Cutter compensation method for flexible intelligent machining production line

Abstract

The invention discloses a cutter compensation method for a flexible intelligent machining production line, and the method comprises the steps: obtaining the actual size of a machined workpiece completed by a target cutter through an indirect detection method; the actual size of the machined workpiece is compared with a preset workpiece size, and a compensation value is obtained; the compensation value is written into the automatic machine tool through a closed-loop control algorithm; when a new workpiece is machined every time, the compensation value takes effect, the target tool is made to deviate by adjusting the X axis and the Z axis, and compensation on abrasion of the target tool is achieved; through the cutter compensation method, the cutter can be quickly and accurately compensated, so that the production efficiency of the flexible intelligent machining production line is improved, and the production cost is reduced.

Description

Technical Field

[0001] The present invention belongs to the technical field of tool compensation methods for production lines, and in particular relates to a tool compensation method for a flexible intelligent machining production line. Background Art

[0002] In recent years, thanks to the rapid development of domestic equipment intelligent manufacturing technology, the level of intelligent manufacturing in the mechanical processing industry has been continuously improved. However, the outstanding contradictions and problems that restrict the rapid development of intelligent manufacturing in the mechanical processing industry still exist. How to ensure the qualified rate of machined products and a certain process capability index for automatic lines is a more prominent problem, and it is also the main reason that restricts the large-scale application of flexible intelligent machining production lines.

[0003] A large number of practical verifications have shown that tool wear is the main factor affecting the qualified rate of machined products. Tool wear refers to the phenomenon of gradual loss of tool material on the friction surface of the tool. In mechanical processing, tool wear will cause the size of the machined part to change. When the size of the machined workpiece is out of tolerance, tool wear must be compensated. There are two main types of common tool compensation, one is tool position compensation, also called tool offset compensation, and the other is tool tip arc radius compensation. In traditional mechanical processing, the operator observes the cutting state and judges whether the tool is worn based on experience. After judging the tool wear, the entire processing program needs to be modified to eliminate the processing error caused by tool wear, which increases the workload of the operator and greatly affects the processing efficiency. The traditional tool compensation method is no longer applicable in the automatic machining production line. Therefore, it is particularly important to study a tool compensation method suitable for automatic production methods. While ensuring product quality and consistency, it also reduces the demand for workers.

[0004] Currently, the following prior arts exist:

[0005] 1. Zhang Chen et al. modeled and analyzed the tool wear of ball-end milling cutters, proposed an error compensation method and verified it. By establishing a machining error model caused by tool wear, the machining step error is simulated, and the CNC machining program is modified in advance for the step with the error exceeding the tolerance to ensure that the actual machined parts meet the accuracy requirements. Although the tool wear model of ball-end milling cutters established by this method and the offline error compensation method proposed provide an effective method and tool for tool replacement and improvement of part machining accuracy, the actual implementation is relatively complicated and requires changing the NC program, which does not meet the conditions for large-scale engineering applications.

[0006] 2. Yan Jian et al. studied the precision control of batch clamping processing based on online detection technology. It is pointed out that the use of online detection methods can quickly reversely infer the specific change value of tool wear from the results of the parts detection, and then modify the tool radius compensation value directly in the machine tool CNC system according to the tool wear value to perform correction processing and correct errors. Online detection uses in-machine detection, and the detection accuracy is limited by the accuracy of the machine tool. In actual use, the accuracy of machine tool guide rails and other components needs to be frequently checked to reduce measurement errors. In addition, the probe is used in the machine tool and is affected by the harsh processing environment in the machine. Regular maintenance is required, which increases the maintenance workload.

[0007] Therefore, developing an effective tool compensation method to improve the production efficiency of the production line and reduce production costs has become a key issue in current research. Summary of the invention

[0008] The purpose of the present invention is to provide a tool compensation method for a flexible intelligent machining production line, which solves the problem in the prior art that tool wear has a significant impact on the production efficiency and cost of the machining production line.

