Wire electrical discharge machine, threshold determination device, and threshold determination method

Abstract

TH)時，判斷為金屬線電極(18)與加工對象物(W)有所接觸之金屬線放電加工機(10)，具備：取得部(34)，取得使金屬線電極(18)與加工對象物(W)之間的電壓(V)變動的要因之設定值(44)；及閾值決定部(36)，根據要因之基準值(32)與所取得的設定值(44)來計算閾值(V;TH)。;

Description

Technical Field

[0001] This invention relates to a wire EDM machine, a threshold determination device, and a threshold determination method. Prior Technology

[0002] A wire electrical discharge machining (EDM) machine applies a voltage between a wire electrode and the workpiece. This voltage decreases when the wire electrode and the workpiece come into contact. A method has been proposed to use the voltage change to determine whether the wire electrode and the workpiece are in contact (see also Japanese Patent Application Publication No. 2013-226612). Summary of the Invention

[0003] The voltage between the metal wire electrode and the workpiece is compared with a predetermined reference voltage (threshold). If the voltage is lower than the threshold, it is determined that the metal wire electrode is in contact with the workpiece.

[0004] However, sometimes even when the wire electrode is in contact with the workpiece, the voltage may still exceed the threshold. This situation presents the problem that it becomes impossible to accurately determine whether the wire electrode is in contact with the workpiece.

[0005] The purpose of this invention is to solve the above-mentioned problems.

[0006] The first aspect of the present invention is a wire electrical discharge machining (EDM) machine that determines that the wire electrode and the workpiece are in contact when the voltage between the wire electrode and the workpiece is lower than a threshold value. The machine includes: an acquisition unit that acquires a set value of a factor that causes the voltage variation between the wire electrode and the workpiece; and a threshold determination unit that calculates a threshold value based on a reference value corresponding to the factor and the acquired set value.

[0007] The second aspect of the present invention is a threshold determination device that determines a threshold for comparison with the voltage between the wire electrode and the workpiece in order to determine whether the wire electrode of the wire electrical discharge machining machine is in contact with the workpiece. The device comprises: an acquisition unit that acquires a set value of a factor that causes the voltage variation between the wire electrode and the workpiece; and a threshold determination unit that calculates the threshold based on a reference value of the factor and the acquired set value.

[0008] The third aspect of the present invention is a threshold determination method. In order to determine whether the wire electrode of the wire electrical discharge machining machine is in contact with the workpiece, a threshold value is determined and compared with the voltage between the wire electrode and the workpiece. The method includes the following steps: an acquisition step, acquiring a set value of the factors that cause the voltage variation between the wire electrode and the workpiece; and a threshold determination step, calculating the threshold value based on the reference value of the factors and the acquired set value.

[0009] According to the present invention, since the threshold is calculated in accordance with the factors that cause the voltage variation between the metal wire electrode and the workpiece, the contact determination between the metal wire electrode and the workpiece based on the comparison of the threshold and the voltage can be performed more accurately.

[0010] The aforementioned objectives, features, and advantages can be more readily understood from the following description of embodiments with reference to the accompanying diagrams. Simple Explanation of the Diagram

[0011] Figure 1 is a structural diagram of a wire EDM machine in an embodiment.

[0012] Figure 2A is a graph showing the first example of the voltage change before and after a short circuit between the metal wire electrode and the workpiece. Figure 2B is a graph showing the second example of the voltage change before and after a short circuit between the metal wire electrode and the workpiece.

[0013] Figure 3 is a schematic diagram of the threshold determination device.

[0014] Figure 4 is a flowchart illustrating the threshold determination method of the implementation mode. Implementation

[0015] [Preferred form of the invention] (Implementation Mode) Figure 1 is a structural diagram of the wire EDM machine 10 in an embodiment.

[0016] The wire electrical discharge machining (EDM) machine 10 includes: a processing tank 12, a platform 14, a motor 16X, a motor 16Y, a wire electrode 18, a power supply 20, a control device 22, and a threshold determination device 24. The control device 22 is, for example, a coefficient value control device.

[0017] The machining tank 12 is a tank that accommodates the platform 14. Furthermore, the machining tank 12 stores the machining fluid LQ.

