Wire Electrical Discharge Machine, Threshold Determination Device, and Threshold Determination Method

Abstract

Provided is a wire electrical discharge machine (10) which, when a voltage (V) between a wire electrode (18) and a workpiece (W) is lower than a threshold value (VTH), determines that the wire electrode (18) and the workpiece (W) have come into contact with each other. The wire electrical discharge machine (10) comprises: an acquisition unit (34) that acquires a set value (44) for a factor that fluctuates the voltage (V) between the wire electrode (18) and the workpiece (W); and a threshold value determination unit (36) that calculates the threshold value (VTH), on the basis of a reference value (32) of the factor and the acquired set value (44).

Description

Technical Field

[0001] The present invention relates to a wire electrical discharge machining apparatus, a threshold determination device, and a threshold determination method.

Background Art

[0002] A wire electrical discharge machining apparatus applies a voltage between a wire electrode and a workpiece. This voltage drops when the wire electrode and the workpiece come into contact. A method has been proposed for determining whether the wire electrode and the workpiece have come into contact by utilizing this change in voltage (see also Japanese Patent Application Laid-Open No. 2013-226612).

Summary of the Invention

[0003] The voltage between the wire electrode and the workpiece is compared with a predetermined reference voltage (threshold value). When the voltage falls below the threshold value, it is determined that the wire electrode and the workpiece have come into contact.

[0004] However, there is a problem that even though the wire electrode and the workpiece have come into contact, the voltage may exceed the threshold value. In this case, it is not accurately determined that the wire electrode and the workpiece have come into contact.

[0005] An object of the present invention is to solve the above-described problems.

[0006] A first aspect of the present invention is a wire electrical discharge machining apparatus that determines that the wire electrode and the workpiece have come into contact when the voltage between the wire electrode and the workpiece falls below a threshold value, the wire electrical discharge machining apparatus including: an acquisition unit that acquires a set value related to a factor that varies the voltage 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] A second aspect of the present invention is a threshold determination device that determines a threshold value to be compared with the voltage between the wire electrode and the workpiece in order to determine whether the wire electrode and the workpiece of a wire electrical discharge machining machine are in contact. The threshold determination device includes an acquisition unit that acquires a set value related to a factor that varies the voltage between the wire electrode and the workpiece, and a threshold determination unit that calculates a threshold value based on a reference value of the factor and the acquired set value.

[0008] A third aspect of the present invention is a threshold determination method for determining a threshold value to be compared with the voltage between the wire electrode and the workpiece in order to determine whether the wire electrode and the workpiece of a wire electrical discharge machining machine are in contact. The threshold determination method includes an acquisition step of acquiring a set value related to a factor that varies the voltage between the wire electrode and the workpiece, and a threshold determination step of calculating a threshold value based on a reference value of the factor and the acquired set value.

[0009] According to the present invention, since the threshold value is calculated according to the factor that varies the voltage between the wire electrode and the workpiece, it is possible to more accurately determine whether the wire electrode and the workpiece are in contact based on the comparison between the threshold value and the voltage.

Brief Description of the Drawings

[0010]

Figure 1

Figure 2

Figure 3

Figure 4

Embodiments for Carrying Out the Invention

[0011] [Embodiment] FIG. 1 is a configuration diagram of a wire electrical discharge machining machine 10 according to an embodiment.

[0012] The wire electrical discharge machining machine 10 includes a machining tank 12, a table 14, a motor 16X, a motor 16Y, a wire electrode 18, a power supply device 20, a control device 22, and a threshold determination device 24. The control device 22 is, for example, a numerical control device.

[0013] The machining tank 12 is a tank that houses the table 14. Further, the machining tank 12 stores a machining fluid LQ.

[0014] The table 14 is a table that supports a workpiece W. The table 14 and the workpiece W are immersed in the machining fluid LQ inside the machining tank 12.

[0015] Each of the motor 16X and the motor 16Y is a motor connected to the table 14. The table 14 moves in the X direction in response to the drive of the motor 16X. Further, the table 14 moves in the Y direction in response to the drive of the motor 16Y. The motor 16X and the motor 16Y are controlled by the control device 22.

