A method to improve the reliability of CNC precision hole processing

Abstract

The present invention belongs to the technical field of CNC machining, and in particular, relates to a method for improving the reliability of CNC precision hole machining, which is to grade the faults of CNC machine tools according to their importance and urgency, and to perform fault response control in combination with the fault level and the machining conditions of the CNC machine tools during operation, so as to achieve an immediate response in the case of an emergency fault, and a delay in responding after the machining of the current hole is completed in the case of a non-emergency fault. This technical solution adjusts the response logic of the PLC to random faults of CNC machine tools, and on the premise of ensuring the safety of equipment, workpieces and personnel, it greatly avoids sudden interruptions in the precision hole machining state of CNC machine tools, thereby avoiding product quality risks to a large extent.

Description

Technical Field

[0001] The invention belongs to the technical field of numerical control machining, and in particular relates to a method for improving the reliability of numerical control fine hole machining. Background Art

[0002] With the development of new technologies, the precision of CNC machine tools is constantly improving, and various functions are constantly being improved. At the same time, the overall complexity of the system is also increasing. The operation of CNC machine tools requires the cooperation of various subsystems (safety protection system, power supply system, CNC device, spindle system, coordinate axis system, hydraulic system, air pressure system, lubrication system, refrigeration system, tool cooling system and chip removal system, etc.). In order to ensure the safety of CNC machine tools and workshop personnel, existing CNC machine tools are stopped immediately when they fail during operation. That is, if any subsystem fails, the fault detection system of the CNC machine tool (in fact, it is the circuit of each subsystem that feeds back the working parameters to the CNC main system) will send the fault information to the CNC main system of the CNC machine tool, and the CNC main system will immediately control the CNC machine tool to stop running. Among the many subsystems of CNC machine tools, auxiliary systems (such as lubrication system, air pressure system, chip removal system, etc.) are easily affected by the processing environment and have a high failure rate. In addition, some failures are caused by design defects and cannot be completely solved in a short time. As a result, CNC machine tools will frequently have random failures. When similar random failures occur during machine processing, it may lead to processing interruption, especially when the machine tool is performing finishing processes such as boring and reaming. Such failure shutdowns may cause scratches on the inner wall of the hole, and re-processing may cause quality problems such as out-of-tolerance hole diameters and uneven connection of the inner wall of the hole. Summary of the invention

[0003] The purpose of the present invention is to propose a method to improve the reliability of CNC precision hole processing based on the above problems. By adjusting the response logic of PLC to the above random failures, sudden interruption of processing can be avoided and quality risks can be avoided to the greatest extent, as follows:

[0004] A method for improving the reliability of CNC precision hole processing comprises the following steps:

[0005] According to the importance and urgency of the CNC machine tool failure, the fault level of the CNC machine tool is evaluated, and the fault level judgment program is written into the PLC control system of the machine tool CNC system;

[0006] Based on the fault level and the processing conditions of the CNC machine tool during operation, a fault response control program is written into the PLC control system of the machine tool CNC system;

[0007] Start the CNC machine tool and run the NC program in the CNC system. Use the CNC machine tool's own fault detection system to monitor the operating status of each subsystem in real time, and feed back the signal parameters reflecting the operating status to the CNC system of the CNC machine tool in real time;

[0008] When a CNC machine tool fails, the fault level of the CNC machine tool is evaluated based on the fault level judgment program, and the fault response control is performed based on the fault level judgment program according to the CNC system. The fault level and processing conditions are judged by the fault level judgment program; wherein the fault response control includes the following situations:

[0009] A. If it is an emergency fault, a fault response will be issued immediately and the CNC machine tool will be controlled to stop running;

[0010] B. If it is a non-emergency fault, the NC program running status is read, the current processing condition of the CNC machine tool is identified through the spindle speed, feed speed and tool information, and whether the CNC machine tool is in the fine hole processing state is determined according to the processing condition; if not, a fault response is immediately issued and the CNC machine tool is controlled to stop running; if so, the fault response is delayed, and after the current hole processing is completed, a fault response is issued and the CNC machine tool is controlled to stop running.

