Die casting is the name given to the process of creating complex metal components through use of molds of the component, also known as dies. The process uses non-ferrous metals which do not contain iron, such as aluminum, zinc and magnesium, due to the desirable properties of the metals such as low weight, higher conductivity, non-magnetic conductivity and resistance to corrosion.
For good reason, die casting is used in a variety of industries, including aerospace, automobile, power sports, healthcare and more. Die casting production is fast, making high production levels of components easy. It produces more components than any other process, with a high degree of accuracy and repeatability.
To learn more about die casting and die casting materials used in the process, read on.
The Die Casting Process
There are three sub-processes that fall under the category of die casting: gravity die casting (or permanent mold casting), low-pressure die casting and high-pressure die casting. The primary difference between the three is in the amount of pressure that is used to force the molten metal into the die.
Regardless of the sub-process, the die casting process can be broken down into six steps.
1. Clamping
After the purity of the alloy is tested, dies are created. To prepare the dies for casting, it is important that the dies are clean, so that no residue from previous productions remain. After cleaning, the ejection lubrication is applied to the die to ensure a smooth release. The die, which is often in halves, is then clamped together for the injection step.
2. Injection
The pure metal, also known as ingot, is added to the furnace and kept at the molten temperature of the metal, which is then transferred to the injection chamber and injected into the die. The pressure is then maintained as the metal solidifies.
3. Cooling
Once the metal solidifies, the cooling process begins. The cooling time depends on a few factors: the geometry of the part (either complex or simple), the type of metal and the wall thickness. The thicker the wall of the part, the longer the cooling time because of the amount of interior metal that also needs to cool.
4. Ejection
After the component is fully cooled, the die halves open and an ejection mechanism pushes the component out. Following the ejection, the die is closed for the next injection cycle.
5. Trimming, Deburring and Burnishing
Before the part is a complete component, it is considered a complete cast unit, which includes the part and the flash. The flash is the extra material that is cast during the process. This must be trimmed off using a trim tool to leave just the main component.
Deburring removes the smaller pieces, called burrs, after the trimming process. Finally, the component is polished, or burnished, to give it a smooth finish.
6. Quality Testing
In the past, manufacturers tested the interiors of components by cutting into them. However, this proved to be an inaccurate test, because the tester could cut into a piece and miss an area with porosity.
Today, top manufacturers use x-ray testing to see the entire interior of components without cutting into them. This allows them to more accurately accept or reject components.
Metals Used in Die Casting
To get to the finished product, there are three primary alloys used as die casting material to choose from: zinc, aluminum and magnesium. Although each is an excellent metal to use, there situations in which one metal is better than the others:
- Zinc alloys: Best used for high-yield designs that have strong resistance to stress
- Aluminum alloys: Best used in projects that require higher temperatures and are one of the longest-lasting materials on the market
- Magnesium alloys: Lighter in weight with a good strength-to-weight ratio
Here are additional features of each alloy.
Zinc
Zinc is one of the most used alloys for die casting due to its lower cost of raw materials. It’s also one of the stronger and stable metals. Plus, it has excellent electrical and thermal conductivity. Its corrosion resistance also allows the components to be long lasting, and it is one of the more castable alloys due to its lower melting point. Although this alloy has many uses, zinc is often used for interior automotive parts and under-the-hood parts.
As mentioned, this alloy is one of the most commonly used, yet manufactures will, at times, choose aluminum over zinc due to aluminum’s manufacturing advantages.
Aluminum
Aluminum is highly economical and one of the more versatile alloys. Aluminum is used for a number of different products and industries — anything from window frames to aerospace materials. One of the main reasons aluminum is often used is because it can withstand some of the highest operating temperatures.
Although aluminum is more expensive than zinc, the benefits far outweigh the costs. Because aluminum is so lightweight, companies in the automotive and powersports industries manufacture their components with the alloy because it is better for vehicle handling. Plus, it has one of the highest strength-to-weight ratios, making it one of the longest-lasting alloys.
Magnesium
Like aluminum and zinc, magnesium is a strong, rigid material and is typically used for electronic products. Although it is a lightweight material, magnesium has a good strength-to-weight ratio and is corrosion resistant.
Compared to aluminum, magnesium is softer, less stable and tends to bend easier under stress. Plus, it is more expensive than aluminum. Magnesium also has a higher melting point than zinc, which can contribute to higher casting costs.
Choosing the Right Partner With the Right Alloy
As you have read, there are many steps and details to die casting and the die casting materials used in the process. To learn more about which alloy works best for your component manufacturing project, contact a representative at VPIC Group today.
