A method for controlling wire electrical discharge machining based on infrared thermal imaging

Abstract

The application relates to the technical field of wire cut electrical discharge machining, and discloses a wire cut electrical discharge machining control method based on infrared thermal imaging. An infrared thermal imager is installed at a proper distance and adjusted to a proper focal length, so that the infrared thermal imager can completely and clearly shoot a machining workpiece. A water pump, a wire feeder and high-frequency pulses in a wire cut electrical discharge machining control system are started, so that the wire cut electrical discharge machine is in a machining state. The infrared thermal imager starts shooting data, and transmits a thermal imaging image to a PC end in real time. The PC obtains the temperature of the edge of the workpiece close to the discharge side of the electrode wire according to a temperature feature extraction algorithm. The PC controls the wire cutting machining according to a wire cutting machining control algorithm based on the machining temperature. The wire cut electrical discharge machining control method based on the infrared thermal imaging is different from a method of determining a threshold value through a large number of experiments, and the desired temperature (threshold value) of the machining workpiece can be determined by searching a metal material melting point table, so that a large amount of materials and time are saved.

Description

A control method for wire electrical discharge machining based on infrared thermal imaging Technical Field

[0001] This invention relates to the field of wire electrical discharge machining (EDM), specifically to a method for controlling wire EDM based on infrared thermal imaging. Background Technology

[0002] The basic working principle of wire electrical discharge machining (EDM) is to use a continuously moving electrode wire as the electrode to perform pulsed spark discharge on a conductive workpiece. The metal is removed through electrothermal energy, achieving the cutting shape. The key to wire EDM lies in the detection of the spark discharge state, with the threshold voltage method being a common method. This method collects the gap voltage between the electrode wire and the workpiece, compares the collected voltage with a threshold voltage to determine the current processing state, and thus adjusts the workpiece feed rate in real time to maintain a normal effective spark discharge gap. However, this control method has two drawbacks:

[0003] (1) Determining the voltage threshold requires a large number of statistical experiments, which consumes a lot of materials, time and effort.

[0004] (2) The discharge voltage between the electrodes of unstable arc discharge and stable arc discharge is small, making it difficult to distinguish them by voltage detection results. This can easily lead to misjudgment of the discharge state during processing, resulting in burn marks on the surface of the workpiece due to excessively high temperature. Summary of the Invention

[0005] (a) Technical problems to be solved

[0006] To address the shortcomings of existing technologies, this invention provides a control method for wire electrical discharge machining based on infrared thermal imaging, which has the advantage of controllable machining temperature and solves the problem of workpiece burns caused by excessively high temperatures during machining.

[0007] (II) Technical Solution

[0008] To achieve the aforementioned effect of reducing workpiece burns, the present invention provides the following technical solution: a control method for wire electrical discharge machining based on infrared thermal imaging, comprising the following steps:

[0009] S1、

[0010] Install the infrared thermal imager at a suitable distance and adjust the focal length so that it can capture a complete and clear image of the workpiece.

[0011] S2,

[0012] Turn on the water pump, wire feed, and high-frequency pulse in the wire EDM control system to put the wire EDM machine into processing mode.

[0013] S3

[0014] The infrared thermal imager begins capturing data and transmits the thermal images to the PC in real time.

[0015] S4

[0016] PC obtains the temperature of the workpiece edge near the electrode wire discharge side based on the temperature feature extraction algorithm.

[0017] S5

[0018] The PC adjusts the feed rate of the workpiece in real time based on the wire EDM machining control algorithm based on the machining temperature, thereby realizing the wire EDM machining.

[0019] Preferably, the specific steps of the workpiece temperature extraction algorithm in S4 include:

[0020] S4.1 Observe the positions of the upper and lower guide wheels in the thermal imaging image of the wire EDM machine, obtain the pixel coordinates (X1,Y1) and (X2,Y2), and construct the rectangular region of interest (ROI) containing coordinates (X1+50,Y1), (X2+50,Y2), (X1+200,Y1), and (X2+200,Y2).

[0021] S4.2 To achieve image noise reduction, mean filtering is used to transform the region of interest (ROI), as shown in the following formula:

[0022]

[0023] Where S represents the filtering window centered at point (x,y), i and j represent the coordinates of the pixels within the filtering window S, M represents the total number of pixels within the filtering window, f(x,y) represents the pixel value at (x,y) in the source image, and g(x,y) represents the pixel value at (x,y) in the filtered image.

[0024] S4.3. Use the Sobel operator to perform edge detection on the region of interest (ROI), where the horizontal and vertical edge detection images Gx(x,y) and Gy(x,y) are respectively:

[0025]

[0026]

[0027] Where g(x, y) is the pixel located at (x, y) after filtering obtained in step S4.2.

