Dolores Riera

Universitat Politècnica de Catalunya | UPC · Department of Mining, Industrial and ICT Engineering (EMIT)

Citation: Pijuan, J.; Cegarra, S.A.; Dosta, S.; Albaladejo-Fuentes, V.; Riera, M.D. Centrifugal Atomization of Glass-Forming Alloy Al Abstract: Centrifugal atomization is a rapid solidification technique for producing metal powders. However, its wide application has been limited to the production of common metal powders and their corresponding allo...

Ultrasonic moulding is a new technology that uses high power ultrasounds to melt and mould thermoplastic polymers to produce samples with mini and micro features. The main feature of this technology is the use of ultrasonic energy as the heating source instead of a conventional injection screw. Even if ultrasonic moulding overcomes some of the draw...

Ultrasonic moulding, also known as ultrasonic microinjection moulding, is a new technology that uses high-power ultrasound to melt and mould thermoplastic polymers to produce samples with mini- and micro-features. The main feature of this technology is the use of ultrasonic energy as the heating source instead of a conventional injection screw. Sin...

UltraSonic Moulding (USM) is a new moulding process powered by ultrasonic energy that plasticizes the polymer pellets pushing them to a vibrating ultrasonic sonotrode. The polymer is then transferred to the mould while it is being melted. This process was first studied by Michaeli et al [1] and since 2010 there is a commercial machine designed and...

The present study shows the results obtained in the experimental measurement of polypropylene heating when applying high power mechanical ultrasounds. The objective is to understand the behaviour of the polypropylene pellets during the ultrasonic moulding process (USM). For this study, a simplified geometry has been considered (a solid cylinder), a...

Press hardened components have become widespread in the automotive industry in structural and crash resistant applications, thanks to the combination of complex shape and high mechanical properties obtained. However, press hardening of coated boron steel results in severe adhesive-based wear, with tool maintenance cycles being as short as 3000 cycl...

In this work, the mechanisms resulting in transfer of aluminium on hot forming tools have been analysed by means of two separate laboratory tests. The influence of chemical affinity in aluminium adhesion has been studied in contact tests, measuring the force used in pulling at low velocity an aluminium ball pressed against a tool surface. The role...

From the point of view of tool makers like our company BATZ, the main challenges in the press hardening process are to increase the process productivity, to produce repeatable parts with tai-lored properties and to improve the life of the hard trimming blades at mass production. The pre-sent paper summarizes the main effects on the hot stamping pro...

Scratch testing is one of the most usual characterisation techniques for systems with thin hard coatings. Scratch tests are performed at run at room temperature, due to the risk of degradation of the indenter diamond tip at high temperature and added test complexity. However, results obtained at room temperature may differ from the final system per...

SmartStripping is an innovative on-site process for green remediation that reduces concentrations of volatile and semi-volatile organic compounds (VOC, sVOC) from unsaturated soils and groundwater. It differs from other technologies as it generates a "closed circular air flow" in the underground that reduces contaminants concentrations, cutting out...

En la industria abundan procesos térmicos o termo-mecánicos durante los cuales se producen distorsiones difíciles de predecir y controlar. Las diferentes velocidades de enfriamiento ocasionadas a lo la rgo de la pieza durante el proceso producen una distribución de fases con volumen específico y propiedades mecánicas diferentes, que generan tension...

. La mayoría de los mecanismos de fallo que determinan la durabilidad de un molde de inyección de aluminio a alta presión están relacionados con las solicitaciones termo-mecánicas de la superficie. En cada ciclo, la superficie de la herramienta está expuesta a elevadas variaciones de temperatura y cargas mecánicas que ocasionan la pérdida de propie...

The groundwater remediation technology called SmartStripping® is an innovative process for groundwater on-site remediation that reduces concentrations of Chlorinated Aliphatic Hydrocarbons (CAHs) dissolved in groundwater at industrial and civil sites and especially at sites with underground storage tanks. The process can be defined as an innovative...

In order to have a machine that functions well it is imperative to ensure that there is a good predictive maintenance. An intelligent system and devices able to detect the fault in its early stage is then convenient. The most common failures in industrial machines are those related to the power transmission systems. Acoustic Emission (AE) is the la...

The stress corrosion cracking resistance of different conventional hot work tool steels used in hot stamping processes will be evaluated. Hot stamping dies have cooling channels to extract the heat from the hot component to be formed, and also to reduce the degradation of the tool material properties due to the high temperatures reached during serv...

The automotive industry has increased significantly the use of advanced high strength steels (AHSS) in many structural components of vehicles, with the aim to reduce weight and also increase safety. The high resistance of these steels is accompanied by a decrease in formability, which makes simulation a requirement to adequately foresee the formabi...

