The Importance of Product Design for Die Casting
Die casting is a versatile method of manufacturing non-ferrous metal parts at high volumes. This process creates parts by injecting molten metal into a die at high pressure and velocity.
Die casting allows very complex components to be made economically and effectively. Thanks to it, we can create parts that vary greatly in size and weight. Different alloys can be chosen depending on the application and the working environment of the product. All in all, die-casting is a useful, adaptable process.
Product design for die casting is important – and tricky
This is especially true when designing parts, like housings, that have aesthetics and mechanical requirements. Thin-walled 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, are required for easy ejection of the part after the die-casting process is complete. We 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.
Getting the design right the first time can drastically affect costs
If the design has been refined and optimized for mass production, the results can be very rewarding. Well-designed die-cast parts are easier to cast and can be manufactured at a higher rate.
When designing parts for die-casting, there are a lot of different aspects to keep in mind. To help you out, we’ve got a list of fundamentals for you to consider.
Die casting is a process that creates parts by injecting molten metal into the die using high pressure and high velocity. After the metal solidifies, the two halves of the die will open and the part is ejected.
It is crucial that there are no undercut areas in the opening direction of the dies. That’s why the orientation of the die-cast component has to be determined before the fabrication of the tooling or die.
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. To facilitate the creation of those undercuts, sliding cores are added to the design of the tooling. During the casting process, they will slide into position to create the undercut features, then slide out during ejection.
However, if the part is going to have undercuts, then the sliding cores should not have any undercuts either.
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.
So the draft angle is 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. Adding proper drafts on the die cast can drastically decrease the part’s 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 components will always have a parting line. This is where the two halves of the dies meet on the part and is noted on the part drawing as the ‘Parting Line’ or P/L.
It’s best to have dimensions with critical tolerances related to one side of the die, either the ejector half or the cover half. Controlling critical tolerances across that parting line is much more difficult than controlling them on either side.
We also recommend 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 processes will be required to minimize or remove these unwanted features 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 corners or edges.
By incorporating rounded edges in the part design, we can avoid sudden changes in direction and enhance the flow of molten metal into the die cavity. Furthermore, the rounded edges minimize the thermal stress on the die-casting die during the production and 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 processes as well as keeping the wall thickness more uniform.
Bosses are narrow features that are embedded on the die casting, and they tend to be more difficult to fill. This problem can be minimized by adding adequate fillets and draft angles to ensure that the molten metal can flow into these areas. If your part has bosses, then these additions will also help the ejection of the finished component.
Die-casting parts are often designed as housings or enclosures for electronics and telecommunication applications. These products will often feature keypads and displays, which in turn, require the die-cast parts to have small openings for keys and connectors. They may also need bigger openings for features like LCD or LED displays. Since features like these block the flow of molten metal to fill the cavity, we recommend that bridges and cross feeders are added in the openings of the die-cast component.
To ensure that these areas have adequate temperature, overflows should also be added in these areas. These 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.
It’s 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 after the solidification process and the component will be very difficult to eject.
Oftentimes, lettering, such as logos, trademarks, identification numbers will be added to the part. Some die-cast parts will also have a 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. They tend to last longer too, 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. Doing this will form protruding features on the die, which makes them more vulnerable to die wear and will require more maintenance in the long run.
Ready to design or need more advice?
For more information about design and tolerance in die-casting, you can download the NADCA Engineering and Design handbook here: