EP0232920A2 - Internal hole saw with a plurality of blades for sawing of crystal bars as well as methods executed by that saw - Google Patents

Abstract

A multi-blade inner hole saw for sawing crystal rods or blocks, in particular silicon-based solar cell base material, into thin slices and sawing processes carried out by means of this saw are specified. According to the invention, the saw has saw blades arranged in mirror symmetry on both sides of a common drive cylinder. During the sawing process, a workpiece is sawn synchronously from each of the saw blades.

Description

The invention relates to a multi-blade internal hole saw for sawing crystal rods into thin slices and to separation processes carried out by means of this saw.

For the production of electronic components or solar cells, the semiconductor or oxidic material used, e.g. B. silicon, germanium, gallium arsenide, indium phosphide, sapphire or gallium-gadolinium garnet often in the form of thin disks typically 0.1 to 1 mm thick, which is usually by sawing the starting material in the form of crystal rods or blocks be won. In most cases, this sawing process is carried out using internal hole saws.

In the known internal hole saws, the saw blade is clamped in a clamping frame on the outer edge. This is held by the cup-like widening tensioning frame support, which is attached to one end of a drive cylinder, which is usually mounted by means of ball, air or hydrodynamic bearings and is set in rotation by a drive unit. This one-sided, top-heavy arrangement requires an uneven load on the Ltkger, which reduces the wear resistance and service life and a slight inclination of the saw blade has the unfavorable effects on the cutting process and the cutting accuracy. This effect is all the more pronounced, the more top-heavy the arrangement, so that naturally hole saws with several saw blades, e.g. _B. according to DE-OS 32 16 200, are more affected than those with only one saw blade. The higher average power is at _M Therefore ehrblattanordnungen always achieved at the expense of cutting precision and service life, which is unsatisfactory in view of ever increasing accuracy requirements.

The object of the invention was to provide a multi-blade internal hole saw as well as separation processes carried out by means of this saw, by means of which a high cutting accuracy and long tool life are guaranteed at high cutting performance.

The task is solved by a multi-blade internal hole saw, which is characterized by saw blades or saw blade groups arranged mirror-symmetrically with respect to the bearings on both sides of a common drive cylinder.

The sawing method carried out by means of such an arrangement is characterized in that the workpieces to be sawn, the number of which corresponds to the number of saw blades or saw blade groups, are brought into the respective cutting position by a parallel or opposite translation movement before each cutting operation and by a synchronous relative movement between the respective Saw blade or the saw blade group and one workpiece each are subjected to a sawing process at the same time.

As workpieces, both individual crystal rods or blocks, as well as groups combined from these, e.g. B. bundles of rods can be used.

In most cases, the multi-blade internal hole saws according to the invention, with one saw blade each, are both ten of the drive cylinder used. However, an increase in saw performance can be achieved by using saw blade groups. Saw blade groups are understood to mean arrangements in which there are several, advantageously 2 saw blades on each side of the drive cylinder, the spacing from one another of which can be smaller, the same or greater than the length of an individual workpiece to be sawn. In the case of n saw blades, this distance is expediently set at most to the nth part of the workpiece length, where n corresponds to an integer greater than or equal to 2. The possible minimum distance is chosen to be greater than the sum of the desired pane thickness and ^k the kerf thickness and is usefully around 4 mm. For the sake of simplicity, only the expression "saw blade" is used in the following; however, the statements also apply analogously to saw blade groups.

The closest distance between the saw blades arranged mirror-symmetrically on both sides of the common drive cylinder depends on the manner in which the workpieces are brought into the respective cutting position. While this distance is in any case chosen to be greater than the workpiece length in the case of a parallel translation movement, it can be both smaller and larger when the workpieces are moved in the opposite direction into the cutting position. Distances below the workpiece length, however, require the use of removal devices if the discs are completely separated during each cutting process, so that their required effective range between the saw blades determines the minimum possible distance. Basically, the distances between the saw blades or saw blade groups in the multi-blade according to the invention internal hole saw can be varied within wide limits, depending on the bearing used and the position of the saw blades; Distances of 3 to 200 cm have proven effective.

The common drive cylinder, on the two sides of which the blades are arranged mirror-symmetrically with respect to the bearings, is preferably used with an inner diameter which is larger than the inner hole diameter of the saw blades and advantageously approximately corresponds to the inner diameter of the clamping system in which they are clamped. These requirements can be met inexpensively with the aid of drive cylinders mounted externally by means of magnetic, air or hydrodynamic bearings. The external storage of rotating systems using such bearings is generally known and is used in many other areas, e.g. _B. used in centrifuges: Also for the power transmission from the actual drive unit, for example an electric motor, to this drive cylinder, various options are available to the person skilled in the art, eg. B. by means of straps, known and therefore do not require further explanation here.