[0018] Platform 14 is a platform that supports the workpiece W. Platform 14 and the workpiece W are immersed in the processing fluid LQ inside the processing tank 12.

[0019] Motors 16X and 16Y are respectively connected to platform 14. Platform 14 moves in the X direction due to the drive of motor 16X. Platform 14 also moves in the Y direction due to the drive of motor 16Y. Motors 16X and 16Y are controlled by control device 22.

[0020] The metal wire electrode 18 is a conductive wire. The metal wire electrode 18 is stretched inside the processing tank 12. The metal wire electrode 18 moves horizontally relative to the platform 14 by moving the platform 14 in the horizontal direction.

[0021] A power supply unit 20 is connected to the wire electrode 18 and the platform 14 (workpiece W). The power supply unit 20 applies a voltage between the wire electrode 18 and the workpiece W to detect the contact between them. This voltage is pulsed. Furthermore, in the following description, unless otherwise specified, voltage V refers to the voltage detected between the wire electrode 18 and the workpiece W.

[0022] Figure 2A is a graph showing the first example of the voltage V change before and after a short circuit between the metal wire electrode 18 and the workpiece W. This graph has a vertical axis showing the magnitude of the voltage V and a horizontal axis showing time.

[0023] During the period before time TC in Figure 2A, the metal wire electrode 18 is not in contact with the workpiece W. The magnitude of the voltage V during this period is V1 (voltage V1).

[0024] At time TC in Figure 2A, the metal wire electrode 18 is sufficiently close to (in contact with) the workpiece W. The metal wire electrode 18 and the workpiece W are in contact with each other and are electrically short-circuited. As a result, even if the waveform of the output voltage of the power supply device 20 remains unchanged before and after time TC, the voltage V (V2) becomes less than the voltage V1 (V1>V2) in the period after time TC.

[0025] The control device 22 controls the motors 16X and 16Y and the power supply device 20 according to a predetermined program. Furthermore, the control device 22 determines whether the metal wire electrode 18 and the workpiece W are short-circuited based on whether the voltage V is lower than a predetermined threshold VTH. That is, the control device 22 determines whether the metal wire electrode 18 and the workpiece W are in contact based on whether the voltage V is lower than the threshold VTH.

[0026] However, the magnitude of the voltage V during the short circuit between the metal wire electrode 18 and the workpiece W varies due to various factors. These factors include the metal wire electrode 18, the workpiece W, and the processing fluid LQ.

[0027] For example, the voltage V during the short circuit between the metal wire electrode 18 and the workpiece W is greater when the resistivity (specific resistance) of the metal wire electrode 18, the workpiece W, and the processing fluid LQ is higher. Furthermore, the voltage V during the short circuit between the metal wire electrode 18 and the workpiece W is greater when the metal wire electrode 18 is thinner or the workpiece W is thinner.

[0028] Figure 2B is a graph showing a second example of the voltage V change before and after a short circuit between the metal wire electrode 18 and the workpiece W. Figure 2B shows a case where, due to the aforementioned factors, the voltage V during the short circuit between the metal wire electrode 18 and the workpiece W is higher than that in Figure 2A. The format of the graph in Figure 2B is based on that of Figure 2A.

[0029] As shown in Figure 2B, due to the aforementioned factors, the voltage V during the short circuit between the metal wire electrode 18 and the workpiece W may sometimes be greater than the threshold VTH (V3>VTH). In this case, it is impossible to determine whether the metal wire electrode 18 is in contact with the workpiece W based on the comparison between the voltage V and the threshold VTH.

[0030] Here, we consider using a data table containing a majority threshold VTH corresponding to combinations of majority factors as a countermeasure. However, if the threshold VTH corresponding to combinations such as the metal wire diameter of the metal wire electrode 18 used by the operator and the plate thickness of the workpiece W is not stored in the data table beforehand, the above method cannot cope with this situation.

[0031] The voltage V can vary if at least one of the majority factors is different. Therefore, the data table above requires including all the numerous threshold values ​​VTH corresponding to various combinations of the majority factors. However, it is practically difficult to include all the numerous threshold values ​​VTH corresponding to various combinations of the majority factors in the data table in advance.

