A conical mandrel tube drawing test designed to assess failure criteria

International audienceCold tube drawing is a metal forming process which enables to produce tubes with high dimensional precision. It consists in reducing tube dimensions by pulling it through a die. Tube outer diameter is calibrated by a die and the tube inner diameter and thickness are calibrated by a mandrel. One of the major concern of metal forming industry is the constant improvement of productivity and product quality. In the aim of pushing the process to the limit the question is how far the material can be processed without occurrence of failure. In the present study, a long conical mandrel with a small cone angle was designed in order to carry out drawing tests up to fracture with experimental conditions very close to the industrial process. The FEM of the process was built in order to access the local stress and strain data. A specific emphasis was put on the friction characterisation. For that purpose force measurement during the conical mandrel experiments enabled to characterise a pressure dependent friction coefficient constitutive law by means of an inverse analysis. Finally, eleven failure criteria were selected to study the drawability of cobalt-chromium alloy tubes. The assessment of failure criteria based on damage variables or damage accumulation variables involved their calibration on uniaxial tensile tests. The experimental studies were completed by SEM fractography which enabled to understand the fracture locus and the propagation direction of the fracture

Precision tube drawing for biomedical applications (Theoretical, Numerical and Experimental study)

Les tubes métalliques de précision sont largement utilisés pour des applications biomédicales. De tels tubes sont fabriqués par étirage à froid car ce procédé garanti le meilleur aspect de surface, le plus grand contrôle des dimensions du tube et le contrôle des propriétés mécaniques. L'objet de cette étude est de modéliser le procédé d'étirage de tube sur mandrin afin d'en améliorer la compréhension et de construire un outil permettant l'optimisation du procédé et de prédire la rupture des tubes en étirage. La construction du modèle élément finis s'appuie sur la réalisation d'essais expérimentaux afin de caractériser les propriétés mécaniques des matériaux et le frottement entre le tube et les outils d'étirage (mandrin, filière). Le comportement mécanique des alliages est caractérisé par des essais de traction sur tube, des essais de traction sur des éprouvettes découpées dans différentes orientations dans un tube déplié et des essais de gonflement de tube. Pour ces derniers, une machine et un outillage de gonflement de tubes ont été développés spécifiquement. Par le biais de ces essais différents aspects ont été étudiés : la viscoplasticité, l'anisotropie plastique, l'hétérogénéité des propriétés dans l'épaisseur du tube, la thermomécanique. Les coefficients de frottements ont été identifiés par analyse inverse sur des essais d'étirage instrumentés par des cellules d'effort. Des essais d'étirage ont été spécifiquement conçus en modifiant la géométrie du mandrin afin de conduire à la rupture des tubes lors de l'étirage. L'objectif de tels essais étant d'identifier la limite de formabilité des tubes. L'approche choisie pour prédire de la rupture a été d'utiliser des critères de ruptures qui pouvaient être calibrés sur des essais de traction uniquement. Les critères ont été calculés au cours de la simulation numérique de l'étirage sur mandrin et ils ont été évalués par rapport à leur capacité à prédire les réductions de section et d'épaisseur maximales. Enfin, des méthodes analytiques de calcul d'effort d'étirage ont été développées et comparées à la modélisation éléments finis.Precision metallic tubes are widely used for biomedical applications. The requirements of such tubes in term of surface quality, precise dimensions and mechanical properties can be achieved by cold tube drawing only. The purpose of this study is to model the mandrel tube drawing in order improve the process understanding and to build a tool both for process optimisation and for failure prediction during drawing. Building the finite element modelling requires to perform a series of experimental tests in order to characterise the material mechanical behaviour and the friction between the tube and the forming tools (mandrel, die). The materials mechanical behaviour is characterized by means of tube tensile tests, tensile tests of oriented samples cut in different directions from flattened tubes and tube bulge test. For the latter, a tube bulge test device was specifically designed. Different aspects were covered by these tests: viscoplasticity, plastic anisotropy, materials properties heterogeneity in the tube thickness, thermomechanics. Friction coefficients were identified by inverse analysis on instrumented tube drawing tests. A specific drawing test was designed in order to identify the tube fracture during drawing by modifying the mandrel geometry. The goal of such test was to identify the tube formability limit. Among the different techniques available to predict tube failure, the approach of failure criterion was chosen. Different failure criteria that could be calibrated on tensile test were selected. Failure criteria were computed during the simulation of the mandrel tube drawing and they were evaluated in term of predictability of the maximum section and thickness reductions before fracture. Finally, analytical methods that enable to compute the drawing force were developed and compared with the finite element modelling.SAVOIE-SCD - Bib.électronique (730659901) / SudocGRENOBLE1/INP-Bib.électronique (384210012) / SudocGRENOBLE2/3-Bib.électronique (384219901) / SudocSudocFranceF

