Super-large-diameter deep hole trepanning machining method capable of preventing core part from drooping

Abstract

The invention relates to an ultra-large-diameter deep hole trepanning processing method capable of preventing a core part from drooping, belongs to the technical field of deep hole processing, and solves the problems that the core part is easy to drop and deflect due to dead weight, the processing coaxiality is out of tolerance, a core part material is broken or a cutter is damaged and the like during the existing ultra-large-diameter (more than 500mm) and ultra-long (more than 8m) pipe blank deep hole trepanning. The method comprises the following steps: carrying out reference ring belt processing and dynamic balance adjustment on a pipe blank; a specific anti-vibration cutter bar system is used for sectional trepanning; the pipe blank is paused when being machined to the position of 2 / 3 of the total length, and a supporting ring is cushioned below the core material in the machined hole so as to provide radial supporting; then the pipe blank is turned over, and jacking is conducted from the other end till the pipe blank is through; and finally, the complete core material is taken out, and finish machining is conducted on the inner hole. According to the invention, the core part is prevented from drooping through the intervention of the support ring, the high-coaxiality (less than or equal to 0.5 mm) trepanning processing of the deep hole of the ultra-large-diameter and ultra-long pipe blank is realized by combining dynamic balance adjustment and a segmented processing strategy, and the complete recovery of the core part material is ensured.

Description

Technical Field

[0001] This invention relates to the field of deep hole machining technology, and in particular to a method for machining ultra-large diameter deep hole bushings to prevent core sagging. Background Technology

[0002] Deep hole sleeve machining of ultra-large diameter (Φ500mm and above) and ultra-long (8 meters and above) tube blanks or forgings is a critical process in the manufacturing of large-scale nuclear power, hydropower, and chemical equipment. Unlike conventional deep hole machining, this type of sleeve process creates a huge core material of the same length as the workpiece. As the sleeve depth increases, this core material loses its bottom support and sags significantly under its own weight. This core problem severely restricts machining accuracy and safety.

[0003] Existing nesting processes have significant shortcomings in addressing this problem: most methods focus only on optimizing the tool and cutting parameters, lacking systematic process countermeasures for core sagging and its resulting chain of problems. Specifically: First, core sagging alters the relative position between the tool and the workpiece, causing the nesting path to deviate, resulting in excessive coaxiality of the final machined inner hole, failing to meet the stringent requirements of high-end equipment. Second, the sagging core material can rub against or even jam against the inner wall of the tool crown, drastically increasing the cutting torque. This can lead to abnormal tool wear or, in severe cases, tool breakage or core fracture. Third, current technologies lack effective intermediate support for the core material during machining, typically only mitigating the problem through conservative strategies such as reducing feed rate and segmented machining, which severely sacrifices machining efficiency and fails to fundamentally solve the problem.

[0004] Therefore, there is an urgent need for a high-precision, high-efficiency nesting method that can overcome the above-mentioned defects and is suitable for ultra-large diameter deep holes with diameters of Φ500mm and above. Summary of the Invention

[0005] Based on the above analysis, the present invention aims to provide a method for machining ultra-large diameter deep holes by preventing core sagging, so as to at least solve one of the problems in the prior art caused by the sagging of the core material due to its own weight, such as skewed nesting path, excessive machining coaxiality, increased cutting load, and even core material jamming or breakage.

[0006] On one hand, embodiments of the present invention provide a method for machining ultra-large diameter deep hole bushings to prevent core sagging, used for machining tube blanks with an inner diameter greater than 500 mm and an axial length greater than 10 meters, characterized by comprising the following steps:

[0007] S1. Machining the alignment ring and center support ring on the outer circle of the tube blank;

[0008] S2. Mill both ends of the tube blank and machine the infeed grooves respectively;

[0009] S3. Assemble the auxiliary body and the nesting tool body on the deep hole drilling machine;

[0010] S4. Install the counterweight on the outer circle of the tube blank and clamp it;

[0011] S5. Check the coaxiality of the tube blank and adjust the machine tool jaws to ensure that the coaxiality is ≤0.5mm;

[0012] S6. Perform single-end feed machining to 2 / 3 of the total length of the tube blank, and retract the tool in sections during the axial feed to check the tool and clean the chips;

[0013] S7. Insert at least three support rings under the core material in the machined hole, wherein the deepest support ring is located more than 1 / 2 of the total length of the tube blank;

[0014] S8. After rechecking that the coaxiality is qualified, flip the tube blank and perform sleeve machining on the other end until it is connected to the previously machined hole;

[0015] S9. Machining a threaded hole on the end face of the core material and removing the complete core material;

[0016] S10. Finish the through-hole to the required dimensions.

[0017] Furthermore, in step S1, the number of the alignment rings is no less than 2, located within a range of 1-1.5 meters from the end face of the tube blank, with a width of 15-40mm; the number of the center support rings is no less than 2, with a width of 500-800mm; the alignment rings and the center support rings must be fully visible and round in the circumferential direction.

[0018] Furthermore, the feature is that, in step S2, the surface roughness of the bottom end face of the feed groove is ≤ Ra6.3; the major diameter of the feed groove is 10 mm larger than the outer diameter of the nesting cutter body, the minor diameter is 10 mm smaller than the inner diameter of the nesting cutter body, and the groove depth is 50-100 mm.

[0019] Furthermore, in step S3, the step of assembling the auxiliary body and the nesting cutter body includes:

[0020] S31. Remove the original center support end cover of the deep hole drilling machine;

[0021] S32. Replace with a copper bushing that matches the machining of extra-large diameter bushings and pre-tighten with screws;

[0022] S33. After applying lubricant to the connection between the copper sleeve and the boring bar, install the boring bar for the extra-large diameter sleeve;

[0023] S34. Reassemble the center frame end cap and pre-tighten the bolts;

[0024] S35. Install the modular nesting cutter head at the front end of the boring bar, and ensure that the alloy guide key (9) on the outer circular surface of the modular nesting cutter head (6) is reliably fastened in its keyway (2-1) by screws (3);

[0025] S36. Conduct a tail shaft box power test.

[0026] Furthermore, in step S4, the counterweight includes a semi-circular counterweight ring pre-tightened to the outer circle of the tube blank by bolts, and a counterweight plate detachably installed at the outer circle of the counterweight ring; the dynamic balance is adjusted by increasing or decreasing the weight of the counterweight plate.