[0011] Preferably, the fault level determination procedure is based on the calculation formula P=P b ×I b +P h ×I h The fault level of the CNC machine tool is evaluated; where: P is the fault scoring index; P b is the importance level of the fault location, P h is the severity level of the failure consequence; I b and I h The weight coefficients of the fault location importance level value and the fault consequence severity level value respectively.

[0012] Preferably, the importance of the fault location and the severity of the fault consequence have five levels respectively, and the five levels correspond to level values ​​of 1 to 5 respectively. The larger the level value is, the higher the importance and severity are.

[0013] Preferably, the weight coefficients of the fault location importance level value and the fault consequence importance level value satisfy the following conditions: 0<I b ≤0.5, 0.5≤I h <1;I b +I h =1.

[0014] Preferably, there are three fault levels; among them, when 3.5<P≤7.5 is a level I fault, when 2.5<P≤3.5 is a level II fault, and when P≤2.5 is a level III fault; level I fault is an emergency fault, and level II and level III faults are non-emergency faults.

[0015] Preferably, the tool types include milling cutters, boring cutters, reamer and drill bits.

[0016] Preferably, the method for judging whether the CNC machine tool is in the precision hole processing state according to the processing conditions is: first, preliminarily judge whether the processing method is milling or hole making according to the type of tool; wherein: if the tool is a milling cutter, it is judged as non-precision hole processing; if the tool is a boring cutter, reamer or drill, it is judged as precision hole processing; then identify the processing progress according to the spindle speed and feed speed to judge whether it is in the hole making stage; if so, it is judged as the precision hole processing state, otherwise, it is judged as the non-precision hole processing state.

[0017] Preferably, the fault response delay is a segmented delay, that is: in the process of writing the fault response control program, a fault response delay time is preset; in the case of a non-emergency fault, when the CNC machine tool is still in the hole-making stage of fine hole processing, it is delayed by the preset fault response delay time; after the preset fault response delay time is completed, it is determined again whether it is in the hole-making stage; if not, the delay ends; if so, it is delayed again by the preset fault response delay time, and so on, until the CNC machine tool completes the current hole-making stage.

[0018] Beneficial effects of the present invention:

[0019] 1) The technical solution classifies the CNC machine tool faults according to their importance and urgency, and performs fault response control in combination with the fault level and the processing conditions of the CNC machine tool during operation, so as to achieve an immediate response in the event of an emergency fault, and a delay in responding after the current hole processing is completed in the event of a non-emergency fault. Therefore, compared with the prior art, this technical solution adjusts the PLC response logic to deal with random faults of the CNC machine tool, and on the premise of ensuring the safety of equipment, workpieces and personnel, it greatly avoids sudden interruptions in the precision hole processing state of the CNC machine tool, thereby largely avoiding product quality risks.

[0020] 2) This technical solution combines the fault location and fault consequences to obtain the fault scoring index by assigning grade values, laying a reasonable foundation for obtaining the fault level, and assigning weight values ​​to the fault location and fault consequences according to the different fault conditions of a single subsystem, further ensuring the rationality and reliability of this technical solution.

[0021] 3) This technical solution rationally utilizes tool types to classify the machining work of CNC machine tools according to machining conditions, excludes fault optimization for milling machining whose machining quality is not affected by interruptions, and only optimizes hole making machining whose quality is affected by interruptions. While complying with the actual workflow, it rationally solves the problem of fine hole machining quality being affected by interruptions. Furthermore, this technical solution sets the fault response delay as a segmented delay and limits the length of a single delay to ensure that a fault response is made in a timely manner after the current hole making stage is completed. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is the basic implementation flow chart of this technical solution;

[0023] Figure 2 This is a schematic diagram of a tool path for fine hole processing;

[0024] Figure 3 A basic list of fault location importance levels for this technical solution;

[0025] Figure 4 A basic list of fault consequence severity levels for this technical solution;

[0026] In the figure:

[0027] 1. Retract the tool; 2. Lift the tool; 3. Move the tool; 4. Lower the tool; 5. Feed the tool; 6. Workpiece; 7. Machined hole; 8. Unmachined hole. DETAILED DESCRIPTION

[0028] In order to make the purpose, technical solution and advantages of the invention clearer, the technical solution of the present invention will be clearly and completely described below in conjunction with the drawings in the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all of the embodiments.

