Novel machining process for steel ultra-slender internal threads

Abstract

The invention relates to the technical field of mechanical precision machining, and discloses a novel steel ultra-slender internal thread machining technology which comprises the steps that a workpiece is clamped on a machining platform at a time, internal thread preprocessing is conducted on the workpiece, so that a prefabricated threaded hole with the finish machining allowance is formed, and a measuring probe is adopted for conducting online detection on the prefabricated threaded hole; the detection result of the prefabricated thread representing the actual geometrical morphology and the spatial pose is obtained; and on the basis of the detection result, determining control parameters for dynamically compensating the movement of the machining tool in subsequent finish machining. According to the method, an ideal force-torque model dynamically changing along with the machining depth is established in advance by utilizing an actual hole pattern contour function established through online detection and combining the physical law of material cutting, and then the machining torque monitored in real time is compared with the model, so that machining abnormities such as chip blockage and the like can be judged immediately and accurately.

Description

Technical Field

[0001] The invention relates to the technical field of mechanical precision processing, in particular to a novel processing technology for ultra-slender steel internal threads. Background Art

[0002] Ultra-slender internal steel threads are a common and critical connection or force transmission element in high-end manufacturing fields such as aerospace, precision instruments, and the defense industry. These threads typically require a large aspect ratio, high precision, and high reliability, making their processing and manufacturing a typical technical challenge.

[0003] In the prior art, the machining of such internal threads often follows a more traditional, multi-step, process path. After roughing or pre-machining, the workpiece often needs to be removed from the machine tool for heat treatment, inspection, or transfer to other specialized equipment for subsequent finishing. In this process model, multiple re-clamping and alignment of the workpiece are almost inevitable, and each repositioning introduces new positioning errors that are difficult to completely eliminate. The cumulative effect of these errors results in significant coaxial deviations between the center axis of the finished thread and the workpiece design datum, making it difficult to meet high-precision requirements.

[0004] More critically, traditional machining methods are inadequate when it comes to dealing with the inherent deviations in pre-machined holes. Due to the influence of uncertain factors such as workpiece clamping stress, stress release within the material, and wear of pre-machined tools, the actual center axis of the pre-threaded hole will inevitably deviate from the theoretical machining axis of the machine tool. However, the conventional finishing program is an "open-loop" execution process that can only blindly drive the tool along the ideal path preset by the machine tool and cannot perceive and adapt to the actual posture deviation of the pre-machined hole. This "blind machining" directly leads to uneven distribution of finishing allowances on the circumference of the hole, which in turn causes uneven cutting forces, which not only affects the geometric accuracy of the thread, but also poses a threat to the life of the tool and the stability of the machining.

[0005] In addition, for ultra-slender internal threads, the smooth discharge of chips is always a core technical challenge. Traditional processes mostly rely on fixed parameters set by experience to execute chip breaking or chip removal cycles. This rigid strategy cannot respond to the ever-changing actual cutting conditions deep in the processing. Once the chips are entangled or blocked deep in the hole, the processing torque will increase sharply, which can easily cause the expensive precision tool to break, and even cause the entire complex workpiece to be scrapped, and the process risk is extremely high. At the same time, the tool used for this type of processing itself also has a slender rod-like structure with poor rigidity. It is easy to bend, deform and vibrate under the action of cutting force. The existing technology lacks an effective means to actively suppress such radial forces during the processing process, making it difficult to stably guarantee the thread profile accuracy and surface quality of the final product.

[0006] In summary, when processing ultra-slender internal threads in steel, the existing technology generally has problems such as cumulative errors caused by multiple clamping, inability to adapt to the actual position deviation of the prefabricated hole, lack of intelligent monitoring of the chip removal process, and difficulty in suppressing the radial deformation of the slender tool. On the whole, it is a rigid, experience-dependent open-loop processing mode, and its process stability, product accuracy and automation level need to be improved. Summary of the Invention

[0007] In view of the shortcomings of the existing technology, the present invention provides a new processing technology for ultra-slender steel internal threads, which solves the problems of low processing precision, long processing cycle and a large number of waste and defective products in the existing technology.

