A method for grading and progressive lead cutting of thick plate laser cutting

Abstract

The application discloses a kind of thick plate laser cutting's hierarchical perforation and progressive lead cutting method, belong to laser processing technical field.The application hierarchical planning to thick plate perforation process and make the focusing position gradually moves to the inside of plate with the number of perforation, the radiation signal of processing area is collected by coaxial photoelectric sensor and according to its sliding average and change rate, the completion and abnormality of each level of perforation are judged, the characteristic quantity related to heat input is obtained by integrating radiation signal in the perforation phase, and the starting cutting speed of lead cutting is self-tuned accordingly, the cutting speed is gradually increased to steady state along the lead cutting path tangent to the profile, and the laser power is changed according to the constant unit length input energy relationship. The application makes thick plate perforation efficient and robust, transition smooth, suppresses the overburning and slagging of lead cutting starting segment, and improves the success rate of starting cutting and the quality of cutting surface.

Description

Technical Field

[0001] This invention belongs to the field of laser processing technology, and particularly relates to a method for graded perforation and progressive cutting of thick plates using laser cutting. Background Technology

[0002] Before cutting any closed or open contour, laser cutting requires drilling a through-hole in the material. The laser beam is then guided through this hole onto the contour to begin cutting. This transition section from drilling to cutting is typically called the lead-in section. For thinner materials, drilling can be completed in one pass. However, as the thickness of the material increases, the energy and time required for a single drilling operation increase rapidly, the molten pool deepens, and slag removal becomes difficult. Therefore, for thicker materials, a staged drilling method is typically used, dividing the single drilling operation into several stages, progressively deepening the penetration while adjusting the focusing position, assist gas, and pulse parameters. The quality of the drilling directly affects the stability of subsequent cutting; good drilling is fundamental to ensuring stable beam and gas flow. Furthermore, photoelectric devices are coaxially mounted on the cutting head to collect radiation signals from the processing area, which can be used to monitor the processing process.

[0003] However, existing methods for piercing and cutting thick plates still have several shortcomings. The switching between piercing stages often relies on a pre-set fixed duration. However, rust, oil stains, and variations in plate thickness can alter the actual melting rhythm. A fixed duration may lead to premature switching before the molten cavity stabilizes, resulting in piercing failure, or it may cause excessive expansion of the molten pit and increased spatter after the molten cavity has stabilized. The number of piercing stages and the focusing positions of each stage are largely determined empirically. The focusing positions fail to advance with the bottom of the molten pit, resulting in poor energy coupling at deeper levels and low piercing efficiency. The parameters for the piercing and cutting stages are set independently. At the end of piercing, the hole diameter is large and the preheating around the hole is heavy. If a steady-state cutting speed and power are immediately applied to the contour, overheating, corner collapse, and slag buildup are likely to occur in the initial cutting section, or even breakage due to thermal imbalance. The transition from piercing to cutting often involves abrupt parameter changes. During the transition, the heat input per unit length is unstable, making it difficult to simultaneously prevent overheating and slag buildup.

[0004] Based on the above problems, it is necessary to provide a thick plate laser cutting method that enables adaptive perforation grading and seamless coordination between the perforation stage and the cutting stage, so as to improve the efficiency, robustness and surface quality of thick plate cutting. Summary of the Invention

[0005] The technical solution of this invention is: a method for graded perforation and progressive cutting in thick plate laser cutting, comprising the following steps:

[0006] S1. Obtain the thickness and material type of the plate to be cut, and plan the perforation process in stages, determining the number of perforation stages and the focusing position, auxiliary gas pressure and pulse duty cycle corresponding to each stage.

[0007] S2. Starting from the first level, pulse perforation is performed on the thick plate step by step, and the focusing position is moved towards the inside of the thick plate step by step as the number of perforation levels increases.

[0008] S3. During the perforation process, the radiation signal of the processing area is collected in real time by a photoelectric sensor coaxially set with the laser beam. The sliding average value and the rate of change of the radiation signal are used to determine whether each perforation level is completed normally. When it is completed normally, the normal level switching is triggered. When the upper limit of the time of this level is reached and it is still not completed normally, abnormal processing is performed. This process is carried out step by step until it is determined that the thick plate has been penetrated.

[0009] S4. Integrate the radiation signal collected during the perforation process to obtain the radiation integral characteristic quantity related to the heat input of this perforation, and determine the starting cutting speed of the progressive cutting based on the radiation integral characteristic quantity.

[0010] S5. Proceed along the cutting path from the perforation position to the entry point of the cutting contour, gradually increasing the cutting speed from the initial cutting speed to the steady-state cutting speed, and making the laser power and cutting speed change in tandem according to the preset unit length input energy relationship, and after the transition is completed, switch to steady-state contour cutting.

[0011] Furthermore, step S1 includes:

[0012] S11. Obtain the plate thickness and material type of the thick plate, and retrieve the single-stage melting depth increment according to the pre-calibrated material-plate thickness-process parameter mapping relationship. The single-stage melting depth increment is the thickness increment of single-stage perforation stable melting obtained under the same laser power, auxiliary gas type, nozzle height, first-stage focusing position and pulse parameters.

[0013] S12. Round up the ratio of the plate thickness to the single-stage melt depth increment to obtain the number of stages, and calculate it using the following formula:

[0014] ;

[0015] In the formula, The number of levels; The thickness of the plate; For the single-stage melting depth increment, and Greater than 0; This is the floor function operator;

[0016] S13. Taking the incident surface of the thick plate as the zero point of the focusing position and the direction pointing towards the interior of the thick plate along the laser incident direction as the positive direction, determine the focusing position of each stage according to the order of the perforation stages; and set the auxiliary gas pressure and pulse duty cycle of each stage according to a preset sequence, so that at least one of the auxiliary gas pressure and pulse duty cycle of at least one subsequent perforation stage is higher than that of its predecessor; the focusing position of each stage is determined by the following formula:

[0017] ;

[0018] In the formula, For the first The focal position of the level; The focal point for the head; The number is the perforation level number, which is an integer from 1 to the number of the levels. This represents the amount of movement of the focal position between two adjacent levels along the positive direction, and Greater than 0; thus, hierarchical perforation planning data is obtained to guide the step-by-step perforation.

[0019] Furthermore, step S2 includes:

[0020] S21. According to the graded perforation planning data, set the focusing position, auxiliary gas pressure and pulse duty cycle to the values ​​corresponding to the first stage, turn on the laser and auxiliary gas, and perform the first stage pulse perforation.

