The Die Casting process is a very versatile method of manufacturing high volume non-ferrous metal parts. This manufacturing process creates parts by injecting molten metal into a die at high pressure and high velocity. This process allows very complex parts to be made economically and effectively. This process can create parts that vary greatly in size and weight. Different alloys can also be chosen depending on the application and the working environment of the product.
Designing products for die casting can be tricking. This is especially true when design housings as it has aesthetics and mechanical requirements. Thin-wall enclosures can be particularly difficult and will often require ribs and bosses on the interior for added strength. Other external and internal features such as draft angle is required for the easy of ejecting the part after the die casting process. We will also often see enclosures with connectors and buttons on the sides which involves using sliding cores on the die to cast those features onto the parts.
The design of a die cast part can drastically affect its manufacturing costs. However, if the design has been refined and optimized for mass product, the results can be very rewarding. Well designed die cast parts are easier to cast and can be manufactured at a higher rate.
As there are a lot of different aspects to consider, below is a list of some fundamental points to consider:
The die casting process create parts by injected molten metal into die using high pressure and high velocity. After the solidification process, the two halves of the die will open and the part is ejected from the moving side of the platen. It is crucial that there are no undercut area in the opening direction of the dies. This is the reason why the orientation of the die cast component has to be determined before the fabrication of the tooling or die to ensure that there are no undercuts in these areas. However, as die cast components become more and more complex, a lot of features are added on the edges of the component to incorporate additional features. It is very common that these features have undercut, therefore sliding cores are added to the design of the tooling. The sliding cores will slide into position during the casting process to create those undercut features on the die cast part and will slide out for the ejection process. It is important to pay attention that no undercuts should be present on the direction of the sliding cores as well.
Draft is the slope or the taper incorporated on the side walls of the die cast part. These surfaces can be identified by analyzing the opening direction of the die and the opening direction of any sliding cores on the die. In other words, the outer and inner walls of the part as well as the openings created using sliding cores. This enables the castings to be easily ejected from the die casting die. By adding proper drafts on the die cast parts can drastically decrease its tendency to adhere to the die, thus improving cycle time and the quality of the surfaces.
Uniform wall thickness:
Consistency of the wall thickness is the key for creating high quality die cast parts. Any unnecessary changes in thickness or abrupt changes in the geometry of the component will cause disruption to the flow of metal entering the cavity. These might cause air enclosures in the castings and poor surface finishing.
Die cast component will always have a parting line. This is where the two halves of the dies meet on the part. This is generally noted on the part drawing as Parting Line or P/L. It is best practice to have dimensions with critical tolerances relate to one side of the die, either the ejector half or the cover half of the die as it is more difficult to control critical tolerances across the parting line. It is also recommended that this area should not have critical cosmetic requirements since the gates and vents will be present along this line and will be visible. Additional process will be required to minimize or remove from the die cast part.
Die Cast parts are rarely flat, therefore it is important to add curved surfaces where two surfaces or intersections meet to avoid creating sharp corner or edges. By incorporating rounded edges in the part design can avoid sudden changes in direction and enhance the flow of molten metal into the die cavity. Furthermore, the rounded edges minimizes the thermal stress on the die casting die during the production and can ensure the longevity of the die.
Bosses are often added on die cast parts as mounting points with other components. Center holes are typically added to the bosses as they help minimize additional machining process as well as keeping the wall thickness more uniform. Bosses are narrow features that are embedded on the die casting die, therefore they tend to be more difficult to fill as molten metal cannot flow into these areas with ease. This problem can be minimized by adding adequate fillet and draft angle to ensure that the molten metal can flow into these areas and will also help the ejection of the die cast component.
Die casting parts are often design as housings or enclosures for electronics and telecommunication applications. These product will often feature keypads and displays which will require the die cast parts to have small openings for keys and connectors as well as bigger openings for features like LCD or LED displays. As these features will block the flow of molten metal to fill the cavity it is recommended that bridges and cross feeders are added in the openings of the die cast component. To ensure that these areas have adequate temperature it is also best practice to add overflows in these areas. These added features will drastically increase the manufacturability of the die cast component and improve the quality of the part. These features can be easily removed with a trimming process or machining process depending on the quality requirement. Secondly, it is also critical to add adequate draft angle to these openings. Without these features the openings on the die cast component will grip tightly on the die still after the solidification process and will be very difficult to eject.
Often times, lettering such as logos, trademarks, identification numbers will be added to the part. Some die cast parts will also have date mark to identify the manufacturing date of the part to distinguish one lot of production from the other. There are two options to create these features. The first method is forming raised letters, this is the primary choice as it is the most cost effective way to produce lettering on a die casting part. Secondly as these features embedded in the die cavity, they tend to last longer as they are protected from the wear and tear that occurs when the metal flows into the cavity at high velocity. The second option is depressed lettering, these will form protruding feature on the die making them more vulnerable to die wear and will require more maintenance.
For more information about design and tolerance, please download the NADCA Engineering and Design handbook: