Method for processing closed deep cavity fillet

Abstract

The application relates to the technical field of machining, in particular to a machining method for a closed deep-cavity round corner; the method comprises the following steps: coaxially fixing a tool bar on a boring bar of a horizontal boring machine, the overhanging length of the tool bar being smaller than the depth of a closed inner cavity of a workpiece; the closed inner cavity comprises two oppositely arranged first planes and two oppositely arranged first curved surfaces; fixing the workpiece on a workbench of the horizontal boring machine, and making the axis of the closed inner cavity parallel to a horizontal plane and the first plane vertical to the horizontal plane; controlling the workbench to rotate in the horizontal plane, so that a preset deflection angle is formed between the axis of the closed inner cavity and the axis of the boring bar; driving the boring bar to drive the tool bar to extend into the closed inner cavity, and cutting the to-be-machined position of the round corner by using a tool. The application utilizes the small length-diameter ratio of the short tool bar, improves machining rigidity, solves the tool bar chatter and tool breaking problem caused by the overhanging length of the tool bar being greater than the depth of the closed deep-cavity round corner, and improves machining stability and machining reliability.

Description

Technical Field

[0001] This application relates to the field of machining technology, specifically to a machining method for rounded corners in a closed deep cavity. Background Technology

[0002] In the field of machining, workpieces such as roller end flat sleeves, engine cylinder blocks, and wind turbine bearings have closed internal cavity structures. These structures have only a single opening, with the remaining walls enclosing the internal space. A transition fillet is provided between adjacent walls of the closed internal cavity, extending axially from the open end to the closed end. When the depth-to-diameter ratio of the fillet is greater than or equal to 5, it is called a closed deep cavity fillet.

[0003] Currently, the fillet of a closed deep cavity is usually machined by boring. The machining method is as follows: the workpiece is clamped and fixed on the worktable of the boring machine, so that the axis of the closed inner cavity is parallel to the boring bar; the tool bar is clamped and fixed on the boring bar of the boring machine, and the tool is installed at the end of the tool bar; during machining, the tool bar is inserted into the inner cavity axially from the opening end of the closed inner cavity, and the boring bar drives the tool bar to rotate and feed axially. The fillet cutting is completed by the cooperation of the rotational motion of the tool and the axial feed.

[0004] However, since the diameter of the boring bar is larger than that of the tool holder, in order to avoid interference between the boring bar and the workpiece during machining and to ensure that the tool holder can machine the closed deep cavity fillet, the overhang length of the tool holder must be greater than the depth of the closed deep cavity fillet. This results in an excessively large length-to-diameter ratio of the tool holder and insufficient machining rigidity. During machining, the tool holder is prone to chatter and even tool breakage, which seriously affects the machining quality, machining efficiency and tool life, and results in poor machining reliability. Summary of the Invention

[0005] The purpose of this application is to provide a machining method for closed deep cavity fillets, which solves the problems of tool chatter and tool breakage caused by the tool holder overhang length being greater than the depth of the closed deep cavity fillet during machining.

[0006] The technical solution adopted by this application to solve its technical problem is: A method for machining the fillet of a closed deep cavity, comprising: The tool holder is coaxially fixed on the boring bar of the horizontal boring machine, and the overhang length of the tool holder is less than the depth of the closed inner cavity of the workpiece; the closed inner cavity includes two oppositely arranged first planes and two oppositely arranged first arc surfaces, and the intersection of the first planes and the first arc surfaces is a rounded corner to be machined. The workpiece is fixed on the worktable of a horizontal boring machine, and the axis of the closed inner cavity is parallel to the horizontal plane and the first plane is perpendicular to the horizontal plane. The worktable is controlled to rotate in the horizontal plane so that a preset deflection angle is formed between the axis of the closed inner cavity and the axis of the boring bar; the preset deflection angle is determined according to the geometric dimensions of the closed inner cavity, the tool bar and the boring bar, so that the tool bar and the boring bar extend into the closed inner cavity and the tool at the end of the tool bar reaches the machining position of the rounded corner; The boring bar is driven to extend the tool bar into the closed inner cavity, and the tool is used to cut the fillet to be machined.

[0007] Furthermore, the formula for calculating the preset deflection angle is as follows: (1) in, The preset deflection angle is expressed in degrees. The diameter of the boring bar is expressed in units of 1. ; The diameter of the tool holder is expressed in units of 1. ; The overhang length of the tool holder, in units of... ; The distance between the two first planes, in units of ; The depth of the enclosed cavity, measured in units of ; This is the angle correction amount, in degrees.

[0008] Furthermore, the angle correction amount .

[0009] Furthermore, the aspect ratio of the fillet is greater than 10.

[0010] Furthermore, the diameter of the tool holder is The overhang length of the tool holder is .

[0011] Furthermore, the cutting tool uses a layered cutting method to process the fillet layer by layer, and the cutting depth of each layer is gradually adjusted according to the wear of the cutting tool.

[0012] Furthermore, the horizontal boring machine is a CNC boring and milling machine.

[0013] Furthermore, the CNC boring and milling machine controls the rotation angle of the worktable and the feed trajectory of the tool holder through a CNC program.

[0014] Furthermore, the workpiece is a roller end flat head sleeve.

[0015] Furthermore, the surface hardness of the enclosed inner cavity is HRC40-45.

[0016] The beneficial effects of this application are: 1. This application controls the rotation of the worktable in the horizontal plane to form a preset deflection angle between the axis of the closed inner cavity and the axis of the boring bar. By using a short tool holder with an overhang length less than the depth of the closed inner cavity, the tool can be sent to the machining position of the fillet to complete the cutting process. This machining method breaks through the technical prejudice of the prior art that requires the use of a custom-made extended tool holder. By utilizing the smaller length-to-diameter ratio of the short tool holder itself, the machining rigidity is significantly improved. It fundamentally solves the problems of tool holder chatter and tool breakage caused by the overhang length of the tool holder being greater than the fillet depth of the closed deep cavity, and improves the machining stability and reliability. It is especially suitable for machining the fillet of extreme deep cavities with a depth-to-diameter ratio greater than 10.