[0021] S22. After the current stage of perforation is completed normally and the normal inter-stage switching is triggered, the focusing position is moved along the positive direction by the amount of movement, and the auxiliary gas pressure and pulse duty cycle are updated to the values ​​corresponding to the next stage, and the next stage of pulse perforation is performed.

[0022] S23. Repeat step S22 to move the focusing position step by step towards the expected perforation depth as the perforation level increases until the final perforation is completed, thereby maintaining the coupling between the laser energy and the bottom of the perforation while the perforation depth increases.

[0023] Furthermore, step S3 includes:

[0024] S31. During the perforation process, the radiation signal of the processing area is collected by the photoelectric sensor at fixed sampling time intervals to obtain the sampling sequence of the radiation signal;

[0025] S32. In the sampling sequence, take a sliding window consisting of a set number of adjacent sampling points, calculate the sliding average of the sliding window, and calculate the rate of change from the sliding average of two adjacent sliding windows. The sliding average and the rate of change are calculated respectively according to the following formulas:

[0026] ;

[0027] ;

[0028] In the formula, For the first Each sampling point corresponds to the sliding average value of the sliding window; The number of sampling points contained in the sliding window; For the first The radiation signal value at each sampling point; For serial number since to Summation operators; The current sampling point number, and Not less than ; For the first The rate of change of each sampling point; For the first Each sampling point corresponds to the sliding average value of the sliding window; The sampling time interval between two adjacent sampling points;

[0029] S33. When the sliding average value is not less than the pre-calibrated level threshold and the absolute value of the rate of change is not greater than the pre-calibrated slope threshold, and the set holding time is maintained continuously, it is determined that the current level perforation is completed normally and the normal level switching is triggered. The absolute value is the value of the rate of change after removing the positive and negative signs.

[0030] S34. When the duration of the current level of perforation reaches the preset time limit but the normal completion condition of step S33 is still not met, an abnormality is handled. The abnormality handling includes at least one of extending the current level of perforation, calling the backup perforation parameters, retrying after reducing the laser power, and shutdown alarm. The abnormality handling is not used as a determination of the normal completion of the current level of perforation.

[0031] S35. Repeat steps S31 to S34 step by step; when the final perforation is completed normally and the holding time is maintained continuously, it is determined that the thick plate has been penetrated, and a penetration determination result that is adaptive to the plate surface state and plate thickness fluctuation is obtained.

[0032] Furthermore, step S4 includes:

[0033] S41. During the entire perforation process from the first stage of perforation to the determination that the thick plate has been penetrated, the collected radiation signals are accumulated and integrated at sampling time intervals to obtain the radiation integral characteristic quantity related to the heat input of this perforation, calculated by the following formula:

[0034] ;

[0035] In the formula, The integral characteristic of the radiation; For the first The radiation signal value at each sampling point; The sampling time interval between two adjacent sampling points; This is an operator that sums up the data at each sampling point during the perforation process. The sampling point number;

[0036] S42. Under the condition that the pre-calibrated upper limit of the radiation integral characteristic is greater than its pre-calibrated lower limit, the radiation integral characteristic is amplitude-limited and normalized to obtain the normalized characteristic, which is calculated by the following formula:

[0037] ;

[0038] In the formula, The normalized feature quantity; The integral characteristic of the radiation; This is the lower limit of the pre-calibrated integral characteristic quantity of radiation; This is the upper limit of the pre-calibrated integral characteristic of the radiation, and Greater than ; This is an operator that retrieves the smaller of the values ​​within the curly braces. This is an operator that takes the larger value within the curly braces.

[0039] S43. Determine the initial cutting speed of the progressive cutting based on the normalized feature value, such that the initial cutting speed decreases as the normalized feature value increases, but does not fall below a preset lower speed limit, calculated using the following formula:

[0040] ;

[0041] In the formula, The initial cutting speed; The preset lower speed limit, and Greater than 0 and less than ; The steady-state cutting speed; The initial tuning coefficient is , and Greater than 0 and less than 1; The normalized feature quantity; This is an operator that takes the larger value within the curly braces; thus, the initial cutting speed of the initiation cut is adapted to the radiation integral characteristic of this perforation.

[0042] Furthermore, step S5 includes:

[0043] S51. Plan the cutting path, such that the starting point of the cutting path is located at the perforation position and the ending point is located at the introduction point of the cutting contour, and the cutting path is tangent to the cutting contour at the introduction point. The cutting path is an arc or a spiral.

[0044] S52. Proceeding along the cutting path, the cutting speed is linearly increased from the initial cutting speed to the steady-state cutting speed according to the progress of the movement. The cutting speed is determined by the following formula:

[0045] ;

[0046] ;

[0047] In the formula, For the progress of the journey Cutting speed at that time; The initial cutting speed; The steady-state cutting speed; For the progress of the journey; The arc length already traveled along the cutting path; The total length of the cutting path;

[0048] S53. While increasing the cutting speed, adjust the laser power so that the laser power and the cutting speed satisfy the following formula for the input energy per unit length:

[0049] ;

[0050] In the formula, For the progress of the journey Laser power at that time; For the progress of the journey Cutting speed at that time; The steady-state cutting power corresponds to the steady-state cutting speed; The steady-state cutting speed is defined as follows: after the travel progress reaches 1, contour cutting is performed according to the steady-state cutting power and the steady-state cutting speed.

[0051] Furthermore, if the auxiliary gas used in the perforation process is the same type as the auxiliary gas used in the steady-state contour cutting, or if the auxiliary gas type is switched after completion, the auxiliary gas pressure is transitioned along the cutting path according to the following formula:

[0052] ;

[0053] In the formula, For the progress of the journey The auxiliary gas pressure at that time; The pressure of the auxiliary gas used to penetrate the thick plate; The auxiliary gas pressure used for the steady-state contour cutting; This refers to the progress of the journey.

[0054] Furthermore, the level threshold and the slope threshold are obtained through pre-calibrated piercing tests: in multiple piercing tests, the values ​​of the sliding average and the rate of change under the conditions of penetration and non-penetration are recorded respectively; the level threshold is a value higher than the sliding average under the condition of non-penetration and lower than the sliding average under the condition of penetration; the slope threshold is a statistical upper limit value of the absolute value of the rate of change in the penetration stabilization stage, or a value that ensures that the misjudgment rate of the penetration and non-penetration conditions is not higher than a preset misjudgment rate.

[0055] The beneficial effects of this invention are as follows:

[0056] This invention determines the number of perforation stages based on the principle of equal penetration depth during the perforation planning stage, and gradually moves the focusing position towards the interior of the thick plate with each perforation stage. This technique ensures that the thickness removed by each perforation stage is approximately equal, and the energy burden of each stage is relatively balanced. Simultaneously, the focusing point moves forward as the bottom of the molten pit advances. Because the focusing point is continuously coupled with the penetration front, the laser energy can be efficiently applied to the bottom of the molten pit, resulting in a smoother perforation process for thick plates, improved perforation efficiency, and reduced slag backflow and lens contamination.