[0008] To achieve the above objectives, the present invention is implemented through the following technical solutions: A new processing technology for ultra-slender steel internal threads, comprising the following steps:

[0009] S1. Clamp the workpiece on the processing platform once and perform internal thread pre-processing on the workpiece to form a prefabricated threaded hole with a finishing allowance;

[0010] S2. Performing online detection on the prefabricated threaded hole using a measuring probe to obtain detection results representing the actual geometric shape and spatial posture of the prefabricated thread;

[0011] S3. Based on the detection result, determining control parameters for dynamically compensating the motion of the machining tool in subsequent finishing;

[0012] S4. Apply the control parameters to drive the machining tool to perform final finishing on the prefabricated threaded hole to form a target internal thread.

[0013] Preferably, in step S2, the specific steps of obtaining the detection results representing the actual geometric form and spatial posture of the prefabricated thread are:

[0014] Detecting contour points of the inner wall of the prefabricated threaded hole on multiple depth sections;

[0015] Applying the least square method to perform circle fitting based on the contour points of each depth section to determine the actual center coordinates and actual radius of each section;

[0016] Performing spatial straight line fitting based on the actual center coordinates of each cross section to calculate an actual center axis vector for representing the spatial position of the prefabricated threaded hole;

[0017] Based on the actual radius of each cross section, an actual hole profile function is established to characterize the geometric shape of the prefabricated threaded hole. The actual hole profile function is used to characterize the relationship between the actual radius of the prefabricated threaded hole and its axial depth.

[0018] Preferably, in step S3, the step of determining control parameters for dynamically compensating the motion of the machining tool in subsequent finishing comprises:

[0019] Based on the actual center axis vector, by comparing the actual center axis vector with the ideal machining axis vector of the machine tool, a spatial posture transformation relationship consisting of a three-dimensional rotation matrix and a three-dimensional translation vector is calculated;

[0020] The spatial pose transformation relationship satisfies:

[0021]

[0022] in, is the target position vector of the tool after compensation; is the position vector of the tool on the programmed path; R is the three-dimensional rotation matrix; is the three-dimensional translation vector;

[0023] Based on the actual hole profile function, the cross-sectional area of ​​the cutting layer that varies with the machining depth is calculated, and an ideal force-torque model is established according to the cross-sectional area;

[0024] The ideal force-torque model satisfies:

[0025] T model (z) = K t ·A c (z)+T fric ;

[0026] Among them, T model (z) is the ideal torque at depth z; K t is the material specific torque coefficient; T fric is the friction torque; A c (z) is the cross-sectional area of ​​the cutting layer;

[0027] The spatial posture transformation relationship and the ideal force-torque model are used together as control parameters for subsequent operations.

[0028] Preferably, in step S4, the specific method of applying the control parameters is: the CNC system applies the spatial posture transformation relationship to perform real-time transformation on the programmed path coordinates of the machining tool to generate a compensated machining trajectory that is precisely aligned with the actual center axis of the prefabricated threaded hole.

[0029] Preferably, in step S4, the specific method of applying the control parameters also includes: during the finishing process, real-time monitoring of the actual axial machining torque, and applying the ideal force-torque model to provide a normal range for the actual axial machining torque that dynamically changes with the machining depth; when the actual axial machining torque exceeds the normal range, the preset chip removal control action is automatically executed.

[0030] Preferably, the preset chip removal control action is: driving the machining tool to pause forward rotation, perform a small angle reversal of 5 to 15 degrees, and then resume forward rotation.

[0031] Preferably, in step S4, driving the machining tool to perform final finishing on the prefabricated threaded hole also includes: real-time monitoring of the radial force exerted on the machining tool, and based on the radial force, driving at least one rotating axis of the machining platform to perform micro-linkage compensation to actively suppress the radial force.

[0032] Preferably, the specific method of the micro linkage compensation is:

[0033] According to the vector direction of the monitored radial force, a compensating movement direction opposite to the direction of the radial force is determined, and the at least one rotating shaft is driven to perform the compensating movement.

[0034] Preferably, the processing platform is a five-axis CNC processing center, and the compensating motion is achieved by the linkage of two rotating axes of the processing center.