[0017] 2. By setting a calculation formula for the preset deflection angle, this application can accurately determine the optimal rotation angle of the worktable based on the geometric dimensions of the closed inner cavity, the tool holder, and the boring bar. This ensures that the tool holder and the boring bar do not interfere when they are inserted into the closed inner cavity, and that the tool at the end of the tool holder can accurately reach the machining position of the rounded corner while retaining an appropriate operating allowance. This achieves the optimal balance between machining feasibility and tool holder rigidity, ensuring a stable and reliable machining process and easy and convenient programming operation. Attached Figure Description

[0018] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of this application and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 It is the design drawing of the workpiece; Figure 2 yes Figure 1 The right view; Figure 3 This is a top view of the process of machining the fillet of a closed deep cavity using the machining method provided in the embodiments of this application; Figure 4 This is a side view of the process of machining the fillet of a closed deep cavity using the machining method provided in the embodiments of this application; Figure 5 It is a state diagram when the deflection angle between the axis of the closed inner cavity and the axis of the boring bar is at the minimum theoretical limit position; Figure 6 It is a geometric diagram showing the relationship between the deflection angle between the axis of the closed inner cavity and the axis of the boring bar when the angle is at the minimum theoretical limit. Figure 7 It is a state diagram when the deflection angle between the axis of the closed inner cavity and the axis of the boring bar is at the maximum theoretical limit position; Figure 8It is a geometric diagram showing the relationship between the deflection angle between the axis of the closed inner cavity and the axis of the boring bar when the angle is at the maximum theoretical limit. Figure 9 This is the design drawing of the roller end flat head sleeve in Example 1; Figure 10 yes Figure 9 Side view; Figure 11 This is a state diagram of the closed deep cavity fillet machining process in Example 1; Figure 12 This is a diagram showing the state of the closed deep cavity fillet machining in Comparative Example 1.

[0020] Figure label: 1-Workpiece; 11-Closed inner cavity; 12-First plane; 13-First arc surface; 14-Rounded corner; 15-Empty tool groove; 2-Bore boring bar; 3-Tool holder; 4-Tool. Detailed Implementation

[0021] The embodiments of this application are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain this application, and should not be construed as limiting this application.

[0022] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application. Unless otherwise specified, the embodiments and features in the embodiments of this application can be combined with each other.

[0023] In the description of this application, the terms "upper," "lower," "left," "right," "front," "rear," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this application. Unless otherwise specified, the above-mentioned orientational descriptions can be flexibly set in actual application, provided that the relative positional relationships shown in the accompanying drawings are satisfied.

[0024] In the description of this application, it should be noted that, unless otherwise expressly specified and limited, the terms "set up," "install," "connect," and "link" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal communication between two components. Those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances.

[0025] In this application, a tool holder with an overhang length greater than the fillet depth of a closed deep cavity is defined as a long tool holder. In existing technologies, when using long tool holders to machine fillets in closed deep cavities, the large length-to-diameter ratio of the long tool holder results in insufficient overall machining rigidity. This leads to chattering of the tool holder during machining, causing significant fluctuations in cutting force and, in severe cases, tool breakage. This not only significantly reduces workpiece machining quality and efficiency and shortens tool life but also results in poor overall machining reliability.

[0026] Tool breakage is a general term for abnormal damage to cutting tools in the field of machining. Considering the chattering conditions during the machining of long tool holders, tool breakage caused by long tool holder machining mainly includes the following four forms: The first type is chipping: When the rigidity of the long tool holder is insufficient, the machining chatter will cause the alternating impact load on the cutting edge of the tool to exceed the strength of the cutting edge structure, eventually causing the cutting edge to break and fall off irregularly; this type accounts for about 70%.

[0027] The second category is breakage: For machining conditions with large allowances of difficult-to-machine materials such as high-temperature alloys and tempered steel, continuous machining chatter will cause the tool holder-tool system to be subjected to alternating bending stress. If chip removal or chip jamming occurs simultaneously during machining, it will further increase the cutting resistance, eventually causing the tool to break off from the shank or the cutting part. This type of case accounts for about 15%.

[0028] The third category is tool tip breakage or edge rolling: In semi-finishing and finishing conditions, machining chatter can cause sudden fluctuations in the cutting depth, resulting in stress concentration at the tool tip. When the tool hardness is too high and the toughness is insufficient, tool tip breakage will occur; when the tool hardness is too low, edge rolling will occur. This type of situation accounts for about 10%.

[0029] The fourth category is damage at the connection between the tool and the tool holder: Under a small number of working conditions, continuous chatter can cause fatigue and loosening at the connection between the tool and the tool holder, resulting in tool misalignment and damage to the workpiece. This also falls under the broad category of tool breakage; this type of situation accounts for about 5%.

[0030] Based on batch production data and typical failure cases of similar long tool holder machining conditions, further evidence is provided to support the machining defects and failure problems of existing technologies. Specific statistical data and case analysis are as follows: 1. Batch processing statistics: In the deep cavity machining of engine cylinder blocks, an automotive parts company uses a solid high-speed steel long tool holder with a length-to-diameter ratio of 8 to process 45# steel tempered workpieces. The nominal tool life is 120 workpieces.

[0031] Actual statistics show that approximately 62% of cutting tools experience tool breakage when processing fewer than 30 workpieces. Of these, 81% of the failed tools exhibited cutting edge chipping, 12% suffered complete tool breakage, and the remaining 7% had damaged tool tips. Under these conditions, the average number of machine downtimes due to tool breakage and tool replacements per shift reached 2.8, directly resulting in an 18% decrease in processing efficiency and a 42% increase in the processing cost per tool.

[0032] 2. Typical Failure Case: A wind turbine hub processing company used a welded long tool holder with a length-to-diameter ratio of 12 to machine deep grooves in wind turbine bearing holes made of low-alloy high-strength steel. The cutting speed was... The feed rate is The amount of knife cuts on the back is Processing Afterwards, the radial runout of the tool holder starts from the initial... Rise to The processing process exhibited noticeable chatter; continuous Subsequently, the cutting edge of the tool chipped off entirely, causing damage to the machined surface of the workpiece. The deep dents ultimately rendered the workpiece unusable, resulting in a direct loss of approximately 12,000 yuan.