[0057] This invention uses a photoelectric sensor coaxially mounted with the laser beam to collect radiation signals from the processing area in real time during the piercing process. It then uses a dual criterion—the sliding average value of the radiation signal and its rate of change—to determine whether each piercing stage is completed correctly. Simultaneously, cases where the piercing process fails to complete correctly even after reaching the time limit are classified as abnormal. This technique allows the switching between piercing stages and the determination of penetration to no longer rely on a fixed time, but rather to adapt to fluctuations in rust, oil, and board thickness. Since the switching occurs after the molten cavity has been established and stabilized, it avoids piercing failure caused by premature switching before the molten cavity has stabilized, and also avoids excessive expansion of the molten pit caused by continuing to linger after the molten cavity has stabilized. Therefore, the success rate of the first cut is improved, and the robustness of the piercing process is enhanced.

[0058] This invention integrates the radiation signal collected during the perforation stage to obtain the radiation integral characteristic quantity related to the heat input of this perforation. Based on this, the initial cutting speed of the progressive induction cutting is self-tuned, and a lower limit is used to constrain it. This technique allows the starting point of the induction cutting stage to be adjusted according to the actual thermal state formed during the perforation, rather than being set independently of the perforation stage. Since the more heat injected into the perforation, the lower the determined initial cutting speed, the heat input of the initial cutting segment decreases accordingly. Therefore, overheating of the initial segment when the preheating around the hole is heavy is suppressed, and the breakage caused by thermal imbalance is reduced.

[0059] This invention, during the initial cutting stage, ensures that the cutting path starts from the piercing position and is tangent to the cutting contour at the entry point. Simultaneously, the laser power and cutting speed are coordinated and varied according to a constant unit-length input energy relationship. This technique ensures a continuous and abrupt transition from the piercing state to the steady-state cutting state, maintaining the heat input per unit length at a steady-state set value during the transition. Because the introduction of the tangential direction avoids the beam re-entering the already expanded melting pit, and the constant unit-length input energy addresses both the requirements of not burning and not slag accumulation, the cutting surface quality of the initial cutting stage is improved, and defects at the start of the cutting are reduced. The interconnected techniques at each stage collectively make the initial cutting process of thick plate laser cutting more efficient, robust, and reliable. Attached Figure Description

[0060] Figure 1 The diagrams show a comparison of the perforation and cutting performance of Examples 1 to 4 and Comparative Examples 1 to 8, where (a) is a grouped bar chart of the first-time success rate of the initial cut and (b) is a grouped bar chart of the length of the initial defect of the initial cut.

[0061] Figure 2 The graphs show the process parameter changes of Examples 1 to 4 and Comparative Examples 1 to 8, where (a) is a line graph showing the piercing time as a function of plate thickness, and (b) is a line graph showing the change of the initial cutting speed ratio as a function of normalized piercing energy.

[0062] Figure 3 The figures are comparison charts of the index distribution of Examples 1 to 4 and Comparative Examples 1 to 8, where (a) is a box plot of the relative fluctuation distribution of the energy of the cutting segment line and (b) is a box plot of the distribution of the length of the cutting initiation defect.

[0063] Figure 4 The correlation analysis diagrams of Examples 1 to 4 and Comparative Examples 1 to 8 are shown, where (a) is a scatter plot of normalized piercing energy and initiation defect length, and (b) is a scatter plot of normalized piercing energy and initiation cutting speed ratio.

[0064] Figure 5 This is a flowchart of the graded perforation and progressive cutting method for thick plate laser cutting according to the present invention. Detailed Implementation

[0065] This specific embodiment provides a detailed description of a graded perforation and progressive cutting method and apparatus for laser cutting of thick plates. The structural forms, step sequences and values ​​involved are all exemplary. Those skilled in the art can implement this technical solution without creative effort, and this technical solution is not limited to the specific forms described below.

[0066] The present invention discloses a method for graded perforation and progressive cutting of thick plates using laser cutting, which generally includes a graded perforation stage and a progressive cutting stage. The graded perforation stage corresponds to steps S1 to S3, and the progressive cutting stage corresponds to steps S4 and S5. The two stages are interconnected via radiation signals acquired coaxially with the laser beam. Figure 5 The following is a step-by-step explanation.

[0067] In step S1, the piercing process of the thick plate is planned in stages. During a single piercing of a thick plate, the molten pool is deep, and slag is difficult to remove, easily leading to slag backflow and lens contamination. Therefore, a single piercing is divided into several stages, with each stage melting through and removing slag step by step. In step S11, the thickness and material type of the plate to be processed are first obtained. Then, based on the pre-defined mapping relationship between material, thickness, and process parameters, the single-stage melt depth increment corresponding to the current material and thickness is retrieved. Single-stage melting depth increment Under the same conditions of laser power, auxiliary gas type, nozzle height, primary focusing position and pulse parameters, the thickness increment that a single-stage perforation can stably penetrate is determined. Its value depends on the laser power and the material and is obtained by perforation depth test calibration.

[0068] In step S12, the ratio of plate thickness to single-stage penetration increment is rounded up to obtain the number of perforation stages. The relationship is as follows.

[0069] ;

[0070] In the formula, For the number of levels; The thickness is in mm. For single-stage penetration depth increments (mm), and Greater than 0; This is the floor operator.

[0071] The number of stages is determined based on the principle of equal melting depth, so that the thickness removed by each stage is roughly equal, the energy burden of each stage is relatively balanced, and the stage is avoided from being too heavy and not fully melting.

[0072] In step S13, the zero point of the focusing position is taken as the incident surface of the thick plate, and the positive direction is the direction pointing inward from the laser incident direction into the thick plate. The focusing positions of each stage are determined according to the order of the perforation stages. The focusing position of each level moves forward in the positive direction with each level, and the relationship is as follows.

[0073] ;

[0074] In the formula, For the first The focal position of the level (mm); The focal position of the first stage (mm); The perforation grade number is taken from 1 to the grade number. Integers; This represents the amount of movement (mm) of the focal position between two adjacent levels along the positive direction, and Greater than 0.

