Die casting is often categorized using the heat and pressure required to inject the molten metal into the die casting mold. However, the part manufacturing process is also categorizable based on the type of material, and zinc die casting is the most common in terms of part strength. This article talks about die-casting using zinc, its application, and its comparison with other materials.
Zinc die casting is a process that involves melting zinc alloys (hence the name zinc alloy die casting) and injecting it into an already prepared die casting mold.
Zinc alloys are applicable in part manufacturing due to their ductility, impact strength, and low melting point. Furthermore, the casting process occurs under lower heat due to the material’s low melting point. Hence the name “hot chamber die casting process.”
Moreover, being a hot chamber process also promote the die’s longevity, time needed before retooling, and reduction in cost compared to other materials compatible with die casting.
There are several zinc alloys for die casting. Each one has unique properties. For example, the Zamak 3 is the common zinc alloy for die casting because of its superb dimensional stability and a balance between the physical and mechanical properties. A summary of zinc alloy suitable for die casting includes:
Zamak 2/Zinc Alloy 2/Kirksite is the strongest and hardest alloy in the Zamak family. As a result, it is applicable in casting parts that require high structural integrity. As a result, they are common materials in the automotive and mechanical sectors.
Zamak 3/Zinc Alloy 3 is a popular zinc alloy with superb dimensional stability and castability. Aside from its physical and mechanical properties, it is compatible with several finishing options, including painting, chromate treatments, and plating.
Zamak 7/Zinc Alloy 7 is a modified Zamak 3 with a lower magnesium content and impurities than other members of the Zamak family. As a result of its constituent, the Zamak 7 is applicable in making parts that require high castability and surface finish. Aside from that, it is very ductile.
Although die casting is compatible with several materials, zinc alloy die casting is popular due to its mechanical properties. For example, it is strong, tough, firm, and cost-effective compared to other alloys. Below are a few advantages of the process.
Like any other die casting process, the entire part is cast as a single unit. Therefore, assembling reduces.
Zinc alloys are strong compared to other alloys compatible with die casting. As a result, design optimization that calls for a reduction in the wall thickness can be put into place. Compared to materials such as aluminum, zinc can still exude structural integrity in such a case. Aside from that, lower material use reduces the die casting cost.
Zinc alloys have an advantage over aluminum and magnesium based on mechanical properties such as strength and durability. This further improves their use in parts that require materials with high strength. Other mechanical properties include corrosion resistance, firmness, and toughness.
Zinc’s excellent bearing and wear properties make it suitable to act as bushings for structures in motion. Furthermore, it is suitable for making parts with complex geometries due to its ability to form joints with other materials.
Mold used in zinc die casting can last about ten times the aluminum die casting mold due to the zinc alloy’s less abrasive and lower melting point. As a result, there is a reduction in mold damage and an extension in the tool’s longevity. Furthermore, this reduces the cost of tooling compared to other materials.
Zinc alloys have a low melting point and require a hot chamber die casting process that occurs at high-pressure injection. This will increase the cycle rate more than other materials, such as aluminum (zinc alloy die casting has a cycle rate that is 150-200% higher than aluminum).
In zinc die casting, injection of the zinc into the die mold is direct. This is unlike aluminum die casting, which requires melting the aluminum in an external container before injection occurs. Also, the casting has a high solidification rate which further improves the number of parts produced and reduces the cost of casting.
There are several finishing options suitable for die casting materials. Common finishing options for the material are included.
· Plating is suitable for improving the functional and aesthetic attributes of the die-cast zinc. Functional improvement can be an increase in corrosion resistance and durability.
· Powder coatings for die-cast zinc are more for aesthetic purposes due to the wide range of colors available. Aside from that, it produces a durable and uniform surface finish on the casted parts.
· Painting serves functional and aesthetic attributes. Like powder coating, they are mainly used for their functional color due to the various colors available. However, painting requires a shorter time and lower production costs, unlike powder coating.
Other finishing options suitable for working with zinc casts include electroplating, mechanical plating, and anodizing. Each one has unique attributes that determine the application of the finished part.
Although it has advantages based on its strength and durability, zinc alloy die casting also has disadvantages. Below are a few disadvantages of the material.
The process has a high filling speed and rapid cooling. As a result, the gas discharge can be late, leading to defects such as pores. Furthermore, defects such as pores and blisters reduce the die casting quality. Aside from that, such castings should not undergo heat treatment as it can lead to damage.
Zinc die casting is stronger but heavier than materials such as aluminum. As a result, they are not suitable for making parts where lightweight is important. This is visible in the lesser use of the process in the aerospace industry.
Die casting has a high initial investment cost. As a result, they are majorly applicable in the mass production of parts. Due to the high die casting cost, they are not cost-effective for small-batch production.