Method for simultaneously cutting a plurality of slices from a workpiece by means of a wire saw

Description

[0001] The invention relates to a method for simultaneously separating a plurality of discs from a workpiece by means of a wire saw, comprising a cut-off grinding process, wherein a workpiece is fed perpendicular to a longitudinal axis of the workpiece against a wire frame of a saw wire which is tensioned between two wire guide rollers and is moved in the longitudinal direction of the saw wire, wherein a cooling lubricant is supplied to the wire frame, and wherein discs are formed between wire sections of the wire frame, which are fastened to a bar and between which separating gaps exist, the bar and the discs are pulled out of the wire frame, and during the withdrawal of the bar and the discs, the separating gaps are sprayed with a liquid by means of a spray device until the wire sections have left the separating gaps, wherein the liquid is supplied under high pressure through nozzles.

[0002] A wide variety of applications require uniform wafers with good plane-parallelism of their front and back surfaces and low in crystalline and structural defects. One example is wafers made of single-crystal semiconductor material for structuring microelectronic components. Such wafers are obtained, for example, by cutting a cylindrical workpiece made of single-crystal silicon using wire sawing. State of the art / problems

[0003] A method and device for wire sawing are known, for example, from DE 10 2016 211 883 A1. During wire sawing, saw wire is guided spirally around at least two wire guide rollers, so that two wire guide rollers span a wire frame facing the workpiece, made up of parallel wire sections. The outer surfaces of the wire guide rollers are provided with a plurality of circular, closed grooves running in planes perpendicular to the axes of the wire guide rollers, which guide the saw wire. Rotating the wire guide rollers in the same direction creates a relative movement between the wire sections and the workpiece. A wire saw also has a feed device to which the workpiece is attached via a bar to which it is glued, and which feeds the workpiece perpendicularly onto the wire frame.The relative movement and the presence of an abrasive cutting medium cause material to be removed from the workpiece upon contact between the workpiece and the wire frame. With continued advance, the wire sections form cutting gaps in the workpiece, and the wire frame slowly works its way through the entire workpiece until it rests completely within the saw bar. The workpiece is then completely cut into slices that hang from the bar like the teeth of a comb, held in place only by the adhesive joint.

[0004] After the cutting process has been completed, the sliced ​​workpiece must be pulled out of the wire frame by reversing the direction of movement of the feed device (ingot retrieval).

[0005] Wire sawing can be divided into wire lapping and wire grinding. In wire lapping, the saw wire is initially free of any abrasive substances, and the cutting media is introduced in the form of a slurry, consisting of freely moving grains in a carrier fluid. In wire grinding, abrasive cutting media are embedded in the surface of the saw wire, and a cutting fluid is introduced that acts as a cooling fluid and contains no abrasive substances.

[0006] Saw wire is usually made of hypereutectic pearlitic steel (piano wire). Plain wire and structured wire (crimped wire) are used.

[0007] In wire cutting lapping, the cutting medium is usually silicon carbide (SiC), and the carrier fluid is usually oil or glycol. In wire cutting grinding, the cutting medium is usually water, possibly with a wetting agent and defoamer additive, and the abrasive embedded in the saw wire is usually diamond. The bar is made of a plastic composite material or sintered carbon.

[0008] During wire sawing, the saw wire is taken from a first supply, usually in the form of a first spool onto which the saw wire is wound, and after use is fed to a second supply, usually also in the form of a second spool. The first spool is referred to as the fresh wire spool and the second spool as the old wire spool. Wire sawing can be carried out with unidirectional or bidirectional wire movement. During unidirectional wire sawing, the saw wire is moved in one longitudinal wire direction from the fresh wire spool to the old wire spool for the entire duration of the cutting process. During wire sawing with bidirectional wire movement, the saw wire is moved during the cutting process by means of at least one pair of direction reversals, wherein a pair of direction reversals comprises a first movement of the saw wire by a first length in a first longitudinal wire direction and a second movement of the saw wire by a second length in a second direction exactly opposite to the first.In particular, wire sawing with bidirectional wire movement can comprise a plurality of such pairs of wire direction reversals, with the first length being selected to be greater than the second length, so that the overall wire supply shifts from the fresh wire spool to the waste wire spool during the cutting process. The latter process is referred to as pilgrim-mode slicing (wire reciprocating slicing).

