The invention relates to a wire saw, especially for cutting hard brittle materials, using diamond wire and pulleys, also called wire guide members, specially adapted to that wire, having a longer life time than conventional pulleys. The invention also relates to pulleys or wire guide members to be used in such wire saws. The wire saw is especially suited for cutting materials such as sapphire, boron, quartz, glass, rare earth metals, etc..

Wafers, e.g. for use in solar cells or semiconductor industry, are cut from a block (also called brick or ingot) of silicone or other suitable materials such as sapphire. For said cutting, a wire cutting device is provided employing a metal wire and abrasives.

Nowadays, wafers are cut more and more using fixed abrasives, meaning that the abrasives are directly attached to the metal wire. Such wires are also referred to as diamond wire, regardless of the cutting elements used.

Wre saws contain as integral parts e.g. sawing wire, pulleys guiding the sawing wire, wire guide rollers forming the wire web, the latter two both called wire guide members. All these wire guide members support, drive, decelerate, or guide the wire or any combination thereof, possibly at different times and in different locations. Normally, there is only one wire guided as to form a wire web that may contain a few to thousands of parallel wire segments allowing multiple cuts in time parallel or just one or a few wires e.g. for bricking and squaring. Also known is a multitude of wire loops although this is not commonly used. Normally, there are two wire guide rollers in a wire saw, but embodiments with more than two rollers are also known from prior art.

All wire guide members suffer from wear and need to be replaced regularly. Since the cutting wire or sawing wire has to be guided through the wire saw by pulleys, they too experience the cutting effect of the cutting wire (with the fixed abrasives) and thus wear down in an undesirable rate.

Between the wire guide rollers, the wire is typically tensioned with 25 Newton, but also tensions of up to 200N or higher is used. Therefore the normal force on the wire guide members may be quite large. JP2006255841 discloses a pulley with a very hard surface that withstands the abrasive action of the wire. This is done by wear resisting members on the wire guide groove formed on the outer peripheral surface. The wear resisting members use materials harder than the surface of the wire guide groove. If diamond wire is used with such a pulley, ideally the surface would have to be harder than or almost as hard as the diamonds (or other abrasive used such as Silicon carbide) on the wire itself to effectively reduce the rate of wear. Clearly for wires using diamonds as abrasive material this may be impossible or at least very expensive. Also coating the pulleys with hard layers is costly. In addition, making the guiding surface hard wears down the wire.

JP2003326450 discloses a comparable solution, now using hard particles with a mean particle diameter of 0.5-30 μηη to make the grooves more wear resistant. Again this solution is not cost-effective since the particles have to be applied to the groove much like the particles of a diamond wire are applied to a metal core. Again, the wire wears off due to the hardness of the grooves.

JPH03281 1 19A does not relate to the field of cutting wafers using a wire saw and shows a wire saw that uses cutting wire with large cutting elements. The elements fit in grooves provided in a wire guide element. Such pulleys are not impaired by the abrasive action of the abrasives attached to the wires since the cutting elements do not touch the supporting surface of the pulley and the wire touching the supporting surfaces has much less abrasive action. When cutting say silicon, such large cutting elements or even small cutting elements placed next to each other in periodic way cannot be used since that would greatly impair the quality of the cut object and too much costly material would be lost. Also the cost of such a wire would be far too high, because the small abrasives would have to be placed individually.

With wire saws using slurry (without fixed abrasives on the wire), the cutting action of the wire was no issue and the pulley did not wear down nearly as fast as pulleys used for fixed abrasives that are supported by the surface of the pulley. The object of the invention is to overcome these problems of the prior art and to provide cost-effective pulleys for wire with fixed abrasives that have longer life-times.

This object is achieved by means of a wire saw having a cutting wire with fixed cutting elements, at least one wire guide member for guiding the cutting wire between a first spool and a second spool, the wire guide member being rotatably mounted to a frame portion of the wire saw as to be rotatable around a rotational axis, the at least one wire guide member comprising a wire supporting surface wherein at least two slots or recesses are provided that define intermediate portions of the wire supporting surface between them, a wire portion of the cutting wire with the length of an intermediate portion containing multiple cutting elements so that the wire portion supported by an intermediate portion during cutting contains multiple cutting elements.

