Low Pressure Die Casting (LPDC) process is one the most common casting process to produce structural automotive components, such as alloy wheels and suspension components. It has been identified that cavity filling and solidification process are two most critical aspects to produce premium quality casting components.During the solidification process of casting alloy, it is a well known phenomenon that metal experiences volumetric shrinkage due to its density difference between liquid and solid phase. When this volumetric shrinkage is not properly compensated, then a casting defect commonly known as solidification shrinkage occurs. The solidification shrinkage has very detrimental effects on structural integrity required for premium quality casting such as aluminium alloy wheels.Literature and practical experiences of foundry men show that it is critical to achieve unidirectional solidification pattern by avoiding an isolated hot spot in order to minimise the solidification shrinkage. However, it is found that the geometry of industrial casting applications is often constrained by other design factors that would not naturally avoid these isolated hot spots. The subject of this research, aluminium alloy wheels, is not excluded from this constraint.In aluminium alloy wheels, an isolated hot spot is commonly observed in an area known as rim and spoke junction due to its geometry constraints. Consequently, the solidification shrinkage is commonly experienced, which is undesirable due to its detrimental effects for the structural integrity of alloy wheels. In order to minimise the solidification shrinkage, forced cooling method is applied to avoid an isolated hot spot. The control of this forced cooling is achieved by cooling media, flow rate of cooling media and duration cooling circuit. Foundry experiments in industrial environment were conducted producing aluminium alloy wheels using commercially treated A356 (Al-Si) alloy, where different durations of cooling circuit were used to understand the sensitivity of solidification shrinkage formation to the duration of cooling circuit. This was followed by metallurgical structure analysis and numerical modelling to suggest the sensitivity of cooling circuit duration in controlling solidification shrinkage.The major finding conclusion of this research is that control of the shrinkage formation is not very sensitive to the duration cooling circuit. It is suggested that as casting solidifies initially from the mould wall, it retracts away from the cast-mould interface due to thermal contraction. Consequently, air gap is formed between casting and mould interface, creating an effective thermal resistance layer. Thereafter, heat transfer across the cast-mould interface is not sensitive to the change in the cooling channel which is a distance to the cast-mould interface.Some limitations of numerical modelling and metallurgical analysis were also identified during this research and recommendations were made to improve the accuracy of local hot spot prediction in production of aluminium alloy wheels. More specifically, numerical modelling of the effect of grain refinement and use of non homogeneous material property (particularly fraction of solid) for rapidly chilled area. Fraction of eutectic rather than secondary dendrites arm spacing is a proper microstructure parameter that can be used to locate the hot spot.

Low Pressure Die Casting (LPDC) process is one the most common casting process to produce structural automotive components, such as alloy wheels and suspension components. It has been identified that cavity filling and solidification process are two most critical aspects to produce premium quality casting components.During the solidification process of casting alloy, it is a well known phenomenon that metal experiences volumetric shrinkage due to its density difference between liquid and solid phase. When this volumetric shrinkage is not properly compensated, then a casting defect commonly known as solidification shrinkage occurs. The solidification shrinkage has very detrimental effects on structural integrity required for premium quality casting such as aluminium alloy wheels.Literature and practical experiences of foundry men show that it is critical to achieve unidirectional solidification pattern by avoiding an isolated hot spot in order to minimise the solidification shrinkage. However, it is found that the geometry of industrial casting applications is often constrained by other design factors that would not naturally avoid these isolated hot spots. The subject of this research, aluminium alloy wheels, is not excluded from this constraint.In aluminium alloy wheels, an isolated hot spot is commonly observed in an area known as rim and spoke junction due to its geometry constraints. Consequently, the solidification shrinkage is commonly experienced, which is undesirable due to its detrimental effects for the structural integrity of alloy wheels. In order to minimise the solidification shrinkage, forced cooling method is applied to avoid an isolated hot spot. The control of this forced cooling is achieved by cooling media, flow rate of cooling media and duration cooling circuit. Foundry experiments in industrial environment were conducted producing aluminium alloy wheels using commercially treated A356 (Al-Si) alloy, where different durations of cooling circuit were used to understand the sensitivity of solidification shrinkage formation to the duration of cooling circuit. This was followed by metallurgical structure analysis and numerical modelling to suggest the sensitivity of cooling circuit duration in controlling solidification shrinkage.The major finding conclusion of this research is that control of the shrinkage formation is not very sensitive to the duration cooling circuit. It is suggested that as casting solidifies initially from the mould wall, it retracts away from the cast-mould interface due to thermal contraction. Consequently, air gap is formed between casting and mould interface, creating an effective thermal resistance layer. Thereafter, heat transfer across the cast-mould interface is not sensitive to the change in the cooling channel which is a distance to the cast-mould interface.Some limitations of numerical modelling and metallurgical analysis were also identified during this research and recommendations were made to improve the accuracy of local hot spot prediction in production of aluminium alloy wheels. More specifically, numerical modelling of the effect of grain refinement and use of non homogeneous material property (particularly fraction of solid) for rapidly chilled area. Fraction of eutectic rather than secondary dendrites arm spacing is a proper microstructure parameter that can be used to locate the hot spot.

Engendrer en temps-réel des déformations visuellement réalistes d'objets 3D, comme par exemple le corps et les vêtements de personnages, est un point crucial en animation, que ce pour des applications au jeu vidéo ou à la production cinématographique. Les méthodes de déformations géométriques actuelles rapides telles que le "skinning" ou l'animation physique à basse résolution ne capturent cependant pas certains comportements naturels essentiels. En particulier les déformations à volume constant du corps, le gonflement des muscles pour un personnage, ou la génération de plis sur ses vêtements dus au fait que leurs surfaces doivent rester développable. Cette thèse présente une série de méthodes rendant les modèles géométriques "actifs", c'est à dire capables de maintenir un certain nombre de contraintes intrinsèques de la surface portant sur le volume englobé ou sur le caractère développable de celle-ci. Nous étudions trois exemples: - l'ajout de contraintes locales de volumes lors de l'animation d'une créature virtuelle par skinning. - l'ajout de plis de vêtements modélisant une surface quasi-inextensible à partir d'une animation à basse résolution donnée en entrée. - la génération d'une surface de type papier froissé, basée sur la préservation de l'isométrie vis-à-vis d'un patron planaire. Dans tous ces modèles, notre approche est procédurale. Elle se base sur la déformation progressive et, potentiellement, le raffinement dynamique de la géométrie juste avant l'étape de rendu. / Generating visually realistic deformation of 3D objects in real-time for character body or garment is essential for the animation field, both for video games applications and movie production. Current fast deformation methods such as "skinning", or low resolution physically based simulations fail to capture some important natural behaviors. For instance constant volume deformation of a body, muscle bulging of a character, or wrinkling its garment which must be modeled by a developable surface. This thesis presents several methods making a geometrical models "active", that is to say able to maintain a certain number of intrinsic constraints of the surface linked to its bounded volume, or its developability. We develop three case studies - The addition of local volume constraints during skinning animation of a virtual creature. - The addition of wrinkles on garments to model stretch minimizing surface starting from a general low resolution animation provided as input. - The generation of folded paper looking surface based on length preservation with respect to its planar pattern. For every cases, we rely on a procedural approach based on progressive deformation, and eventually, on-the-fly refinement of the geometry just before the rendering stage.