[0027] Furthermore, in step S6, within the first 300mm of axial feed, the tool is retracted once every 100mm of feed to check the tool condition; in subsequent machining, the tool is retracted once every 500mm of feed to clean up chips.

[0028] Furthermore, in step S7, the support ring is made of nylon, the single-sided gap between the outer diameter of the support ring and the inner diameter of the tube blank is 1-3mm, and the single-sided gap between the inner diameter of the support ring and the diameter of the core material is 1-3mm.

[0029] Furthermore, in step S8, the coaxiality is checked again by using a dial indicator to check the coaxiality between the outer circles at both ends and the machined inner hole, which is required to be no greater than 0.5mm.

[0030] Furthermore, in step S10, the finishing of the inner hole is performed by using a boring head to expand and bore, ultimately ensuring that the inner hole roughness is ≤ Ra6.3.

[0031] On the other hand, the present invention proposes a deep hole bushing machining system for performing the above-described method, the system comprising:

[0032] A counterweight is installed on the outer circle of the tube blank to achieve dynamic balance;

[0033] A support ring is inserted under the core material within the machined hole.

[0034] In addition, an anti-vibration tool holder system, the anti-vibration tool holder system including a boring bar and a modular nesting tool crown, wherein an alloy guide key and a vibration damping wood are provided on the outer circular surface of the modular nesting tool crown.

[0035] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects:

[0036] 1) This invention provides radial support to the core material by inserting a support ring under the core material within the machined hole after it has been nested to a certain depth at one end, directly counteracting its sagging tendency caused by its own weight. This method, combined with high-precision (coaxiality ≤ 0.5mm) inspection and adjustment during key processes (such as initial clamping and after workpiece flipping), solves the problem of skewed nesting paths caused by core sagging, ensuring excellent coaxiality and straightness in ultra-long deep holes.

[0037] 2) This invention compensates for any imbalances that may arise from the workpiece itself or the clamping process by installing a counterweight with adjustable weight and position on the outer circumference of the tube blank, thus achieving dynamic balance during the machining rotation process. This measure, in conjunction with the anti-sagging technology of the support ring, reduces machining resistance, sudden changes in tool load, and the risk of jamming caused by centrifugal vibration and core deflection, making the cutting process more stable and controllable.

[0038] 3) This invention employs a segmented nesting and segmented tool retraction machining process. This not only controls cumulative errors by shortening the depth of continuous machining in a single pass, but also facilitates timely tool condition checks and chip removal during the tool retraction interval. It can prevent chip clogging, promptly detect and replace damaged inserts or guide elements, and avoid abnormal tool wear, chipping, or even workpiece scrapping caused by latent faults, thus improving the safety and consistency of finished product quality in ultra-long stroke nesting machining.

[0039] 4) Addressing the issue that existing technologies often struggle to balance wear resistance and vibration absorption with a single guiding element, this invention employs a composite anti-vibration guiding structure on the outer surface of the modular nesting tool crown, consisting of an alloy guide key and damping wood. The high wear resistance of the alloy guide key provides rigid support, while the damping wood absorbs and attenuates cutting vibrations. This synergistic effect effectively suppresses chatter and runout that easily occur during the machining of ultra-large diameter deep holes, ensuring the dimensional accuracy, straightness, and surface quality of the inner hole.

[0040] 5) This invention assembles a standardized, quickly detachable insert and tool holder on the front face of a modular nesting tool crown. An axial straight groove chip removal channel is opened in the crown body, together forming a high-efficiency cutting and chip removal unit, which improves chip removal smoothness and tool maintenance convenience, and extends tool life. By replacing the tool crown with different radial dimensions, the machining hole diameter can be flexibly adjusted, significantly improving the versatility and economy of the tool holder system.

[0041] 6) This invention addresses extreme working conditions in machining deep holes with ultra-large diameters (>500mm) by employing a composite engagement scheme combining a transmission cam key and screws. The transmission cam key bears the main circumferential cutting torque, preventing relative rotation; the evenly distributed screws provide axial preload, resisting vibration and loosening. Compared to single-connection methods, this composite connection offers higher connection rigidity, stronger anti-loosening capability, and more reliable power transmission, improving connection stability and system lifespan.

[0042] In this invention, the above-described technical solutions can be combined with each other to achieve more preferred combinations. Other features and advantages of this invention will be set forth in the following description, and some advantages may become apparent from the description or be learned by practicing the invention. The objects and other advantages of this invention can be realized and obtained from what is particularly pointed out in the description and drawings. Attached Figure Description

[0043] The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Throughout the drawings, the same reference numerals denote the same parts.

[0044] Figure 1 This is a process flow diagram of the ultra-large diameter deep hole sleeve processing method of the present invention;

[0045] Figure 2 This is a schematic diagram of the anti-vibration tool holder system assembly described in this invention;

[0046] Figure 3 for Figure 2 A schematic diagram of the modular nesting blade crown described in the figure;

[0047] Figure 4 This is a schematic diagram illustrating the working state of the support ring supporting the core material during the sleeve processing of the present invention;

[0048] Figure 5 This is a schematic diagram of the structure of the counterweight described in this invention;

[0049] Figure 6 This is a schematic diagram of the blade mounting structure described in this invention.

[0050] Figure label:

[0051] 1. Anti-vibration tool holder system assembly; 2. Transmission key; 2-1. Keyway; 3. Screw; 3-1. Threaded hole; 4. Support ring; 5. Boring bar; 6. Modular nesting tool crown; 7. Tool holder; 8. Insert; 9. Alloy guide key; 10. Vibration damping wood; 11. Chip removal channel; 12. Counterweight; 13. Clamping bolt; 14. Workpiece; 15. Pressure plate. Detailed Implementation

[0052] Preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings, which form part of this application and are used together with the embodiments of the present invention to illustrate the principles of the present invention, but are not intended to limit the scope of the present invention.

[0053] To address the technical bottlenecks in existing technologies for machining ultra-large diameter deep hole bushings (Φ500mm and above), such as difficulty in vibration control, poor coaxiality, core sagging, poor chip removal, and low machining efficiency, this invention provides a systematic process solution. Through the coordinated control of multiple links including "dynamic balance control, high-precision benchmark, segmented machining, and active support," this invention achieves high-precision (coaxiality ≤0.5mm) and high-efficiency machining.

