A segmented variable parameter whole-chipping method for machining alumina ceramic blind holes based on an ultra-long overhanging PCD composite drill bit

Abstract

The application discloses a segmented variable parameter full chip removal method for machining alumina ceramic blind holes based on an ultra-long overhanging PCD composite drill bit. The method divides the target hole depth into multiple continuous stages, and stepwise reduces the spindle speed, cutting feed speed and single net deepening amount with the increase of the hole depth; each stage adopts a full chip removal cycle of completely exiting to a fixed chip removal position after single cutting, and cutting again after buffering at the re-approaching position above the last cutting endpoint when re-entering the hole. The application helps to suppress self-excited vibration, avoid high-speed resonance area, significantly reduce high-frequency vibration and early broken needle risk, improve chip removal and cooling conditions, improve tool durability and blind hole machining quality, and realize efficient and stable machining of large length-diameter ratio ceramic deep blind holes.

Description

Technical Field

[0001] This application relates to the field of precision machining technology for hard and brittle materials, and mainly to a segmented variable parameter full chip removal method for machining blind holes in alumina ceramics based on an ultra-long overhanging PCD composite drill bit. Background Technology

[0002] Alumina ceramics, as a typical engineering ceramic material, are widely used in cutting-edge industrial fields such as aerospace, semiconductor manufacturing, precision instruments, and electronics due to their high hardness, high wear resistance, high temperature resistance, and good chemical stability. With the development of integrated and lightweight structures in high-end equipment, the demand for machining high-precision, high aspect ratio blind holes in alumina ceramic components is increasing. Because polycrystalline diamond (PCD) possesses extremely high hardness and excellent wear resistance, using PCD composite drill bits for drilling alumina ceramics has become an important technical approach to achieving high-efficiency, high-precision hole machining.

[0003] However, in the actual process of machining blind holes in alumina ceramics using PCD composite drills with small diameters and extremely long overhangs (free end overhang typically ≥93mm), sudden shank breakage and chipping are highly likely to occur because traditional processes often employ constant high speeds or the common G83 / G73 pecking drill cycle. In the initial drilling stage, after the PCD cutting edge at the tool tip cuts into the extremely hard alumina ceramic surface, it is subject to strong radial geometric constraints from the inner hole wall, and the radial displacement of the tool tip is rigidly locked. Meanwhile, the ultra-long carbide shank, exposed outside the hole for tens of millimeters, lacks rigid support under high-speed rotation, easily triggering high-frequency resonance at the first critical speed and large-amplitude radial oscillation, resulting in extreme shearing and alternating bending stress conditions with front-end jamming and severe rear-end resonance. This enormous alternating stress is concentrated in the weld transition zone between the PCD cutting edge and the carbide shank, or in the shank neck immediately adjacent to the cutting edge. When machining reaches a critical depth of approximately 10mm, the accumulated oscillating alternating energy in the pure overhang section reaches the fatigue limit of the carbide matrix, causing the shank to suddenly bend and fracture at just 10mm into the hole. The remaining cutting edge inside the hole can also directly lead to the scrapping of the entire high-value ceramic workpiece. Furthermore, deep blind hole machining is not a simple adjustment of a single cutting parameter. Simply reducing the feed rate or improving cooling conditions cannot eliminate the shank fatigue fracture caused by high-speed resonance. On the other hand, excessively reducing the speed throughout the process can lead to a chain reaction of problems such as poor chip removal, chip accumulation and compression, and excessively long machining cycles, making it impossible to balance vibration suppression, chip removal, hole entry safety, and machining efficiency.

[0004] In summary, developing a segmented variable-parameter full chip removal method for machining alumina ceramic blind holes using an ultra-long overhanging PCD composite drill bit, which can effectively suppress chatter during machining with ultra-long overhanging tools, improve chip removal inside blind holes, and dynamically match cutting parameters according to hole depth, is of great significance and necessity for improving the machining quality and efficiency of deep blind holes in alumina ceramics, reducing the risk of chipping and tool breakage, and extending the service life of PCD tools. Summary of the Invention

[0005] To address the technical problems in existing technologies, such as high-speed vibration and early needle breakage, poor chip removal leading to cutting edge damage, and difficulty in balancing vibration suppression, chip removal, and processing efficiency when machining blind holes in alumina ceramics with small-diameter ultra-long overhang drill bits, this application proposes a segmented variable-parameter full chip removal method based on ultra-long overhang PCD composite drill bits for machining blind holes in alumina ceramics.