Precision tube drawing for biomedical applications : Theoretical, Numerical and Experimental study

Les tubes métalliques de précision sont largement utilisés pour des applications biomédicales. De tels tubes sont fabriqués par étirage à froid car ce procédé garanti le meilleur aspect de surface, le plus grand contrôle des dimensions du tube et le contrôle des propriétés mécaniques. L'objet de cette étude est de modéliser le procédé d'étirage de tube sur mandrin afin d'en améliorer la compréhension et de construire un outil permettant l'optimisation du procédé et de prédire la rupture des tubes en étirage. La construction du modèle élément finis s'appuie sur la réalisation d'essais expérimentaux afin de caractériser les propriétés mécaniques des matériaux et le frottement entre le tube et les outils d'étirage (mandrin, filière). Le comportement mécanique des alliages est caractérisé par des essais de traction sur tube, des essais de traction sur des éprouvettes découpées dans différentes orientations dans un tube déplié et des essais de gonflement de tube. Pour ces derniers, une machine et un outillage de gonflement de tubes ont été développés spécifiquement. Par le biais de ces essais différents aspects ont été étudiés : la viscoplasticité, l'anisotropie plastique, l'hétérogénéité des propriétés dans l'épaisseur du tube, la thermomécanique. Les coefficients de frottements ont été identifiés par analyse inverse sur des essais d'étirage instrumentés par des cellules d'effort. Des essais d'étirage ont été spécifiquement conçus en modifiant la géométrie du mandrin afin de conduire à la rupture des tubes lors de l'étirage. L'objectif de tels essais étant d'identifier la limite de formabilité des tubes. L'approche choisie pour prédire de la rupture a été d'utiliser des critères de ruptures qui pouvaient être calibrés sur des essais de traction uniquement. Les critères ont été calculés au cours de la simulation numérique de l'étirage sur mandrin et ils ont été évalués par rapport à leur capacité à prédire les réductions de section et d'épaisseur maximales. Enfin, des méthodes analytiques de calcul d'effort d'étirage ont été développées et comparées à la modélisation éléments finis.Precision metallic tubes are widely used for biomedical applications. The requirements of such tubes in term of surface quality, precise dimensions and mechanical properties can be achieved by cold tube drawing only. The purpose of this study is to model the mandrel tube drawing in order improve the process understanding and to build a tool both for process optimisation and for failure prediction during drawing. Building the finite element modelling requires to perform a series of experimental tests in order to characterise the material mechanical behaviour and the friction between the tube and the forming tools (mandrel, die). The materials mechanical behaviour is characterized by means of tube tensile tests, tensile tests of oriented samples cut in different directions from flattened tubes and tube bulge test. For the latter, a tube bulge test device was specifically designed. Different aspects were covered by these tests: viscoplasticity, plastic anisotropy, materials properties heterogeneity in the tube thickness, thermomechanics. Friction coefficients were identified by inverse analysis on instrumented tube drawing tests. A specific drawing test was designed in order to identify the tube fracture during drawing by modifying the mandrel geometry. The goal of such test was to identify the tube formability limit. Among the different techniques available to predict tube failure, the approach of failure criterion was chosen. Different failure criteria that could be calibrated on tensile test were selected. Failure criteria were computed during the simulation of the mandrel tube drawing and they were evaluated in term of predictability of the maximum section and thickness reductions before fracture. Finally, analytical methods that enable to compute the drawing force were developed and compared with the finite element modelling