[0035] Preferably, the specific method of determining the compensation motion amplitude is:

[0036] A proportional-integral control law is applied with the magnitude of the monitored radial force as input to calculate and output the amplitude of the compensating motion performed by the two rotating axes.

[0037] The present invention provides a new processing technology for ultra-slender steel internal threads. It has the following beneficial effects:

[0038] 1. The present invention uses a measuring probe to conduct online detection of the actual geometric shape and spatial posture of the prefabricated threaded hole in one clamping, accurately obtains its real central axis vector, and then calculates the spatial posture transformation relationship for compensation based on the vector, and applies it to the subsequent finishing process, thereby realizing dynamic guidance of the tool motion trajectory, solving the problem of inconsistency between the pre-machined hole axis and the theoretical axis of the machine tool caused by workpiece clamping errors, internal stress deformation and other factors, ensuring that the final thread can be completely coaxial with the actual reference of the hole, and improving the geometric accuracy and position accuracy of ultra-slender internal thread processing.

[0039] 2. The present invention utilizes the actual hole profile function established by online detection and combines it with the physical laws of material cutting to pre-establish an ideal force-torque model that changes dynamically with the processing depth, and uses this as the "healthy state" benchmark during the finishing process. By comparing the real-time monitored processing torque with the model, it can instantly and accurately judge processing anomalies such as chip blockage and automatically trigger the preset chip removal control action, effectively solving the technical problem of poor chip removal in deep slender holes, enhancing the reliability of the processing process, and avoiding the risk of tool damage or workpiece scrapping.

[0040] 3. The present invention monitors the radial force exerted on the machining tool in real time during the finishing process, and drives the rotating axis of the machining platform to perform a micro-linkage to generate a compensating motion in the opposite direction of the monitored radial force. Its control goal is to minimize the modulus of the radial force, effectively suppressing the bending deformation and vibration of the tool under the action of the cutting force, thereby ensuring the accuracy of the thread profile and achieving higher surface quality.

[0041] 4. The present invention integrates all processes such as pre-processing, online detection, and compensation processing in one clamping, constructing a complete closed-loop adaptive processing flow. It ensures accuracy by eliminating the cumulative error introduced by repeated clamping and positioning, and reduces the dependence on operator experience and the need for manual intervention through intelligent control of force-position coordination, thereby improving the overall production efficiency and process success rate of highly difficult processing tasks such as ultra-slender steel internal threads.

[0042] 5. The present invention deeply integrates digital measurement technology, physical modeling technology and advanced control strategies into the machining process, so that the entire machining process is no longer a traditional "open-loop" execution based on theoretical models, but is transformed into a "closed-loop" adaptive process based on the actual state of the workpiece and real-time feedback from machining. It can better cope with uncertainties such as material batch differences, tool wear, thermal deformation, etc., and make the machining process more robust and adaptable. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 A diagram showing the steps of the method of the present invention;

[0044] Figure 2 This is a flow chart of step S1 of the present invention;

[0045] Figure 3 This is a flow chart of step S2 of the present invention;

[0046] Figure 4 This is a flow chart of step S3 of the present invention;

[0047] Figure 5 This is a flow chart of step S4 of the present invention. DETAILED DESCRIPTION

[0048] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0049] Please see the attached Figure 1 -Attached Figure 5 An embodiment of the present invention provides a new processing technology for ultra-slender internal threads of steel, including S1, clamping the workpiece on a processing platform at one time, and pre-processing the internal threads of the workpiece to form a prefabricated threaded hole with a finishing allowance.

[0050] Regarding step S1, in this embodiment, to implement the process described herein, it is first necessary to select a suitable machining platform. Preferably, the machining platform is a high-precision CNC machining center with multi-axis linkage, such as a five-axis CNC machining center. This type of platform can provide the necessary degrees of freedom of motion and high-precision positioning and posture control support for subsequent steps, making it an ideal platform for implementing the technical concepts of the present invention.