[0006] According to one aspect of the present invention, a segmented variable-parameter full chip removal method for machining blind holes in alumina ceramics based on an ultra-long overhang PCD composite drill bit is proposed. The method employs an ultra-long overhang PCD composite drill bit with an overhang ratio of 19.54~19.97 after clamping. The ultra-long overhang PCD composite drill bit includes a PCD cutting edge and a carbide shank. The method specifically includes the following steps: S1. Position the drive tool to a safe position, start the spindle rotation and introduce cooling medium; S2. Divide the target hole depth into at least two consecutive hole depth stages, and complete the machining of each stage sequentially. As the hole depth increases, the spindle speed, cutting feed rate, and net depth per pass in the later hole depth stage are all smaller than those in the previous hole depth stage. The machining of each hole depth stage includes the following control steps: S21. The cutting tool is moved to the fixed chip removal position; S22. Control the tool to repeatedly execute the following single cutting cycle until the current cutting depth reaches the preset endpoint or target hole depth of the current hole depth stage: control the tool to be fed into the hole from the fixed chip removal position at an idle moving speed higher than the current cutting feed speed, and stop at a reapproach position 0.04mm away from the surface to be machined or the previous cutting endpoint along the retraction direction; switch to the cutting feed speed corresponding to the current hole depth stage, control the tool to pass the previous cutting endpoint, and advance forward by the single net deepening amount corresponding to the current hole depth stage to form the current cutting endpoint; after the current cutting is completed, the tool completely withdraws from the hole opening along the axial direction at the idle moving speed and returns to the fixed chip removal position; S3. The cutting tool returns to the safe position, completing the machining process.

[0007] This invention reduces the dynamic cutting load on a single cutting edge by controlling the target hole depth in stages and gradually decreasing the spindle speed, cutting feed rate, and net depth per pass as the hole depth increases. This avoids the resonance zone of ultra-long overhanging tools, effectively disrupts the conditions for self-excited vibration, and eliminates the risk of high-frequency vibration in machining with large length-to-diameter ratios. Simultaneously, by combining a full chip removal path that completely exits the hole after a single cut, fluid flushing and thermal convection are used to promptly and smoothly remove residual chips and cutting heat, reducing the possibility of chip blockage, secondary cutting, and localized heat accumulation. Furthermore, the combination of a high-feed, rapid return under no-load conditions and a micro-hover re-approach mechanism avoids the mechanical impact of high-speed tool descent on the hard and brittle ceramic matrix and shortens the non-cutting stroke time. This achieves a balance between stability and overall efficiency in machining deep blind holes in ceramics, while preventing early tool breakage and PCD edge damage.

[0008] Preferably, the ultra-long overhang PCD composite drill bit includes a PCD cutting edge and a carbide shank. This structure provides excellent bending flexibility of the shank while ensuring extremely high wear resistance of the cutting edge. The nominal diameter of the ultra-long overhang PCD composite drill bit is 4.658 mm, and the overhang length after clamping is 91~93 mm. According to the cantilever beam model in mechanics of materials, the bending stiffness k of the tool is inversely proportional to the cube of the overhang length L. When the overhang ratio approaches 20, the radial stiffness of the tool drops sharply, making it extremely sensitive to radial cutting force fluctuations. Ordinary drilling methods or conventional Peck drills, under such large overhangs, are prone to inducing high-frequency self-excited vibrations at the moment the cutting edge contacts the alumina ceramic. The overhang ratio of this invention is a typical extreme working condition where segmented reduction of force and full chip removal path play a role in vibration suppression and protection.

[0009] Preferably, the specific steps of S1 are as follows: S11. Clamp the tool, set the dial indicator or micrometer probe at the tip of the tool, slowly rotate the spindle and detect the radial runout; the radial runout ≤ 0.01mm, which can eliminate the periodic centrifugal excitation force and single-edge off-center load impact caused by the initial eccentricity of the tool installation from the source, and greatly reduce the initial chatter amplitude of the ultra-long overhang tool. S12. Clamp the workpiece, align the workpiece and set the coordinate system; define the direction parallel to the rotation axis of the ultra-long overhanging PCD composite drill as the Z-axis direction, establish the surface of the workpiece to be machined as the Z-axis zero point, and complete the tool length compensation. S13. Drive the tool to a safe position, start the spindle rotation and introduce cooling medium.