[0033] Modal vibration tests were conducted on the long tool holder in this typical failure case. The test results showed that the first natural frequency of the long tool holder was only [missing information]. The cutting excitation frequency during machining is close to the tool's natural frequency, causing resonance. During machining, the tool chatter acceleration amplitude reaches... This is the industry-permitted threshold. 3.7 times that of the previous year; under continuous chatter conditions, the impact stress on the tool is as high as [missing information]. Far exceeding carbide cutting tools The allowable impact stress is the core reason for the frequent tool breakage failure under this working condition.

[0034] To address the technical problems of tool bar chatter and tool breakage during the machining of fillets in enclosed deep cavities using long tool bars, those skilled in the art have conducted extensive research on suppressing tool bar chatter and improving machining stability. Existing improvement schemes mainly focus on three directions: modification of tool bar materials, optimization of tool bar structure, and optimization and adjustment of cutting process parameters. Details are as follows: Tool holder material modification and improvement schemes mainly include two approaches: replacement with high-stiffness lightweight new materials and modification with composite damping materials. The high-stiffness lightweight material approach primarily uses new materials such as carbon fiber composites, high-entropy alloys, and silicon carbide ceramic matrix composites to replace traditional alloy structural steel in tool holder fabrication. Carbon fiber composite tool holders fully utilize the material's high specific modulus by adjusting the fiber layup direction to match the cutting force direction; high-entropy alloy tool holders improve overall strength and hardness by controlling the precipitated phases within the alloy; and silicon carbide ceramic matrix tool holders achieve increased rigidity by relying on the intrinsic high elastic modulus of ceramics. The composite damping material modification approach involves filling the cavity inside a solid tool holder with viscoelastic damping materials such as butyl rubber or polyurethane damping adhesive, or by compositely applying a constraint damping layer to the surface of the tool holder matrix, relying on the internal friction characteristics of the damping material to dissipate cutting vibration energy.

[0035] The effects of the improved tool holder material modification scheme: The specific modulus of carbon fiber composite tool holders can reach 3 to 5 times that of traditional 40Cr steel tool holders. Under the same external dimensions, the static stiffness is increased by more than 40%, and the machining amplitude can be reduced by 30% to 55%. The surface roughness of slender deep cavity parts can be reduced from... Down to However, this material has weak lateral impact resistance, is prone to wear at the tool holder connection point, and has high manufacturing costs, making it only suitable for semi-finishing and finishing applications. High-entropy alloy tool holders have 20%–30% higher strength than high-speed steel and improved wear resistance, but the increase in specific modulus is limited, resulting in an overall vibration reduction effect of only about 15%, and a weak vibration suppression effect on tool holders with large aspect ratios. Silicon carbide ceramic-based tool holders can achieve an elastic modulus of up to [missing value]. The above methods significantly improve rigidity, but the material is brittle and prone to fracture under impact loads, resulting in a very narrow range of applicable working conditions. Modified tool holders infused with damping materials can reduce vibration amplitude by 20% to 40%, showing good suppression of low- and medium-frequency vibrations. However, under high-temperature cutting environments, the damping material is prone to aging and softening, with vibration reduction performance decreasing by more than 50%, leading to insufficient machining stability.

[0036] The optimization and improvement schemes for tool holder structures mainly include two methods: variable cross-section structure optimization and damping vibration reduction structure design. Variable cross-section structure optimization primarily includes stepped variable cross-section structures, continuous conical or parabolic variable cross-section structures, and hollow variable cross-section structures with unequal wall thicknesses. By changing the axial cross-sectional dimensions and wall thickness distribution of the tool holder, the stiffness distribution is reconstructed without increasing the weight of the tool holder, thus optimizing the natural frequency. Damping vibration reduction structure design is mainly divided into passive damping structures and active damping structures, specifically including dry friction damping structures, impact damping structures, nested multi-layer damping structures, and piezoelectric active vibration reduction structures. Flutter suppression is achieved through friction energy dissipation, impact energy dissipation, dielectric damping energy dissipation, or active reverse vibration cancellation.

[0037] The effect of the optimized and improved tool holder structure: the variable cross-section structure can avoid... In the conventional cutting excitation frequency range, increasing the first-order natural frequency of the tool holder by 15%–30% can reduce vibration amplitude by 20%–30%, and improve machining accuracy by 1–2 grades. However, variable cross-section structures significantly increase the stress concentration factor of the tool holder, and the fatigue life of stepped structures is reduced by 15%–25% compared to constant cross-section tool holders. They are prone to breakage under high cutting depths, and irregularly shaped variable cross-section tool holders are more difficult to manufacture, increasing costs by more than 40%. Dry friction damping structures have a suppressive effect on broadband cutting vibrations, reducing amplitude by 30%–50%. They are stable and less affected by temperature, but the friction contact surface is prone to wear, and the damping effect will decrease by 10%–20% after long-term use, requiring regular maintenance. Impact damping structures have a good suppressive effect on high-frequency, high-impact vibrations, reducing amplitude by about 25%, but the vibration reduction effect on low frequencies is less than 15%. Nested multi-layer damping structures can reduce vibration amplitude by 40%–60%, but the structure is complex, the axial dimension is limited, and it is not suitable for scenarios with excessive machining depth. Active damping structures can achieve vibration reduction of over 60% and have strong self-adaptive capabilities, but they require a matching measurement and control system, are complex in structure, and are costly, making them difficult to widely apply.

[0038] Cutting process parameter optimization and adjustment scheme: The main optimization of cutting parameters is achieved by matching the dynamic characteristics of the tool holder. Specifically, this includes reducing cutting parameters such as spindle speed, feed rate, and depth of cut to reduce cutting excitation force; selecting a stable cutting speed through stability lobe diagram to avoid resonance range; optimizing tool path and tool step distance to weaken periodic cutting excitation; and optimizing cutting edge parameters such as tool rake angle, clearance angle, and tool tip radius to reduce overall cutting load and excitation energy.