[0051] The steel workpiece to be machined is clamped and positioned in a single step on the selected machining platform. This "single clamping" constitutes a key technical prerequisite for the inventive process flow. It means that from this pre-machining step until all subsequent probing and finishing steps are complete, the workpiece's reference position and orientation relative to the machine table remain constant. This approach fundamentally eliminates the cumulative positioning errors introduced by secondary or multiple clamping and alignment of the workpiece in traditional sequential machining, establishing a solid and reliable foundation for achieving high precision throughout the entire process flow.

[0052] After the workpiece is clamped, the machine tool executes a pre-set roughing program while maintaining the clamped state to pre-process the internal threads. This pre-machining operation aims to remove the majority of the material, creating a pre-threaded hole with a complete basic thread profile but with systematically uniform, minimal finishing allowances in critical dimensions (such as the pitch diameter). This pre-threaded hole serves as the reference and benchmark for all subsequent intelligent machining steps.

[0053] Setting the finishing allowance is a key technical aspect of this step. It's not an arbitrary amount, but rather a pre-set value based on the workpiece material, thread specifications, and the characteristics of the subsequent finishing tool. The purpose of this allowance is to ensure that the subsequent final finishing operation only bears a small and stable cutting load.

[0054] This design not only helps protect finishing tools and extend their service life, but more importantly, it creates ideal machining conditions for subsequent dynamic compensation control based on online probing results. Due to the low cutting load, tool deformation and wear during finishing are effectively controlled, making the final finishing a highly controllable "shaping" process primarily aimed at correcting the geometric form and spatial orientation errors of the prefabricated threaded hole. This provides a fundamental process guarantee for achieving the target high-precision, high-quality internal thread.

[0055] S2. Use a measuring probe to perform online detection on the prefabricated threaded hole to obtain detection results that represent the actual geometric shape and spatial posture of the prefabricated thread.

[0056] In step S2, the specific steps for obtaining the detection results representing the actual geometric shape and spatial posture of the prefabricated thread are as follows:

[0057] Detect the contour points of the inner wall of prefabricated threaded holes at multiple depth sections;

[0058] The least square method is used to perform circle fitting based on the contour points of each depth section to determine the actual center coordinates and actual radius of each section;

[0059] Based on the actual center coordinates of each section, a spatial straight line fitting is performed to calculate the actual center axis vector used to characterize the spatial position of the prefabricated threaded hole;

[0060] Based on the actual radius of each section, an actual hole profile function is established to characterize the geometric morphology of the prefabricated threaded hole. The actual hole profile function is used to characterize the relationship between the actual radius of the prefabricated threaded hole and its axial depth.

[0061] Regarding step S2, in this embodiment, after completing the pre-processing of step S1, under the premise of maintaining the original clamping state of the workpiece unchanged, the process flow of the present invention seamlessly transitions to the online detection step. The CNC system replaces the machining tool with a pre-calibrated on-machine measurement probe, such as a contact trigger probe, through the automatic tool change (ATC) function. The core technical meaning of the "online" is that the detection process and the machining process are completed on the same device and in the same clamping, thereby ensuring the identity of the detection coordinate system and the machining coordinate system, and providing a reference for error-free transfer for subsequent high-precision compensation.

[0062] The core task of this step is to precisely measure the physical prefabricated threaded hole formed in step S1 and convert it into a set of digital information that fully represents its true state, namely the "detection results." This detection result acquisition process is automatically controlled by the CNC system and specifically includes the following interrelated sub-steps:

[0063] First, contour point data is collected. A control system drives the measurement probe into the prefabricated threaded hole and performs touch-and-go measurements along its axial direction at at least two predefined depth sections. At each depth section, the probe's lateral probe makes multiple contacts with the inner wall of the prefabricated threaded hole, accurately recording the 3D coordinates of a series of contour points, generating point cloud data that describes the inner wall profile of that section.

[0064] Next, geometric fitting of the cross-sectional features is performed. For each depth section's collected contour point cloud data, the CNC system or higher-level computing unit invokes a built-in geometric fitting algorithm, preferably using the least-squares method for circle fitting. This algorithm aims to calculate the ideal circle with the smallest overall deviation from all contour points of the cross-sectional area, given measurement errors and imperfections in the hole itself. The result of this fitting calculation is the actual center coordinates and radius of each measured cross-sectional area.