The length of an intermediate portion is measured in circumferential direction, i.e. in the axial direction of the cutting wire supported by the wire guide member. The first spool and second spool may be the spool supplying new cutting wire and the spool collecting used up cutting wire respectively. During cutting the wire may move back and forth between those spools or any intermediate spools. Wire guide members will also be referred to as pulleys or wire guide rollers. Other parts of the wire saw are known from the state of the art and will not be described here. The recesses defining the intermediate portions may have any form or shape. They only have to divide the intermediate portions in the areas where the cutting wire lies on the wire supporting surface (see figure 7a). They may extend over part or the complete width (see figure 7b) of the wire supporting surface or be (blind) holes or depressions in that surface. The important thing is that the slots define intermediate portions that carry the wire and have end portions supporting the wire. It is (mainly) the end portions that can expand and contract with the wire thus preventing wear to the pulley, as will be explained below.

The wire portion is any segment of the wire that at any given time, say during cutting, extends over an intermediate portion. It is typically later (in its run thru the wire saw) used for cutting.

The wire supporting surface is a wire contact surface of the wire guide member, i.e. the surface of the wire guide member coming into contact with the cutting wire.

Preferably, the material forming the wire supporting surface, particularly the material of the lining, is a homogeneous material, particularly being free from pores, voids, cavities or cells, so that irregular and undefined abrasion of the wire supporting surface is avoided.

Preferably, the wire saw is a wafer slicing wire saw, wherein preferably the cutting wire forms a wire web, or a brick slicing wire saw.

Preferably, the wire guide member according to the invention is used in a wet cutting process, i.e. with cutting liquid or slurry. As will be explained in relation to the figures, providing recesses or slots in the wire supporting surface will enable the material of the wire guide member to adjust to the expansion (pulley accelerates wire) or contraction (pulley decelerates wire) of the wire 2, the expansion and contraction being the result of change in tension in the wire before and after the pulley.

Since the cutting wire has abrasives attached to it, any shift between the wire guiding member and the wire will cause abrasive or cutting action.

Ideally the wire guiding member has a circular wire supporting surface as with a normal pulley. Preferably the wire guiding member is detachably mounted to the wire saw, so that it can be replaced readily. Pulleys in wire saws often have multiple tangential grooves that can support the wire. Once one groove is worn down, an adjacent groove can be used so that the pulley may be replaced less often. This is also possible for the inventive wire guiding means as far as it forms a pulley. Slots can extend over multiple such tangential grooves, each groove may have its own slots or some grooves may have no slots. A pulley may incorporated any combined thereof.

The inventive wire guiding member may be used for any of guiding the wire to a wire web (e.g. formed by wire guide rollers) or cutting section or forming a wire web or cutting section itself. Preferably the invention is used for driven or decelerating pulleys since they suffer the most wear off. Preferably the slots are distributed equally around the wire supporting surface, the distance between two neighboring slots being more or less equal for all slots.

Preferably the slots extend in a direction making an angle of no more than 30 degrees, preferably no more than 10 degrees with the axial direction (direction of the rotational axis of the wire guide member). Even more preferably the slots extend substantially in the direction of the rotational axis of the wire guide member. Slots may also have a v-, u- or any other shape.

It is preferred that the length of the intermediate portions is smaller than 30mm, preferably smaller than 10mm, even more preferred smaller than 5mm, the length being defined as the length of the wire supporting surface of that portion in direction the wire runs or put differently, about the length of the wire that can be supported by the wire supporting surface. Making the intermediate portions small gives them the needed flexibility to adjust to the expansion and contraction of the wire. Even more preferred the intermediate portions are at least 100 times larger than the average distance between the cutting elements, preferably at least 1.000 times larger and even more preferred at least 10.000 times larger, the average distance between the cutting elements being defined as the number of elements on a wire of unit of length, measured over a representative length of the wire. In another embodiment the length of the intermediate portions is at least 20 times larger than the average distance between the cutting elements, preferably at least 200 times larger and even more preferred at least 2.000 times larger.

