Numerical control devices and computer-readable storage media

Abstract

A numerical control device for controlling electrical discharge machining (EDM) includes: a program path generation unit that parses a machining program consisting of multiple machining steps including roughing, semi-finishing, and final finishing to generate program paths for each machining step; a machining condition storage unit that stores multiple machining conditions suitable for machining steps and at least one machining condition suitable for unmachined portions; and a machining condition modification unit that, when unmachined portions are generated in a previous machining step, modifies the machining conditions of the current machining step to machining conditions suitable for the unmachined portions.

Description

Technical Field

[0001] This invention relates to a numerical control device for controlling an electrical discharge machining (EDM) machine and a computer-readable storage medium. Background Technology

[0002] Previously, there were electrical discharge machining (EDM) machines that utilized the electrical discharge phenomenon between the workpiece and a traveling electrode for machining. In EDM, after cutting out the material once, the machining was repeated two or three times by tracing the side of the workpiece, thereby improving shape accuracy and reducing surface roughness.

[0003] During repeated machining, the energy of electrical discharge machining (EDM), determined by the voltage (current) value and pulse width, gradually decreases in the order of roughing, semi-finishing, and final finishing. In the roughing stage, the machined surface is uneven; therefore, the voltage (current) value or pulse width is gradually reduced to flatten the surface. The distance between the electrodes that generates the discharge is called the discharge gap, which can be predicted based on machining conditions such as the current value and pulse width. In EDM, the diameter correction amount based on the predicted value is used as the machining radius to generate the correction path and determine overcutting.

[0004] Patent Document 1 describes a wire electrical discharge machining apparatus comprising: a processing unit that forms a product portion as an inner portion by cutting off an outer frame portion from a workpiece; and a control device 2 that controls the processing unit to process a first boundary region in the boundary between the outer frame portion and the product portion in such a way that a portion of the boundary between the outer frame portion and the product portion remains as a cutting residue. After connecting the component that will become the product portion and the component that will become the outer frame portion using a conductive component, the product portion is cut off from the outer frame portion by processing a second boundary region in the boundary as a cutting residue. Furthermore, when processing the workpiece, the first boundary region is processed multiple times, and the second boundary region is processed multiple times. When n is set to a natural number of 2 or more, the control device 2 sets a first processing condition for processing the first boundary region for the nth time and a second processing condition for processing the second boundary region for the nth time, based on the processing condition when processing the first boundary region.

[0005] Existing technical documents

[0006] Patent documents

[0007] Patent Document 1: Japanese Patent No. 5622977 Summary of the Invention

[0008] The problem that the invention aims to solve

[0009] As shown in Patent Document 1, in online electrical discharge machining, a cutting residue is intentionally generated. After processing the portion other than the cutting residue, the cutting residue is finally cut off to separate the product part (core). In Patent Document 1, the machining accuracy is improved by changing the machining conditions before and during core cutting.

[0010] The processing conditions differ for roughing, semi-finishing, and final finishing. The processing path varies depending on the processing conditions, which sometimes results in unprocessed portions. Even if processing conditions are set to suit each process, if unprocessed portions are generated during roughing, they may still be processed during semi-finishing, thus creating a mismatch between the processing conditions and the workpiece.

[0011] In the field of electrical discharge machining (EDM), there is a technique that aims to perform machining under appropriate processing conditions.

[0012] Methods for solving problems

[0013] As one aspect of this disclosure, the numerical control device is a numerical control device for controlling electrical discharge machining. The numerical control device includes: a program path generation unit that parses a machining program consisting of multiple machining steps including roughing, semi-finishing, and final finishing to generate program paths for each machining step; a machining condition storage unit that stores multiple machining conditions suitable for the machining steps and at least one machining condition suitable for unmachined portions; and a machining condition modification unit that, if unmachined portions are generated in a previous machining step, modifies the machining conditions of the current machining step to machining conditions suitable for the unmachined portions.

[0014] As one aspect of this disclosure, a storage medium storing computer-readable commands is executed by one or more processors to perform the following processes: parsing a machining program consisting of multiple machining operations including roughing, semi-finishing, and final finishing to generate program paths in each machining operation; storing multiple machining conditions suitable for the machining operations and at least one machining condition suitable for unmachined portions; and, if unmachined portions are generated in a previous machining operation, changing the machining conditions of the current machining operation to machining conditions suitable for the unmachined portions.

