High-pressure die casting is an important process in the manufacturing of high-volume and low-cost automotive components such as automatic transmission housings and gear box components. Liquid metal (generally aluminum or magnesium) is injected into the die at high speeds (30 m/s to 100 m/s) and under high pressure through complex gate and runner systems. The geometric complexity of the dies leads to strongly three-dimensional (3-D) fluid flow with significant free-surface fragmentation and splashing. The order in which the various parts of the die fill and the positioning of the air vents are crucial to forming homogeneous cast components with minimal entrapped voids. This is influenced by the design of the gating system and the geometry of the die. Numerical simulation offers a powerful and cost-effective way to study the effectiveness of different die designs and filling processes, ultimately leading to improvements in both product quality and process productivity, including more effective control of the die filling and die thermal performance.
Smoothed-particle hydrodynamics (SPH) is a Lagrangian method for modeling heat and mass flows. Due to its mesh-free nature and the handling of boundaries using SPH nodes, this method can handle complex splashing and fragmenting free surface flows and the motion of multiple solid equipment parts relatively easily. In traditional mesh-based methods used in commercial fluid-flow packages, large mesh deformations are generated by the motion of the equipment, leading to significant numerical problems. In addition, the tracking of the free surface is diffusive and inaccurate for the resolutions used.
For SPH, materials are discretized into particles that can move subject to equations of motion arising from the governing partial differential equations. The particles are moving interpolation points that carry with them (convect) physical properties and state information, such as the mass of the fluid that the particle represents, its temperature, momentum, enthalpy, density, and other properties. The inter-particle forces are calculated by smoothing the information from nearby particles in a way that ensures that the resultant particle motion is consistent with the motion of a corresponding real fluid, as determined by the governing equation (e.g., the Navier-Stokes equations).
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