When developing products that require aluminum castings, multiple casting methods need to be considered. Sand, gravity, low pressure and permanent mold processes can all produce aluminum castings.
Sand, gravity, low pressure and permanent mold processes produce castings by filling a mold with molten metal using gravity or low pressure. Equipment required for these processes is relatively simple, and they can produce high-integrity castings despite long cycle times. High pressure die casting machines inject metal at a speed of over one hundred inches per second and then compress the solidified casting with high pressure. High pressure die casting requires complex and expensive equipment, but can produce high quality castings very quickly. So, why choose high pressure die casting over other processes?
Wall thickness: High pressure die casting allows for the thinnest walls of any casting process. The high injection speed allows metal to fill thin and complex cavities before the metal starts to solidify. Aluminum wall thicknesses can be less than 2 millimeters and zinc wall thicknesses can reach 1 millimeter. The ability to cast thin walls is a significant advantage for design engineers. Complex geometries can also be produced to accommodate many applications and result in very light parts.
Tolerance: Die casting can achieve the most precise tolerances of any other casting process. Die casting molds are made of H13 tool steel, which can be precision machined and polished to microns. The durability of the steel and the rapid solidification time of the process allow for consistent tight tolerances throughout the life of the mold.
Porosity: Air and gas trapped inside castings are referred to as porosity. High pressure die casting may produce more turbulence during filling compared to other processes, but this does not necessarily mean more porosity. High pressure die casting uses rapid solidification and high pressure to compensate for turbulent filling, maximizing the reduction of porosity in parts. It creates near-vacuum conditions in the mold cavity during filling to optimize casting integrity.
Microstructure: The characteristics of castings are the result of their crystalline structure, which occurs during solidification. Faster solidification creates a tight matrix of small grains. The smaller the grain, the better the performance because it is the grain boundaries, not the grains themselves, that are prone to failure under stress. High pressure die casting produces the best overall performance due to its superior solidification rate.
Strength-to-weight ratio: When thin walls are combined with a fine microstructure, the result is a strong, lightweight, unbeatable casting.