Wire management method for high-speed wire cutting

Abstract

The present invention relates to a high-speed reciprocating wire cutting process, wherein an electrode wire is conveyed and precisely guided through a machining area by means of a wire travel loop, and the cutting process is performed by repeating: - running the electrode wire in a first direction until a first reciprocating position, - stopping and reversing the travel direction of the electrode wire, - running the electrode wire in a second direction until a second reciprocating position, - stopping and reversing the travel direction of the electrode wire. If the cutting process monitoring shows that the cutting process must be interrupted, a cutting process interruption sequence is executed, and the cutting process interruption sequence includes continuing the cutting process until the first or second electrode wire reciprocating position, and pausing or stopping the cutting process at the wire reciprocating position.

Description

Technical Field

[0001] The present invention relates to methods and machines for high-speed wire cutting, and in particular to improved wire management methods. Background Art

[0002] The method disclosed herein relates to high-speed wire cutting. This electrical cutting method is sometimes called high-speed wire electrochemical discharge wire cutting, fast wire cutting, high-speed reciprocating wire cutting, high-speed WEDM, or simply HS-WEDM or HS-WECDM or FW. In the following, it is referred to as a high-speed wire cutting process or HS-WECDM. The HS-WECDM process is carried out by applying a pulse voltage to a gap in an electrolyte with a certain conductivity, so the process includes electrochemical processing parts (dissolution) and electrothermal processing parts. The wire travel direction is periodically reciprocated back and forth, whereby the electrode wire is used multiple times. This is possible because of the low wire wear of the negative polarity pulse and due to the fact that molybdenum is generally used as the wire material. In addition, the wire travel speed is as high as about 20m / s. The high travel speed of HS-WECDM drags the processing fluid through the incision so that the removed material particles generated during cutting are discharged together with the processing fluid.

[0003] The HS-WECDM servo control system regulates the feed rate to ensure a proper and stable discharge gap. The servo control system is based on a process signal, such as a voltage, measured in the gap. The process signal is used to derive a signal error, which is used as feedback for the control of the axis feed rate. However, the machining process is not always stable; under certain conditions, the machining slows down or stops. The reasons may be dirt in the gap, deterioration of the machining fluid, formation of burns at the workpiece, deposition of machining debris, obstruction of the cutting cut, etc.

[0004] The HS-WECDM control unit monitors the feed rate and detects slowdowns and stops in the cutting process, or measures process signals and derives abnormal cutting conditions. Some HS-WECDMs take countermeasures to resolve such jams and attempt to complete the current process. Provisions include, for example, reversing the feed direction and returning a fixed distance along the path while monitoring process conditions, and then returning to the front-most cutting position.

[0005] However, it is not always possible to solve problems that occur during cutting with the aid of an automatic cycle, for example, if an already cut incision is blocked and cannot be reopened. In addition, if abnormal cutting conditions are not eliminated at the source of the blockage, the risk of wire breakage increases. Summary of the invention

[0006] A first aspect of the present invention relates to a high-speed reciprocating wire cutting process, in which an electrode wire is transported and precisely guided through a processing area by means of a wire travel loop, and the cutting process is performed by repeating the following: running the electrode wire in a first direction until a first reciprocating position, stopping and reversing the travel direction of the electrode wire, running the electrode wire in a second direction until a second reciprocating position, stopping and reversing the travel direction of the electrode wire, characterized in that if the cutting process monitoring shows that the cutting process must be interrupted (stuck or there is an increased risk of wire breakage), a cutting process interruption sequence is executed, and the cutting process interruption sequence includes continuing the cutting process until the first or second electrode wire reciprocating position, and pausing or stopping the cutting process at the wire reciprocating position.

[0007] In the high-speed reciprocating wire cutting process according to the present invention, the electrode wire is transported and accurately guided through the processing area with the help of a wire travel loop, and the cutting process is carried out by repeating the following: running the electrode wire in a first direction until a first reciprocating position, stopping and reversing the travel direction of the electrode wire, running the electrode wire in a second direction until a second reciprocating position, stopping and reversing the travel direction of the electrode wire, characterized in that if the cutting process monitoring shows that the cutting process must be interrupted, a cutting process interruption sequence is executed, and the cutting process interruption sequence includes continuing the cutting process until the first or second electrode wire reciprocating position, and pausing or stopping the cutting process at the wire reciprocating position.