The stress corrosion cracking resistance of different conventional hot work tool steels used in hot stamping processes will be evaluated. Hot stamping dies have cooling channels to extract the heat from the hot component to be formed, and also to reduce the degradation of the tool material properties due to the high temperatures reached during serv...

In this paper, the variation of the Young’s modulus with plastic deformation during unloading in a tensile test with has been determined for a wide range of Dual-phase steels, covering from DP 1400 to DP 780. As a general rule, the higher strength steels have a lower variation (8%) and as the strength decreases, this diminution increases, arriving...

The automotive industry has increased significantly the use of advanced high strength steels (AHSS) in many structural components, with the aim to reduce weight and also to increase safety. The high resistance of these steels is accompanied by a decrease in formability, which makes simulation a requirement to adequately foresee the formability of a...

Experimental and numerical studies of powder flow during the die filling stage in powder metallurgy cold compaction processes are presented. An experimental setting consisting of a horizontal pneumatically activated shoe, a vertical die and high-speed video system has been designed. The experiments show the existence of three flow regimes: continuo...

En el sector automovilístico se ha incrementado el uso de aceros de alta y muy alta resistencia para conformar piezas de carrocería. La utilización de estos nuevos aceros lleva asociada una problemática específica en la construcción de los útiles de conformado. El elevado límite elástico de estos aceros obliga a utilizar elevadas presiones de confo...

La inspección con ultrasonidos mediante láser es un método de ensayo no destructivo con las mismas aplicaciones de un equipo de ultrasonidos convencional, excepto que no requiere contacto con la pieza a inspeccionar ya que emplea dos láseres: uno para generar las ondas acústicas y el otro para detectar la vibración superficial. La combinación de la...

La introducción de los nuevos aceros avanzados de alta resistencia (AHSS) para ser utilizados en procesos de conformado en frío presenta, aparte de numerosas ventajas, varias problemáticas. Una de las más importantes es que los aceros AHSS poseen una recuperación elástica (springback) mayor después del conformado de las diferentes piezas comparada...

This work carries out a research about the elastic behaviour of metallic powder compacts. Cylindrical specimens with different levels of density have been submitted to uniaxial compression tests with loading and unloading cycles. The analysis of the elastic loadings shows a non-linear elasticity, which can be mathematically represented by means of...

In the present work, the feasibility of creating low strength zones in flanges of tailored hardened 22MnB5 is evaluated by means of the combining high and low thermal conductivity tool materials. Finite Element (FE) simulations are performed in order to determine the temperature distribution in sheets when different tool materials and cooling strat...

Experimental and numerical studies of powder flow during the die filling stage in powder metallurgy cold compaction processes are presented. An experimental setting consisting of a horizontal pneumatically activated shoe, a vertical die and high-speed video system has been designed. The experiments show the existence of three flow regimes: continuo...

The excellent combination of high mechanical strength, high elongation and strain hardening of Advanced High Strength Steels (AHSS) has permitted their increasing use in the automobile industry to reduce vehicle weight and thereby fuel consumption while improving crash performance. However, the implementation of AHSS has generated difficulties rela...

Hot stamping is a thermo-mechanical technique that enables to give to a metallic blank the desired geometry and properties in a single step, where deformation at high temperature, phase transformations and heat transfer are occurring simultaneously and affect mutually. They are several variables controlling the quality of the final component and th...

In this paper the evolution of the Young’s Modulus (E) during unloading is studied along the tensile deformation for an advanced high strength steel DOCOL 1200. The defined Apparent Young’s Modulus (EA) decreases non-linearly with plastic deformation tending to a saturation value as higher values of plastic strain. In order to know if this knowledg...

The extensive use of Advanced High Strength Steels (AHSS) in structural and safety-related automotive components has been hampered due to the mechanical performance of forming tools. The high load requirements during the cold forming of AHSS increase to a great extent the tool demands in terms of toughness and hardness properties. The main alternat...

Due to the demand for lighter structures AHSS are becoming the steels of choice on structural automotive applications. Although their sheet forming behavior has long since been under study, not much work has been done on their fracture resistance properties. It is especially true in toughness measurements since the thickness of the metal sheet does...

Hot stamping is a thermo-mechanical technique that enables to give to a metallic blank the desired geometry and properties in a single step, where deformation at high temperature, phase transformations and heat transfer are occurring simultaneously and affect mutually. They are several variables controlling the quality of the final component and th...

