers, which have then been characterized. The optimum treating conditions were found with the use of Biopectinase K (100% related to fiber weight) at 45 °C, pH 4.5 for 6 h, with bath renewal after three hours. The first spinning trials show that these fibers are suitable to be used for the production of yarns. The next step is the weaving process to obtain a technical fabric for composites production.

Advantages of Fused Deposition Modeling for Making Electrically Conductive Plastic Patterns

There are many applications where electrically conductive plastic patterns are needed. The most usual way to make electrically conductive patterns is coating a plastic part by a thin layer of metal. It’s well known the different procedures for metalizing plastic parts but most of them aim to obtain either aesthetic or functional metallic coating with high level of adherence, finishing and electrical conductivity if necessary. This aim requires complex process and time expense, however in the present research work only electrical conductivity is needed. This particular requirement allows to develop a simplified process of coating adapted to a specific target: electroforming starting from rapid prototyping (RP) metalized parts. Additive technologies based on extrusion such as Fused Deposition Modeling(FDM) provide patterns or prototypes suitable to be metalized by electroless plating and to be used as patterns for making electroforming. A different behavior of ABS FDM parts has been found in terms of metalizing procedure. This paper is focused on the proposed simplified method of electroless plating for obtaining patterns with high level of electrical conductivity and reproducibility of original RP plastic part.

Rapid prototyping applied to a new development in moulds for rotational moulding

The aim of this work has been to adapt and apply the advantages of rapid prototyping and electroforming technologies to try to achieve an innovative mould design for rotational moulding. The new innovative design integrates an electroformed shell, manufactured starting from a rapid prototyping mandrel, with different designed standard aluminium tools. The shell holder enables mould assembly with high precision manufacture of a shell in a few minutes. The overall mould cost is significantly decreased because it is only necessary to manufacture one or two shells each time; however, the rest of the elements of the mould are standard and usable for an infinite number of shells, depending on size.

New lightweight optimisation method applied in parts made by selective laser sintering and Polyjet technologies

The continuous evolution of materials and technologies of additive manufacturing has led to a competitive production process even for functional parts. The capabilities of these technologies for manufacturing complex geometries allow the definition of new designs that cannot be obtained with any other manufacturing processes. An application where this capability can be exploited is the lightening of parts using internal structures. This allows to obtain more efficient parts and, at the same time, reduce the costs of material and manufacturing time. A new lightweight optimisation method to optimise the design of these structures and minimise weight while keeping the minimal mechanical properties is presented in this paper. This method is based on genetic algorithms, metamodels and finite element analysis (FEA). This combination reduces the number of FEA simulations required during the optimisation process, thereby reducing the design time. This methodology is experimentally applied to a reference geometry oriented both for selective laser sintering (SLS) and Polyjet technologies. In both cases, an optimised and a non-optimised design are manufactured and tested in order to experimentally compare the stiffness results between them. The optimum design achieved a specific stiffness 72.82% higher than the non-optimised design in the SLS case study, and 3.14 times higher in the Polyjet case study.

Process for reinforcing SLS parts by epoxy resin

Purpose – The purpose of this paper is to report on the use of a combination of selective laser sintering (SLS) and vacuum casting to create plastic composites made by additive manufacturing. Design/methodology/approach – The research has been carried out by approaching a new concept of the final part consistent in a plastic component, where the main body is made by SLS and the internal long fibres for reinforcing are made by vacuum casting of high-resistance epoxy resin. The part is designed for optimal number and distribution of the internal fibres taking into account the target relative stiffness (N/mm*kg). The methodology is applied to a pedal clutch of a car which has been tested in an equipment for fatigue and durability, being compared to the correspondent design for injection moulding. Findings – Research has proven that the approach introduces relevant improvement in mechanical properties of the base resin consistent in PA 3200GF (EOS), reinforced by internal long fibres of resin VG SP5. Experime...

Computer Cathodic Orientation Device: Functional Properties of Electroformed Nickel Shells

A new developed device, computer cathodic orientation system, was tested to analyze functional properties of electroformed shells of nickel. Several applications, such as rapid tooling, may require thickness uniformity, where the tool or mold is made by electroforming, starting from the 3D model. This system enables the programed movement of the cathode (the model) in front of the anode with the main objective of achieving thickness uniformity. Different strategies were carried out, and parameters such as thicknesses and flexural modulus were measured for each sample. Results showed the apparent influence of this apparatus on the thickness distribution and the flexural modulus. Either the rate of mean thickness or central thickness was improved when the strategy of modifying relative position took place. Also, the flexural modulus was influenced by the approach carried out in the sequence of movement.