[0010] More preferably, the safe position is a position with a Z-axis coordinate Z ≥ 5mm. The fixed chip removal position is a position with a Z-axis coordinate Z = 2mm. This position utilizes the hydrodynamic scouring effect to allow the high-pressure cooling medium to act directly on the fully extracted tool tip and spiral groove, achieving rapid chip scouring and cooling, while greatly reducing the idle stroke of chip removal. The axial clearance between the re-approach position and the previous cutting endpoint is 0.04mm. Setting this axial clearance can buffer the kinetic energy impact during high-speed cutting, avoiding contact stress concentration and chipping caused by the tool tip directly hitting the hard and brittle ceramic bottom surface, which is conducive to achieving a smooth mechanical transition from high-speed no-load cutting to micro-cutting feed.

[0011] Preferably, the target hole depth includes a first hole depth stage, a second hole depth stage, and a third hole depth stage; the first hole depth stage is 0 < d1 ≤ 30 mm, the second hole depth stage is 30 mm < d2 ≤ 55 mm, and the third hole depth stage is 55 mm < d3 ≤ target hole depth; d1, d2, and d3 represent the hole depth values ​​of the first hole depth stage, the second hole depth stage, and the third hole depth stage, respectively.

[0012] More preferably, the spindle speeds in the first hole depth stage, the second hole depth stage, and the third hole depth stage are 2200 rpm, 2000 rpm, and 1800 rpm, respectively.

[0013] More preferably, the cutting feed rates for the first hole depth stage, the second hole depth stage, and the third hole depth stage are 12 mm / min, 10 mm / min, and 8 mm / min, respectively.

[0014] More preferably, the net depth increase per cycle in the first hole depth stage, the second hole depth stage, and the third hole depth stage is 0.03 mm, 0.02 mm, and 0.01 mm, respectively.

[0015] In this scheme, a higher rotation speed and single-pass depth of cut are used in the shallow hole stage to ensure material removal efficiency. As the hole depth increases to the middle stage, appropriately lowering the cutting parameters can suppress the chattering tendency of ultra-long overhanging tools. After entering the deep hole stage, switching to the lowest rotation speed and micro-cutting depth can control the amount of chips generated in a single cut to an extremely low level, which is conducive to the full chip removal action to carry the chips out of the narrow hole and avoid chip blockage and tool jamming in the deep hole section.

[0016] Preferably, the no-load traverse speed is 3000 mm / min. This no-load traverse speed is significantly higher than the cutting feed rate, ensuring that the actions of retracting the tool and reapproaching the previous cutting endpoint constitute a smaller proportion of the total machining time, thus avoiding excessively prolonged machining cycles due to complete chip removal with each tool.

[0017] Preferably, the target hole depth is greater than 55 mm and not greater than 89 mm.

[0018] Compared with the prior art, the present invention has the following beneficial effects: This invention significantly suppresses centrifugal vibration caused by eccentricity by progressively reducing spindle speed, feed rate, and depth of cut as hole depth increases, and by implementing rigorous tool tip runout detection. This effectively alleviates the severe chatter problem when machining hard and brittle alumina ceramics with tools of a large length-to-diameter ratio of nearly 20 times the diameter. It also significantly reduces the breakage rate and chipping risk of high-value PCD drill bits, significantly improves workpiece machining yield, and greatly saves on consumable costs for expensive diamond tools.

[0019] This invention employs a full chip removal control path that completely withdraws the chip from the hole after a single cut. The fixed chip removal position is set above the blind hole opening, allowing the high-pressure cooling medium to directly flush the tool tip and spiral groove that have been completely withdrawn from the hole. Combined with the strict control of chip volume in the micro-cutting stage of deep hole drilling, this helps to reduce secondary cutting caused by chip accumulation and jamming in the deep blind hole, as well as thermal stress damage caused by the accumulation of cutting heat, thus ensuring machining stability and hole wall surface quality.

[0020] This invention employs a CNC control mechanism combining high-feed return under no-load conditions with a micro-hover re-approach. When re-entering the hole, it pauses 0.04mm above the previous cutting endpoint for buffering before switching back to cutting feed. This helps buffer the mechanical impact of high-speed cutting on the hard and brittle ceramic matrix, preventing chipping from collisions. Simultaneously, a high no-load traverse speed of up to 3000mm / min is used during the complete chip removal and re-entry stages, shortening the non-cutting auxiliary time caused by frequent full chip removal. This enables efficient and safe machining with the PCD composite drill bit. Compared to the long cycle of 6 hours required for high-difficulty single-hole grinding with early traditional grinding heads, the single-hole machining cycle is significantly shortened to 3 hours, doubling the machining efficiency. It balances high safety protection with overall machining efficiency, effectively addressing both machining safety and non-cutting time control.