[0032] Based on the above, the threshold determination device 24 of this embodiment will be described below. The threshold determination device 24 is connected to the control device 22 to form a communicable electronic device (computer). Alternatively, the threshold determination device 24 may also be incorporated into the control device 22 as part of the control device 22.

[0033] Figure 3 is a schematic diagram of the threshold determination device 24.

[0034] The threshold determination device 24 includes a memory unit 26 and an arithmetic unit 28.

[0035] The memory unit 26 has one or more memory modules. The memory unit 26 may include, for example, RAM (Random Access Memory) and ROM (Read Only Memory).

[0036] The memory unit 26 includes the memory threshold determination program 30, multiple reference values ​​32 (α0, β0, γ0), and the reference threshold VTH0. To avoid excessive diagrammatic complexity, Figure 3 only shows one reference value 32.

[0037] The threshold determination program 30 is used to set the threshold VTH corresponding to the majority factors.

[0038] Most reference values ​​32 are predetermined values ​​corresponding to most factors. Most reference values ​​32 include the reference value α0 of the metal wire electrode 18, the reference value β0 of the workpiece W, and the reference value γ0 of the processing fluid LQ.

[0039] The reference value α0 of the metal wire electrode 18 is predetermined based on the metal wire diameter and the specific resistance of the metal wire electrode.

[0040] The reference value β0 of the workpiece W is predetermined based on the thickness of the workpiece, the resistivity of the workpiece, etc.

[0041] The reference value γ0 of the processing fluid LQ is predetermined based on the specific resistivity of the given processing fluid.

[0042] Furthermore, the predetermined wire electrode may differ from the wire electrode 18 actually present in the wire EDM machine 10. The predetermined workpiece may also differ from the workpiece W actually contained in the machining tank 12. The predetermined machining fluid may also differ from the machining fluid LQ actually stored in the machining tank 12. Therefore, most of the reference values ​​32 may also be constants predetermined by, for example, the manufacturer of the wire EDM machine 10.

[0043] The reference threshold VTH0 is a voltage value (constant) determined by the combination of reference values ​​32 of the majority of factors. The number of reference thresholds VTH0 stored in the memory unit 26 is one.

[0044] The memory unit 26 can also store various data, programs, etc. as needed, in addition to the threshold determination program 30, the majority of reference values ​​32, and the reference threshold VTH0.

[0045] The arithmetic unit 28 includes processing circuitry. This processing circuitry includes one or more processors. However, the processing circuitry of the arithmetic unit 28 may also include ASIC (Application Specific Integrated Circuit), FPGA (Field-Programmable Gate Array), and discrete components, etc.

[0046] The arithmetic unit 28 includes an acquisition unit 34 and a threshold determination unit 36. The threshold determination unit 36 ​​includes an evaluation value calculation unit 38, a correction value calculation unit 40, and a threshold calculation unit 42. The acquisition unit 34 and the threshold determination unit 36 ​​are implemented by the processor of the arithmetic unit 28 executing the threshold determination program 30. However, at least a portion of the acquisition unit 34 and the threshold determination unit 36 ​​can also be implemented by the aforementioned ASIC, FPGA, discrete components, etc.

[0047] The acquisition unit 34 acquires a plurality of setting values ​​44. These plurality of setting values ​​44 are values ​​set on the wire electrical discharge machine 10 related to a plurality of factors. The plurality of setting values ​​44 include various setting values ​​44 such as the wire diameter of the wire electrode 18 provided by the wire electrical discharge machine 10 and the resistivity of the wire electrode 18. Furthermore, the plurality of setting values ​​44 also include various setting values ​​44 such as the thickness of the workpiece W contained in the processing tank 12, the resistivity of the workpiece W, and the resistivity of the processing fluid LQ stored in the processing tank 12.

[0048] The acquisition unit 34 acquires, for example, a plurality of setting values ​​44 from data set in the control device 22 as processing conditions for electrical discharge machining. However, the operator may also input at least one of the plurality of setting values ​​44 into the threshold determination device 24 via an input device such as an operation panel or touch panel. In this case, the acquisition unit 34 acquires the value input by the operator into the threshold determination device 24 as the setting value 44.

[0049] The memory unit 26 can also store most of the acquired setting values ​​44. In addition, to avoid complicated diagrams, Figure 3 only shows one setting value 44.