[0016] The wire electrode 18 is a conductive wire rod. The wire electrode 18 is stretched in the machining tank 12. The wire electrode 18 moves relative to the table 14 in the horizontal direction as the table 14 moves in the horizontal direction.

[0017] The power supply device 20 is connected to the wire electrode 18 and the table 14 (workpiece W). The power supply device 20 applies a voltage for detecting contact between the wire electrode 18 and the workpiece W between the wire electrode 18 and the workpiece W. This voltage is a pulsed voltage. In the following description, the voltage V refers to the voltage detected between the wire electrode 18 and the workpiece W unless otherwise specified.

[0018] FIG. 2A is a graph showing a first example of the change in voltage V before and after the short circuit between the wire electrode 18 and the workpiece W. This graph has a vertical axis indicating the magnitude of the voltage V and a horizontal axis which is the time axis.

[0019] Before the time point TC in FIG. 2A, the wire electrode 18 and the workpiece W are non-contact. The magnitude of the voltage V in this time period is V1 (voltage V1).

[0020] At the time point TC in FIG. 2A, the wire electrode 18 and the workpiece W are sufficiently close (in contact). The wire electrode 18 and the workpiece W are in electrical short circuit by contacting each other. As a result, even if the waveform of the output voltage of the power supply device 20 does not change before and after the time point TC, the voltage V (V2) in the time period after the time point TC becomes smaller than the voltage V1 (V1 > V2).

[0021] The control device 22 controls the motor 16X, the motor 16Y, and the power supply device 20 according to a predetermined program. Further, the control device 22 determines whether or not the wire electrode 18 and the workpiece W are short-circuited based on whether or not the voltage V has fallen below a predetermined threshold value V TH That is, the control device 22 determines whether or not the wire electrode 18 and the workpiece W are in contact based on whether or not the voltage V has fallen below the threshold value V TH However, the magnitude of the voltage V while the wire electrode 18 and the workpiece W are short-circuited changes due to a plurality of factors. The plurality of factors include the wire electrode 18, the workpiece W, and the machining fluid LQ.

[0022] For example, the voltage V while the wire electrode 18 and the workpiece W are short-circuited is larger as the electrical resistivity (specific resistance) of each of the wire electrode 18, the workpiece W, and the machining fluid LQ is higher. Also, the voltage V while the wire electrode 18 and the workpiece W are short-circuited is larger as the wire electrode 18 is thinner or the plate thickness of the workpiece W is thinner.

[0023]

[0024] ​FIG. 2B is a graph showing a second example of the change in voltage V before and after the short circuit between the wire electrode 18 and the object to be processed W. In FIG. 2B, due to the above-described plurality of factors, the magnitude of the voltage V while the wire electrode 18 and the object to be processed W are short-circuited is higher than that in the case of FIG. 2A. The format of the graph in FIG. 2B conforms to the graph in FIG. 2A.

[0025] As shown in FIG. 2B, due to the above-described plurality of factors, the voltage V while the wire electrode 18 and the object to be processed W are short-circuited may show a V3 greater than the threshold value V TH (V3 > V TH ). In this case, it is not possible to determine that the wire electrode 18 and the object to be processed W have come into contact based on the comparison between the voltage V and the threshold value V TH .

[0026] Here, a method using a data table storing a plurality of threshold values V TH corresponding to combinations of a plurality of factors is considered as a countermeasure. However, when the threshold value V TH corresponding to the combination of the wire diameter of the wire electrode 18 used by the operator, the plate thickness of the object to be processed W, etc. is not stored in the data table in advance, the above method cannot be applied.

[0027] The voltage V may vary if at least one of the plurality of factors is different. Therefore, the data table is required to cover a huge number of threshold values V TH corresponding to all combinations of the plurality of factors. However, it is not realistic to cover in advance a huge number of threshold values V TH corresponding to all combinations of the plurality of factors in the data table.

[0028] Based on the above, the threshold determination device 24 according to the present embodiment will be described below. The threshold determination device 24 is an electronic device (computer) communicably connected to the control device 22. Note that the threshold determination device 24 may be incorporated into the control device 22 as a part of the control device 22.