[0008] According to the invention, the cutting process is thus monitored to identify situations in which the machining process is stuck. If it is determined that the machining process is stuck, a cutting process interruption sequence is executed, wherein the cutting process is first continued until the first or second electrode wire reciprocation position. In other words, upon the occurrence of a persistent problem indicated by the process monitoring, the cutting process is not interrupted immediately, but continues for the time required for the wire loop to advance the electrode wire to the wire reciprocation position, wherein the process is either paused in view of resuming the current cutting process or is stopped completely.

[0009] Below is an example of the operations performed after an interruption. The operator can determine the reason why the process was paused or stopped and can try to continue the cutting process. If he determines that the process cannot be continued from within the cutting cut, he can usually decide to restart the entire cutting operation from the starting point. In this case, he can try to carefully move the machine axis against the cutting direction. If this is not possible, the electrode wire must be removed from the cut. The operator separates the electrode wire from the wire drum and pulls the wire through the cut. Now, he moves the machine axis to the following position, in which he carries the electrode wire through the wire travel loop and tightens the end of the electrode wire at the wire drum. Finally, he moves the axis to the starting position. For example, the operator can continue the current processing from the original starting point.

[0010] According to another embodiment, one or more separation attempts are performed before the cutting process interruption sequence. When process monitoring shows that certain cutting conditions deviate from predetermined limits, the separation attempt is intended to restore normal cutting conditions. If the separation attempt is successful, the cutting process interruption sequence is bypassed and the cutting process automatically continues to the end of the program. It is known in the prior art that the operator can manually pause / restart the cutting process at any time, for example to check the progress of the processing, or to solve problems related to the current processing. According to the present invention, one or more separation attempts are automatically performed during the cutting process to solve the interference. The user can select one or more actions to be performed in the separation attempt.

[0011] Preferably, the split attempts include one or more of the following:

[0012] -Keep in the front cutting position,

[0013] - Reverse the feed direction and move back along the cutting path to a predefined length and / or while monitoring the cutting process parameters, then return to the front most cutting position,

[0014] - Changing one or more process parameters.

[0015] The separation attempt includes maintaining at the front-most cutting position. Here, the separation is attempted by continuing the HS-WECDM process at zero feed rate ("stationary" processing). Here, the wire loop, flushing and generator parameters may not be substantially changed.

[0016] The separation attempt is triggered by process monitoring when a predetermined condition is met.The conditions determining the execution of the separation attempt and the conditions determining the execution of the cutting process interruption sequence may be the same or different.

[0017] According to a preferred embodiment, the cutting process interruption sequence is executed if the cutting process monitoring finds at least one of the following conditions:

[0018] -The instantaneous cutting rate drops below the minimum cutting rate Vsmin,

[0019] - the average cutting rate drops below the minimum average cutting rate Vsavg,min,

[0020] - Deterioration of the cutting process,

[0021] - the number of separate attempts exceeds the predefined value nu,max,

[0022] - The number of earlier cutting process interruption sequences exceeds a predefined value ni,max.

[0023] Process monitoring includes observing one or more parameters of the cutting process. For example, the instantaneous cutting rate is compared with a minimum cutting rate Vsmin, and if the instantaneous cutting rate drops below said minimum cutting rate Vsmin, a cutting process interruption sequence is performed. In this way, the progress of the cutting process at the frontmost cutting position is monitored. In the same way, the average cutting rate is compared with a minimum average cutting rate Vsavg,min, thereby indicating an average cutting rate that is too slow.

[0024] In addition, process monitoring continuously checks the real-time cutting process signal to detect critical conditions. This includes, in particular, determining the occurrence and frequency of normal pulses, short pulses and open pulses. This is used to avoid workpiece damage, excessive wear or breakage of the electrode wire, etc.