[0009] The technical solution adopted by the present invention is: a tool compensation method for a flexible intelligent machining production line, comprising the following steps:

[0010] Step 1: Obtain the actual size of the machined workpiece completed by the target tool through an indirect detection method;

[0011] Step 2: Compare the actual size of the processed workpiece with the preset workpiece size to obtain a compensation value;

[0012] Step 3: Write the compensation value into the automated machine tool through a closed-loop control algorithm. Each time a new workpiece is processed, the compensation value is first made effective. The target tool is offset by adjusting the X-axis and Z-axis to compensate for the wear of the target tool.

[0013] The present invention is also characterized in that:

[0014] Each workpiece and tool has a unique number.

[0015] The indirect detection methods in step 1 include a cutting force method, a torque method, a cutting vibration method, a workpiece size method or a workpiece surface roughness method.

[0016] In step 2, the actual size of the processed workpiece is compared with the preset workpiece size through a comparator, and the comparator is fixedly installed at the machining final inspection process position of the flexible intelligent machining production line.

[0017] The preset workpiece size in step 2 is the middle value of the tolerance zone.

[0018] Step 2 specifically includes the following steps:

[0019] Step 2.1: The actual size D of the processed workpiece f With the preset workpiece size D r Compare and obtain the effective deviation value;

[0020] Step 2.2: Based on the proportional operation and output limiting, the compensation signal U is obtained according to the deviation value. out :

[0021] U out =K p (D r -D f ) (1)

[0022] In formula (1), K p is the proportional coefficient; set the output upper limit value to U outmax , the lower limit of the output is U outmin ;but

[0023] When U out >U outmax hour,

[0024] U out =U outmax (2)

[0025] When U out outmin hour,

[0026] U out =U outmin (3)

[0027] Step 2.3: Compensation signal U out The output value is compared with the pulse signal given by the CNC system, and the servo drive is controlled by the CNC system of the automated machine tool. The servo motor drives the turret to compensate the tool.

[0028] When comparing in step 2.1,

[0029] (1) When D r -D f =e, that is, when the actual size of the machined workpiece is smaller than the preset workpiece size, negative compensation is performed on the target tool;

[0030] (2) When D r -D f =-e, that is, when the actual size of the machined workpiece is larger than the preset workpiece size, positive compensation is performed on the target tool;

[0031] (3) When D r -D f =0, that is, when the actual size of the machined workpiece is equal to the preset workpiece size, there is no need to compensate the target tool;​

[0032] (4) When D r -D f >e max , that is, when the difference between the preset workpiece size and the actual size of the processed workpiece is greater than the average value of the tolerance zone, it indicates that the processed workpiece is unqualified. At this time, the machine tool is stopped and the fault is manually repaired;

[0033] (5) When D r -D f <e min , that is, when the difference between the preset workpiece size and the actual size of the machined workpiece is less than the preset minimum size, it indicates that the tool is broken or chipped. At this time, the machine tool is stopped and the tool is replaced;

[0034] When the above conditions (1) and (2) are met, the effective deviation value is obtained.

[0035] In step 3, the compensation value is first made effective each time a new workpiece is processed. Specifically, if the current D r -D f The value is less than the previous D r -D f value, the last compensation is considered valid; if the current D r -D f The value is greater than the previous D r -D f When the value is exceeded, the last compensation is considered invalid, and the cause is analyzed and processed.

[0036] In step 3, the X-axis and Z-axis are set with the tool tip of the target tool as the center of the circle.

[0037] The compensation for the wear of the target tool in step 3 includes: tool length compensation and tool tip arc radius compensation.