[0009] Wire saws are also known in which the workpiece can be pivoted about an axis parallel to the longitudinal axis of the workpiece during the cutting process. In particular, this rotational movement can be carried out in the form of a continuous sequence of a plurality of pairs of rotation changes, wherein a pair of rotation changes comprises a clockwise rotation at a first angular speed through a first angle and a subsequent counterclockwise rotation at a second angular speed through a second angle. The first and second angular speeds and the first and second angles can also vary during the cutting process, for example depending on the cutting depth or depending on the current length of the saw wire in the workpiece. Such a recurring rocking movement of the workpiece is also referred to as rocking of the workpiece.A suitable device for this purpose is described, for example, in US 2022 / 0134600 A1.

[0010] During the cutting process, material is removed primarily along the contact surface along which the saw wire is in material-removing contact with the workpiece and which extends opposite to the direction of the workpiece feed. This contact surface is referred to as the main rake face. The contact surface that the saw wire makes with the workpiece perpendicular to this direction, i.e. in the direction of the workpiece axis, is referred to as the secondary rake face because no forces act here as a result of the workpiece feed and therefore initially no material is removed. The sum of all momentary secondary rake faces of a cutting gap over the entire cutting process forms the front and back of a pair of adjacent discs.

[0011] In wire sawing without rocking, the main cutting surface extends along the entire arc length from the point where the saw wire enters the cutting gap to the point where it exits the cutting gap. In wire sawing with rocking, the main cutting surface always consists only of the short arc section with which the saw wire contacts the parting line between the workpiece and the cutting gap, which is curved due to the rocking. Rocking improves the supply of coolant or slurry to the cutting gap, even with workpieces with large diameters.

[0012] In lapping, the material removal rate is proportional to the pressure on the main rake face. In cut-off grinding, the material removal rate increases disproportionately with the pressure on the main rake face. Rocking allows for faster cut-off grinding (but not faster cut-off lapping) than without rocking.

[0013] During wire sawing, the sliced ​​workpiece is pulled out of the wire frame by resetting the feed of the workpiece. The saw wire is moved slowly in the longitudinal direction of the wire and cutting fluid is added to draw cutting fluid into the cutting gap as a cooling lubricant. This prevents friction between the saw wire in the cutting gap and individual wire sections from jamming between the opposite secondary rake faces of a cutting gap. During ingot retrieval after wire cutting lapping, the slow wire movement causes most of the slurry to drip off the saw wire before it enters the cutting gap, so that the thickness of the slurry film surrounding the saw wire in the cutting gap is significantly less than the thickness of the slurry film during the previous cutting process. During ingot retrieval after wire cutting lapping, the saw wire therefore has play in the cutting gap and does not jam.This promotes a uniform gliding of the wire frame through the cutting gaps and finally out of them, without the saw wire jamming between the secondary chip surfaces of the gap or causing material removal from the secondary chip surfaces.

[0014] During wire cutting, there is no slurry of cutting media surrounding the saw wire. The width of the cutting gap is therefore identical to the wire diameter, including the diamonds embedded in the saw wire. During ingot retrieval, the saw wire has no play within the cutting gap and therefore frequently jams at different cutting depths. The slow longitudinal movement of the wire immediately causes additional material removal, and notches form in the walls of the cutting gap. Since the walls of a cutting gap form the front side of one wheel and the back side of the immediately adjacent wheel, notches are created in the resulting discs after separation. Discs with notches in the surface are unsuitable for demanding applications.

[0015] While the saw wire jams at a certain cutting depth during ingot retrieval after wire cutting, the feed device is further retracted. Consequently, the saw wire is deflected in the transverse direction and thus elastically stretched in the longitudinal direction. The saw wire experiences an increasing restoring force. When this force has increased sufficiently, the saw wire jumps from the cutting depth at which it jammed during retrieval to a lower cutting depth, where it jams again, and so on (stick-and-slip movement of the saw wire). If the tensile force due to the longitudinal stretching caused by the transverse deflection of the saw wire exceeds the material strength of the saw wire, the saw wire will break during ingot retrieval.In this case, the workpiece must be completely removed from the defective wire frame, the wire scraps removed manually from the cutting gaps, and the wire frame repaired before the next cutting process. This is time-consuming and costly.

