Fundamentals of high-speed spindle design

The needed components can be selected including bearings, shaft design, motor, lubrication system, tooling style, drawbar system, housing and cooling system. As we have seen, bearings will impact a spindle design to the greatest degree. High speed spindle designs most often run bearings systems up to the limit, in order to be the most productive. And, as integral motors are limited in maximum torque available, higher speeds will yield higher power. To reach these speeds, and maintain a reasonable life, precision bearings must be used, along with complex bearing lubrication systems. Oil jet or mist systems not only boost the speed of the bearings, they also provide cooling and cleaning functions as well. Maintenance is critical to the performance of precision bearing systems. Positive over-pressure and labyrinth air seals also should be used to protect the bearing environment.

 

In addition to the bearings, the spindle shaft design must be capable of providing a strong motor, suitable tooling retention system, and stiffness without developing bending problems. And, all rotating components must operate in a balanced condition.

 

The spindle housing must support and locate the bearings accurately, and provide the utilities needed by the spindle system. It must be robust and stiff, as the housing transfers all forces from the spindle to the machine tool.

 

In general, a high speed spindle design will be the result of many compromises. Bearing size and type will dictate maximum speeds possible. Increasing pre-loads and additional tandem bearings will increase stiffness, but speed will be sacrificed High power motors will not fit into the design envelope, and more complex drive systems are required. Higher speeds require higher precision tooling systems, better balance, and cleanliness to obtain the desired results. Shop discipline must be strict. Operators should be well trained and encouraged to learn more about the machine tool.

 

The ultimate spindle would have the following characteristics: Unlimited Speed, High Power, Long Life, Self-Balancing and Self-Diagnostic.

 

As unattainable as these qualities may sound, they will be fulfilled in the future. High speeds can be accomplished through the use of magnetic or fluid bearings. These non-contact bearing systems will exhibit no mechanical wear, so their life will be very long. Electronic sensors will monitor all aspects of the spindle operation, including cutting loads. Imbalance can be compensated for as the spindle runs. Diagnostic information can be relayed to the CNC for action. Superconducting materials and new motor technologies will provide compact, high power motor system's that produce little heat. Thermal affects on the spindle shaft can be compensated for electronically.