Strong Spindle Connections: The Key to Machining Titanium

WHY BENDING CAPACITY IS IMPORTANT
As mentioned earlier, when machining tough materials like titanium, cutting speeds are relatively low due to thermal effects on cutting tools. In response, machine tool builders have improved stiffness and damping on spindles and machine structures over the years. Spindles have been designed with abundant torque at low rotational speeds.

The spindle connection must provide torque and bending capacity compatible with machine-tool specifications and the requirements for higher productivity. It becomes obvious in end-milling applications, where projection lengths are typically greater, the limiting factor is spindle interface’s bending capacity. As an example, an indexable helical cutter with 25 mm (9.84 in) projection from spindle face, 80 mm (3.15 in) in diameter generates 4620 Nm (3407.5 ft. lbs.) of bending moment and less than 900 Nm (663.8 ft-lb) of torque.

The most critical parameters of a taper-face spindle connection are the clamping force and radial interference.  Maximizing clamping force and selecting appropriate values of interference can further improve connection rigidity.

SO WHAT IS RIGHT FOR YOU?
The response to this traditionally weak point has been with the proven KM^™ quick-change system; now we are introducing the next-generation KM4X™. Some systems may be able to transmit considerable amount of torque, but cutting forces also generate bending moments that will exceed the interface’s limits before torque limits are exceeded. The combination of the KM4X^™ system’s high clamping force and interference level lead to a robust connection and extremely high stiffness and bending capacity for greatly improved performance in titanium machining.  KM4X™ overcomes the limitation on bending capacity present in other connections, allowing maximum available spindle power and torque to be utilized in critical operations like milling of high-strength materials.

Manufacturers have several spindle interface choices when making a machine tool investment. With more materials that are tougher to machine and require considerably higher cutting forces, choosing wisely to achieve and maximize cutting-edge performance is a must. Rules and recommendations are by nature general.

Kennametal delivers productivity to customers seeking peak performance in demanding environments by providing innovative custom and standard wear-resistant solutions. This proven productivity is enabled through our advanced materials sciences and application knowledge. Our commitment to a sustainable environment provides additional value to our customers. Companies operating in everything from airframes to coal mining, from engines to oil wells and from turbochargers to construction recognize the company for extraordinary contributions to their value chains.

In fiscal year 2011, customers bought approximately $2.4 billion of Kennametal products and services – delivered by approximately 11,000 talented employees doing business in more than 60 countries – with more than 50 percent of these revenues coming from outside North America. www.kennametal.com

This article originally appeared in the SME Aerospace & Defense Yearbook 2011; the Society of Manufacturing Engineers (Dearborn, MI). www.sme.org