GB2195275A

GB2195275A - Saw head

Info

Publication number: GB2195275A
Application number: GB08722391A
Authority: GB
Inventors: Hubert Hinzen
Original assignee: GMN Georg Mueller Nuernberg AG
Current assignee: GMN Georg Mueller Nuernberg AG
Priority date: 1986-09-25
Filing date: 1987-09-23
Publication date: 1988-04-07
Anticipated expiration: 2007-09-23
Also published as: GB8722391D0; IT1230696B; CH673098A5; FR2604380B1; DE3632557A1; JPS6389270A; KR880003692A; DE3632557C2; FR2604380A1; IT8721866A0; GB2195275B

Abstract

A saw head for saws with internal holes includes a rotatable disc-shaped base member (11) with an upper and a lower clamping ring mounted thereon, the saw blade (1) being secured between the two clamping rings. The lower clamping ring (6) rests on the disc shaped base member (11) via an intermediate ring (7), the clamping ring (6), intermediate ring (7) and base member (11) being joined together by means of adjustable bolts (8). Spacers are provided between the clamping ring (6) and the intermediate ring (7) consisting of springs 9, preferably disc springs, or sleeves (12) of plastically deformable material. <IMAGE>

Description

SPECIFICATION Saw head Saws with an internal hole are used extensively to cut rod-shaped semifinished products into disc-shaped workpieces. A particularly preferred field of application for saws with an internal hole of this kind is the cutting up of base semiconductor material, since saws with an internal hole make it possible to use very thin saw blades and thereby keep the machining losses to a minimum, while on the other hand, saws with an internal hole make it possible to achieve good surface qualities in the disc-shaped workpieces ("wafers") which are sawn off. Saws of this kind are used to machine all the semiconductor materials currently in use. Examples of these include silicon, gallium arsenide and germanium. The materials in question are generally known. Saws with an internal hole are also currently used for machining other materials.

The saw head of an internal-hole saw consists of a rotating disc-shaped base member on which are mounted a lower clamping ring and an upper clamping ring, the saw blade being secured between these two clamping rings. The clamping of the saw blade is carried out, according to the prior art, by mechanical or hydraulic means, the very thin saw blade being tensioned beyond its elastic limit in order to give the saw blade the required rigidity and make it possible to conduct away the forces occurring at the cutting edge. In the saw heads known hitherto, however, there is the disadvantage that during the clamping action deformation occurs in the clamping rings which in turn causes the originally flat saw blade to become warped in an undulating configuration in the circmferential direction.The resulting out of true of a saw blade may be in the region of 0.1 mm, on the outer edge of a large saw, and a saw blade out of true of this order will considerably affect the quality of the sawing operation. Furthermore, this defect of the saw heads used hitherto is not remedied by making the surrounding structure any more rigid.

According to the invention there is provided a saw head for saws with internal holes, including a rotatable disc-shaped base member with an upper and a lower clamping ring mounted thereon, the saw blade being secured between the two clamping rings, the lower clamping ring resting on the disc-shaped base member via individually actuatable adjustment devices uniformly distributed around the circumference of the lower clamping ring.

With individually adjustable positioning devices it is possible to achieve fine adjustment of the saw blade with a view to optimising its flat condition.

The invention is hereinafter explained in detail with reference to the accompanying drawings, wherein: Figure 1 shows a saw head according to the prior art; and Figure 2 shows an exemplary embodiment of a saw head according to the invention.

In the saw head according to the prior art shown in Fig. 1, a saw blade in the form of a thin, circular high-strength metal sheet 1 is clamped like a drum skin between the lower clamping ring 10 and the upper clamping ring 13 and is then tensioned.

The saw blade tensioned in this way has in its centre a concentric hole the inner edge of which is provided with a diamond covering 2 which acts as a cutting edge. The saw blade with its internal hole rotates about the central spindle 3. The bar 4 which is to be cut up is inserted into the hole in the axial direction.

Relative movement then takes place between the bar and the cutting edge until the discshaped disc 5 or wafer has been severed.

With this known method of clamping the saw blade in the saw head, deformation occurs within the clamping rings which results in warping of the originally flat saw blade in the circumferential direction.

In the embodiment of the present invention illustrated in Fig. 2, the lower clamping ring 10 is replaced by a clamping ring 6 and another intermediate ring 7. The intermediate ring 7 may be formed integrally with the discshaped base member 11 or attached thereto.

According to the embodiment of the invention illustrated in Fig. 2, the intermediate ring 7 is pierced by bolt holes and the clamping ring 6 has threaded holes by means of which the clamping ring 6 and intermediate ring 7 can be joined together by means of a plurality of bolts 8. Around the bolts or between the individual bolts are provided springs 9 which maintain the clamping ring 6 and the intermediate ring 7 at the distance from one another prescribed by the bolt setting. The springs used are preferably disc springs on account of the high forces occurring. However, it is also possible to use, instead of these springs, sleeves provided around the individual bolts 8 or between them, consisting of a material which undergoes plastic deformation when the bolts are tightened.

The spacing between the clamping ring 6 and clamping ring 7 is varied by turning the bolts 8. If springs are used the bolts 8 will not be loosened, within certain limits determined by the spring characteristics, since they are stressed by the springs 9. As already mentioned, it is also possible to use deformable sleeves 12. As a rule, the elastic resilience of the sleeve will not be sufficient, which means that plastic deformation of the sleeves 12 by the screw 8 is required. The sleeves preferably consist of non-ferrous metal.

If sleeves are used the parts 6 and 7 may be tightened simply by tightening the bolt 8; if the bolt 8 is unscrewed this would result is loosening of the connection.

If the saw blade 1 has an undulating out of true in the circumferential direction, this may be counteracted by varying the setting of the bolts. In the region where the out of true of the saw blade is at its maximum the bolts 8 have to be tightened more. The use of springs also offers the possibility of adjusting the bolts in the opposite direction where the out of true of the saw blade is at its minimum. By repeating the processes of "measuring the out of true of the saw blade" and "correcting the out of true of the saw blade" several times, the out of true can be reduced to a few microns. Care must be taken to ensure, by suitable design of the rigidity of the rings 6 and 7, that a particular degree of adjustment in the axial direction achieved by turning the bolt will also result in the desired correction of the out of true of the saw blade.

Claims

1. Saw head for saws with internal holes, including a rotatable disc-shaped base member with an upper and a lower clamping ring mounted thereon, the saw blade being secured between the two clamping rings, the lower clamping ring resting on the disc-shaped base member via individually actuatable adjustment devices uniformly distributed around the circumference of the lower clamping ring.

2. Saw head as claimed in claim 1 wherein the lower clamping ring rests on the disc shaped base member via an intermediate ring, the clamping ring, intermediate ring and base member being joined together by means of bolts, whilst spacers are provided between the clamping ring and the intermediate ring.

3. Saw head as claimed in claim 2 wherein the spacers consist of springs, preferably disc springs.

4. Saw head as claimed in claim 2 wherein the spacers consist of sleeves of plastically deformable material.

5. Saw head as claimed in any of claims 1 to 4 wherein the spacing between the individually actuatable adjustment devices is approximately equal and is between 5 and 15 cm.

6. Saw head substantially as herein described with reference to Fig. 2 of the accompanying drawings.