[0015] Invention Effects

[0016] According to one aspect of the present invention, electrical discharge machining can be performed under appropriate processing conditions. Attached Figure Description

[0017] Figure 1 It is a diagram showing the hardware structure of a numerical control device.

[0018] Figure 2This is a block diagram of a numerical control device.

[0019] Figure 3 It is a diagram illustrating the program path.

[0020] Figure 4A This is a graph showing the relationship between the machining radius and overcut (overcut occurs).

[0021] Figure 4B This is a graph showing the relationship between the machining radius and overcut (without overcut).

[0022] Figure 5 This is a diagram representing an example of an avoidance path.

[0023] Figure 6 This is a diagram illustrating an example of processing conditions.

[0024] Figure 7 This is a graph showing the relationship between the discharge gap and the wire diameter correction.

[0025] Figure 8A This is a diagram showing the production of unprocessed portions during rough machining.

[0026] Figure 8B This diagram shows the processing of already processed parts during semi-finishing.

[0027] Figure 8C This diagram shows the processing of unprocessed parts during semi-finishing.

[0028] Figure 9A This diagram shows the machining path of the groove based on the machining conditions of the unprocessed part.

[0029] Figure 9B This diagram shows the machining circuit for the groove machining under semi-finishing conditions.

[0030] Figure 10A This diagram shows the machining process for the groove under semi-finishing conditions.

[0031] Figure 10B This diagram shows the machining circuit for the groove machining under semi-finishing conditions.

[0032] Figure 11A This is a diagram showing the production of unprocessed portions during rough machining.

[0033] Figure 11B It is a diagram showing the processing of previously unprocessed parts.

[0034] Figure 12 It is a flowchart illustrating the processing of information associated with the unprocessed portion.

[0035] Figure 13This is a flowchart illustrating the process of changing processing conditions. Detailed Implementation

[0036] Reference Figure 1 This invention describes the hardware structure of the numerical control device 100 that controls the wire electrical discharge machining (EDM) machine 200. The wire EDM machine 200 is cited as an example in this disclosure. This invention is generally applicable to electrical discharge machining processes, including die-cutting EDM.

[0037] The CPU 111 of the numerical control device 100 is the processor that controls the numerical control device 100 as a whole. The CPU 111 reads the system program processed in the ROM 112 via the bus 122 and controls the numerical control device 100 as a whole according to the system program. Temporary calculation data, display data, and various data input by the user via the input unit 71 are temporarily stored in the RAM 113.

[0038] The display unit 70 is a monitor or similar device attached to the numerical control device 100. The display unit 70 displays the operation screen, setting screen, etc. of the numerical control device 100.

[0039] The input unit 71 may be a keyboard, touch panel, or the like, integrated with or separate from the display unit 70. The user operates the input unit 71 to input data onto the screen displayed on the display unit 70. Alternatively, the display unit 70 and the input unit 71 may also be a portable terminal.

[0040] The non-volatile memory 114 is a memory that maintains its stored state even when the power supply to the numerical control device 100 is disconnected, for example, by backup via a battery (not shown). The non-volatile memory 114 stores programs read from external devices via an interface (not shown), programs input via the input unit 71, and various data obtained from various parts of the numerical control device 100, the wire EDM machine 200, etc. (e.g., setting parameters obtained from the wire EDM machine 200). The programs and various data stored in the non-volatile memory 114 can also be expanded in the RAM 113 during execution / use. Furthermore, various system programs are pre-written into the ROM 112.

[0041] The controller 40 of the wire or worktable of the wire EDM machine 200 converts the axis movement commands from the CPU 111 into pulse signals and outputs them to the driver 41. The driver 41 converts the pulse signals into current to drive the servo motor of the wire EDM machine 200. The servo motor moves the wire and the worktable according to the control of the numerical control device 100. By controlling the servo motor, the discharge gap and the speed of the wire, which will be described later, can be controlled.

[0042] The processing power supply 202 applies voltage between the upper and lower power supply components and the workpiece. The wire electrical discharge machining (EDM) machine 200 performs EDM on the workpiece by generating a discharge between the workpiece mounted on the worktable and the wire electrode. The voltage and current applied to the wire vary depending on the processing conditions described later.

