Below are brief descriptions illustrating the differences between permanent mold casting and die casting. Following the descriptions is a simple charts showing comparisons of key casting factors.

Permanent Mold Process
Permanent Mold is a casting process utilizing low pressure, or gravity die casting. The typical process is as follows: The mold, made of steel, is pre-heated. A coating is applied to the mold in those areas which come into direct contact to the molten aluminum. Cores, if required, are inserted into the mold, and the mold is closed. The molten metal is heated to the proper temperature, and then poured into the closed mold. Typical aluminum alloys used are commercial 319 and 356. After a proper dwell time allowing for the metal to solidify, any cores are removed. The mold is opened and the casting is removed. Secondary trimming, finishing operations and machining may now be performed to the part.

Benefits of the permanent mold casting process include moderate equipment costs, good fatigue and wear resistance, and it allows for the best pressure techniques which in turn provides for low gas porosity. Higher production rates can be achieved compared to sand casting, but the process is slower than die casting.

The permanent mold process is excellent for pressure-tight, non-porous castings as compared to die castings. The size of permanent mold castings can be produced to over one hundred pounds.

Die Casting Process
The die casting process may be most economical when piece part requirements are in the mid to high volumes. Die casting is also known as a high-pressure process. Tooling is frequently the most expensive of the various casting processes, but typically achieves the lowest piece price cost.

The basic die casting process is as follows:
A die cast die (cover and ejector half) is set into a die cast machine. Die cast machines can range from less than 100 tons to over 2,000 tons of clamping pressure. The die casting machine closes and clamps the cover and ejector halves. The alloy is poured and then "shot" at a high rate of pressure and speed into the closed die cast die. Typical alloys for die casting include aluminum alloys 360, 380, 383, 384, 390, and 413, and various zinc and magnesium alloys.

After a shorter dwell time than the permanent mold process, the casting is removed and any secondary trimming, finishing, and machining operations may be performed.

The main benefits of die casting are higher production rates achieved due to shorter solidification times and the use of multiple cavities (in turn, lower piece price), minimum wall thickness, best attainable tolerances (nearest net shape), best surface finishes, and the best fatigue and wear properties. Limitations include higher equipment costs, part complexity, and porosity potential.

Learn more about:
Factors Effecting Casting Decisions