[0054] On one hand, a specific embodiment of the present invention discloses a method for machining ultra-large diameter deep hole bushings to prevent core sagging, particularly suitable for machining tube blanks with an inner diameter greater than Φ500mm and an axial length greater than 10 meters, such as... Figure 1 As shown, the method includes the following steps:

[0055] S1. Machining the alignment ring and center support ring on the outer circle of the tube blank;

[0056] S2. Mill both ends of the tube blank and machine the infeed grooves respectively;

[0057] S3. Assemble the auxiliary body and the nesting tool body on the deep hole drilling machine;

[0058] S4. Install the counterweight 12 on the outer circle of the tube blank and clamp it;

[0059] S5. Use a dial indicator to check the coaxiality of the tube blank and adjust the machine tool clamps to ensure that the coaxiality is ≤0.5mm;

[0060] S6. Perform single-end feed machining to 2 / 3 of the total length of the tube blank, and retract the tool in sections during the axial feed to check the tool and clean the chips;

[0061] S7. Insert at least three support rings 4 under the core material within the machined hole, as shown in the working state. Figure 4 As shown, radial support is provided for the core material to prevent it from sagging due to its own weight, with the deepest support ring 4 located more than 1 / 2 of the total length of the tube blank.

[0062] S8. After rechecking that the coaxiality is qualified, flip the tube blank and perform sleeve machining on the other end until it is connected to the previously machined hole;

[0063] S9. Machining threaded hole 3-1 on the end face of the core material and removing the complete core material;

[0064] S10. Finish the through-hole to the required dimensions.

[0065] The nesting process described in this method refers to the process of separating a complete cylinder (i.e., core material) with the same diameter as the target inner hole from a solid or thick-walled tube blank through circumferential cutting.

[0066] When implementing, such as Figure 1First, precise benchmark machining of the outer diameter of the tube blank (S1, S2) establishes the positioning and clamping foundation for all subsequent processes. Then, by assembling the auxiliary body and the nesting tool body (S3), hardware support is provided for efficient cutting. Before machining begins, a counterweight 12 is installed for dynamic balancing (S4), and high-precision coaxiality alignment is performed (S5), eliminating systemic vibrations caused by mass eccentricity and high-center rotation at the source. During the nesting process, this invention employs a strategy combining segmented nesting and active support: by machining one end to 2 / 3 (S6) and then switching ends for nesting (S8), the accumulation of elastic deformation caused by the long overhang of the tool is controlled; by inserting a support ring 4 under the core material (S7), the downward torque generated by the core material's own weight is actively counteracted, avoiding friction and interference between the core material and the inner wall of the tool body. These two actions work together to ensure the straightness of the deep hole. Finally, finishing (S10) ensures the dimensional accuracy and surface quality of the inner hole.

[0067] Compared with existing technologies, the solution provided in this embodiment integrates process control, dynamic stability, and structural innovation to form a complete process system:

[0068] First, dynamic balancing (S4) and high-precision coaxiality alignment (S5) eliminate macroscopic vibration sources at the system level. At the same time, the unique composite guide design on the nesting tool crown assembled in step S3 effectively suppresses cutting chatter at the micro level. Together, these three constitute a multi-layered anti-vibration system, which greatly improves the stability of the tool holder-workpiece system under high-speed rotation, thereby enabling the machined hole to have excellent straightness and coaxiality.

[0069] Secondly, the core support structure inserted in step S7 provides continuous radial support for the extra-long core material during processing, effectively preventing sagging and wobbling due to its own weight. This avoids the risks of accelerated tool wear, increased processing resistance, and even jamming. Finally, segmented nesting and end-changing machining (S6, S8) combined with forced segmented tool retraction and chip removal (S6) normalizes chip removal and tool status monitoring during processing, ensuring the continuity and safety of the process. Therefore, it improves overall processing efficiency and consistency in batch production.

[0070] Furthermore, in step S1, the number of the alignment rings is no less than 2 (e.g., 2, 3, 4, 5, or 6), located within a range of 1-1.5 meters (e.g., 1 meter, 1.1 meter, 1.2 meter, 1.3 meter, 1.4 meter, or 1.5 meter) from the end face of the tube blank, and the width is 15-40 mm (e.g., 15 mm, 20 mm, 25 mm, 30 mm, 35 mm, or 40 mm); the number of the center frame rings is no less than 2 (e.g., 2, 3, 4, 5, or 6), and the width is 500-800 mm (e.g., 500 mm, 600 mm, 700 mm, or 800 mm).

[0071] During implementation, these rings need to be machined on a heavy-duty horizontal lathe, ensuring that the alignment ring and the center rest ring are fully polished and rounded in the circumference, i.e., machined until all surfaces are polished and have good roundness. This design enables the center rest of the deep hole drilling machine to obtain a uniform, stable, and high-precision clamping reference, laying a solid foundation for the straightness of subsequent long-stroke machining.

[0072] Furthermore, in step S2, the surface roughness of the bottom end face of the feed groove must be ≤Ra6.3 (e.g., Ra2.5, Ra3.0, Ra4.0, Ra5.0, Ra6.0, Ra6.3, etc.) to reduce impact during cutting. The major diameter of the feed groove must be 10mm larger than the outer diameter of the tool body, and the minor diameter must be 10mm smaller than the inner diameter of the tool body. The groove depth is between 50mm and 100mm (e.g., 55mm, 60mm, 70mm, 80mm, 90mm, 100mm). This dimensional design provides sufficient guiding space for the tool crown, ensuring that it can smoothly and centrally enter the cutting state, effectively avoiding tool damage or initial path deviation caused by groove interference.

[0073] Further, in step S3, the auxiliary body and the nesting tool body are assembled. The key component of this nesting tool body is a modular nesting tool crown, which has a tool holder for mounting the cutting insert and a chip removal channel for chip removal. The steps of assembling the auxiliary body and the nesting tool body include:

[0074] S31. Remove the original center frame end cover of the deep hole drilling machine;

[0075] S32. Replace with a special copper bushing that matches the machining of extra-large diameter bushings, and use screws for pre-tightening and fixing;

[0076] S33. After applying lubricant to the connection between the copper sleeve and the boring bar, install the boring bar specifically designed for this extra-large diameter sleeve.