[0039] The effects of optimizing cutting process parameters: Optimizing process parameters requires no changes to the tool holder structure and material, and increases production costs almost nothing. Proper parameter matching can reduce vibration amplitude by 20%–40%, making it practical for small-batch machining. However, to ensure machining stability, cutting parameters need to be significantly reduced, leading to a 30%–50% decrease in overall machining efficiency, severely restricting batch production efficiency. Furthermore, process optimization can only slightly weaken vibration and cannot compensate for the inherent deficiency of insufficient rigidity in long tool holders. For ultra-large overhang tool holders with a length-to-diameter ratio exceeding 10, even sacrificing machining efficiency to lower parameters still fails to meet the requirements of high-precision, high-reliability machining of deep cavities, and cannot fundamentally eliminate chatter and tool breakage problems.

[0040] As can be seen from the above, material improvement solutions generally suffer from poor adaptability to working conditions, insufficient impact resistance, poor high-temperature stability, or excessively high manufacturing costs, making it difficult to balance vibration reduction performance and reliability. Structural optimization solutions are limited by the confined installation space of the tool holder and the stroke constraints of deep cavity machining; most vibration reduction structures cannot adapt to extreme working conditions with large length-to-diameter ratios, and generally suffer from stress concentration, low fatigue life, complex structures, and high costs. Process parameter optimization solutions do not require tooling modifications, but at the cost of machining efficiency, resulting in limited vibration reduction effects and only addressing the symptoms, not the root cause, failing to fundamentally solve the core problems of insufficient tool holder rigidity, low natural frequency, and susceptibility to resonance.

[0041] Therefore, all three improvement directions mentioned above have obvious technical bottlenecks and cannot solve the chatter failure problem in the machining of closed deep cavities with long tool holders with large length-to-diameter ratios in an efficient, stable, and low-cost manner, and their overall limitations are prominent.

[0042] Based on this, see Figure 1 , Figure 2 , Figure 3 , Figure 4 This application provides a method for machining the fillet of a closed deep cavity, including the following steps: S1. The tool holder 3 is coaxially fixed on the boring bar 2 of the horizontal boring machine. The overhang length of the tool holder 3 is less than the depth of the closed inner cavity 11 of the workpiece 1. The closed inner cavity 11 includes two oppositely arranged first planes 12 and two oppositely arranged first arc surfaces 13. The intersection of the first planes 12 and the first arc surfaces 13 is the machining position of the fillet 14.

[0043] Specifically, the machining tool of this application adopts a horizontal boring machine. The front end of the horizontal boring machine spindle is fixed with a boring bar 2 for clamping the tool bar 3. The boring bar 2 is driven to rotate by the spindle, and its diameter is usually larger than the diameter of the tool bar 3. The diameter of the boring bar 2 determines the maximum diameter that the tool bar 3 can be selected, and also affects the interference boundary when the tool bar 3 extends into the closed inner cavity 11.

[0044] A tool 4 is mounted on one end of the tool holder 3. The tool 4 adopts a disc-shaped structure that matches the outer diameter of the tool holder 3 and is adapted to the size of the fillet 14 to be machined. The other end of the tool holder 3 is coaxially mounted on the boring bar 2. During the installation process, a locking structure is used to achieve rigid fixation, strictly ensuring the coaxiality accuracy of the tool holder 3 and the boring bar 2, meeting the precision machining requirements of the machine tool, and ensuring that the overall structure is tight and free from loosening, radial offset, and axial movement after assembly.

[0045] During the selection and installation of the tool holder 3, the overhang length of the tool holder 3 is strictly controlled, ensuring that its actual overhang length is less than the overall depth of the enclosed inner cavity 11 of the workpiece 1. In this embodiment, the overhang length of the tool holder 3 refers to the overall axial length extending from the mounting end face of the boring bar 2 to the outermost end of the tool 4; this length includes the axial thickness of the tool 4 itself, and is the total effective working length of the tool holder 3 and the tool 4 involved in the machining process. Under cutting conditions, the overhang length of the tool holder 3 is the core factor determining the rigidity of the machining system. The larger the overhang length of the tool holder 3, the worse its rigidity, and the more prone it is to chatter.

[0046] In this application, the tool holder 3 with an overhang length less than the depth of the closed deep cavity fillet is defined as a short tool holder. By using a short tool holder, the length-to-diameter ratio of the tool holder 3 is significantly reduced, thereby maximizing the overall rigidity of the tool holder 3. This suppresses machining failures such as cutting chatter and tool breakage from the structural root, providing structural protection for high-precision and high-stability machining of the closed deep cavity fillet.

[0047] See Figure 1 , Figure 2 The figure shows the design drawing of workpiece 1. Workpiece 1 has a closed inner cavity 11 with one end open and the other closed. A tool groove 15 is provided at the bottom of the closed end of the inner cavity 11, which effectively avoids dead angles in tool processing and provides retraction and chip space for rounded corner cutting. The inner wall of the closed inner cavity 11 is enclosed by two oppositely arranged first planes 12 and two oppositely arranged first arc surfaces 13. The two first planes 12 are parallel to each other, and the two first arc surfaces 13 are symmetrically arranged. A continuous fillet 14 is provided at the intersection of each first plane 12 and the adjacent first arc surface 13. This fillet 14 extends along the entire axial direction of the closed inner cavity 11, continuously extending from the open end to the closed end, forming a closed deep cavity fillet structure with a large depth-to-diameter ratio, which is also the core processing object of this application.

[0048] Before actual processing, the first plane 12 and the first arc surface 13 of the closed inner cavity 11 of workpiece 1 are pre-processed to ensure that the dimensional accuracy and positional accuracy of the first plane 12 and the first arc surface 13 meet the design requirements. The intersection of the processed first plane 12 and the first arc surface 13 is used as the position to be processed for the fillet 14. After the pre-processing of workpiece 1 is completed, it is ready for use.

[0049] S2. Fix workpiece 1 on the worktable of the horizontal boring machine, and make the axis of the closed inner cavity 11 parallel to the horizontal plane and the first plane 12 perpendicular to the horizontal plane.