[0029] FIG. 3 is a configuration diagram of the threshold determination device 24.

[0030] The threshold determination device 24 includes a storage unit 26 and an arithmetic unit 28.

[0031] The storage unit 26 includes one or more memories. The storage unit 26 includes, for example, a RAM (Random Access Memory), a ROM (Read Only Memory), and the like.

[0032] The storage unit 26 stores a threshold determination program 30, a plurality of reference values 32 (α0, β0, γ0), and a reference threshold V TH0 and. Note that, in order to avoid complication of the drawing, FIG. 3 shows only one reference value 32.

[0033] The threshold determination program 30 is a program for setting a threshold V according to a plurality of factors. TH

[0034] The plurality of reference values 32 are numerical values determined in advance according to a plurality of factors. The plurality of reference values 32 include a reference value α0 of the wire electrode 18, a reference value β0 of the workpiece W, and a reference value γ0 of the processing liquid LQ.

[0035] The reference value α0 of the wire electrode 18 is determined in advance based on the wire diameter of a predetermined wire electrode, the specific resistance of a predetermined wire electrode, etc.

[0036] The reference value β0 of the workpiece W is determined in advance based on the thickness of a predetermined workpiece and the specific resistance of a predetermined workpiece, etc.

[0037] The reference value γ0 of the processing liquid LQ is determined in advance based on the specific resistance of a predetermined processing liquid.

[0038] ​Note that the predetermined wire electrode may be different from the wire electrode 18 actually provided in the wire electrical discharge machining machine 10. The predetermined workpiece may be different from the workpiece W actually accommodated in the machining tank 12. The predetermined machining fluid may be different from the machining fluid LQ actually stored in the machining tank 12. Therefore, each of the plurality of reference values 32 may be, for example, a constant specified in advance by the manufacturer of the wire electrical discharge machining machine 10.

[0039] Reference threshold value V TH0 is a voltage value (constant) determined according to the combination of the reference values 32 of a plurality of factors. The number of the reference threshold values V stored in the storage unit 26 TH0 is one.

[0040] In addition to the threshold determination program 30, the plurality of reference values 32, and the reference threshold value V, the storage unit 26 may store various data, programs, etc. as necessary. TH0

[0041] The arithmetic unit 28 includes a processing circuit. This processing circuit includes one or more processors. However, the processing circuit of the arithmetic unit 28 may include an ASIC (Application Specific Integrated Circuit), an FPGA (Field-Programmable Gate Array), discrete devices, etc.

[0042] 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 amount calculation unit 40, and a threshold calculation unit 42. The acquisition unit 34 and the threshold determination unit 36 are realized by the processor of the arithmetic unit 28 executing the threshold determination program 30. However, at least a part of the acquisition unit 34 and the threshold determination unit 36 may be realized by the aforementioned ASIC, FPGA, discrete devices, etc.

[0043] The acquisition unit 34 acquires a plurality of set values 44. The plurality of set values 44 are numerical values set for the wire electrical discharge machine 10 regarding a plurality of factors. The plurality of set values 44 include the set value 44 of each of the wire diameter of the wire electrode 18 provided in the wire electrical discharge machine 10 and the specific resistance of the wire electrode 18. Further, the plurality of set values 44 also include the set value 44 of each of the thickness of the workpiece W accommodated in the machining tank 12, the specific resistance of the workpiece W, and the specific resistance of the machining fluid LQ stored in the machining tank 12.

[0044] The acquisition unit 34 acquires a plurality of set values 44 from, for example, the data set in the control device 22 as the machining conditions of the electrical discharge machining. However, at least one of the plurality of set values 44 may be input by the operator to the threshold determination device 24 via an input device such as an operation panel or a touch panel. In that case, the acquisition unit 34 acquires the numerical value input by the operator to the threshold determination device 24 as the set value 44.

[0045] The storage unit 26 may store the acquired plurality of set values 44. Note that, to avoid making the drawing complicated, only one set value 44 is shown in FIG. 3.