[0077] S34. Reassemble the center frame end cap and pre-tighten the bolts;

[0078] S35. Install the modular nesting cutter head at the front end of the boring bar, and ensure that the alloy guide key (9) on the outer circular surface of the modular nesting cutter head (6) is reliably fastened in its keyway (2-1) by screws (3);

[0079] S36. Conduct a tail shaft box power test.

[0080] Specifically, in step S33, lubricant should be evenly applied to the mating surfaces of the copper bushing and the boring bar, preferably using a high-pressure resistant special grease. In step S35, the modular bushing cutter head is fixedly connected to the mating flange at the front end of the boring bar via its tail flange and high-strength bolts. All connecting bolts must be tightened twice in a diagonal sequence. In step S36, the tail shaft box power test needs to be conducted under different speeds and loads to verify the smooth operation of the entire transmission system under the torque required for ultra-large diameter bushing.

[0081] Furthermore, in step S4, the counterweight includes a semi-circular counterweight ring pre-tightened to the outer circumference of the tube blank by bolts, and a counterweight plate detachably installed on the outer circumference of the counterweight ring; the dynamic balance is adjusted by increasing or decreasing the weight of the counterweight plate. The weight of the counterweight plate needs to be calculated and tested on-site based on the weight and position of asymmetrical structures (such as nozzles) on the tube blank until there is no significant vibration when the tube blank rotates. This adjustable counterweight method achieves dynamic balance correction for tube blanks with complex structures.

[0082] Furthermore, in step S6, within the first 300mm of axial feed, the tool is retracted every 100mm to check the condition of the insert, carbide guide key, and vibration damping wood; during subsequent machining, the tool is retracted every 500mm to clean chips and inspect the tool. This operation ensures timely chip removal, preventing chip entanglement and compression that could lead to tool breakage, workpiece surface scratches, or even blockage of the chip removal channel. It also facilitates real-time monitoring of tool wear, enabling predictive replacement.

[0083] Furthermore, in step S7, the inserted support ring is made of a non-metallic material with sufficient strength and that is not easily damaged by the machined hole wall, preferably nylon. The single-sided gap between the outer diameter of the support ring and the inner diameter of the tube blank is controlled at 1-3 mm, preferably 2 mm (e.g., 1 mm, 1.5 mm, 2 mm, 2.5 mm, 3 mm), and the single-sided gap between the inner diameter of the support ring and the diameter of the core material is also controlled at 1-3 mm, preferably 2 mm (e.g., 1 mm, 1.5 mm, 2 mm, 2.5 mm, 3 mm). This gap configuration ensures that the support ring can be smoothly inserted and provides stable radial constraint for the core material.

[0084] By placing the deepest support ring at a position exceeding half the length of the tube blank, it provides crucial support for the cantilever section where the core material experiences maximum deflection due to its own weight. This design uses the core material as the load-bearing body and the multiple support rings as elastic fulcrums, transforming the originally prone-to-sagging cantilever beam structure into a stable continuous beam structure, thus suppressing the overall deformation and sway of the core material.

[0085] Furthermore, in step S8, the coaxiality is checked again by using a dial indicator to check the coaxiality between the outer circles at both ends and the machined inner hole, which is required to be no greater than 0.5mm (e.g., 0.1mm, 0.2mm, 0.3mm, 0.4mm, 0.5mm).

[0086] For example, a dial indicator can be attached to the machine tool guide rail, with its probe contacting the pre-machined outer diameter reference surfaces at both ends of the tube blank and the inner wall of the formed tube. Coaxiality is assessed by detecting the radial runout of the tube blank during low-speed rotation. The runout values ​​of the four generatrices (upper, lower, left, and right) are particularly examined, and the maximum value is used as the evaluation criterion.

[0087] By evaluating the spatial consistency between the inner hole axis and the outer circle datum, a basis for controlling the uniformity of the part's wall thickness is provided. This review aims to confirm whether the geometric accuracy of the workpiece-machine tool system still meets the requirements after the initial nesting process. It is a prerequisite for performing subsequent end-change machining, thereby effectively preventing error accumulation and ensuring the overall straightness of the final through hole.

[0088] Furthermore, in step S10, the finishing of the inner hole is performed by using a boring head to expand and bore, ultimately ensuring that the inner hole roughness is ≤ Ra6.3 (e.g., Ra2.5, Ra3.0, Ra4.0, Ra5.0, Ra6.0, Ra6.3, etc.).

[0089] During implementation, a dedicated precision boring head body is used to replace the lower sleeve tool body for precision boring of the through-hole. A single-edged boring bar is preferred for the finishing process, and its cutting parameters need to be adjusted according to the material of the tube blank. For example, when machining high-hardness materials such as titanium alloys and nickel-based superalloys, a relatively low cutting speed and a small feed per revolution should be used to ensure the durability of the cutting edge while obtaining good surface quality.

[0090] This finishing process corrects the microscopic shape errors left over from the nesting process and further improves the straightness of the inner hole axis. Thus, while accurately machining the inner hole dimensions to the tolerance range required by the product drawings, it ensures that the surface roughness consistently meets and exceeds the technical specification of Ra6.3, so as to meet the high standard assembly and use requirements of the final product.

[0091] Furthermore, the tube blank is a high-hardness, difficult-to-machine material, including titanium alloy or nickel-based high-temperature alloy; the modular cutting head used in the sleeve machining can be adapted to the machining requirements of different specifications of internal holes through structural adjustment.

[0092] The method of this invention is particularly suitable for machining difficult-to-machine materials with high hardness and high strength, such as titanium alloys and nickel-based superalloys. This invention includes dynamic balance control, segmented machining vibration reduction, forced chip removal, and a high-rigidity tool system, which can address the challenges posed by the high cutting forces, high cutting temperatures, and severe work hardening tendency of such materials. Simultaneously, the modular tool crown design allows for flexible adaptation to different internal hole machining requirements by changing different specifications of the tool crown or adjusting the radial extension of the insert, thereby achieving versatility and economy in machining tools.

[0093] On the other hand, embodiments of the present invention also propose a deep hole bushing machining system for performing the above-described method for preventing core sagging in ultra-large diameter deep holes. The system includes:

[0094] Counterweight 12 is installed on the outer circle of the tube blank to achieve dynamic balance;

[0095] Use bolt 13 to fasten the counterweight 12;

[0096] Support ring 4 is inserted under the core material inside the machined hole;

[0097] In addition, a vibration-damping tool holder system, the vibration-damping tool holder system including a boring bar 5 and a modular nesting tool crown 6, wherein an alloy guide key 9 and a shock-absorbing wood 10 are provided on the outer circular surface of the modular nesting tool crown 6.