La introducción en la industria del automóvil de nuevos aceros de alta resistencia, ha permitido la disminución del peso estructural aumentando la resistencia a impacto de los vehículos. Sin embargo, las dificultades encontradas en la conformación de estos aceros –desgaste y rotura de matrices, springback elevado- han forzado la búsqueda de nuevos...

AbstractSemi-insulating silicon carbide (SiC) is a fully processable semiconductors substrate that is commonly used as an alternative to conventional silicon (Si) in high-power applications. Here we examine the feasibility of using SiC as a substrate for the development of minimally invasive multi-sensor micro-probes in the context of organ monitor...

It might seem that elastic behaviour plays a secondary role during powder compaction. This is true only during the initial densification of the powder in the die in which very inelastic mechanisms, i.e. particle sliding and rearrangement, are acting. However, as densification proceeds plastic deformation of particles, mainly in metals, becomes the...

Powder metallurgical industry is very interested in spreading its applications and improve the quality of the PM products. Therefore, a detailed knowledge of their processes, in order to control them, is necessary. Many different types of models have been used to represent the mechanical behaviour of these materials; however, nowadays, most of the...

Powder metallurgical industry is very interested in spreading its applications and improve the quality of the PM products. Therefore, a detailed knowledge of their processes, in order to control them, is necessary. Many different types of models have been used to represent the mechanical behaviour of these materials; however, nowadays, most of the...

En el sector automovilístico se están dando importantes cambios en cuanto a las exigencias mecánicas de los materiales, dando lugar a la aplicación de los aceros de alta resistencia mecánica, con el fin de reducir los espesores en piezas de la carrocería. No obstante, la utilización de estos nuevos aceros, lleva asociada una problemática específica...

La industria pulvimetalúrgica está interesada en extender las aplicaciones y mejorar la calidad de sus productos. Para ello, necesita un conocimiento detallado de sus procesos que permita su control. La representación del comportamiento mecánico de estos materiales se ha realizado utilizando diversos tipos de modelos; en la actualidad, la mayoría d...

Die filling is the first step in the process of powder compaction. The density distribution depends of the powder characteristics and method of filling. In this work we present the first results obtained with different experimental methods of the filling. Results have been analyzed using a video system which permits the observation of the powder fl...

The aim of this work is to show the potential of the Particle Finite Element Method (PFEM) in the simulation of the powder transfer stage, in powder metallurgy industrial processes. The most innovative aspects of the work are: a) the intensive use of the particle finite element method technology to trace the motion of a representative set of partic...

Die filling is the initial stage in the powder metallurgy process. During this stage heterogeneous density distributions inside the mould can be originated, which can give place to defects in the compacted part. In this work an experimental study of the behaviour of the powder during the filling stage is presented. Three filling regimes have been o...

The aim of this work is to show the potential of the Particle Finite Element Method (PFEM) in the simulation of the powder transfer stage, in powder metallurgy industrial processes. The most innovative aspects of the work are: a) the intensive use of the particle finite element method technology to trace the motion of a representative set of partic...

Die filling is the first step in the process of powder compaction. The density distribution depends of the powder characteristics and method of filling. In this work we present the first results obtained with different experimental methods of the filling. Results have been analyzed using a video system which permits the observation of the powder fl...

Powder transfer inside the compacting die is a frequent and important stage in the elaboration of PM parts of complex shapes. It introduces shear bands inside the uncompressed powder given place to initial unhomogeneities that can produce defects and even failures in the compacted part. In this work, the extent and size of these shear bands are stu...

.In the field of Powder Metallurgy industrial powders are generally mixes of different constituents with complex behaviour. The response of a powder during compaction can be described in terms of a suitable constitutive law, which can be calibrated using a range of experimental tests with different degrees of sophistication. This paper deals with c...

In this work, a plasticity model for granular materials, based on the Drucker–Prager/CAP model, is applied to represent the behaviour of the metallic powders during their cold die compaction. The elastic deformation has been simulated by means of a non-linear law. These constitutive equations have been implemented in a commercial code to simulate t...

Die filling is the first step in the process of powder compaction. The density distribution depends of the powder characteristics and method of filling. In this work we present the first results obtained with different experimental methods of the filling. Results have been analyzed using a video system which permits the observation of the powder fl...

The mechanisms governing the densification of powdered materials under compaction are highly dependent on the deformation and the state of stress in the contact among particles. Therefore, a micromechanical model can be very useful in studying the phenomena involved in the compaction process. In this work numerical simulations showing the distribut...

The mechanical response in service of a component is mainly determined by its elastic behaviour. Traditionally, metallic materials have been characterized by means of tensile tests, even in the case of sintered ones. In this condition, the elasticity of sintered parts has been always supposed to be linear, with a Young modulus dependent on the dens...