[0038] The beneficial effects of the present invention are as follows: the tool compensation method for a flexible intelligent machining production line of the present invention detects the final machining position size of the finishing tool in real time, compares it with the corresponding position size of the standard workpiece, obtains the tool compensation value and writes it into the numerical control system, thereby realizing fast and accurate compensation of the tool, thereby improving the production efficiency of the flexible intelligent machining production line and reducing production costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 It is a flow chart of a tool compensation method for a flexible intelligent machining production line of the present invention;

[0040] Figure 2 A schematic diagram of the structure of a tool after wear provided by the present invention;

[0041] Figure 3It is a schematic diagram of the structure of the Equator 300 (heightened type) gauging instrument in the prior art;

[0042] Figure 4 A schematic diagram of the principle of real-time wear compensation based on online detection provided by the present invention;

[0043] Figure 5 A schematic diagram of the compensation process provided by the present invention;

[0044] Figure 6 This is a schematic diagram of the actual processing effect of the pump accessories provided by the present invention. DETAILED DESCRIPTION

[0045] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments.

[0046] Example 1

[0047] The present invention provides a tool compensation method for a flexible intelligent machining production line, such as Figure 1 As shown, the specific steps include:

[0048] S1. Obtain the actual size of the machined workpiece completed by the target tool through an indirect detection method;

[0049] S2, comparing the actual size of the processed workpiece with the preset workpiece size to obtain a compensation value;

[0050] S3. The compensation value is written into the automated machine tool through a closed-loop control algorithm. Each time a new workpiece is processed, the compensation value is first made effective, and the target tool is offset by adjusting the X-axis and Z-axis to achieve compensation for the wear of the target tool.

[0051] Through the above-mentioned method, the tool compensation method for a flexible intelligent machining production line of the present invention has the following characteristics:

[0052] 1) Each time a new workpiece is processed, the compensation value is first made effective, and the tool offset is achieved by adjusting the X-axis and the Z-axis to compensate for the tool wear, thereby ensuring that the workpiece size is within the tolerance range, thereby achieving closed-loop control of the entire processing process and ensuring processing reliability.

[0053] 2) The present invention is compatible with online compensation of workpieces of multiple specifications. Through the unique coding of each workpiece, it can ensure the calling of the correct detection program and compensation program, thereby realizing automatic compensation of the tool of the corresponding tool number of the corresponding machine tool.

[0054] 3) The present invention is applicable to a fully automatic machining production line, and can significantly improve production efficiency and reduce tool costs.

[0055] 4) The present invention can verify the effectiveness of compensation, and when the compensation does not meet expectations, an alarm will be issued to remind human intervention for analysis.

[0056] 5) The centralized control system of the production line in the present invention can record the number of each workpiece and the corresponding measurement results. The results can be saved locally or uploaded to the quality management system, thereby realizing the traceability of the workpiece processing quality.

[0057] Example 2

[0058] 1. Tool wear analysis:

[0059] During the metal turning process, due to the influence of mechanical force, heat, chemical reaction, grinding and other factors, the blade tip is constantly worn, causing the actual tool position to deviate from the designed tool position, resulting in processing errors. Wear mainly occurs on the rake and flank faces of the turning tool, such as Figure 2 As shown in the figure, crater wear generally occurs on the rake face. As the width of the crater increases, the strength of the cutting edge is greatly weakened, eventually leading to chipping. On the back face, due to the strong friction between the back face and the workpiece, a small facet with a zero back angle is quickly worn out below the cutting edge, increasing the cutting force and cutting heat, and even generating vibration, causing tool failure and deterioration of the machined surface quality, seriously affecting the machining quality and production efficiency.

[0060] Before the tool fails, the machining error can be compensated by a certain method, thereby achieving the tool wear compensation effect. To compensate for the machining error, a mathematical model of tool wear needs to be established to analyze the relationship between tool wear and the resulting machining error. Thus, the machining error generated can be compensated according to the tool wear condition, except for the case of tool breakage. The wear amount △WZ(△ t ) and tool tip arc wear △Wr(△ t) It indicates the error in the tool length direction and tool tip radius direction during the cutting process, and characterizes the influence of tool wear on machining accuracy.

[0061] Tool wear during cutting is related to many factors. To simplify the analysis, only a few factors with greater influence are considered, including spindle speed, feed speed, cutting depth, processing material, etc. Tool wear is more obvious during hard turning, mainly due to the influence of processing material.

[0062] 2. Tool compensation analysis:

[0063] In the process of CNC programming, in order to make programming more convenient, the tip of the CNC tool is usually imagined as a point, which is called the tool position point or tool tip point.