[0016] Occasionally the saw wire breaks during the cutting process due to overloading or material defects in the saw wire. The partially cut workpiece must then be moved out of the defective wire frame by resetting the feed device, the wire scraps removed from the cutting gaps, the wire frame repaired, the wire sections rethreaded into the existing cutting gaps and the workpiece fed back to the cutting depth at which the wire break occurred in order to complete the cutting process. With wire lapping, threading and feeding the workpiece in the wire frame is effortless and without the saw wire getting stuck at certain cutting depths, as the surrounding slurry film allows the saw wire sufficient play in the cutting gap. With wire grinding, where the saw wire has no freedom of movement, the saw wire jams when feeding the workpiece, and notches are created.

[0017] Even if the diamond-tipped saw wire does not visibly jam during the feed of the workpiece after a wire break or when resetting the feed during an ingot retrieval, the lack of freedom of movement always leads to additional material removal from the side walls bordering the gap and thus to damage to the front and back surfaces of the affected discs. Such damage causes material stresses in the damaged surface, which, if the stresses on the front and back surfaces of the disc are not exactly balanced (which is usually not the case), cause the disc to deform elastically. This elastic deformation due to surface damage is superimposed on the plastic deformation, and the plastic deformation cannot be determined in isolation by determining the disc shape using measurements after wire sawing, and thus cannot be specifically eliminated by suitable measures.The latter is necessary because the elastic deformation disappears when the damaged layers are removed in the subsequent material-removing processing, while the plastic deformation remains if it is not eliminated by targeted material removal.

[0018] US 2009 / 0223539 A1, for example, describes a method for cleaning panes for solar applications. After the cutting process is completed and they are removed from the wire saw, the panes are immersed in a cleaning bath with their adhesive joint still attached to the saw bar (sacrificial bar). Several separate spray nozzles spray rinsing fluid onto the cutting joints. Where the rinsing fluid is sprayed, the cutting gap in the water bath widens, thus enhancing the cleaning effect. By moving the nozzles relative to the workpiece, all cutting gaps can be widened one after the other and thus successively cleaned. The described method does not contribute to avoiding the consequences of stick-and-slip movement of the saw wire during ingot retrieval.

[0019] JP 2006-66793 A describes a similar process in which a block of cut disks is sprayed with a spray liquid from the side using spray nozzles for cleaning purposes after the cutting process has been completed and removed from the wire saw.

[0020] US 2011 / 0168212 describes a similar process for cleaning thin, easily breakable solar wafers after sawing and removing the severed workpiece from the wire saw.

[0021] JP2004-106360 describes a process in which, after wire cutting and ingot retrieval of a workpiece, a rinsing liquid is sent through channels in the bar to clean the cutting gap.

[0022] A method according to the preamble of the appended claim 1 can be found in EP 2 955 745 A1.

[0023] The object of the invention is to avoid stick-and-slip movements of the saw wire and their adverse consequences.

[0024] The object of the invention is achieved by a method for simultaneously separating a plurality of discs from a workpiece by means of a wire saw, comprising a cut-off grinding process, wherein a workpiece is fed perpendicular to a longitudinal axis of the workpiece against a wire frame of a saw wire which is tensioned between two wire guide rollers and is moved in the longitudinal direction of the saw wire, wherein a cooling lubricant is supplied to the wire frame, and wherein discs are formed between wire sections of the wire frame, which discs are attached to a bar and between which cutting gaps exist, the bar and the discs are pulled out of the wire frame, and while the bar and the discs are pulled out, the cutting gaps are sprayed with a liquid by means of a spray device until the wire sections have left the cutting gaps, wherein the liquid is supplied under high pressure through nozzles which are attached to nozzle bars which are moved in an oscillating manner parallel to the longitudinal axis of the workpiece, the liquid and entrained air temporarily excite the discs to oscillate.

[0025] The nozzles spray liquid onto the separation gap during withdrawal.