En este trabajo se ha llevado a cabo la simulación, mediante métodos numéricos, del comportamiento elástico de arreglos regulares de partículas metálicas, con el fin de validar una ecuación constitutiva obtenida experimentalmente en trabajos previos. La simulación muestra que la tensión aplicada varía potencialmente con la componente elástica de la...

En este trabajo se ha llevado a cabo la simulación, mediante métodos numéricos, del comportamiento elástico de arreglos regulares de partículas metálicas, con el fin de validar una ecuación constitutiva obtenida experimentalmente en trabajos previos. La simulación muestra que la tensión aplicada varía potencialmente con la componente elástica de la...

In this work an industrial simulation, by means of the FE ABAQUS standard code, of a complete process of metal powder cold compaction is presented. The simulation considers the p`lacing of an insert, the powder compaction and the final ejection of the compact. The effect of the insert material on the dimensional characteristics of the component is...

Cold die compaction can produce different effects on the dimensional and mechanical behaviour of green PM compacts. They can be due to different causes, such as residual stresses, microcracks and others. Residual stresses should be relieved by means of applying thermal annealing treatments. In this work, the authors present the results obtained fro...

In the Metalworking Industry the design and the control of the processes have been traditionally based on the experience and, sometimes, considered as an art. The application of numerical methods reduces the costs of the design and elaboration processes and contributes to the improvement of the product quality. In this work the authors present the...

Powder Metallurgical Industry is very interested in spreading its applications and improve the quality of the PM products. Therefore, a detailed knowledge of their processes, in order to control them, is necessary. Many different types of models have been used to represent the mechanical behaviour of these materials; however, nowadays, most of the...

In the Metalworking Industry the design and the control of the processes have been traditionally based on the experience and, sometimes, considered as an art. The application of numerical methods reduce the costs of the design and elaboration processes and contributes to the improvement of the product quality. In this work the authors present the s...

The Poisson´s ratio of green powder compacts is a quite unknown elastic parameter. During an uniaxial compression test the monitoring of axial and radial deformations of cylindrical specimens have allowed to study the Poisson´s coefficient of green powdermetallurgical compacts. The variation of this parameter during cyclic loading is studied togeth...

The Brazilian test has been widely used in determining the tensile fracture strength of fragile and quasi-fragile materials. In this work the application of this test to study the fracture behaviour of powdermetallurgical compacts is analysed. Disc shaped specimens of 20 mm in diameter and 5 mm thickness, compacted to different levels of density, h...

During cold powder compaction processes, loose powder is pressed under tooling action, exhibiting plastic deformations which allow shaping and densification. However, always present elastic deformations are proved to be essential specially during ejection and have to be well known for predicting spring back components. In this work an atomized iron...

Resumen En este trabajo se estudia el comportamiento elástico de compactos de polvos metálicos. Para ello, se han preparado probetas cilíndricas y se han sometido a ensayos de compresión uniaxial con ciclos de carga y descarga. El análisis de las cargas elásticas muestra una elasticidad no lineal, que puede representarse matemáticamente por medio d...

The brazilian test has been widely used to determine, in a indirect way, the tensile fracture resistance of materials such as concrete, rocks, ... More recently, its use has been extended to characterize advanced ceramics. In this work, its application to the study of the fracture behaviour of metal powder compacts is analyzed. Disks of 20 mm diame...

Uniaxial compression tests have been performed on compacts of different densities, prepared by die pressing, in order to characterize the mechanical behaviour of an iron based powder. The experimental results obtained by continuously loading or by loading and unloading, allow to define a relationship between the applied axial stress and the volumet...

The simulation by means of finite elements of the forming processes of mechanical components is a very useful tool for their design and validation. In this work, the simulation of the compaction of a metal powder is presented. The finite element software Abaqus is used together with the modified CAM-clay plasticity model in order to represent the e...

In this work the elastic behaviour of metal powders compacted to different densities is studied. The authors apply a model based on the experimental observation that the elastic volumetric strain and the hydrostatic component of the applied stress are exponentially related. While a complete analysis should include both the volumetric and deviatory...

Tradicionalmente, los programas de elementos finitos de propósito general incluyen ecuaciones constitutivas idealizadas en sus modelos de deformación plástica. Esto se debe, en parte, a que no hay suficientes ecuaciones constitutivas verdaderas desarrolladas para todo tipo de aleaciones. El presente grupo de investigación ha desarrollado para un ac...

In this work the elastic behaviour of metal powders compacted to different densities is studied. The observed behaviour can be explained by the contribution of two terms: one of them accounting for the non-linear elastic behaviour of the porous structure and another one for the linear elastic behaviour of the metal particles.