[0065] Then, based on the above fitting results, the key parameters characterizing the spatial posture are calculated. The system takes the actual center coordinates of all measured sections as a spatial point set, and performs spatial straight line fitting on the point set. The least squares method can also be used to obtain the best fitting straight line. This calculated spatial straight line is the actual central axis vector used to characterize the overall spatial posture of the prefabricated threaded hole. This vector is not the machining axis of the machine tool theory, but accurately reflects the actual inclination and offset state of the prefabricated threaded hole axis caused by factors such as workpiece clamping error and internal stress release deformation.

[0066] At the same time, a function model is established to characterize the geometric morphology. The system uses the actual radius of each section obtained in the geometric fitting step and its corresponding axial depth coordinates to establish an actual hole profile function through interpolation or function fitting. This function accurately describes the continuous change relationship between the actual radius of the prefabricated threaded hole and its axial depth. This function can digitally characterize the deviation of the hole in the macroscopic geometric morphology, such as the actual taper, drum shape, saddle shape or wave shape. The technical purpose of establishing this function is to provide key geometric input for the subsequent establishment of an ideal force-torque model that changes dynamically with depth, because the changing hole diameter directly leads to a changing cutting allowance.

[0067] Finally, the calculated actual center axis vector and the established actual hole profile function together constitute the complete detection result output in this step.

[0068] S3. Based on the detection results, determine the control parameters for dynamic compensation of the motion of the machining tool in subsequent finishing.

[0069] In step S3, the step of determining the control parameters for dynamic compensation of the motion of the machining tool in subsequent finishing includes:

[0070] Based on the actual center axis vector, by comparing the actual center axis vector with the ideal machining axis vector of the machine tool, a spatial posture transformation relationship consisting of a three-dimensional rotation matrix and a three-dimensional translation vector is calculated;

[0071] The spatial pose transformation relationship satisfies:

[0072]

[0073] in, is the target position vector of the tool after compensation; is the position vector of the tool on the programmed path; R is the three-dimensional rotation matrix; is the three-dimensional translation vector;

[0074] Based on the actual hole profile function, the cross-sectional area of ​​the cutting layer that changes with the machining depth is calculated, and an ideal force-torque model is established based on the cross-sectional area;

[0075] The ideal force-torque model satisfies:

[0076] T model (z) = K t ·A c (z)+T fric ;

[0077] Among them, T model (z) is the ideal torque at depth z; K t is the material specific torque coefficient; T fric is the friction torque; A c (z) is the cross-sectional area of ​​the cutting layer;

[0078] The spatial posture transformation relationship and the ideal force-torque model are used together as control parameters for subsequent operations.

[0079] In this embodiment, step S3 is the core decision-making process that connects the preceding and following stages of the present invention's process flow. Its technical task is to apply the "detection result" data obtained in step S2, which represents the true state of the prefabricated threaded hole, to a series of pre-set algorithm models to generate a set of personalized dynamic compensation control parameters to guide the subsequent finishing steps. This process is automatically completed in the CNC system or a higher-level computer that communicates with it.

[0080] The control parameter determination process specifically includes two parallel core parts, which respectively process the spatial posture deviation and geometric shape deviation of the prefabricated threaded hole:

[0081] The first part involves calculating the spatial position transformation relationship. The technical purpose of this part is to generate macro-control instructions for correcting the tool's motion trajectory and posture to ensure that the tool can accurately move along the actual center axis of the prefabricated threaded hole.

[0082] The calculation process begins by calling the actual center axis vector obtained in step S2. The system then performs a spatial geometric comparison of this vector with the vector of the theoretically ideal machining axis preset in the machine coordinate system (for example, the default tool feed axis in NC programming, typically the Z axis). This comparison accurately determines the spatial deflection angle and position offset of the actual axis of the prefabricated threaded hole relative to the ideal axis.