[0043] The discharge detection unit 203 measures the waveforms of the discharge voltage and discharge current between the electrodes. The discharge detection unit 203 can be, for example, an oscilloscope or a current sensor. An oscilloscope can detect the discharge phenomenon occurring between the electrodes. A current sensor measures the discharge current flowing through the power supply line.

[0044] The numerical control device 100 adjusts the speed of the line based on the discharge voltage and discharge current obtained from the discharge detection unit 203, depending on whether it is a normal discharge, a short circuit, or a continuous discharge state.

[0045] Figure 2 This is a block diagram of the numerical control device 100. The numerical control device 100 includes a machining program storage unit 11, a machining program parsing unit 12, a correction path generation unit 13, an over-cutting determination unit 14, an avoidance path generation unit 15, an unprocessed path detection unit 16, a machining condition modification unit 17, a machining condition storage unit 18, and an interpolation processing unit 19.

[0046] The machining program parsing unit 12 generates a program path based on the machining program stored in the machining program storage unit 11. The program path varies depending on the machining process. Figure 3 An example representing a program path. The first machining step is roughing, the second machining step is semi-finishing (first step), the third machining step is semi-finishing (second step), and the fourth machining step is final finishing.

[0047] From roughing to semi-finishing, most machining processes have a finishing allowance set. When a finishing allowance is set in the machining program, the program path is moved to accommodate that allowance. Typically, a larger finishing allowance is retained during roughing, the finishing allowance is reduced during semi-finishing, and finally, the finishing allowance is reduced to zero during final finishing.

[0048] The correction path generation unit 13 corrects the program path based on the wire diameter correction amount. The wire diameter correction amount is the machining radius of the wire. In wire diameter correction, a path (correction path) is generated that offsets the program path from the wire diameter correction amount. The wire diameter correction amount varies depending on the machining conditions. Generally, the wire diameter correction amount is large for rough machining and small for final finishing.

[0049] In the present disclosure, a correction path for roughing is generated in the initial machining process, a correction path for semi-finishing (first machining) is generated in the second machining process, a correction path for semi-finishing (second machining) is generated in the third machining process, and a correction path for final finishing is generated in the fourth machining process.

[0050] The overcut determination unit 14 determines whether there is an overcut section in the path after the line diameter correction.

[0051] Figure 4A , Figure 4B This indicates the relationship between the machining radius and the overcut. Figure 4A In the program path, machining proceeds in a straight line from the right side of the attached drawing to the left side, and from point A to the lower right of the attached drawing. If machining is performed according to the correction path, overcutting will occur at point B. Figure 4B In machining, when processing conditions are changed, such as voltage and current decreasing, the machining radius of the wire decreases. A smaller machining radius prevents overcutting. Rough machining has a large machining radius and a large allowance for finishing, making overcutting more likely and resulting in unfinished portions.

[0052] The avoidance path generation unit 15 generates a path to avoid over-cutting (avoidance path). Figure 5 This is an example of avoiding a path. In Figure 5 In the case of overcutting during roughing, an avoidance path is generated to prevent hole machining. In the subsequent machining (semi-finishing (first time)), since no overcutting occurs, no avoidance path is generated, and a correction path is used instead. In the subsequent machining (semi-finishing (second time), final finishing), no overcutting occurs either, so no avoidance path is generated, and a correction path is used instead.

[0053] The unprocessed path detection unit 16 detects unprocessed paths by comparing the corrected path with the avoidance path. The unprocessed path detection unit 16 stores information related to the unprocessed portion (unprocessed portion association information).

[0054] The processing condition change unit 17 reads the associated information of the unprocessed part in the pre-processing and selects processing conditions suitable for the processing shape of the unprocessed part. (1) to (3) are the processing condition selection steps. If an unprocessed part is generated in the pre-processing, (1) the processing condition change unit 17 compares the current processing correction path with the pre-processing avoidance path and determines the shape of the unprocessed part. (2) The processing condition change unit 17 determines whether the unprocessed part of the roughing process is being processed for the first time in the current processing. (3) When the unprocessed part is processed by changing the processing conditions, it determines whether overcutting has occurred. The processing condition change unit 17 changes the processing conditions when all conditions (1) to (3) are met.

[0055] The specific processing of (1) to (3) is explained.

