One of the items that needs to be addressed by any purchaser of aluminum die castings is die maintenance, repair, and replacement. This may not be an issue with low volume projects that last a few years since the number of parts produced will be lower than the die life but, there may be some replacement die components that will need to be dealt with during the product life.
The purchaser should be aware that the life of a die can be unpredictable. Die life is a function of many factors; among them are part design, part configuration in the die, part quality expectations, type of tool steel used for the die, the heat treatment of the die and the type of alloy being die cast. Some of the higher silicon die cast alloys are more abrasive and tend to wear out the dies, especially at the gate inlet areas first.
Even when the die caster makes every effort to extend die life, early failure is still possible. It is also possible for a die to have an unpredictably long life. An understanding of expected die life should be discussed in the initial phases of a project. There have been recent advances with die coatings that can be applied after the heat treatment. These coatings add cost but we have seen an improvement in prolonging tooling life in the gate areas and it also retards heat checking somewhat.
Progressive die casters can provide tool steel specifications and heat treat specifications that have been developed through extensive NADCA research programs. NADCA has spent considerable amount of time in this area at some research facilities in the US.
One of the things a purchaser can do is to reference the NADCA specifications for the building and heat treating of the casting die. The specifications include recommendations for stress relief during machining, the removal of the “white layer” after EDM operations and a number of other considerations. One of the most important aspects of tool construction is the heat treat process – here many items are critical to die life such as the quench rate, type of heat treat furnace used, and the number of final temperings that are applied to the die blocks. Die shops not familiar with aluminum die casting, or shops that build for a price do not follow the proper guidelines for a high quality tool, thus the issues with die life long after the purchase is made.
When tooling is procured through a reputable and progressive die caster, tooling costs may be somewhat higher than if a purchaser dealt directly with the tool builder. Die cast tooling should not be procured from a tool builder that has no experience with aluminum die casting or not knowledgeable in the NADCA steel and heat treatment specifications. The price may be less but if the tool fails prematurely it will cost more in the long run, especially if the die fails and production is shut down due to the die failure.
The die caster should be closely involved in evaluations and decisions that will translate the product design into the optimum die casting die for successful production. This translates into proper drafts, radii, ejector pin locations, gating, and parting line considerations. The increased costs almost always represent a bargain in terms of overall costs during the life of the die.
An inexperienced purchaser who purchases tooling purely on a cost basis will find that the costs over the life of a die are significantly higher because of a lower-quality tool, although this will not be immediately apparent when the tool starts running.
It cannot be emphasized too strongly that good quality tooling will cost more in the beginning but pay for itself many times over in the life of a typical die casting die. Proper tooling both in die materials and construction as well as design are critical to quality production parts over the long term.
If you have any parts that you would like to consider as an aluminum die casting please send your prints or files to firstname.lastname@example.org.
By Leonard Cordaro, President of Premier Engineered Products