[0083] Based on this deviation information, the system uses coordinate transformation theory to calculate a spatial pose transformation relationship that can accurately transform the ideal machining axis vector to completely coincide with the actual center axis vector. This relationship is mathematically fully described by a three-dimensional rotation matrix and a three-dimensional translation vector. Its specific application follows the following affine transformation model:

[0084]

[0085] in, is the target position vector that the tool should actually reach in the machine tool coordinate system after transformation compensation; is the position vector of the tool on the original, ideal programming path; R is the three-dimensional rotation matrix, which is used to adjust the tool posture in real time so that its axis is always parallel to the actual center axis of the prefabricated threaded hole; It is a three-dimensional translation vector, which is used to correct the center position of the tool in real time so that it is always located on the actual center axis of the prefabricated threaded hole.

[0086] The second part is the establishment of an ideal force-torque model. The technical purpose of this part is to provide a predictable "health" status benchmark that changes dynamically with depth during the subsequent finishing process. This is used to monitor the machining status in real time, especially to determine whether the chip removal is smooth.

[0087] The model is built by invoking the actual hole profile function obtained in step S2. Based on this function and the known geometry of the finishing tool (such as the nominal diameter of the tap), the system can calculate the instantaneous cutting layer cross-sectional area of ​​the material layer that the tool needs to remove at any axial depth during the finishing process.

[0088] After obtaining the cross-sectional area of ​​the cutting layer that varies with depth, the system establishes an ideal force-torque model based on the preset cutting physics laws for the current workpiece material and tool. Taking axial torque as an example, the model preferably satisfies the following relationship:

[0089] T model (z) = K t ·A c (z)+T fric ;

[0090] Among them, T model (z) is the predicted value of the ideal axial torque that should be generated theoretically when the tool performs normal cutting without abnormal chip accumulation at depth z; K t is the material specific torque coefficient, which is an empirical constant related to factors such as the cutting performance of the workpiece material, the tool rake angle, and the number of edges. It can be obtained through experimental calibration or by referring to a cutting manual. fric is the friction torque, which represents the relatively constant friction torque component generated by the contact between the tool and the non-cutting part of the workpiece during the cutting process; A c (z) is the instantaneous cross-sectional area of ​​the cutting layer at depth z, which directly reflects the real-time change of the cutting load caused by the geometric deviation of the prefabricated threaded hole.

[0091] This model is "ideal" because it describes how the machining torque should vary smoothly with actual changes in hole shape, assuming normal chip evacuation.

[0092] Ultimately, the spatial pose transformation relationship calculated above, along with the established ideal force-torque model, is used to determine the control parameters for subsequent operations. This set of parameters is loaded into the CNC system's memory and serves as the direct control basis for the subsequent adaptive finishing phase, providing complete decision-making information for intelligent machining with force-position coordination.

[0093] S4. Apply control parameters to drive the machining tool to perform final finishing on the prefabricated threaded hole to form the target internal thread.

[0094] In step S4, the specific method of applying the control parameters also includes: during the finishing process, real-time monitoring of the actual axial machining torque, and applying the ideal force-torque model to provide a normal range for the actual axial machining torque that changes dynamically with the machining depth. When the actual axial machining torque exceeds the normal range, the preset chip removal control action is automatically executed.

[0095] The preset chip removal control action is to drive the machining tool to pause forward rotation, perform a small angle reversal of 5 to 15 degrees, and then resume forward rotation.

[0096] In step S4, driving the machining tool to perform final finishing on the prefabricated threaded hole also includes: real-time monitoring of the radial force exerted on the machining tool, and based on the radial force, driving at least one rotating axis of the machining platform to perform micro-linkage compensation to actively suppress the radial force.

[0097] The specific method of micro linkage compensation is:

[0098] According to the vector direction of the monitored radial force, a compensating movement direction opposite to the direction of the radial force is determined, and at least one rotating shaft is driven to perform the compensating movement.

[0099] The processing platform is a five-axis CNC machining center, and the compensation movement is achieved by the linkage of the two rotating axes of the machining center.

[0100] The specific method for determining the compensation motion amplitude is:

[0101] A proportional-integral control law is applied with the magnitude of the monitored radial force as input to calculate and output the amplitude of the compensating motion of the two rotating axes.

