WO2013076400A1

WO2013076400A1 - Metal wire for saw

Info

Publication number: WO2013076400A1
Application number: PCT/FR2012/052598
Authority: WO
Inventors: Jean-Bernard PELLETIER
Original assignee: Sodetal
Priority date: 2011-11-24
Filing date: 2012-11-12
Publication date: 2013-05-30
Also published as: FR2983099B1; FR2983099A1

Abstract

The invention relates to a metal wire for a saw, said wire having a non-circular cross-section and being twisted about itself, thereby defining a helix having a pitch of between 3 and 10 millimetres.

Description

METAL WIRE FOR SAW

FIELD OF THE INVENTION The present invention relates to the field of cutting high hardness materials, and more particularly cutting silicon blocks, but also germanium, sapphire, and generally all hard materials.

It is more particularly a saw wire for ensuring such a cutting, both by cutting speed, the quality of the cut (silicon is an expensive material, it should be able to optimize the cuts, while limiting losses of noble material), and also having a relatively long life. BACKGROUND

The implementation of metal cutting son is now widely used in the context of the cutting of silicon ingots, and generally semiconductor materials, crystals, ceramic materials, etc. Such saw threads are traditionally made of a metal monofilament placed in contact with the block or the silicon ingot or the material to be cut, and being moved in contact with this block or this ingot continuously or alternatively, while by exerting traction against said block, to ensure the effectiveness of the action of the wire and corollary its cutting.

Such a cutting wire is generally associated, during the actual cutting phase, with a powder of abrasive material and oil and / or glycol, said abrasive particles being driven by the wire and applied against the ingot or cutting block, in order to optimize the cutting itself. Such an abrasive material is generally applied to the outer surface of the wire just before the wire comes into contact with the cutting area. The effectiveness of the cutting depends on a certain number of parameters, among which, of course, the characteristics of the material to be cut, but also the speed of translation of the wire which acts continuously or alternatively, in addition to importantly, the ability of the wire to drive the particles of the abrasive material, and bringing them into contact with said block to be cut.

For this purpose, it has been proposed to adhere said abrasive particles to the outer surface of the wire by various techniques. The first of them is to implement relatively soft metal son, said metal particles being depressed, and somehow crimped to the surface of fil, to ensure this pre-adhesion. However, experience has shown that the yarns thus obtained are of reduced efficiency since, during the sawing step, the abrasive particles are easily loosened from the metal wire, so that the efficiency and the quality of the sawing are Significantly altered.

It has also been proposed, for example in WO 90/12670, the implementation of a metal monofilament provided on its surface with microcavities, said microcavities being intended to receive and drive the particles of abrasive material during the step effective sawing.

It has also been proposed, in another embodiment, to vary the diameter of the wire so as to define grooves or circumferential grooves, again intended to receive and corollary result in said abrasive particles.

It turns out that if by this means improves the quality of the abrasive particle entrainment, however, this modification of the outer surface of the wire is slow to obtain and generates an additional cost incompatible with the products resulting from such cuts. It has also been proposed, for example in document EP 1 827 745, to confer on the wire corrugations oriented in two different planes, integrating the principal direction of the wire, so as to define a volume greater than that defined by the single mono filament, the volume of which the envelope contains the peaks of said undulations, and thus capable of generating effective entrainment of the abrasive particles. However, experience shows that this embodiment is of limited effectiveness in driving the abrasive particles, and that, by the way, because of the effective tension to which the wire is subjected, said ripples are not perennial over time, thereby affecting the ability of the wire to perform its role of driving said particles of abrasive material.

The object of the invention is to provide a wire of the type in question, avoiding these disadvantages, easy to manufacture, and a low cost.

SUMMARY OF THE INVENTION

For this purpose, the invention provides a saw wire having a cross section, that is to say a section substantially perpendicular to the main dimension of the wire, non-circular, said wire being further twisted on itself.

In other words, the invention consists in implementing not a traditional metal wire of circular cross-section, as is the case in all saw wires known from the prior art, but of a section by ellipsoidal example, or racetrack-shaped, or otherwise, and conferring on the wire in question a twist on itself, so as to generate an effective envelope of the wire over its entire length, resulting from the combination of the section non-circular and the twisting of the wire on itself, suitable for promoting the entrainment of abrasive particles. This envelope is constant and inscribed in a circle whose diameter D is equal to the maximum dimension of the cross section of the wire, and in this case to the original diameter of said wire.

It thus generates a volume born from the substantially cylindrical envelope defined by the rotation on itself of the wire resulting from the twist which is printed to it, besides the flattening of said wire on itself, making it possible to capture more particles abrasive, and corollary to increase the amount of abrasive particles thus transported by the wire. This configuration makes it possible to keep the cross section of the envelope constant, regardless of the tension applied to the saw wire, so that the cutting quality is optimized, since, as well, the footprint of the associated saw wire abrasive material particles are also constant. Thus the loss of material resulting from cutting, and more particularly silicon, better known by the English expression "kerf loss" is itself constant and better controlled, which is a significant advantage because of the cost even of this "noble" matter.

The invention also relates to the method of producing the metal wire in question. Thus, the wire, resulting from the drawing operation, and therefore rectilinear, is subjected to the rolling action, especially cold, and then rolling output, it is subjected to a twist on itself according to a not determined.