[0046] The evaluation value calculation unit 38 calculates a plurality of evaluation values 46 (α, β, γ) based on the acquired plurality of set values 44. The plurality of evaluation values 46 include the evaluation value α of the wire electrode 18, the evaluation value β of the workpiece W, and the evaluation value γ of the machining fluid LQ.

[0047] The evaluation value α of the wire electrode 18 is calculated based on at least one of the wire diameter of the wire electrode 18 actually provided in the wire electrical discharge machine 10 and the specific resistance of the wire electrode 18.

[0048] For example, the evaluation value calculation unit 38 makes the evaluation value α smaller as the wire diameter of the wire electrode 18 is thinner, and makes the evaluation value α larger as the wire diameter of the wire electrode 18 is thicker.

[0049] Further, for example, the evaluation value calculation unit 38 increases the evaluation value α as the specific resistance of the wire electrode 18 is lower, and decreases the evaluation value α as the specific resistance of the wire electrode 18 is higher.

[0050] However, when the wire electrode 18 has the same wire diameter, specific resistance, etc. as a predetermined wire electrode used to determine the reference value α0, the evaluation value α becomes the same value as the reference value α0.

[0051] The evaluation value β of the workpiece W is calculated based on at least one of the thickness of the workpiece W actually accommodated in the processing tank 12 and the specific resistance of the workpiece W.

[0052] For example, the evaluation value calculation unit 38 decreases the evaluation value β as the plate thickness of the workpiece W is thinner, and increases the evaluation value β as the plate thickness of the workpiece W is thicker.

[0053] Further, for example, the evaluation value calculation unit 38 increases the evaluation value β as the specific resistance of the workpiece W is lower, and decreases the evaluation value β as the specific resistance of the workpiece W is higher.

[0054] However, when the workpiece W has the same plate thickness, specific resistance, etc. as a predetermined workpiece used to determine the reference value β0, the evaluation value β becomes the same value as the reference value β0.

[0055] The evaluation value γ of the processing liquid LQ is calculated based on the specific resistance of the processing liquid LQ actually stored in the processing tank 12.

[0056] The evaluation value calculation unit 38 increases the evaluation value γ as the specific resistance of the processing liquid LQ is lower, and decreases the evaluation value γ as the specific resistance of the processing liquid LQ is higher.

[0057] However, when the processing liquid LQ has the same specific resistance, etc. as a predetermined processing liquid used to determine the reference value γ0, the evaluation value γ becomes the same value as the reference value γ0.

[0058] The memory unit 26 may store the calculated plurality of evaluation values 46. Note that, to avoid complication of the drawings, FIG. 3 shows only one evaluation value 46.

[0059] The correction amount calculation unit 40 of the threshold determination unit 36 calculates a correction amount σ based on the differences between a plurality of reference values 32 and a plurality of evaluation values 46. The correction amount calculation unit 40 calculates the correction amount σ based on Equation (1). In Equation (1), σ represents the correction amount σ. α0 represents the reference value α0 of the wire electrode 18. α represents the evaluation value α of the 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 machining fluid LQ. γ represents the evaluation value γ of the machining fluid LQ. Each of A, B, and C is a weight coefficient of 0 or more (A, B, C ≧ 0). Each of A, B, and C is determined based on, for example, experiments while considering the magnitudes of the influences exerted by the wire electrode 18, the workpiece W, and the machining fluid LQ on the voltage V fluctuations.

[0060]

Equation

[0061] According to Equation (1), the correction amount σ changes according to the differences between each reference value 32 and the evaluation value 46 corresponding to each reference value 32.

[0062] The memory unit 26 may store the calculated correction amount σ.

[0063] The threshold calculation unit 42 calculates the threshold V TH0 by correcting it based on the correction amount σ, thereby calculating the threshold V TH The threshold calculation unit 42 calculates the threshold V TH based on the following Equation (2). In Equation (2), V TH represents the threshold V TH V TH0 represents the reference threshold V TH0 σ represents the correction amount σ calculated by Equation (1).

[0064] [Number]

[0065] According to the above threshold determination device 24, the reference threshold V TH0 is corrected as follows in (1) to (5) below.