[0050] Specifically, the pre-processed workpiece 1 is clamped and fixed onto the worktable of a horizontal boring machine. A dedicated positioning fixture is used for precise positioning, and a clamping plate is used to lock and tighten the workpiece, strictly limiting its degrees of freedom to ensure no displacement, loosening, vibration, or shifting throughout the machining process. This eliminates clamping errors that could affect the final machining accuracy. After the workpiece is clamped in place, precise posture correction is performed, fine-tuning the placement of workpiece 1 to ensure the axis of the closed inner cavity 11 is parallel to the machine tool's horizontal plane. Simultaneously, the two first planes 12 of the closed inner cavity 11 are strictly perpendicular to the horizontal plane. This establishes a stable and precise unified machining datum, ensuring consistency in subsequent worktable deflection, tool insertion, feed, and fillet cutting processes. This provides reliable posture assurance for interference-free, high-precision machining of the closed deep cavity fillets.

[0051] S3. Control the worktable to rotate in the horizontal plane so that the axis of the closed inner cavity 11 and the axis of the boring bar 2 form a preset deflection angle; the preset deflection angle is determined according to the geometric dimensions of the closed inner cavity 11, the tool bar 3 and the boring bar 2, so that the tool bar 3 and the boring bar 2 extend into the closed inner cavity 11, and the tool 4 at the end of the tool bar 3 reaches the machining position of the fillet 14.

[0052] See Figure 3 , Figure 4 By controlling the worktable to rotate at a set angle in the horizontal plane, the axis of the boring bar 2 and the axis of the closed inner cavity 11 are changed from parallel to intersecting, forming a preset deflection angle. Under the tilted machining posture with the axis offset, the boring bar 2 and the short tool bar 3 can be inserted into the closed inner cavity 11 without interference, and the tool 4 mounted at the end of the tool bar 3 can be accurately aligned with and completely cover the entire area to be machined of the rounded corner 14, and can reach the rounded corner machining position at the closed end of the inner cavity.

[0053] The preset deflection angle is the optimal interference avoidance angle for matching the workpiece 1 and the tool structure. It is not set arbitrarily. It needs to be determined by comprehensive calculation based on the inner diameter of the closed inner cavity 11, the cavity depth, the position of the fillet, and the geometric parameters of the outer diameter of the boring bar 2 and the tool holder 3. By strictly checking the geometric interference boundary of each structure, it is ensured that the selected deflection angle not only meets the assembly conditions of the boring bar 2 and the tool holder 3 for collision-free feed, but also ensures that the cutting stroke of the tool 4 can completely cover the entire machining range of the fillet 14 from the open end to the closed end.

[0054] This application achieves axis deflection and misalignment feed by rotating the worktable, breaking the technological limitation of traditional coaxial feed which requires increasing the overhang length of the tool holder to process the rounded corners of the closed end of the deep cavity. Under the premise of always maintaining the short overhang and high rigidity of the tool holder, it successfully completes the full-range effective processing of the rounded corners of the closed deep cavity, thus avoiding the interference problem of traditional coaxial feed from the perspective of technological principle.

[0055] S4. Drive the boring bar 2 to drive the tool bar 3 into the closed inner cavity 11, and use the tool 4 to cut the position to be machined on the fillet 14.

[0056] Specifically, the machining system of the horizontal boring machine is started, and the boring bar 2 drives the tool bar 3 and the end tool 4 to extend axially into the closed inner cavity 11. Relying on the rotational motion of the spindle and the axial feed motion of the horizontal boring machine, the cutting edge of the tool continuously cuts the rounded corner to be machined at the connection between the first plane 12 and the first arc surface 13, and completes the overall forming of the rounded corner of the closed deep cavity.

[0057] See Figure 4 After completing the cutting of the rounded corner of the closed deep cavity on one side, the workpiece is kept in its original clamping state. The relative machining position of the tool and the inner cavity can be switched by controlling the worktable to rotate in the opposite direction by the same preset deflection angle. The workpiece can be disassembled and reassembled to complete the cutting of the rounded corner on the other side in sequence.

[0058] For workpieces with four symmetrical rounded corners in a closed inner cavity 11, such as roller end flat head sleeves, the machining of all four rounded corners can be completed in a single clamping state by adjusting the angle of the worktable twice and cooperating with the feed cutting process of the corresponding station. This eliminates the need for frequent disassembly and assembly of the workpiece, effectively reduces the cumulative clamping error, and improves the consistency and machining efficiency of multiple rounded corner machining.

[0059] The machining method for rounded corners of a closed deep cavity provided in this application involves controlling the rotation of the worktable in the horizontal plane to create a preset deflection angle between the axis of the closed inner cavity 11 and the axis of the boring bar 2. By using a short tool holder with an overhang length less than the depth of the closed inner cavity, the tool 4 can be delivered to the machining position of the rounded corner 14 to complete the cutting process. This machining method breaks through the technical prejudice of the prior art that requires the use of a custom-made extended tool holder. By utilizing the smaller length-to-diameter ratio of the short tool holder itself, the machining rigidity is significantly improved. This fundamentally solves the problems of tool holder chatter and tool breakage caused by the overhang length of the tool holder being greater than the depth of the rounded corner of the closed deep cavity, thereby improving machining stability and reliability.

[0060] In some embodiments, the formula for calculating the preset deflection angle is: (1) in, The preset deflection angle is expressed in degrees. The diameter of the boring bar is expressed in units of 1. ; The diameter of the tool holder is expressed in units of 1. ; The overhang length of the tool holder, in units of... ; The distance between the two first planes, in units of ; The depth of the enclosed cavity, measured in units of ; This is the angle correction amount, in degrees.

[0061] Specifically, the calculation of the preset deflection angle is based on the following geometric constraints: 1. Determination of the minimum theoretical deflection angle; See Figure 5 When the deflection angle between the axis of the boring bar 2 and the axis of the closed inner cavity 11 is at the minimum theoretical limit position, the edge of the left end face of the boring bar 2 just contacts the first plane 12 below; at this time, in the figure This is the minimum theoretical deflection angle between the axis of the closed inner cavity 11 and the axis of the boring bar 2.

