Die Casting Metallurgy

Evaluation of the gas porosity and mechanical properties of vacuum assisted pore-free die-cast Al-Si-Cu alloy

The pressure die casting involves die designs incorporating cooling channels positioned to facilitate the controlled extraction of energy from a solidifying casting. It is now known that subcooled nucleate boiling can occur in cooling channels and this paper is concerned with novel cooling channel shapes that are optimized to promote and enhance this boiling and thus reduce casting times. Shape sensitivity analysis is applied to a boundary element model using the material derivative adjoint variable technique. Mesh node positions on the cooling channels are used as the design parameters. The sensitivities are used in a conjugate gradient non-linear optimization routine. It is shown that with this approach cooling channels can be designed to maximize boiling heat transfer whilst at the same time allow some degree of control of spatial temperature variation over the die cavity surface. Simulation and experimental results are presented for a traditional die and an optimized die. A 60 per cent reduction in cycle time is achieved with the optimized die. Copyright © 2001 John Wiley & Sons, Ltd.

Novel cooling channel shapes in pressure die casting

The rate of heat extraction during the pressure die casting process is central to both the quality and the cost of finished castings. Recent efforts to reduce the thermal resistance of dies by optimizing the effectiveness of the cooling channels have shown the potential for improvement. Reducing the thermal resistance of the coolant boundary layer means that a significant proportion of the total thermal resistance becomes attributable to the die steel. Further significant reductions in die thermal resistance can be obtained by replacing the steel with copper. This paper investigates the feasibility of using copper dies, reinforced with steel inserts and coated with a thin layer of wear resistant material, which is deposited using the thermal arc spray process. Experimental work relating to the thermal spray process has been undertaken to establish bond strengths and thermal conductivities for various process parameters. Moreover, experimental investigations have been carried out using two copper coated dies, the first of which was a pseudodie block beaten by an infrared heater The second die was tested on a die casting machine and produced zinc alloy castings at a greatly increased production rate when compared to its steel counterpart. The experimental results from the two dies are compared with those predicted by an in-house thermal-cum-stress model based on the boundary element method. Reasonable agreement between the predicted and experimental results is shown and the feasibility of copper-alloyed dies for pressure die casting is established.

Experimental Investigation Into the Thermal Behavior of Copper-Alloyed Dies in Pressure Die Casting

Sputtered coatings of Mo, W, Pt, Ag, Au, Co, Cr, Ni, Ag + Cu, Mo + Pt, Si3N4, A1N, Cr3C2, Ta5Si3, and ZrO2 were applied to a 2-inch-square, 7-inch-long thermal fatigue test specimen which was then internally water cooled and alternately immersed in molten aluminum and cooled in air. After 15,000 cycles the thermal fatigue cracks at the specimen corners were measured. Results indicate that a significant improvement in thermal fatigue resistance was obtained with platinum, molybdenum, and tungsten coatings. Metallographic examination indicates that the improvement in thermal fatigue resistance resulted from protection of the surface of the die steel from oxidation. The high yield strength and ductility of molybdenum and tungsten contributed to the better thermal fatigue resistance.

https://ntrs.nasa.gov/api/citations/19810023701/downloads/19810023701.pdf

Thermal fatigue behavior of H-13 die steel for aluminum die casting with various ion sputtered coatings

The range of diecasting machines has increased, in size and locking force, making possible the production of engine cylinder blocks, transmission housings, and other large and complex components, especially in aluminium alloys. Instrumentation has been developed to measure and control the speed and pressure of metal injection, temperature control of the dies, measurement of machine locking force, and oscillographic monitoring of the diecasting process, sometimes with a computer built into the equipment. Large diecasting plants can now receive molten aluminium alloy consignments direct from the secondary metal smelter. In molten-metal handling in the diecasting plant, further developments are being made in furnace design, both for bulk metal melting of scrap, runners, and ingots and in the bale-out furnaces adjacent to the diecasting machines. Several producers of zinc alloy diecastings are now making their own alloy, under carefully controlled conditions. During the past ten years most diecasting ...

A. C. Street

Papers

Developments in Pressure Diecasting