[0075] As the perforation progresses, the bottom of the molten pit continuously advances into the thick plate, causing the focusing position to move forward synchronously in the positive direction. This allows the laser to maintain a high power density at the bottom of the molten pit, thereby preserving the coupling between energy and the penetration front. Preferably, the magnitude is equivalent to the single-stage melting depth increment, so that the focal point approximately follows the advancement of the bottom of the molten pit. In step S13, the auxiliary gas pressure and pulse duty cycle of each stage are also set according to a preset sequence, and at least one of the auxiliary gas pressure and pulse duty cycle of at least one subsequent piercing stage is higher than that of its predecessor piercing stage, in order to enhance the removal of slag from deeper molten pits. Steps S11 to S13 yield staged piercing planning data for guiding step-by-step piercing.

[0076] In step S2, pulse piercing is performed step-by-step according to the graded piercing planning data. In step S21, the focusing position, auxiliary gas pressure, and pulse duty cycle are set to the values ​​corresponding to the first stage, and the laser and auxiliary gas are turned on to perform the first stage pulse piercing. In step S22, after the current stage of piercing is completed normally and a normal inter-stage switching is triggered, the focusing position is moved in the positive direction by the aforementioned movement amount, and the auxiliary gas pressure and pulse duty cycle are updated to the values ​​corresponding to the next stage, and then the next stage of pulse piercing is performed. In step S23, step S22 is repeated, and the focusing position moves step-by-step towards the expected piercing depth as the number of piercing stages increases until the final stage of piercing is completed. Here, the focusing position moves forward step-by-step according to a preset movement amount, rather than relying on real-time feedback of the molten pit depth, which is convenient to implement on conventional CNC systems.

[0077] In step S3, the completion status of each stage of perforation is determined online. During the perforation process, the molten pool and plasma radiate light signals outward. These radiation signals are received by a photoelectric sensor via an optical path coaxially arranged with the laser beam, and their intensity is related to the state of the molten pool and the degree of penetration. In step S31, the radiation signals of the processing area are collected by the photoelectric sensor at fixed sampling time intervals to obtain a sampling sequence of radiation signals.

[0078] In step S32, a sliding window consisting of a set number of adjacent sampling points is taken in the sampling sequence, the sliding average value of the radiation signal within the sliding window is calculated, and the rate of change is calculated from the sliding average value of two adjacent sliding windows. The sliding average value and the rate of change are determined according to the following relationship.

[0079] ;

[0080] ;

[0081] In the formula, For the first Each sampling point corresponds to the sliding average value of the sliding window; This represents the number of sampling points contained in the sliding window. For the first The radiation signal value at each sampling point; For serial number since to Summation operators; The current sampling point number, and Not less than ; For the first The rate of change of each sampling point; For the first Each sampling point corresponds to the sliding average value of the sliding window; The sampling time interval (s) between two adjacent sampling points.

[0082] Moving average is used to suppress random noise in the radiated signal, making the signal trend more stable. The rate of change reflects how quickly the moving average changes over time; as the molten cavity stabilizes, the rate of change approaches a smaller value. Both moving average and numerical difference are conventional signal processing methods, making them easy to implement in real time in the controller.

[0083] In step S33, when the sliding average value is not less than the pre-calibrated level threshold and the absolute value of the rate of change is not greater than the pre-calibrated slope threshold, and the set holding time is maintained continuously, it is determined that the current stage of perforation is completed normally, and a normal stage switching is triggered. The aforementioned absolute value refers to the value of the rate of change after removing the positive and negative signs. The level threshold is used to characterize that the melt cavity of this stage has been established, and the slope threshold is used to characterize that the melt cavity tends to be stable. The use of both utilizes both the amplitude and rate of change of the radiation signal, which has good adaptability to board surface corrosion, oil stains, and board thickness fluctuations, avoiding premature switching before the melt cavity is stable, and also avoiding continued lingering after the melt cavity has stabilized.

[0084] In step S34, if the duration of the current perforation reaches the preset upper limit but the normal completion condition of step S33 is still not met, an anomaly handling is performed. This anomaly handling includes at least one of the following: extending the current perforation stage, calling backup perforation parameters, retrying after reducing laser power, and a shutdown alarm. This anomaly handling is not considered a determination of normal completion of the current perforation stage. Distinguishing between normal completion and anomaly handling avoids mistakenly proceeding to the next stage before true penetration, thereby maintaining the reliability of subsequent determinations and penetration results.

[0085] In step S35, steps S31 to S34 are repeated sequentially. When the final stage of perforation is completed normally and the above-mentioned holding time is maintained continuously, it is determined that the thick plate has been penetrated. The normal completion condition of the final stage is used as the penetration criterion, so that the penetration determination has a clear and repeatable standard. Steps S31 to S35 yield a penetration determination result that is adaptive to the plate surface condition and plate thickness fluctuations.

[0086] In step S4, the radiation signal during the perforation stage is integrated to quantify the relative level of heat injected into the thick plate during this perforation. In step S41, throughout the entire perforation process from the first stage of perforation to the determination that the thick plate has been penetrated, the collected radiation signal is accumulated and integrated at sampling time intervals to obtain the radiation integral characteristic quantity related to the heat input of this perforation. The relationship is as follows.

[0087] ;

[0088] In the formula, It is a characteristic quantity of the radiation integral; For the first The radiation signal value at each sampling point; The sampling time interval (s) between two adjacent sampling points; This is an operator that sums up the data at each sampling point during the perforation process. This is the sequence number of the sampling point.

[0089] This integral is a rectangular numerical integral over the discrete radiated signal. The radiated light energy is related to the energy injected during the perforation process, and is also affected by the material emissivity, dust, sensor wavelength, and gain. It represents a relative quantity related to heat input, rather than the actual value of heat input. The correspondence between heat input and heat input is obtained through pre-calibration.

[0090] In step S42, under the condition that the pre-calibrated upper limit of the radiation integral characteristic is greater than its pre-calibrated lower limit, the radiation integral characteristic is subjected to amplitude limiting normalization to obtain the normalized characteristic. The relationship is as follows.

[0091] ;

[0092] In the formula, These are normalized feature quantities; It is a characteristic quantity of the radiation integral; This is the lower limit of the pre-calibrated integral characteristic quantity of radiation; This is the upper limit of the pre-calibrated integral characteristic of radiation, and Greater than ; This is an operator that retrieves the smaller of the values ​​within the curly braces. This is an operator that takes the larger of the values ​​within the curly braces.

[0093] Limiting normalization maps the feature quantity to the range of 0 to 1. The process of taking the larger and smaller values ​​ensures that the normalization result remains between 0 and 1 when the feature quantity exceeds the upper and lower limits of the calibration. The condition that the upper limit of the calibration is greater than the lower limit of the calibration avoids the denominator being zero, thereby ensuring the numerical stability of subsequent calculations.

