Gear cutting – milling – or planing – Milling – With means to dampen vibration
Reexamination Certificate
1999-09-23
2001-08-28
Howell, Daniel W. (Department: 3722)
Gear cutting, milling, or planing
Milling
With means to dampen vibration
C279S052000, C408S143000, C408S23900A, C409S234000
Reexamination Certificate
active
06280126
ABSTRACT:
The present invention relates to tool holders used in machine tool spindles and the like, being more particularly concerned with the problems arising from the vibration and chatter of such tools in operation as they are held in their holder at their inner ends, where the tool is held at one region by a rigid clamping action.
BACKGROUND
Machine tool spindles use tool holders, such as HSK or CAT type tool holders, to allow for the facile and automatic changing of tools. The tool holders accommodate different size tools through the use of inserts or collets, and they rigidly clamp a tool at its inner end (shank) so that the dominant compliance is the cantilevered tool itself. Long tools, particularly, are prone to vibration and chatter, and their holders provide little damping. Some inserts use hydraulic fluid to create pressure on a membrane which squeezes the tool (a typical unit is sold under the name HydroLock), but then fluid film gaps are large, and the pressure is isostatic, and the clamping/damping is applied at one point only, so bending moments are poorly resisted/damped.
OBJECT OF THE INVENTION
A principal object of this invention, accordingly, is to provide a new and improved modular damped tool holder and holding method that will not only grip the tool rigidly at its inner region, but will also provide support at an adjacent annular region with a damping structure that imparts good stiffness and damping for the tool, as well.
A further objective is to enable the tuning of the relative tool length and diameter to the damping region length and diameter and damping coefficient, readily to optimize the damping and stiffness.
Another objective of the invention is to provide such a novel structure that can accommodate as a damper structure, a surface self-compensated hydrostatic bearing damping structure, a passive fluid filled cavity with non-circumferential leakage seals to act as the damping structure, or a viscoelastic or other damping material around the toolshank to act as the damping structure, or the like, and in a modular construction that can be easily used with standard tool holders.
Other and further objectives will be pointed out hereafter and are more particularly delineated in the appended claims.
SUMMARY
In summary, the invention embraces a damped tool holder system having, in combination, a longitudinally extending cylindrical tool provided with a forward outer cutting or operating end and a rearward inner end which is to be held within a tool holder; a coaxial tool holder receiving the inner end of the tool; a rigid mechanical support connection between the tool and the tool holder at a fist region thereof; and a second annular support connection between the tool and the tool holder at a second region thereof spaced from but adjacent the first region and effected by a vibration damping annular film structure disposed therebetween at said second region.
Specifically, the tool is held rigidly at its inner end region in the holder, as by a shrink-fit or press-fit, and it is supported at another spaced but adjacent region by a damping structure, which also provides for centering of the tool with a high spring rate, while achieving a large degree of damping of the vibration and the chatter of the tool in use. To make the system modular, a standard tool holder can be used, and a sleeve can be shrunk over the tool to maximize the diameter of the effective damping region. The sleeve is then rigidly held at one end within a solid collet, and an annulus of damping structure provides support in the region between the other end of the sleeve and the solid collet. The solid collet, in turn, is anchored into the standard tool holder, in a manner similar to a standard slit collet. Damping structure embodiments in the region adjacent to the damped inner end of the tool may include the use of a hydrostatic bearing, a passive fluid-filled squeeze film zone, a viscoelastic material or an otherwise lossy material. The principle is also applied to a damped toolholder where the tool is also clamped in the toolholder at two or more spaced but adjacent regions to damp moment loads applied to the tool.
To effectuate the above, the effective shank diameter of the tool, in the preferred embodiments, is increased to a standard size using a sleeve that can be shrunk fit or pressed over the tool shank, or the shank of the tool may be monolithically increased to a standard size. The sleeve then fits into the cylindrical bore of a tapered sleeve collet (without the slits), and is help clamped at the inner end, typically by such shrink or press fit, and with a small clearance left between the sleeve and the inside of the solid collet. In this small clearance region adjacent to the clamped end region, a damping structure, such as a cylindrical surface self-compensated hydrostatic bearing, or a sealed passive fluid film annulus, or a viscoelastic or other lossy material annulus, as before mentioned, acts to provide stiffness and damping to the sleeve with respect to the solid collet. The collet itself is rigidly held in the standard toolholder by a nut that clamps it in place.
In the case where the damping structure is a hydrostatic bearing, as is later-explained in
FIG. 1
, fluid for the hydrostatic bearing may be introduced by a fluid commutator; or, more typically, by the same system that is commonly used to supply high pressure cutting fluid to the center of the tool (through-tool cooling). A hold supplied in the through-tool cooling supply, as later more fully explained in connection with hereafter described
FIGS. 1-4
, will bleed off some of the coolant to the surface self-compensated hydrostatic bearing, and exit fluid from the bearing is then either collected and channeled back into the tool, or it may flow out the front of the tool holder to wash over the part being machined. For the case of a modular toolholder that allows the tool to be easily changed, screws may force fluid into two distinct zones (as later explained in connection with the embodiment of hereinafter described
FIG. 14
) acting as a force couple to dampen bending moment vibrations applied to the tool by squeeze film mechanisms.
Preferred and best mode embodiments and designs are later described in detail.
REFERENCES:
patent: 3364800 (1968-01-01), Benjamin et al
patent: 4320999 (1982-03-01), Briese
patent: 4705439 (1987-11-01), Hoyle et al.
patent: 5378091 (1995-01-01), Nakamura
patent: 5405220 (1995-04-01), Ishikawa
patent: 5462293 (1995-10-01), Samelius et al.
patent: 5649714 (1997-07-01), Uchida et al.
patent: 5674032 (1997-10-01), Slocum et al.
Slocum Alexander H.
Wasson Kevin
AESOP, Inc.
Howell Daniel W.
Rines and Rines
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