[0050] The evaluation value calculation unit 38 calculates a majority of evaluation values ​​46 (α, β, γ) based on the majority of set values ​​44 obtained. The majority of evaluation values ​​46 include the evaluation value α of the metal wire electrode 18, the evaluation value β of the workpiece W, and the evaluation value γ of the processing fluid LQ.

[0051] The evaluation value α of the metal wire electrode 18 is calculated based on at least one of the metal wire diameter of the metal wire electrode 18 actually provided by the metal wire electrical discharge machine 10 and the specific resistance of the metal wire electrode 18.

[0052] For example, the evaluation value calculation unit 38 makes the evaluation value α smaller when the metal wire diameter of the metal wire electrode 18 is thinner, and makes the evaluation value α larger when the metal wire diameter of the metal wire electrode 18 is thicker.

[0053] For example, the evaluation value calculation unit 38 makes the evaluation value α larger when the specific resistance of the metal wire electrode 18 is lower, and makes the evaluation value α smaller when the specific resistance of the metal wire electrode 18 is higher.

[0054] However, when the metal wire electrode 18 has the same metal wire diameter, specific resistance, etc. as the predetermined metal wire electrode used to determine the reference value α0, the evaluation value α will become the same as the reference value α0.

[0055] The evaluation value β of the workpiece W is calculated based on at least one of the thickness of the workpiece W actually contained in the processing tank 12 and the specific resistivity of the workpiece W.

[0056] For example, the evaluation value calculation unit 38 makes the evaluation value β smaller when the plate thickness of the workpiece W is thinner, and makes the evaluation value β larger when the plate thickness of the workpiece W is thicker.

[0057] For example, the evaluation value calculation unit 38 makes the evaluation value β larger when the resistivity of the workpiece W is lower, and makes the evaluation value β smaller when the resistivity of the workpiece W is higher.

[0058] However, when the workpiece W has the same plate thickness, resistivity, etc. as the predetermined workpiece used to determine the reference value β0, the evaluation value β will become the same as the reference value β0.

[0059] The evaluation value γ of the processing fluid LQ is calculated based on the resistivity of the processing fluid LQ actually stored in the processing tank 12.

[0060] The evaluation value calculation unit 38 makes the evaluation value γ larger when the specific resistance of the processing fluid LQ is lower, and makes the evaluation value γ smaller when the specific resistance of the processing fluid LQ is higher.

[0061] However, when the processing fluid LQ has the same specific resistivity as the predetermined processing fluid used to determine the reference value γ0, the evaluation value γ will become the same as the reference value γ0.

[0062] The memory unit 26 can also store most of the calculated evaluation values ​​46. In addition, to avoid complicated diagrams, Figure 3 only shows one evaluation value 46.

[0063] The correction calculation unit 40 of the threshold determination unit 36 ​​calculates the correction amount σ based on the difference between the majority reference value 32 and the majority evaluation value 46. The correction calculation unit 40 calculates the correction amount σ according to the calculation formula (1). In the calculation formula (1), σ represents the correction amount σ. α0 represents the reference value α0 of the metal wire electrode 18. α represents the evaluation value α of the metal wire electrode 18. β0 represents the reference value β0 of the workpiece W. β represents the evaluation value β of the workpiece W. γ0 represents the reference value γ0 of the processing fluid LQ. γ represents the evaluation value γ of the processing fluid LQ. A, B, and C are weighting coefficients of 0 or higher (A, B, C ≧ 0). A, B, and C are determined by considering the magnitude of the influence of the metal wire electrode 18, the workpiece W, and the processing fluid LQ on the voltage V variation, for example, based on experiments.

[0064] [Calculation Formula 1]

[0065] According to the calculation formula (1), the correction amount σ varies in response to the differences between each benchmark value 32 and the evaluation value 46 corresponding to each benchmark value 32.

[0066] The memory unit 26 can also store the calculated correction amount σ.

[0067] The threshold calculation unit 42 corrects the reference threshold VTH0 based on the correction amount σ, thereby calculating the threshold VTH. The threshold calculation unit 42 calculates the threshold VTH based on the next calculation formula (2). In the calculation formula (2), VTH displays the threshold VTH. VTH0 displays the reference threshold VTH0. σ displays the correction amount σ calculated by the calculation formula (1).