[0021] This invention effectively suppresses the vibration of the spindle speed, cutting feed rate, and net depth per pass by gradually decreasing the spindle speed, cutting feed rate, and net depth per pass as the hole depth increases, and coordinates this with a full chip removal control path that completely withdraws the drill bit from the hole after a single cut. This avoids early needle breakage caused by vibration and improves chip removal conditions in deep holes, providing a stable and repeatable method for machining deep blind holes with large aspect ratios in hard and brittle materials. Attached Figure Description

[0022] The accompanying drawings are used to further illustrate the embodiments of this application and do not constitute a limitation on the scope of protection of this application. The same reference numerals in different drawings denote the same or corresponding parts.

[0023] Figure 1 A flowchart of a segmented variable-parameter full chip removal method for machining alumina ceramic blind holes based on an ultra-long overhang PCD composite drill bit is shown. Figure 2 A schematic diagram of the clamping structure for an ultra-long overhanging PCD composite drill bit is shown. Figure 3 A schematic diagram of the radial runout detection of the tip of an ultra-long overhanging PCD composite drill bit is shown. Figure 4 This diagram illustrates a single full chip removal cycle with the tool fixed at the chip removal position. Figure 5 This diagram illustrates a single full chip removal cycle – rapid tool feed and re-approach position. Figure 6 This diagram illustrates a single full chip removal cycle – from the moment the tool makes a small cut to the end of the current cut. Figure 7 This diagram illustrates a single full chip removal cycle – with the tool completely withdrawing from the borehole. Figure 8 The time-domain waveform of the ambient sound signal collected under comparative operating conditions is shown; Figure 9 The normalized relative amplitude spectrum of the ambient sound signal collected under comparative operating conditions is shown. Explanation of reference numerals in the attached drawings: 1-Spindle end; 2-Chuck; 3-Extra-long overhang PCD composite drill bit; 31-PCD cutting edge; 32-Carbide shank; 4-Runout gauge; 41-Stylus; 5-Gate holder; 6-Workpiece; 61-Hole; 62-Blind hole; 7-Fixed chip removal position; 8-Reapproach position; 9-Previous cutting endpoint; 10-Current cutting endpoint; 11-Cooling medium. Detailed Implementation

[0024] The present application will now be described in further detail with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are for illustrative purposes only and are not intended to limit the invention. Furthermore, it should be noted that, for ease of description, only the parts relevant to the invention are shown in the accompanying drawings.

[0025] Where there is no conflict, the embodiments and features described in this application can be combined with each other. The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0026] This invention provides a segmented, variable-parameter, full chip removal method for machining alumina ceramic blind holes using an ultra-long overhang PCD composite drill bit, with reference to... Figure 1 This includes the following steps: S1. Preparation Procedure: S11. Mount the cutting tool, such as Figure 2As shown, the ultra-long overhang PCD composite drill bit 3 includes a PCD cutting edge 31 and a carbide shank 32, which are clamped onto the spindle end 1 via a chuck 2. Because the overhang length is close to 20 times the diameter, the shank and spindle axis are essentially aligned when the tool is rotating, while the tip of the PCD cutting edge experiences a slight radial offset under centrifugal force and cutting force. Figure 2 The dashed line on the outer side of the medium-hard alloy shank 32 indicates the limit position of the swing. The nominal diameter of the extra-long overhang PCD composite drill bit 3 is 4.658 mm, and the overhang length after clamping is 91~93 mm. The ratio of the overhang length after clamping to the nominal diameter is 19.54~19.97. After clamping, the runout gauge 4 is installed in a suitable position on the machine tool through the gauge holder 5, so that the probe 41 is in contact with the PCD cutting edge 31, and the center of the probe and the dial coincides with the tool axis. Figure 3 Slowly rotate the spindle to detect the radial runout of the tool within one rotation cycle. Slowly rotate the spindle and check if the radial runout is within 0.01mm. If it does not meet the requirements, readjust the clamping state. S12. Clamp workpiece 6, align workpiece 6 and set the coordinate system; define the direction parallel to the rotation axis of the ultra-long overhanging PCD composite drill bit 3 as the Z-axis direction, establish the surface to be machined of workpiece 6 as the Z-axis zero point, and complete tool length compensation. S13. Drive the tool to a safe position, start the spindle rotation and introduce cooling medium 11; the safe position is set to a position with Z-axis coordinate Z≥5mm.