[0094] In step S43, the initial cutting speed of the progressive initiation is determined based on the normalized feature value, so that the initial cutting speed decreases as the normalized feature value increases, but does not fall below the preset speed lower limit. The relationship is as follows.

[0095] ;

[0096] In the formula, The initial cutting speed (mm / min); The preset lower speed limit (mm / min) is, and Greater than 0 and less than ; The steady-state cutting speed is (mm / min). The initial tuning coefficient is , and Greater than 0 and less than 1; These are normalized feature quantities; This is an operator that takes the larger of the values ​​within the curly braces.

[0097] When a large amount of heat is injected during the perforation process, the normalized characteristic value is larger, resulting in a lower initial cutting speed. This reduces the heat input at the beginning of the cutting process, preventing overheating of the initial section under conditions of heavy preheating around the hole. This lower speed limit is thus maintained. The starting point setting coefficient is used to prevent the cutting from stalling or becoming unstable due to an excessively low initial cutting speed. The initial cutting speed is limited to between 0 and 1, ensuring it does not exceed the steady-state cutting speed. This matches the initial state of the pilot cut with the actual thermal state formed during the piercing process, demonstrating the information connection between the piercing stage and the pilot cut stage, which differs from the conventional practice of setting piercing and cutting independently.

[0098] In step S5, the perforation state is smoothly transitioned to the steady-state cutting state along the lead-in cutting path. In step S51, the lead-in cutting path is planned, with its starting point at the perforation location and its ending point at the entry point of the cutting contour. The lead-in cutting path is tangent to the cutting contour at the entry point, and is either an arc or a spiral. The tangency at the entry point ensures that the cutting direction is continuous and without abrupt changes when entering the contour. Using a spiral lead-in cutting path also allows the beam to gradually move away from the enlarged perforation crater, preventing the beam from re-entering the crater. The length of the lead-in cutting path is preferably on the order of the plate thickness to accommodate a smooth transition in speed and power.

[0099] In step S52, the cutting speed is increased linearly from the initial cutting speed to the steady-state cutting speed according to the progress of the cutting. The cutting speed is determined according to the following relationship.

[0100] ;

[0101] ;

[0102] In the formula, For the progress of the journey Cutting speed (mm / min); The initial cutting speed (mm / min); The steady-state cutting speed is (mm / min). For the progress of the journey; This represents the arc length (mm) already traveled along the tangent path; This represents the total length (mm) of the cutting path.

[0103] Progress As the value increases from 0 to 1, the cutting speed increases linearly from the initial cutting speed to the steady-state cutting speed, making the speed change continuous and gradual.

[0104] In step S53, the laser power is adjusted while the cutting speed is increased to maintain a steady-state set value for the input energy per unit length during the cutting process. The input energy per unit length is proportional to the ratio of laser power to cutting speed. During steady-state cutting, this ratio is the ratio of steady-state cutting power to steady-state cutting speed. To maintain the input energy per unit length at a steady-state set value during the cutting process, the ratio of laser power to cutting speed at any point in the travel distance is set to be equal to the ratio of steady-state cutting power to steady-state cutting speed, thus obtaining the following relationship.

[0105] ;

[0106] In the formula, For the progress of the journey Laser power (W) at that time; For the progress of the journey Cutting speed (mm / min); The steady-state cutting power (W) corresponding to the steady-state cutting speed; The steady-state cutting speed is (mm / min).

[0107] This formula allows the corresponding laser power to be directly obtained when the current cutting speed is known, so that the power changes synchronously with the speed. The input energy per unit length is kept at a steady-state set value during the transition process, which avoids overheating due to high input energy and slag buildup due to low input energy. After the progress reaches 1, contour cutting is performed according to the steady-state cutting power and steady-state cutting speed.

[0108] Regarding the auxiliary gas, when the auxiliary gas used in the piercing process is the same as the auxiliary gas used in the steady-state contour cutting, or after the auxiliary gas type is switched, the auxiliary gas pressure is smoothly transitioned with the progress of the cutting path, and the relationship is as follows.

[0109] ;

[0110] In the formula, For the progress of the journey The auxiliary gas pressure (MPa) at that time; The auxiliary gas pressure (MPa) used when penetrating thick plates; The auxiliary gas pressure (MPa) used for steady-state contour cutting; This refers to the progress of the journey.

[0111] The auxiliary gas pressure smoothly transitions from the pressure during penetration to the pressure of steady-state cutting as the progress of the process, coordinating with the transition of speed and power. When different types of auxiliary gases are used for piercing and cutting, the gas type is switched first and then the pressure is transitioned in the manner described above to adapt to the response of different gas paths.

[0112] The level threshold and slope threshold used in steps S33 and S34 can be obtained through prior puncture tests. In multiple puncture tests, the moving average and rate of change values ​​for both penetrating and non-penetrating scenarios are recorded. The level threshold is set to a value higher than the moving average for the non-penetrating scenario but lower than the moving average for the penetrating scenario. The slope threshold is set to the statistical upper limit of the absolute value of the rate of change during the penetrating stabilization phase, or a value that ensures the false positive rate for both penetrating and non-penetrating scenarios does not exceed a preset false positive rate. The thresholds obtained using this calibration method are repeatable and easily reproduced on different devices and batches.

[0113] Example 1, taking the laser cutting of a 16mm thick Q235 carbon structural steel plate as an example, uses a 6kW fiber laser cutting machine and the thick plate laser cutting device of the present invention. In step S1, the piercing process is planned in stages. In step S11, the single-stage penetration depth increment is retrieved according to the pre-calibrated mapping relationship between material, plate thickness and process parameters. In step S12, the ratio of plate thickness to single-stage penetration depth increment is rounded up to determine the number of stages as 4. In step S13, the focusing position of each stage is determined by taking the incident side surface of the plate as the zero point of focus and the direction pointing into the plate as the positive direction, and the focusing position of each stage is moved forward step by step in the positive direction. The auxiliary gas pressure and pulse duty cycle of each stage are set according to the preset sequence so that at least one of the auxiliary gas pressure and pulse duty cycle of the subsequent piercing stage is not lower than that of the previous stage. In step S2, perforation is performed stage by stage. Step S21 performs the first-stage perforation according to the parameters of the first stage. Step S22, after the current stage is completed normally and a normal inter-stage switching is triggered, the focusing position is moved by a certain amount in the positive direction and the air pressure and duty cycle are updated before proceeding to the next stage. Step S23 is repeated until the fourth stage perforation is completed. During the perforation process, the stage judgment in step S3 is performed. Step S31 acquires coaxial radiation signals at a fixed sampling interval to obtain a sampling sequence. Step S32 calculates the moving average and rate of change. Step S33 determines that the current stage is completed normally when the moving average is not less than the level threshold and the absolute value of the rate of change is not greater than the slope threshold and is maintained for the specified duration. Step S34 performs abnormal handling if the condition is not met even after reaching the upper limit of the duration. Step S35 determines that the plate is penetrated when the final stage is completed normally. Subsequently, in step S4, step S41 integrates the radiation signal of the perforation stage to obtain the radiation integral characteristic. Step S42 performs amplitude limiting and normalization. Step S43 determines the starting cutting speed based on the normalized characteristic and constrains it with a lower speed limit. In step S5, step S51 plans a circular arc cutting path from the piercing position to the contour introduction point and tangent to the introduction point; step S52 linearly increases the cutting speed along the path to a steady-state cutting speed; and step S53 coordinates the laser power and cutting speed according to a constant linear energy relationship. O2 is used as the auxiliary gas, and the same gas is used for piercing and cutting, with the transition of auxiliary gas pressure according to the present invention. The level threshold and slope threshold are calibrated according to the piercing test method described in step S3 of the present invention.

