CH680840A5 - Wire cutting device for spark or electroerosion machining systems - comprises fixed blade and rotary blade arranged under electrode wire engagement rollers - Google Patents

Abstract

A cutting device is arranged underneath the electrode wire engagement rollers of the machine and comprises a fixed blade (3) with a linear edge over the full length of one side forming the base of the blade as well as a lateral surface approximately vertical incorporating the line of the ridge of the linear edge over which the electrode wire (4) unreels; a rotary blade (2) having a linear edge the length of a side forming the top of the rotary blade and arranged approximately parallel to the edge of the fixed blade (3) and able to turn towards the electrode wire (4) in order to cut the wire in co-operation with the fixed blade (3). USE/ADVANTAGE - The device is designed for operation with a spark or electro-erosion machining system to cut the associated electrode wire. Its major advantage is that the section of the wire affected by the cutting is reduced thus minimising adverse effects on the machining operation.

Description

1

CH 680 840 A5

2

Description

The present invention relates to a wire cutting device for use in combination with a wire-electrode sparking machine.

A conventional electric sparking machine using a wire electrode has a supply coil or roller and a take-up coil or roller for moving a wire electrode to cause electrical discharges to occur between the wire electrode and a work piece , such as a metal mold for molding plastic materials, arranged in a fixed position on a machine table which is adapted to be driven, so as to drill predetermined holes in metal molds. The feed roller or spool of wire generally has a capacity of about 5 km of 0.2 mm wire, for example, which is roughly equivalent to 24-hour continuous operation, so the machine can operate all the night without stewardship.

In such wire electrode sparking machines, it is now common practice that instead of tensioning the wire used which is unwound from the set of pick-up rollers of the machine, on a take-up or counter coil. spool, the wire is collected directly and sequentially from the set of pick-up rollers in a wire receptacle in the manner of a “spontaneous fall”. The wire used cannot be reused as it is, but must be melted for regeneration. Since the take-up reel or counter-reel system has this regeneration drawback, the above-mentioned spontaneous drop system is generally considered to be the most advantageous. Furthermore, when a wire electrode sparking machine having an automatic connection function is used, it is generally inevitable to adopt this spontaneous fall system.

However, in such spontaneous fall systems, as long as the used yarn is continuously received in a yarn receptacle, the large volume of accumulated yarn quickly saturates the receptacle and, in extreme cases, the heaped yarn is caught by the take-up rollers of the wire electrode ignition machine.

Therefore, it is necessary for the operator to control the flow of the wire used during the operation of the wire electrode sparking machine, thus blocking the attempt to set up fully automated production lines.

For these reasons, prior art uses a system such that the wire used is passed over a pair of pinion-shaped rollers to wave the wire and thereby reduce the apparent length of the wire. Despite this, the space occupied by the accumulated wire is still large and the receptacle is filled over a short period of time.

It can be envisaged to cut the wire used sequentially with a wire cutting means of the knife or pliers type but although its diameter is only about 0.2 to 0.3 mm, the brass electrode wire is so hard that sparks are produced when cutting with cutting means and tend to decrease the effective life of the cutting edge.

The above-mentioned drawbacks are overcome by the present invention which provides a wire cutter for use in combination with a wire electrode sparking machine and which comprises, arranged under the wire take-up rollers sparking machine, a stationary knife having a linear edge along one side thereof forming a base and an approximately vertical lateral surface comprising the edge line of said linear edge along which an electrical wire unwound towards the bottom from said gripping rollers can move and a rotary knife having a linear edge along one side thereof forming an apex and in an arrangement approximately parallel with the edge of said fixed knife and adapted to pivot towards said wire thereby shearing the wire in cooperation with said fixed knife.

