A High Pressure Die Casting Process

Update:Dec 02 2016
Summary:

Furthermore, mold designs could - and did - change, eve […]

Furthermore, mold designs could - and did - change, even after production had started, and those changes meant molds might have different designs, different ages and wearing patterns, and different casting qualities. In addition to mold changes, variations in production parameters like die casting machine pressures, pouring velocities and transitions, lubrication volumes and locations, solidification and cycle times changed throughout the casting process. The never-ending need to adjust and improve the casting ended only when the casting was not needed anymore. Working toward a better casting quality kept a huge team active with involvements of the process engineer, the machine operator, mold maintenance and toolmaker, quality office, casting designer, casting machining, even assembly and material planning and handling group.

In times past, paper and pencil were the most important tools a casting designer had - and the development of a casting was a process that was tedious and time consuming. A paper design was created; the blue print was introduced to the die caster - who teamed up with a toolmaker. Together, a die-casting machine was selected; the process and mold layout developed and costs estimated. Quotations were made. The bidding winner gave permission to his tool vendor to order die steel and start with mold designing. When finished, the mold was sent to the die caster for a first test. After building it into the machine, castings were made and checked for imperfections.

It was not until this point in the process that those involved got any idea about the quality of the casting. If the casting didn't measure up to the desired standards, changes would have to be made. Different process settings and minor die corrections could be done at the die-casting machine immediately - but if the first trial showed that the mold had to be changed, steel had to be ground away and welded back in other places, and that work had to be done at the tool vendor's facility. The mold traveled back and forth between toolmaker and die caster until an acceptable casting quality was achieved. The time between starting the casting design and shipping good castings could take weeks, months or years depending on the complexity and size.

While there was a time when this type of 'engineering' was necessary, the economic realities of today make it financially unfeasible to continue in this way - but even so, this "engineering" can be found in companies that are struggling their way through tough times.

Process simulation software tailored to the specifics of the high-pressure die casting process helps to avoid the uncertainties of 'trial and error' and provides a clear picture for the die caster about what to expect throughout the die design and casting process. With this software, it is possible for the engineers to simulate, understand, change and optimize the casting conditions before the process is ever introduced to the shop floor.

The process started in the early days and was done first using the low pressure injection method. But as time passed by with the technology rising, the use of high end, high pressure techniques like two of the most common squeeze casting and semi-solid casting processes have become more effective than the previous method. Before, only tin and lead were involved in this process; but today even copper, alloys and magnesium can already be used and done with the famous high-pressure method.

Actually, dies are composed of two part molds namely the ejector die and the fixer die. These molds are composed of alloy tool steel. Moreover, there are four types of dies; namely single cavity, multiple cavity, unit die and combinations die.

The first type, single cavity, as the name implies is made to produce a component. The second one, the multiple cavity die, is used to create a number of equal or matching parts. The third type which is the unit die is used to produce various types at the same time. And lastly, the combinations die is used to create a number of varying parts for an assembly.

The creation of the die cast products is done under high speed and pressure where the molten metal is injected to the die. With the use of high pressure and speed, smooth and accurate castings can be produced. This pressure exerted on the materials should be maintained until the metal forms and solidifies into the desired shapes. Right after the metal becomes hard, immediately open the die and remove the output product.