[0114] Example 2, taking a 20mm thick Q235 carbon steel plate as an example, uses O2 as the auxiliary gas and has 4 stages. The remaining steps are the same as in Example 1, except that the focusing position of each stage, the auxiliary gas pressure, the pulse duty cycle, the steady-state cutting speed and the steady-state cutting power are adjusted accordingly for the plate thickness.

[0115] Example 3, taking a 30mm thick 06Cr19Ni10 stainless steel plate as an example, uses N2 as the auxiliary gas, has 6 stages, takes a cutting path of length equivalent to the plate thickness and uses a spiral, sets the starting point setting coefficient and the lower speed limit according to the stainless steel process, and the rest is the same as in Example 1.

[0116] Example 4 uses a 40mm thick Q345 low-alloy high-strength structural steel plate as an example. The auxiliary gas is O2, the number of stages is 8, and the pilot-cutting path is correspondingly lengthened. The rest is the same as in Example 1. The above examples cover the range of values ​​for the present invention in terms of material, plate thickness, auxiliary gas, number of stages, and pilot-cutting path.

[0117] Comparative Example 1 uses the same plate thickness, laser, and device as Example 1, with a plate thickness of 16mm. The difference lies in the use of a three-stage perforation process with fixed duration. Each stage has a preset duration, a fixed focusing position, and no dual-threshold judgment of the coaxial radiation signal. After perforation, the material directly enters the contour at a steady-state cutting speed and power. This means that step S4 (energy integration and starting point self-tuning) and step S5 (constant linear energy coordination and tangential introduction) are not performed. Comparative Examples 2, 3, and 4 use the same method for plate thicknesses of 20mm, 30mm, and 40mm, respectively.

[0118] Comparative Example 5, with a plate thickness of 16mm, performed the same piercing stage as Example 1, namely, executing steps S1 to S3: equal penetration depth grading, progressive focus shifting, and dual threshold grading. The difference was only in the lead-in cutting stage; after piercing, the plate directly entered the contour at a steady-state cutting speed and power, without executing step S4's start-up self-tuning or step S5's constant line energy coordination. Comparative Examples 6, 7, and 8 used the same method for plate thicknesses of 20, 30, and 40mm, respectively. Comparative Examples 1 to 8 serve to distinguish the roles of the technical means in the piercing and lead-in cutting stages.

[0119] The following experimental examples used the same batch size and environment. The four plate thicknesses of 16, 20, 30, and 40 mm in the figures correspond to Examples 1, 2, 3, and 4, respectively. Comparative Examples 1 to 4 and Comparative Examples 5 to 8 correspond to the four plate thicknesses in the same order. The piercing time was read from the cutting machine control system's time log. The length of the initial defect, the quality of the cut surface, and the surface condition were measured. The plate grade and chemical composition were determined according to relevant standards. Each working condition was repeated 20 times to statistically analyze the success rate. The main indicators for each example are shown in Tables 1 and 2.

[0120] Table 1. Success rate of initial cutting and piercing time:

[0121]

[0122] Table 2, Length of the initial cut defect:

[0123]

[0124] Experiment 1 employed the methods of Examples 1 to 4, Comparative Examples 1 to 4, and Comparative Examples 5 to 8, replicating 20 pieces for each of the four plate thicknesses. The first-cut success rate and the length of the initial cut defect were statistically analyzed. The first-cut success rate refers to the percentage of pieces that achieved continuous, uninterrupted cuts and whose initial cut defect length met the required cut surface quality grade in a single cut. The initial cut defect length was the measured length of the initial section with slag and the unqualified section of the cut surface after the initial cut entered the contour. The experimental results are as follows: Figure 1 As shown.

[0125] Depend on Figure 1 As can be seen in (a), for the same plate thickness, the first-cut success rate of the embodiment is higher than that of Comparative Examples 5 to 8, which in turn is higher than that of Comparative Examples 1 to 4, and the difference increases with the thickness of the plate. Figure 1 As shown in (b), the length of the initial defect in the embodiment is significantly shorter than that in the two comparative examples, and its increase with increasing plate thickness is minimal. This indicates that the embodiment uses the dual-threshold closed-loop classification of step S3 of the present invention in the perforation stage, making the perforation switching adaptive to the plate surface state and plate thickness fluctuations, avoiding accidental entry into the next stage before full melting, thus improving the success rate; the embodiment uses the starting point self-tuning of step S4 and the constant line energy synergy of step S5 of the present invention in the initial cutting stage, suppressing overburning of the initial segment, thus shortening the defect length. Comparative examples 5 to 8 are the same as the embodiment only in the perforation stage, and their success rate is higher than that of comparative examples 1 to 4, but the defect length is still relatively large, indicating that the perforation stage and the initial cutting stage play independent roles.

[0126] Experimental Example 2 employed the methods described in the previous examples. The piercing time refers to the duration from the start of the first stage of piercing until the judgment plate is penetrated, as read from the control system's time log. The ratio of the initial cutting speed to the steady-state cutting speed was determined by the normalized piercing energy according to step S43 of this invention. Experimental results are as follows: Figure 2 As shown.