The invention will be better understood on reading the detailed description which follows, taken with reference to the appended drawings which are given solely by way of example, and in which:

- fig. 1 is a side elevational view showing a wire cutting device implementing the principle of the present invention;

- fig. 2 is a plan view of the device shown in FIG. 1;

- fig. 3 is a front view taken along line A-A of FIG. 1;

- fig. 4 is a plan view showing, on an exaggerated scale, a method for mounting a rotary knife;

- fig. 5 is a longitudinal sectional view showing a wire guide tube for use in the present invention;

- fig. 6 is a perspective view showing another wire cutting device implementing the principle of the present invention;

- fig. 7 is a schematic view illustrating the relationship of the play between feed rollers with the diameter of the wire electrode;

- fig. 8 is a front view in partial section of yet another wire cutter implementing the principle of the present invention, and which is somewhat similar to the device shown in FIG. 6;

- fig. 9 is a sectional view taken along line A-A of FIG. 8;

- fig. 10 is a front view showing a cover intended to be used to protect the device against falling pieces of wire; and

- fig. 11 is a side elevational view showing a front cover.

Referring to the first embodiment shown in Figs. 1, 2, 3 and 4, a wire cutting device generally referenced in C is installed at the downstream end of a wire electrode sparking machine (not shown) used for the machining of metal molds intended for be used in the molding of plastic materials. The device C comprises a gear motor 1 which has nominal characteristics of 90 W and 200 V, by

5

10

15

20

25

30

35

40

45

50

55

60

65

2

3

CH 680 840 A5

4

for example, a rotary knife 2 made of ceramic material which is driven by said gear motor 1, and a fixed knife 3 made of ceramic material which is arranged juxtaposed with respect to said rotary knife 2. In operation, a brass wire 4 with a diameter of 0.11 to 0.33 mm which is unrolled at a speed of 80 to 250 mm / sec of the wire electrode ignition machine is cut successively into pieces of a predetermined length, for example 60 mm, and is received in a wire receptacle (not shown).

In the above arrangement, the rotary knife 2 is a rectangular parallelepipedal element equipped with a cutting edge on one side of its top and is mounted on a rotary shaft 5 at an angle of inclination a of 5 ° in the plan view (fig. 4).

The wire 4 is unwound down like a “spontaneous fall” from a set of drive or take-up rollers (referenced 40 in fig. 5), then is sheared by and between said knife rotary 2 and said fixed knife 3 which is described in detail below.

The fixed knife 3 is shaped more or less like the rotary knife 2 and has a cutting edge along the edge on one side of its base. The fixed knife 3 is positioned above the rotary knife 2. Consequently, the wire 4 unwound downwards as mentioned above moves along one side or lateral face of the fixed knife 3. The fixed knife 3 is mounted on a support 6 of the fixed knife which has the shape of a rectangular bar, with its cutting edge making a deflection angle ß of about 1 ° relative to the support 6 (fig. 1).

In the above arrangement, the wire 4 hanging downwards at approximately a right angle to the cutting edge of the fixed knife 3 is sheared by the joint action of the fixed knife 3 and the rotary knife 2 at an angle of inclination a of 5 ° with respect to the axis of the wire 4. The cross section of the cut wire is characterized by a larger shear section and, consequently, by a smaller breaking section than that of the wire sheared with the conventional wire cutting means, which shows that the device of the present invention is more efficient for cutting. The term "shear section" as used herein means the section sheared by the cutting means per se and the corresponding section surface has a shiny surface. On the other hand, the term "breaking surface" means the surface cut by breaking, and not by the cutting edges and, in this case, the section in section has a rough surface. The larger the shear section, the greater the cutting performance of the cutting means.

The rotary knife 2 and the fixed knife 3 are described in more detail below.

The rotary knife 2 is driven together with the rotation of the gear motor 1, at a speed of about 180 to 190 rpm, for example. The speed of rotation of the gear motor 1 is reduced by a speed reducer 7 carrying a reduction shaft 8 at one end thereof, and said rotary shaft 5 is rigidly fixed to this reduction shaft 8 via 'a key 9. The rotary shaft 5 is formed of a notched surface forming a flat 10 on which a support 11 of the rotary knife is mounted and is fixedly held in position by means of screws 12. The support 11 of the rotary knife is formed from L-shaped faces 11 a and 11 b (fig. 3) against which the rotary knife 2 is pressed intimately by means of a spacer 13 and is held so fixed by means of a screw 14, with an axis 15 projecting from said face 11b, the face 11a being used for positioning.