As stated above, the cutting wire of length of an intermediate portion contains multiple cutting element, preferably a piece of the cutting wire of the length of the intermediate portions contains are least 100, preferably more than 1.000, even more preferred more than 10.000 cutting elements. By doing so the intermediate portions remain of reasonable size so that they can still support the normal force exerted on them by the wire.

It is further preferred that the length of the recesses being smaller than 10 mm, preferably smaller than 5mm, even more preferred smaller than 2mm, the length being defined just like the length of the intermediate portions, now with an imaginary (while no longer present) wire supporting surface. Making the recesses small makes the wire run smooth while still allowing the needed expansion and contraction of the end portions of the intermediate portions. Even more preferably the recesses are wider than at least 10 times the average distance between the cutting elements (defined above) in the axial direction of the cutting wire, preferably at least 100 times larger that and even more preferred at least 1.000 times larger. By having multiple cutting elements in a recess, say 10, preferably more than 50, even more preferred more than 200 cutting elements, there will accordingly be enough wire between the cutting elements that is free to expand or contract, not being hindered by the (rigid) cutting elements.

Preferably the length of at least one intermediate portion, preferably of all intermediate portions, is shorter (measured along the wire supporting surface) than the stick zone of the pulley without slots (otherwise having the same function, being of the same materials etc.), say 20% shorter, more preferred 40% shorter or even more preferred more than 50% shorter. Put differently, the intermediate portions should cover a smaller angle (360 number of slots, provided the slots are divided equally) than the angle of the stick zone. If the intermediate portions are short enough, no slippage will occur (the stick zone covers the whole intermediate portions) and expansion and contraction of the wire will occur in the slots, not damaging the wire carrier surface or the wire. Moreover, in the stick zone, the wire does not move relative to the pulley, thus causing no abrasive action. If the intermediate portions are smaller than the stick zone, no relative movement will occur. The stick zone and slip zone are dependent on the speed of the wire before and after the pulley, the tension applied and the materials used for the wire and the pulley. An expression for the stick and the slip zone will be given in relation to the figures.

Preferably, the length of an intermediate portion divided by the length of a recess is smaller than 25mm, preferably smaller than 10mm, even more preferred smaller than 2mm.

The cutting elements may be substantially smaller than the wire diameter. Cutting wire typically is 50 to 450μηη in diameter (diameter of core and mantel, without cutting elements). Cutting elements typically range from 5 to 100 μηη. Preferably the average diameter of the cutting elements is at least 2 times smaller, even more preferred at least 5 times smaller than the diameter of the wire. The cutting elements may be distributed over the complete surface of the wire, normally in a non-periodic manner. Moreover cutting elements may be distributed randomly. The cutting elements may be distributed equally over the wire or in a structured way in any direction and in any shape. The wire may e.g. contain regions with no or very little cutting elements dividing (in axial direction of the wire) regions with many cutting elements to give scrap from the cutting room to collect and be transported from the cut. The wire typically has a core made of steel or (fiber reinforced) polymer and a mantel of copper, nickel or alloys thereof for holding the diamonds that typically is around 20 μηη thick. Preferably, the cutting elements are smaller than the diameter of the cutting wire and are distributed over the surface of the cutting wire, preferably in a non-periodic manner and preferably multiple cutting elements lay in one cross-section of the cutting wire.

Preferably, the abrasive particles that have an average distance (defined above and in relation to figure 4) of less than 100 μηη, preferably less than less than 10 μηη, even more preferred less than 1 μηη. These average particle distances are especially suited for cutting hard brittle material.

Preferably, the wire guide member contains a core and a lining forming the wire supporting surface, the lining preferably being made of a softer material than the core. Making the material of the lining softer will make the intermediate portions deflect more easily, while the wire guide member as a whole remains stable. In order to keep the deflection of the intermediate portions small, the intermediate portions should not become too big, see above. The pulley core may be made of harder material such as a metal (aluminum) or a fiber reinforced polymer.

Preferably, the slots or recesses end within the lining, i.e. they do not continue in the core of the wire guide member. Moreover, they may extend all the way through the lining but not into the core. In such a way only the lining has to be adapted according to the invention with slots or recesses, wherein usual cores can be used without adaption. The lining may be made of a polymer such as a polyurethane and may have a Young's modulus of from 50 to 800 MPa.

