Rubén Paz

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.

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.

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...

Lightweight Optimization for Additive Manufacturing Parts Based on Genetic Algorithms, Metamodels and Finite Element Analysis

Additive manufacturing (AM) has become in a competitive method for short series production and high flexibility applications even for functional parts. Few constraints in the manufacturing process involve a great design freedom, allowing minimization of weight by using internal cellular and lattice structures, while minimal mechanical requirements are kept. Weight minimization implies a lower use of material and hence a reduction in manufacturing time, leading to a cost reduction. However, design optimization requires a greater effort in the design process, which also results in more costs. In order to reduce the design process, an optimization method based on genetic algorithms (GAs) and computer aided design/finite element method (CAD/FEM) simulations is proposed to optimize the cellular structure design and minimize the weight for AM parts. New optimization strategies based on GAs combined with surrogate models are evaluated and compared to reduce as much as possible the number of FEM simulations.

Knowledge Transfer and Standards Needs in Additive Manufacturing

Although AM technologies have high potential in terms of productivity and competitiveness for companies, their diffusion is still relatively limited among manufacturers and end users. In the context of two European Projects (KTRM and SASAM), this chapter presents an approach of how to transfer knowledge to people working in the manufacturing industry or design. This transfer of knowledge is not only based on technology itself but also on any other relevant issues such as business models or standardization in the field of AM. A survey and road map are presented to show the needs of the AM community in terms of training and standards. Also, the chapter highlights that the new standards and technical reports, from ISO-ASTM, can provide valuable support for knowledge transfer, being the link between training and the implementation of standards a key factor to spread AM technologies. The structure, proposed by ISO TC261 and ASTM F42, for development of future standards, is shown as the most suitable to follow in terms of training as well.

Banana Fiber Processing for the Production of Technical Textiles to Reinforce Polymeric Matrices

Banana fibers have been extracted by mechanical means from banana tree pseudostems, as a strategy to reevaluate banana crops residues. Extracted long fibers are cut to 45 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. This fiber has then been transformed into yarns and woven to produce a technical textile with different textile structures. Woven material was then used to produce a composite by compression molding, using polypropylene (PP) as polymeric matrix.

Nickel–copper electroforming process applied to rotational mould starting from additive manufacturing

This paper focuses on the development of a more energy-efficient mould for rotational moulding of plastic parts where the tool is made by electroforming of two materials (Ni–Cu), starting from a model of additive manufacturing. Studies on the poor adhesion between nickel and copper layer have not been previously carried out. The paper presents the entire design process of the mould, the electroforming process and activation procedures, and the mould testing under real conditions, comparing it with a conventional CNC machined aluminium mould. Also presented is an experimental study of different treatments of electroformed Ni substrate to provide good adherence for the electroforming of Cu. The best treatment (nitric acid) was applied to a mould for rotational moulding. The main findings of the work are a viable approach for good adherence between Ni and Cu, the advantage of additive manufacturing and electroforming as well as the standardisation of such innovative tooling in rotational moulding.