[0066] (1) During the short circuit between the wire electrode 18 and the workpiece W, the voltage V increases as the wire diameter becomes thinner. In contrast, the reference threshold V TH0 is corrected to a larger threshold V TH as the wire diameter becomes thinner.

[0067] (2) During the short circuit between the wire electrode 18 and the workpiece W, the voltage V increases as the specific resistance of the wire electrode 18 becomes higher. In contrast, the reference threshold V TH0 is corrected to a larger threshold V TH as the specific resistance of the wire electrode 18 becomes higher.

[0068] (3) During the short circuit between the wire electrode 18 and the workpiece W, the voltage V increases as the specific resistance of the workpiece W becomes higher. In contrast, the reference threshold V TH0 is corrected to a larger threshold V TH as the specific resistance of the workpiece W becomes higher.

[0069] (4) During the short circuit between the wire electrode 18 and the workpiece W, the voltage V increases as the plate thickness of the workpiece W becomes thinner. In contrast, the reference threshold V TH0 is corrected to a larger threshold V TH as the plate thickness of the workpiece W becomes thinner.

[0070] (5) During the short circuit between the wire electrode 18 and the workpiece W, the voltage V increases as the specific resistance of the machining fluid LQ becomes higher. In contrast, the reference threshold V TH0 is corrected to a larger threshold V TH as the specific resistance of the machining fluid LQ becomes higher.

[0071] The threshold determination unit 36 uses the calculated threshold V THand output it to the control device 22. The storage unit 26 may store the calculated threshold value V TH thereof.

[0072] The control device 22 determines whether the wire electrode 18 and the workpiece W are in contact with each other by using the threshold value V TH input from the threshold value determination device 24. By using the threshold value V TH calculated according to a plurality of factors, the contact determination between the wire electrode 18 and the workpiece W can be performed more accurately.

[0073] Moreover, the threshold value V TH is derived by correcting one reference threshold value V TH0 based on the correction amount σ. That is, according to the present embodiment, it is not necessary to store in advance in the storage unit 26 a huge number of threshold values V TH corresponding to all combinations of a plurality of factors.

[0074] FIG. 4 is a flowchart illustrating the flow of the threshold value determination method according to the embodiment.

[0075] The threshold value determination device 24 can execute the threshold value determination method of FIG. 4. This threshold value determination method includes an acquisition step S1 and a threshold value determination step S2.

[0076] The acquisition step S1 is a step in which the acquisition unit 34 acquires a plurality of setting values 44 related to a plurality of factors.

[0077] The threshold value determination step S2 is a step in which the threshold value determination unit 36 determines the threshold value V TH based on the reference value 32 corresponding to a plurality of factors and the plurality of acquired setting values 44. The threshold value determination step S2 includes an evaluation value calculation step S21, a correction amount calculation step S22, and a threshold value calculation step S23.

[0078] The evaluation value calculation step S21 is a step in which the evaluation value calculation unit 38 calculates a plurality of evaluation values 46 based on the plurality of setting values 44.

[0079] The correction amount calculation step S22 is a step in which the correction amount calculation unit 40 calculates a correction amount σ based on a plurality of evaluation values 46 and a plurality of reference values 32. The correction amount calculation unit 40 calculates the correction amount σ based on, for example, the aforementioned mathematical formula (1).

[0080] In the threshold value calculation step S23, the threshold value calculation unit 42 calculates a threshold value V TH0 and the correction amount σ Multiply to calculate the threshold value V TH This is a step of calculating. The threshold value calculation unit 42 calculates the threshold value V TH based on the aforementioned mathematical formula (2).

[0081] The control device 22 can more accurately determine the contact between the wire electrode 18 and the workpiece W by using the threshold value V TH calculated in the threshold value calculation step S23.

[0082] [Modification Example] The following describes a modification example according to the above embodiment. However, descriptions overlapping with the above embodiment are omitted as much as possible in the following description. Components described in the above embodiment are given the same reference numerals as those in the above embodiment unless otherwise specified.

[0083] (Modification Example 1) External factors such as the ambient temperature, atmospheric pressure, and electromagnetic waves around the wire electrical discharge machine 10 (processing tank 12) can also be factors that cause fluctuations in the voltage V1.