[0025] In addition, the number of separation attempts is counted to determine the problem that persists. This may include counting the number of earlier successful or unsuccessful separation attempts. It may also include counting the number of unsuccessful separation attempts currently triggered by process monitoring.

[0026] Finally, the process monitoring counts the number of times the cutting process interruption sequence has been caused by the process monitoring.

[0027] According to further embodiments, the cutting process interruption sequence comprises one of the following:

[0028] - continuing the cutting process in the current wire travel direction up to a first reciprocating position and stopping said cutting process at the first reciprocating position, or

[0029] - continuing the cutting process in the current wire travel direction up to a first reciprocating position, reversing the wire travel direction and continuing the cutting process up to a second reciprocating position, and stopping said cutting process at the second reciprocating position, or

[0030] - immediately interrupting the cutting process, reversing the wire travel direction and continuing the cutting process up to a second reciprocating position, and stopping the cutting process at the second reciprocating position.

[0031] Therefore, it is possible to define how the wire travel circuit should operate, taking into account the specific construction of the machine or for other reasons. For example, a conventional high-speed reciprocating wire-cutting machine 100 has a single wire drum unit 10, in which the electrode wire 1 is unwound and wound up simultaneously. This makes the machine simple, but limits the amount of wire available between reciprocating movements. As described, a high-speed reciprocating wire-cutting machine 200 with two separate wire drum units 20, 30 can store multiple electrode wire layers, so that the available amount is much larger, the reciprocating interval becomes negligible compared to the cutting time, the autonomy is much higher, etc. Here, it may be preferred to interrupt the cutting process at a specific reciprocating position, such as Figure 4, the left wire drum 21 is filled with wire and the right wire drum 31 is empty. The reason may be the better accessibility of the wire travel circuit for changing the electrode wire or because of certain technical provisions that exist only on one side of the wire travel circuit.

[0032] In the case of very large amounts of wire stored on the wire drum, it may be advantageous to quickly interrupt the cutting process and reverse the wire travel direction at an intermediate position to quickly reach the designated reciprocating position and thus save time. In other cases, the cutting process continues in the current wire travel direction until the first or second reciprocating direction at which the cutting process is interrupted.

[0033] According to another embodiment, the cutting process interrupt sequence also includes issuing a warning message. Preferably, as soon as the process monitoring encounters a condition for which the cutting process interrupt sequence is executed, a warning message is issued. The message can be displayed on the control unit of the machine and / or transmitted by email, SMS, signal light, by means of an information exchange protocol (e.g., OPC UA) or other form. The message may include more or less detailed information about the condition encountered, but may also include information about the remaining distance to be cut or the percentage of work completed. In an embodiment, the user can reply to instruct the machine by selecting one of the available options on how to operate.

[0034] According to another embodiment, the interruption sequence of the cutting process further comprises storing the frontmost cutting position. The frontmost cutting position is the maximum axis position reached during the cutting process. This position is stored at the time of the interruption in view of a later continuation of the cutting process.

[0035] According to another embodiment, if it is determined that the remaining cutting length is less than a predefined remaining cutting length value lleft,min, the cutting process interrupt sequence is bypassed or postponed. The last part of the cutting process is sometimes unstable, for example due to the movement of the workpiece to be separated, due to changing flushing conditions, or other reasons. Here, process monitoring may erroneously derive / believe that the process is getting stuck, which is not necessarily true. For this reason, if the remaining cutting length is less than the predefined remaining cutting length value, the user may want to skip or postpone the cutting process interrupt sequence. The remaining cutting length is the length of the remaining cutting until separation. In this embodiment, the user can set the remaining cutting length value lleft,min to adopt different behaviors near the separation point. The remaining cutting length includes an intermediate remaining cutting length, and if the workpiece to be separated includes more than one part, there is an intermediate remaining cutting length. The remaining cutting length and the intermediate remaining cutting length can be derived from CAD data for an additive manufacturing (AM) build process, or learned from an earlier cutting process with the same geometry.

