Machine-tool builder Mitsui Seiki and tooling system provider Kennametal conducted recent tests with the goal of achieving the ultimate system for machining titanium.
When it comes to sourcing capital equipment for machining specialty materials, many organizations would do well to remember the 10-speed bicycle analogy. People shop and buy a 10-speed bike for recreational or workout goals, but when riding rarely go beyond two or three of the most comfortable gears. Tour de France riders and other finely tuned athletes both size and operate all their components (frame, pedals, shifters, wheels, etc.) to get the absolute most out of their equipment, whether climbing mountains or racing in the flats.
A test was conducted on a titanium (Ti-6Al-4V) workpiece on the Mitsui-Seiki HPX63 CNC horizontal machining center equipped with four Kennametal tools, each using the KM4X 100 spindle connection.
Machining high-strength, high-temperature alloys like titanium is a significant mountain to climb for many shops. Machine tool builders have responded with milling and turning centers that feature improved stiffness and damping on spindles and sizable machine structures and motors, all to provide the significant cutting forces required while minimizing undesirable vibrations that deteriorate part quality and tool life.
Achieving the ultimate system for machining titanium for maximum metal removal means paying close attention to the machine tool that provides the force, the cutting tool characteristics where the cutting edge meets the workpiece, and the spindle connection -- the "handshake" between the machine tool and the cutter.
In April 2012, machine-tool builder Mitsui Seiki (Franklin Lakes, NJ), in connection with tooling and tooling systems provider Kennametal Inc. (Latrobe, PA), conducted a test cut on a titanium (Ti-6Al-4V) workpiece on the Mitsui-Seiki HPX63 CNC horizontal machining center equipped with four Kennametal tools, each using the KM4X 100 spindle connection.
Key design criteria of the HPX63 include a large work capacity featuring a swing diameter up to 1050 mm and available work height (Y axis) up to 1050mm. Axis stroke is 1000mm in X and 900mm in Z. Pallet size is 630mm. The B-axis rotary table offers 12 rpm and high-torque, high-acceleration availability. Rapid travel rates are 32m/min with 0.5G acceleration/deceleration, and the cutting feed rate is 12m/min.
A spindle connection that makes the best utilization of available power possible is an important consideration to achieving the ultimate system.
Made for precision work, its castings are metallurgically configured for the utmost stiffness, its box way axis slides are hardened, ground, and hand-scraped. Positioning accuracy and repeatability is 0.001mm. The spindle, Mitsui's own, automatically compensates for thermal changes and does not require a "warm up" period. The company offers several spindle options to meet user needs for direct or gear drives and the amount of torque and rpm requirements.
Overall, the ruggedness, rigidity, and precision of the HPX-63 make it ideal for machining titanium, Inconnel, tool steels, stainless steels, and aluminum for the aerospace, energy, compressor, mold and die, fixtures and tooling, automotive prototyping, and general precision machining industries.
A spindle connection that makes the best utilization of available power possible is an important consideration to achieving the ultimate system. Most tools in the market are solid and the spindles have relatively low clamping force. Connection stiffness is limited, as radial interference needs to be kept to a minimum. The required tolerances to achieve consistent face contact are thus very tight, leading to high manufacturing costs.
The Spindle Connection
KM4X™ from Kennametal represents the next generation of KM. Some systems may be able to transmit a considerable amount of torque, but cutting forces also generate bending moments that will exceed the interface's limits prior to reaching torque limits. By using three-surface contact for improved stability and optimized clamping force distribution and interference fit, KM4X™ engineering results in three times the bending moment resistant capacity compared to other tool systems.
Sizing the right machine tool with the right tools and connection can result in an ultimate productivity system for cutting titanium and other difficult-to-machine alloys.
In the test cut, the HPX63 was equipped with a high-torque, high-power spindle with maximum 26/22 kW power and 1081 Nm torque. The KM4X100 spindle connection generated 85kNm clamping force, more than twice an HSK100 and three times that of a BT50 (40kNm and 25 kNm, respectively).
The Cutting Tools
The four different cutting tools employed in the test were (1) a 203.2 mm diam. face mill with seven square indexable inserts, (2) the same diameter face mill with seven round inserts, (3) a 76.21 mm diam., 228.6 mm long helical (HARVI Ultra™) cutter with five helical rows of 11 inserts each, and a flat-bottom indexable (FBI) drill unit at 125 mm diam. with six indexable inserts.
With the power of the machine tool and spindle and superior clamping force of the spindle connection, test cut results were phenomenal across the board. For the square-insert face mill, the material-removal rate reached 88.74 cc/min. at 64 min-1 spindle speed, 12 mm depth of cut, and 45 mm cutting width, feeding at 164.3 mm/min.
At 73 min-1 spindle speed, 177.8 mm cutting width, 3 mm depth of cut, and 88.9 mm/min cutting feed, the round insert face mill achieved a 47.42 cc/min. material-removal rate.
The HARVI Ultra™ helical cutter, cutting in X and Y directions simultaneously, topped 309 cc/min. material-removal rate at a spindle speed of 171 min-1, 101.6 mm/min. cutting feed, 40 mm depth of cut and 76.21 mm cutting width.
The FBI drill made a flat-bottomed hole in the titanium workpiece at 102 min-1 spindle speed, 10.2 mm/min. feed, and 125 mm hole diameter at 125.2 cc/min. material-removal rate. Following the first hole, the workpiece was rotated 45 degrees away from the spindle and an angled hole was drilled pushing through the edge of the previous hole. In spite of the heavy interrupted cuts, both machine tool and drill performed well.
With the power of the machine tool and spindle and superior clamping force of the spindle connection, test cut results were phenomenal across the board.
To the Max
Compared to commodity or general-purpose machine tools, the HPX63 is able to reach between 1.5 and two times the material-removal rate in machining titanium alloy. And the KM4X spindle connection had enough clamping force and interference fit to allow a customer to use the higher RPMs and torque levels the machine tool and spindle can provide. More productivity potential is gained from the machine tool and more cutting performance is gained from the tool.
Moreover, a KM4X100 spindle connection will reach performance levels of an HSK125, but makes unnecessary the longer spindle, bigger tool-changer arm, larger tool magazine, and all the related increases a larger-footprint machine would require. Sizing the right machine tool with the right tools and connection can result in an ultimate productivity system for cutting titanium and other difficult-to-machine alloys. The connection can stay viable right up to the machine tool's performance potential, which will drive the most out of the cutting edge. Milling, drilling, and even turning just got more productive.
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