[0084] Based on the above, the acquisition unit 34 may further acquire setting values 44 such as the ambient temperature, atmospheric pressure, and electromagnetic waves (frequencies of electromagnetic waves) around the wire electrical discharge machine 10. The setting values 44 of external factors are acquired based on the output signals of predetermined sensors such as, for example, a temperature sensor and an atmospheric pressure sensor.

[0085] The storage unit 26 may store a reference value 32 (δ0) of external factors. The reference value δ0 is determined in advance based on a predetermined temperature, a predetermined atmospheric pressure, a predetermined frequency of electromagnetic waves, etc.

[0086] The evaluation value calculation unit 38 may calculate an evaluation value 46 (δ) of external factors based on the set values 44 such as temperature, atmospheric pressure, and electromagnetic waves acquired by the acquisition unit 34. Here, when the acquired temperature, atmospheric pressure, electromagnetic waves, etc. are the same as the predetermined temperature, predetermined atmospheric pressure, and predetermined frequency of electromagnetic waves used to determine the reference value δ0, the evaluation value δ becomes the same value as the reference value δ0.

[0087] The correction amount calculation unit 40 may calculate a correction amount σ using the following mathematical formula (3). In mathematical formula (3), δ0 represents the reference value δ0 of external factors. δ represents the evaluation value δ of external factors. D is a weighting coefficient. Other characters conform to mathematical formula (1).

[0088]

Number

[0089] According to this modification example, a threshold value V TH is calculated.

[0090] (Modification Example 2) The reference value β0 of the workpiece W and the evaluation value β of the workpiece W may be determined using a value indicating the state (surface roughness) of the processed surface. That is, the reference value β0 and the evaluation value β may be determined using at least one of the plate thickness, specific resistance, and state of the processed surface of the workpiece W.

[0091] (Modification Example 3) The reference value γ0 of the processing fluid LQ and the evaluation value γ of the processing fluid LQ may be determined using the liquid temperature, flow rate, etc. of the processing fluid LQ. That is, the reference value γ0 and the evaluation value γ may be determined using at least one of the specific resistance, liquid temperature, flow rate, etc. of the processing fluid LQ. Note that the flow rate of the processing fluid LQ is the speed at which the processing fluid LQ is jetted from the jet nozzle arranged in the processing tank 12.

[0092] (Combination of Multiple Modification Examples) The multiple modification examples described above may be appropriately combined within a non - conflicting range.

[0093] [Invention Obtained from Embodiment] The inventions that can be understood from the above embodiments and modified examples are described below.

[0094] <First Invention>[ A wire electrical discharge machining machine (10) that determines that the wire electrode (18) and the workpiece (W) are in contact when the voltage (V) between the wire electrode and the workpiece is lower than a threshold value (V TH ), comprising: an acquisition unit (34) that acquires a set value (44) regarding a factor that varies the voltage between the wire electrode and the workpiece; a threshold determination unit (36) that calculates a threshold value (V TH ) based on a reference value (32) corresponding to the factor and the acquired set value.

[0095] Accordingly, since the threshold value is calculated according to the factor that varies the voltage between the wire electrode and the workpiece, it is possible to more accurately determine the contact between the wire electrode and the workpiece based on the comparison between the threshold value and the voltage.

[0096] The threshold determination unit (36) includes: an evaluation value calculation unit (38) that calculates an evaluation value (46) corresponding to the factor based on the set value; a correction amount calculation unit (40) that calculates a correction amount (σ) based on the difference between the reference value and the evaluation value; and a threshold calculation unit (42) that calculates the threshold value by correcting a reference threshold value (V TH0 ) corresponding to the reference value based on the correction amount. The correction amount calculation unit may increase the correction amount as the evaluation value is smaller than the reference value, and decrease the correction amount as the evaluation value is larger than the reference value. Accordingly, since the threshold value is calculated based on the difference between the reference value and the evaluation value, for example, it is not necessary to previously cover a huge number of threshold values corresponding to all variations of the wire diameter in a data table.