[0068] [Calculation Formula 2]

[0069] Based on the threshold determination device 24, the reference threshold VTH0 is corrected in the manner described in (1) to (5) below.

[0070] (1) The voltage V during the short circuit between the metal wire electrode 18 and the workpiece W increases as the metal wire diameter becomes thinner. To address this, the reference threshold VTH0 is adjusted to a larger threshold VTH as the metal wire diameter becomes thinner.

[0071] (2) The voltage V during the short circuit between the metal wire electrode 18 and the workpiece W is larger when the specific resistance of the metal wire electrode 18 is higher. To address this, the reference threshold VTH0 is adjusted to a larger threshold VTH when the specific resistance of the metal wire electrode 18 is higher.

[0072] (3) The voltage V during the short circuit between the metal wire electrode 18 and the workpiece W increases with the higher the specific resistance of the workpiece W. To address this, the reference threshold VTH0 is adjusted to a larger threshold VTH when the specific resistance of the workpiece W is higher.

[0073] (4) The voltage V during the short circuit between the metal wire electrode 18 and the workpiece W increases as the thickness of the workpiece W decreases. To address this, the reference threshold VTH0 is adjusted to a larger threshold VTH as the thickness of the workpiece W decreases.

[0074] (5) The voltage V during the short circuit between the metal wire electrode 18 and the workpiece W increases with the higher the specific resistance of the processing fluid LQ. To address this, the reference threshold VTH0 is adjusted to a larger threshold VTH when the specific resistance of the processing fluid LQ is higher.

[0075] The threshold determination unit 36 ​​outputs the calculated threshold VTH to the control device 22. Alternatively, the memory unit 26 can also store the calculated threshold VTH.

[0076] The control device 22 uses the threshold VTH input from the threshold determination device 24 to determine whether the metal wire electrode 18 is in contact with the workpiece W. By using the threshold VTH calculated in accordance with multiple factors, the control device 22 can more accurately determine whether the metal wire electrode 18 is in contact with the workpiece W.

[0077] Furthermore, the threshold VTH is derived by modifying a base threshold VTH0 based on the correction amount σ. That is, according to this embodiment, it is not necessary to pre-memorize the large number of thresholds VTH corresponding to various combinations of multiple factors in the memory unit 26.

[0078] Figure 4 is a flowchart illustrating the threshold determination method of the implementation mode.

[0079] The threshold determination device 24 can execute the threshold determination method of FIG4. This threshold determination method includes an acquisition step S1 and a threshold determination step S2.

[0080] Step S1 is the step of obtaining the majority setting values ​​44 of the majority factors by the acquisition unit 34.

[0081] The threshold determination step S2 is the step by which the threshold determination unit 36 ​​determines the threshold VTH based on the reference value 32 corresponding to the majority factors and the obtained majority setting value 44. The threshold determination step S2 includes the evaluation value calculation step S21, the correction amount calculation step S22, and the threshold calculation step S23.

[0082] The evaluation value calculation step S21 is the step in which the evaluation value calculation unit 38 calculates the majority evaluation value 46 based on the majority setting value 44.

[0083] The correction calculation step S22 is the step in which the correction calculation unit 40 calculates the correction amount σ based on the majority of evaluation values ​​46 and the majority of reference values ​​32. The correction calculation unit 40 calculates the correction amount σ, for example, based on the aforementioned calculation formula (1).

[0084] The threshold calculation step S23 is the step by which the threshold calculation unit 42 calculates the threshold VTH by multiplying the reference threshold VTH0 by the correction amount σ. The threshold calculation unit 42 calculates the threshold VTH according to the aforementioned calculation formula (2).

[0085] By using the threshold VTH calculated in the threshold calculation step S23, the control device 22 can more accurately determine the contact between the metal wire electrode 18 and the workpiece W.

[0086] [Variation Example] The following describes variations of the above embodiments. However, descriptions that are repeated in the above embodiments are omitted as much as possible in the following description. Unless otherwise stated, the constituent elements described in the above embodiments are marked with the same element symbols as in the above embodiments.

[0087] (Variation Example 1) External factors such as ambient temperature, air pressure, and electromagnetic waves around the wire EDM machine 10 (processing tank 12) may also be factors that cause voltage V1 to change.