[0036] For example, the user may set a predefined minimum remaining cutting length value lleft,min to 0.5 mm. Process monitoring continuously derives the remaining cutting length, e.g., knowing the axis position at which the first spark has been detected, the current axis position, and the total cutting length. Now, if the instantaneous cutting rate drops below a predetermined minimum cutting rate Vsmin=0.8 mm / s and the remaining cutting length is less than 0.5 mm, the control is set to, for example, skip a split attempt or not execute a cutting process interruption sequence, or postpone these measures.

[0037] Furthermore, the cutting process can be continued using reduced cutting parameters when approaching separation of the workpieces.

[0038] Preferably, default settings are predetermined with respect to the type and number of split attempts and / or with respect to the conditions for determining the execution of a cutting process interruption sequence and / or with respect to the cutting process interruption sequence itself.

[0039] By automatically interrupting the cutting process at the wire reciprocating position in the exemplary high-speed reciprocating wire cutting machine 200 having the wire barrel units 20 and 30, a very small amount of electrode wire is left at the wire barrel 31 at one side of the wire travel loop, while most of the wire is stored at the wire barrel 21 at the other end of the wire travel loop. This is advantageous in view of the resumption of the cutting process.

[0040] Furthermore, by automatically interrupting the cutting process at the wire reciprocating position, waste of electrode wire is avoided or at least reduced. In particular, if the electrode wire is not excessively worn or damaged by the cutting process, the same electrode wire can be reinstalled on the wire travel loop and reused. Furthermore, the fact that the electrode wire 1 is already fully wound around one drum unit 20 or 30 (or, fully wound around one side of a single wire drum unit 10) is very practical for discharge operation when it is necessary to replace the electrode wire.

[0041] According to another embodiment, the cutting process is stopped at the wire reciprocating position, whereby a small amount of electrode wire is stored on a first wire drum and a large amount of electrode wire is stored on a second wire drum, characterized in that the electrode wire is automatically separated at the first drum and in that the electrode wire is automatically removed from the incision by reversing the wire travel direction.

[0042] This embodiment provides additional automation features to relieve the operator. Here, when the wire reciprocating position is reached, the short section of the electrode wire remains on the wire drum and in the wire travel loop. The end of the short section of the electrode wire fixed at the drum is now separated. For example, the end is held by means of a preloaded spring, which is electromagnetically activated to open. Now, by reversing the wire travel direction, the electrode wire is removed from the drum and through the incision. In this way, the machine axis of the HS-WECDM can move freely.

[0043] Preferably, the withdrawal of the wire is monitored to determine that it is successful before any further operations are initiated.

[0044] Accordingly, when the wire is successfully removed from the incision, the machine axis is optionally moved to a starting position or to a position suitable for inserting the electrode wire in the wire travel loop.

[0045] Additional aspects are set forth in the following description and in the accompanying drawings. Other features are inherent in the disclosed methods and products or will become apparent to those skilled in the art from the following detailed description of the embodiments and the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] The preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings, which are shown as follows:

[0047] Figure 1 High-speed reciprocating wire cutting machine;

[0048] Figure 2 Figure 1 The package unit of the machine shown in;

[0049] Figure 3 High-speed reciprocating wire cutting machine;

[0050] Figure 4 Figure 3 The bobbin of the machine is shown. DETAILED DESCRIPTION

[0051] Figure 1 An exemplary high-speed reciprocating wire cutting machine 100 is shown, which includes a base 106 on which a column 101 is mounted. A cross member 102 is mounted on a Z-slide (indicated by a dashed line Z) at the column 101 so that an upper wire guide head 112 can be positioned vertically. A lower wire guide arm 103 carrying a lower wire guide head 113 is fixedly mounted at the column 101. An X-slide 104, a Y-slide 105 and a worktable 110 are sequentially mounted on the base 106 so that a workpiece 2 mounted on the worktable 110 can move in an X / Y plane.

[0052] The reciprocating wire feed circuit comprises a wire package unit 10 and a plurality of rollers, by means of which the electrode wire 1 is fed through the processing area. The wire feed circuit comprises a wire tensioning unit, which is a simple weight-loaded roller 108 in the illustrated case. Figure 2 is a simplified spatial view of a yarn barrel unit 10, which comprises a yarn barrel 11 and a yarn barrel motor 12. The yarn barrel motor 12 is coupled to the yarn barrel 11 by means of a first transmission (not shown) which rotates the barrel and a second transmission (not shown) which converts the rotational motion into a translational motion to translate the barrel. Thus, the rotation and the translation are synchronized.

