Determination of interfacial heat-transfer boundary conditions in an aluminum low-pressure permanent mold test casting

Abstract

Great advances in casting modeling/simulation software have been made in the past several years. However, software predictions are only as accurate as the material and processing properties used as inputs. The process of low-pressure semipermanent mold casting is widely used by the automotive industry in the production of aluminum cylinder head castings. However, the process is highly sensitive to various casting parameters and many of the influences are not well understood. This report presents results from casting experiments and simulations using a specially designed casting, the "wing casting." The casting experiments demonstrated the variation in temperature change in different parts of the casting for different processing parameters. Boundary conditions were determined for different areas on the mold surface and those parameters were discussed in terms of temperature sensitivity in the casting behavior. It was also demonstrated that boundary conditions play a major role in the thermal behavior in the casting during solidification. Finally, changes in the mold/casting surface geometry were found to have a large influence on the value of the boundary conditions.

Effect of pressure on heat transfer coefficient at the metal/mold interface of A356 aluminum alloy

“…Since solidification of a casting involves both a change of phase and temperature variable thermal properties, the inverse heat conduction becomes nonlinear. Most of the methods of calculation of timedependent h i existing in literature are based on numerical techniques, generally known as methods of solving the inverse heat conduction problem [13][14][15][16]. IHCP method is based on a complete mathematical description of physics of the process, supplemented with experimentally obtained temperature measurements in metal and/or mold.…”

Heat Transfer Coefficient at Cast-Mold Interface During Centrifugal Casting: Calculation of Air Gap

“…[15] and [16], are coupled via the heat flux at the cast-mold interface. A thin-wall model, also known as a zero-capacity model, was used to numerically simplify the situation at the interface by considering only a thermal resistance, exerted by the coating and possibly the air gap.…”

“…[10] and [11], and temperature, Eqs. [15] and [16], were all solved using the finite difference method with second-order accurate central difference schemes for derivatives (including points at the boundaries). In the radial direction, the casting and the mold were divided into N S and N M uniformly spaced grid points with the dimensions dr S and dr M of 1 mm (Figure 1).…”

“…The same grids with uniform spacing were used for both quantities u and T. For Eqs. [15] and [16], the implicit backward Euler method was used for time-stepping. In addition, an iterative approach was necessary for heat conduction equations due to temperature-dependent thermophysical properties, the nonlinear heat flux q at the cast-mold interface (Eq.…”

“…(2) For time t n+1 , solve heat conduction equations, Eqs. [15] and [16], coupled by the heat flux at the interface (Eq. [17]), with the air gap thickness d a from the previous time t n and obtain new temperature T and solid fraction g s fields.…”