[0062] See Figure 6 Based on the geometric relationships in the diagram, the minimum theoretical deflection angle is... satisfy: ;in, The radius of boring bar 2 With the radius of tool holder 3 The difference, that is ; The overhang length of tool holder 3 .

[0063] Therefore, we can conclude that: . This represents the lower limit of the deflection angle between the axis of the closed inner cavity 11 and the axis of the boring bar 2. If the actual deflection angle is less than... If this happens, the left end face of the boring bar 2 will interfere with the end face of the opening end of the closed inner cavity 11, causing the boring bar 2 to be unable to extend into the closed inner cavity 11.

[0064] 2. Determination of the maximum theoretical deflection angle; See Figure 7 When the deflection angle between the axis of the boring bar 2 and the axis of the closed inner cavity 11 is at its maximum theoretical limit, the left end of the tool 4 just reaches the left end of the lower first plane 12, and at the same time, the outer cylindrical surface of the boring bar 2 just contacts the right end of the upper first plane 12; at this time, in the figure This is the maximum theoretical deflection angle between the axis of the closed inner cavity 11 and the axis of the boring bar 2.

[0065] See Figure 8 Based on the geometric relationships in the diagram, the maximum theoretical deflection angle is... satisfy: , , , .

[0066] in, The distance between the two first planes ; Depth of the enclosed cavity ; The radius of boring bar 2 With the radius of tool holder 3 The sum of .

[0067] Therefore, we can conclude that: . This represents the upper limit of the deflection angle between the axis of the closed inner cavity 11 and the axis of the boring bar 2. If the actual deflection angle is greater than... If this happens, the outer cylindrical surface of the boring bar 2 will interfere with the opening end of the closed inner cavity 11, or the tool 4 will be unable to reach the machining position of the fillet 14.

[0068] 3. Determining the optimal deflection angle; The above geometric interference analysis shows that the deflection angle between the axis of the closed inner cavity 11 and the axis of the boring bar 2 is... It needs to be limited to the minimum theoretical deflection angle. With the maximum theoretical deflection angle Within the range. However, due to and These are all limit theory perspectives corresponding to geometric boundaries, and cannot be directly applied to actual mass production. When in a critical interference state, the machining safety margin is extremely small, and even minor assembly deviations of equipment and workpieces can easily lead to scratch interference risks; Similarly, being in a critical interference state, and with the machining posture of tool holder 3 being too tilted, the cutting force direction will shift and the force distribution will be uneven, reducing machining stability.

[0069] Therefore, this embodiment selects the optimal machining deflection angle. The specific method for determining the value is as follows: take the minimum theoretical deflection angle. With the maximum theoretical deflection angle The average value is calculated and rounded to the nearest integer angle. Simultaneously, an angle correction amount adapted to actual working conditions is introduced for minor adjustments, effectively accommodating both theoretical interference boundaries and actual machining conditions. That is: .

[0070] Accordingly, by setting a calculation formula for the preset deflection angle, this application can accurately determine the optimal rotation angle of the worktable based on the geometric dimensions of the closed inner cavity 11, the tool holder 3, and the boring bar 2. This ensures that the tool holder 3 and the boring bar 2 do not interfere when they are inserted into the closed inner cavity 11, and that the tool 4 at the end of the tool holder 3 can accurately reach the machining position of the fillet 14 while retaining an appropriate operating allowance. This achieves the optimal balance between machining feasibility and tool holder rigidity, ensuring that the machining process is stable and reliable and the programming operation is simple and easy to perform.

[0071] In some embodiments, the angle correction amount .

[0072] thus, .

[0073] Specifically, the calculation process introduces... Correction amount matching The floor function is equivalent to the floor function. and The average angle is rounded to the nearest integer to obtain the integer deflection angle with the smallest difference from the theoretical average. Using integer angles facilitates CNC program editing and input, matches the indexing accuracy of the horizontal boring machine's table rotation, reduces the programming complexity associated with decimal angles, and avoids positioning deviations caused by insufficient machine tool angle resolution. Meanwhile, The correction amount ensures that the rounded angle value is biased towards the safe side, that is, biased towards... and The position is closer to the middle, which increases the safety margin for interference-free processing.

[0074] It is understandable that this solution is not limited to This single correction amount, the angle correction amount in other embodiments Alternatively, you can choose Different values ​​can be flexibly selected based on the inner cavity size of the workpiece, the outer diameter of the boring bar, the size of the cutting tool, and the machining allowance on site.

[0075] In some embodiments, the aspect ratio of fillet 14 is greater than 10. The aspect ratio of fillet 14 refers to the ratio of the depth of fillet 14 along the axial direction to the diameter of fillet 14.

[0076] When the depth-to-diameter ratio of the fillet 14 is greater than 10, it falls into the category of extreme deep cavity machining. Under such extreme conditions, the existing extended tool holder solution is almost impossible to implement reliably. However, this application adopts a method of using a short tool holder in conjunction with the deflection of the worktable to still stably complete the machining, significantly expanding the technological capability boundary of deep cavity fillet machining.

[0077] In some embodiments, the diameter of the tool holder 3 is The overhang length of the tool holder 3 is .

[0078] Tool holder 3 diameter The selection of the diameter range takes into account machining rigidity, tool versatility, and machine tool spindle interface specifications. This diameter range ensures that the tool holder 3 has sufficient moment of inertia to resist bending deformation caused by cutting forces, while also taking into account compatibility with common CNC boring and milling machine spindle interfaces.

[0079] Tool holder 3 overhang length The selection of the length is an optimization result that minimizes the overhang length to improve rigidity, while ensuring that it can extend into the closed inner cavity 11 and reach the machining position of the fillet 14. This length range is matched with the diameter range to control the length-to-diameter ratio of the tool holder 3 within a certain range. The aspect ratio is much lower than the existing technology with a length-to-diameter ratio of over 15, thus ensuring the rigidity of the machining process.