[0088] Continuing from the above, the acquisition unit 34 can also further acquire set values ​​44 of ambient temperature, air pressure, electromagnetic waves (electromagnetic wave frequency), etc., around the wire EDM machine 10. The set values ​​44 of external factors are acquired, for example, based on the output signals of predetermined sensors such as temperature sensors and air pressure sensors.

[0089] The memory unit 26 can also store the reference value δ0 of external factors. The reference value δ0 is predetermined based on the given temperature, given air pressure, given frequency of electromagnetic waves, etc.

[0090] The evaluation value calculation unit 38 can also calculate the evaluation value δ of external factors based on the set values ​​44 such as temperature, air pressure, and electromagnetic waves obtained by the acquisition unit 34. Here, when the obtained temperature, air pressure, electromagnetic waves, etc. are the same as the predetermined temperature, predetermined air pressure, and predetermined frequency of electromagnetic waves used to determine the reference value δ0, the evaluation value δ will become the same as the reference value δ0.

[0091] The correction calculation unit 40 can also use the following formula (3) to calculate the correction amount σ. In formula (3), δ0 shows the baseline value δ0 of the external factor. δ shows the evaluation value δ of the external factor. D is the weighting coefficient. Other text is compared with formula (1).

[0092] [Calculation Formula 3]

[0093] Based on this variation, the threshold VTH is calculated, taking into account external factors.

[0094] (Variation Example 2) The reference value β0 and the evaluation value β of the workpiece W can also be determined using the values ​​that indicate the surface condition (surface roughness). That is, the reference value β0 and the evaluation value β can also be determined using at least one of the following: the thickness of the workpiece W, its resistivity, and the surface condition of the machined surface.

[0095] (Variation Example 3) The baseline value γ0 and the evaluation value γ of the processing fluid LQ can also be determined using the temperature and flow rate of the processing fluid LQ. That is, the baseline value γ0 and the evaluation value γ can be determined using at least one of the specific resistivity, temperature, and flow rate of the processing fluid LQ. Furthermore, the flow rate of the processing fluid LQ is determined by the speed at which the processing fluid LQ is ejected from the jet nozzles disposed within the processing tank 12.

[0096] (A combination of most variations) Most of the aforementioned variations can also be appropriately combined within a non-contradictory range.

[0097] [Inventions obtained through implementation] The invention described below is based on the above-described embodiments and variations.

[0098] <First Invention> A wire electrical discharge machining (10) determines that the wire electrode is in contact with the workpiece when the voltage (V) between the wire electrode (18) and the workpiece (W) is lower than a threshold value (VTH). The machine includes: an acquisition unit (34) that acquires a set value (44) of a factor that causes the voltage change between the wire electrode and the workpiece; and a threshold determination unit (36) that calculates the threshold value (VTH) based on a reference value (32) corresponding to the factor and the acquired set value.

[0099] Therefore, since the threshold is calculated in accordance with the factors that cause voltage variation between the wire electrode and the workpiece, the contact determination between the wire electrode and the workpiece based on the comparison of the threshold and the voltage can be performed more accurately.

[0100] The aforementioned threshold determination unit (36) comprises: an evaluation value calculation unit (38) that calculates the evaluation value (46) corresponding to the aforementioned factor based on the aforementioned set value; a correction amount calculation unit (40) that calculates a correction amount (σ) based on the difference between the aforementioned benchmark value and the aforementioned evaluation value; and a threshold calculation unit (42) that corrects the benchmark threshold (VTH0) corresponding to the aforementioned benchmark value based on the aforementioned correction amount, thereby calculating the aforementioned threshold; and the correction amount calculation unit increases the correction amount when the aforementioned evaluation value is smaller than the aforementioned benchmark value, and decreases the correction amount when the aforementioned evaluation value is larger than the aforementioned benchmark value. Therefore, since the threshold is calculated based on the difference between the benchmark value and the evaluation value, it is not necessary to include all the large number of thresholds corresponding to various changes in metal wire diameter in the data sheet beforehand.