Etirage de tubes de précision pour applications biomédicales : contribution à l'analyse et l'amélioration du procédé par expérimentation, modélisation et simulation numérique

Precision metallic tubes are widely used for biomedical applications. The requirements of such tubes in term of surface quality, precise dimensions and mechanical properties can be achieved by cold tube drawing only. The purpose of this study is to model the mandrel tube drawing in order improve the process understanding and to build a tool both for process optimisation and for failure prediction during drawing. Building the finite element modelling requires to perform a series of experimental tests in order to characterise the material mechanical behaviour and the friction between the tube and the forming tools (mandrel, die). The materials mechanical behaviour is characterized by means of tube tensile tests, tensile tests of oriented samples cut in different directions from flattened tubes and tube bulge test. For the latter, a tube bulge test device was specifically designed. Different aspects were covered by these tests: viscoplasticity, plastic anisotropy, materials properties heterogeneity in the tube thickness, thermomechanics. Friction coefficients were identified by inverse analysis on instrumented tube drawing tests. A specific drawing test was designed in order to identify the tube fracture during drawing by modifying the mandrel geometry. The goal of such test was to identify the tube formability limit. Among the different techniques available to predict tube failure, the approach of failure criterion was chosen. Different failure criteria that could be calibrated on tensile test were selected. Failure criteria were computed during the simulation of the mandrel tube drawing and they were evaluated in term of predictability of the maximum section and thickness reductions before fracture. Finally, analytical methods that enable to compute the drawing force were developed and compared with the finite element modelling.Les tubes métalliques de précision sont largement utilisés pour des applications biomédicales. De tels tubes sont fabriqués par étirage à froid car ce procédé garanti le meilleur aspect de surface, le plus grand contrôle des dimensions du tube et le contrôle des propriétés mécaniques. L'objet de cette étude est de modéliser le procédé d'étirage de tube sur mandrin afin d'en améliorer la compréhension et de construire un outil permettant l'optimisation du procédé et de prédire la rupture des tubes en étirage. La construction du modèle élément finis s'appuie sur la réalisation d'essais expérimentaux afin de caractériser les propriétés mécaniques des matériaux et le frottement entre le tube et les outils d'étirage (mandrin, filière). Le comportement mécanique des alliages est caractérisé par des essais de traction sur tube, des essais de traction sur des éprouvettes découpées dans différentes orientations dans un tube déplié et des essais de gonflement de tube. Pour ces derniers, une machine et un outillage de gonflement de tubes ont été développés spécifiquement. Par le biais de ces essais différents aspects ont été étudiés : la viscoplasticité, l'anisotropie plastique, l'hétérogénéité des propriétés dans l'épaisseur du tube, la thermomécanique. Les coefficients de frottements ont été identifiés par analyse inverse sur des essais d'étirage instrumentés par des cellules d'effort. Des essais d'étirage ont été spécifiquement conçus en modifiant la géométrie du mandrin afin de conduire à la rupture des tubes lors de l'étirage. L'objectif de tels essais étant d'identifier la limite de formabilité des tubes. L'approche choisie pour prédire de la rupture a été d'utiliser des critères de ruptures qui pouvaient être calibrés sur des essais de traction uniquement. Les critères ont été calculés au cours de la simulation numérique de l'étirage sur mandrin et ils ont été évalués par rapport à leur capacité à prédire les réductions de section et d'épaisseur maximales. Enfin, des méthodes analytiques de calcul d'effort d'étirage ont été développées et comparées à la modélisation éléments finis

Design of specific experimental tests to evaluate formability prediction of cold drawing CoCr Tubes

