A new approach offers manufacturers of titanium parts four times the productivity and double the tool life.
The appeal of titanium is no mystery. Its material properties of toughness, strength, corrosion resistance, thermal stability, and lightweight are highly beneficial to the construction of today’s aircraft. However, aerospace manufacturers producing titanium parts quickly discover the difficulty these material properties present during the machining process. The combination of titanium’s poor thermal conductivity, strong alloying tendency, and chemical reactivity with cutting tools are a detriment to tool life, metal-removal rates, and ultimately the manufacturer’s profit margin.Producing titanium parts efficiently requires a delicate balance between productivity and profitability. However, in standard machining practices these two factors share an inverse relationship, meaning greater productivity can come at a higher cost due to rapid tool degradation, while the desire to increase profit margins by extending tool life may result in decreased metal-removal rates and extended cycle times.“Overcoming this issue requires a new approach in which all components of the machining process are developed and integrated specific to the material’s unique challenges,” says Mark Larson, Makino’s titanium process R&D manager. “This requires a reassessment of even the most basic machine tool design considerations. This was the concept for our new T-Series 5-axis horizontal machining centers with ADVANTiGE technologies, and the results speak for themselves – four times the productivity and double the tool life.”
Changing the Rules
In the past, and even in some shops today, typical machining of titanium uses multi-spindle gantries and machines with geared head spindles. While these technologies have been effective, the growing complexity of part geometries and required accuracies have brought forth several limitations, including machine and spindle vibration, poor chip removal, slow acceleration and deceleration times, limited tooling options, limited 3D machining capabilities without multiple setups, programming issues, limited workpiece access, and a lack of automation capabilities. In support of the aerospace industry’s demand for titanium, Makino established a Global Titanium Research and Development Center at their North American headquarters in Mason, OH. This facility is managed by a select group of engineers, all of whom possess the knowledge and experience around titanium in both academic and industrial backgrounds. “We are assessing every component of the titanium machining process, including tooling, cutting strategies, and machine design,” Larson states. “This has led to dramatic changes in our approach to machine and spindle rigidity, vibration damping, chip removal, coolant delivery, cutting strategies, and automation capabilities.”The company’s latest breakthrough, ADVANTiGE, is a comprehensive set of technologies that includes an extra-rigid machine construction – Active Damping System; high-pressure, high-flow coolant system – Coolant Microsizer System; and an Autonomic Spindle Technology. Each technology, designed specifically for the titanium machining process, provides dramatic improvements in both tool life and productivity.
Creating a Rigid Platform
The rigidity of a machine tool is one of the single most important components in titanium machining, heavily influencing the equipment’s stable cutting parameters. Machines designed with low rigidity offer limited stable cutting zones, dramatically reducing the achievable maximum level of productivity across all spindle speeds. To increase the productivity of a low-rigidity machine, manufacturers have only one option: taking lighter cuts and increasing spindle speeds, resulting in dramatic reductions in tool life. “Higher rigidity machines provide a more flexible, stable cutting zone,” Larson says. “This is the basic building block for ADVANTiGE, allowing a solid, reliable platform for all other technologies while further suppressing vibration for reduced tool chipping and improved metal-removal rates. This principle was our primary goal in the design of our T-Series machinery.” The T4 5-axis horizontal machining center, Makino’s product for ADVANTiGE, is designed specifically for the machining of large titanium aerospace structural parts. Constructed of a massive bed, 1.7m wide column, box guideway system and large-diameter ballscrews, this machine provides immense rigidity.
Vibration Damping System
Complementing the rigid machine structure, ADVANTiGE also incorporates an Active Damping System into the machine’s slideways. By adjusting frictional forces based on low-frequency vibration sensing, this technology avoids structure resonance in real time, enabling deeper cuts, higher metal-removal rates, and reduced tool wear, benefits necessary for efficient titanium machining. Makino’s Active Damping System contains four major components. As previously noted, the first component is a rigid machine structure to limit the machine’s overall maximum resonance. Second is a stiff connection between the servomotor and the major component of the machine control, which prevents shaking from occurring between the motor and that component. Next is a controlled mechanical damping. A controlled damping factor enables the system to respond and adjust its structure in such a way as to absorb vibration energy, reducing machine vibration. Last, an advanced servo control is used to almost instantaneously detect vibration energy from the cutting force and generate an opposing force to absorb and cancel out vibration.
Heavy cutting forces resulting from the titanium machining process can also create hazardous vibrations inside the work zone and are capable of dramatically reducing tool life. To eliminate this vibration, Makino has developed an Autonomic Spindle Technology. This developmental-technology can detect, think, decide, and react to the displacement caused by excessive cutting forces. Makino’s Autonomic Spindle Technology uses displacement sensors in X-, Y-, and Z-axis to detect the direction and level of displacement. This information, processed by the machine’s control software, measures the stability of the current cutting conditions. If cutting conditions are unstable, the machine automatically adjusts machining parameters in real time to establish stable cutting. This adjustment allows for optimal productivity with extended tool life, an important quality when working with costly titanium tooling.
Titanium’s poor thermal conductivity also bears adverse conditions for cutting tools where deflection of heat, from the cutting zone onto the tool, causes rapid tool destruction. In order to reduce heat in the cutting zone, chips must be removed quickly and thoroughly when coolant is continuously applied to the work zone.
The ADVANTiGE solution is a high-pressure, high-volume coolant system featuring an overhead shower, spindle nozzles, and through-spindle coolant. At a maximum delivery of 1,500psi and 55gpm, this coolant system blasts chilled coolant to the work zone with enough pressure to evacuate chips at metal-removal rates of 24.4 cubic inches per minute. Adjustments to the pressure and volume can also be made through enhanced M-code functionality in the control unit to best suit the operation at hand.
When machining titanium, there are three significant forms of tool damage: mechanical, heat, and adhesion. Through ADVANTiGE’s rigidity, damping, coolant, and adaptive spindle technologies, mechanical and heat damage are effectively minimized. To address adhesion damage, Makino is developing a Coolant Microsizer System. This tool-life extension developmental-technology improves the cooling lubricity of a tool by reducing coolant particle sizes for more efficient delivery to the cutting zone.
One solution for increasing productivity without reducing tool life is the addition of pallet changing and automation capabilities. Using these technologies enables manufacturers to reduce spindle downtime and operator maintenance.
In addition to ADVANTiGE technologies, Makino’s T4 features a unique two-pallet system with rotating table units located on either side of the machine. At one position, the table units are positioned horizontally for easy part loading/unloading via an overhead crane. Pallets are rotated to a vertical position to meet the spindle’s horizontal orientation, providing improved chip evacuation and coolant flow. The machine’s simultaneous pallet change provides a chip-to-chip time of approximately two minutes. T-Series machining centers can also be integrated with an automatic pallet transfer and storage system in a highly flexible Makino Machining Complex (MMC2) for extended periods of unattended operation.
“The economics of titanium aerospace part production are changing,” Larson says. “By improving productivity and profitability simultaneously, aerospace manufacturers have new opportunities to lead this industry in future developments of aircraft designs and capabilities. “And while we have seen amazing results through our ADVANTiGE technologies, there is no single solution for all titanium machining applications. Our goal is to continue pursuing optimal cutting strategies, providing manufacturers with detailed best practices for all types of machining processes.”
Source: Aerospace Manufacturing & Design