[0027] S2. By calling the machining subroutine once through the main program, the target hole depth is divided into at least two consecutive hole depth stages, and the machining of each stage is completed sequentially. As the hole depth increases, the spindle speed, cutting feed rate, and net depth per pass in the later hole depth stage are all less than those in the previous hole depth stage. The machining of each hole depth stage includes the following control steps: S21. Move the tool to the fixed chip removal position 7 with Z-axis coordinate Z=2mm; S22. Refer to in order Figures 4-7The tool is controlled to repeatedly execute the following single cutting cycle until the current cutting depth reaches the preset endpoint or target hole depth of the current hole depth stage: the tool is fed into the blind hole 62 from the fixed chip removal position 7 at an idle moving speed higher than the current cutting feed speed, and stops at the reapproach position 8 above the surface to be machined (during the first cut) or the endpoint of the previous cut (during subsequent cycles). The axial clearance between the reapproach position 8 and the surface to be machined or the endpoint of the previous cut 9 is set to 0.04 mm. After reaching the reapproach position 8, the cutting feed speed corresponding to the current hole depth stage is switched, and the tool is controlled to cross the endpoint of the previous cut 9 and advance forward by the single net depth increase (Δd) corresponding to the current hole depth stage to form the current cutting endpoint 10. After the current cut is completed, the tool is completely withdrawn from the hole opening 61 along the axial direction at an idle moving speed and returns to the fixed chip removal position 7. S3. After the target hole depth is machined, the drive tool returns to the safe position completely by axial movement, the spindle rotation stops and the cooling medium is turned off, and the machining is completed.

[0028] Specifically, the target hole depth is greater than 55mm and not greater than 89mm, and is divided into three consecutive hole depth stages, including the first hole depth stage of 0<d1≤30mm, the second hole depth stage of 30mm<d2≤55mm, and the third hole depth stage of 55mm<d3≤target hole depth, where d1, d2, and d3 represent the hole depth values ​​of the first hole depth stage, the second hole depth stage, and the third hole depth stage, respectively.

[0029] In a specific embodiment, considering the characteristics of the tool's long atmospheric overhang and weak radial stiffness in the first hole depth stage, the spindle speed is actively reduced to 2200 rpm, coupled with a single net depth of 0.03 mm and a feed rate of 12 mm / min for cutting. This parameter matching avoids the main resonance peak region of the long carbide shank, suppressing the continuous accumulation of self-excited vibration and resonant oscillation, thus ensuring the efficiency of shallow hole removal while smoothing out high-frequency chatter caused by cutting force fluctuations. On the other hand, it effectively improves the strong alternating bending stress generated by "cutting edge constraint and high-frequency oscillation of shank" when cutting to a depth of around 10 mm at traditional high speeds, avoiding excessive stress concentration in the weld transition zone and neck, and significantly reducing the probability of early fatigue fracture of the tool.

[0030] Upon entering the second depth stage, as the cutter body gradually penetrates deeper, the machined hole wall exerts a certain radial constraint on the cutter body along the cutting path. At this point, the spindle speed is gradually reduced to 2000 rpm, and the cutting feed rate is adjusted to 10 mm / min, reducing the net depth of cut per pass to 0.02 mm. This adjustment in parameter compliance at this stage helps reduce the load change of the cutter body during the transition from free overhang to hole wall constraint; simultaneously, by slightly reducing the depth of cut per pass, the chip volume per unit time is effectively controlled, alleviating the friction and chip clogging risks caused by the extended chip removal channel in the medium-deep hole section.

[0031] In the third depth stage, to address the challenges of heat dissipation and increasing chip removal resistance in the deep hole region, the spindle speed was further reduced to 1800 rpm, the feed rate to 8 mm / min, and the net depth per pass controlled at 0.01 mm. These extremely low load parameters maintained instantaneous cutting torque and alternating shear force at low levels, reducing thermal stress and mechanical load during deep hole cutting. Simultaneously, the fine chips generated by micro-cutting facilitated the removal of residual chips by the high-pressure cooling medium during each full chip removal cycle, reducing secondary cutting and tool jamming caused by chip accumulation and compression at the bottom of the blind hole, thus ensuring stable drilling and hole wall quality in the deep hole section.

[0032] Example 1 A segmented, variable-parameter, full chip removal method for machining blind holes in alumina ceramics using an ultra-long overhang PCD composite drill bit is disclosed. The drill bit is a composite deep-hole drill bit combining a PCD cutting edge and a carbide shank. The nominal diameter of the drill bit is 4.658 mm, and the free end overhang length after clamping is 92 mm (overhang to diameter ratio of 19.75). The specific machining process and control steps are as follows: A1. Clamping the cutting tool, workpiece, and positioning.

