The rationality of the structure and process adaptability of die-casting parts are critical factors determining the smooth progress of subsequent work. For example, the design of fillets and radii, mastery of shrinkage laws, the arrangement of ejection mechanisms, the types and severity of defects, and more, all depend on the quality of the die-casting process itself.
Fillets & Radii
Contrary to popular belief, fillets and radii are not the same thing. Although both refer to rounded edges in the design of aluminum die-casting parts, the internal rounded edges are called fillets, while the external rounded edges are called radii.
Radii and fillets are extremely important features for any aluminum die-casting part design. They can significantly reduce turbulence generated during the metal injection process, ensuring smoother metal flow. Therefore, parts can achieve better structural integrity.
Here are some design suggestions for radii/fillets:
- Sharp corners where two intersecting surfaces meet should be connected using radii/fillets. This can prevent high stress concentration at that part of the mold or component.
- Edges or corners along the mold parting line do not require radii/fillets.
- Provide sufficient draft angle for fillets perpendicular to the parting line.
You can follow these guidelines to design radii/fillets in your components.
Shrinkage
Shrinkage is a very common and inevitable phenomenon in aluminum die-casting. Any metal alloy will shrink to some extent when the molten metal begins to cool and solidify. Therefore, designers must make necessary adjustments to the product design to allow for shrinkage.
Thicker sections are prone to shrinkage, leading to the formation of internal pores. Local overheating can also cause shrinkage, resulting in pores. These areas need to be locally cooled by improving mold design. However, this may increase the casting cycle time.
Designers should consider the following factors when designing to reduce shrinkage in aluminum die-castings:
- Avoid using large/thick sections in the design. If possible, redesign using thinner sections and metal-saving cores.
- Add flat or vertical ribs can improve the feeding characteristics and reduce the tendency for shrinkage.
- Add squeeze pins can reduce the shrinkage porosity in the localized area.
Boss
Bosses are necessary for parts that need to be mounted in other positions. They serve as stand-offs and mounting points. However, improper design and positioning of bosses can lead to manufacturing difficulties, thus increasing costs.
Bosses can also increase material requirements and the weight of aluminum casting. In order to obtain lighter parts, bosses can be redesigned in the following ways.
In a part design, some factors you should consider for bosses design:
- If a hole needs to be added in the center of the boss, try to maintain uniform wall thickness.
- Provide a larger fillet for the boss so that molten metal can flow smoothly into it.
- Ribs are recommended because they can help the boss fill fully and also provide extra strength for the boss.
- Provide sufficient draft angle for the boss to make it easier for the casting to be demolded.
Side Cores/ Slides
Any holes and undercuts parallel to the parting line in the design will greatly increase the complexity of aluminum die casting, and even make it impossible to cast through conventional means. The introduction of side cores/slides can easily manufacture parts with holes and undercuts.
Cores are used to form holes in a part, while slides are used in the design with undercuts. However, they significantly increase the cost to die construction. Since cores and slides are pulled out separately from half of the main mold, they have a great impact on the casting cycle of parts.
The use of slides within a die may also lead to the offset of parting lines. This is due to the force applied by the mechanical lock to keep the slide in position during the casting process. This situation is more common in unit dies.
Designers should try to make such geometric features parallel to the pulling direction of the mold, or redesign the part to eliminate the need for cores/slides. Here is an example that demonstrates how to redesign a part to eliminate the need for side cores.
However, in some cases, you must introduce cores/slides to cast a feature that does not require machining later. You can design core slides or pulls to reduce the need for most or all secondary machining operation.
In this way, the difficulties brought by the increased tooling cost and slower casting cycle at the beginning are compensated by reducing secondary maching operations. This method also greatly extends the reuse rate of parts.
The working mechanism of side cores/slides is that the pulling of side cores and the movement of slides are usually driven by angle pins or hydraulic cylinders. The angle pin is a mechanical mean for the movement of cores/slides. The opening and closing sequence of the main die can activate it.
Therefore, angle pins do not require an additional power source to function and are an economical means of production. However, angle pins can interfere with the removal of castings and are only suitable for a shorter slide.
Top slides are also difficult to use with angle pins and can only be achieved through springs. The use of hydraulic methods can solve these problems. You can choose and define the cycle yourself and use the top slide with it. This will not interfere with the recovery of castings.
There are other methods available for core/slide movement. Designers must choose the appropriate method by analyzing the budget, production volume, part size, length of core/slide travel into the casting, etc.
You can discuss with your die casting manufacturer to obtain appropriate suggestions on designing the side core pull/slide mechanism. Welcome to consult DAYE Diecasting, and we will be happy to help you.
Undercut
Undercut usually refers to a recessed geometric feature or surface of a part that cannot be processed with a straight cutting tool. In the case of die casting, undercut refers to the feature that restrict the ejection of the casting with a single pull mechanism.
Therefore, when designing a part, you must consider the potential difficulties that may arise during tooling and casting in advance. Sometimes, you can eliminate the influence of the undercut by cleverly selecting the orientation of the aluminum die casting. Without the use of side cores, it is impossible to eliminate the influence of the undercut in most cases.
However, adding side cores to the design will complicate the mold manufacturing and casting process, resulting in higher costs and longer installation time than traditional aluminum die casting.
So, when designing the undercut, you should keep the following important points in mind:
- Discuss with your manufacturer to see if he can use special cutting tools such as T-shaped or V-shaped tools that can reach inaccessible places.
- Keep the number of external undercuts to a minimum because they require side cores, which will increase tooling costs.
- Adjust the parting line can solve some undercuts.
- Redesign your parts to eliminate internal undercuts.
- Avoid undercuts that are not facing the die pull direction. They cannot be ejected without placing side cores.
- Undercuts beneath bosses can hinder the ejection of the aluminum casting.
If possible, it is best to avoid any type of undercuts in the design.