For US machine builder Fives Cincinnati, Kennametal’s KM4XTM spindle connection is critical to achieving new levels of metal removal on its industry-leading “super-profilers”.

What does production superiority mean to aircraft manufacturers? In a word: billions. In the land of the giants, US-based Boeing beat European rival Airbus in net new orders and deliveries in the first quarter of 2015. While the first quarter is the traditionally slow quarter for new orders, it’s deliveries that generate the most revenue, and Boeing handed over a record number of jets for the period. For manufacturers of all sizes and types of aircraft, and their entire supply chain of components and parts suppliers working in difficult-to-machine materials, production delays can mean order cancellations, and cancellations can mean shifts to better-equipped builders.

One technology provider that knows this better than most is Fives Cincinnati, whose plant in Hebron, Kentucky, produces Cincinnati machining centres, composites fibre-placement systems, and multi-spindle Cincinnati profilers. Fives Cincinnati is recognised as a preeminent provider of manufacturing solutions in key industrial markets including aerospace, automotive and truck, heavy equipment, oil and gas, rail, wind energy and general machining. With manufacturing and support operations strategically located worldwide, Fives Cincinnati and its metal cutting and composites businesses offer comprehensive lines of equipment and technologies, including automated assembly, laser-welding and cutting, turning, milling, composites-processing and software, along with associated support and services (maintenance, spare parts, retrofit, overhauling and upgrading).

With more than 650 profilers in the field all over the world, the company claims there isn’t a commercial aircraft flying that hasn’t been touched by one of its Cincinnati profilers. Available in three- and five-spindle gantry configurations, the latest-generation of these powerful giants, the Cincinnati XTi Profiler, is designed for manufacturers that process multiple materials, with 7,000rpm spindles that can cut aluminium and steel, and high-torque (2523Nm) spindles available for processing titanium and other hard alloys.

Described as “the only multi-spindle platform available for titanium roughing”, company literature states that the XT sets the metal removal rate (MRR) record for machining titanium, at more than 100 cubic inches per minute. These massive machines, with 4,267mm of X-axis travel (expandable in increments of 3,658mm), 3,683mm in Y, and 711mm in Z, now are setting new records with optional KM4X100 spindle connections from Kennametal.

From weakest link to strongest feature

Whether profiling on large gantry machines or milling on smaller machining centres, processing tough material like titanium is a constant challenge. Machining hard alloys while adding the pressure of improving production efficiencies means maximising metal removal in the face of low cutting speeds and significant cutting forces. Machine tool builders like Fives Cincinnati have responded with specialty milling and profiling centres that feature improved stiffness and damping on spindles and sizable machine structures, all to minimise undesirable vibrations that deteriorate part quality, throughput, and tool life. Although these advances have added to greater productivity, the weakest point historically has been the spindle connection.

The tool-spindle connection, the “handshake” between the machine tool and the cutting tool, determines how much material the machine can remove on a given operation. This is because this interface must withstand high loads and yet maintain its rigidity until tool deflection is too high or the onset of chatter is reached. Spindles 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.

This becomes obvious in end-milling applications, where projection lengths are typically greater – the limiting factor is the spindle interface’s bending capacity. As an example, an indexable helical cutter with 250mm projection from spindle face, 80mm in diameter, generates 4620Nm of bending moment and less than 900Nm of torque when removing 360 cubic metres/min of Ti6Al4V at radial depth of cut (RDOC) of 12.7mm and an axial depth of cut (ADOC) of 63.5mm.

By combining high clamping force and optimised interference levels, Kennametal’s next-generation spindle connection KM4X provides a robust connection, extremely high stiffness, and bending load capacity. For titanium processors, this means greatly improved performance in machining high-strength alloys and other materials, enabling extremely high metal removal rates and more completed parts per day.

Adding to machine design

Together with Kennametal Senior Account Manager Mike Malott, Fives Cincinnati Applications Engineer Robert Snodgrass began evaluating KM4X approximately four years ago.

“The engineering is impressive,” he says. “It definitely allowed us to start thinking that there’s more to machine design, that a stiffer spindle helps meet customer demand for more effective metal cutting and increased throughput.”

“Remember, typical aero-structure components start out as forgings with much of the material being removed to achieve finished part specifications,” says Kennametal Vice-President Mark Huston. “The ‘buy-to-fly’ ratio – the weight you buy in raw material vs. the weight that flies in finished form can be 4:1, 8:1 or more depending on the component.”

First-generation Cincinnati profilers achieved an MRR of four cubic inches per minute in titanium, due to machine structure and tool-spindle connection limitations. With the XT-generation of Cincinnati profilers and face-contact HSK125 spindle connections, the MRR increased to 50 cubic inches per minute. With the KM4X100, the MRR doubled to 100 cubic inches per minute.

“Even at 100 cubic inches per minute, our benchmark testing for the XT profilers using the KM4X were well below the machine’s theoretical limits for bending moment resistance,” Snodgrass adds. He noted that previous-generation tests employed large CAT60-taper toolholders that, when compared to 50-taper versions, are like driving a tank versus an SUV. The KM4X achieved double the MRR versus the 60-taper toolholder. Compared with CAT50, HSK100 or KM4X100, the CAT60 is almost twice the weight.

“This changes spindle and machine design a ton,” says Ken Wichman, Fives Cincinnati Product Manager. “Many gantry machines have manual tool exchange even though automatic tool exchange/storage is available. The enhanced bending moment resistance of the KM4X allows lighter tooling when compared to a CAT or HSK tool with an equivalent bending moment resistance. Ergonomically, this is a huge benefit to the operator. For customers choosing automatic tool exchange/storage, the smaller KM4X can accommodate more tools in a given footprint.”

“We pride ourselves in keeping customers productive,” adds Fives Cincinnati Vice-President Mark Logan. “Not only is a more powerful spindle connection like KM4X changing new machine design, it also can be a significant boost for existing machines in the field. This gives us the chance to offer a notable upgrade in retrofits while still pushing the limits on profiler models to come.”

“The industry needs to set new standards for producing titanium parts at the lowest cost per piece, and the XT Profiler provides that capability and more,” says Chip Storie, Fives Cincinnati Executive Vice-President. “With a massive cross-rail, robust spindle design, dedicated foundation, and high-pressure coolant system, we expect to exceed 100 cubic inches per minute metal removal. This is going to change the way the industry approaches titanium machining.”