History and Applications
The use of aluminum molds in 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. Nowadays, they are gradually becoming popular among companies outside the automotive sector.
An increasing number of customers are raising the question: how can the service life of these molds be extended so that they can be suitable for limited production? With the development of this trend, customers are beginning to explore using aluminum molds as real production tools, and even raising more questions, such as:
(1) What level of final surface finish might a mold need to achieve for better part release?
(2) Does it require a paper-like surface finish or a diamond-like surface finish? Does it need to undergo shot peening polishing?
(3) What requirements need to be met to prevent its corrosion and wear?
Before processing and handling the mold, all these issues should be properly addressed.
Due to the development of new technologies and aluminum formwork, especially for the design of injection molds, aluminum molds are also increasingly commonly used in the fields of blow molds, R.I.M. molds, rubber molds, structural foam molds, and R.T.M. molds.
Extend Service Life
Everyone hopes to extend the production service life of molds. For example, molds made with traditional tool steel may have their surfaces plated with hard chrome or nickel, or coated with more specialized engineering coatings. This helps prevent surface wear or corrosion and facilitates better demolding. Later, in pursuit of the same goal, aluminum molds began to be used, and practical solutions were found.
Gloss Level
In order to be able to injection mold parts with good decorative qualities, manufacturers not only aim to extend the service life of molds but also hope that the surface of aluminum molds can maintain a certain level of gloss. Therefore, it is recommended to use a non-electrolytic nickel spraying process, as this method helps to prolong the surface finish life of the mold, making it relatively easier to produce decorative parts.
Since aluminum is relatively soft, without a surface coating, it is easily worn by plastic, accelerating its damage and thereby changing the gloss of injection-molded parts. A non-electrolytic nickel coating can increase the mold surface by 50RC, making it sufficient to protect and extend the gloss and structure of the mold surface.
Surface finish
Even more advantageous is that electroless nickel coatings can achieve better surface finish quality than the aluminum material itself. However, it must be noted that some surface treatment is required before the mold can be electroplated. For example, in order to reach lens-level quality, it is recommended to first machine the surface of the aluminum mold to the SPIA-3 finish level, and then apply a high-phosphorus electroless nickel coating of 0.0003~0.0005 before further polishing to achieve diamond-level surface finish quality.
On the other hand, this process saves a significant amount of time and cost. Normally, aluminum also presents various defects that are often invisible to the naked eye and can only be clearly seen on injection-molded parts, which inevitably leads to material waste and the time spent returning to the test bench to re-test in order to analyze and correct the problems. Electroless nickel coating helps eliminate these defects before the mold goes into production or minimizes them.
Since the electroless nickel coating deposits uniformly on all surfaces of the mold, it fully covers the entire part, including all threaded and pin holes, effectively improving the structural integrity of the aluminum mold. Another advantage is that the application of electroless nickel coating does not affect the properties of aluminum, as it is applied under low-temperature conditions of 180°C.
Corrosion Protection and Water Lines
If corrosion is a concern, using nickel-polytetrafluoroethylene coatings, boron nitride nickel coatings, and non-electroplated nickel coatings can provide the best corrosion protection. After applying any of the above types of engineering coatings, there is no longer any need to spray additional protective or anti-corrosion layers on the mold during periods of downtime.
Water lines can also benefit from non-electroplated nickel coatings on aluminum molds. When used, there is no need to worry about shrinkage of the water lines or white, scale-like coatings. It can reduce the processing cycle because the plated material can actually eliminate these issues. Therefore, as long as the plug is not removed from the mold before application, the water lines will also be covered by the coating once the entire mold is sprayed.
At 50 RC, directly sprayed non-electroplated nickel coatings can provide general wear protection, but optimal protection can be achieved with PVC gas; nickel-polytetrafluoroethylene coatings at 50 RC offer moderate protection against wear, improve lubricity, and provide good corrosion protection; boron nitride nickel coatings at 54 RC offer excellent wear protection, as well as good release performance and corrosion protection.
It should also be noted that aluminum has different grades, which require different treatment methods to ensure proper adhesion to any plating material. Therefore, it is always very helpful to understand your substrate, or to find a plating distributor with certain equipment to provide you with an analysis. This can ensure the best adhesion on your skateboards, mold closures, parting lines, and other mold components.