[0056] like Figure 6As shown, the numerical control device 100 stores machining conditions. These machining conditions include general machining conditions such as roughing, semi-finishing (first time), semi-finishing (second time), and final finishing, as well as machining conditions for unmachined portions. Each machining condition includes settings such as "voltage," "on-time," "feed speed," and "wire diameter correction amount." Machining conditions for unmachined portions are set according to shapes such as "for corners" and "for grooves." Machining condition "S21" is for "corners," and machining condition "S22" is for "grooves." The machining condition modification unit 17 compares the pre-machining correction path with the pre-machining avoidance path to determine the machining shape and reads the machining conditions corresponding to the machining path. In the example of this disclosure, the machining condition modification unit 17 reads the "groove machining" machining condition "S22."

[0057] The processing condition change unit 17 determines whether over-cutting has occurred under the read processing conditions. For example... Figure 7 As shown, a gap called the "discharge gap" exists between the wire and the machined surface. The "discharge gap" is the gap where discharge occurs. The size of the "discharge gap" changes when the machining conditions are changed. The machining radius is equivalent to "wire diameter + discharge gap". The "wire diameter" is the radius of the machined wire. The "wire diameter" also changes when the wire is changed during roughing and finishing. The "wire diameter correction amount", "wire diameter + discharge gap", and "machining radius" are approximately equal. When the machining conditions are changed, the machining radius changes, and overcutting may occur. To avoid this, the machining condition change unit 17 determines whether overcutting will occur under the new machining conditions. If overcutting does not occur, the current machining conditions are changed to the machining conditions for the unmachined portion.

[0058] During electrical discharge machining (EDM), the discharge gap remains approximately constant. The numerical control unit 100 controls the wire speed through feedback control to maintain a fixed discharge gap. If the wire is too close to the workpiece, a short circuit occurs. When the wire speed decreases due to a mismatch between machining conditions and machining quantity, the numerical control unit 100 reduces the wire speed to maintain a constant discharge gap.

[0059] Reference Figures 8A to 8C The changes in processing conditions for the unprocessed parts are explained.

[0060] During roughing, when the numerical control device 100 determines that overcut has occurred, it generates an avoidance path to prevent overcutting. The line moves along the avoidance path, creating an unprocessed portion. Figure 8A When roughing is completed, semi-finishing (first time) begins. In semi-finishing (first time), machining is performed under the finishing machining conditions "S2: Semi-finishing (first time)". Figure 8BWhen the line approaches the unprocessed portion, the numerical control device 100 begins processing to change the processing conditions. The numerical control device 100 compares the pre-processed correction path with the pre-processed avoidance path to determine the processing shape. The numerical control device 100 selects the processing condition corresponding to the processing shape as processing condition "S22: Unprocessed portion (for groove)", and determines whether overcutting occurs under this processing condition. If it determines that no overcutting has occurred, the numerical control device 100 changes the processing conditions to process the unprocessed portion. Figure 8C ).

[0061] Other methods for judging over-intervention include (4), (5), and (6).

[0062] (4) Do not change the machining conditions when the current machining is final finishing. During final finishing, the finishing allowance is zero. If the machining voltage is increased during final finishing, overcutting will occur. Therefore, do not change the machining conditions during final finishing.

[0063] (5) Switch machining conditions between the outgoing and returning paths based on the machining shape. In the case of slot machining, the outgoing path processes the unprocessed portion. Figure 9A However, the parts that have been processed once are finished in the circuit. Figure 9B Therefore, the processing conditions are switched to outgoing and return paths. According to... Figure 6 In the processing conditions, select processing condition "S22: Unprocessed part (for groove)" in the outgoing path, and switch to processing condition "S2: Semi-finishing (first time)" in the loop.

[0064] (6) When only roughing and final finishing are performed, the processing conditions remain unchanged. For example... Figure 10A As shown, when machining the unmachined portion after roughing through final finishing, if the voltage is increased, the length of "wire diameter + discharge gap" will exceed the "distance between wire center and workpiece," sometimes resulting in overcutting. In this case, the machining conditions are not changed. (In the case of a loop...) Figure 10B It is not an unprocessed part, therefore the processing conditions are not changed.

[0065] The effects of this disclosure will be explained by comparing it with conventional groove processing.