Preferably the inventive pulley has at least 10, preferably at least 20 and even more preferred at least 100 recesses. Preferably the inventive wire guide member has a diameter of less than 1 .000mm, preferably less than 600mm even more preferred less than 400 mm.

Preferably, the wire guide member is selected from the group consisting of pulleys and wire guide rollers.

Preferably, the slots or recesses may be more than 0.5 mm deep, preferably more than 1 mm deep, even more preferred more than 2 mm deep to ensure good flexibility of the wire receiving surface near their end portions, the depth being measured from the supporting surface in the direction towards the rotational axis (radially) of the wire guide member.

Preferably, the slots or recesses open only to the wire supporting surface, i.e. they are formed as blind holes. In this way the mechanical properties, particularly the stiffness of the wire guiding member are not adversely affected by the slots or recesses. Also the lining stays stronger so that it can be handle more easily, e.g. when being replaced.

Preferably, the depth of the slots or recesses is smaller than 3cm, preferably smaller than 1 ,5cm, the depth being measured from the supporting surface in the direction towards the rotational axis (radially). Mechanical properties, particularly the stiffness of the wire guiding member are not adversely affected by such slots or recesses. Preferably, the wire guide member is free from fluid ducts, which ducts would adversely affect mechanical properties of the wire guide member and make it too complicated.

Preferably, the wire guide member is free from ducts extending in or towards the peripheral region of the guide member. The peripheral region is that region being close to the wire supporting surface. Thus, the mechanical properties of the supporting surface are not adversely affected.

Preferably, the wire guide member has less than six fluid ducts.

The inventive wire guide member may be used as pulley, wire guide rollers or any other guiding element, driven, acting to decelerate or having very little rotational friction. Preferably, the wire guide member is a wire guide roller forming the wire web of the wire saw.

The wire saw and its wire guiding element(s) and/or wire guide rollers and cutting wire may be seen as a system. The invention thus also relates to a system comprising a wire saw according to any of the preceding embodiments and a fixed abrasive cutting wire. The invention also relates to the use of a wire saw according to the invention for slicing wafers, wherein preferably the cutting wire of the wire saw forms a wire web.

Further embodiments of the invention are indicated in the figures and in the dependent claims. The embodiments shown in the figures are an example of the invention and do not limit the invention in any way. The list of reference marks forms part of the disclosure. The invention will now be explained in detail by the drawings. In the drawings:

Fig. 1 shows a wire saw in part

Fig. 2 shows the relationship between the maximum wrap-around angle around a pulley and the tension in the wire

Fig. 3 shows the tension distribution in the stick and slip zone

Fig. 4 shows a section of a cutting wire with fixed abrasives, also-called diamond wire Fig. 5 shows an embodiment of the inventive pulley made out of one piece of material Fig. 6 shows an embodiment of the inventive pulley with a lining

Fig. 7 shows a top view of two embodiments of the recesses in the wire supporting surface The present invention will be described with reference to exemplary embodiments and the present invention is not limited to a particular wire saw or component parts thereof, except as defined in the appended claims. Embodiments of the present invention may be used with a variety of methods and systems. It will be apparent to one skilled in the art that the present invention may be practiced in a variety of ways within the scope of the claims. All features shown in relation to the figures may be applied mutatis mutandis to the invention as described in the claims.

As used herein, the indefinite article ("a", "an") denotes the presence of at least one of the referenced item, and the term 'a plurality' or 'multiple' denotes the presence of more than one.

Figure 1 shows an example of a wire saw 1 as known from the state of the art. Wire saws according to the invention may have two, three or even more wire guide rollers (each of which, like each pulley, may have a drive) and may be suited to cutting one or more multiple workpieces in time parallel. Parts not relevant to the current invention are omitted. Fig. 1 shows a frame portion 31 to which wire guide members or pulleys are rotatably mounted. A wire guide member or pulley may be directly or indirectly (e.g. pulley 15) mounted to a frame portion of the wire saw 1 . The wire saw shown is for slicing wafers. Also part of the invention is wire saws having only one or a couple of wires for cutting that may or may not extend parallel to each other. Such wire saws may be used for cropping, bricking, squaring etc. The wire saw may contain one single wire running through the workpiece to be cut or may have multiple wires that may form loops. The wire saw may be suitable for cutting hard materials such as silicon, sapphire, boron, quartz, glass, stone, ceramic, rare earth metals etc.