[0028] The image G(x, y) after edge detection is:

[0029] G(x, y) = G x (x, y) + G y (x, y)

[0030] S4.4: To achieve image segmentation of the workpiece area, G(x, y) is projected onto the x-axis and y-axis respectively, and then the maximum and minimum values ​​of the projected x-axis and y-axis are calculated as follows:

[0031] x max =max(G(x, 0))

[0032] x min =min(G(x,0))

[0033] y max =max(G(0,y))

[0034] y min =min(G(0,y))

[0035] The area R(x, y) for machining the workpiece is defined by the coordinates of the upper left corner (x, y). min y min ) and the coordinates of the lower right corner (x max y max A rectangular area composed of ).

[0036] S4.5. Map pixels to temperature for the image region of the workpiece being processed, and calculate the average temperature of this region as the actual temperature (Temp) of the workpiece at time k. a (k)

[0037]

[0038] Where R(x, y, k) represents the pixel in (x, y) of the processing region R at time k, M represents the number of pixels in region R, and Y operation represents the mapping relationship from pixel to temperature, which can be obtained from infrared imaging equipment manufacturers.

[0039] Preferably, the specific algorithm steps of the wire EDM machining control algorithm based on machining temperature in S5 include:

[0040] S5.1. Based on the melting point table of metallic materials, determine the desired temperature (Temp) for processing the workpiece. e

[0041] S5.2, The actual temperature of the machined workpiece obtained in S4, Temp. a (k) and the expected temperature of the workpiece being processed (Temp) eBy taking the difference, we obtain the deviation value:

[0042] Err(k) = Temp a (k)-Temp e

[0043] S5.3. This invention uses an incremental PID algorithm to control the workpiece feed speed. Therefore, the expected deviation between adjacent output processing temperatures is:

[0044] Δu(k)=u(k)-u(k-1)=K p *[Err(k)-Err(k-1)]+K i *Err(k)+K d *[Err(k)-2*Err(k-1)+Err(k-2)]

[0045] In the above formula, K p K i With K d These represent the proportional coefficient, integral coefficient, and differential coefficient, respectively, and Err(k) is the deviation value obtained in step S5.2.

[0046] S5.4 Since the feed rate of the workpiece is proportional to the temperature deviation Δu(k), the expected value of the workpiece feed rate output based on the PID algorithm is:

[0047] V e (k)=V e (k-1)+K x *Δu(k)

[0048] In the above formula, K x The adjustment coefficient ranges from 0 to 1. When the coefficient is closer to 1, the feed rate response is faster and the machining time is shorter, but the surface finish of the workpiece is worse. When the coefficient is closer to 0, the feed rate response is slower and the machining time is longer, but the surface finish of the workpiece is better. This coefficient is set according to the actual machining requirements.

[0049] S5.5. Since the workpiece feed rate in the wire EDM control system is finite in actual machining, while the desired output speed obtained from S5.4 is infinite, threshold processing is required to obtain the actual output workpiece feed rate:

[0050]

[0051] Where V max This represents the maximum feed rate for workpiece machining in the wire EDM control system.

[0052] (III) Beneficial Effects

[0053] Compared with the prior art, the present invention provides a control method for wire electrical discharge machining based on infrared thermal imaging, which has the following beneficial effects:

[0054] 1. Unlike the threshold voltage method, which requires extensive experimentation to determine the threshold, this infrared thermal imaging-based wire EDM machining control method only requires consulting a metal material melting point table to determine the desired temperature (threshold) of the workpiece, saving a significant amount of materials and time.

[0055] 2. The infrared thermal imaging-based wire EDM machining control method differs from the method of collecting discharge current and voltage during machining. This invention obtains the real-time temperature of the workpiece during machining based on infrared thermal imaging images, and controls the machining based on the real-time temperature during machining. This can effectively avoid the phenomenon of burn stripes on the workpiece due to excessively high temperature, and improve the surface quality of the machined workpiece. Attached Figure Description

[0056] Figure 1 is a schematic diagram of the overall process of the present invention;

[0057] Figure 2 is a flowchart of the workpiece temperature extraction algorithm.

[0058] Figure 3 is an overall flowchart of the wire EDM machining control algorithm based on the temperature of the workpiece being processed. Detailed Implementation

[0059] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0060] Please refer to Figures 1-3. This invention provides a technical solution: a method for controlling wire electrical discharge machining based on infrared thermal imaging, comprising the following steps:

[0061] S1、

[0062] Install the infrared thermal imager at a suitable distance and adjust the focal length so that it can capture a complete and clear image of the workpiece.

[0063] S2,

[0064] Turn on the water pump, wire feed, and high-frequency pulse in the wire EDM control system to put the wire EDM machine into processing mode.