[0026] This swirls the surrounding air, causing the discs to vibrate due to the Bernoulli effect. The nozzle bars perform an oscillating stroke parallel to the workpiece axis, causing fluid to temporarily impinge on each cutting gap from at least one nozzle in the plane of the corresponding cutting gap. This injects fluid deep into the cutting gap, and the change in spray pressure caused by the oscillating movement causes a continuous, periodic fanning out of all the cutting gaps as the bar and discs are withdrawn from the cutting gaps.

[0027] The pressure at which the liquid is supplied through the nozzles is preferably selected so that the outlet speed of the flushing agent corresponds to the speed at which the wire is moved relative to the workpiece.

[0028] The nozzles are part of a spraying device comprising at least one nozzle bar each, which is arranged to the side of the wire guide rollers of the wire frame, between the respective wire guide roller and the workpiece. The nozzle bars can perform a reciprocating movement parallel to the workpiece axis and are preferably arranged parallel to the rotational axes of the wire guide rollers.

[0029] Particularly preferred are exactly two nozzle bars, one of which is arranged on the fresh wire inlet side and one of which is arranged on the old wire outlet side of the workpiece as viewed in the direction of the workpiece axis. The nozzles are preferably aligned so that each nozzle generates a partial jet of liquid that is tangential to the wire frame and in one of the planes in which the separating gaps run. The amplitude of the oscillating movement with which the respective nozzle bar is moved parallel to the longitudinal axis of the workpiece is preferably at least half the distance between two adjacent nozzles. The total stroke, corresponding to double the amplitude, is therefore at least the distance between two nozzles. This ensures that after one period of oscillating movement, each nozzle sweeps over all the separating gaps located between this nozzle and the adjacent nozzle.

[0030] The number of nozzles per nozzle bar is preferably 10 to 50. The highest possible number of nozzles is particularly preferred. The upper limit is only the dimensions of the nozzles. This reduces the required stroke of the oscillating movement of the nozzle bar, and the separation gaps are covered at shorter intervals.

[0031] During the cut-off grinding process, the workpiece is advanced using a feed device. The wire guide rollers rotate in the same direction, so that the wire sections move relative to the workpiece. As they engage the workpiece, material is removed as a result of the feed movement. At the end of the cut-off grinding process, the workpiece is completely cut, and a multitude of parallel cutting gaps are created between the wheels, which are held by the bar.

[0032] The extraction of the bar and the discs from the cutting gaps involves resetting the feed device while moving the wire sections in the longitudinal direction of the wire in the presence of cooling lubricant.

[0033] The workpiece is preferably a circular cylindrical rod made of single-crystal semiconductor material.

[0034] The method preferably also includes pivoting the workpiece about an axis parallel to the workpiece's longitudinal axis during the abrasive cutting operation, wherein the workpiece performs a plurality of pairs of pivoting movements, and each pair of pivoting movements comprises a first pivoting movement through a first angle at a first angular velocity and a subsequent second pivoting movement through a second angle at a second angular velocity. The first and second angular velocities and the first and second angles of two pairs of consecutive pairs of pivoting movements are preferably different.

[0035] The saw wire is preferably a hypereutectic pearlitic steel wire (piano wire) with cutting media affixed to its surface. The cutting media are preferably diamonds.

[0036] The saw wire can be moved longitudinally during the abrasive cutting process with or without a reversal of direction. When moving the saw wire longitudinally with a reversal of direction, the saw wire is moved by means of a plurality of piling steps, wherein each piling step comprises a first movement of the wire in a first longitudinal direction by a first length and a second movement of the saw wire in a second longitudinal direction, exactly opposite to the first longitudinal direction of the wire, by a second length, and wherein the first length is greater than the second length.

[0037] The cooling lubricant and the liquid preferably consist of water, optionally containing a liquid additive. Both can have identical or different compositions. The liquid additive is preferably a wetting agent, a corrosion inhibitor, a viscosity-influencing agent, for example, glycol and / or methylcellulose, a defoamer, or any desired mixture of these agents.

[0038] The procedure according to the invention is preferably also used to respond appropriately to an interruption in the abrasive cutting process, particularly as a result of a saw wire break. It prevents wire sections from getting stuck when pulling the workpiece out after the wire break and returning it to the position before the wire break, and prevents scoring or elastic deformation from impairing the quality of the wheels.