As shown in fig. 4, the face 11b is arranged at an angle of inclination of a = 5 ° relative to the longitudinal axis 0 of the rotary shaft 5 in a plan view.

To prevent deflection with eccentricity of the rotary shaft 5 during rotation, the basic position of the rotary shaft 5 is supported by a bearing 16. This bearing 16 is fitted in a bearing support 17 which is held so rigid, with a screw 19, to a flange 18 attached to the end face of the speed reducer 7. The reference numeral 20 represents a bearing retaining means and the reference numeral 21 represents a bearing retaining screw.

The fixed knife 3 is fixedly mounted on the top of said flange 18. Thus, a frame 23 for mounting the fixed knife, which is formed of fork-shaped elements 22, 22 at its front end, is mounted so rigid on top of the flange or collar 18 by means of screws 24. Said support 6 of the fixed knife which is shaped in the form of a rectangular bar is inserted vertically between the elements mentioned above in the form of a fork 22 , 22 and this fixed knife support 6 is biased and rigidly held by two pressure screws 25 and 25 extending in a horizontal direction. Furthermore, the support 6 of the fixed knife is pushed by an adjustment screw 26 arranged at right angles to the upper pressure screw 25. Consequently, as soon as the adjustment screw 26 is advanced or moved back, the position vertical of the support 6 of the fixed knife is inclined slightly relative to the vertical so as to give a certain angle of deflection (ß = 1 °) to the cutting edge of the fixed knife 3.

The lower end of said support 6 of the fixed knife is formed integrally or integrally with a block 6a extending horizontally and said fixed knife 3 is rigidly held on the lateral side of said block 6a by a screw 28 via a spacer or spacer 27.

This fixed knife 3 is positioned by means of a pin or pin 34 projecting from the lateral side of the block 6a and from a shoulder 6b of the block 6a (FIG. 1). The free end of the screw 28 carries a nut 29 provided with a wire guide which is formed by a guide groove 29a shaped like a funnel which guides the wire down along the lateral side of the fixed knife 3.

In the embodiment described above, the next buffer or means for reserving the wire is provided. Thus, a plastic block 30 for guiding the wire is rigidly mounted on top of said block 6a by means of a screw 31 and is provided with a funnel-shaped guide orifice 30a.

5

10

15

20

25

30

35

40

45

50

55

60

65

3

5

CH 680 840 A5

6

extending across it. A guide tube 32 which acts as a buffer or for reserving the wire projects from the top of said wire guide block 30.

The guide tube 32 is described in more detail below. Thus, a simulation test using a model of this bushel forming buffer produced the following results. As shown in fig. 5, when a brass wire 4 with a diameter of 0.3 mm has been introduced into a guide tube 32 with an internal diameter of d = 4 mm and an effective length of L = 114 mm with a load of F = 130 g, wire 4 was found to be introduced as a bent spiral with two inflections. When the load F was further increased, the wire bent to generate a permanent stress so that the downward feeding of the wire could not occur gradually and, therefore, it was impossible to cut a straight wire. The theoretical total length £ of wire 4 under the load of 130 g was given by

& = / (2ird) 2 + L2

Z = ✓ (2ir * 4) 2 + 1142 = 116.74 = 117

Therefore, the wire can be introduced with an additional 117-114 = 3 mm. In other words, the wire 4 can be temporarily retained (placed in reserve by buffer) inside the guide tube 32 by the equivalent of approximately 3 mm.

On the other hand, the wire feeding speed at the level of the set of take-up rollers 40 of the wire-electrode sparking machine in service is at most 250 mm / sec, while the peripheral speed of linear edge of rotary knife 2 is 556 mm / sec and the thickness of rotary knife 2 is 47 mm. Therefore, the length of the wire subject to temporary stoppage by the thickness of the rotary knife 2 is 2.02 mm. Of course, as soon as the rotary knife passes beyond the shearing position, the wire 4 is immediately released. Therefore, if the thickness of the rotary knife is reduced, the length of the temporarily held wire is also reduced. Since this length of approximately 2 mm which is temporarily retained is in the range of 3 mm in length of the wire retained in said guide tube 32 (since the distance from the set of gripping rollers 40 to the rotary knife 2 in the machine in service is greater than 200 mm, the length which can be retained is greater), the guide tube 32 mentioned above has been determined to operate as a buffer or effective means of storage to preserve the elastic deformation of the wire 4. It has likewise been determined that for a wire electrode with a diameter of 0.3 mm, the internal diameter of the guide tube 32 is 4 to 8 mm.