[0080] Accordingly, a tool holder with a diameter of 3 is adopted. and overhang length The optimized parameter range ensures that the length-to-diameter ratio of tool holder 3 is controlled within a reasonable range, providing sufficient machining rigidity and significantly reducing the risk of chatter and tool breakage. Furthermore, this parameter range matches the specifications of common CNC boring and milling machines, eliminating the need for custom-made tool holders and reducing tool procurement costs and inventory management complexity.

[0081] In some embodiments, the tool 4 processes the fillet 14 layer by layer using a layer-by-layer cutting method, and the cutting depth of each layer is gradually adjusted according to the wear of the tool 4.

[0082] Specifically, layered cutting refers to dividing the total machining allowance of the fillet 14 into several layers, with the tool 4 cutting layer by layer. After each layer is cut, the tool 4 retracts axially or radially before moving on to the next layer. Layered cutting effectively disperses cutting forces, reduces the load on a single cut, and further protects the tool holder 3 and the tool 4.

[0083] The depth of cut for each layer is gradually adjusted according to the wear condition of tool 4. Specifically, in the early stage of tool 4 wear, the cutting edge is sharp, and a larger depth of cut can be used to improve efficiency. As tool 4 wears more severely and the cutting force increases, the depth of cut should be gradually reduced to maintain a stable cutting state and extend the service life of tool 4. The depth of cut can be adjusted through variable parameters in the CNC program, or it can be manually intervened by the operator according to the actual machining conditions.

[0084] Correspondingly, the layered cutting method effectively reduces the single cutting load. Combined with the dynamic adjustment strategy of the cutting depth, the tool 4 maintains a reasonable cutting state throughout the machining process, which further improves machining stability and tool life, and reduces tool consumption costs.

[0085] In some embodiments, the horizontal boring machine is a CNC boring and milling machine, which controls the rotation angle of the worktable and the feed trajectory of the tool holder 3 through a CNC program.

[0086] Specifically, the CNC boring and milling machine has a high-precision CNC positioning system and multi-axis linkage capability, which can accurately control the rotation angle of the worktable in the horizontal plane, as well as the feed trajectory and cutting parameters of the tool holder 3, providing a reliable hardware platform for the implementation of the solution in this application.

[0087] The preset deflection angle is calculated by the CNC program according to formula (1). The system automatically generates table rotation commands, controlling the table to precisely rotate to the target angle. Simultaneously, based on the geometry and dimensions of the fillet 14, the CNC program generates the feed trajectory of the tool holder 3, including axial feed, radial feed, and circular interpolation commands, enabling the tool 4 to precisely machine the fillet 14. For example, the CNC program can be written using macro programs from FANUC or Siemens systems, allowing for flexible adjustment of machining parameters through variable assignment and conditional judgments.

[0088] Correspondingly, the high-precision CNC system of the CNC boring and milling machine ensures precise control of the table rotation angle and accurate execution of the tool feed trajectory, enabling the proposed solution to be stably implemented on standardized CNC machine tools without requiring special modifications to the machine tool. This results in good equipment versatility and process repeatability. By automating the control of the table rotation angle and tool feed trajectory through CNC programming, errors and uncertainties from manual operation are eliminated, significantly improving machining accuracy and consistency. Simultaneously, it reduces the labor intensity and technical threshold for operators, facilitating the standardization and promotion of processes in mass production.

[0089] In some embodiments, workpiece 1 is a roll end flat sleeve. Specifically, the roll end flat sleeve is a key component of the universal joint product. Its enclosed inner cavity 11 has a flat hole feature. The two inner hole flat surfaces are two first planes 12, and the two arc surfaces are two first arc surfaces 13. The four rounded corners 14 where the inner hole flat surfaces and arc surfaces transition to each other are stress concentration areas and interference areas for assembling the roll flat head. They must be precisely machined according to the drawing requirements. The distance between the two oppositely arranged first planes 12 and the radius of curvature of the two oppositely arranged first arc surfaces 13 together determine the position and size of the rounded corners 14.

[0090] In some embodiments, the surface hardness of the closed inner cavity 11 of the roll end flat sleeve is HRC40-45. Specifically, in the current hot strip mill technology upgrade, the inner hole flat surface and arc surface of the roll end flat sleeve are laser clad to improve wear resistance. To ensure the cladding surface size, the actual cladding extends beyond the edge and covers four rounded corners 14, with the cladding material hardness reaching HRC40-45. The high hardness surface places higher demands on the cutting performance of the tool 4, and also intensifies the cutting load on the tool holder 3. Under this condition, if the existing extended tool holder solution is adopted, the chatter and tool breakage problems of the tool holder 3 will be more serious. This application adopts a short tool holder combined with a worktable deflection method, so that the tool 4 can still be stably processed under extreme conditions of high hardness and large cutting load, ensuring the surface quality and dimensional accuracy of the rounded corners 14, and meeting the high reliability requirements of hot strip mill universal joint products.

[0091] The technical solution of this application will be further illustrated below through embodiments and comparative examples.

[0092] Example 1: See Figure 9 , Figure 10 Taking the flat end sleeve of a hot continuous rolling mill project as an example, the depth of the enclosed inner cavity... The distance between the two first planes 12 The radius of the 14-rounded corner The aspect ratio of the fillet radius 14 is .

[0093] See Figure 11 The diameter of boring bar 2 The diameter of tool holder 3 The overhang length of tool holder 3 Angle correction amount .

[0094] Preset deflection angle .

[0095] See Figure 11 Specific machining method: The tool holder 3 is coaxially fixed on the boring bar 2 of the CNC boring and milling machine, and the overhang length of the tool holder 3 is... The flat end of the roller is clamped onto the worktable, so that the axis of the closed inner cavity 11 is parallel to the axis of the boring bar 2 and the first plane 12 is perpendicular to the horizontal plane. The worktable is rotated 16° in the horizontal plane, so that the axis of the closed inner cavity 11 and the axis of the boring bar 2 form a 16° deflection angle. The boring bar 2 is driven to move the tool holder 3 into the closed inner cavity 11, and the tool 4 is used to perform layer-by-layer cutting of the fillet 14. After one fillet 14 is processed, the remaining fillets 14 are processed according to the above processing method.