[0033] A11. Clamp the tool, place the dial indicator probe against the tool tip, and slowly rotate the spindle. Measure the radial runout of the tool tip. If it is no greater than 0.01mm, the runout accuracy requirement is met.

[0034] A12. Clamp and align the alumina ceramic workpiece, set the direction parallel to the rotation axis of the ultra-long overhanging PCD composite drill bit as the Z-axis direction, set the surface to be machined on the workpiece as the Z-axis zero point (Z=0), and perform tool length compensation.

[0035] A13. Position the drive tool to a safe position at Z=5mm, start the spindle rotation, and introduce cooling water.

[0036] A2. In the CNC system, the target depth of 79.7mm is divided into 3 consecutive stages by single-step G01 linear interpolation in conjunction with a macro program, and then processed sequentially.

[0037] Phase 1 (0 < d1 ≤ 30 mm): Control the tool to rapidly descend from the safe position to the fixed chip removal position Z=2.0 mm at an idle speed of 3000 mm / min; then continue advancing at a feed rate of 3000 mm / min, stopping at a re-approach position Z=0.04 mm above the surface to be machined; at this point, switch the spindle speed to 2200 rpm, the cutting feed rate to 12 mm / min, and set the single net depth of cut to 0.03 mm, controlling the tool to advance into the workpiece to Z=-0.03 mm; after this cutting is completed, the tool is completely withdrawn from the hole opening axially at an idle speed of 3000 mm / min, retracting to Z=2.0 mm for high-pressure water flushing and cleaning; repeat this micro-cutting full chip removal cycle 1000 times until Z=-30.0 mm is reached. After cutting, retract to Z=2.0 mm.

[0038] Second stage (30mm < d2 ≤ 55mm): At the fixed chip removal position Z=2.0mm, the spindle speed is reduced to 2000rpm, the cutting feed rate is adjusted to 10mm / min, and the net depth of cut per pass is reduced to 0.02mm. The tool is controlled to rapidly descend from the fixed chip removal position Z=2.0mm to 0.04mm above the previous cutting endpoint (Z=-29.96mm) at an idle traverse speed of 3000mm / min; then, at a cutting feed rate of 10mm / min, it crosses Z=-30.0mm and advances 0.02mm to Z=-30.02mm; after completing the cut, it is again fully retracted to Z=2.0mm at an idle traverse speed of 3000mm / min; this micro-cutting full chip removal cycle is repeated 1250 times until it advances to Z=-55.0mm. After the cut is completed, the tool is retracted back to Z=2.0mm.

[0039] The third stage (55mm < d3 ≤ 79.7mm): At the fixed chip removal position Z=2.0mm, the spindle speed is further reduced in steps to 1800rpm, the cutting feed rate is reduced to 8mm / min, and the net depth per pass is controlled to 0.01mm. Each time the tool re-enters the hole, it is rapidly advanced at 3000mm / min to a buffered position 0.04mm above the previous endpoint, and then switched to a feed rate of 8mm / min for micro-cutting. After a single cut, it is quickly retracted at 3000mm / min to Z=2.0mm. This micro-cutting and full chip removal cycle is repeated 2470 times, and the tool is smoothly advanced to the target bottom Z=-79.7mm.

[0040] A3. After the target hole depth is machined, the tool is completely withdrawn from the bottom of the hole at an idle speed of 3000 mm / min and returned to the fixed chip removal position at Z=2.0 mm, then returned to the safe position at Z=5 mm. Subsequently, the spindle rotation is stopped and the cooling medium is turned off, completing the single-hole machining. The single-hole machining time is approximately 3 hours.

[0041] Using this segmented variable-parameter full chip removal method, continuous blind hole machining experiments were conducted under the same machining conditions using an ultra-long overhang PCD composite drill bit of the same specification. Based on existing test records, in a set of single-tool continuous machining samples, the completion of 45 blind holes with a depth of 79.7 mm was used as the quality control tool change node. Upon reaching this node, the tool did not break and still possessed cutting capability; therefore, it automatically changed tools because the hole wall surface quality met the preset tool change control standard. Based on 45 blind holes, the cumulative drilling depth per tool was 3586.5 mm.