[0098] In implementation, firstly, the dynamic balance of the workpiece 14 system is achieved through the counterweight 12. Then, the anti-vibration tool holder system is activated for nesting, utilizing its composite anti-vibration guiding structure to provide stable guidance and vibration reduction throughout the machining process. When machining reaches a certain depth and the risk of core sagging increases, machining is paused and a support ring 4 is inserted to provide auxiliary support for the core material. Before the workpiece 14 is flipped for docking, the dynamic balance and coaxiality must be checked again. Through the dynamic balance control of the counterweight 12, the vibration suppression and guidance of the anti-vibration tool holder, and the auxiliary stabilization of the support ring 4, a triple guarantee mechanism is formed, effectively addressing the technical difficulties in nesting ultra-large diameter deep holes, ultimately achieving high-precision, high-reliability machining and complete removal of the core material.

[0099] Specifically, the counterweight 12 can compensate for the inherent mass imbalance of the tube blank and its clamping system by increasing or decreasing the number of counterweight plates or adjusting the installation position of the counterweight plates. This eliminates the centrifugal vibration of the workpiece 14 caused by poor dynamic balance, providing a stable rotational reference for subsequent high-precision nesting machining.

[0100] Specifically, the support ring 4 is an independent annular component that is inserted from the end under the core material within the machined hole after the single-end nesting has been machined to a predetermined depth. The support ring 4 maintains minute gaps between its outer diameter and the hole wall, and between its inner diameter and the core material. It is positioned under its own weight and slight external force, and its key function is to provide intermediate radial support for the gradually elongating core material. This design directly resists the sagging tendency of the core material due to its own weight, preventing risks such as nesting path deviation, uneven tool load, and core material jamming caused by sagging.

[0101] Specifically, the anti-vibration tool holder system is the core component for performing cutting, such as... Figure 2 As shown, the core of the anti-vibration tool bar system assembly 1 includes a boring bar 5 and a modular nesting tool crown 6 installed at its front end.

[0102] Combination Figure 3 As shown, the modular nesting cutter crown 6 itself is a ring structure, which is engaged with the front end of the boring bar 5 through the transmission convex key 2 and screw 3 to form a rigidly connected whole.

[0103] Specifically, the transmission key 2 is located at the front end of the boring bar 5 and cooperates with the keyway 2-1 formed at the root of the modular nesting cutter crown 6 to transmit torque; the screw 3 passes through the root of the modular nesting cutter crown 6 and connects to the threaded hole 3-1 on the front end face of the boring bar 5 to provide axial clamping force. This structure ensures the connection rigidity and stability of the cutter crown under heavy-load cutting.

[0104] The modular nesting cutter crown 6 integrates a complete cutting and guiding functional unit: its end is provided with a cutter holder 7 for mounting the cutting blade 8; a chip removal channel 11 is formed inside the ring for chip discharge; more importantly, on the outer circumferential surface of the modular nesting cutter crown 6, at least one alloy guide key 9 and at least one vibration damping block 10 are arranged along the circumference and / or axial direction. The alloy guide key 9 and the vibration damping block 10 are arranged adjacently or alternately to form a composite vibration-resistant guiding structure.

[0105] When implementing, such as Figure 2 As shown, the anti-vibration tool holder system assembly 1 is rotated and fed under the drive of the deep hole drilling machine. The alloy guide key 9 provides macroscopic rigid support and geometric guidance to ensure the straightness of the machining path; while the damping wood 10 absorbs and attenuates cutting vibrations at the microscopic level through its damping characteristics. The two work together, combining rigidity and flexibility, to achieve high wear resistance and high vibration reduction, which are difficult to achieve with a single guide element.

[0106] Specifically, driven by the deep hole drilling machine, the anti-vibration tool holder system uses the boring bar 5 to rotate and axially feed the modular nesting cutter crown 6 at its front end, performing annular cutting on the workpiece 14. During this process, the alloy guide key 9, located on the outer circumference of the cutter crown, has a hardness (e.g., HRC35-55) much higher than that of the workpiece 14 material. It can closely adhere to and slide across the machined inner hole wall, acting as a rigid support and precise guide element, effectively resisting radial off-center loads caused by the enormous cutting force and ensuring the straightness of the machining path. Simultaneously, the vibration damping wood 10 (usually engineering nylon, phenolic resin, or other polymer composite materials) arranged adjacent to or alternating with the alloy guide key 9 possesses certain elasticity and damping characteristics. When the tool holder system generates high-frequency micro-amplitude vibrations due to cutting force fluctuations, material inhomogeneity, or long overhangs, the vibration damping wood 10, through contact friction with the hole wall and its own deformation, can quickly absorb and dissipate vibration energy, thereby suppressing the generation and transmission of vibration.

[0107] Compared to existing technologies that only use cemented carbide guide blocks, the composite guide structure provided in this embodiment creates a synergistic effect through the combination of materials and functions: the alloy guide key 9 provides macroscopic geometric constraints and rigid support for the system, ensuring the straightness of the machining path; while the vibration damping wood 10 absorbs and dissipates vibration energy by introducing vibration damping, thereby improving the microscopic dynamic performance of the system. The synergistic effect of both enhances the overall rigidity of the tool holder system and suppresses harmful vibrations under harsh working conditions of ultra-large diameters and ultra-long strokes. Ultimately, it improves machining accuracy (such as hole straightness and coaxiality) and surface quality (avoiding chatter marks) while enhancing the reliability of the machining process (reducing the risk of chipping, tool deflection, and tool breakage).

[0108] Furthermore, in combination Figure 3 To ensure smooth chip removal and prevent tool damage due to blockage, the modular nesting cutter crown 6 has a chip removal channel 11 inside its crown body. The chip removal channel 11 is preferably a straight groove extending axially along the crown body. The number of chip removal channels 11 can be multiple (e.g., 4, 6, or 8) depending on the diameter of the nesting material, and they are evenly distributed around the circumference. Compared to spiral grooves or other complex flow channels, this straight groove design is simple in structure, easy to manufacture, and provides less resistance to the passage of large volumes of chips.