[0066] Figure 11A , Figure 11B This is the traditional wire electrical discharge machining (EDM). As a prerequisite, unmachined portions are created during the roughing process of the groove machining. In the semi-finishing (first stage) following the roughing, machining begins under the machining condition "S2: Semi-finishing (first stage)". Figure 11A Then, even when the unprocessed portion is reached, it is processed under the specified processing conditions "S2: Semi-finishing (first time)". Figure 11B The amount of machining on the unprocessed portion is greater than that on the finishing portion, creating a mismatch between the actual machining and the machining conditions, resulting in a decrease in line speed. Furthermore, the closer the line is to the workpiece, the higher the likelihood of a short circuit. If the line is closer to the workpiece, the command speed for feedback control also slows down in order to maintain a constant discharge gap.

[0067] The numerical control device 100 of this disclosure detects the generation of unprocessed portions during pre-processing and changes the processing conditions to be suitable for the unprocessed portions when processing the unprocessed portions in the current processing. This prevents a decrease in processing speed and frequent short circuits.

[0068] In this disclosure, the determination is made by changing the processing conditions, so that even if the processing radius of the wire EDM is increased, overcutting will not occur.

[0069] Reference Figure 12 The process of recording information associated with the unprocessed portion during processing is explained.

[0070] The machining program parsing unit 12 parses the machining program and generates a program path (step S1). In step S1, sometimes a roughing machining program path, a semi-finishing machining program path, and a final finishing machining program path are generated. Here, we will describe the generation of a roughing machining program path.

[0071] The correction path generation unit 13 generates a correction path based on the wire diameter correction amount correction procedure path (step S2).

[0072] The overcut determination unit determines whether there is an overcut portion in the correction path (step S3). If it is determined that an overcut has occurred (step S4; yes), the avoidance path generation unit 15 generates a path to avoid the overcut (avoidance path) (step S5).

[0073] The unprocessed path detection unit 16 compares the corrected path with the avoidance path to detect the unprocessed portion. The unprocessed path detection unit 16 stores information related to the unprocessed portion, such as its location (step S6).

[0074] When processing continues (step S7: Yes), the numerical control device 100 transfers the processing to step S1 and generates a program path. If processing ends (step S7: No), the processing of recording information associated with the unprocessed portion ends.

[0075] Reference Figure 13 The flowchart illustrates the handling of changes in processing conditions. As a prerequisite, for the purpose of changing processing conditions, pre-processing is assumed to have ended. Pre-processing refers to the processing steps preceding the current processing step.

[0076] The processing condition modification unit 17 determines whether it is approaching the unprocessed part in the pre-processing stage based on the unprocessed part association information. If the current processing is not approaching the unprocessed part (step S11; no), monitoring continues. If the current processing is approaching the unprocessed part (step S11; yes), the processing condition modification unit 17 determines the processing shape of the unprocessed part (step S12). The processing shape may include "groove", "corner", etc., but is not limited to these.

[0077] The processing condition change unit 17 determines whether the unprocessed portion is a roughing part. Roughing involves a large amount of machining on the unprocessed portion, thus it is suitable for processing conditions with a larger machining volume than finishing.

[0078] When the unprocessed portion is rough-machined (step S13; Yes), the machining condition changing unit 17 selects machining conditions suitable for the machining shape of the unprocessed portion from the machining condition storage unit 18 (step S14). The machining condition changing unit 17 determines whether overcutting occurs under the machining conditions corresponding to the machining shape of the unprocessed portion (step S15).

[0079] If overcutting occurs (step S16; Yes), do not change the processing conditions and proceed to step S11. If overcutting does not occur (step S16; No), change the processing conditions (step 17).

[0080] Here, if the current processing step ends (step S18: Yes), the processing condition change process ends. If the current processing step continues (step S18: No), proceed to step S11 to continue the processing condition change process.

[0081] As explained above, in wire electrical discharge machining (EDM) of a workpiece that is repeatedly processed multiple times, the numerical control device 100 of this disclosure determines the shape of the unprocessed portion when there is an unprocessed portion in the pre-processing, selects processing conditions suitable for the shape of the unprocessed portion, and determines whether overcutting has occurred after processing is performed under these processing conditions. If overcutting has occurred, the numerical control device 100 does not change the processing conditions. If overcutting has not occurred, the processing conditions are changed.