[0064] The function of a CNC machine tool to automatically change the machine tool coordinate axis or tool position according to the actual size of the tool so that the actual machining contour is completely consistent with the programmed trajectory is called tool compensation. There are two types of tool compensation for CNC lathes: tool length compensation and tool tip arc radius compensation, as follows:

[0065] (1) Tool length compensation: Tool length compensation is also called tool offset compensation. Tool offset is a function used to compensate for the difference between the assumed tool length and the reference tool length. The lathe CNC system stipulates that the X-axis and Z-axis can realize tool offset at the same time.

[0066] (2) Tool tip radius compensation

[0067] In actual processing, due to tool wear and the need for fine processing, the tip of the turning tool is often ground into an arc with a smaller radius. At this time, the tool position point is the center of the tool tip arc.

[0068] In order to ensure the contour shape of the workpiece, the center of the tool tip arc is not allowed to coincide with the contour of the workpiece during machining, but should be offset from the workpiece contour by a radius value. This offset is called tool tip arc radius compensation. The blade radius offset of the arc turning tool is the same.

[0069] 3. Online detection method of tool wear:

[0070] At present, the online detection methods for tool wear at home and abroad are divided into direct detection methods and indirect detection methods. Direct detection methods include optical fiber method, television camera method, contact resistance method and optical method, which directly detect the size of the tool after wear. Indirect detection methods include cutting force method, torque method, cutting vibration method, workpiece size method and workpiece surface roughness method, which indirectly reflect the wear of the tool through these measurements.

[0071] The present invention adopts the indirect detection method of workpiece size method, that is, detecting the corresponding position size of the workpiece processed by the tool, and reversely calculating the specific change value of tool wear from the result of the part detection. In order to avoid the influence of machine tool accuracy on detection accuracy during in-machine detection and the influence of the detection process on production efficiency, the present invention adopts the method of online off-machine detection, which ensures measurement accuracy on the one hand and production efficiency of the production line on the other hand. And the present invention adopts Renishaw's Equator 300 (heightened type) comparator, the structure diagram of which is shown in the figure. Figure 3 As shown in the figure, the comparator is fixedly installed in the final inspection process of the flexible intelligent machining production line. Each finished workpiece is measured by the comparator for the position and size of the corresponding tool number. The centralized control system of the production line automatically reads the measurement results, traces the lathe number and tool number, and writes the compensation value to the corresponding machine tool according to the compensation algorithm. When the tool is severely worn or broken, the system alarms.

[0072] 4. Real-time wear compensation principle based on online detection

[0073] like Figure 4 As shown in the figure, the classic PI control algorithm is used. When the workpiece processed by the target tool enters the online detection device, the online detection device detects the actual size D of the workpiece processed by the target tool based on the indirect detection method. f ; and the actual size D f With the preset workpiece size D r Comparison is performed. If there is a deviation value e, a compensation signal is obtained through proportional operation and output limiting. The compensation signal is compared with the pulse signal given by the numerical control system, and the output value is controlled by the automatic machine tool CNC system to control the servo driver, and the servo motor drives the turret to work and compensate the tool. In the present invention, the preset workpiece size is the middle value of the tolerance zone, that is, the average value of the maximum limit size and the minimum limit size in the tolerance zone.

[0074] Taking the external turning tool as an example, the compensation principle is as follows:

[0075] (1) When D r -D f =e, that is, when the actual size of the processed outer circle is smaller than the preset workpiece size, negative compensation is performed on the target tool.

[0076] (2) When D r -D f =-e, that is, when the actual size of the processed outer circle is larger than the preset workpiece size, it indicates that the target tool is worn, and positive compensation is performed on the target tool.

[0077] (3) When D r -D f =0, that is, when the actual size of the processed outer circle is equal to the preset workpiece size, it means that the processing size is just right and there is no need to compensate the target tool.