The main parts of the wire saw 1 are a first and a second spool 3, 4 with cutting wire 2 driven by respective drives 5, 6. The cutting wire 2 extends from those spools to a wire web 7 or cutting section held by wire guide rollers 24 that is used for cutting a work piece 8. Not shown is how the latter is mounted. In this embodiment the wire web 7 is driven by a drive 9. Tensioning means 1 1 , also-called dancers, are provided to tension the wire 2. The drives 6 are connected to a controller 10 for controlling amongst others the movement and the tension of the wire 2 and the movement of the workpiece 8 and thus the cutting action. The table the workpiece is attached to is not shown. The controller 10 also controls the movement of this table. The wire is guided between the spools 3, 4 by numerous wire guide members or pulleys 12, 13, 14, 15, 16. Not all pulleys have a reference number but all stated below applies to all pulleys.

The pulleys all guide the cutting wire 2. Normally the wire 2 will have a different tension on different sides of the pulley. This is especially true for driven pulleys (no driving means for the pulleys shown).

In figure 2 on the left side of the pulley 17, the wire experiences a first tension T-|. On the right side the second tension equals T ₂ . As was stated above, Ti and T ₂ do not have to be equal. This is the so-called capstan effect. The difference in tension may be caused by rotational friction on the pulley, because it accelerated or because it decelerates. The capstan equation describes the maximum tension difference ΔΤ _μ = T ₂ - Ti= e ^Mp _M ax, with μ the coefficient of friction and _Max the maximum wrap-around angle in radians over which no slippage occurs: the stick zone.

The speed of the wire builds up or falls off only over part of the wrap-around angle: the so-called slip zone. In the stick zone no slip occurs and the speed of the wire and the pulley are identical. Only in the slip zone, the wire expands. This is shown in figure 3.

The thickness of the curved "track" around the pulley represents the tension in the wire.

The speeds of the wire before the stick zone and after the slip zone are indicated as vi and v ₂ respectively. The speed of the circumference of the pulley (=wire supporting surface) equals the speed of the wire in the stick zone.

If a moment is exerted by the pulley on the wire or vice versa, the tension on one side is increased or reduces. For example Ti becomes T ₂ =T M/R. R being the radius of the pulley.

It was found that the wear of the pulleys in wire sawing machines using diamond cutting wire is mainly due to slippage of the wire in the slip zone. The angle the slip zone extends over β _5]ιρ is given by ln(T ₂ / T-i)/ μ.

Figure 4 shows a portion of the diamond wire 2, also called cutting wire 2 with fixed abrasives or cutting elements 20. The wire 2 is buildup from a core or core wire 18 with a mantel 19 that holds diamonds as cutting elements 20. The buildup of the wire 2 is not relevant to the invention. Any other wire with fixed abrasives with or without structure (structured wire) as known from the state of the art may be used. The shown wire section has 24 diamonds attached to its front surface. Assuming there is an equal amount on the back side, this wire would have an average distance d (as used in this document) between the diamonds of 48 divided by L.

Figure 5 shows part of an embodiment of an inventive pulley 17 having a radius R. The pulley supports a wire 2 with fixed abrasives 20. Along the wire supporting surface 22 of the pulley 17 slots 21 are provided, also called grooves, recesses or gaps, that in this case extend over the compete width of the pulley 17. In this embodiment the slots 21 are distributed over the complete (360°) wire supporting surface or outer peripheral surface 22 of pulley 17 that carries the wire 2. Each a degrees, typically every 3° to 30°, a new slot 21 is provided. The wire 2 only lies on a portion (part of the 360°) of the pulley 17. The pulley rotates around its rotational axis A. The mounting of the pulley and its lower part are not shown. The intermediate portions 27 have length I and support a wire portion over the range 30 or angle, typically of equal length.

