GB2246739A

GB2246739A - Cutting an aperture in brittle material

Info

Publication number: GB2246739A
Application number: GB9112403A
Authority: GB
Inventors: Michael John Radley Young
Original assignee: S R A DEV Ltd
Current assignee: S R A DEV Ltd
Priority date: 1990-06-08
Filing date: 1991-06-10
Publication date: 1992-02-12
Anticipated expiration: 2011-06-10
Also published as: GB9112403D0; GB2246739B

Abstract

An apparatus for cutting an aperture in a tile or glass sheet comprising a hard pointed tip (11), a piezo electric ceramic transducer (14) adapted to impart ultrasonic vibration to said tip, high frequency generator means (2), low frequency generator means (1) and means (4) selectively to combine the outputs of said high and low frequency generator means. The apparatus is applied to the material at a location generally remote from the edge of said intended aperture, and an ultra-sonic vibration composed of a comparatively high frequency component and a comparatively low frequency component is applied whereby a zone of said material at said location is removed. Then an ultra-sonic vibration composed only of said high frequency component is applied along the edge of the aperture whereby the edge is cut to form the aperture. <IMAGE>

Description

METHOD AND APPARATUS FOR CUTTING AN APERTURE IN BRITTLE MATERIAL The present invention relates to a method and apparatus for cutting an aperture in brittle material, such as a ceramic tile or sheet of glass.

It is known from co-pending published application no. 2218374A to cut brittle materials by means of ultrasonicly induced stress cracking across the brittle material. Cutting by this method is not limited to straight lines, as is usual in cutting tiles, but may be used to cut curved and angled sections from tiles. However, it cannot always be used successfully in cutting an aperture from a tile or other sheet of brittle material. This is because controlled stress cracking achieved by use of the above method removes little or no material along the cutting line.

This makes it difficult to separate a completely enclosed portion of tile or even one enclosed only on three sides if the cut penetrates by a factor greater than twice the width of the cut. The term aperture is intended to cover both enclosed holes and also slots such as described above. Such apertures are often needed when laying tiles or the like around plumbing or electrical fittings.

Prior to the introduction of ultrasonic controlled stress cracking, such an aperture would have been made by sawing or drilling the tile. These processes are slow and dirty, and it is almost impossible to achieve a radiussed curve at the end of an enclosed notch.

It is an object of the present invention to provide an improved method and apparatus for cutting such an aperture in brittle material.

According to one aspect of the present invention, there is provided a method of cutting an aperture in brittle material comprising the steps of removing a portion of said material within the space to be occupied by the aperture and then applying to the material along the edge of said intended aperture, by means of a pointed tool, an ultrasonic vibration to cause stress cracking along said edge whereby the brittle material is broken to form the aperture.

According to another aspect of the present invention, there is provided a method of cutting an aperture in brittle material comprising the steps of applying to the material at a location generally remote from the edge of said intended aperture, via a pointed tool, an ultra-sonic vibration composed of a comparatively high frequency component and a comparatively low frequency component, whereby a zone of said material at said location is removed, and then applying to the material along the edge of said intended aperture, via said tool, an ultra-sonic vibration composed only of said high frequency component, whereby the edge is cut to form the aperture.

The comparatively high frequency component of the ultra-sonic vibration may be in the region of 30 kHz.

Application of the high frequency component alone may induce multiple stress cracking of the material along the edge of the aperture being formed.

The low frequency component may comprise a carrier wave of frequency between 50 Hz and 2 kHz.

Application of this low frequency component may cause material adjacent a stress crack, formed by said high frequency component, to break up and be removable.

According to another aspect of the present invention there is provided an apparatus for carrying out a method as described above, which apparatus comprises a hard pointed tip, a piezo electric ceramic transducer adapted to impart ultrasonic vibration to said tip, high frequency generator means, low frequency generator means and means selectively to combine the outputs of said high and low frequency generator means.