[0078] (4) When D r -D f >e max , that is, the difference between the preset workpiece size and the actual size of the processed outer circle is greater than the average value of the tolerance zone e max When the error message is displayed, it indicates that the processed workpiece is defective. It is possible that the tool is not aligned correctly or the tool head is loose. In this case, the machine tool is required to be stopped and the fault must be repaired manually.

[0079] (5) When D r -D f <e min , that is, the difference between the preset workpiece size and the actual size of the processed outer circle is less than the preset minimum size e min When the tool is broken or chipped, the system alarms, the machine tool stops, and the tool is replaced manually.min Determined based on empirical values.

[0080] Compensation value (compensation signal) setting method:

[0081] U out =K p (D r -D f ) (1)

[0082] K p is the proportional coefficient, and the output upper limit is set to U outmax , the lower limit of the output is U outmin .

[0083] but

[0084] When U out >U outmax hour,

[0085] U out =U outmax (2)

[0086] When U out outmin hour,

[0087] U out =U outmin (3)

[0088] The specific compensation process is as follows: Figure 5 As shown:

[0089] (1) The processed workpiece is clamped by an industrial robot to the comparator inspection fixture. The comparator retrieves the corresponding inspection program based on the material number sent by the production line centralized control system to complete the inspection, and the inspection results are stored in a local file.

[0090] (2) The production line centralized control system reads the test results and determines whether they are out of tolerance, i.e. D r -D f Is it greater than e? max If it is greater than, it indicates that there is an out-of-tolerance phenomenon. At this time, the system alarms and reminds, and the cause of the out-of-tolerance is manually checked and processed, and the workpiece is scrapped. If it is not out of tolerance, it is determined whether the last compensation is valid. If the current D r -D f The value is less than the previous D r -D f value, the last compensation is considered valid; if the current D r -D f The value is greater than the previous D r -D f When the value is set, the last compensation is considered invalid. ​

[0091] (3) If the last compensation was effective, the compensation algorithm is run and the compensation value is obtained by referring to the above formulas (1), (2) and (3). If the compensation is invalid, an alarm is triggered and the reason for the invalidity is manually analyzed and processed.

[0092] (4) The centralized control system of the production line runs the compensation algorithm, communicates with the machine tool, and updates the compensation value obtained in step (3) to the compensation subroutine of the CNC. The compensation subroutine mainly implements the following functions: 1) receiving the compensation value obtained in step (3); 2) facilitating CNC calling to make the compensation value effective.

[0093] (5) When the main machining program starts machining, the compensation subroutine is automatically called. At this time, the updated compensation value takes effect. The tool offset is achieved by adjusting the X-axis and Z-axis to compensate for tool wear, ensuring that the workpiece size is within the tolerance range.

[0094] Example 3

[0095] like Figure 6 As shown in the figure, a pump accessory part is processed. The material of the part is chromium-nickel-molybdenum alloy. It is finely processed after carburizing and quenching. The hardness is 59-65HRC, which is relatively high. The machine tool is Neway's NL322HA CNC horizontal lathe. Taguchi's CBN carbide tool is selected. Due to the high hardness of the workpiece, the tool wears seriously during the processing, which easily leads to the phenomenon of out-of-tolerance of the size of the workpiece after processing. The production line is a fully automatic production line. When working normally, the operator cannot enter the production line, so it is unrealistic to manually adjust the tool compensation value. In order to ensure the processing quality of the product, the blade needs to be replaced frequently, which affects the production efficiency and increases the production cost. After introducing the above tool compensation method, the workpiece processing quality is effectively improved, the tool life is extended, and the processing efficiency is improved, which is suitable for mass production. It has broad application prospects in the field of machining.

[0096] In summary, tool wear is ultimately reflected in the workpiece processing conditions, that is, the size and position deviation. The present invention introduces online detection equipment to detect the final processing position size of the finishing tool in real time, compares it with the corresponding position size of the standard workpiece, obtains the tool compensation value and writes it into the CNC system to achieve online compensation of the tool. It is implemented by one-time programming, and there is no need for repeated programming and modification during production, which is convenient for maintenance. It is suitable for large-scale engineering applications.