[0097] There are a plurality of the factors, and the plurality of the factors include the machining fluid (LQ) in which the object to be machined is immersed, the wire electrode, and the object to be machined. The correction amount calculation unit calculates the correction amount based on one or more of the plurality of the factors, and the threshold value calculation unit calculates the threshold value by calculating the correction amount and the reference threshold value corresponding to the reference value of the one or more factors. Multiply By doing so, threshold values corresponding to all combinations of the above-described plurality of factors can be derived.

[0098] The one or more factors include the wire electrode. The evaluation value calculation unit may decrease the evaluation value of the wire electrode as the wire diameter of the wire electrode is thinner or the specific resistance of the wire electrode is higher, and may increase the evaluation value of the wire electrode as the wire diameter is thicker or the specific resistance of the wire electrode is lower. Thereby, the contact determination between the wire electrode and the object to be machined based on the comparison between the threshold value and the voltage can be performed more accurately.

[0099] The one or more factors include the object to be machined. The evaluation value calculation unit may decrease the evaluation value of the object to be machined as the specific resistance of the object to be machined is higher or the object to be machined is thinner, and may increase the evaluation value of the object to be machined as the specific resistance of the object to be machined is lower or the object to be machined is thicker. Thereby, the contact determination between the wire electrode and the object to be machined based on the comparison between the threshold value and the voltage can be performed more accurately.

[0100] The one or more factors include the machining fluid. The evaluation value calculation unit may decrease the evaluation value of the machining fluid as the specific resistance of the machining fluid is higher, and may increase the evaluation value of the machining fluid as the specific resistance of the machining fluid is lower. Thereby, the contact determination between the wire electrode and the object to be machined based on the comparison between the threshold value and the voltage can be performed more accurately.

[0101] The plurality of the factors further includes external factors, and the external factors include at least one of the temperature around the wire electrical discharge machine, the atmospheric pressure, and electromagnetic waves. The correction amount calculation unit may calculate the correction amount based on at least one of the machining fluid, the wire electrode, and the workpiece among the plurality of the factors and the external factors. Thereby, since the threshold value is determined in consideration of the external factors, it becomes possible to more accurately determine whether or not the wire electrode and the workpiece are in contact with each other.

[0102] <Second Invention> The second invention is a threshold value determination device (24) for determining whether or not the wire electrode (18) of a wire electrical discharge machine (10) and a workpiece (W) are in contact with each other, and a threshold value (V TH ) to be compared with the voltage (V) between the wire electrode and the workpiece, the obtaining unit (34) for obtaining a set value (44) regarding a factor for varying the voltage between the wire electrode and the workpiece, and based on the reference value (32) of the factor and the obtained set value, a threshold value determination unit (36) for calculating the threshold value (V TH ).

[0103] Thereby, since the threshold value is calculated according to the factor for varying the voltage (V) between the wire electrode and the workpiece, it becomes possible to more accurately perform the contact determination between the wire electrode and the workpiece based on the comparison between the threshold value and the voltage.

[0104] <Third Invention> The third invention is a threshold value determination method for determining whether or not the wire electrode (18) of a wire electrical discharge machine (10) and a workpiece (W) are in contact with each other, and a threshold value (V TH ) to be compared with the voltage (V) between the wire electrode and the workpiece, an obtaining step (S1) for obtaining a set value (44) regarding a factor for varying the voltage between the wire electrode and the workpiece, and a threshold value determination step (S2) for calculating the threshold value (V TH ) based on the reference value (32) of the factor and the obtained set value.

[0105] Accordingly, since the threshold value is calculated according to the factor that varies the voltage (V) between the wire electrode and the object to be processed, the contact determination between the wire electrode and the object to be processed based on the comparison between the threshold value and the voltage can be performed more accurately.