[0029] Therefore, the following detailed description of the invention provided in the accompanying drawings is not intended to limit the scope of the invention claimed for protection, but merely represents selected embodiments of the invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0030] Example 1

[0031] This embodiment discloses a method for improving the reliability of CNC precision hole processing, as a preferred embodiment of the present invention, such as Figure 1 As shown, the following steps are included:

[0032] According to the importance and urgency of CNC machine tool faults, the faults of CNC machine tools are graded and a fault grade judgment program is written into the PLC control system of the machine tool CNC system. Among them, the fault urgency assessment is mainly based on the common faults of each subsystem and the consequences caused by the faults.

[0033] Based on the fault level and the processing conditions of the CNC machine tool during operation, a fault response control program is written into the PLC control system of the machine tool CNC system.

[0034] Start the CNC machine tool and run the NC program in the CNC system to process the workpiece. During the processing of the workpiece, the CNC machine tool's own fault detection system is used to monitor the operating status of each subsystem in real time, and the signal parameters reflecting the operating status are fed back to the CNC system of the CNC machine tool in real time. The CNC system determines whether the CNC machine tool has a fault based on the received signal parameters.

[0035] When a CNC machine tool fails, the PLC control system will evaluate the fault level of the CNC machine tool based on the fault level judgment program, and perform fault response control based on the fault level judgment program according to the CNC system. The relevant information of the processing condition is fed back to the PLC through the interface signal between the NC and PLC. The fault response control includes the following situations:

[0036] A. If it is an emergency fault, a fault response will be issued immediately and the CNC machine tool will be controlled to stop running to protect the safety of personnel, equipment and workpieces.

[0037] B. If it is a non-emergency fault, the NC program running status is read, the current processing condition of the CNC machine tool is identified through the spindle speed, feed speed and tool information, and whether the CNC machine tool is in the fine hole processing state is determined according to the processing condition; if not, a fault response is immediately issued and the CNC machine tool is controlled to stop running; if so, the fault response is delayed, and after the current hole processing is completed, a fault response is issued and the CNC machine tool is controlled to stop running.

[0038] Among them, the so-called fine hole processing state, when the machine tool performs batch fine hole processing, the processing flow of a single hole is as follows Figure 2 As shown in the figure, after machining a hole (the machined hole in the figure), the tool is retracted at a slower feed rate F1, then raised to a safe height at a slightly faster feed rate F2, and then moved to the top of the hole to be machined at the fastest feed rate F3, and then the tool is lowered and advanced at the feed rates F2 and F1 respectively to start machining the next hole, that is, entering the next fine hole machining state. Based on this, it is possible to determine whether the CNC machine tool has completed the current hole machining by monitoring the changes in the machine tool feed rate.

[0039] To sum up, this technical solution classifies CNC machine tool faults according to their importance and urgency, and performs fault response control in combination with the fault level and the processing conditions of the CNC machine tool during operation, so as to achieve an immediate response in the event of an emergency fault, and a delay in responding after the processing of the current hole is completed in the event of a non-emergency fault. Therefore, compared with the prior art, this technical solution adjusts the PLC's response logic to deal with random faults of CNC machine tools, and on the premise of ensuring the safety of equipment, workpieces and personnel, it greatly avoids sudden interruptions in the precision hole processing state of CNC machine tools, thereby avoiding product quality risks to a large extent.