A second embodiment of the present invention is described below, now referring to FIG. 6. Being different from the first embodiment, this second embodiment comprises a pair of feed or advance rollers 38 and is capable of being associated with a wire electrode sparking machine equipped with an automatic system. wire connection.

Referring to fig. 6, a rotary knife 2 is rigidly fixed on a rotary shaft 5, which is driven by a gear motor 1 (fig. 1), by means of screws through a support 11 of rotary knife and d 'a spacer means or spacer 13. Therefore, the mounting scheme of the rotary knife 2 is similar to that of the first embodiment.

On the other hand, the fixed knife 3 is mounted in a different way from that of the first embodiment. Thus, a fixed knife mounting frame 23 is rigidly held on the front of a flange 18 similar to that used in the first embodiment by means of a screw 26 ', and a knife support fixed 6 is fixed to said mounting frame of the fixed knife 23 by means of screws 34, 34. This fixed knife support 6 is formed by a shoulder at one end thereof, and the fixed knife 3 is mounted at the most forward end of the latter by means of a spacer or spacer 27. A grooved block 35 having a guide groove 29a which, in operation, is rigidly fixed to a block of wire guide 30 by means of a set of screws (not shown) is superimposed on the lateral side of this fixed knife 3. The fixed knife support 6, the spacer or spacer 27, the fixed knife 3 , the block 35 with guide grooves and the guide block for the wire 30 are fixed to form a unit integral or one-piece via a screw 28 screwed onto the carrier 6 of the fixed knife.

The grooved block 35 and the wire guide block 30 are provided with an elongated groove or slot 30b, the main diameter of which extends in the direction of the cutting edge of the fixed knife 3 and said screw 28 extends through said elongated groove 30b.

The wire guide block 30 mentioned above is shaped as an inverted L-shaped letter and a nozzle 36 is embedded in the upper arm of the block 30, with a guide tube 32 which is disposed on said nozzle 36 .

Furthermore, a graduated pin or pin 37 is slidably inserted in the guide block 30 in the vicinity of the nozzle 36. This pin 37 projects from the front face of said flange 18.

The feed or feed rollers 38, 38 are arranged in the cut-out space of the fixed knife support 6. One of the supply rollers 38, 38 is driven by means of a rope or belt 39 from said rotary shaft 5 and the other roller follows the above-mentioned driving roller.

Consequently, in order to adjust the cutting position of the wire of the rotary knife 2 and the fixed knife 3, the screw 28 is left free at first, the grooved block 35 and the wire guide block 30 are moved in the 'extent of said elongated groove

5

10

15

20

25

30

35

40

45

50

55

60

65

7

CH 680 840 A5

8

30b, and finally the screw 28 is tightened. Thus, the wire cutting position is changed to ensure a clean cut by the fixed and rotary knives.

Referring to fig. 7, the pair of feed or feed rollers 38 is disposed between said fixed knife holder 6 and the upper arm of the wire guide block 30 and, as mentioned above, one of the feed rollers 38 is driven from the rotary shaft 5 via the cord or belt 39, while the other feed roller follows the aforementioned driving roller. This driven roller is pivotally mounted on one end of a lever 47 supported by a pin or pin 46, with a spring 48 which is loaded at the pivot point, while a lever stop screw 49 is put in place. abutment against the other end of said lever 47.

A clearance C is interposed as follows between these two supply rollers 38, 38. Thus, so that these supply rollers 38, 38 can effectively clamp the wire 4, the diameter D of the respective rollers should be sufficiently large. However, when compact feed rollers 38, 38 are to be used, the wire 4 cannot be effectively clamped. Consequently, in this embodiment, the clearance C has been interposed for compact feed rollers so as to help in the gripping of the wire 4. Thus, the initial gripping force (clamping force) applied to the wire 4 is explained as follows.