[0096] During actual machining, the vibration amplitude of the tool holder was controlled within 0.15mm, the cutting process was smooth, no abnormal chatter occurred, and no tool breakage or chipping occurred throughout the process. After machining, the four fillets were inspected using an R31.5 template. The contour tolerance and dimensional accuracy of the fillets met the design requirements of the drawings, and the surface roughness reached Ra3.2, which meets the requirements of the drawings and assembly.

[0097] This small batch processing completed 4 roll end flat head sleeves. No issues such as tool bar chatter, interference, scratches, or tool breakage occurred. The processing time for each piece was approximately 16 hours. The tool showed slight wear after the cumulative cutting length reached 300mm. The operator could continue processing by indexing the tool to a new cutting edge, eliminating the need for frequent tool changes and significantly improving processing continuity.

[0098] Comparative Example 1: See Figure 9 , Figure 10 Taking the flat end sleeve of a hot continuous rolling mill project as an example, the depth of the enclosed inner cavity... The distance between the two first planes 12 The radius of the 14-rounded corner The aspect ratio of the fillet radius 14 is .

[0099] See Figure 12 The diameter of boring bar 2 The diameter of the tool holder The overhang length of the tool holder must be greater than 96. The length-to-diameter ratio of the tool holder is greater than 15. During machining, the axis of the closed inner cavity 11 is always parallel to the axis of the boring bar 2.

[0100] During machining, the tool holder vibrated noticeably, producing a harsh chatter noise. The machining length was [missing information]. This causes the cutting tool to chip and become damaged, and at the same time, the square hole at the front end of the tool holder used to clamp the tool is also damaged. Although the tool holder can be repaired and reused by turning the damaged part and then remachining the square hole, the above process is cumbersome, and the processing time for a single piece is about 80 hours, which cannot meet the production schedule requirements.

[0101] As can be seen from the above, in terms of processing efficiency, the processing time for a single piece in Example 1 is 16 hours, while the processing time for a single piece in Comparative Example 1 is approximately 80 hours; the processing efficiency of Example 1 is improved by about 80%. In terms of tool life, in Example 1, only slight wear occurs after the cumulative cutting length of a single tool reaches 300mm, and the rounding of all 4 products can be completed. In Comparative Example 1, the single tool is damaged due to chipping after processing only 10mm.

[0102] In summary, the machining method for closed deep cavity fillets provided in this application improves upon the problem of insufficient tool rigidity in machining closed deep cavity fillets with large depth-to-diameter ratios by employing a short tool holder in conjunction with a worktable deflection method and implementing parameter design based on the deflection angle formula. Testing shows that the fillet contour accuracy can be controlled within 0.03mm, and the surface roughness reaches Ra3.2. It can achieve one-time forming of closed deep cavity fillets with depth-to-diameter ratios of 15 or higher, eliminating the need for subsequent manual re-grinding. It also improves machining stability, machining efficiency, and tool life, meeting the requirements of mass production.

[0103] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application.

Claims

1. A method for machining the fillet of a closed deep cavity, characterized in that, include: The tool holder (3) is coaxially fixed on the boring bar (2) of the horizontal boring machine. The overhang length of the tool holder (3) is less than the depth of the closed inner cavity (11) of the workpiece (1). The closed inner cavity (11) includes two oppositely arranged first planes (12) and two oppositely arranged first arc surfaces (13). The intersection of the first planes (12) and the first arc surfaces (13) is the machining position with rounded corners (14). The workpiece (1) is fixed on the worktable of the horizontal boring machine, and the axis of the closed inner cavity (11) is parallel to the horizontal plane and the first plane (12) is perpendicular to the horizontal plane. The worktable is controlled to rotate in the horizontal plane so that the axis of the closed inner cavity (11) and the axis of the boring bar (2) form a preset deflection angle; the preset deflection angle is determined according to the geometric dimensions of the closed inner cavity (11), the tool bar (3) and the boring bar (2), so that the tool bar (3) and the boring bar (2) extend into the closed inner cavity (11), and the tool (4) at the end of the tool bar (3) reaches the machining position of the fillet (14); The boring bar (2) is driven to drive the tool bar (3) to extend into the closed inner cavity (11), and the tool (4) is used to cut the fillet (14) to be processed.

2. The method for machining the fillet of a closed deep cavity according to claim 1, characterized in that, The formula for calculating the preset deflection angle is: in, The preset deflection angle is expressed in degrees. The diameter of the boring bar is expressed in units of 1. ; The diameter of the tool holder is expressed in units of 1. ; The overhang length of the tool holder, in units of... ; The distance between the two first planes, in units of ; The depth of the enclosed cavity, measured in units of ; This is the angle correction amount, in degrees.

3. The method for machining the fillet of a closed deep cavity according to claim 2, characterized in that, The angle correction amount .

4. The method for machining the fillet of a closed deep cavity according to any one of claims 1 to 3, characterized in that, The radius of the fillet (14) is greater than 10.

5. The method for machining the fillet of a closed deep cavity according to any one of claims 1 to 3, characterized in that, The diameter of the tool holder is The overhang length of the tool holder is .

6. The method for machining the fillet of a closed deep cavity according to any one of claims 1 to 3, characterized in that, The cutting tool (4) processes the fillet (14) layer by layer using a layered cutting method, and the cutting depth of each layer is gradually adjusted according to the wear of the cutting tool (4).

7. The method for machining the fillet of a closed deep cavity according to any one of claims 1 to 3, characterized in that, The horizontal boring machine is a CNC boring and milling machine.

8. The method for machining the fillet of a closed deep cavity according to claim 7, characterized in that, The CNC boring and milling machine controls the rotation angle of the worktable and the feed trajectory of the tool holder (3) through a CNC program.

9. The method for machining the fillet of a closed deep cavity according to any one of claims 1 to 3, characterized in that, The workpiece (1) is a roller end flat head sleeve.

10. The method for machining the fillet of a closed deep cavity according to claim 9, characterized in that, The surface hardness of the closed inner cavity (11) is HRC40-45.

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