[0040] Example 2

[0041] This embodiment discloses a method for improving the reliability of CNC precision hole processing, which, as a preferred embodiment of the present invention, comprises the following steps:

[0042] According to the importance and urgency of the CNC machine tool failure, the fault level of the CNC machine tool is evaluated, and a fault level judgment program is written into the PLC control system of the machine tool CNC system. The fault level judgment program is based on the calculation formula P = P b ×I b +P h ×I h The fault level of the CNC machine tool is evaluated. Where: P is the fault scoring index; P b is the importance level value of the fault part. The staff counted the common faults that have occurred in CNC machine tools for a long time and assigned them level values ​​based on empirical methods, such as Figure 3 As shown in the figure, there are five levels of fault location importance, and the five levels correspond to level values ​​1 to 5. The larger the level value, the higher the importance. h It is the severity level of the fault consequence. The staff counted the common faults that have occurred in CNC machine tools for a long time, counted the actual fault consequences of the corresponding faults, deduced the theoretical fault consequences, and assigned the fault consequences a level value based on the empirical method, such as Figure 4 As shown in the figure, there are five levels of severity of fault consequences, and the five levels correspond to level values ​​1 to 5 respectively. The larger the level value, the higher the severity. b and I h The weight coefficients of the importance level of the fault part and the severity level of the fault consequence are respectively. A subsystem may have multiple faults of different importance, and the severity of these faults is also different. In this way, the weight coefficient plays a role. The staff counted the common faults that have occurred in CNC for a long time and used multi-factor statistical methods to obtain the corresponding weight coefficients. The weight coefficients meet the following conditions: 0<I b ≤0.5, 0.5≤I h <1;I b +I h =1.

[0043] Based on the fault level and the processing conditions of the CNC machine tool during operation, a fault response control program is written into the PLC control system of the machine tool CNC system.

[0044] Start the CNC machine tool and run the NC program in the CNC system. Use the CNC machine tool's own fault detection system to monitor the operating status of each subsystem in real time, and feed back the signal parameters reflecting the operating status to the CNC system of the CNC machine tool in real time.

[0045] When a CNC machine tool fails, the fault level of the CNC machine tool is evaluated based on the fault level judgment program, and the fault response control is performed based on the fault level judgment program according to the CNC system. The fault level and processing conditions are judged by the fault level judgment program; wherein the fault response control includes the following situations:

[0046] A. If it is an emergency fault, a fault response will be issued immediately and the CNC machine tool will be controlled to stop running;

[0047] B. If it is a non-emergency fault, the NC program running status is read, the current processing condition of the CNC machine tool is identified through the spindle speed, feed speed and tool information, and whether the CNC machine tool is in the fine hole processing state is determined according to the processing condition; if not, a fault response is immediately issued and the CNC machine tool is controlled to stop running; if so, the fault response is delayed, and after the current hole processing is completed, a fault response is issued and the CNC machine tool is controlled to stop running.

[0048] This technical solution combines the fault location and fault consequences to obtain the fault scoring index by assigning grade values, laying a reasonable foundation for obtaining the fault level, and assigning weight values ​​to the fault location and fault consequences according to the different fault conditions of a single subsystem, further ensuring the rationality and reliability of this technical solution.

[0049] Example 3

[0050] This embodiment discloses a method for improving the reliability of CNC precision hole processing. As a preferred implementation scheme of the present invention, based on Example 2, the fault level is set to three; among them, when 3.5<P≤7.5, it is a level I fault, when 2.5<P≤3.5, it is a level II fault, and when P≤2.5, it is a level III fault; level I fault is an emergency fault, and level II fault and level III fault are non-emergency faults. Based on this, a real case is provided: a part processed by a five-axis CNC gantry machining center involves boring and reaming of a large number of high-precision holes. During a boring process, a cutting fluid interruption fault occurred. After the machine tool alarm, the feed stopped, the processing was interrupted, and the tool stayed in the hole, which almost caused part quality problems. Upon inspection, the tool cooling system of the machining center adopted a complex filtering device to meet the high-precision filtering requirements of the cutting fluid. When machining the part, due to the large amount of powder generated by cutting, the powder entered the filtering device with the cutting fluid, resulting in partial blockage of the filtering device, which in turn caused poor circulation of the cutting fluid, and the interruption of the coolant during processing triggered an alarm. Since the structure of the filter device is complex and it is difficult to complete the transformation in a short period of time, the method of the present technical solution is used to optimize the fault response logic of the CNC machine tool to eliminate hidden dangers.

