Aluminum injection molds used to be thought ideal only for low-volume applications using commodity materials. That is changing as OEMs look more closely at tooling costs and cycle times to reduce piece-part pricing, and overall manufacturing cost.

Not long ago, aluminum tooling was considered “soft” tooling that couldn’t withstand the rigors of high-temperature, high-volume injection molding. And it was never to be used with glass-filled materials. However, that’s all changing for a variety of reasons, says Dave Wirth, Midwest sales manager/aluminum mold specialist for Clinton Aluminum & Stainless Steel.

“What we’re seeing now is the perfect storm that’s creating a renewed interest in aluminum for high-volume-production injection molding applications, particularly in the automotive industry,” says Wirth.

Not that there’s been little interest in past years. According to Wirth, some molders have been using aluminum tooling for years, but not telling anyone about it, using it as a competitive edge. It’s not just the initial mold cost that results in savings; aluminum tooling can also provide a substantial reduction in piece-part costs due to shorter cycle times.

“Everyone is looking at piece-part costs right now,” says Wirth. “Additionally, volumes in automotive have dropped along with model changes, so over the past 15 years we’re seeing shorter product life cycles.”

And it’s not just in automotive. Wirth notes that a number of years ago, a major appliance maker would make 10 million shots off tooling an appliance. Today, because of a shorter product life span, they are averaging 1 million to 2 million shots. Ditto for office furniture, he adds. “If you build an aluminum tool, you can save money on the production cost of the mold, but more importantly, you’ll have a 20%-40% decrease in cycle times, and many of these major OEMs are looking at piece-part cost as the biggest factor,” Wirth says.

A major office furniture OEM looked at the cycle time cost savings for a chair base and found that over 2 million cycles, it saved $0.02/sec. “They could pay for four molds with the money they saved switching from steel to aluminum for the tooling,” explains Wirth.

Honda’s the proof
Aluminum tooling was given a great deal of credibility when Honda Motor Corp., which had done a study on aluminum vs. steel tools some years ago, released it to its supplier base. The company compared softer tool steels (P-20) with 4130/SD18 aluminum, which contains more sulfur for improved machining. P-20 costs more vs. 4130/DS18. Using 4130, Honda saw an 8.6% improvement in material cost. Machining costs improved 8.0%. (See study details below.)

Honda has built several tools using mold supplier Unique Tool & Gauge Inc. (UTG; Windsor, ON) and another company. Darcy King, UTG’s president, says, “The major automakers are interested in aluminum tooling for a number of reasons. We started years ago developing tooling in the 7000 grades of aluminum with Honda. We started building tools with them and, based on the performance of the 7000 series, this aluminum is now commonly used.”

Wirth notes that for the OEM and the molder, 50% of the cost of the part is cycle time. “If you can save 20%-40% in cycle time, the cost savings is enormous depending on the size of the mold.

The Honda study looked at the molding materials it was going using, and the majority was PP, TPO, and polyethylene, “A sweet spot for alum tooling,” commented Wirth. “These materials plus lower production runs and the focus on piece-part costs gave Honda a huge advantage. You can’t do these things the same way with a steel mold.”

When the Honda study kicked off about eight years ago, the automaker invited hundreds of mold shops to a co-management meeting, including UTG, which was already involved in the co-management model with Honda. A number of years ago, UTG had its own molding facility in Brownsville, TX, and whenever it built molds for its own molding jobs, it built them out of M1, explains King. Because of that experience with aluminum tools, King knew UTG could help Honda improve cycle times and reduce tooling costs.

“As a toolmaker, we were looking at cost savings, so we decided to bring this idea of aluminum tooling to Honda. “At the end of the co-management meeting process we were the last shop standing. We made the team.”

Use only what you need
The co-management team approach of working with Honda created an environment of cultivating ideas in which everything is open to discussion. One subject was how to help the automaker be more competitive. “At that time, M1 was about all that was available and there was only one 7000 Series aluminum available when we first started,” says King. “Since then it’s been one heck of an experience. The results Honda got using aluminum were phenomenal. They’ve been able to reduce cycle time dramatically, in most cases today up to 50%-80%.”

The concern over high-volume molding runs for automotive has been allayed with the Honda test. For Honda, 100,000 shots is low production; however, it has 600,000 shots on the Accord rear deck tray, proving what aluminum can do compared to steel. Wirth notes, “A lot of guys are overdoing their steel molds and killing their bottom line.”