[0042] Comparative Example 1 The same ultra-long overhang PCD composite drill bit (nominal diameter 4.658 mm, overhang length 92 mm) and alumina ceramic workpiece of the same specifications as in Example 1 were used. The difference is that Comparative Example 1 did not use the segmented variable parameter full chip removal control of the present invention, but instead used a constant spindle speed of 3000 rpm, a cutting feed rate of 10 mm / min, and a single net depth of cut of 0.05 mm for drilling.

[0043] During the cutting process, the tool vibrates violently when it enters the workpiece. When the machining depth reaches 10mm, the tool shank breaks suddenly due to obvious vibration, making it impossible to complete a blind hole.

[0044] Comparative Example 2 The same ultra-long overhang PCD composite drill bit (nominal diameter 4.658 mm, overhang length 92 mm) and alumina ceramic workpiece of the same specifications as in Example 1 were used. The difference was that the spindle speed was kept constant at 3000 rpm, the cutting feed rate was kept constant at 10 mm / min, and the net depth per pass was reduced only for different depth ranges.

[0045] The net depth increase per pass is 0.03mm for depths of 0 < d1 ≤ 30mm; 0.02mm for depths of 30mm < d2 ≤ 55mm; and 0.01mm for depths of 55mm < d3 ≤ 79.7mm. External cooling high-pressure water is also used. Although the high-pressure water ensures no dry grinding and no chip jamming, the tool still breaks at around 10mm because the spindle speed is still in the resonant frequency range.

[0046] This strongly confirms that the cause of the tool breakage was bending fatigue triggered by high-speed resonance, rather than chip removal resistance.

[0047] To further reveal the instability mechanism of ultra-long overhanging drill bits in the machining of alumina ceramics from the perspective of vibroacoustic characteristics, time-domain waveform and frequency-domain feature analysis was performed on the environmental sound signal collected under a comparative working condition (constant 3000 rpm rotation speed and 10 mm / min cutting feed rate) without the segmented variable parameter control of this invention. The results are as follows: Figure 8 and Figure 9As shown. It should be noted that, Figure 9 The spectrum in the image only represents the relative amplitude distribution of the attached audio signal, and does not directly identify the acoustic peaks as the tool resonance frequency.

[0048] like Figure 8 As shown, under the comparative working condition, the time-domain waveform of the collected sound signal exhibits significant high-amplitude burst pulses and periodic violent fluctuations during the cutting process, indicating that the ultra-long overhang PCD composite drill bit is accompanied by continuous and unstable alternating impacts and strong vibrations when cutting into the hard and brittle alumina ceramic hole at high speed.

[0049] like Figure 9 As shown, spectral analysis of the ambient sound signal reveals concentrated high-amplitude characteristic peaks in the 1400–1600 Hz frequency range and around 2100 Hz, along with multiple secondary response peaks in the low-frequency region around 100 Hz and the high-frequency region around 2670 Hz. These spectral characteristics indicate that under the high-speed cutting excitation of 3000 rpm (comparative example), the tool and workpiece system experienced significant acoustic energy accumulation and resonance amplification.

[0050] In summary, the primary cause of early tool breakage in machining deep blind holes with large aspect ratios using ultra-long overhanging tools is bending fatigue induced by high-speed resonance, rather than simply chip removal resistance. This invention, through segmented, stepped reduction of spindle speed and cutting parameters, helps avoid the tool resonance zone and suppresses self-excited vibration. Simultaneously, the full chip removal path that completely extracts the hole opening and the hovering buffer re-approach mechanism effectively balances vibration suppression, chip removal and heat dissipation, and machining efficiency. Compared to the limitations of traditional processes where breakage occurs around 10mm and complete holes cannot be finished, this invention significantly improves machining stability, enabling the smooth machining of 45 79.7mm deep blind holes while maintaining cutting capability at tool change points. This provides an effective process solution for addressing the problems of tool vibration and needle breakage when machining hard and brittle ceramics with ultra-long overhanging tools.

[0051] The above specific embodiments are used to illustrate the technical solution of this application, and are not intended to limit the scope of protection of this application. The scope of protection of this application is determined by the claims.