The advantage of a large inner diameter of the drive cylinder, which preferably corresponds approximately to the inner diameter of the clamping frame, is that in cutting processes in which the crystal rods are first broken down into a plurality of interconnected disks without removal, the machinable length of the workpiece is not, as in conventional internal hole saws. is limited by the cup-like narrowing shape of the tenter frame. Basically, however, embodiments based on the conventional internal hole saws with a wide clamping frame and narrow drive cylinder are also conceivable, in which, for example, a central, narrow drive cylinder is widened in a cup-like manner on both sides to accommodate the clamping frame. In principle, the clamping frame and saw blades can also be arranged within the drive cylinder.

1, by way of example and of course not in the sense of a restriction, a possible explained _{for a} multi-blade internal hole saw according to the invention and the sawing method that can be carried out with it.

Between the frame block 1 and the frame superstructure 2 is one with the help of an external bearing 3, for. B. an air, magnetic or hydrodynamic bearing mounted drive cylinder 4. Mirror-symmetrical to the bearing, this carries on both sides a clamping frame 5, which can be designed, for example, in the manner known from conventional hole saws and in which a saw blade 6 is clamped is. By using appropriate multi-sheet clamping frames, the present arrangement can also be converted for more than two simultaneous cutting operations with the drive cylinder 4 unchanged. According to the preferred embodiment, the inner diameters of the clamping frame 5 and the drive cylinder 4 are approximately the same size, although different inner diameters cannot be excluded.

For reasons of clarity, the actual drive unit, usually an electric motor, and the power transmission, advantageously a flat belt, by means of which the drive cylinder 4 and thus the saw blades 6 are set in rotation, are not shown. Basically e.g. power transmission using V-belts or toothed belts is also conceivable.

The workpieces 7, z. B. crystal rods or blocks of cast, multi-crystalline silicon with columnar structure. are optionally attached to the workpiece carrier 9 with an additional cutting pad 8, e.g. B. by cementing or gluing. This lies on both ends of the feed carriage 10, and can be driven by a drive 11, for. B. a stepper motor, perform translational movements to the Bring workpieces into the intended cutting kit. The workpiece carrier 9 can advantageously also be supported, for example, by pneumatic or hydraulic supports 12.

The embodiment with a workpiece carrier 9 bridging the feed carriage 10, which is guided through the inner hole opening of both saw blades 6 and the drive cylinder 4 and rests on both ends, is preferred in the context of the invention, in particular with additional supports 12, since it is during the sawing process guaranteed particularly favorable vibration behavior. However, it is of course also conceivable to have arrangements with two separate workpiece carriers, one on one side and with the free end facing the saw blades, which carry out an opposite translation movement of the workpieces.

The feed, which causes a relative movement between the workpieces 7 and the rotating saw blades 6 during the actual sawing process, is done with the aid of the feed carriage 13 and can preferably be hydraulically by means of a feed cylinder 14, but also by means of another drive z. B. controlled by an electric motor.

Of course, variations of the kinematics, z. B. Infeed and feed by translational movement of the drive cylinder 4 with stationary workpieces 7, or arrangements with a stationary drive cylinder 4 are not excluded. In addition, embodiments are conceivable, the z. B. are provided with additional devices for removing separated panes, for example according to US-PS 444 54 94, or with filling stations that fill the kerfs between the panes in cutting processes in which the crystal rods are separated into a plurality of interconnected panes and so stabilize the connection of the washers.

1, for example, silicon blocks made of solar cell base material, which typically have a cross section of 10 × 10 cm and a length of approximately 30 cm, can be sawn according to the methods described below. First of all, these blocks, which are advantageously provided on their underside with a cutting base made of, for example, glass, ceramic or carbon, are attached to the workpiece carrier, for example clamped, glued on or cemented on. One of the blocks comes outside, one inside the two in this case z. B. about 35 cm apart saw blades (outer diameter z. B. about 55 cm, inner hole diameter z. B. about 18 cm) and advantageously so that both occupy an identical position relative to the saw blade acting on them . Such an identical relative position of the blocks to the saw blade is not absolutely necessary, but is recommended in view of an optimal cutting yield and a uniform load on the saw blades and bearings during the entire sawing process.