In known manner, the rolling induces a flattening of the wire on itself, the degree of flattening being of course adjustable, depending on the desired importance, in combination with the twisting of the wire on itself, the volume thus generated for receive the particles of abrasive material.

In the same way, the machines providing a twisting of the wire on itself are also widely known, this twisting of the wire on itself also occurring cold.

BRIEF DESCRIPTION OF THE FIGURES The manner in which the invention can be implemented and the advantages that result therefrom will emerge more clearly from the exemplary embodiment which follows, given by way of indication and not limitation, in support of the appended figures.

Figure 1 is a schematic cross-sectional representation of the wire according to the invention.

Figure 2 is a schematic perspective representation of the wire according to the invention.

Figure 3 is a schematic representation of a device adapted to achieve the wire of the invention. DETAILED DESCRIPTION OF THE INVENTION

FIGS. 1 and 2 show a schematic representation of the saw wire according to the invention.

This wire (1) is made of steel, and for example high carbon steel.

According to a first feature of the invention, and as can be seen in Figures 1 and 2, this wire does not have a circular cross section, but flattened.

In this case, the wire shown is of racetrack-shaped cross section, that is to say that it has a flattening at the two ends of one of its diameters, thus defining two perpendicular preferred dimensions. one with respect to the other, one having a length slightly greater than the original diameter d wire drawn from drawing, the other having a length less than said diameter d.

As indicated below, this particular section is obtained by rolling. In addition, this wire undergoes a twist on itself. In doing so, because of the dissymmetry resulting from the flattening of the wire on itself, it generates a kind of helix, which again, the pitch p can be adjusted.

Thus, and according to the invention, the combination of the pitch p of the helix on the one hand, and the degree of flattening of the wire on the other hand, makes it possible to define a volume resulting from the envelope, itself defined by rotating both ends of the wire at its largest dimension of the section of said wire. This envelope (2) has been materialized by discontinuous lines in FIG. 1. It has a cross section of diameter D. This volume is able to drive the abrasive particles during the sawing step. These abrasive particles consist for example of silicon carbide (SiC) associated with glycol. As already indicated, the flattening of the wire may be obtained by rolling. In doing so, and already, it does not significantly affect the physical and mechanical characteristics of the wire, which in fact retains its elongation properties. Typically, the initial diameter d of the wire may be between 0.08 and 0.5 mm, advantageously between 0.10 and 0.30 mm.

As a result of the rolling, the ratio of the smallest dimension Ep to the diameter d of the wire may be between 0.8 and 0.9. In other words, it is desired to obtain a flattening sufficient to ensure that the particles of abrasive material are contained in the volume of the envelope materialized in Figure 1, while retaining the mechanical properties of the wire.

If we choose a pitch p of the helix between 3 and 10 millimeters, and advantageously between 4 and 6 millimeters, combined with the aforementioned value of the flattening of the wire, a volume suitable for the collection is defined, then Γ efficient driving of the particles of abrasive material.

In addition, due to the quasi-preservation of the intrinsic properties of the wire, the elongation phenomena likely to be encountered with the wires of the prior art are avoided, effectively optimizing the efficiency of the sawing as well as the tension Rated on the wire during sawing can be retained. Thus, the cross section of the envelope is maintained constant, and therefore corollary of the overlayer of abrasive material present at its periphery, so that the resultant cutting quality is optimized.

In addition, because of the improved ability to drive the abrasive material, and especially the larger amount of particles that can be conveyed, the cutting speed can be increased. In addition, still due to the improved ability to drive the abrasive material, the wear of the wire is reduced, said abrasive material particles remaining longer in the envelope defined above. In doing so, the service life of the wire according to the invention is optimized with respect to the metal wires used in the prior art, helping to reduce the costs of sawing. The wire of the invention makes it possible to cut blocks or ingots, in particular silicon, constituting a relatively coarse cut. It can also be implemented, by choosing a diameter d smaller, and typically close to 120 μιη, to achieve the cutting of wafers or silicon wafers.

It therefore follows from the invention a certain number of advantages among which we can mention: a lack of any elongation of the saw wire during the cutting step, and in any case comparable with the traditional son of circular cross section, helping to improve the efficiency of cutting;

- Optimized cutting quality because of the one hand, the conservation of the right of way of the cutting area, and secondly, the largest amount of abrasive material transported;

a reduction in the loss of cut material resulting directly from the optimization of the cutting quality.

Claims

CLAIMS / Saw wire characterized in that it has a non-circular cross section, and in that it is twisted on itself, thereby defining a helix, whose pitch is between 3 and 10 millimeters. 1 metal wire for sawing according to claim 1, characterized in that the pitch of the helix is between 4 and 6 millimeters. Saw wire according to one of Claims 1 and 2, characterized in that the cross-section of the wire is elliptical in shape. Saw wire according to one of Claims 1 and 2, characterized in that the cross-section of the wire is in the form of a racetrack. Saw wire according to one of Claims 1 to 4, characterized in that the ratio of the smallest dimension to the largest dimension of the cross-section of the wire is between 0.80 and 0.80. for producing a saw wire, characterized in that it consists of:

- to subject a rectilinear wire of circular section to a rolling action;

- Then, rolling output, to submit the wire to a twist on itself in a determined step. Process for the production of a saw wire according to claim 6, characterized in that the rolling and twisting steps are performed cold.