Arc spray coating technology has found increasing use in rapid mold manufacturing due to its cost-effectiveness, faster production times, and ability to deliver molds with high accuracy and durability. Compared to silicone rubber molds, metal spray coating molds offer a significantly longer lifespan, making them suitable for small-batch production on injection molding machines. The parts produced with these molds exhibit the same quality as those produced through traditional injection molding processes. However, there are specific considerations when using arc spray-coated molds, particularly concerning the performance and longevity of the low-melting-point metal coating on the mold cavity. To achieve the best results, injection molding parameters should be adjusted to account for the unique characteristics of metal-coated molds.

Key Injection Molding Parameters for Metal Spray Coating Molds

1. Injection Pressure
   The injection pressure is one of the most important parameters influencing both the quality of the molded part and the longevity of the mold. Since rapid mold cavities are made of low-melting-point metals, which offer good plasticity, it is important to control the injection pressure to prevent premature wear of the mold. High injection pressures may lead to early damage to the mold, while too low of a pressure could result in incomplete filling of the mold. The injection pressure should be optimized to ensure the part is fully formed while preserving the mold’s integrity. When dealing with materials with low viscosity, it is recommended to keep the injection pressure lower to extend the mold’s lifespan.
2. Clamping Force
   The clamping force required for the arc spray-coated mold’s cavity is supported by two mold frames, which typically do not provide the same rigidity as steel molds. If the clamping force is too high, the mold frame may deform significantly, which can result in excessive pressure on the mold cavity surfaces. This, in turn, can cause the metal spray coating to fail, leading to mold damage or even complete mold failure. On the other hand, if the clamping force is too low, issues such as flash (excess plastic around the part) and overflow of molten plastic from the mold cavity may occur, accelerating wear on the mold and reducing its lifespan. It is crucial to maintain an appropriate clamping force that allows for the production of high-quality parts while avoiding excessive stress on the mold.
3. Mold Temperature Control
   In injection molding, molten plastic rapidly cools from around 200°C to approximately 60°C during the forming process. The heat generated during this cooling process is transferred to the metal spray coating and the mold’s base material. The temperature of the base material is crucial for both the mold’s longevity and the quality of the finished product. Typically, the base material is a mixture of epoxy resin and aluminum powder, which closely matches the thermal expansion characteristics of the metal spray coating. This ensures that the mold deforms uniformly under heat, preventing issues such as warping or cracking. However, it is essential to monitor the temperature carefully. If the temperature exceeds a certain threshold, the epoxy resin could reach its thermal deformation temperature, leading to cracks and reduced mold life. Proper temperature control is key to maintaining mold integrity and ensuring high-quality molded parts.
4. Holding Pressure and Holding Time
   Holding pressure and holding time significantly influence the final product’s quality. During the holding phase, the molten plastic is kept under pressure to compensate for shrinkage as it cools. If the holding pressure is too low, the plastic may not completely fill the cavity before it solidifies, leading to defects such as sink marks or incomplete parts. Similarly, the holding time should be adequate to allow for proper cooling and solidification of the part. For materials with average flow properties, it may be necessary to adjust the injection pressure to ensure the mold cavity is completely filled before the material starts to solidify.

Case Study: Injection Molding of a Plastic Flowerpot Base Using Arc Spray Molds

For small-batch production of products such as plastic flowerpot bases, traditional machining methods for creating mold cavities are time-consuming and expensive. The process typically involves reverse engineering to obtain data for the mold cavity, which can lead to accuracy errors or the loss of certain features. Steel molds are also costly and take a long time to manufacture. In this case, the arc spray coating method was selected as a more cost-effective and time-efficient solution.

Using the arc spray process, the mold cavity was coated, and backing materials were applied to support the metal spray shell. The design and fabrication of the mold frame were also completed. The mold was then used in an injection molding machine (SZY-300) to produce parts using ABS material. The resulting products had smooth surfaces, high gloss, and accurately replicated the patterns and text on the mold surface, demonstrating the high precision of arc spray-coated molds. The process proved to be a highly effective way of manufacturing precise and durable molds for small-batch production.

Conclusion

Arc spray coating provides a powerful and efficient method for producing molds with exceptional precision and durability. When applied to injection molding, metal spray-coated molds offer a significant advantage over traditional silicone rubber molds, particularly in terms of lifespan. By adjusting key parameters such as injection pressure, clamping force, mold temperature, and holding pressure, manufacturers can optimize the performance of these molds to produce high-quality parts. This technique not only reduces production costs and time but also ensures that the parts produced meet the same high standards as those made with conventional injection molding processes.