A hydraulically driven high-speed spindle system for milling, machining, facing, drilling, and joining metallic and nonmetallic materials has been developed. Spindles are the most critical elements of high-speed milling machines. The keys to successful design of high-speed spindles are strength, rigidity, and balance.

The hydraulically driven spindle includes a hydraulically driven gearmotor. The rotation of the motor is transmitted to the main shaft of the spindle. The main shaft supports a fixture that holds the tool to effect the desired operation. The main shaft is supported by a series of bearings that withstand axial and radial loads encountered during use. The pressure and flow rate can be adjusted manually or controlled by a computer. This system includes a hydraulic subsystem that supplies pressurized fluid to drive the spindle.

Pressurized fluid is fed into the hydraulically driven spindle for machining, milling, drilling, tapping, facing, and joining. Hydraulic fluid volumetric flow rate, fluid pressure, gear size, and geometry of the hydraulic motor are variables which govern spindle torque and rotational speed, ranging from 5,000 to 6,000 rpm and operating at 1,000- to 6,000-psi (6.9- to 4-MPa) pressures.

The bearing system for this hydraulically driven spindle can be made of recently developed fluid bearings or of roller element type bearings. The balls in the bearings in this system can be made of standard steel or of newly-developed ceramics for increased rigidity, accuracy, and longer life. Bearings that are designed for use at lower speeds with air/oil or air/mist lubrication can be used at higher speeds, provided they are lubricated with grease.

High-speed machining allows for the production of thin wall sections with minimal deformation. High-speed machining can make it possible to reduce the number of parts, sometimes even making it possible to fabricate, as unitary parts, objects that would ordinarily have to be assembled from multiple pieces. Therefore, production and assembly times are reduced.

For the purpose of fabricating complex and thin-walled parts, high-speed machining of solid stock can be an alternative to casting and to the more expensive use of composite materials. Use of this hydraulically driven spindle system for high-speed machining reduces times and cost of the manufacturing process and helps to ensure defect-free finished parts.

Another significant advantage of high-speed machining is minimization of effects of heat on machined parts. Most of the cutting heat is removed, reducing thermal warping and increasing the life of the cutting tool. In many cases, the need for a cooling fluid is eliminated. Also, elimination of cutting fluids reduces subsequent contributions to pollution and aids in the recovery and recycling of such expensive materials as aluminum-lithium alloys.

This work was done by Majid K. Babai and Samuel C. Geise of Marshall Space Flight Center.

Inquiries concerning rights for the commercial use of this invention should be addressed to

the Patent Counsel
Marshall Space Flight Center; (205) 544-0021

Refer to MFS-26430.

Motion Control Tech Briefs Magazine

This article first appeared in the June, 1998 issue of Motion Control Tech Briefs Magazine.

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