[0053] For example, the electrode wire 1 is loaded on the wire drum unit according to the following: one end section of the electrode wire 1 is fixed at one side of the wire drum 11, is arranged on rollers and the electrode wire 1 is advanced through the processing area, and then the electrode wire 1 is returned to the wire drum 11, where the electrode wire 1 is wound on the wire drum many times in a single layer to fill the drum. The second end section of the electrode wire 1 is fixed at the second side of the wire drum 11. In operation, the wire is unwound at one side of the wire drum 11 and is rewound simultaneously at the other side after passing through the processing area. Here, the capacity of the wire drum 11 is limited by its diameter, its length and the fact that a single wire layer is wound on the wire drum.

[0054] Figure 3 Another exemplary high-speed reciprocating wire cutting machine is shown. The exemplary high-speed reciprocating wire cutting machine 200 has a horizontal electrode wire arrangement, and Figure 1 The high-speed reciprocating wire cutting machine 100 shown in FIG. 1 has a conventional vertical electrode wire arrangement. The machine 200 includes a base 206 and a left column and a right column 201 mounted thereon. A cross member 202 is mounted between the columns 201. A wire guide frame 207 carrying a left wire guide head 212 and a right wire guide head 213 is mounted on a Z-slide (indicated by a dotted line Z) at the cross member 202 so that the two guide heads can be positioned vertically.

[0055] The workpiece is mounted on a table 210, and the table 210 is mounted on an X slide 204 so that the workpiece can be horizontally translated. Here, the workpiece is a substrate 4 with an additively manufactured metal part 3 built thereon. The AM part is separated from the substrate by means of a high-speed reciprocating wire cutting process.

[0056] also, Figure 3 The machine shown in FIG. 1 comprises two package units 20, 30. Figure 2 Compared to the illustrated single wire drum unit 10 (which unwinds and rewinds the electrode wire at the same time), the wire drum units 20, 30 either unwind or rewind during a single wire reciprocating cycle. This means that the electrode wire can be stored in multiple wire layers by controlling the rotation and translation of the drum units 20, 30, respectively, so that the capacity of the wire drum is significantly increased. The electrode wire is tensioned by controlling the rotation speed of the wire drum units 20 and 30. The tension is monitored by means of an adjustment roller 208 including a sensor (not shown), which provides a feedback signal to adjust the unwinding speed and / or the rewinding speed.

[0057] In a high-speed reciprocating wire-cutting machine 200 having two wire drums 21, 31, in the wire reciprocating position, one drum is full and the other is empty, as shown in FIG. Figure 4 As shown in .

[0058] As mentioned introductory, during the cutting process, situations may occur in which the machining is not completed for some reason. Sometimes the electrode wire must be removed from the cut to resume or terminate the machining. For example, it may happen that the cutting cut is blocked, the machining is stuck, it is not possible to retract along the cutting path (cut closure, short loop), and / or there is a risk of wire breakage or the wire is at the wear limit and must be replaced.

[0059] It is well known that installing or replacing electrode wire in a high speed reciprocating wire EDM machine is a tedious and time consuming task. The present invention aims to facilitate this task.

[0060] For the avoidance of doubt, it is foreseeable that the provisions of the present invention apply to both types of machines, a high speed reciprocating wire EDM machine having a single package unit 10 , and a machine having two package units 20 , 30 .

[0061] Reference numerals

[0062] 1. Wire electrode

[0063] 2 Workpiece

[0064] 3 AM Section

[0065] 4AM substrate

[0066] 10, 20, 30 wire package units

[0067] 11, 21, 31 wire tube

[0068] 12. Wire drum motor

[0069] 100, 200 High-speed reciprocating wire cutting machine

[0070] 101, 201 columns

[0071] 102, 202 Horizontal parts

[0072] 103 Wire guide arm

[0073] 104, 204 X-axis sliding part

[0074] 105 Y-axis sliding part

[0075] ZZ axis

[0076] 106, 206 machine base

[0077] 108 Weight Loaded Roller

[0078] 110, 210 workbench

[0079] 112 Upper wire guide

[0080] 113 Lower wire guide

[0081] 212 Left thread guide head

[0082] 213 Right wire guide head

[0083] 207 Wire Guide Frame

[0084] 208 Adjustment roller.