SF = F-2ftan (a-p) (1)

p = tan "V (2)

"- C0S_1 (^) 0)

or

SF: grip force (gr)

F: feeding force (gr)

f: spring biasing force of the roller 28 (gr)

a: contact angle p .: coefficient of friction p: angle of friction

D: diameter of the feed roller 38 (mm) d: diameter of the wire 4 (mm)

Knowing that F = 0 and f is an appropriate value, the necessary condition for SF> 0

is given by p> a (4)

Using ji, D and d, the above expression (4) can be rewritten:

H> tan (cos "1 (5)

By substituting the real machine value n = 0.17 (ceramic rollers) in the above expression (5), this gives:

D> 70.7 d

Thus, so that the wire 4 can be taken exclusively by the frictional force of the feed rollers 38 in the absence of the feed force or advance on the wire 4, the roll diameter D should be 71 times larger than the diameter of the wire d. Stated differently, it was determined

that the minimum of D = 22 mm is essential for d = 0.3.

However, for D = 22 mm, the installation clearance proves to be too large to provide a compact system. For D = 15, D / d = 50> 71, this being unsatisfactory, and it has been confirmed experimentally that the wire could not be taken successively. If the wire 4 is as thin as d = ê 0.2, D / d = 75> 71, which thus allows the setting.

Consequently, it can be envisaged to increase p in expression (4), that is to say the coefficient of friction p., But since the feed rollers 38 are used continuously, the metal dust wire 4 is deposited on the surfaces of the rollers to restore p. = 0.17 adequately.

In the present embodiment, the gripping force has been increased by decreasing the value of a in expression (4) for a diameter of the roller D = 15, i.e. D / d = 50, without change in the value of n.

, -l / D + C-d \ / c \

"'= COS (—p—) (6)

where C is the clearance between the rollers.

We have found that C = 0.4 • d is appropriate.

Supposing that, in expression (6), D = 15, d = 0.3 and C = 0.12,

a '= 8.888.

On the other hand, in expression (3),

"= 11.48

Thus, if n = 0.17, P = 9-65 and, therefore, p <a so that wire 4 cannot be taken. Now if p> a ', wire 4 can be taken.

Furthermore, according to formula (6), as soon as the coefficient of friction p is established, the feed rollers 38 can be used effectively for a longer period of time although they are compact.

We will now refer to Figs. 8 to 11, which represent a device similar to that shown in FIG. 6, but equipped with a cover to protect the device against the pieces of wire produced. In all of these views, like reference numerals represent like elements.

A reduction shaft 8 on which said rotary shaft 5 is fitted and locked by a key, extends from a gear motor 1. The base of this rotary shaft 5 is supported by a ball bearing 16 which is adjusted in a bearing support 17 which, in operation, is rigidly fixed to a flange of said gear motor 1. On the other hand, the front end of the rotary shaft 5 is formed by a cut surface 10 forming a flat surface on which a support 11 for an L-shaped rotary knife is mounted and locked in position by screws 12,12. A rotary knife 2 is adjusted against the support of the rotary knife 11 mentioned above by means of a spacer or spacer 13 and is locked in position by means of a screw 14.

A fixed knife 3 is installed as follows. Thus, a fixed knife mounting frame 66 is rigidly mounted in front of said flange 18 by a screw 67 and a fixed knife holder 6 and re5

10

15

20

25

30

35

40

45

50

55

60

65

5

9

CH 680 840 A5

10

rigidly connected to said mounting frame of the fixed knife 66 by means of screws 68, 68. Said fixed knife 3 by means of a spacer or spacer 69 is covered by the surface of the front end of said fixed knife support 6 and, moreover, a guide plate 70 and a grooved block 71 are successively covered. Furthermore, the guide block 72 of the wire is moreover covered on the grooved block 71 and the total assembly is locked by means of a screw 73 to form an integral or monobloc unit. The grooved block 71 is formed of a guide groove 71a in the form of a funnel which extends through the thickness of the block. The wire guide block 72 is formed in the form of an inverted letter L and a nozzle 74 is embedded in the upper arm of the block 72 while a guide tube 75 projects from the top of said nozzle 74.