Explanation of Signs

[0106] 10…Wire electrical discharge machining machine 18…Wire electrode 24…Threshold determination device 32…Reference value 34…Acquisition unit 36…Threshold determination unit 38…Evaluation value calculation unit 40…Correction amount calculation unit 42…Threshold calculation unit 44…Set value 46…Evaluation value LQ…Processing fluid V…Voltage V TH …Threshold value V TH0 …Reference threshold value W…Object to be processed σ…Correction amount

Claims

1. A wire electrical discharge machining machine (10) that determines that the wire electrode (18) and the workpiece (W) are in contact when the voltage (V) between the wire electrode and the workpiece falls below a threshold value (V ＴＨ ), comprising: an acquisition unit (34) that acquires a set value (44) related to a factor that varies the voltage between the wire electrode and the workpiece; A threshold determination unit (36) that calculates the threshold value based on a reference value (32) corresponding to the factor and the acquired set value; A wire electrical discharge machining machine comprising:

2. The wire electrical discharge machining machine according to claim 1, wherein the threshold determination unit (36) comprises an evaluation value calculation unit (38) that calculates an evaluation value (46) corresponding to the factor based on the set value; a correction amount calculation unit (40) that calculates a correction amount (σ) based on the difference between the reference value and the evaluation value; and a threshold calculation unit (42) that calculates the threshold value by correcting a reference threshold value (V ＴＨ０ ) corresponding to the reference value based on the correction amount; and the correction amount calculation unit increases the correction amount as the evaluation value is smaller than the reference value, and decreases the correction amount as the evaluation value is larger than the reference value.

3. The wire electrical discharge machining machine according to claim 2, wherein there are a plurality of the factors, the plurality of factors include a machining fluid (LQ) in which the workpiece is immersed, the wire electrode, and the workpiece, the correction amount calculation unit calculates the correction amount based on one or more of the plurality of factors, and the threshold calculation unit calculates the threshold value by multiplying the correction amount by the reference threshold value corresponding to the reference value of the one or more factors.

4. The wire electrical discharge machining apparatus according to claim 3, wherein the one or more factors include the wire electrode, the evaluation value calculation unit decreases the evaluation value of the wire electrode as the wire diameter of the wire electrode is thinner or the specific resistance of the wire electrode is higher, and increases the evaluation value of the wire electrode as the wire diameter is thicker or the specific resistance of the wire electrode is lower. Wire electrical discharge machining apparatus.

5. The wire electrical discharge machining apparatus according to claim 3 or 4, wherein the one or more factors include the object to be machined, the evaluation value calculation unit decreases the evaluation value of the object to be machined as the specific resistance of the object to be machined is higher or the object to be machined is thinner, and increases the evaluation value of the object to be machined as the specific resistance of the object to be machined is lower or the object to be machined is thicker. Wire electrical discharge machining apparatus.

6. The wire electrical discharge machining apparatus according to any one of claims 3 to 5, wherein the one or more factors include the machining fluid, the evaluation value calculation unit decreases the evaluation value of the machining fluid as the specific resistance of the machining fluid is higher, and increases the evaluation value of the machining fluid as the specific resistance of the machining fluid is lower. Wire electrical discharge machining apparatus.

7. The wire electrical discharge machining apparatus according to any one of claims 3 to 6, wherein the plurality of factors further include external factors, the external factors include at least one of the ambient temperature, atmospheric pressure, and electromagnetic waves around the wire electrical discharge machining apparatus, the correction amount calculation unit calculates the correction amount based on at least one of the machining fluid, the wire electrode, and the object to be machined among the plurality of factors and the external factors. Wire electrical discharge machining apparatus.

8. A threshold determination device (24) for determining a threshold value (V ＴＨ ) to be compared with the voltage (V) between the wire electrode and the workpiece to determine whether the wire electrode (18) of the wire electrical discharge machine (10) and the workpiece (W) are in contact, comprising an acquisition unit (34) for acquiring a set value (44) regarding a factor that varies the voltage between the wire electrode and the workpiece, and a threshold determination unit (36) for calculating the threshold value based on the reference value (32) of the factor and the acquired set value. Threshold determination device. **Claim 9** A threshold determination method for determining whether the wire electrode (18) of the wire electrical discharge machine (10) and the workpiece (W) are in contact by comparing the voltage (V) between the wire electrode and the workpiece with a threshold value (V ＴＨ ), the method comprising: an acquisition step (S1) of acquiring a set value (44) regarding a factor that varies the voltage between the wire electrode and the workpiece, and a threshold determination step (S2) of calculating the threshold value based on the reference value (32) of the factor and the acquired set value. Threshold determination method.

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