Temperature control of a high-performance spindle: For the team developing a more effective spindle, one of the design challenges was an unexpected source of heat

Modern Machine Shop, Dec, 2001 by Jack McCabe

Aesop Inc.

Ford Motor Company

General Motors Corporation

Giddings & Lewis

Manufacturing Laboratories, Inc.

ORSCO, Inc.

PCC Olofsson

SETCO Sales Company

The Torrington Company

Spindle Research: Toward A Predictive Model

The project under which the 75-hp spindle was developed has a broader range than this. Overall, the project focused on advancing spindle technology in three application areas:

* High-torque spindles on roller bearings for roughing operations in production,

* Mid-market spindles on hybridceramic bearings for general-purpose machine tools, and

* Clustered spindles on hydrostatic bearings for generating precision hole patterns at automotive production rates.

While thermal considerations were the first hurdle on the way to improving spindle technology, chatter is the final hurdle. The essential question posed by spindle users is Will this spindle take the cuts I need to make within tolerances and without overheating, stalling or chattering?

Current technology can answer only part of this question without resorting to cutting tests. Rotor dynamics analysis can predict the tolerance a spindle can hold, but only if chatter is not involved. And thanks to developments from the spindle project, finite element analysis can predict overheating and stalling.

But no analysis exists that can accurately predict chatter. The spindle must be built so the fundamental dynamic characteristics can be measured. And depending on how important friction damping is, data from an "identical" spindle from the same manufacturer may not be adequate. (Why this is so is addressed in a paper by the author, "Two Spindles for High-Velocity Machine Tools," submitted for publication in the Society of Manufacturing Engineers 'Journal of Manufacturing Systems.)

The inability to predict this friction damping is the fundamental obstacle. It arises from relative motion at interfaces whose properties may change with tolerances, temperature and time, and the chatter thresh-hold is sensitive to the changes. Quantifying the damping for a spindle model appears to be the only remaining problem to solve before a complete spindle analysis code can be written.

Details of the design, manufacturing, and testing of prototype spindles are given in a 210-page technical report, An Evaluation of the Design and Performance of Three Advanced Spindles, available from NCMS. Visit www.ncms.org or contact Cindi Bousley at (734) 995-3075 or cindib@ncms.org.

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