[0082] The numerical control device 100 can also be set to the following function: determine whether the current machining is the final finishing process, and if it is the final finishing process, do not change the machining conditions.

[0083] When processing involves reciprocating motions, a function can also be set to change the processing conditions on the outgoing path but not on the return path.

[0084] When the width of the groove in "groove machining" is equal to the "wire diameter + discharge gap", a function can also be set to not change the machining conditions.

[0085] This disclosure can also be applied to all electrical discharge machining (EDM), including die-cutting EDM. Wire EDM is an EDM where the tool electrode is a wire. The tool electrode can also be a conductor (metal) of a shape other than a wire. In die-cutting EDM, an electrode is used instead of a wire. In die-cutting EDM, unprocessed portions are sometimes generated, similar to those in wire EDM. In this case, the machining conditions are changed to machine the unprocessed portions under appropriate machining conditions. The correction amount for general EDM is defined as the electrode shape correction amount. The electrode shape correction amount is the electrode shape plus the discharge gap amount. Wire diameter correction amount is a type of electrode shape correction amount. Electrode shape correction amounts are used in program path correction, avoidance path generation, and overcut determination.

[0086] Symbol Explanation

[0087] 100 numerical control device

[0088] 11. Processing program storage unit

[0089] 12. Machining Program Analysis Department

[0090] 13. Correction Path Generation Unit

[0091] 16 Unprocessed Path Detection Department

[0092] 17. Processing Condition Change Department

[0093] 18 Processing Conditions Storage Department

[0094] 111 CPU

[0095] 112ROM

[0096] 113 RAM

[0097] 114 non-volatile memory,

[0098] 201 servo motor,

[0099] 202 Processing Power Supply

[0100] 203 Discharge Detection Department.

Claims

1. A numerical control device for controlling electrical discharge machining, characterized in that, The numerical control device has: The program path generation unit parses the machining program, which consists of multiple machining operations including roughing, semi-finishing, and final finishing, and generates the program path for each machining operation. A processing condition storage unit stores multiple processing conditions suitable for the processing step and at least one processing condition suitable for the unprocessed portion; and The processing condition modification unit changes the processing conditions of the current processing step to processing conditions suitable for the unprocessed portion when an unprocessed portion is generated in a previous processing step.

2. The numerical control device according to claim 1, characterized in that, The numerical control device has: The correction path generation unit generates a correction path after the program path has been corrected using electrode shape correction amount; The overcut determination unit determines whether overcutting has occurred when processing has been performed using the corrected path. The avoidance path generation unit generates a path to avoid the excessive cut-in, i.e., an avoidance path. as well as The unprocessed path detection unit detects the unprocessed portion based on the correction path and the avoidance path.

3. The numerical control device according to claim 1, characterized in that, The processing condition storage unit stores the shape of the unprocessed portion in correspondence with the processing conditions. The processing conditions are changed to processing conditions that correspond to the shape of the unprocessed portion.

4. The numerical control device according to claim 1, characterized in that, The processing condition change unit determines whether the change to the processing conditions of the unprocessed portion has overstepped its bounds. If overstepping has occurred, the processing conditions are not changed.

5. The numerical control device according to claim 1, characterized in that, The processing condition changing unit does not change the processing conditions when the current processing step is final finishing.

6. The numerical control device according to claim 1, characterized in that, When the processing condition changing unit processes the unprocessed portion along the same repetitive path, it does not change the processing conditions of the loop.

7. A storage medium for storing computer-readable commands, characterized in that, The following processing is performed by executing the command through one or more processors: The machining program, which consists of multiple machining operations including roughing, semi-finishing, and final finishing, is analyzed to generate the program path for each machining operation. The system stores multiple processing conditions suitable for the processing steps and at least one processing condition suitable for the unprocessed portion; and If an unprocessed portion is generated during a previous processing step, the processing conditions of the current processing step are changed to processing conditions suitable for the unprocessed portion.

8. The storage medium for storing computer-readable commands according to claim 7, characterized in that, Generate a corrected path after the program path has been corrected using electrode shape correction; Determine whether overcutting has occurred when processing has been performed using the corrected path; Generate a path to avoid the excessive intrusion, i.e., an avoidance path; as well as Unprocessed portions are detected based on the correction path and the avoidance path.

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