Sign up for the PlasticsToday NewsFeed newsletter.
May 15, 2001
3 Min Read
It cycles faster and is easier to machine than tool steel. Now newer, harder, premium aluminum alloys are touted as tough enough for production tools. An experienced aluminum toolbuilder and supplier, Rafael Kilim of Almo (London, U.K.) believes that proper design is more important than designer-label hardness when it comes to getting best results.
Kilim says he has found four standard aluminum alloys suitable for injection molding (specified here by their international codes)—2014A and 2024, which are copper alloyed, and 7075 and 7022, which are zinc alloyed. All of these are used as aerospace grades with very good consistency, Kilim reports. They are also hard enough to give good machinability, he says.
"In the hardness range of 145 to 150 Brunel, excluding the 6000 Series, which is in the 90 Brunel range, all of these alloys can be readily obtained from aerospace aluminum wholesalers at vastly reduced costs," he says.
Though some of the specially tempered brand-name alloys have a small improvement in hardness, Kilim says a small decrease in elongation occurs, which increases the tendency of the material to develop cracks.
Still, he says he has found that any of these four basic alloys is suitable for moldmaking. "I feel that an unnecessary premium is attached to the trade names," he adds. "To obtain the best results using aluminum tooling, an understanding of how to design in aluminum plays a far greater role than any slight improvements in alloy hardness."
The Case For Tailored Performance
However, consultant and aluminum tooling missionary David G. Bank (Geneseo, NY) argues, "All aluminum alloys are not created equal." Bank says even better results can be achieved when moldmakers settle for something better than a standard, off-the-rack aluminum.
Designer-label alloys are usually hybrids tailored to a particular market application, like injection molds, he says. A mold experiences continuous heating and cooling cycles, variable pressures, and continuous use with a variety of plastics. High machinability, thermal conductivity, and corrosion and fracture resistance play important roles, as do stability, weldability, polishability, and availability.
There is much more than just comparing hardness when it comes to selecting the best aluminum tooling alloy, he says. There also is something to be said for the quality and consistency of brand-name products, according to Bank. In his former life as a rapid toolbuilder, he says he tried them all—including 2024, 6061, and 7075—but settled on Alcoa's QC-7 and used it exclusively for years.
"Today, everyone is searching for ways to reduce cost, beat their competitors, shorten cycle time, and improve their bottom line," Bank summarizes. "Considering overall mold costs, saving pennies on buying your mold materials is not the answer."
Though they may sometimes differ, both Bank and Kilim agree that significantly reduced mold manufacturing time and improved cycle times can be achieved through the use of aluminum molds.
Design Tips for Aluminum Tools
In the end, Kilim recommends that mold designers and moldmakers rely on their experience, taking into account elements such as the number of cavities, planned production quantities, plastic part design, plastic material used, where the mold will run (in-house or with a contract molder), and customer expectations.
You May Also Like
Foam Expo Explores Manufacturing OptimizationFeb 29, 2024|1 Min Read
Entek to Unveil New Twin-screw Technology at NPE2024Feb 29, 2024|2 Min Read
Does This Patent Signal a Turning Point in Sustainable Plastics?Feb 28, 2024|4 Min Read
Resin Price Report: PE Price Increase Now UncertainFeb 28, 2024|3 Min Read