[0102] Step S4, in this embodiment, is the final step in the process flow. Its core is to convert the complete "control parameters" determined in step S3 into actual physical movements of the machine tool. This process, through a force-position coordinated closed-loop control strategy, enables intelligent, high-precision finishing of ultra-slender internal threads. This process begins after the machine tool automatically switches to a finishing tool (e.g., a high-precision tap).

[0103] Specifically, the application of the control parameters is reflected in the following mutually coordinated control levels:

[0104] First, there is the guidance of spatial posture and trajectory compensation.

[0105] Throughout the entire process of the finishing tool feeding into the pre-threaded hole, the CNC system continuously and in real time applies the spatial position transformation relationship determined in step S3. This process means that the tool's actual motion trajectory and posture are dynamically guided. It no longer moves along the machine tool's inherent, theoretically ideal axis. Instead, it generates a compensated machining trajectory that is precisely aligned with the actual center axis of the pre-threaded hole detected in step S2. The technical purpose of this control method is to macroscopically eliminate geometric errors introduced by workpiece clamping errors and pre-threaded hole axis drift, ensuring that the final thread and hole datum are completely coaxial.

[0106] Secondly, there is the torque adaptive control of the machining process.

[0107] While the trajectory guidance is in progress, a force / torque sensor integrated into the machine tool spindle or toolholder begins operating, monitoring the actual axial machining torque acting on the tool during the finishing process. The CNC system continuously compares this real-time torque value with the predicted value based on the ideal force-torque model established in step S3, which varies with depth z.

[0108] The ideal force-torque model acts as a dynamic "health benchmark" here, which provides a normal range for the actual axial machining torque at each depth that changes dynamically with the machining depth. When the actual axial machining torque exceeds the normal range, the system interprets this event as a machining abnormality, which is usually caused by a sudden increase in cutting resistance due to the accumulation of chips on the front cutting edge and the failure to be discharged smoothly. To deal with this situation, the system will immediately and automatically execute the preset chip removal control action. A preferred chip removal control action is: the control system drives the machining tool to pause its forward rotation and reverse it at a small angle of 5 to 15 degrees. This action is intended to use the reverse cutting force to break or loosen the bonded chips, and then resume forward rotation to continue normal thread processing. This adaptive control based on real-time force feedback effectively solves the common problem of poor chip removal in the machining of slender internal threads.

[0109] Furthermore, in a preferred embodiment of the present invention, active suppression control of radial force can also be performed in parallel during the finishing process.

[0110] The force / torque sensor not only monitors the axial torque, but also monitors the radial force acting on the tool in real time. For slender tools, radial force is the primary factor causing tool bending, vibration, and final thread profile errors.

[0111] When the system detects that the radial force exceeds a certain threshold, it starts the active suppression program. The program drives at least one rotating axis of the processing platform to perform micro-linkage compensation. On the five-axis CNC machining center, which is the preferred processing platform, the micro-linkage compensation is collaboratively performed by the two rotating axes (such as the A axis and the C axis) of the processing center. The control target of the compensation is to minimize the modulus of the monitored radial force. The implementation principle is that the control system calculates a compensating motion instruction in real time based on the size and direction of the monitored radial force. The instruction drives the rotating axis to generate a compensating motion that can be opposite to the direction of the monitored radial force. This motion is equivalent to applying a dynamic, non-contact "virtual support" to the slender tool, actively offsetting the lateral force acting on the tool, thereby significantly enhancing the stability of the processing process.

[0112] Through the synergistic effect of the above-mentioned three levels of macro-trajectory guidance, axial force adaptive control and radial force active suppression, the process of the present invention can ultimately complete the finishing of ultra-slender steel internal threads efficiently and stably in one clamping to form the target internal threads that meet high-precision requirements.

[0113] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A new processing technology for ultra-slender steel internal threads, characterized in that: The following steps are involved: S1. Clamp the workpiece on the processing platform once and perform internal thread pre-processing on the workpiece to form a prefabricated threaded hole with a finishing allowance; S2. Performing online detection on the prefabricated threaded hole using a measuring probe to obtain detection results representing the actual geometric shape and spatial posture of the prefabricated thread; S3. Based on the detection result, determining control parameters for dynamically compensating the motion of the machining tool in subsequent finishing; S4. Apply the control parameters to drive the machining tool to perform final finishing on the prefabricated threaded hole to form a target internal thread.

