Good connections: Drilling Performance

All images courtesy Kennametal

The Ti6Al4V machining tests using a Mitsui Seiki HPX63 CNC HMC equipped with four Kennametal cutting tools, each using the KM4X100 spindle connection, involved severe interrupted cutting. As shown here, that included drilling a flat-bottom hole, rotating the workpiece 45° and then drilling another flat-bottom hole through the edge of the first hole.

When sourcing capital equipment for machining specialty materials, many shops would do well to consider the 10-speed bicycle analogy. People shop for and buy a 10-speed bike for recreation or exercise, but when riding it rarely go beyond two or three of the most comfortable gears. Elite riders, on the other hand, both size and operate all their components (such as the frame, pedals, shifters and wheels) to maximize their equipment, whether climbing mountains or racing in the flats.

Machining high-strength, high-temperature alloys, such as titanium, is challenging. Machine tool builders have responded with stiffer milling and turning centers, damping spindles and sizable machine structures and motors, all to provide the significant horsepower, torque and thrust forces required while minimizing undesirable vibrations that lower part quality and tool life.

Achieving the ultimate system to precisely machine titanium at maximum metal-removal rates (mrr) requires close attention to the machine tool, the tool/workpiece interface and the spindle connection—the “handshake” between the machine tool and the toolholder.

Tool Test Team

In April 2012, machine tool builder Mitsui Seiki (U.S.A.) Inc., Franklin Lakes, N.J., teamed with toolmaker Kennametal Inc., Latrobe, Pa., to conduct cutting tests on a Ti6Al4V workpiece using a Mitsui Seiki HPX63 CNC horizontal machining center equipped with four Kennametal cutting tools, each using the KM4X100 spindle connection.

Key design criteria for the HPX63 that allow it to machine titanium include a large work capacity with a swing diameter up to 1,050mm, an available work height (Y-axis) up to 1,050mm, an X-axis stroke of 1,000mm and a 900mm stroke in the Z-axis. The pallet is 630mm. The B-axis rotary table offers 12 rpm with high-torque, high-acceleration availability. Rapid travel rates are 32 m/min. with 0.5G acceleration/deceleration, and the cutting feed rate is 12 m/min.

Made for ultraprecision work, the HPX63’s castings are metallurgically configured for a high level of stiffness, while its box way axis slides are hardened, ground and hand-scraped. Positioning accuracy and repeatability is 0.001mm.

The Mitsui spindle automatically compensates for thermal changes and does not require a warm-up period. The builder offers several spindle options to meet user needs for direct or gear drives and the amount of torque and spindle speed required.

Overall, the ruggedness, rigidity and precision of the HPX63 make it ideal for machining titanium, as well as Inconel, tool steel, stainless steel and aluminum.

The Spindle Connection

A spindle connection that makes the best possible utilization of available machine power by efficiently transferring that power to the tool is key to achieving an optimal titanium machining system. With traditional toolholders, that can be difficult to accomplish in certain applications.

Most toolholders are solid, such as CAT, BT and DV styles. Face-contact versions of those holder styles are also solid. Most spindles used with these toolholders have a relatively low clamping force. This is because with a traditional steep-taper spindle, the drawbar and spindle provide the only force to clamp a tool, and a spring pack pulling that drawbar provides that force.