[0039] Interrupting the cutting process occurs while continuing to move the saw wire in the longitudinal direction. This involves pulling the workpiece out of the cutting gaps, returning it to the cutting gaps, and resuming the cutting process. While the workpiece is being returned, fluid is sprayed through the nozzles into the cutting gaps, and the nozzle bars are moved parallel to the workpiece's longitudinal axis.

[0040] Preferably, the saw wire is moved longitudinally during the cutting process at a speed that is at least ten times faster than the speed of the saw wire's movement longitudinally when the workpiece is pulled out and returned when the cutting process is interrupted.

[0041] The invention is presented below with reference to drawings using a preferred embodiment of a wire saw. Short description of the characters

[0042] Fig. 1 shows features of the wire saw and the workpiece that contribute to understanding the invention. Fig. 2(A) and (B) show details of a spray device suitable for carrying out the method according to the invention. List of reference symbols used

[0043] 1 workpiece 2 bar 3 Direction of delivery 4 saw wire 5 left wire guide roller 6 right wire guide roller 7 axis of rotation 8 axis of rotation 9 Direction of wire feed 10 Direction of wire discharge 11 Direction of rotation of the wire guide roller 12 bar 13 bar 14 nozzle 15 cooling lubricant 16 left nozzle bar 17 right nozzle bar 18 Axis of the left nozzle bar 19 Axis of the right nozzle bar 20 nozzle 21 liquid 22Separation gap 23 groove 24 Wire gate 25 Adhesive joint 26 Longitudinal axis of the workpiece 27 oscillating movement 28 oscillating movement 29 Direction of movement 30 widened separation gap 31 nozzle 32 Nozzle 33 diamonds 34 disc 35 entrained air Detailed description of an embodiment according to the invention

[0044] As in Fig. 1As shown, during wire sawing, saw wire 4 is guided in a spiral around at least two wire guide rollers such that two wire guide rollers 5 and 6 span a wire frame 24 facing the workpiece 1 made up of wire sections running parallel to one another. The wire guide rollers have the shape of right circular cylinders with axes of rotation 7 and 8 that are aligned parallel to one another and about which they can be rotated in directions 11. The outer surfaces of the wire guide rollers are provided with a plurality of circularly closed grooves 23 that run in planes perpendicular to the axes of rotation 7 and 8 and guide the saw wire 4. Rotating the wire guide rollers in the same direction creates a relative movement between the wire sections and the workpiece.Fresh saw wire is taken from a first wire supply, the so-called fresh wire spool (direction 9), and used saw wire is fed to a second wire supply, the so-called old wire spool (direction 10). The wire saw also has a feed device to which the workpiece 1 is attached to a bar 2 by adhesive bonding 25 and which feeds the workpiece perpendicularly onto the wire frame (direction 3). The relative movement and the presence of an abrasive cutting agent cause material to be removed from the workpiece upon contact between the workpiece and the wire frame. Through continued feed, relative movement, and supply of cutting agent, each wire section of the wire frame 24 forms a separating gap 22 by means of continued material removal from the workpiece. The side walls of a separating gap 22 each delimit the back of one and the front of a second disk 34 of a pair of immediately adjacent disks.

[0045] The cutting medium consists of diamonds 33, which are firmly embedded in the surface of the wire 1. During the cutting-off process, a cooling lubricant 15, which itself contains no abrasive cutting media (hard materials), is added to the wire frame 24 via two bars 12, 13, which are equipped with nozzles 14, to the left and right of the workpiece. The cutting-off process is complete when the entire wire frame has worked its way completely through the workpiece and has come to rest in the bar 2. The discs 34 of the completely cut workpiece then hang from the half-cut bar like the teeth of a comb, connected to the bar 2 only by the adhesive joint 25.