International audienceHigh precision small metallic tubes are widely used in medical applications. Tubes for such applications are made by means of a cold drawing process. It consists in progressively reducing the inner and outer diameters of tubes. Small tubes processing requires a specific control of all the forming parameters in order to reach the highest dimensional precision and quality. In the industrial context of continuously improving tube quality and reducing production costs, there is a strong need to deeper understand the mechanisms of cold tube drawing and to determine the limits of the process. The process understanding gives rise to three main problematics which are strongly linked. The first issue is the material mechanical behavior and more precisely the plastic response that must be known and modeled with a very good accuracy. The second one is the friction between the tube and the drawing tools. Friction is influenced by the nature of the contacting materials, the surface aspect, the drawing speed, and the used lubricant, thus its determination is rather complex. Finally, the last issue is the prediction of the onset of ductile fracture. In this study, both experimental and finite elements simulations were used for process optimization. Concerning experimental analysis both laboratory and industrial experimental tools were developed. The material of study was a CoCr alloy namely L605. First the material visco-plastic constitutive equation was characterized by means of pure tensile test at high strain rates close to strain rates reached during drawing process. Second a high pressure tube bulge test was developed in order to reach more complex stress states. Strain, displacement and curvature fields were measured using a stereo-correlation system coupled to tube bulge test. Next stress state fields were evaluated from curvature fields and pressure measurement under membrane hypothesis. The two previous tests were used to calibrate phenomenological failure criteria aiming to predict formability limit. Third, an industrial drawing experiment was specifically developed to study friction between the tubes and the drawing tools and to find formability limit. It consists in a mandrel drawing test in which the mandrel geometry was modified. The newly developed conical mandrel enabled to draw tubes from zero section reduction up to a section reduction leading to fracture. Parallel to the experimental analysis, finite element modeling of tube drawing was performed. It enabled to determine the friction coefficients through an inverse analysis. Phenomenological failure criteria were computed on the conical mandrel drawing simulations. The fracture loci predicted by the phenomenological ductile failure criteria and the experimentally observed ones were compared quantitatively. A further study was performed in order to evaluate the influence of some forming parameters on tube formability

Simulation of Drawing of Small Stainless Steel Platinum Medical Tubes-Influence of the Tool Parameters on the Forming Limit

International audienceTube cold drawing processes are used to reduce tube diameters and thickness, while pulling them through a conical converging die with or without inner plug. An accurate modelling of the material deformation and friction behaviour is required in order to well describe these processes. The study concerns a stainless steel platinum alloy. The material behaviour is characterised through tensile tests at strain rates as close as possible to the high strain rates reached during the drawing process. The results are fitted with an isotropic temperature-independent Johnson Cook constitutive equation. The modelling of floating plug drawing is performed on a ABAQUS/Explicit model. Friction coefficient is difficult to estimate with mechanical experimental tests, thus an inverse analysis is carried out to fit this parameter thanks to finite element simulation and experimental drawing tests. Drawing force measurements are recorded during the forming process. The Cockroft-Latham criterion is applied to understand the different process parameters influence on tube drawing and its accuracy for drawing process is evaluated

Cold drawing of 316L stainless steel thin-walled tubes: experiments and finite element analysis

International audienceDrawing process of thin walled tubes used to fabricate catheters and stents for medical applications was studied. Medical use needs accurate dimensions and a smooth finish of the inner and outer surfaces. This paper deals with 316L stainless steel tubes which are manufactured by means of cold drawing with or without inner plug (mandrel drawing and hollow sinking, respectively). To improve the quality of the finish of the tubes, numerical modelling can be used. In this way, a thermomechanical study of the drawing process is proposed to determine experimentally the physical parameters. This study proposes to evaluate the different parameters of the constitutive equations, of the thermal and friction models using specific experimental tests or using an inverse analysis on the drawing process. These parameters are validated by analysing other tube drawings. Finally the importance of physical parameters fit on drawing limits is emphasised, using a Cockcroft-Latham failure criterion

Contents

préparée au sein des laboratoires TIMC-IMAG (UMR CNRS 5525) et 3SR (UM