Figure 6 shows an embodiment of an inventive pulley with a lining 23. In this embodiment the slots 21 are provided in the lining 23. Alternatively the core 25 of the pulley 17 may have additional slots (the lining still having slots, possibly that do not run through the complete width of the lining) or the slots may extend through the lining into the pulley.

In both figures 5 and 6 it is clearly visible that the diamonds 20 in the wire 2 are spaced apart much closer than the slots 21 in the pulley 17, meaning that between two slots multiple cutting elements are present. The diamonds are drawn too large and too far apart for clarity.

As can be clearly seen from figs. 5 and 6, the wire supporting surface 22 is a wire contact surface of the wire guide member 17, i.e. the surface of the wire guide member 17 coming into contact with the cutting wire 2. Each pulley 12, 13, 14, 15, 16 shown in figure 1 (also pulleys without reference number) may be replaced by an inventive pulley. Each pulley may be made of different materials and have different slot types and sizes, adjusted to its function. Even the wire guide rollers 24 may profit from axial slots or grooves. The wire guide rollers also being considered as wire guiding members or pulleys. The lining 23 of the pulley may have any cross-section suitable for holding the wire 2. It may have one or multiple grooves in V-shape or in the shape of a flat bed for holding the wire 2. Some applicable groove shapes are shown in US5907988. The slots 21 prevent the wear of the wire guide pulleys in the following two ways:

As the wire 2 moves over the slots 21 , it is free to expand and it can do so without rubbing over the wire supporting surface 22 thus wearing the surface off.

In addition, if wire portions supported by intermediate portions 27 expand, the intermediate portion 27 is free to adjust its shape to this expansion. Moreover, the intermediate portions 27 may expand and/or bend in the direction the wire 2 expands in since it is no longer held at its end portions 28 and 29. Note that the intermediate portion 27 returns to its relaxed state once it no longer supports the expanded wire 2. Therefore according to the invention it is beneficial if the wire at most runs around no more than 270° of the wire guide member, preferably runs around no more than 180° and even more preferred does not run around more than about 120°.

The same arguments hold for contraction of the wire 2. The intermediate portions 27 can contract and bend in the direction the wire 2 contracts in. The wire is free to contract when it moves over the slots 21. Figure 7 shows two top views (looking in a direction perpendicular to the rotational axis of the wire guiding member 17) in part. In Figure 7a the slots 21 do not extend over the complete (axial) width of the pulley 17, but still define intermediate portions 27 (portion between the slots underneath the wire that is supported) of the wire supporting surface 22 holding the wire 2. The end portions 28, 29 can deflect as desired. Figure 7b shows recesses 21 extending over the complete width of the pulley 17.

The invention is not restricted to the embodiments shown. Single or multiple

combinations thereof are possible. Other variants will be obvious for the person skilled in the art and are considered to lie within the scope of the invention as formulated in the following claims. Individual features described in above specification, particularly with respect to the figures may be combined with each other to form other embodiments and/or applied mutatis mutandis to what is described in the claims and to the rest of the description. List of reference signs

1 Wire saw

2 Cutting wire with fixed abrasives also-called diamond wire

3 First spool for cutting wire

4 Second spool for cutting wire

5 Drive

6 Drive

7 Wire web

8 workpiece

9 Drive

10 Tensioning means

1 1 Drive

12 Pulley

13 Pulley

14 Pulley

15 Pulley

16 Pulley

17 Pulley

18 Wire core

19 Wire mantel

20 Fixed abrasives also called diamonds or cutting elements

21 Recesses, slots or grooves

22 Wire supporting surface of the pulley

23 Pulley lining

24 Wire guide roller

25 Pulley core

26 Dancer

27 Intermediate portion

28 End portion

29 End portion

30 Range a wire portion is supported

31 Frame portion of the wire saw 1 a Angle between two adjacent recesses or slots

ΔΤ _Μ Maximum tension difference

iviax Maximum wrap-around angle in radians A Rotational axis of the pulley

d Distance between two abrasive particles on the diamond wire

I Length of intermediate portion

L Length of wire section shown in figure 4

M Moment exerted by the pulley on the wire or vice versa

Ti First tension

T ₂ Second tension

R Radius of the pulley

W Diameter of cutting wire