[0051] This fault involves the tool cooling system. According to the calculation of P = 2 × 0.3 + 3 × 0.7 = 2.7, this fault belongs to the II level fault, and the fault response logic of the CNC machine tool can be optimized. Because the processing time of a single hole is short and the cutting volume during boring is small, a short interruption of the cutting fluid will not affect the processing quality. After optimizing the fault response logic of the machine tool, there were two failures of cutting fluid interruption during boring, and the alarm delay was effective. After the machine tool completed the processing of the current hole and lifted the tool, the alarm information was output and the processing was interrupted, achieving the intended purpose.

[0052] Example 4

[0053] This embodiment discloses a method for improving the reliability of CNC precision hole processing, which, as a preferred embodiment of the present invention, comprises the following steps:

[0054] According to the importance and urgency of the CNC machine tool faults, the faults of the CNC machine tools are evaluated at different levels, and a fault level judgment program is written into the PLC control system of the machine tool CNC system.

[0055] Based on the fault level and the processing conditions of the CNC machine tool during operation, a fault response control program is written into the PLC control system of the machine tool CNC system.

[0056] Start the CNC machine tool and run the NC program in the CNC system. Use the CNC machine tool's own fault detection system to monitor the operating status of each subsystem in real time, and feed back the signal parameters reflecting the operating status to the CNC system of the CNC machine tool in real time.

[0057] When a CNC machine tool fails, the fault level of the CNC machine tool is evaluated based on the fault level judgment program, and the fault response control is performed based on the fault level judgment program according to the CNC system. The fault level and processing conditions are judged by the fault level judgment program; wherein the fault response control includes the following situations:

[0058] A. If it is an emergency fault, a fault response will be issued immediately and the CNC machine tool will be controlled to stop running;

[0059] B. If it is a non-emergency fault, the NC program running status is read, the current processing condition of the CNC machine tool is identified through the spindle speed, feed speed and tool information, and whether the CNC machine tool is in the fine hole processing state is determined according to the processing condition; if not, a fault response is immediately issued and the CNC machine tool is controlled to stop running; if so, the fault response is delayed, and after the current hole processing is completed, a fault response is issued and the CNC machine tool is controlled to stop running.

[0060] Among them, tool types include milling cutters, boring cutters, reamers and drill bits. Based on this, the method for judging whether the CNC machine tool is in the state of fine hole processing according to the processing conditions is as follows: first, preliminarily judge whether the processing method is milling or hole making according to the type of tool; among them: if the tool is a milling cutter, it is judged as non-fine hole processing; if the tool is a boring cutter, reamer or drill bit, it is judged as fine hole processing; then identify the processing progress according to the spindle speed and feed speed to judge whether it is in the hole making stage; if so, it is judged as the state of fine hole processing, otherwise, it is judged as the state of non-fine hole processing.

[0061] Furthermore, the fault response delay is a segmented delay, that is: in the process of writing the fault response control program, a fault response delay time is preset; in the case of non-emergency faults, when the CNC machine tool is still in the hole-making stage of fine hole processing, it is delayed by the preset fault response delay time; after the preset fault response delay time is completed, it is determined again whether it is in the hole-making stage; if not, the delay ends; if so, it is delayed again by the preset fault response delay time, and so on, until the CNC machine tool completes the current hole-making stage.

[0062] In the processing of aviation parts, precision hole processing is an important processing content. When using CNC machine tools for precision hole processing such as boring and reaming, in order to ensure good processing quality, the spindle speed and feed speed are usually low, which is significantly different from the processing parameters such as profile milling, and it is easy to identify whether the machine tool is in the precision hole processing process. The single hole processing process has the characteristics of short processing time and fast feed change, which makes it easy to identify whether the machine tool is in the cutting state. In addition, the quality of profile milling is not easily affected by interruptions, and even if it is affected by interruptions, there is room for remedy. Based on this, this technical solution reasonably uses the tool type to classify the processing work of the CNC machine tool according to the processing conditions, excludes the fault optimization of milling processing whose processing quality is not affected by interruptions, and only optimizes the hole making processing whose quality is affected by interruptions. While conforming to the actual workflow, it reasonably solves the problem of the quality of precision hole processing being affected by interruptions. Furthermore, this technical solution sets the fault response delay as a segmented delay and limits the length of a single delay to ensure that a fault response is made in time after the current hole making stage is completed.

