CA1066494A

CA1066494A - Collet

Info

Publication number: CA1066494A
Application number: CA282,373A
Authority: CA
Inventors: Arnold Klink
Original assignee: Carl Freudenberg KG
Current assignee: Carl Freudenberg KG
Priority date: 1976-07-10
Filing date: 1977-07-08
Publication date: 1979-11-20
Also published as: SE417581B; JPS537889A; NL7704721A; FR2361185A1; SE7707882L; DE7621839U1; FR2361185B1; CH616099A5; GB1576284A

Abstract

ABSTRACT OF THE DISCLOSURE

Collets for handling and clamping workpieces having a circularly profiled clamping surface are described. Each collet consists of a chuck with clamping fingers forming a generally circular clamping surface which is moved into operative engagement with the surface of the article to be clamped. One or more grooves are provided in the clamping fingers in which elastomeric rings are received and in which the rings protrude from the grooves beyond the clamping surface. The elastomeric rings may be toroidal O-rings and the grooves be provided with bottoms having a rectangular section. Collets engageable with the respective articles by either outward or inward movement of the clamping surface are described.

Description

~066494 The present invention relates to a conically clamping collet for the mechanical handling of workpieces with a circular profiled clamping surface.
- Automatic lathes or milling machines for the machining of solid cyllndrical parts, for various reasons,are frequently fitted with special chucks which are adapted to the particular workpiece concerned. Collets which are driven hydraulically, pneumatically or electrically and are opened and closed by the axial movement of a conical bushing are widely used. Por the proper operatlon of such collets it is important for 10` their clamping surfaces to present a circular clamping profile in the closed state.
This requirement leads to difficultles,in that workpieces with diameters which may deviate from the norm will not be uniformly clamped over their entire circumference,and pressure against the workpiece becomes concentrated at a few clamping points. In order to remedy this to a certain extent, collets having six or nine finger chucks are used, departing from the usual three-member chuck. However, the basic diffi-culty described above, cannot be overcome in this way.
Another disadvantage of such collets has now become evident in the machlnlng of delicate artlcles such as deep-drawn sheet metal parts.
When such parts do not meet the correct tolerances of roundness in the deep-drawlng process, subsequent machlning is necessary. The parts have to be clamped in a collet to effect this. In doing 80, however, elastic alteration of the profile occurs in adaptlng to the cylindrical clamplng surface of the collet. In consequence, notwithstanding the machining, the flnlshed parts show considerable departures from the ideally round profile upon removal from the machine.
The present disclosure meets the problems presented by the prior art and enables the construction of a reliable accurately clamping collet which 18 simple in operation.
More particularly in accordance with the invention there is ~h provided, a collet for articles having a generally circular surface to be clamped, comprising, a chuck, clamping fingers to said chuck providing a generally circular clamping surface for operatively clamping 6aid article surface, means for ving said fingers for clamping said article surface, a circumferentially disposed groove in said chuck formed in sait fingers, an elastomeric ring received in said groove, said groove being formed with a depth less than the thickne6s of said elastomeric ring, said ring thereby being enabled for protruding out of said groove beyond said clamping surface of said fingers. At least a pair of grooves may be provided in the clamping surface of the chuck, each with its elastomeric ring. Preferably, the elastomeric rings are toroidal 0-rings and the bottom of each groove has 8 rectangular cross section.
Specific embodiments of the invention will now be described having reference to the accompanying drawings in which;
Figure 1 shows,partially in section, an externally clamping collet with a six-finger chuck; and Figure 2 shows, also partly in section, an internally clamping collet.
The collet of Figure 1 comprises basically a tapered chuck 1, with six fingers 6 cooperating tapered clamp ring 2 and adJustlng ring 3.
The design of the chuck is not restricted to a six-finger form; and a three-, nine- or more-finger embodiment may be chosen instead, if desired.
The chuck has grooves 4 in the clamping surfaces of the fingers 6,the bottoms of which preferably have a rectangular profile and the depths of which are less than the diameter of 0-rings 5 therein received.
In general, in order to obtain a satisfactory seat for the work-pieces to be clamped, it is sufficient for the 0-ringg to protrude above the clamping surface by about 0.5mm in the unloaded state. This figure, however, ~066494 should only be taken as a guideline, and may be greater or less, depending on the specific properties of the pieces to be held and on the clamping diameter. The best protrusion for the particular circumstance can, if necessary, be determined by simple testing, and offers no difficulty to the man skilled in the art.
The axial positioning of the 0-rings relative to the chuck will not be described in detail since this i8 detèrmined directly from the form of the workpiece to be clamped, and is merely arranged so that the clamping is effective.
Figure 2 shows an embodiment of the new collet, which is intended for internal clamping of suitable workpieces. It functions similarly to the device in Figure 1, but the clamping surface is formed by the outer diameter of chuck 10. Chuck 10 is operated by the axial displacement of tapered shank 12, which is in direct sliding contact with the conical inside face of the chuck. The chuck 10 is retained in axial position by engaging sleeve 13. As in the previous embodiment, here again the chuck may have three-, 8iX-, nine- or more-fingers.
The arrangement and function of grooves 14, which receive 0-rings is similar to that of Figure 1. Here, however, it must be kept in mind that the protrusion of the 0-rings above the clamping surface in the unloaded state should be greater than in the case of the outside-clamping chuck of Figure 1, since,unlike the compression occurring there during the clamping process, there is a stretching of the rings with consequent decrease of their thickness diameter.
Basic advantages of the new collets are that the clamped work-pieces are held in an extremely reliable way while avoiding any undesired deformations or damage, and especially important, is that a circumfer-entially symmetrical clamping is assured even with workpieces whose profile is not exactly circular.

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE PROPERTY
OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A collet for articles having a generally circular surface to be clamped, comprising, a chuck, clamping fingers to said chuck providing a generally circular clamping surface for operatively clamping said article surface, means for moving said fingers for clamping said article surface, a circumferentially disposed groove in said chuck formed in said fingers, an elastomeric ring received in said groove, said groove being formed with a depth less than the thickness of said elastomeric ring, said ring thereby being enabled for protruding out of said groove beyond said clamping surface of said fingers.

2. A collet as defined in claim 1, the chuck having at least a pair of said grooves formed in said fingers displaced from one another axially of said circular clamping surface of said chuck.

3. A collet as defined in claim 1 or 2, said groove having a bottom of rectangular section, said elastomeric ring being a toroidal O-ring.