Claims

1. High-speed reciprocating wire cutting method, in which the electrode wire is fed and accurately guided through the processing area by means of a wire travel loop, and the cutting method is carried out by repeating the following: - running the electrode wire in a first direction to a first reciprocating position, - stopping and reversing the direction of travel of the electrode wire, - running the electrode wire in a second direction to a second reciprocating position, - stopping and reversing the direction of travel of the electrode wire, Features If cutting method monitoring shows that the cutting method must be interrupted, a cutting method interruption sequence is executed, and the cutting method interruption sequence includes continuing the cutting method until the first or second reciprocating position and pausing or stopping the cutting method at the first or second reciprocating position.

2. The high-speed reciprocating wire cutting method according to claim 1, wherein one or more separate attempts are performed before the cutting method interrupts the sequence.

3. The high-speed reciprocating wire cutting method according to claim 2, wherein the separation attempt comprises one or more of the following: a. Keep at the front cutting position, b. Reversing the feed direction and moving back along the cutting path to a predefined length and / or while monitoring the cutting method parameters, and then returning to said front-most cutting position, c. Change one or more method parameters.

4. The high-speed reciprocating wire cutting method according to any one of claims 1 to 3, characterized in that: If the cutting method monitoring finds at least one of the following conditions, the cutting method interruption sequence is executed: a. The instantaneous cutting rate drops below the minimum cutting rate Vsmin, b. The average cutting rate is reduced to below the minimum average cutting rate Vsavg,min, c. The cutting method is degraded, d. The number of separate attempts exceeds the predefined value nu,max, e. The number of interrupt sequences of the earlier cutting method exceeds a predefined value ni,max.

5. The high-speed reciprocating wire cutting method according to any one of claims 1 to 3, characterized in that: The cutting method interruption sequence includes one of the following: a. continuing the cutting method in the current wire travel direction until the first reciprocating position, and stopping the cutting method at the first reciprocating position, or b. continuing the cutting method in the current wire travel direction until the first reciprocating position, reversing the wire travel direction and continuing the cutting method until the second reciprocating position, and stopping the cutting method at the second reciprocating position, or c. immediately interrupting the cutting method, reversing the wire travel direction and continuing the cutting method until the second reciprocating position, and stopping the cutting method at the second reciprocating position.

6. The high-speed reciprocating wire cutting method according to any one of claims 1 to 3, characterized in that: The cutting method interruption sequence also includes issuing a warning message.

7. The high-speed reciprocating wire cutting method according to claim 3, characterized in that: The cutting method interruption sequence further comprises storing the frontmost cutting position.

8. The high-speed reciprocating wire cutting method according to any one of claims 1 to 3, characterized in that: If it is determined that the remaining cutting length is less than a predefined remaining cutting length value lleft,min, the cutting method interruption sequence is bypassed or postponed.

9. The high-speed reciprocating wire cutting method according to claim 1, wherein the cutting method stops at the first or second reciprocating position, whereby a small amount of electrode wire is stored on the first wire drum and a large amount of electrode wire is stored on the second wire drum, characterized in that The electrode wire is automatically separated at the first wire barrel and is automatically removed from the incision by reversing the wire travel direction.

10. A control unit configured to control the method according to any one of claims 1 to 9.

11. The control unit according to claim 10, wherein the control unit is configured to control the cutting method to interrupt a sequence and / or separate attempts.

12. High-speed wire-cut electrochemical discharge machine tool, comprising: reciprocating A wire travel circuit, the reciprocating wire travel circuit comprising at least one wire drum unit and a plurality of rollers, by which the electrode wire is advanced through the processing area; and a control unit according to claim 10 or 11.

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