2. A novel processing technology for ultra-slender steel internal threads according to claim 1, characterized in that: In step S2, the specific steps of obtaining the detection results representing the actual geometric shape and spatial posture of the prefabricated thread are: Detecting contour points of the inner wall of the prefabricated threaded hole on multiple depth sections; Applying the least square method to perform circle fitting based on the contour points of each depth section to determine the actual center coordinates and actual radius of each section; Performing spatial straight line fitting based on the actual center coordinates of each cross section to calculate an actual center axis vector for representing the spatial position of the prefabricated threaded hole; Based on the actual radius of each cross section, an actual hole profile function is established to characterize the geometric shape of the prefabricated threaded hole. The actual hole profile function is used to characterize the relationship between the actual radius of the prefabricated threaded hole and its axial depth.

3. A novel processing technology for ultra-slender steel internal threads according to claim 2, characterized in that: In step S3, the step of determining the control parameters for dynamically compensating the motion of the machining tool in subsequent finishing includes: Based on the actual center axis vector, by comparing the actual center axis vector with the ideal machining axis vector of the machine tool, a spatial posture transformation relationship consisting of a three-dimensional rotation matrix and a three-dimensional translation vector is calculated; The spatial pose transformation relationship satisfies: in, is the target position vector of the tool after compensation; is the position vector of the tool on the programmed path; R is the three-dimensional rotation matrix; is the three-dimensional translation vector; Based on the actual hole profile function, the cross-sectional area of ​​the cutting layer that varies with the machining depth is calculated, and an ideal force-torque model is established according to the cross-sectional area; The ideal force-torque model satisfies: T model (z)=K t ·A c (z)+T fric ; Among them, T model (z) is the ideal torque at depth z; K t is the material specific torque coefficient; T fric is the friction torque; A c (z) is the cross-sectional area of ​​the cutting layer; The spatial posture transformation relationship and the ideal force-torque model are used together as control parameters for subsequent operations.

4. A novel processing technology for ultra-slender steel internal threads according to claim 1, characterized in that: In step S4, the specific method of applying the control parameters is: the CNC system applies the spatial posture transformation relationship to perform real-time transformation on the programmed path coordinates of the machining tool to generate a compensated machining trajectory that is precisely aligned with the actual center axis of the prefabricated threaded hole.

5. A novel processing technology for ultra-slender steel internal threads according to claim 3, characterized in that: In step S4, the specific method of applying the control parameters also includes: during the finishing process, real-time monitoring of the actual axial machining torque, and applying the ideal force-torque model to provide a normal range for the actual axial machining torque that dynamically changes with the machining depth; when the actual axial machining torque exceeds the normal range, the preset chip removal control action is automatically executed.

6. A novel processing technology for ultra-slender steel internal threads according to claim 5, characterized in that: The preset chip removal control action is: driving the machining tool to pause forward rotation, perform a small angle reversal of 5 to 15 degrees, and then resume forward rotation.

7. The novel processing technology for ultra-slender steel internal threads according to claim 1 is characterized in that: In step S4, driving the machining tool to perform final finishing on the prefabricated threaded hole also includes: real-time monitoring of the radial force applied to the machining tool, and based on the radial force, driving at least one rotating axis of the machining platform to perform micro-linkage compensation to actively suppress the radial force.

8. A novel processing technology for ultra-slender steel internal threads according to claim 7, characterized in that: The specific method of the micro linkage compensation is: According to the vector direction of the monitored radial force, a compensating movement direction opposite to the direction of the radial force is determined, and the at least one rotating shaft is driven to perform the compensating movement.

9. A novel processing technology for ultra-slender steel internal threads according to claim 8, characterized in that: The processing platform is a five-axis CNC processing center, and the compensation movement is achieved by the linkage of two rotating axes of the processing center.

10. A novel processing technology for ultra-slender steel internal threads according to claim 9, characterized in that: The specific method of determining the compensation motion amplitude is: A proportional-integral control law is applied with the magnitude of the monitored radial force as input to calculate and output the amplitude of the compensating motion performed by the two rotating axes.

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