In short, die casting is the method of injecting liquid metal into a reusable steel mold or die, very quickly, under high pressure.
Its advantages are very attractive for many use cases. While there are start up costs, once the die is in production, it’s possible to produce a large number of parts swiftly, affordably and with high dimensional repeatability.
Your parts come out dimensionally accurate and with durability and a particularly good surface finish. This makes die casting a critical technique for many industries: from construction to marine technology to medical technology — a person uses a product that has one or multiple die castings every day.
WHAT MATERIALS ARE USED IN DIE CASTING?
At Simalex, we die cast with a large range of aluminum, zinc, and magnesium alloys. This gives us the ability to offer mechanical properties more suitable to a customer’s needs:
- Weight of the part
- Thermal and electrical conductivity
- Corrosion resistance
- Impact strength
The flexibility in materials presents a major advantage for many companies looking to get custom parts. Feel free to contact us if you want a more detailed understanding of what sorts of materials are possible.
HOW DOES DIE CASTING WORK?
THERE ARE FOUR STEPS IN DIE CASTING: DIE PREPARATION, FILLING, EJECTION, AND TRIM/DEGATE.
Before injecting the molten metal, the mold cavity must be prepared with a lubricant to ease the removal of the cast part. This is water-based lubricant that also helps to maintain the die temperature.
Application of the mold release when done correctly will not affect the quality of the casting.
This is the part where the molten metal is forced into the cavity. The metal is ladled from the furnace into the shot cylinder and injected by the shot rod. The metal flows through the runner and into the gate, which is the where the material starts filling the cavity.
In the die there are overflows, vents or even vacuum assist so that there is somewhere for the air, gas, and excess material to go.
When injecting molten metal into the cavity there are different speeds that are used.
First, you have your slow shot. The idea here is to move metal through the cold chamber until it is 100% full (at the shot rod’s starting position, the cold chamber is usually 40-50% full).
Once the cold chamber is 100% full, your fast shot comes on. The fast shot’s purpose is to move the material into the cavity of the die before it starts to solidify.
Intensification is the last part of the shot profile. This is where the metal is moved in a semi-solid state to minimize or reduce gas and shrinkage porosity to an acceptable level.
Die Casting machines have a “die open” timer that controls how long the mold will stay closed. The amount of time is dependent on the size/weight of the casting and how long it takes to become completely solid.
The part is ejected by pins in the die that are completely flush with the surfaces in the mold cavity when it is closed — once the die opens, the pins are pushed forward hydraulically to push the part out of the mold.
When the part is removed from the die, it still has the runner and overflows attached to it. These are usually removed by means of a Trim Die, but can be removed manually as well. The runners and overflows are recycled on-site back into the furnace.
HOT VERSUS COLD CHAMBER DIE CASTING
There are two main types of die casting: hot chamber and cold chamber.
Hot chamber die casting melts the metal in a furnace that’s part of the machine itself. The metal is then directly forced into the die through a goose neck and sprue system. When the melting pot is internal, the materials used have lower melting points. Additionally, alloy choice is also limited to materials that won’t erode or dissolve the metal of the machine when in the liquid state. Typical materials used in hot chamber die casting are zinc, lead and magnesium alloys.
Cold chamber die casting is preferred for metals that have high melting points like aluminum, brass, copper and occasionally magnesium. Additional equipment is required for the cold chamber machine such as a ladling system and an external furnace to hold and sometimes melt the alloy. This method of casting allows the use of materials that may be stronger and have versatile industry applications.
DIE CASTING WITH SIMALEX
At Simalex, we do both hot and cold chamber die casting. While we’re capable of tackling high-volume runs with our automated cells, we’re also able to handle lower volume runs with some of our manually operated machines. In fact, we do lower volume runs that most other die casters will not even consider. Our ability to do very quick die changes, alloy selection, and low cost tooling options give us a competitive edge that other casters are just not setup for.