[0046] The wire saw shown is equipped with a left nozzle bar 16 and a right nozzle bar 17. The nozzle bars 16, 17 carry a plurality of nozzles 20 that spray a liquid 21 onto the cutting gap 22 of the workpiece 1. The axes 18 and 19 of the nozzle bars are arranged parallel to one another and parallel to the rotational axes 7 and 8 of the wire guide rollers 5 and 6 spanning the wire frame 24, and perpendicular to the cutting gap 22 of the workpiece 1 and parallel to the longitudinal axis 26 of the workpiece 1, respectively. The nozzle bars perform oscillating movements 27 and 28 in the directions of their axes 18 and 19. Due to this periodic displacement, the jets of liquid 21 leaving the individual nozzles 20 sweep over the cutting gap 22 of the workpiece 1 at periodic intervals.

[0047] The preferred arrangement according to Fig. 1shows the nozzle bar 16 to the left of the workpiece 1, i.e. on the fresh wire input side, and the nozzle bar 17 to the right of the workpiece 1, i.e. on the old wire output side, and both, seen from the direction of the feed device, below the wire gate 24. Alternatively, the nozzle bars can also be arranged above the wire gate 24.

[0048] As already mentioned, the method according to the invention can also be carried out with a wire saw, in which the workpiece can be pivoted about an axis parallel to the longitudinal axis of the workpiece during the cut-off grinding process. During this rocking, at any one time only a portion of the entire wire section running within a cutting gap comes into material-removing contact with the workpiece. Viewed in the longitudinal direction of the wire, gaps are formed between the saw wire and the workpiece in front of and behind this current contact surface, extending in the direction of the workpiece feed. If the nozzle bars are arranged above the wire frame, the fluid can get particularly well between the saw wire and the workpiece. If the nozzle bars are arranged below the wire frame, hardly any fluid can get between the saw wire and the workpiece despite rocking.On the other hand, in this case, the separated parts of the workpiece that protrude below the wire frame - the later discs - are particularly well stimulated to oscillate by the Bernoulli effect of the liquid jet and thus to periodically increase and decrease the width of the cutting gap.

[0049] Fig. 2 (A) and (B) shows details of a spraying device comprising the nozzle bars 16 and 17 in a top view (viewed from the direction of the feed device) of the left nozzle bar 16 and a part of the workpiece 1 with the separating gaps 22 and the longitudinal axis 26 of the workpiece.

[0050] Fig. 2 (A)shows the nozzle bar 16 with axis 18 parallel to the longitudinal axis 26 of the workpiece at the beginning of the oscillating movement 27 parallel to axis 18. There are nozzles 31, part of whose jet of liquid 21 runs exactly in the plane of a respective separating gap 22, whereby liquid 21 is pressed deep into the separating gap 22. In the course of this, the pair of adjacent disks 34 separated by the separating gap 22 is elastically pushed away from the separating gap in directions of movement 29, whereby the separating gap elastically widens to form a widened separating gap 30. In addition, there are nozzles 32, no part of whose jet of liquid 21 runs within the plane of a separating gap 22, and thus do not elastically widen any separating gap. The jets of liquid 21 entrain air 35 from the environment by means of momentum exchange (entrainment).

[0051] When the left nozzle bar 16 has performed the oscillating movement 27 in the direction of the axis 18, it reaches the Fig. 2 (B) shown position of the other end of their oscillating movement. The nozzles 31, some of whose jets force liquid into a separation gap and thus widen it, are now in a different position and widen different separation gaps than those in the arrangement according to Fig. 2 (A) The amplitude of the oscillating movement 27 is at least the value of the distance between two adjacent nozzles.

[0052] During the oscillating motion 27, the jets of liquid 21 (liquid incompressible) and the air 35 (air / gas compressible) entrained by the jets sweep over discs 34 and separation gaps 22. Since they flow around the discs and separation gaps at different levels during the oscillating motion, the discs 34 are excited to oscillate by the dynamic air pressure changes of the air entrained by the jets (Bernoulli effect). In other words, elastic deflections of the discs and periodically widening and narrowing separation gaps are stimulated.

[0053] Investigations underlying the present invention to prevent stick-and-slip of the saw wire during ingot retrieval and when repositioning a workpiece after an interruption of the abrasive cutting process have shown that vibration excitation of the wheels is necessary to reduce the frictional forces of the saw wire in the narrow cutting gap. Widening the cutting gap by forcing fluid into alternating cutting gaps and the associated cleaning effect as the only measure is too slow. This does not prevent the saw wire from generating scoring or strain-induced warpage during ingot retrieval or when repositioning the workpiece after an interruption of the abrasive cutting process.