[0109] Furthermore, to achieve efficient and controllable annular cutting, the front end face of the modular nesting cutter crown 6 is equipped with multiple cutter holders 7, each of which has a positioning structure and is secured by a pressure plate 15 (e.g., ...). Figure 6 As shown), the blade 8 is mounted on the screw 3 or other detachable means and pressed and fixed thereon to achieve reliable clamping and quick replacement of the blade. This structure forms a functional synergy with the composite vibration-resistant guiding structure of the present invention:

[0110] During implementation, multiple inserts 8 are arranged in a ring along the end face of the cutter crown. The cutting force is balanced with the composite guide surface composed of alloy guide keys 9 and vibration-damping wood 10. The composite anti-vibration guide structure suppresses machining vibration, providing a stable working environment for the inserts 8 and improving their service life and cutting reliability, especially when machining high-hardness materials, in ultra-large diameter nesting. Simultaneously, the guiding stability ensures that the inserts 8 can work on a path closer to the theoretical trajectory, achieving precise control over the size and shape of ultra-large diameter inner holes.

[0111] Furthermore, the alloy guide key 9 is fastened to the keyway 2-1 opened on the outer circumference of the modular nesting tool crown 6 by screws 3. This connection method is firm and reliable, and easy to replace after the guide key wears out. The vibration damping wood 10 can be fixed by interference fit, adhesive, or screws 3. The mounting surface of the vibration damping wood 10 can be slightly higher than the working surface of the alloy guide key 9 in the free state, so that the vibration damping wood 10 can generate a certain amount of pre-compression after being installed in the inner hole, thereby ensuring that it always participates in guiding and vibration damping.

[0112] Furthermore, the mounting surface of the shock-absorbing wood 10 and the working surface of the alloy guide key 9 together form the composite guide outer circle of the modular nesting cutter crown 6. The diameter of this outer circle is slightly smaller than the target machining hole diameter, forming a reasonable guide clearance.

[0113] Furthermore, the transmission key 2 mates with the keyway 2-1 at the front end of the boring bar 5, primarily for transmitting torque and bearing circumferential force; the screw 3 mates with the threaded hole 3-1 at the root of the modular nesting tool crown 6, primarily for providing axial tension and eliminating gaps between the mating surfaces. This combination of key-transmitted torque and screw-3-provided clamping connection, compared to a single connection method, offers higher connection rigidity, stronger anti-loosening capability, and more reliable power transmission, making it an effective measure for achieving high-rigidity engagement of heavy-duty, large-diameter tool holders.

[0114] Furthermore, the sum of the axial coverage lengths of the alloy guide key 9 and the damping wood 10 is not less than 200 mm. Multiple sections of guide keys and damping wood 10 can be provided, distributed continuously or intermittently in the axial direction, but the total effective guide length must meet this lower limit. This guide length, significantly greater than that of conventional deep hole machining, provides sufficient straightening for ultra-long stroke machining, further suppressing radial drift of the tool holder, and is one of the key design features for ensuring hole straightness.

[0115] Furthermore, to accommodate the machining dimensions of this system, the diameter of the boring bar 5 is greater than 400mm. This matches the ultra-large diameter (>Φ500mm) nesting conditions targeted by this invention, and its structural rigidity and load-bearing capacity are unmatched by conventional small-diameter boring bars 5.

[0116] Furthermore, to enhance the versatility and economy of the tool holder system, the modular nesting cutter head 6 adopts a customizable design. By replacing the cutter head body with one of different radial base dimensions, or adjusting the radial extension of the insert 8 on the tool holder 7, nesting machining of different hole diameters within a certain range can be achieved. This design allows a single boring bar 5 system to adapt to various product specifications, significantly reducing equipment investment costs and tooling preparation time. Simultaneously, the insert 8 groove shape and guide key layout can be specifically adjusted for the material properties of different workpieces 14, thereby flexibly meeting the differentiated machining needs of key components in multiple high-end manufacturing fields such as aerospace, energy, and chemical engineering.

[0117] The alloy guide key 9 is not limited to a certain hard alloy, but can also be a cermet, cubic boron nitride (PCBN) polycrystalline material or other high hardness and high wear resistance materials.

[0118] The material of the damping wood 10 is not limited to nylon, but can also be polyurethane, modified epoxy resin board, or composite material impregnated with damping liquid, as long as it has the required damping characteristics and sufficient durability.

[0119] The alloy guide key 9 (key) and the shock-absorbing wood 10 (wood) can be arranged in the circumferential direction in an alternating pattern of one key and one wood, or in a group distribution of multiple keys and multiple woods. The specific quantity and layout can be optimized according to the vibration spectrum and stability requirements in actual processing.

[0120] The boring bar 5 can be a solid body or a hollow rod made of thick-walled seamless steel pipe. The latter can reduce the overall weight while ensuring rigidity.

[0121] In summary, this invention solves the technical challenges of machining deep holes with ultra-large diameters (> Φ500 mm) and ultra-long strokes (> 8 meters) through an innovative anti-vibration tool holder system and supporting processing methods. The system, with its composite anti-vibration guiding structure consisting of alloy guide keys 9 and vibration-damping wood 10, suppresses machining vibrations and improves the dynamic stability and rigidity of the tool holder system under ultra-large diameter conditions. Simultaneously, the modular tool crown design allows for flexible adaptation to machining internal holes of different specifications, enhancing the equipment's versatility and economy. At the process level, the timely intervention of the support ring 4 resists the sagging of the core material due to its own weight; combined with precise dynamic balancing adjustments and a segmented machining strategy, high coaxiality (≤ 0.5 mm) precision nesting of deep holes in ultra-long tube blanks is achieved. Ultimately, this invention, while ensuring high precision and high reliability, achieves complete core material recovery, providing a complete solution for the efficient machining of large, critical components.

[0122] The present invention will be described in more detail below through specific embodiments. These embodiments are merely descriptions of the best implementation of the invention and do not limit the scope of the invention in any way.

[0123] Example 1

[0124] The object to be processed in this embodiment is a solid forging of 34CrNi3MoV alloy steel with an outer diameter of Φ3000mm and a length of 10000mm. The inner diameter of the target blank is Φ500mm.

[0125] A method for machining ultra-large diameter deep hole bushings to prevent core sagging includes the following steps:

[0126] S1: Machining a 30mm wide alignment ring at each of the two end faces, 1.5 meters away; machining two 600mm wide center support rings at the middle position. All rings are machined circumferentially until they are completely smooth and round.