Claims

1. A tool compensation method for a flexible intelligent machining production line, characterized in that: The following steps are involved: Step 1: Obtain the actual size of the machined workpiece completed by the target tool through an indirect detection method; Step 2: Compare the actual size of the processed workpiece with the preset workpiece size to obtain a compensation value; Step 3: Write the compensation value into the automated machine tool through a closed-loop control algorithm. Each time a new workpiece is processed, the compensation value is first made effective. The target tool is offset by adjusting the X-axis and Z-axis to compensate for the wear of the target tool.

2. The tool compensation method for a flexible intelligent machining production line according to claim 1, characterized in that: Each workpiece and tool has a unique number.

3. The tool compensation method for a flexible intelligent machining production line according to claim 1, characterized in that: The indirect detection method in step 1 includes a cutting force method, a torque method, a cutting vibration method, a workpiece size method or a workpiece surface roughness method.

4. The tool compensation method for a flexible intelligent machining production line according to claim 1, characterized in that: In the step 2, the actual size of the processed workpiece is compared with the preset workpiece size by using a comparator, and the comparator is fixedly installed at the machining final inspection process position of the flexible intelligent machining production line.

5. The tool compensation method for a flexible intelligent machining production line according to claim 1, characterized in that: The preset workpiece size in step 2 is the middle value of the tolerance zone.

6. The tool compensation method for a flexible intelligent machining production line according to claim 1, characterized in that: The step 2 specifically includes the following steps: Step 2.1: The actual size D of the processed workpiece f With the preset workpiece size D r Compare and obtain the effective deviation value; Step 2.2: Based on the proportional operation and output limiting, the compensation signal U is obtained according to the deviation value. out : U out =K p (D r -D f ) (1) In formula (1), K p is the proportional coefficient; set the output upper limit value to U outmax , the lower limit of the output is U outmin ;but This U out >U outmax Time, IN out =U outmax (2) When U out outmin hour,​ IN out =U outmin (3) Step 2.3: Compensation signal U out The output value is compared with the pulse signal given by the CNC system, and the servo drive is controlled by the CNC system of the automated machine tool. The servo motor drives the turret to compensate the tool.

7. The tool compensation method for a flexible intelligent machining production line according to claim 6, characterized in that: When comparing in step 2.1, (1) When D r -D f =e, that is, when the actual size of the machined workpiece is smaller than the preset workpiece size, negative compensation is performed on the target tool; (2) When D r -D f =-e, that is, when the actual size of the machined workpiece is larger than the preset workpiece size, positive compensation is performed on the target tool; (3) When D r -D f =0, that is, when the actual size of the machined workpiece is equal to the preset workpiece size, there is no need to compensate the target tool; (4) When D r -D f >e max , that is, when the difference between the preset workpiece size and the actual size of the processed workpiece is greater than the average value of the tolerance zone, it indicates that the processed workpiece is unqualified. At this time, the machine tool is stopped and the fault is manually repaired; (5) When D r -D f <e min , that is, when the difference between the preset workpiece size and the actual size of the machined workpiece is less than the preset minimum size, it indicates that the tool is broken or chipped. At this time, the machine tool is stopped and the tool is replaced; When the above conditions (1) and (2) are met, the effective deviation value is obtained.

8. The tool compensation method for a flexible intelligent machining production line according to claim 7, characterized in that: In step 3, the compensation value is first made effective each time a new workpiece is processed. Specifically, if the current D r -D f The value is less than the previous D r -D f value, the last compensation is considered valid; if the current D r -D f The value is greater than the previous D r -D f When the value is exceeded, the last compensation is considered invalid, and the cause is analyzed and processed.

9. The tool compensation method for a flexible intelligent machining production line according to claim 1, characterized in that: In step 3, the tool tip point of the target tool is used as the center of the circle to set the X-axis and the Z-axis.

10. The tool compensation method for a flexible intelligent machining production line according to claim 1, characterized in that: The compensation for the wear of the target tool in step 3 includes: tool length compensation and tool tip arc radius compensation.

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