Ask the Expert: Advancements in Titanium Machining for Aerospace

Ask the Expert: Advancements in Titanium Machining for Aerospace

In this question-and-answer session with Mark Larson, AeroEngine Manager at Makino, we take a detailed look at developments that adapt titanium machining to achieve the following results:
  • Deeper axial cutting
  • 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. The result is a thorough understanding of how cutting parameters like surface speed, chip thickness, and radial engagement impact tool life. By researching these cutting conditions, we’ve been able to create more effective programs which optimize 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 task 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 spindle configuration including A and C axes, 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 balanced 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 high machine stiffness and vibration damping characteristics.

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

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 highly stiff, stable machine platform that is up to the task of titanium machining, the key to further productivity improvements lies in optimizing cutting parameters and automating the part handling.
Optimizing the cutting parameters to achieve the highest material-removal rates while balancing tool life will deliver  the lowest cost per part machining process achievable. Adding automation can eliminate several other labor costs as well.  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 an impact on productivity. For instance, Makino’s T-Series titanium machining centers come standard with automatic pallet changers, which maximize machine utilization by making sure there is work ready for the spindle.. Additionally, the machines can be 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 they encounter re-cutting  chips and unexpected chatter conditions. However, these tools run at low 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 when on typical machining platforms, these tools can are highly susceptible to chipping when vibration occurs.

This takes us back to the importance of designing a purpose-built machine platform which reduces and eliminates chatter. 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 higher the stiffness of 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 axial depth of the tool engagement helps remove several passes from the machining process, cutting down on production time and achieving historically low cost per part.