Claims

1. A method for improving the reliability of CNC precision hole processing, characterized in that: The following steps are involved: According to the importance and urgency of the CNC machine tool fault, the fault of the CNC machine tool is evaluated, and a fault level judgment program is written into the PLC control system of the machine tool CNC system; the fault level judgment program is based on the calculation formula P = P b ×I b +P h ×I h The fault level of the CNC machine tool is evaluated, P is the fault scoring index, P b is the importance level of the fault location, P h is the severity level of the failure consequence, I b and I h are the weight coefficients of the fault location importance level value and the fault consequence severity level value respectively; There are five levels for the importance of the fault location and the severity of the fault consequences. The five levels correspond to the level values ​​of 1 to 5. The larger the level value, the higher the importance and severity. The weight coefficients of the importance level value of the fault location and the importance level value of the fault consequence meet the following conditions: 0<I b ≤0.5, 0.5≤I h <1;I b +I h =1; There are three fault levels; among them, when 3.5<P≤7.5, it is a level I fault, when 2.5<P≤3.5, it is a level II fault, and when P≤2.5, it is a level III fault; level I fault is an emergency fault, and level II and level III faults are non-emergency faults; Based on the fault level and the processing conditions of the CNC machine tool during operation, a fault response control program is written into the PLC control system of the machine tool CNC system; Start the CNC machine tool and run the NC program in the CNC system. Use the CNC machine tool's own fault detection system to monitor the operating status of each subsystem in real time, and feed back the signal parameters reflecting the operating status to the CNC system of the CNC machine tool in real time; When a CNC machine tool fails, the fault level of the CNC machine tool is evaluated based on the fault level judgment program, and the fault response control is performed based on the fault level judgment program according to the CNC system. The fault level and processing conditions are judged by the fault level judgment program; wherein the fault response control includes the following situations: A. If it is an emergency fault, a fault response will be issued immediately and the CNC machine tool will be controlled to stop running; B. If it is a non-emergency fault, the NC program running status is read, the current processing condition of the CNC machine tool is identified through the spindle speed, feed speed and tool information, and whether the CNC machine tool is in the fine hole processing state is determined according to the processing condition; if not, a fault response is immediately issued and the CNC machine tool is controlled to stop running; if so, the fault response is delayed, and after the current hole processing is completed, a fault response is issued and the CNC machine tool is controlled to stop running.

2. A method for improving the reliability of CNC precision hole processing as claimed in claim 1, characterized in that: Tool types include milling cutters, boring cutters, reamers and drills.

3. A method for improving the reliability of CNC precision hole processing as claimed in claim 2, characterized in that: The method for judging whether the CNC machine tool is in the fine hole processing state according to the processing conditions is: First, the processing method is preliminarily determined to be milling or hole making according to the type of tool; among them: if the tool is a milling cutter, it is determined to be non-fine hole processing; if the tool is a boring cutter, reamer or drill, it is determined to be fine hole processing; then the processing progress is identified according to the spindle speed and feed speed to determine whether it is in the hole making stage; if so, it is determined to be a fine hole processing state, otherwise, it is determined to be a non-fine hole processing state.

4. A method for improving the reliability of CNC precision hole processing as claimed in claim 3, characterized in that: The fault response delay is a segmented delay, that is: In the process of writing the fault response control program, a fault response delay time is preset; In the case of non-emergency faults, when the CNC machine tool is still in the hole-making stage of fine hole processing, the preset fault response delay time is used for delay; After the preset fault response delay time is completed, it is determined again whether it is in the hole making stage; if not, the delay ends; if so, it is delayed again with the preset fault response delay time, and so on, until the CNC machine tool completes the current hole making stage.

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