Consideration of residual stress and geometry during heat treatment to decrease shaft bending

In automotive industry, heat treatment of components is implicitly related to distortion. This phenomenon is particularly obvious in the case of gearbox parts because of their typical geometry and precise requirements. Even if distortion can be anticipated to an extent by experience, it remains complex to comprehend. Scientific literature and industrial experience show that the whole manufacturing process chain has an influence on final heat treatment distortions. This paper presents an approach to estimate the influence of some factors on the distortion, based on the idea of a distortion potential taking into account not only geometry but also the manufacturing process history. Then the idea is developed through experiments on an industrial manufacturing process to understand the impact of residual stress due to machining on shaft bending and teeth distortion during heat treatment. Instead of being measured, residual stress is being neutralized. By comparing lots between each other, connections between gear teeth geometry and manufacturing steps before heat treatment are obtained. As a consequence, geometrical nonconformities roots can be determined more easily thanks to this diagnosis tool, and corrective actions can be applied. Secondly, the influence of product geometry on bending is experimentally considered. Moreover, metallurgical observations enable to explain the influence of workpieces geometry on shaft bending. Thanks to the obtained results, process and product recommendations to decrease shafts bending are proposed

Forging process control: Influence of key parameters variation on product specifications deviations

Process control in forging industry is essential to ensure a better quality of the product with a lower cost at the end of the manufacturing process. To control the process, a number of key parameters must be monitored to prevent product or forging plan deviations. This paper will illustrate how a variation in a process parameter can create product specifications deviations and how key parameters influence product final state. The illustration work is done on a part obtained via hot forging. An analysis is made on product parameters such as geometry, by varying the key process parameter values previously determined from a created methodology. This later is represented as a decision support system that connects product specifications (geometry, absence of defects…) or other forging specifications (tool wear, involved energy...) to the process parameters

Evaluation of process causes and influences of residual stress on gear distortion

In the automotive industry, heat treatment of components is implicitly related to distortion. This phenomenon is particularly obvious in the case of gears because of their typical and precise geometry. Even if distortion can be anticipated to an extent by experience, it remains complex to comprehend. This paper presents an approach to estimate the distortion based on the idea of a distortion potential taking into account not only geometry but also the manufacturing process history. Then the idea is developed through simulation and experiments including annealing to understand the impact of residual stress on gear distortion in an industrial case study

A generic methodology to improve the control of forging process parameters

One of the common problems in forging processes is the lack of key process parameters control, as well as their identification. Certain controlled parameters exist, such as temperature or stroke length, which are usually identified and controlled through a systematic approach. Their selection depends particularly on the part to produce or on customer’s constraints, rather than a rational approach. In this paper, a methodology is proposed to select the key process parameters. There are some methodologies which already exist, such as the DMAIC, which are used to determine the control parameters and their influences on the desired specifications. However, this approach has certain drawbacks. For example, the key parameters are selected by experts, which makes each case study time consuming. The aim is to develop a generic methodology to improve the manufacturing process in the forging industry. The methodology is represented as a decision support system that connects product specifications (geometry, absence of defects…) or other forging specifications (tool wear, involved energy...) to the process parameters. The latter will be able to define the key parameters, their values and their appropriate way of control. These links will be setup using the empirical rules and physical laws

Effect of the plasticity model on the yield surface evolution after abrupt strain-path changes

Abrupt strain path changes without elastic unloading have been used in the literature to investigate the yield surface of sheet metals, both experimentally and theoretically. Such pioneering studies emphasized an apparent non-normality of the plastic strain rate tensor with respect to the trace of the yield surface in stress space, following such a strain-path change. They inspired numerous subsequent developments of plasticity models including non-associated flow rules. In this paper, this type of abrupt strain-path changes is investigated using state-of-the-art plasticity models. The aim is to emphasize the respective contributions of elasticity, isotropic-kinematic hardening, and rate sensitivity, to the apparent violation of the normality condition. The results show that these classical ingredients of plasticity models significantly contribute to the apparent vertex and loss of normality. These effects are quantified for typical sheet metals subject to biaxial-to-shear orthogonal strain path change.Bourse CS

Contribution à la caractérisation des moyens de mise en forme : application aux presses à vis

The metal forming industry uses more and more numerical simulation, and especially the Finite Element software Forge®, with the aim to fulfill 3 main objectives: predict tooling lifetime, predict the amount of energy required to obtain the part desired and predict the thermomechanical path leading to the optimal final microstructure. Currently, numerical simulations allow good predictions regarding forging operations with currently used material, like steel. But to remain competitive forging industries cannot work only with steel, and have to innovate by developing new forging process for high performance material. But concerning the forging operations of these new high performing material, significant difference are observed between numerical and experimental results. In particular regarding the prediction of energy required to correctly forge a part. This study aims at understanding this disparity between numerical and experimental results, in the special case of screw presses. For that, the first step describes the functioning of screw presses but also the screw presses model implemented into the Forge software. Experimental results of upsetting tests in 2 different conditions have then been compared to results obtained numerically by simulating the corresponding forging tests. Significant differences are observed, and the necessity to define a stiffness coefficient for the press is highlighted. Two methods have been carried out to determine the stiffness of the press, a theoretical one and an experimental one. Concerning the experimental one, external tools of acquisition like a rapid camera and a 3D tracking points system have been used to analyze the press behavior during blows. Finally, stiffness values obtained with the two different methods are compared

Contribution à l'identification des origines des déformations révélées au traitement thermique. Application à l'analyse d'une gamme de fabrication d'arbres à dentures de boites de vitesses.