[0065] S3

[0066] The infrared thermal imager begins capturing data and transmits the thermal images to the PC in real time.

[0067] S4

[0068] PC obtains the temperature of the workpiece edge near the electrode wire discharge side based on the temperature feature extraction algorithm.

[0069] S5

[0070] The PC adjusts the feed rate of the workpiece in real time based on the wire EDM machining control algorithm based on the machining temperature, thereby realizing the wire EDM machining.

[0071] The overall flow of the workpiece temperature extraction algorithm in S4 above is shown in Figure 2, and the specific steps include:

[0072] S4.1 Observe the positions of the upper and lower guide wheels in the thermal imaging image of the wire EDM machine, obtain the pixel coordinates (X1,Y1) and (X2,Y2), and construct the rectangular region of interest (ROI) containing coordinates (X1+50,Y1), (X2+50,Y2), (X1+200,Y1), and (X2+200,Y2).

[0073] S4.2 To achieve image noise reduction, mean filtering is used to transform the region of interest (ROI), as shown in the following formula:

[0074]

[0075] Where S represents the filtering window centered at point (x,y), i and j represent the coordinates of the pixels within the filtering window S, M represents the total number of pixels within the filtering window, f(x,y) represents the pixel value at (x,y) in the source image, and g(x,y) represents the pixel value at (x,y) in the filtered image.

[0076] S4.3. Use the Sobel operator to perform edge detection on the region of interest (ROI), where the image G after horizontal and vertical edge detection is... x (x, y) and G y (x, y) are respectively:

[0077]

[0078]

[0079] Where g(x, y) is the pixel located at (x, y) after filtering obtained in step S4.2.

[0080] The image G(x, y) after edge detection is:

[0081] G(x, y) = G x (x, y) + G y (x, y)

[0082] S4.4 To achieve image segmentation of the workpiece area, G(x, y) is projected onto the x-axis and y-axis respectively, and then the maximum and minimum values ​​of the projected x-axis and y-axis are calculated as follows:

[0083] x max =max(G(x, 0))

[0084] x min =min(G(x,0))

[0085] y max =max(G(0,y))

[0086] y min =min(G(0,y))

[0087] The area R(x, y) for machining the workpiece is defined by the coordinates of the upper left corner (x, y). min y min ) and the coordinates of the lower right corner (x max y max A rectangular area composed of ).

[0088] S4.5. Map pixels to temperature for the image region of the workpiece being processed, and calculate the average temperature of this region as the actual temperature (Temp) of the workpiece at time k. a (k)

[0089]

[0090] Where R(x, y, k) represents the pixel in (x, y) of the processing region R at time k, M represents the number of pixels in region R, and Y operation represents the mapping relationship from pixel to temperature, which can be obtained from infrared imaging equipment manufacturers.

[0091] The overall flowchart of the wire EDM machining control algorithm based on machining temperature in S5 above is shown in Figure 3. The specific algorithm steps include:

[0092] S5.1. Based on the melting point table of metallic materials, determine the desired temperature (Temp) for processing the workpiece. e

[0093] S5.2, The actual temperature of the machined workpiece obtained in S4, Temp. a (k) and the expected temperature of the workpiece being processed (Temp) e By taking the difference, we obtain the deviation value:

[0094] Err(k) = Temp a (k)-Temp e

[0095] S5.3. This invention uses an incremental PID algorithm to control the workpiece feed speed. Therefore, the expected deviation between adjacent output processing temperatures is:

[0096] Δu(k)=u(k)-u(k-1)=K p *[Err(k)-Err(k-1)]+K i *Err(k)+K d *[Err(k)-2*Err(k-1)+Err(k-2)]

[0097] In the above formula, K p K i With K d These represent the proportional coefficient, integral coefficient, and differential coefficient, respectively, and Err(k) is the deviation value obtained in step S5.2.

[0098] S5.4 Since the feed rate of the workpiece is proportional to the temperature deviation Δu(k), the expected value of the workpiece feed rate output based on the PID algorithm is:

[0099] V e (k)=V e (k-1)+K x *Δu(k)

[0100] In the above formula, K x The adjustment coefficient ranges from 0 to 1. When the coefficient is closer to 1, the feed rate response is faster and the machining time is shorter, but the surface finish of the workpiece is worse. When the coefficient is closer to 0, the feed rate response is slower and the machining time is longer, but the surface finish of the workpiece is better. This coefficient is set according to the actual machining requirements.

[0101] S5.5. Since the workpiece feed rate in the wire EDM control system is finite in actual machining, while the desired output speed obtained from S5.4 is infinite, threshold processing is required to obtain the actual output workpiece feed rate:

[0102]

[0103] Where V max This represents the maximum feed rate for workpiece machining in the wire EDM control system.