[0101] There may be multiple factors mentioned above. These multiple factors include the processing fluid (LQ) used to immerse the workpiece, the metal wire electrode, and the workpiece itself. The correction calculation unit calculates the correction amount based on one or more of these multiple factors. The threshold calculation unit multiplies the correction amount by a reference threshold corresponding to the reference value of one or more of these multiple factors to calculate the threshold. This allows for the derivation of thresholds corresponding to various combinations of the multiple factors.

[0102] The aforementioned factors may also include the aforementioned metal wire electrode. When the diameter of the metal wire electrode is thinner, or the specific resistance of the metal wire electrode is higher, the aforementioned evaluation value calculation unit makes the aforementioned evaluation value of the metal wire electrode smaller; conversely, when the diameter of the metal wire electrode is thicker, or the specific resistance of the metal wire electrode is lower, the aforementioned evaluation value of the metal wire electrode is larger. This allows for a more accurate determination of the contact between the metal wire electrode and the workpiece based on a comparison of a threshold and voltage.

[0103] The aforementioned factors may also include the workpiece being processed. When the resistivity of the workpiece is higher or thinner, the aforementioned evaluation value calculation unit makes the aforementioned evaluation value of the workpiece smaller; conversely, when the resistivity of the workpiece is lower or thicker, the aforementioned evaluation value of the workpiece is larger. This allows for a more accurate determination of the contact between the metal wire electrode and the workpiece based on a comparison of a threshold and voltage.

[0104] The aforementioned factors may also include the aforementioned processing fluid. The aforementioned evaluation value calculation unit adjusts the aforementioned evaluation value of the processing fluid to be smaller when the specific resistance of the processing fluid is higher, and larger when the aforementioned specific resistance of the processing fluid is lower. This allows for a more accurate determination of the contact between the metal wire electrode and the workpiece based on a comparison of a threshold and voltage.

[0105] Most of the aforementioned factors may also include external factors, such as ambient temperature, air pressure, and electromagnetic waves around the wire EDM machine. The correction calculation unit calculates the correction amount based on at least one of the aforementioned factors, including the processing fluid, the wire electrode, and the workpiece, as well as the external factors. Therefore, by taking external factors into account when determining the threshold, it is possible to more accurately determine whether the wire electrode is in contact with the workpiece.

[0106] <Second Invention> The second invention is a threshold determination device (24) for determining whether the wire electrode (18) of the wire electrical discharge machining (10) is in contact with the workpiece (W), and for determining and comparing the voltage (V) between the wire electrode and the workpiece. The device includes: an acquisition unit (34) for acquiring a set value (44) of a factor that causes the voltage variation between the wire electrode and the workpiece; and a threshold determination unit (36) for calculating the threshold (VTH) based on a reference value (32) of the factor and the acquired set value.

[0107] Therefore, since the threshold is calculated in accordance with the factors that cause the voltage (V) between the wire electrode and the workpiece to change, it is possible to more accurately determine the contact between the wire electrode and the workpiece based on the comparison between the threshold and the voltage.

[0108] <Third Invention> The third invention is a threshold determination method. In order to determine whether the wire electrode (18) of the wire electrical discharge machining (10) is in contact with the workpiece (W), a threshold (VTH) is determined and compared with the voltage (V) between the wire electrode and the workpiece. The method includes the following steps: an acquisition step (S1), acquiring a setting value (44) of the factors that cause the voltage variation between the wire electrode and the workpiece; and a threshold determination step (S2), calculating the threshold (VTH) based on the reference value (32) of the factors and the acquired setting value.

[0109] Therefore, since the threshold is calculated in accordance with the factors that cause the voltage (V) between the wire electrode and the workpiece to change, it is possible to more accurately determine the contact between the wire electrode and the workpiece based on the comparison between the threshold and the voltage.

[0110] Furthermore, the present invention is not limited to the above-described embodiments and variations. Various configurations may be adopted as long as they do not depart from the spirit of the present invention.

