Improve the lifespan, glossiness, and corrosion resistance of aluminum molds

Application

Applying aluminum molds to the injection molding process is not entirely a new concept. Initially, prototype molds were commonly made of aluminum, and the automotive industry has been using such molds for many years. They have now gradually become popular in companies outside the automotive industry.

(1) What level of final surface finish is required for the mold to be plated in order to facilitate better part demolding?

(2) Does it need to achieve a paper-like surface finish or a diamond-like surface finish? Does it require shot peening and polishing treatment?

(3) What requirements need to be met to prevent corrosion and wear?
All these questions should be well answered before processing the mold.
Due to new technologies and the development of aluminum templates, especially for injection mold design, aluminum molds are becoming increasingly common for blow molds, R.I.M. molds, rubber molds, structural foam molds, and R.T.M. molds. Although they may not be suitable for all applications, in fact, their use is becoming increasingly widespread.

Extending Service Life

Everyone hopes to extend the service life of molds in production. For example, when using traditional tool steel to manufacture molds, the surface can be plated with hard chrome or nickel, or use more specialized engineering coatings. This can prevent surface wear or corrosion and facilitate easier demolding. Later, to achieve the same goal, aluminum molds began to be used, and practical solutions were found.

Gloss Level

In order to produce decorative parts through injection molding, besides extending the service life of molds, manufacturers also hope that the surface of aluminum molds can maintain a certain degree of gloss. Therefore, it is suggested to use a non-electroplated nickel spray process, as this method helps prolong the surface finish of the mold, making it relatively easier to produce decorative parts.

Since aluminum is softer in texture, without a surface coating, it is easily worn by plastic, accelerating damage and altering the gloss of injection molded parts. A non-electroplated nickel coating can increase the mold surface hardness by 50RC, which is sufficient to protect and extend the gloss and structure of the mold surface.

Surface Finish

More advantageously, non-electroplated nickel coatings can achieve a better surface finish quality than the aluminum material itself. However, it must be noted that before the mold can be electroplated, some surface treatment is required first. For example, to reach lens-grade quality levels, it is recommended to first process the surface of the aluminum mold to SPIA-3 finish level, and then apply a 0.0003~0.0005 high-phosphorus non-electroplated nickel coating before further polishing to achieve diamond-grade surface finish quality.

On the other hand, this process saves a considerable amount of time and costs. Normally, aluminum materials can also have various defects, which are often invisible to the naked eye and can only be clearly seen on injection-molded parts. This will inevitably lead to material wastage and time spent returning to the trial bench for re-testing to analyze and correct the problems. Non-electroplated nickel coatings help eliminate these defects before mold production or minimize them.

Since the non-electroplated nickel coating is uniformly deposited on all surfaces of the mold, it covers the entire part, including all threaded holes and pin holes, effectively improving the structural integrity of aluminum molds. Another advantage is that applying the non-electroplated nickel coating does not affect the properties of the aluminum, as it is applied under low-temperature conditions of 180℃.

Corrosion Protection and Waterlines

If corrosion is a concern, using nickel-PTFE coatings, boron nitride nickel coatings, and non-electroplated nickel coatings will provide the best corrosion protection. After applying any of the above types of engineering coatings, it is no longer necessary to spray any additional protective or anti-corrosion layers on the mold during production downtime.

Waterlines can also benefit from the non-electroplated nickel coating on aluminum molds. If used, there is no need to worry about shrinkage of the waterlines or white, scale-like coatings; it can reduce processing time because the plated material can effectively eliminate these issues. Therefore, as long as the plug is not removed from the mold before application, once the entire mold is sprayed, the waterlines will also be covered by the coating.

At 50 RC, directly sprayed non-electroplated nickel coatings can provide general wear protection, but optimal protection can be achieved through PVC gas; nickel-polytetrafluoroethylene coatings at 50 RC offer moderate protection against wear, can improve lubricity, and provide good corrosion resistance; while boron nitride nickel coatings at 54 RC have excellent wear protection, as well as good release properties and corrosion protection.