Tire molds are as intricate as many high-end components in the aerospace industry. Engineers continuously design and innovate complex, variable tread patterns, especially around the tire's sidewalls, which present significant machining challenges for mold shops like Northeast Tire Mold.
Based in Akron, Ohio, the shop processes solid modules directly from raw materials instead of using castings. Each set of molds consists of several individually machined sector modules—typically eight—that are assembled to form a complete circular mold.
**Challenges**
Each sector module is arranged around the circumference of the mold at various pitches, sometimes up to 12 different ones. If the pattern isn't complex enough, the same pitch must be used across all modules. The precision required between adjacent modules is critical, as thermal expansion during the molding process can cause misalignment. Additionally, there are no true flat surfaces in directly machined molds. To maintain accuracy, Northeast Tire Mold must keep the total indicator reading (TIR) below 0.005 inches. This means each individual module must be machined to ±0.001 inches tolerance, ensuring the overall mold remains under 0.003 inches.
**Tool Clamping Solution**
Since the 1960s, direct machining has been used for tire molds, but it was time-consuming and expensive. With the advancement of 5-axis machining and software, the process has become much more efficient. Today, direct machining requires high-speed 5-axis machines and precise tooling. Northeast Tire Mold chose the powRgrip tool clamping system from REGO-FIX to meet these demands.
The shop now uses powRgrip tool jackets, a balancing system, and over 200 collets and shanks that allow tools up to 11.8 inches in length. Unlike other systems that use thermal or hydraulic methods, powRgrip relies on mechanical clamping, delivering a runout error of less than 0.0001 inches. It’s fast, easy to use, and allows tool changes in under 10 seconds without requiring heating, enabling immediate use after replacement.
Mr. Mike Christie, vice president of Northeast Tire Mold, notes that powRgrip offers longer tool life and better performance compared to traditional hot-sleeve systems. He also highlights its versatility in handling smaller tool sizes, reducing inventory needs.
**Real-World Application**
Northeast Tire Mold produces about 250 molds annually, ranging from small motorcycle tires to large truck tires. Most are made from 1020 steel or 6061 aluminum. Each mold takes between 3 to 16 hours to machine, depending on complexity.
The two Alzmetall 5-axis machines operate 24/7, with one programmer managing the process using Openmind software. Each machine holds up to 60 tools, and an average of 40 tools are used per workpiece. Small end mills, such as a 0.027-inch diameter tool, are often used to machine deep features, with a length-to-diameter ratio of 15:1. Thanks to the low TIR provided by powRgrip, these tools last significantly longer, improving both efficiency and precision.
**Production Strategy**
The shop follows a strategy of roughing out material quickly and then finishing with high precision. Using advanced machines and REGO-FIX tooling, they achieve excellent surface finishes, minimizing the need for secondary operations. For example, what once took 40 hours of manual grinding can now be completed in just 8 hours.
“We’re outperforming our competitors by a 2:1 ratio,†says Chris Sipe, president of Northeast Tire Mold. “With skilled staff, modern equipment, and precise tooling, we can deliver complete tire molds in 8 weeks or less. Some experimental molds even come out in 10 days.â€
“Our molds are so accurate that customers can replace individual modules and still have full compatibility with existing ones. We’re the only company that can offer this level of precision and flexibility.â€
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