[0127] S2: The major diameter of the feed grooves at both ends is Φ510mm, the minor diameter is Φ380mm, the groove depth is 80mm, and the surface finish of the groove bottom is Ra2.5.

[0128] S3: Assemble the auxiliary body and the nesting tool body on the deep hole drilling machine: Remove the original center frame end cover of the deep hole drilling machine; replace it with a copper sleeve that matches the ultra-large diameter nesting machining and pre-tighten it with screw 3; apply lubricant to the connection between the copper sleeve and the boring bar 5, and then install the ultra-large diameter nesting boring bar 5; reassemble the center frame end cover and pre-tighten it with bolts; install the modular nesting tool crown 6 at the front end of the boring bar 5; finally, conduct a tail shaft box power test.

[0129] S4: Install and clamp the counterweight 12 on the outer circle of the tube blank. The counterweight 12 includes a semi-circular counterweight ring pre-tightened to the outer circle of the tube blank by bolts. Due to the good roundness of the forging, dynamic balance is achieved by installing only the counterweight ring without adding an additional counterweight plate.

[0130] S5: Use a dial indicator to check the coaxiality of the tube blank and adjust the machine tool jaws to adjust the coaxiality to 0.04mm.

[0131] S6: Perform single-end feed machining to 2 / 3 of the total length of the tube blank. During the axial feed, strictly retract the tool in segments: within the first 300mm, retract the tool once every 100mm of feed and check the tool condition; in subsequent machining, retract the tool once every 500mm of feed and clean up the chips.

[0132] S7: Insert four nylon support rings 4 with an outer diameter of Φ498mm and an inner diameter of Φ502mm into the core material inside the machined hole, with the deepest point located at a position more than 1 / 2 of the total length (i.e., more than 5000mm).

[0133] S8: After checking the coaxiality (0.4mm) again with a dial indicator and confirming it is qualified, flip the tube blank and perform sleeve machining on the other end until it is connected to the previously machined hole.

[0134] S9: Machining a threaded hole 3-1 on the end face of the core material and removing the complete core material.

[0135] S10: Finish the through-hole to the required dimensions. Use a boring head for reaming and boring, resulting in a final inner hole surface roughness of Ra2.8 and a straightness of 0.12mm / length.

[0136] A deep hole bushing machining system for performing the above-described method, the system comprising:

[0137] Counterweight 12 is installed on the outer circle of the tube blank to achieve dynamic balance;

[0138] Support ring 4 is inserted under the core material inside the machined hole;

[0139] In addition, a vibration-damping tool holder system, the vibration-damping tool holder system including a boring bar 5 and a modular nesting tool crown 6, wherein an alloy guide key 9 and a shock-absorbing wood 10 are provided on the outer circular surface of the modular nesting tool crown 6.

[0140] Specifically, the boring bar 5 is a thick-walled hollow alloy steel rod with a diameter of Φ430mm. The modular nesting tool crown 6 is connected to the front end of the boring bar 5 through the flange at its root, and is rigidly engaged with the front end of the boring bar 5 by means of a transmission key 2 and eight M16 high-strength screws 3.

[0141] like Figure 3 As shown, on the outer circumferential surface of the modular nesting cutter crown 6, four sets of YG8 carbide (HRC50 hardness) alloy guide keys 9 and four sets of MC nylon vibration damping blocks 10 are arranged circumferentially, alternating evenly in a "one key, one block" configuration. The axial length of each alloy guide key 9 and vibration damping block 10 is 120mm, with a total guiding length of 960mm. On the front end face of the cutter crown, eight cutter holders 7 are evenly installed circumferentially, and each cutter holder 7 is fastened with a PCBN material cutting insert 8 by a locking bolt 13. The inner ring of the cutter crown also has a chip removal channel 11 for chip discharge.

[0142] Example 2

[0143] The object to be processed in this embodiment is an INCONEL 718 nickel-based high-temperature alloy tube blank with an offset nozzle, with an outer diameter of Φ2000mm, a length of 11000mm, and a target inner hole of Φ500mm.

[0144] The only difference between the processing method and Example 1 is that in step S4, three counterweight plates with a total weight of 150kg are installed on the counterweight ring on the symmetrical side of the nozzle to achieve dynamic balance. In step S6, during the first 300mm of axial feed, when the tool is retracted every 100mm of feed, micro-chipping of the outer insert 8 is found. After timely replacement, the tool returns to normal.

[0145] The deep hole sleeve processing system used is the same as that in Example 1.

[0146] Result: The machining was successfully completed. The final coaxiality was 0.45mm, the straightness was 0.15mm / length, the core material was removed without jamming and was completely removed, and the surface roughness of the inner hole after finishing was Ra3.0.

[0147] Example 3

[0148] The processing object and processing method steps in this embodiment are exactly the same as those in Embodiment 1.

[0149] The deep hole sleeve processing system used has the same counterweight 12 and support ring 4 as in Example 1.

[0150] The difference lies in the specific layout of the composite anti-vibration guide structure in the anti-vibration tool holder system assembly 1: on the outer circular surface of the modular nesting tool crown 6, the alloy guide key 9 and the shock-absorbing wood 10 are symmetrically distributed in a "two keys and two woods" group.

[0151] Results: The machining process was smoother, and the uniformity of circumferential resistance was better. The final machining effect was comparable to that of Example 1, with a final coaxiality of 0.4 mm, an inner hole straightness of 0.11 mm / length, and a surface roughness of Ra2.7.

[0152] Comparative Example 1

[0153] This comparative example uses the same workpiece 14 and deep hole sleeve machining system as in Example 1, but the support ring 4 padding step (S7) is not performed. When machining to about 2 / 3 depth, a significant increase in feed resistance is felt. After continuing machining to the breakthrough point, deep marks of friction between the core material and the inner wall of the sleeve rod are found in the middle.

[0154] The results showed that the straightness of the inner hole was out of tolerance (0.55mm / total length), and the core material was partially bent, making it unusable for other purposes.

[0155] Comparative Example 2

[0156] This comparative example uses the same INCONEL 718 billet and deep hole sleeve machining system as Example 2, but step S4 (counterweight 12 was not installed and adjusted) was not performed. After machining started, the machine tool and workpiece 14 system vibrated significantly, forcing a shutdown. Normal machining was only possible after step S4 was re-executed and dynamic balance was achieved.