Al Standaert, technical sales engineer for UTG, states that OEMs and their mold suppliers need to ask, “Is this tool overbuilt for what is needed? They use H-13 that has been nitrided, which will last much longer than the mold is needed. With the 7000 Series being as strong as it is—the hardness has doubled—and now that Honda and Unique have proven the benefit of aluminum molds, we’re seeing a huge increase in the demand to build aluminum tools.”

King adds, “It would have been a tough sell if Honda hadn’t done this study. People are seeing Honda’s success, and without that, aluminum would have never had the credibility it has today with high-volume automotive applications. Honda is a firm believer in this, and that’s promoted it in the industry. It’s hard to get people to change.”

Getting everyone in sync
King has a few caveats for mold manufacturers thinking about producing aluminum tooling. “There’s a lot to what we do and you don’t build and aluminum tool in a conventional way,” he says. “There was a lot of R&D that went into building these molds for Honda, and Honda and Unique operated in a co-management model of doing business. Honda organized the process so there was more free sharing of information.”

He also cautions molders running aluminum tooling, “We’ve had to go back and show some of these molders how to mold with these tools. The main factor is the conductivity of the aluminum and the biggest component is how these tools are built. The whole ideology of designing and building these tools is completely different from P-20 or other steels. It’s a unique process but developing faster cycle times makes it a winner.”

King notes that there’s been some pushback from molders who are used to working with steel molds. “That’s what they know and it’s hard for some of them to accept change,” he says. “Yet, anyone we’ve worked with can see the benefits and keep coming back for more. It just makes sense. A new customer sees the cycle time and they get absolutely giddy at the cycle time savings—50%-80% reductions. There were many OEMs that didn’t believe us, so we had to prove it out.”

 Unique set up a tryout on a 32-by-36-inch automotive part with thick wall sections and got a 17-second cycle. “The part took hardly any cooling time,” King states.

All companies involved in a project with aluminum tooling share in the savings. “We’ve always told our customers—any car manufacturer—that it’s important to work with the supplier and share the savings, which is another reason aluminum has taken off as well as it has. It has to be a win for everyone. Molders can take the cycle time savings and use it to their advantage. If one of my Tier One molding customers gets an aluminum mold, that mold will never go anywhere else because the customer will be so happy with the results. In fact, one molder was going to lose a program to an alternative process, but then decided to go to aluminum to keep the program, and they were ecstatic at the results and were able to keep the program.”

The study
Honda’s saw a 30% reduction in actual pricing for the 11 tools vs. their initial estimated pricing. Benefits realized by Honda using the soft steels included:
• Improved machinability.
• Application for high to medium volumes.
• Acceptable for use in most parts except mirror-finish applications.

Benefits to molders and moldmakers working with aluminum alloy molds include:
• High-strength alloys originally developed for aircraft are suitable for most mold applications.
• Toolmakers get faster machining and shorter lead times.
• Molders get shorter processing times and less part distortion due to better heat dissipation (six times faster than steels).

Honda built two sets of tools, and paid for a backup steel tool. The purpose was:
• Evaluate tool build efficiencies and process cycle time improvement while protecting Honda’s suppliers and Honda plants from downtime concerns.
• Monitor tool maintenance and durability concerns.
• Honda and UTG paid for third-party testing to validate material composition, mechanical properties, abrasion resistance, and compression strength.
• Honda and UTG paid for a Texture Plaque developed to further understand aluminum alloy texturing capability as well as repair methods.
• Based on low-volume results, Honda began to focus on high-volume applications to validate aluminum alloy durability.

The results:
               P-20                          Aluminum tooling                             Cycle time savings
Tool #1    17 weeks lead time     13 weeks lead time (12% savings)    30%
Tool #2    16 weeks lead time     15 weeks lead time (6% savings)      15%

Third-party testing results came back with the following:
• P-20 was the hardest, strongest, and most abrasion-resistant material.
• All aluminum alloys exhibited increased hardness, strength, and abrasion resistance, confirming data provided by aluminum alloy suppliers.
• Cyclic compression testing showed all materials could withstand loading of this nature. Higher cycling would provide further understanding of full life expectancy.

Overall benefits:
• Investment savings through machining efficiencies.
• Process cost savings due to improved thermal conductivity.
• Reduced number of molds and injection presses required to mold parts.
• Different grades of aluminum can be applied based on program volume.
• Lower injection and clamp pressure as compared to steel tool.

Model shot life:
P-20/S55C steel: 3 million-plus shots
413/SD18 soft steel: 2.75 million shots
7000 Series aluminum alloy: 2.2 million shots
M1 and 7000 Series hybrid: 750,000 shots

—Clare Goldsberry