[0127] Depend on Figure 2 As can be seen in Figure (a), the piercing time of the Example is basically the same as that of Comparative Examples 5 to 8 and significantly lower than that of Comparative Examples 1 to 4. At 40 mm, the piercing time of the Example is about 30% lower than that of Comparative Examples 1 to 4. Figure 2As can be seen in (b), the initial cutting speed ratio in the embodiments monotonically decreases with increasing normalized piercing energy, while the comparative examples always maintain a ratio of 1. The decrease in piercing time stems from the equal melt depth grading in step S1 and the dual threshold grading in step S3 of the present invention, which allows each grade to switch immediately after the melt cavity is established and stabilized, avoiding ineffective dwell time caused by a fixed duration. The fact that the piercing time in the embodiments is consistent with that in comparative examples 5 to 8 indicates that this benefit comes from the piercing stage and is unrelated to the initial cutting stage. The monotonic decrease in the initial cutting speed ratio reflects the self-tuning of the starting point in step S43 of the present invention, and the relationship is as follows: ;

[0128] In the formula, The initial cutting speed (mm / min); The lower limit of speed (mm / min); The steady-state cutting speed is (mm / min). The initial tuning coefficient; Normalized perforation energy; This is an operator that takes the larger of the values ​​within the curly braces.

[0129] The more heat injected during perforation, the greater the normalized perforation energy and the heavier the residual heat around the hole. The lower the starting speed determined by the above formula, the lower the heat input in the initial section can be reduced and overheating can be suppressed by entering the contour at a lower speed.

[0130] Experimental Example 3 employed the methods described in the previous examples. The relative fluctuation of the cutting segment's linear energy was defined as the percentage of the ratio of the standard deviation to the mean of the input energy per unit length of the cutting segment. The input energy per unit length was characterized by the ratio of laser power to cutting speed. The length of the initial defect in the cutting was measured according to relevant standards, and the distribution was obtained by summarizing multiple samples from each example. The experimental results are as follows: Figure 3 As shown.

[0131] Depend on Figure 3 As can be seen in (a), the linear energy fluctuations in the examples are relatively concentrated at a lower level, while those in Comparative Examples 1 to 4 and Comparative Examples 5 to 8 are significantly higher and more dispersed. Figure 3 As can be seen in (b), the overall distribution of the initial defect length in the example is relatively low and the dispersion is small, while the median and dispersion of the two comparative examples are significantly larger. This indicates that the example ensures that the laser power and cutting speed meet the requirements of step S53 of the present invention in the initial cutting segment. The first method maintains a steady-state input energy value per unit length, resulting in minimal fluctuations. The comparative method, however, abruptly enters a steady-state state, leading to a mismatch in the input energy per unit length at the beginning, resulting in large fluctuations and a larger defect distribution. Excessive input energy per unit length leads to overheating, while insufficient input energy results in slag buildup; both occur randomly with abrupt changes.

[0132] Experimental Example 4 employs the methods described in the previous examples. The normalized perforation energy is obtained by integrating and normalizing the radiation signal during the perforation stage according to step S42 of this invention; the ratio of the initial cutting speed to the steady-state cutting speed is read from the control system log. Experimental results are as follows: Figure 4 As shown.

[0133] Depend on Figure 4 As can be seen in (a), the initiation defect lengths of Comparative Examples 1 to 4 and Comparative Examples 5 to 8 increase significantly with increasing normalized piercing energy, while the defect lengths of the Examples only increase slowly with increasing normalized piercing energy and remain at a low level. Figure 4 As can be seen in (b), the initial cutting speed of the embodiment decreases with increasing normalized piercing energy, while the ratio remains constant at 1 in the comparative example. This indicates the relationship between the initial defect length and the residual heat of the piercing. The more heat injected into the piercing, the greater the normalized piercing energy, and the heavier the preheating around the hole. If the comparative example directly cuts at a steady-state speed, the initial segment is more prone to overheating, resulting in a longer defect. The embodiment, according to step S43 of the present invention, reduces the initial cutting speed with increasing normalized piercing energy, thereby suppressing overheating of the initial segment and shortening the defect length.

[0134] Although embodiments of this application have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting this application. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of this application.

Claims

1. A method for graded perforation and progressive cutting in thick plate laser cutting, characterized in that, Includes the following steps: S1. Obtain the thickness and material type of the plate to be cut, and plan the perforation process in stages, determining the number of perforation stages and the focusing position, auxiliary gas pressure and pulse duty cycle corresponding to each stage. S2. Starting from the first level, pulse perforation is performed on the thick plate step by step, and the focusing position is moved towards the interior of the thick plate step by step as the perforation level increases; S3. During the perforation process, the radiation signal of the processing area is collected in real time by a photoelectric sensor coaxially set with the laser beam. The sliding average value and the rate of change of the radiation signal are used to determine whether each perforation level is completed normally. When it is completed normally, the normal level switching is triggered. When the upper limit of the time of this level is reached and it is still not completed normally, abnormal processing is performed. This process is carried out step by step until it is determined that the thick plate has been penetrated. S4. Integrate the radiation signal collected during the perforation process to obtain the radiation integral characteristic quantity related to the heat input of this perforation, and determine the starting cutting speed of the progressive cutting based on the radiation integral characteristic quantity. S5. Proceed along the cutting path from the perforation position to the entry point of the cutting contour, gradually increasing the cutting speed from the initial cutting speed to the steady-state cutting speed, and making the laser power and cutting speed change in tandem according to the preset unit length input energy relationship, and after the transition is completed, switch to steady-state contour cutting.

2. The method for graded perforation and progressive cutting of thick plate laser cutting according to claim 1, characterized in that, Step S1 includes: S11. Obtain the plate thickness and material type of the thick plate, and retrieve the single-stage melting depth increment according to the pre-calibrated material-plate thickness-process parameter mapping relationship. The single-stage melting depth increment is the thickness increment of single-stage perforation stable melting obtained under the same laser power, auxiliary gas type, nozzle height, first-stage focusing position and pulse parameters. S12. Round up the ratio of the plate thickness to the single-stage melt depth increment to obtain the number of stages, and calculate it using the following formula: ； In the formula, The number of levels; The thickness of the plate; For the single-stage melting depth increment, and Greater than 0; This is the floor function operator; S13. Taking the incident surface of the thick plate as the zero point of the focusing position and the direction pointing towards the interior of the thick plate along the laser incident direction as the positive direction, determine the focusing position of each stage according to the order of the perforation stages; and set the auxiliary gas pressure and pulse duty cycle of each stage according to a preset sequence, so that at least one of the auxiliary gas pressure and pulse duty cycle of at least one subsequent perforation stage is higher than that of its predecessor; the focusing position of each stage is determined by the following formula: ； In the formula, For the first The focal position of the level; The focal point for the head; The number is the perforation level number, which is an integer from 1 to the number of the levels. This represents the amount of movement of the focal position between two adjacent levels along the positive direction, and Greater than 0; thus, hierarchical perforation planning data is obtained to guide the step-by-step perforation.