[0054] Only the excitation of vibrations of the discs by means of the Bernoulli effect through a jet of liquid and entrained air proves to be suitable for solving the problem.

Claims

1. Method for simultaneously separating a multiplicity of slices (34) from a workpiece (1) by means of a wire saw, comprising a cutting-off grinding operation, wherein a workpiece (1) is fed perpendicularly with respect to a longitudinal axis (26) of the workpiece (1) against a wire gate (24), tensioned between two wire guide rollers (5, 6), of a saw wire (4) which is moved in the longitudinal direction of the saw wire (4), wherein a cooling lubricant (15) is fed to the wire gate (24), and wherein slices (34) which are attached to a bar (2) and between which there are separation gaps (22) are formed between wire portions of the wire gate (24); the extraction of the bar (2) and the slices (34) from the wire gate, and, during the extraction of the bar (2) and the slices (34), the spraying of the separation gaps (22) with a liquid (21) by means of a spraying device until the wire portions have left the separation gaps (22), wherein the liquid (21) is supplied under high pressure through nozzles (20, 31, 32), characterized in that that the nozzles are attached to nozzle bars (16, 17) which are moved in an oscillating manner parallel to the longitudinal axis (26) of the workpiece (1), wherein the liquid (21) and entrained air (35) cause the slices (34) to vibrate temporarily.

2. Method according to Claim 1, characterized in that an amplitude of the oscillating movement (27, 28) is equal to or greater than the sum of the spacing of two adjacent nozzles.

3. Method according to Claim 1 or Claim 2, characterized by interrupting the cutting-off grinding operation while continuing the movement of the saw wire (4) in the longitudinal direction, comprising the removal of the workpiece (1) from the separation gaps (22); the return of the workpiece (1) into the separation gaps; and the continuation of the cutting-off grinding operation, wherein, during the return of the workpiece (1), fluid (21) is sprayed through the nozzles (31, 32) into the separation gaps (22), and the nozzle bars (16, 17) are moved parallel to the longitudinal axis (26) of the workpiece (1).

4. Method according to one of claims 1 to 3, characterized by the pivoting of the workpiece (1) around an axis parallel to the longitudinal axis (26) of the workpiece (1) during the cutting-off grinding operation, wherein the workpiece (1) carries out a multiplicity of pairs of pivot movements, and a pair of pivot movements comprises a first pivot by a first angle at a first angular velocity and a subsequent second pivot by a second angle at a second angular velocity.

5. Method according to Claim 4, characterized in that the first and second angular velocities and the first and second angles of two pairs of successive pairs of pivot movements are different.

6. Method according to one of Claims 1 to 5, characterized in that the cooling lubricant (15) comprises water and a first liquid additive, and the liquid (21) comprises water and a second liquid additive.

7. Method according to Claim 6, characterized in that the first and the second liquid additive are identical and comprise a wetting agent or a corrosion inhibitor or a viscosity-influencing agent, a defoaming agent or a mixture thereof.

8. Method according to one of Claims 1 to 7, characterized in that the saw wire (4) consists of hypereutectic pearlitic steel wire, on the surface of which diamonds (33) are fixed as cutting means.

9. Method according to one of Claims 1 to 8, characterized in that the workpiece (1) is a circular-cylindrical rod of mono-crystalline semiconductor material.

10. Method according to Claim 3, characterized by the movement of the saw wire (4) in the longitudinal direction during the cutting-off grinding operation at a speed which is at least ten times faster than the speed of movement of the saw wire (4) in the longitudinal direction when removing and returning the workpiece (1).

11. Method according to one of Claims 1 to 10, characterized by the movement of the saw wire (4) in the longitudinal direction without a reversal of the direction.

12. Method according to one of Claims 1 to 10, characterized by moving the saw wire (4) in the longitudinal direction with a reversal of the direction, wherein the saw wire (4) is moved by means of a multiplicity of pilger steps, wherein a pilger step comprises in each case a first movement of the wire (4) in a first longitudinal direction by a first length and a second movement of the saw wire (4) in a second longitudinal direction, exactly opposite the first longitudinal direction, by a second length, and the first length is greater than the second length.