Arc spray coating is a highly effective technique for producing molds, offering advantages like cost-effectiveness, efficiency, and versatility in various industrial applications. This method utilizes a specialized spray gun to apply a metal coating onto a substrate, which forms the mold cavity. The arc spray process has seen significant advancements with modern equipment and materials, making it an increasingly popular choice for mold manufacturing.

1. Arc Spray Equipment

The arc spray coating system generally consists of several key components: spray power supply, wire feed mechanism, spray gun, and compressed air. These elements work together to ensure that the molten metal is atomized into fine droplets and accelerated at high speeds to form a strong, uniform coating on the substrate.

• XDP-5 Arc Spray Equipment: Manufactured by Shenyang University of Technology, the XDP-5 arc spray equipment is known for its stable performance and reliability. It is easy to maintain and can handle heavy-duty spraying tasks.
• CMDAS Series: Produced by Beijing Xindi Surface Technology Engineering Co., this arc spray equipment series allows for the use of different wire types, such as 3mm or 2mm metal wires, while operating with the same power supply. This flexibility helps accommodate various spray coating needs.
• ASS Arc Spray Molding Machine: Developed specifically to complement laser rapid prototyping technology, the ASS arc spray molding machine is designed for quick mold manufacturing. It uses an advanced wire-feeding mechanism that eliminates the shortcomings of traditional external wire feeding. This machine features a rotating workbench and fully isolated protective housing, ensuring stability and safety during operation. Additionally, the ASS machine employs a new type of molding material and two innovative molding processes, allowing the production of highly durable and high-precision molds.

2. Arc Spray Materials for Molding

The materials used in arc spray coating play a crucial role in determining the performance and durability of the mold. The selected materials must have a low melting point and low shrinkage rate while ensuring excellent mechanical properties and a dense coating structure.

Key considerations for selecting arc spray materials include:

• Sufficient Hardness and Strength: The materials should offer adequate hardness, compressive strength, and bending resistance, ensuring that the mold can withstand practical use.
• Low Melting Point: Materials with a low melting point are preferred for arc spray coating because they help reduce the thermal stresses that can cause deformation and loss of adhesion between the coating and the mold surface.

Several materials are commonly used for arc spray coating in mold manufacturing, each with its advantages and limitations:

• Aluminum (Al) and Zinc (Zn) Based Alloys: These materials have relatively low melting points, making them ideal for spraying without damaging the plastic substrate. They are also highly ductile, and their thermal shrinkage stress can be alleviated during the spray process. Zinc-based coatings, in particular, offer excellent sprayability and form fine, compact layers, but they have a lower hardness compared to aluminum. Zinc coatings typically have a hardness of around 40–50 HV, which limits their use in high-performance molds.
• Zinc-Aluminum (Zn-Al) Alloys: These alloys combine the excellent sprayability of zinc with the enhanced mechanical properties of aluminum. They offer a balance between low melting points, good thermal conductivity, and higher coating hardness. These coatings are ideal for mold applications that require both high precision and durability.
• Aluminum Bronze and Copper-based Alloys: Though these materials are often used in other spray applications, they have higher melting points, which can cause issues with thermal stress and material shrinkage. Additionally, they tend to have a larger pore volume and higher risk of cracking or delamination during spraying.
• Nickel-Cobalt (Ni-Co) Coatings: For increased mold hardness, pre-electroforming a 0.4–0.6mm Ni-Co alloy layer on the mold surface before spraying has been shown to significantly enhance surface hardness. After spray coating with zinc-aluminum alloys, heat treatment can further increase hardness to 600 HV or more, providing outstanding wear resistance and extending mold life.

Key Characteristics of Ideal Arc Spray Materials for Molds

For mold manufacturing, the following characteristics are crucial:

• Low Melting Point: Materials like zinc and aluminum alloys are ideal as they prevent damage to the substrate and reduce thermal stresses.
• Good Mechanical Properties: The material should provide a high level of hardness and strength, as well as resistance to wear and pressure.
• Fine Coating Structure: Materials that produce a dense, fine-grain coating structure are preferred, as they help minimize porosity and surface roughness.
• Thermal Conductivity: Enhanced thermal conductivity is essential, especially in molds that must withstand high temperatures during production. Zinc-aluminum alloys, for instance, offer good thermal conductivity, making them suitable for injection molding applications.

Challenges in Using High Melting Point Materials

While high melting point metals such as steel, copper, and nickel offer superior mechanical properties, they also pose challenges during arc spray coating:

• High Thermal Stress: The high thermal expansion of these metals can lead to significant thermal stresses during the spray process, which can deform the model or weaken the bond between the coating and the substrate.
• Risk of Surface Damage: High melting point materials tend to burn or damage the model’s surface, negatively impacting the quality and roughness of the mold’s surface.

Conclusion

Arc spray coating technology offers an efficient and cost-effective solution for mold manufacturing, particularly for applications requiring quick turnaround times and small to medium production runs. The right equipment, such as the XDP-5 or ASS arc spray molding machine, combined with appropriate materials like zinc-aluminum alloys or zinc coatings, can produce molds with excellent durability, precision, and cost-efficiency.

As this technology continues to evolve, more industries are likely to adopt it for rapid prototyping and mold production, particularly in industries like automotive, electronics, and packaging.