Die casting is a metal casing process that entails forcing molten metal into a mold cavity under high pressure. Conversely, low pressure die casting machine is used to perform low pressure die casting (LPDC), a common process used in foundries today wherein the die is slowly filled with molten metal, reducing turbulence.
Low pressure die casting machines are widely used in automotive applications including wheels, suspension, steering and engine parts. Other applications in which a low pressure die casting machine is used include pipe benders and bell housings. Low pressure die casting machines are able to achieve castings with superb metallurgical quality.
In a low pressure die casting process, the dies are usually made of grey cast iron. Alloy cast iron or tool steel are used despite longer production runes. The die casting process also uses a wide variety of aluminum alloys which mostly contains silicon to enhance fluidity. Compared with other die castings, relatively high concentration of impurity can be tolerated and even preferred since “sticking” can be minimized as well as improving the hot strength of castings. Furthermore, because of non-equilibrium cooling, alloys that contain copper may age after casting, causing an alternation in dimensions. If dimensional stability is critical for the casting process, a heat treatment that stabilizes and relieves stresses is required.
As casting techniques have been significantly developed over the years, casting types have also become diversified. Low pressure die casting, as one of the prevalent casting types, is very essential and has a great many advantages.
The primary advantage of low pressure die casting machines is the high utilization rate of raw materials when a low pressure casting method is used by the practice. The process can be undertaken without using any riser or runner. This leads to reduced processing time overall and improved working efficiency greatly. Also, the casting is able to form directional solidification, which minimizes internal defects thanks to the nature of the process.
Conversely, low pressure die casting machines face certain limitations. Although a low pressure die casting process is free of runner and riser problems, it is not ideal for batch processing, which in turns affect the productivity of this casting process as the production cycle will be long. Moreover, low pressure die casting requires high control for all aspects of data, so it becomes limited to be applicable only to certain fields.
Die design is very important in the low pressure die casting process. An inappropriate design can lead to many problems with the die casting. Some of the important things to look out for are outlined below:
High die temperature is necessary to avoid premature chilling which may result in less massive dies. Die walls are normally kept at a consistent thickness with the outside fitting the contours of the inside. Since most dies are cast, problems are less likely to arise. You can consider increasing the thickness of the die if you need to further control solidification for which high temperature is required.
The internal cavities for a low pressure die casting is created using sand cores and undercuts. Retractable metal cores are used to make holes, even though this may increase tool and maintenance cost and reduce accuracy. Moreover, venting of the die cavity needs to be achieved by including flash in the die. Alternatively, you can also enable flash to form at the parting lines, but you need to make certain that the die coatings do not seal the gap.
To remove inclusions during the low pressure casting process, overflows and risers are normally included. They may also be used to hold the casting which allows the automatic removal of the casting. Because of the positive surface finish, surface accuracy and detail are superior to gravity die casting, but not better than high pressure die casting. Lastly, low pressure die casting has very similar design capability than that of gravity die casting. Approximately one-millimeter-thick fins and walls can be produced.
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