An embodiment of the invention will now be more particularly described by way of example and with reference to the accompanying drawings, in which: Figure 1 is a schematic circuit diagram of the electrical feed to the cutter; Figure 2 shows schematically the method of cutting an aperture in a tile; and Figure 3 shows schematically a cutting tool for use in methods embodying the invention.

Referring now to Figure 1, a low frequency generator 1 and a high frequency generator 2 are fed via a power convertor 3 from mains electricity. The high frequency generator produces a frequency of 30 kHz, which is locked by virtue of a feed back loop. The low frequency generator produces a low frequency carrier wave of between 50 Hz and 2000 Hz.

For the initial stages of cutting, the outputs of both frequency generators are combined in a drive circuit 4, which in turn feeds a power output device 5 and an output circuit 6, the output of which is fed to a piezo electric ceramic transducer in a tool. The vibration of the transducer is transmitted to a pointed tip of the tool.

In order to cut an aperture in a tile or other similar hard brittle material, an initial slot is first cut within the aperture to be cut. Referring to Figure 2, such an initial slot 7 extends the length of the groove to be cut from an edge of the tile to the apex of the rounded end of the groove. A line is drawn with the tip of the tool. The high frequency vibrations induce stress cracking along this line while the low frequency vibrations cause break-up of the material by virtue of a percussive effect. Thus a slot is cut.

The low frequency vibrations are then switched out and a line drawn using the tip of the tool around the periphery of the groove to be cut. The high frequency vibrations induce stress cracking along this line, as may seen at 8 in Figure 2. Since a void has been created along the length of the slot 7, the material separated by the stress crack 8 can be easily removed.

As is known, forming a curved end to the groove is not a problem using high frequency stress cracking.

The method is equally applicable to completely enclosed apertures in the centre of a tile.

A tool for use in the above method is shown in Figure 3. A pointed carbide tip 11 is operatively connected to a horn 14 of the transducer via a copper washer 13. The tip 11 is shaped to be retained in position by a retaining nut 12. The purpose of the washer is to provide a comparatively smooth surface better to transmit the vibration to the comparatively rough carbide tip.

It has been found that the efficiency of the cutting process is greatly enhanced by using a cutting tip of the design shown in Figure 3. The tip shape and method of coupling ensure that a pure longitudinal mode is maintained throughout the oscillatory system; this is necessary in order to generate microcracks during the high frequency cutting phase. It also greatly enhances the effectiveness of the percussive low frequency mode when material is removed from the work piece.

Claims

CLAIMS:

1. A method of cutting an aperture in brittle material comprising the steps of applying to the material at a location generally remote from the edge of said intended aperture, via a pointed tool, an ultra-sonic vibration composed of a comparatively high frequency component and a comparatively low frequency component, whereby a zone of said material at said location is removed, and then applying to the material along the edge of said intended aperture, via said tool, an ultra-sonic vibration composed only of said high frequency component, whereby the edge is cut to form the aperture.

2. A method as claimed in claim 1, wherein the comparatively high frequency component of the ultra-sonic vibration is in the region of 30 kHz.

3. A method as claimed in either claim 1 or claim 2, wherein the low frequency component comprises a carrier wave of frequency between 50 Hz and 2 kHz.

4. A method of cutting an aperture in brittle material substantially as described herein with reference to the accompanying drawings.

5. A method of cutting an aperture in brittle material comprising the steps of removing a portion of said material within the space to be occupied by the aperture and then applying to the material along the edge of the intended aperture, by means of a pointed tool, an ultra-sonic vibration to cause stress cracking along said edge whereby the brittle material is broken to form the aperture.

6. An apparatus for carrying out a method as claimed in any one of the preceding claims, which apparatus comprises a hard pointed tip, a piezo electric ceramic transducer adapted to impart ultrasonic vibration to said tip, high frequency generator means, low frequency generator means and means selectively to combine the outputs of said high and low frequency generator means.

7. An apparatus as claimed in claim 6, wherein said hard tip comprises a pointed carbide tip.

8. An apparatus as claimed in either claim 6 or claim 7, wherein the tip is connected operatively to the transducer via a copper washer.

9. An apparatus substantially as described herein with reference to the accompanying drawings.