Claims

1. A segmented variable-parameter full chip removal method for machining alumina ceramic blind holes based on an ultra-long overhanging PCD composite drill bit, characterized in that, An ultra-long overhang PCD composite drill bit with an overhang ratio of 19.54~19.97 after clamping is used. The ultra-long overhang PCD composite drill bit includes a PCD cutting edge and a carbide shank. The segmented variable parameter full chip removal method includes the following steps: S1. Position the drive tool to a safe position, start the spindle rotation and introduce cooling medium; S2. Divide the target hole depth into at least two consecutive hole depth stages, and complete the machining of each stage sequentially. As the hole depth increases, the spindle speed, cutting feed rate, and net depth per pass in the later hole depth stage are all smaller than those in the previous hole depth stage. The machining of each hole depth stage includes the following control steps: S21. The cutting tool is moved to the fixed chip removal position; S22. Control the tool to repeatedly execute the following single cutting cycle until the current cutting depth reaches the preset endpoint or target hole depth of the current hole depth stage: control the tool to be fed into the hole from the fixed chip removal position at an idle moving speed higher than the current cutting feed speed, and stop at a reapproach position 0.04mm away from the surface to be machined or the previous cutting endpoint along the retraction direction; switch to the cutting feed speed corresponding to the current hole depth stage, control the tool to pass the previous cutting endpoint, and advance forward by the single net deepening amount corresponding to the current hole depth stage to form the current cutting endpoint; after the current cutting is completed, the tool completely withdraws from the hole opening along the axial direction at the idle moving speed and returns to the fixed chip removal position; S3. The cutting tool returns to the safe position, completing the machining process.

2. The segmented variable-parameter full chip removal method for machining alumina ceramic blind holes based on an ultra-long overhanging PCD composite drill bit according to claim 1, characterized in that, The nominal diameter of the ultra-long overhang PCD composite drill bit is 4.658 mm, and the overhang length of the tool after clamping is 91~93 mm.

3. The segmented variable-parameter full chip removal method for machining alumina ceramic blind holes based on an ultra-long overhanging PCD composite drill bit according to claim 1, characterized in that, The specific steps of S1 are as follows: S11. Clamp the cutting tool, set the dial indicator or micrometer probe at the tip of the cutting tool, slowly rotate the spindle and detect the radial runout; the radial runout ≤ 0.01 mm; S12. Clamp the workpiece, align the workpiece and set the coordinate system; define the direction parallel to the rotation axis of the ultra-long overhanging PCD composite drill as the Z-axis direction, establish the surface of the workpiece to be machined as the Z-axis zero point, and complete the tool length compensation. S13. Drive the tool to a safe position, start the spindle rotation and introduce cooling medium.

4. The segmented variable-parameter full chip removal method for machining alumina ceramic blind holes based on an ultra-long overhanging PCD composite drill bit according to claim 3, characterized in that, The safe position is the position with Z-axis coordinate Z≥5mm; the fixed chip removal position is the position with Z-axis coordinate Z=2mm.

5. The segmented variable-parameter full chip removal method for machining alumina ceramic blind holes based on an ultra-long overhanging PCD composite drill bit according to claim 1, characterized in that, The target hole depth includes a first hole depth stage, a second hole depth stage, and a third hole depth stage; the first hole depth stage is 0 < d1 ≤ 30 mm, the second hole depth stage is 30 mm < d2 ≤ 55 mm, and the third hole depth stage is 55 mm < d3 ≤ target hole depth; d1, d2, and d3 represent the hole depth values ​​of the first hole depth stage, the second hole depth stage, and the third hole depth stage, respectively.

6. The segmented variable-parameter full chip removal method for machining alumina ceramic blind holes based on an ultra-long overhanging PCD composite drill bit according to claim 5, characterized in that, The spindle speeds in the first hole depth stage, the second hole depth stage, and the third hole depth stage are 2200 rpm, 2000 rpm, and 1800 rpm, respectively.

7. The segmented variable-parameter full chip removal method for machining alumina ceramic blind holes based on an ultra-long overhanging PCD composite drill bit according to claim 5, characterized in that, The cutting feed rates for the first hole depth stage, the second hole depth stage, and the third hole depth stage are 12 mm / min, 10 mm / min, and 8 mm / min, respectively.

8. The segmented variable-parameter full chip removal method for machining alumina ceramic blind holes based on an ultra-long overhanging PCD composite drill bit according to claim 5, characterized in that, The single net deepening amount in the first hole depth stage, the second hole depth stage, and the third hole depth stage is 0.03 mm, 0.02 mm, and 0.01 mm, respectively.

9. The segmented variable-parameter full chip removal method for machining alumina ceramic blind holes based on an ultra-long overhanging PCD composite drill bit according to claim 1, characterized in that, The no-load moving speed is 3000 mm / min.

10. The segmented variable-parameter full chip removal method for machining alumina ceramic blind holes based on an ultra-long overhanging PCD composite drill bit according to claim 1, characterized in that, The target hole depth is >55mm and ≤89mm.

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