3. The method for graded perforation and progressive cutting of thick plate laser cutting according to claim 2, characterized in that, Step S2 includes: S21. According to the graded perforation planning data, set the focusing position, auxiliary gas pressure and pulse duty cycle to the values ​​corresponding to the first stage, turn on the laser and auxiliary gas, and perform the first stage pulse perforation. S22. After the current stage of perforation is completed normally and the normal inter-stage switching is triggered, the focusing position is moved along the positive direction by the amount of movement, and the auxiliary gas pressure and pulse duty cycle are updated to the values ​​corresponding to the next stage, and the next stage of pulse perforation is performed. S23. Repeat step S22 to move the focusing position step by step towards the expected perforation depth as the perforation level increases until the final perforation is completed, thereby maintaining the coupling between the laser energy and the bottom of the perforation while the perforation depth increases.

4. The method for graded perforation and progressive cutting of thick plate laser cutting according to claim 1, characterized in that, Step S3 includes: S31. During the perforation process, the radiation signal of the processing area is collected by the photoelectric sensor at fixed sampling time intervals to obtain the sampling sequence of the radiation signal; S32. In the sampling sequence, take a sliding window consisting of a set number of adjacent sampling points, calculate the sliding average of the sliding window, and calculate the rate of change from the sliding average of two adjacent sliding windows. The sliding average and the rate of change are calculated respectively according to the following formulas: ； ； In the formula, For the first Each sampling point corresponds to the sliding average value of the sliding window; The number of sampling points contained in the sliding window; For the first The radiation signal value at each sampling point; For serial number since to Summation operators; The current sampling point number, and Not less than ; For the first The rate of change of each sampling point; For the first Each sampling point corresponds to the sliding average value of the sliding window; The sampling time interval between two adjacent sampling points; S33. When the sliding average value is not less than the pre-calibrated level threshold and the absolute value of the rate of change is not greater than the pre-calibrated slope threshold, and the set holding time is maintained continuously, it is determined that the current level perforation is completed normally and the normal level switching is triggered. The absolute value is the value of the rate of change after removing the positive and negative signs. S34. When the duration of the current level of perforation reaches the preset time limit but the normal completion condition of step S33 is still not met, an abnormality is handled. The abnormality handling includes at least one of extending the current level of perforation, calling the backup perforation parameters, retrying after reducing the laser power, and shutdown alarm. The abnormality handling is not used as a determination of the normal completion of the current level of perforation. S35. Repeat steps S31 to S34 step by step; when the final perforation is completed normally and the holding time is maintained continuously, it is determined that the thick plate has been penetrated, and a penetration determination result that is adaptive to the plate surface state and plate thickness fluctuation is obtained.

5. The method for graded perforation and progressive cutting of thick plate laser cutting according to claim 1, characterized in that, Step S4 includes: S41. During the entire perforation process from the first stage of perforation to the determination that the thick plate has been penetrated, the collected radiation signals are accumulated and integrated at sampling time intervals to obtain the radiation integral characteristic quantity related to the heat input of this perforation, calculated by the following formula: ； In the formula, The integral characteristic of the radiation; For the first The radiation signal value at each sampling point; The sampling time interval between two adjacent sampling points; This is an operator that sums up the data at each sampling point during the perforation process. The sampling point number; S42. Under the condition that the pre-calibrated upper limit of the radiation integral characteristic is greater than its pre-calibrated lower limit, the radiation integral characteristic is amplitude-limited and normalized to obtain the normalized characteristic, which is calculated by the following formula: ； In the formula, The normalized feature quantity; The integral characteristic of the radiation; This is the lower limit of the pre-calibrated integral characteristic quantity of radiation; This is the upper limit of the pre-calibrated integral characteristic of the radiation, and Greater than ; This is an operator that retrieves the smaller of the values ​​within the curly braces. This is an operator that takes the larger value within the curly braces. S43. Determine the initial cutting speed of the progressive cutting based on the normalized feature value, such that the initial cutting speed decreases as the normalized feature value increases, but does not fall below a preset lower speed limit, calculated using the following formula: ； In the formula, The initial cutting speed; The preset lower speed limit, and Greater than 0 and less than ; The steady-state cutting speed; The initial tuning coefficient is , and Greater than 0 and less than 1; The normalized feature quantity; This is an operator that takes the larger value within the curly braces; thus, the initial cutting speed of the initiation cut is adapted to the radiation integral characteristic of this perforation.

6. The method for graded perforation and progressive cutting of thick plate laser cutting according to claim 1, characterized in that, Step S5 includes: S51. Plan the cutting path, such that the starting point of the cutting path is located at the perforation position and the ending point is located at the introduction point of the cutting contour, and the cutting path is tangent to the cutting contour at the introduction point. The cutting path is an arc or a spiral. S52. Proceed along the cutting path, and linearly increase the cutting speed from the initial cutting speed to the steady-state cutting speed according to the progress of the movement. The cutting speed is determined by the following formula: ； ； In the formula, For the progress of the journey Cutting speed at that time; The initial cutting speed; The steady-state cutting speed; For the progress of the journey; The arc length already traveled along the cutting path; The total length of the cutting path; S53. While increasing the cutting speed, adjust the laser power so that the laser power and the cutting speed satisfy the following formula for the input energy per unit length: ； In the formula, For the progress of the journey Laser power at that time; For the progress of the journey Cutting speed at that time; The steady-state cutting power corresponds to the steady-state cutting speed; The steady-state cutting speed is defined as follows: after the travel progress reaches 1, contour cutting is performed according to the steady-state cutting power and the steady-state cutting speed.

7. The method for graded perforation and progressive cutting of thick plate laser cutting according to claim 6, characterized in that, When the auxiliary gas used in the perforation process is the same type as the auxiliary gas used in the steady-state contour cutting, or after the auxiliary gas type is switched, the auxiliary gas pressure is transitioned along the cutting path according to the following formula: ； In the formula, For the progress of the journey The auxiliary gas pressure at that time; The pressure of the auxiliary gas used to penetrate the thick plate; The auxiliary gas pressure used for the steady-state contour cutting; This refers to the progress of the journey.

8. The method for graded perforation and progressive cutting of thick plate laser cutting according to claim 4, characterized in that, The level threshold and the slope threshold are obtained through pre-calibrated perforation tests: in multiple perforation tests, the values ​​of the sliding average and the rate of change under the conditions of penetration and non-penetration are recorded respectively; the level threshold is a value that is higher than the sliding average under the condition of non-penetration and lower than the sliding average under the condition of penetration; the slope threshold is a statistical upper limit value of the absolute value of the rate of change in the penetration stabilization stage, or a value that ensures that the misjudgment rate under the conditions of penetration and non-penetration is not higher than a preset misjudgment rate.

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