ASK THE EXPERT: Advancements in titanium machining for aerospace

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The cornerstone of efficient and profitable titanium machining is employing a machine tool that has been built specifically for the job. PHOTO courtesy Makino.

Mark Larson, AeroEngine Manager at Makino, provides a detailed look at developments that adapt titanium machining to achieve these results:

  • Enable deeper axial cutting
  • Ensure excellent chip clearance
  • Cut closer to finished forms using 5-axis toolpaths during roughing
  • Mitigate heat generation with proper cooling and lubrication

Q: What developments in machining technologies and cutting strategies should I be aware of to simplify titanium machining?

A: Through years of research and development, the machine tool industry has learned a great deal about the machining characteristics of titanium. Today, manufacturers no longer need to rely on trial-and-error processing techniques. We have specialized machines, tooling, work holding and other accessories designed specifically for the job, and they are quite effective solutions at that.

The cornerstone of efficient and profitable titanium machining is employing a machine tool that has been built specifically for the job. This was the primary directive for the development of Makino’s T-Series machining centers. Some of the characteristics found in these machines include high-power, high-torque spindles, extremely rigid casting structures, high-pressure, high-volume coolant systems for effective cooling and chip evacuation, and a multi-axis configuration that enables operators to perform roughing processes that interpolate offset from the final finished shape of the part. Together, these technologies dramatically reduce machining passes and extend the tool life and speed of the finish process by eliminating steps and extra material left by a traditional roughing process.

Complementing the development of these purpose-built machine technologies, engineers have also invested thousands of hours into the testing and analysis of new titanium cutting strategies. Such tactics include a thorough comprehension of cutting forces, chip thickness, radial engagement and how each of these impact tool life. By evaluating these cutting conditions, we’ve been able to better understand and control programs in relation to tool engagement and surface speed to achieve a highly profitable balance between productivity and tool life that exceeds previous limitations.

Q: If torque is a key component to machining titanium, why not focus on increasing machine torque even further?

A: Torque is certainly a critical factor in the machining of titanium, which is why the Makino T-Series machines incorporate 1000Nm (787 ft-lbs) spindles. However, all components of a machine tool are interconnected in some way, which means all components of a machine must be up to the tasks of controlling or eliminating the vibration incurred from high-torque machining of titanium. For example, incorporating a 1000Nm spindle within the T-Series led to many unique design considerations, including a unique A/C-axis configuration within the spindle, large XYZ guides, stiff castings and large CNC drives designed in balance to ensure success in the machining process.

Manufacturers should be cautious as they evaluate machines with exceptionally high levels of torque. There are many machine builders on the market that have repurposed existing general-purpose machine platforms by simply cranking up the torque. As a result, the machines experience significant vibration when increasing tool engagement due to an imbalance in the machine design. The vibrations can sometimes even be felt in the floors several feet away from the machine.

So, while high levels of torque are certainly necessary for efficient cutting of titanium, manufacturers should ultimately spend more time researching how a machine’s design has been rebalanced to accommodate more aggressive cutting forces.

Q: To avoid these vibration issues, what types of machine designs and technologies should I seek?

A: When it comes to machining titanium, traditional vibration solutions are no longer valid. These solutions were designed to combat vibration resulting from high-rpm processes, which is a very different type of issue. Reducing and eliminating vibration in titanium processes requires machine stiffness and rigidity, vibration damping characteristics and specialized CNC software responses.

The primary and most critical feature is the innate stiffness and rigidity of the machine design. This can be a difficult attribute to evaluate on many machines, but there are some key characteristics that manufacturers should look out for. These features include massive bed castings, wide, solid column designs, box guideway systems and large-diameter ballscrews. Combined, these characteristics can reduce the magnitude of deflection, damping out most vibration issues.

Another, less tangible means for reducing vibration is the use of CNC software. An example of this is Active Damping technology, a proprietary technology developed by Makino. This technology enables the CNC to take an active role during processing to counter the development of vibration.

Q: Once I’ve identified an appropriate machine platform, how else can I improve productive capabilities? Is automation a viable option?

A: If you’ve properly identified a rigid, stable machine platform that is up to the task of titanium machining, the key to further improving productivity lies in optimizing cutting processes to achieve the required quality standards using the highest material-removal rates while maintaining the lowest cost per part achievable. The result of these optimizations can largely impact the amount of labor time required to produce each part in three ways:

  • Provide a reliable process to reduce the amount of labor required to monitor machines, freeing operators to work on higher-value projects.
  • Combine 5- and 6-axis capabilities with roughing and finishing on the same machine slashes
    costs associated with part handling.
  • Eliminate post-machining blending and polishing activities by producing high-quality finishes.

Different forms of automation can make a dynamic impact on productivity. For instance, Makino’s T-Series titanium machining centers come standard with automatics pallet changers, which minimizes machine downtime resulting from workpiece changeovers. The machines can also be easily integrated into Makino’s MMC2 automated pallet-handling systems, providing automatic pallet transfers, loading and production scheduling for improved flexibility. These and other forms of automation let manufacturers get the most value out of their investments and have become nearly interdependent with Makino’s titanium machining processes.

Q: What tooling technologies been developed specifically for titanium that support these new machine technologies?

A: Historically, many manufacturers have used high-speed steel cutters to compensate for the vibration that would result from machining titanium on general-purpose machine platforms. Steel cutters are highly resistant to damage even when encountering recutting of chips and other unpredictable issues. However, these tools demand lower cutting speeds, which limits productivity and profitability. Recent advancements made on the machine side have yielded more flexibility in tool selection. Today, lab testing suggests that carbide-based tools with sharp cutting edges and high-relief angles tend to achieve the longest tool life, but in the field, these tools can also be highly susceptible to chipping and cracking when vibration occurs.

This takes us back to the importance of designing a purpose-built machine platform that reduces and eliminates vibration. By investing in a stiff, damped and actively monitored machine, such as Makino’s T-Series machines, manufacturers are able to mitigate tool damage and achieve the maximum benefits of their tooling. The more rigid the machine platform, the greater the tooling flexibility. In T-Series processes, we have been able to take advantage of long tool lengths, extending them axially to cut deeper while simultaneously running 5-axis toolpaths. Extending the tool length helps remove several passes from the machining process, cutting down on production time and achieving historically low cost per part.

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