Tire molds are as intricate as many high-end components in the aerospace industry. Engineers continuously develop and innovate complex, variable tread patterns, especially around the tire's sidewalls, which pose significant machining challenges for mold shops like Northeast Tire Mold.
Based in Akron, Ohio, this shop directly processes solid modules of raw materials instead of using castings. Each set of molds consists of several individually machined sector modules—typically eight—that are combined to form a complete circular mold.
**Challenges**
One major challenge is that each sector module is arranged around the entire circumference of the mold at different pitches, up to 12 variations. If the pattern isn’t complex enough, the same pitch must be used across all modules. Each module must match the next, and thermal expansion during the molding process must be considered. Additionally, there are no real flat surfaces in a directly machined mold. To maintain precision, Northeast Tire Mold ensures that the total indicator runout (TIR) stays below 0.005 inches, requiring individual module tolerances of ±0.001 inches to keep the overall tolerance under 0.003 inches.
**Tool Clamping Solution**
Although direct machining has been used since the 1960s, it was once time-consuming and costly. However, with advancements in 5-axis machining and software, the process has become faster and more cost-effective. Today, direct machining of tire molds requires high-speed 5-axis machines and precise tooling systems.
Northeast Tire Mold chose the powRgrip tool clamping system from REGO-FIX before purchasing its first 5-axis machine. The system includes a tool balancing unit and about 200 tool jackets, allowing tool lengths up to 11.8 inches. Unlike other systems that use thermal or hydraulic methods, powRgrip uses mechanical properties to create a strong, precise clamping force with less than 0.0001-inch runout. It’s quick to operate, enabling tool changes in under 10 seconds without heating, so tools can be used immediately after replacement.
According to Mr. Mike Christie, vice president of Northeast Tire Mold, the powRgrip system outperforms traditional hot-sleeve tool holders. The collets last longer, and the system supports a range of tool sizes, reducing inventory needs. For example, a single powRgrip jacket can accommodate multiple tool diameters, unlike hot-sleeve systems that require a separate holder for each size.
**Real-World Application**
For small tools, such as a 0.027-inch diameter end mill that is 15 times its length, low runout is critical. Using powRgrip, the tool life increases significantly—from a few hundred minutes with hot-sleeve systems to around 1,400 minutes. This precision not only improves accuracy but also extends tool life and enhances surface finish.
Northeast Tire Mold produces approximately 250 molds per year, ranging from ATV tires to car and light truck tires. Most molds are made from 1020 tool steel or 6061 aluminum alloy. Each mold block takes between 3 to 16 hours to machine, depending on complexity.
The two Alzmetall 5-axis machines run 24/7, with one programmer handling programming via Openmind software. Each machine holds up to 60 tools, and an average of 40 tools are used per workpiece. Many of these are spares to ensure continuous operation.
All carbide tools are installed in powRgrip tool jackets. Spindle speeds reach 24,000 rpm, with feed rates up to 315 inches per minute. Aluminum modules are processed with coolant, while steel modules use dry cutting. The three grooves in the powRgrip chuck allow coolant to reach the tool, lubricating it and removing chips effectively.
The shop’s strategy is to remove material quickly during roughing and then finish with high precision. This reduces secondary operations, saving time and improving efficiency. For instance, a fitter grinding operation that once took 40 hours is now completed in just 8 hours.
“We’re twice as efficient as our competitors,†says Chris Sipe, president of Northeast Tire Mold. “They need four machines, but we do it with two. Skilled staff, advanced machines, software, and precision tools are key, but our own manufacturing and production processes make the difference.â€
The company can deliver a full tire mold in 8 weeks or less, and experimental molds in as little as 10 days. Their molds are so precise that customers can replace just one module and still use it with existing ones. Northeast Tire Mold is the first to offer this level of modularity and precision.
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