[0111] 10: Wire EDM machine 12: Machining slot 14: Platform 16X: Electric motor 16Y: Electric motor 18: Metal wire electrode 20: Power supply device 22: Control device 24: Threshold Determination Device 26: Memory Department 28: Arithmetic Department 30: Threshold Determination Program 32: Baseline value 34: Acquisition Department 36: Threshold Determination Department 38: Evaluation Value Calculation Department 40: Correction Calculation Department 42: Threshold Calculation Unit 44: Setting value 46: Evaluation Value A, B, C: Weighting coefficients LQ: Processing Fluid V: Voltage VTH: Threshold VTH0: Baseline Threshold W: Object to be processed α: Evaluation value α0: Baseline value β: Evaluation value β0: Baseline value γ: Evaluation value γ0: Baseline value σ: Correction amount δ: Evaluation value δ0: Reference value

Claims

1. A wire electrical discharge machining (10) for determining that the wire electrode is in contact with the workpiece when the voltage (V) between the wire electrode (18) and the workpiece (W) is lower than a threshold value (VTH), comprising: an acquisition unit (34) for acquiring a setting value (44) of a factor that causes the voltage variation between the wire electrode and the workpiece; and a threshold determination unit (36) for calculating the threshold value (VTH) based on a reference value (32) corresponding to the factor and the acquired setting value.

2. The wire electrical discharge machining machine as described in claim 1, wherein, The threshold determination unit (36) includes: an evaluation value calculation unit (38) for calculating an evaluation value (46) corresponding to the factor based on the set value; a correction amount calculation unit (40) for calculating a correction amount (σ) based on the difference between the benchmark value and the evaluation value; and a threshold calculation unit (42) for correcting the benchmark threshold (VTH0) corresponding to the benchmark value based on the correction amount, thereby calculating the threshold; and the correction amount calculation unit increases the correction amount when the evaluation value is smaller than the benchmark value, and decreases the correction amount when the evaluation value is larger than the benchmark value.

3. The wire electrical discharge machining machine as described in claim 2, wherein, There are multiple factors, including: the processing fluid (LQ) that soaks the workpiece, the metal wire electrode, and the workpiece; and the correction calculation unit calculates the correction amount based on one or more of the multiple factors, and the threshold calculation unit multiplies the correction amount by the reference threshold corresponding to the reference value of the one or more factors to calculate the threshold.

4. As in claim 3, the wire EDM machine, wherein one or more of the factors include the wire electrode, the evaluation value calculation unit makes the evaluation value of the wire electrode smaller when the wire diameter of the wire electrode is thinner or the resistivity of the wire electrode is higher, and makes the evaluation value of the wire electrode larger when the wire diameter is thicker or the resistivity of the wire electrode is lower.

5. The wire electrical discharge machining machine as requested in item 3 or 4, wherein, The factor that includes the workpiece is evaluated by the evaluation value calculation unit. When the resistivity of the workpiece is higher or the workpiece is thinner, the evaluation value of the workpiece is smaller. When the resistivity of the workpiece is lower or the workpiece is thicker, the evaluation value of the workpiece is larger.

6. The wire electrical discharge machining machine as requested in item 3 or 4, wherein, The factor that includes the processing fluid is such that the evaluation value calculation unit makes the evaluation value of the processing fluid smaller when the specific resistance of the processing fluid is higher, and makes the evaluation value of the processing fluid larger when the specific resistance of the processing fluid is lower.

7. The wire electrical discharge machining machine as requested in item 3 or 4, wherein, Most of these factors include external factors, which include at least one of the ambient temperature, air pressure, and electromagnetic waves of the wire EDM machine. The correction calculation unit calculates the correction amount based on at least one of the processing fluid, the wire electrode, and the workpiece, along with the external factors.

8. A threshold determination device for determining a threshold (VTH) for comparing the voltage (V) between the wire electrode (18) of a wire electrical discharge machining (10) and the workpiece (W) to determine whether there is contact between them, comprising: an acquisition unit (34) for acquiring a setting value (44) of a factor that causes the voltage variation between the wire electrode and the workpiece; and a threshold determination unit (36) for calculating the threshold (VTH) based on a reference value (32) of the factor and the acquired setting value.

9. A threshold determination method for determining a threshold (VTH) for comparing the voltage (V) between the wire electrode (18) of a wire electrical discharge machining (10) and the workpiece (W) to determine whether they are in contact, comprising the following steps: an acquisition step (S1) of acquiring a set value (44) of a factor that causes the voltage variation between the wire electrode and the workpiece; and a threshold determination step (S2) of calculating the threshold (VTH) based on a reference value (32) of the factor and the acquired set value.

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