A pair of feed or feed rollers 38 is disposed between the fixed knife holder 6 and the upper arm of the wire guide block 72 and one of the rollers 38 is driven from an intermediate position of said shaft rotary 5 by means of a rope or strap 39. Thus, a pulley 80 and said feed roller 38 are adjusted on a shaft of the feed roller 79 which is rotatably supported by a support 78. This roller feed is made of a ceramic material and rigidly fixed to the shaft of the feed roller 79 by means of an assembly screw 81.

The device mentioned above is covered externally by means of a cover 52 in the form of a bottomless box. Furthermore, a cord or belt cover 53 is fixed in position between said rotary and fixed knives 2, 3 and the cord or belt 39 to protect the cord or belt 39, in particular against the flight of pieces of the cut wire.

This belt cover 53 includes a plate member 55 having a central opening 54 for free adjustment on the rotary shaft 5, as shown in FIG. 10, and an element forming a curved guide plate 56 arranged as facing the direction of rotation of the rotary knife 2 as illustrated in FIG. 11, and the plate element 55 is rigidly fixed to the front of the bearing support 17 by means of a screw 57.

For the above-mentioned construction, this embodiment operates as follows. The wire 4 which is unwound from the take-up rollers of the wire-electrode sparking machine is guided by the guide tube 32 and temporarily retained therein and then drawn into play between the feed rollers through the nozzle 36. The wire 4 clamped by the feed rollers 38 is guided by the guide groove 29a and moves downward along the lateral side of the stationary knife 3. The wire 4 moving down is sheared by the rotary knife 2 and the stationary knife 3 into pieces. The pieces of wire 4 fall into a receptacle for the wire since their flow is controlled by the box-shaped cover 52, the plate element 55 and the guide plate 56.

Claims (10)

Claims 1. A wire cutting device intended to be used in combination with a wire electrode sparking machine, characterized in that it comprises, arranged under the wire take-up rolls of the sparking machine, a fixed knife (3) having a linear edge along a base side thereof and an approximately vertical lateral surface having the edge line of said linear edge along which a wire electrode (4) unwound downward from of said gripping rollers can move and a rotary knife (2) having a linear edge along an apex side thereof and in approximately parallel arrangement with the edge of said fixed knife and adapted to rotate towards said wire (4 ) thereby shearing the wire in cooperation with said fixed knife (3). 2. A wire cutting device according to claim 1, characterized in that said rotary knife (2) is inclined at a slight angle (a) in a plane parallel to its axis of rotation. 3. A wire cutting device according to claim 1, characterized in that said rotary knife (2) is inclined at an angle (a) of about 5 °. 4. A wire cutting device according to one of claims 1 to 3, characterized in that said fixed knife (3) is inclined at a slight angle (p) in a plane comprising the axis of rotation of said rotary knife. 5. A wire cutting device according to claim 4, characterized in that said small angle (ß) of the fixed knife (3) is about 1 °. 6. Wire cutting device according to one of claims 1 to 5, characterized in that it comprises a guide tube (32) forming a wire buffer (4) between the gripping rollers of the machine and said fixed knife (3). 7. A wire cutting device according to claim 6, characterized in that it comprises means (28, 30b) for moving said guide tube (32) relative to the cutting edges of said fixed (3) and rotary knives ( 2). 8. A wire cutting device according to claim 6 or 7, characterized in that it comprises a pair of feed rollers (38) of the wire (4) between the lower end of the guide tube (32) and said fixed knife (3). 9. A wire cutting device according to claim 8, characterized in that the relation D> 71 • d is maintained between the diameter (D) of said rollers and the diameter (d) of the wire and the relation C = 0.4 - d is maintained between the clearance between the feed rollers of said pair of rollers and the diameter d of the wire. 10. A wire cutting device according to one of claims 1 to 9, characterized in that it comprises a cover (53) comprising a plate element (55) fitted on the rotary shaft of said rotary knife (2) and generally extending in a direction normal to said shaft and a curved side plate member (56) connected to said plate member (55) covering at least the total length of said fixed (3) and rotary (2) knives on the side where the cut wire is discharged. 5 10 15 20 25 30 35 40 45 50 55 60 65 6