Then both blocks are moved in the same way into the inner opening of the saw blades by a translational movement of the workpiece carrier until the intended cutting position is reached. An upward movement of the feed carriage 13 then leads the blocks to the, for example, diamond-coated cutting edge of the rotating saw blades, which begins to work into the respective workpiece with the formation of a kerf until the desired disk has finally formed. In saws, such as that corresponding to FIG. 1, in which no disc removal is provided, this disc is not completely separated from the rest of the block, but rather a connection ensuring a stable mounting of the disc, advantageously via the cutting base, is left. Then the feed carriage is moved back to the starting position, the workpiece carrier moves both blocks in the same direction into the next cutting position, and the next cut is made by moving the feed carriage upwards into the workpiece. This process is repeated until the blocks have been sawn into a plurality of interconnected disks in the desired manner, that is to say also with the exception of contaminated sections or edge regions. These are then removed, so that finally by breaking the connection, for. B. grinding, sawing, melting or dissolving, the individual disks can be obtained.

A variant of this sawing method is also conceivable, in which the starting position of both blocks is on the outside of the saw blades and their translational movement leads in opposite directions into the interior of the drive cylinder. However, this procedure requires a considerable distance between the saw blades to accommodate both blocks. It may therefore be necessary to reduce the space requirement by first sawing the workpieces in half, then moving them back to the starting position, turning them 180 °, and finally continuing the sawing process from the other end. A reduction in the space requirement can also be achieved by sawing the workpiece in several stages and removing the sawn-off section in each case.

In general, those sawing methods in which the panes are not completely separated from the rest of the block (so-called comb cut) are preferred in the context of the invention, since the often complex removal devices can be dispensed with. Of course, the sawing process with complete separation and removal of the panes is not excluded. Variants with external or internal disc removal (infeed of the workpieces by opposing translation from the inside to the outside or from the outside in) or with disc removal on the inside and outside on one side (when the workpieces are delivered by means of parallel translation) can be used.

During the sawing process, the heat generated and the material removed are removed in the usual way by a coolant which, for example, reaches the separation point via a hose system, can drain through a system of slots and can finally be collected and, if necessary, fed back in after a reprocessing step . The control of the feed or infeed can also be carried out in the known manner by hand, but preferably by means of hydraulics or stepper motors.

The multi-blade internal hole saw according to the invention and the sawing process carried out by means of this saw are particularly suitable for sawing into silicon-based solar cell base material, which is usually obtained in the form of silicon blocks with a cross section of approx. 10 × 10 cm and a length of approx. 20 to 40 cm by a casting process mostly from 350 to 500 µm thick. Equally, however, the semiconductor or oxide materials mentioned at the outset can be cut into thin slices of 0.1 to 1 mm in thickness. Furthermore, other substances in rod form, e.g. Quartz or other glass or rods based on carbon can be cut into thin disks up to 30 mm thick.

Due to the mirror-symmetrical structure, even loads act on saw blades and bearings during sawing. This results in higher cutting accuracy, improved running properties, more uniform saw blade stress and longer tool life compared to conventional multi-blade internal hole saws. In addition, the ease of repair is greater, since in the event of defects on one of the saw blades, only this one needs to be replaced.

Claims (6)

1. _M saw blade inner hole saw for sawing crystal rods into thin slices, characterized by saw blades or saw blade groups (6) which are arranged in mirror symmetry with respect to the sides of the common drive cylinder (4) with respect to the bearings (3). 2. Multi-blade internal hole saw according to claim 1, characterized in that the saw blades or saw blade groups (6) have a distance from one another which is greater than the length of a workpiece (7) to be sawn. 3. Multi-blade internal hole saw according to claims 1 and 2, characterized by a through the inner hole opening of both saw blades or saw blade groups (6) and the drive cylinder (4) guided, supported on both outer ends of the workpiece holder (9). 4. A method for sawing crystal rods by means of a multi-blade internal hole saw according to claims 1 to 3, characterized in that the workpieces, the number of which corresponds to the number of saw blades or saw blade groups, brought into the respective cutting position before each cutting operation by means of an identical or opposite translation movement and be subjected to a sawing process simultaneously by means of a synchronous relative movement between the respective saw blade or the saw blade group and each workpiece. 5. The method according to claim 4, characterized in that the crystal rods are cut into a plurality of interconnected disks during the sawing process, the connection of which is only separated in an additional step after the sawing process has ended. 6. The method according to claim 4, characterized in that the discs are completely separated from the crystal rod during each sawing process and removed by means of a removal device.

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