[0157] Comparative Example 3

[0158] This comparative example uses the same workpiece 14 as in Example 1, but employs a conventional rigid tool holder with only a carbide guide key 9 installed, without the shock-absorbing wood 10.

[0159] Results: A high-frequency whistling sound was audible during the machining process, and micro-vibration marks were visible to the naked eye on the hole wall. The final inner hole roughness was only Ra5.6, and the straightness was 0.25mm / total length.

[0160] Characterization results and analysis

[0161] The characterization results of the above-described embodiments and comparative examples are shown in Table 1 below.

[0162] Table 1. Comparison of processing effects between the examples and comparative examples

[0163]

[0164] As can be seen from Table 1, in Examples 1-3 using the complete technical solution of this invention, the final coaxiality is better than 0.5 mm, the straightness is better than 0.15 mm / length, the inner hole roughness reaches Ra3.0 or better, the core material is in good condition and usable, and no jamming or vibration problems occur during processing. In contrast, Comparative Examples 1-3, due to the omission of core support, dynamic balancing correction, or replacement of the composite anti-vibration guide structure, respectively, resulted in serious deviations in coaxiality and straightness, deterioration of inner hole roughness, scrap or damage to the core material, and problems such as high feed resistance or severe vibration during processing. This demonstrates the necessity of the synergistic effect of the various technical features of this invention.

[0165] In summary, this invention solves the problem of machining deep hole sleeves with ultra-large diameters of Φ500mm and above through a complete, systematic and mutually supportive process and equipment solution, providing a reliable technical guarantee for achieving high-quality and mass production of high-end large components.

[0166] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for machining ultra-large diameter deep hole bushings to prevent core sagging, used for machining tube blanks with an inner diameter greater than 500 mm and an axial length greater than 8 meters, characterized in that... Includes the following steps: S1. Machining the alignment ring and center support ring on the outer circle of the tube blank; S2. Mill both ends of the tube blank and machine the infeed grooves respectively; S3. Assemble the auxiliary body and the nesting tool body on the deep hole drilling machine; S4. Install the counterweight (12) on the outer circle of the tube blank and clamp it; S5. Check the coaxiality of the tube blank and adjust the machine tool jaws to ensure that the coaxiality is ≤0.5mm; S6. Perform single-end feed machining to 2 / 3 of the total length of the tube blank, and retract the tool in sections during the axial feed to check the tool and clean the chips; S7. Insert at least three support rings (4) under the core material in the machined hole, wherein the deepest support ring (4) is located more than 1 / 2 of the total length of the tube blank; S8. After rechecking that the coaxiality is qualified, flip the tube blank and perform sleeve machining on the other end until it is connected to the previously machined hole; S9. Machining a threaded hole (3-1) on the end face of the core material and removing the complete core material; S10. Finish the through-hole to the required dimensions.

2. The method for machining ultra-large diameter deep hole bushings according to claim 1, characterized in that, In step S1, there shall be no fewer than two alignment rings, located within 1-1.5 meters from the end face of the tube blank, with a width of 15-40 mm; there shall be no fewer than two center support rings, with a width of 500-800 mm; the alignment rings and center support rings shall be fully visible and round in the circumferential direction.

3. The method for machining ultra-large diameter deep hole bushings according to claim 1, characterized in that, In step S2, the surface roughness of the bottom end face of the feed groove is ≤ Ra6.3; the major diameter of the feed groove is 10mm larger than the outer diameter of the nesting cutter body, the minor diameter is 10mm smaller than the inner diameter of the nesting cutter body, and the groove depth is 50-100mm.

4. The method for machining ultra-large diameter deep hole bushings according to claim 1, characterized in that, Step S3, the step of assembling the auxiliary body and the nesting cutter body includes: S31. Remove the original center support end cover of the deep hole drilling machine; S32. Replace with a copper bushing that matches the machining of extra-large diameter bushings and pre-tighten with screws (3); S33. After applying lubricant to the connection between the copper sleeve and the boring bar (5), install the boring bar (5) for the extra-large diameter sleeve; S34. Reassemble the center frame end cap and pre-tighten the bolts; S35. Install the modular nesting cutter head (6) at the front end of the boring bar (5) and ensure that the alloy guide key (9) on the outer circular surface of the modular nesting cutter head (6) is reliably fastened in its keyway (2-1) by screws (3); S36. Conduct a tail shaft box power test.

5. The method for machining ultra-large diameter deep hole bushings according to claim 1, characterized in that, In step S4, the counterweight (12) includes a semi-circular counterweight ring pre-tightened on the outer circle of the tube blank by bolts, and a counterweight plate detachably installed on the outer circle of the counterweight ring; the dynamic balance is adjusted by increasing or decreasing the weight of the counterweight plate.

6. The method for machining ultra-large diameter deep hole bushings according to claim 1, characterized in that, In step S6, within the first 300mm of axial feed, the tool is retracted once every 100mm of feed to check the tool condition; in subsequent machining, the tool is retracted once every 500mm of feed to clean up chips.

7. The method for machining ultra-large diameter deep hole bushings according to claim 1, characterized in that, In step S7, the support ring (4) is made of nylon, the single-sided gap between the outer diameter of the support ring (4) and the inner diameter of the tube blank is 1-3mm, and the single-sided gap between the inner diameter of the support ring (4) and the diameter of the core material is 1-3mm.

8. The method for machining ultra-large diameter deep hole bushings according to claim 1, characterized in that, In step S8, the coaxiality check is performed by using a dial indicator to check the coaxiality between the outer circles at both ends and the machined inner hole, which is required to be no greater than 0.5 mm.

9. The method for machining ultra-large diameter deep hole bushings according to claim 1, characterized in that, In step S10, the finishing of the inner hole is performed by using a boring head to expand and bore, ultimately ensuring that the inner hole roughness is ≤ Ra6.

3.

10. A deep hole bushing machining system for performing the method according to any one of claims 1-9, characterized in that, The system includes: A counterweight (12) is installed on the outer circle of the tube blank to achieve dynamic balance; Support ring (4) is inserted under the core material in the machined hole; In addition, an anti-vibration tool bar system, the anti-vibration tool bar system including a boring bar (5) and a modular nesting tool crown (6), wherein an alloy guide key (9) and a shock-absorbing wood (10) are provided on the outer circular surface of the modular nesting tool crown (6).

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