[0104] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A control method for wire electrical discharge machining based on infrared thermal imaging, characterized in that, Includes the following steps: S1. Install the infrared thermal imager at a suitable distance and adjust the focal length to capture a complete and clear image of the workpiece. S2. Turn on the water pump, wire feed, and high-frequency pulse in the wire EDM control system to put the wire EDM machine into processing mode. S3. The infrared thermal imager starts capturing data and transmits the thermal image to the PC in real time. S4. S401. The PC uses a workpiece temperature extraction algorithm to obtain the temperature of the workpiece edge near the electrode wire discharge side. S402. Observe the positions of the upper and lower wire guide wheels in the thermal image and obtain the pixel coordinates (X1, Y1) and (X2, Y2). Construct a rectangular region of interest (ROI) with coordinates (X1+50, Y1), (X2+50, Y2), (X1+500, Y1), and (X2+500, Y2). S403. To reduce image noise, use mean filtering to transform the ROI. The formula is as follows: S404. Use the Sobel operator to perform edge detection on the region of interest (ROI), where the image G after horizontal and vertical edge detection is... x (x,y) and G y (x, y) are respectively: The image G(x,y) after edge detection is: S405. To achieve image segmentation of the workpiece area, G(x,y) is projected onto the x-axis and y-axis respectively, and then the maximum and minimum values ​​of the projected x-axis and y-axis are calculated as follows: The area R(x,y) for machining the workpiece is defined by the coordinates of the upper left corner ( , ) and the coordinates of the lower right corner ( , S406. Map the pixels of the image region of the workpiece to temperature, and calculate the average temperature of the image region of the workpiece as the actual temperature of the workpiece at time k. S5, S501, and PC utilize a wire EDM control algorithm based on machining temperature to adjust the workpiece feed rate in real time, enabling wire EDM machining. S502 determines the desired workpiece temperature based on a metal melting point table. S503, The actual temperature of the workpiece obtained in step S401 is... With respect to the expected temperature of the workpiece being processed By taking the difference, we obtain the deviation value: S504. If the feed rate of the workpiece is controlled by an incremental PID algorithm, the expected deviation between adjacent output processing temperatures is: Δu(k) = u(k) - u(k-1) = K p *[Err(k)-Err(k-1)]+K i *Err(k)+K d *[Err(k)-2*Err(k-1)+Err(k-2)]; S505. Since the feed rate of the machined workpiece is proportional to the temperature deviation Δu(k), the expected value of the feed rate of the machined workpiece based on the PID algorithm is: V e (k)=V e (k-1)+K x *Δu(k); S506. In actual machining, the workpiece feed speed in the wire EDM control system is finite, while the desired output speed obtained in step 5.4 is infinite. Therefore, threshold processing is required to obtain the actual output workpiece feed speed: 。 2. The method for controlling wire electrical discharge machining based on infrared thermal imaging according to claim 1, characterized in that, In step S403, S represents a filtering window centered at point (x,y), i and j represent the coordinates of pixels within the filtering window S, M represents the total number of pixels within the filtering window, f(x,y) represents the pixel value located in the source image at (x,y), and g(x,y) represents the pixel value located in the filtered image at (x,y).

3. The method for controlling wire electrical discharge machining based on infrared thermal imaging according to claim 1, characterized in that, In step S404, g(x,y) is the pixel located at (x,y) after filtering obtained in step S403.

4. The method for controlling wire electrical discharge machining based on infrared thermal imaging according to claim 1, characterized in that, In step S406, the above Let M represent the number of pixels in the processing region R at time k in the range (i,j), M represent the number of pixels in region R, and Y represent the mapping relationship between pixels and temperature, which can be obtained from infrared imaging equipment manufacturers.

5. The method for controlling wire electrical discharge machining based on infrared thermal imaging according to claim 1, characterized in that, In step S504, K in the formula p K i With K d These represent the proportional coefficient, integral coefficient, and differential coefficient, respectively, and Err(k) is the deviation value obtained in step S503.

6. The method for controlling wire electrical discharge machining based on infrared thermal imaging according to claim 1, characterized in that, In step S505, K in the formula x The adjustment coefficient is between 0 and 1. When the coefficient is closer to 1, the feed rate response is faster and the processing time is shorter, but the surface finish of the workpiece is worse. When the coefficient is closer to 0, the feed rate response is slower and the processing time is longer, but the surface finish of the workpiece is better. This coefficient is set according to the actual processing requirements.

7. The method for controlling wire electrical discharge machining based on infrared thermal imaging according to claim 1, characterized in that, In step S506, V max This represents the maximum feed rate of the workpiece in the wire EDM control system.

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