Le traitement thermique est un procédé très largement utilisé dans l'industrie automobile et en particulier sur les pièces à dentures. Appliqué en général après usinage, il permet d'améliorer les propriétés mécaniques des pièces. Dans le même temps, plusieurs phénomènes physiques conduisent à des déformations, qui peuvent conduire au non-respect des tolérances dimensionnelles et géométriques. Ces déformations sont certes liées au traitement thermique mais également à l'ensemble de la gamme de fabrication en amont de celui-ci.L'objet de ce travail de recherche est d'améliorer d'une part la connaissance des phénomènes physiques mis en jeu au traitement thermique et d'autre part l'identification des déformations géométriques. Dans un premier temps, les déformations propres à chaque étape de fabrication sont identifiées. Puis au sein de la gamme, les sources d'origine dans la signature géométrique finale sont séparées. Une gamme de fabrication numérique illustre cette méthode.D'autre part, les contraintes résiduelles sont identifiées comme influentes sur l'évolution de la géométrie. Leur impact sur les déformations au traitement thermique est obtenu grâce à plusieurs campagnes d'essais sur site industriel. De cette façon, chaque caractéristique géométrique est reliée à une ou plusieurs étapes de fabrication en particulier. Ces résultats fournissent une aide au diagnostic des causes de non-conformités au traitement thermique. En parallèle, des modifications sur la gamme de fabrication sont proposées.Heat treatment is widely used in automotive industry, especially in the case of gears. This process is habitually used after machining and increases mechanical properties of work pieces. In the meantime, several phenomena lead to distortions and sometimes to geometrical non-conformities. Distortions are due to heat treatment but also to previous manufacturing processes.The objective of this study is to improve both the understanding of physical phenomena occurring during heat treatment and the identification of distortion. First, distortions of each single manufacturing step are identified. Then, causes of final geometry amongst the overall process are ranked. A numerical manufacturing process is used as an example to illustrate this method.Secondly, residual stress influence on heat treatment distortion is revealed thanks to several industrial experiments. Thus, each single geometrical criterion is linked to a manufacturing step. These results provide a diagnosis tool helping to determine distortion causes. Moreover, evolutions on industrial process are proposed.PARIS-Arts et Métiers (751132303) / SudocSudocFranceF

Contribution to characterization of metal forming machines: application to screw presses

Finite Element analyses are established in the metal forming industry, with the aim to fulfill three objectives: predict tooling lifetime, predict the energy required to obtain the desired part and predict the thermomechanical path leading to the optimal microstructure. Currently, simulations allow good predictions regarding forging operations with currently used material, like steel, but concerning high performing materials, significant difference are observed between numerical and experimental results. This study aims at understanding this disparity between numerical and experimental results, for screw presses. Different methods have been employed to determine the press stiffness, using fast cameras and 3D tracking points systems

Contribution à la caractérisation des moyens de mise en forme : Application aux presses à vis

L'industrie de la forge utilise de plus en plus la simulation numérique, et notamment le logiciel Eléments Finis Forge®, et ce pour répondre à 3 objectifs principaux: prédire la casse des outillages, prédire la quantité d'énergie nécessaire pour arriver à la mise en forme souhaitée d'une pièce et prédire le chemin thermomécanique adéquat pour obtenir une microstructure finale optimale. Actuellement la simulation numérique permet de bonnes prédictions pour ce qui concerne la mise en forme de matériaux couramment utilisés comme les aciers. Mais pour rester compétitives les forges ne peuvent plus se permettre de forger uniquement des aciers et doivent innover notamment en mettant au point des procédés de forgeage pour des matériaux à haute valeur ajoutée. Or pour la mise en forme de ces nouveaux matériaux à hautes performances, des différences significatives sont observées entre les prédictions obtenues par simulation et les résultats de l'expérimentation. Notamment pour ce qui concerne la prédiction de l'énergie nécessaire à la mise en forme d'une pièce. Cette étude cherche donc à comprendre d'où vient cette disparité entre les résultats numériques et expérimentaux, dans le cas particulier des presses à vis. Pour cela, la première étape est d'abord de bien comprendre le fonctionnement des presses à vis, mais aussi de comprendre le modèle de presse à vis implémenté dans le logiciel Forge. Des résultats expérimentaux d'essais de refoulement dans 2 cas distincts sont ensuite comparés aux résultats obtenus par simulation numérique des mêmes essais. Des différences significatives apparaissent, et la nécessité de la définition de raideur de presse est mise en évidence. Deux méthodes ont été mise en ?uvre pour déterminer la raideur de presse, une théorique et une expérimentale. Pour la méthode expérimentale des outils d'acquisition extérieurs comme une caméra rapide et un système de suivi de points dans l'espace ont été utilisé pour capter le comportement de la presse lors des frappes. Les valeurs des raideurs obtenues sont finalement comparées

Gear metrology of statistical tolerancing by numerical simulation

Tolerance verification permits to check the product conformity and to verify assumptions made by the designer. For conformity assessment, the uncertainty associated with the values of the measurands must be known. In the ISO TS 17450 part 2, the notion of the uncertainty is generalized to the specification and the verification. The uncertainty is divided into correlation uncertainty, specification uncertainty and measurement uncertainty. Correlation uncertainty characterizes the fact that the intended functionality and the controlled characteristics may not be perfectly correlated. Therefore, we propose a new specified characteristics based on the statistical tolerancing approach which is directly in relationship with the design intent: the probability distribution of maximum range of the transmission error (the transmission error is the main source of vibratory and acoustic nuisances), and the evaluation of this characteristic based on 3D acquisition by Monte Carlo simulation and Tooth Contact Analysis. Moreover, the measurement uncertainty of the evaluation of this characteristic is estimated by Monte Carlo Simulation