Arc spray coating is an advanced technique used for mold manufacturing that provides an efficient, cost-effective method for creating durable and precise molds. The process involves spraying molten metal onto a substrate to form a protective coating, which serves as the mold cavity. The basic structure of arc-sprayed molds is composed of three key parts: the metal spray coating, the backing layer, and the steel structure. These components work together to create a mold that is strong, thermally efficient, and highly accurate.

1. Structure of Arc Spray Molds

The basic structure of an arc spray mold can be divided into three distinct layers:

• Metal Spray Coating: This layer forms the outer surface of the mold and is composed of fine metal droplets that are sprayed onto the mold surface. For zinc alloy molds, the spray coating is made up of zinc alloy microdroplets. During the spraying process, the zinc alloy wire is heated and melted, then atomized by compressed air into fine droplets. These droplets are then sprayed onto the mold surface, where they solidify to form a hard, dense metal shell that acts as the mold cavity’s surface layer. This layer typically has a thickness of 2-3mm. The spray coating provides strength, hardness, low surface roughness, and good thermal conductivity, ensuring that the mold accurately replicates the original prototype. However, due to its thinness, the spray coating alone cannot withstand the pressure during molding. As a result, it requires reinforcement with a backing layer.
• Backing Layer: The backing layer is essential for strengthening the mold and supporting the spray coating. It is made from a thicker material that is directly filled into the mold and adhered to the underside of the spray coating. The primary purpose of this layer is to provide structural support and improve the strength of the mold. Common backing materials include resin sand, epoxy resin, and low-melting alloys such as bismuth-tin alloy. If the mold requires cooling, cooling channels should be embedded within the backing layer before casting the backing material. Once solidified, the channels remain fixed within the mold, allowing for efficient cooling during the molding process.
• Steel Structure: The steel structure of the mold includes components like the mold frame, mold casing, and inserts. This part provides the necessary mechanical support for the mold, ensuring its stability during the molding process. The combination of these three layers—metal spray coating, backing layer, and steel structure—creates a well-rounded and durable mold, with the materials distributed in a gradient from outer to inner layers. This arrangement optimizes the use of materials with different properties and is something that traditional mold-making methods cannot achieve.

2. Spray Coating Pre-Treatment for Mother Mold

Successfully applying a low-melting metal spray coating to the fine surface of a mother mold is highly dependent on the characteristics of the mold material, which is often temperature-sensitive. To ensure a smooth, durable coating, the mother mold material must be clean, free from contaminants, and airtight. It should also be easy to polish for a smooth finish.

Before spraying, the following pre-treatment steps are crucial:

1. Cleaning: Use a suitable cleaning agent to remove any grease, oil, or dirt from the surface of the mother mold. This ensures that the spray coating adheres properly to the mold surface.
2. Protective Coating: After cleaning, apply a thin layer of protective agent to the mold surface. This helps prevent any damage to the mold during the spraying process. Once the protective layer has dried, the mold is ready for the arc spray coating application.

By following these pre-treatment steps, the mold surface is properly prepared, ensuring the success of the arc spray coating process.

3. Advantages of Arc Spray Coating for Mold Manufacturing

Arc spray coating offers several benefits for mold manufacturing, particularly when compared to traditional molding methods:

• Material Efficiency: The use of a gradient structure (metal spray coating, backing layer, and steel structure) allows for the optimal use of materials with different properties, making the mold more efficient and durable.
• High Precision: The metal spray coating accurately replicates the shape of the original prototype, ensuring that the mold’s dimensions are precise and the final product meets design specifications.
• Cost-Effectiveness: The combination of low-cost materials like zinc alloys, along with the speed and efficiency of the arc spray process, makes this method an affordable solution for mold production.
• Thermal Performance: The metal spray coating layer provides excellent thermal conductivity, which is crucial for many molding applications, particularly in high-temperature processes like injection molding.
• Customizability: The backing layer and steel structure can be customized to meet specific strength, cooling, and mechanical support requirements for different mold types.

Conclusion

Arc spray coating is a versatile and efficient technique for mold manufacturing that offers high precision, cost-effectiveness, and the ability to create durable molds with complex geometries. The combination of a fine metal spray coating, a robust backing layer, and a solid steel structure ensures that the molds produced through this process are capable of withstanding the rigors of molding applications, providing accurate and reliable results. The pre-treatment steps for mother molds and the selection of suitable materials further enhance the effectiveness of the arc spray coating process, making it an ideal choice for industries that require quick turnaround times and high-quality molds.