All die casting designs are unique and require custom tooling to produce the part. The complexity and size of the tooling are often surprising to those not familiar with the process. In this article, we will review the pieces of tooling required to produce a high-pressure die casting.
What tooling do I need?
Every casting requires a cast die and a trim die. Custom CNC fixtures will also be required if machining operations will be performed.
Cast Die
High Pressure Die Cast dies are heavy-duty steel molds designed to cast aluminum or zinc with high pressure. Want to know the difference between aluminum and Zinc? Read this article.
Figure 1: Complete Die Cast Die
A die cast die has two halves, the cover and ejector die. The cover die can be identified by the shot hole where the cold chamber (shot sleeve) is inserted.
Figure 2: Cover Die
The ejector die contains the runner and ejection system. The face of the casting with features such as cores, slides and metal savers is typically placed in the ejector half. This causes the casting to shrink onto the ejector with more force than the cover and allows the casting to be stripped from the cover half as the machine opens. The ejector pins move forward which strip the casting from the ejector die.
Figure 3: Ejector Die
Figure 4: Ejector Plate and Pins Removed from Ejector Die
Figure 5: Ejector Die Cavity with Ejector Pins Forward
The die cavity is the working portion of the die that forms the casting. The die cavity is made from high-quality, heat-treated H-13 tool steel which can withstand the high speeds, temperature, and pressure of the casting process.
The cavity also includes the runner, overflows, and venting system to transport the molten metal from the shot sleeve to the die cavity. Proper gating and venting design are crucial to producing a quality casting. At General Die Casters, we use Magmasoft flow simulation software to design and test the system before the die is constructed.
Figure 6: Magmasoft flow simulation with metal in the cold chamber
The die cavity is held in place by the holder block. The holder block is machined from 4140 steel because it will not be exposed to molten metal. The holder block also houses the alignment pins and bushings to ensure the cover and ejector cavities are perfectly matched. Moving slide components such as hydraulic cylinders, and mechanical cams are also housed in the holder block.
Figure 7: Holder Block with Cavity Removed
Moving slides are used when a casting design has internal features that are perpendicular to the parting line. Slides move into place during the injection of the metal and then retract before the part is ejected from the die. Slides can move mechanically with cams or with hydraulic cylinders.
Figure 8: Die with 3 mechanical slides
Cast dies can be designed to produce a single part or multiple cavities at once. We cover this topic in detail in our article, How many cavities should I build in my cast tool?
Figure 9: Twelve Cavity Die Layout
Small, simple castings can often be produced using unit dies. Unit dies are small, inexpensive dies that are placed into a standard unit holder. Unit dies contain the cavity, venting, and a portion of the runner system. The customer purchases and owns the unit die, while the die caster typically owns the unit holder. A few standard size unit dies are 10”x 12”, 12”x 14” and 15”x 18”. Unit dies can be manufactured for a fraction of a cost as an independent die because you are essentially purchasing the cavity portion of the die. At General Die Casters, we own several sizes of unitholders for various size castings.
Figure 10: Unit holder without unit dies in a machine
At General Die Casters we work closely with a small group of expert toolmakers to completely design the die using 3D modeling software, verifying that every feature will function as expected and meet our performance requirements.
Figure 11: Complex 2 cavity die with 8 slides
Trim Dies
When a casting is removed from the cast die, it is attached to the runner, overflows, and venting system. There will also be some flash around the parting line and covering cored holes. Flash occurs when molten metal squeezes outside the cavity. This excess material must be removed before the casting can be processed further. This is accomplished with custom trim dies.
Figure 12: Die-cast parts and gates which require trimming
A trim die is used to shear the runner and overflows from the casting as well as punch open cored holes. Trim dies are placed into vertical hydraulic presses, typically 30-100 tons. Like cast dies, trim dies may be very simple and inexpensive, but can also become complicated with moving punches.
The bottom portion of the trim die contains the nests. The nests securely hold and support the casting during trimming to ensure it is not distorted. The top portion of the trim die contains the shears. The shears remove gates and overflows while punches will open cored holes. Springs and nitrogen shocks are used to strip the casting from the shears once trimming is complete.
Figure 13: Trim Die Bottom Half Figure 14: Trim Die Top Half
CNC Machining Fixtures
Specially designed fixtures are required to hold the casting when CNC milling and tapping are required. Fixtures are designed to securely hold the casting while allowing access to all features that require machining. Castings are secured using mechanical clamps or with hydraulic cylinders.
Castings that require turning on a CNC lathe will also require special jaws, but they are typically less complex and costly than those for CNC mills.
At General Die Casters, we have a large variety of CNC equipment for all types of machining and any size production run. We will work with one of our fixture suppliers to design an economical solution for your machining needs.
Figure 15: Horizontal CNC Machining Fixture
The complexity and cost of die cast tooling may seem daunting. At General Die Casters we will evaluate your needs and present a comprehensive tooling quote for your project. We will then work with one of our experienced tool and die suppliers to design and build our customer's custom tooling.
We encourage you to contact us today to discuss your project and learn how we can optimize the cost and quality of your die casting project.
