Small-diameter deep-hole stepped drilling method and drill bit

Abstract

The present application relates to the technical field of drill bit, in particular to a small-diameter deep-hole stepped drilling method and drill bit. It comprises a guiding and centering part, a stepped cutting part and a tool shank part connected in sequence, and the tool body is provided with main chip removal grooves and auxiliary shearing grooves with different lead angles, and the grooves are staggered in phase. The drill bit axis is provided with a high-pressure internal cooling channel, and a micro radial jet hole with a specific back-swept angle is arranged near the rear flank surface of each cutting part. The self-adaptive drilling method matched with the drill bit automatically switches to a high-frequency pulsating feed mode when the spindle load increases by real-time monitoring of the spindle load, so that the feed speed fluctuates periodically according to an asymmetric waveform. Through the synergistic effect of mechanical shearing, directional jet and feed pulsation, the present application realizes the instant breaking, directional discharge and effective cooling of chips, solves the problems of chip removal blockage, insufficient cooling and poor precision in small-diameter deep-hole stepped machining, and significantly improves the machining efficiency, coaxial accuracy and tool life.

Description

Technical Field

[0001] This invention relates to the field of drill bit technology, and more specifically, to a method and drill bit for step drilling of small-diameter deep holes. Background Technology

[0002] In aerospace, precision mold making, and medical device industries, there is a widespread need to machine small-diameter, multi-step deep holes in high-strength alloys, titanium alloys, and other materials. This type of machining faces significant technical bottlenecks. Traditional processes use standard twist drills of different diameters to process in steps and layers. This method requires repeated tool retraction, tool changing, and tool setting, resulting in large cumulative positioning errors and extremely poor coaxiality of each step (usually exceeding 0.05mm). Furthermore, it is inefficient and has a high proportion of idle stroke. For holes with a depth-to-diameter ratio exceeding 15, subsequent drill bits are easily misaligned in the already machined small-diameter guide hole, exacerbating the axial deviation.

[0003] To improve efficiency and coaxiality, integral step drills have emerged. However, limited by the conventional single-lead helical flute design, they suffer from insufficient chip space when machining deep holes, especially small-diameter sections. Chips cannot be smoothly discharged within the narrow helical flutes, quickly forming a "chip blockage chain," leading to a sharp increase in drilling torque and temperature. This directly causes: chip extrusion causing the drill bit to chip or break at the step diameter change (stress concentration zone); poor chip removal preventing coolant from reaching the cutting zone, resulting in overheating, burning, and work hardening of the workpiece material; and excessive forced chip removal severely scratching the machined hole walls, deteriorating surface quality.

[0004] For drill bits with a diameter of 5mm or less, integrating an effective internal cooling channel is extremely difficult to manufacture and significantly weakens the strength of the tool core. Externally poured coolant is thrown off by centrifugal force at the entrance of small-diameter deep holes, making it difficult to enter the cutting zone. At the same time, small-diameter drill bits have a large length-to-diameter ratio and poor inherent rigidity, making them prone to tool deflection and runout during entry and deep hole drilling, resulting in excessive straightness of the hole axis (for example, deviations of more than 0.1mm at a depth of 100mm).

[0005] Some advanced solutions attempt to use variable lead spiral grooves or high-pressure internal cooling, but for small-diameter step drills, simple lead changes cannot solve the problem of mixing and interference of multi-stage chips in a limited space; while micro internal cooling channels are often limited by size and their outlet positions are fixed, which cannot provide independent and precise cooling and chip removal assistance for each step cutting edge, resulting in limited effectiveness and serious sacrifice of tool strength. Summary of the Invention

[0006] The purpose of this invention is to provide a method and drill bit for step drilling of small-diameter deep holes to solve the problems mentioned in the background art.

[0007] To achieve the above objectives, in one aspect, the present invention provides a composite drill bit, which, from the drill tip to the shank direction, sequentially includes a coaxially integrally formed guide and centering portion, at least two stages of stepped cutting portions with increasing diameters, and a reinforced shank portion. Specifically: On the cylindrical surface of the drill bit body, two independent helical grooves are machined: one is the main chip removal groove, whose lead P1 is designed to be (8-12) times the maximum diameter D of the drill bit, mainly responsible for quickly removing large-volume chips; the other is the auxiliary shearing groove, whose lead P2 is designed to be (3-6) times the diameter D of the drill bit, and P2 < P1; the key is that the two helical grooves are staggered in spatial phase (usually the phase difference is 100°-140°). The main function of the auxiliary shearing groove is not to directly contain chips, but its helical edge acts like a mobile "shearing knife" when the drill bit rotates, performing periodic, mechanical secondary shearing and crushing of the continuous long chips entering the main chip removal groove, turning long chips into shorter chips that are easier to remove; at the same time, the double helical groove structure expands the coverage area of ​​the coolant, enhances the turbulence of the fluid, and is conducive to heat dissipation.

[0008] The drill bit features a high-pressure internal cooling channel along its central axis. Crucially, one or more micro-radial jet conversion holes (diameter Φ0.08-0.3mm, adaptable to different drill bit diameters) are located near the flank face and close to the cutting edge of each stepped cutting section. These conversion holes connect the axial internal cooling channel to the outer surface of the tool. The axial direction of the jet holes is precisely calculated and optimized, ensuring a 15°-25° sweep angle between the outlet direction and the drill bit's rotation direction. Its working principle is as follows: the high-pressure coolant is delivered through the internal cooling channel to each conversion hole and converted into a high-energy radial high-speed jet. Due to the sweep angle design, this jet has two core functions: Directional flushing: The jet is ejected close to the newly formed cutting surface and the root of the chip, like a "hydraulic knife" to "pry" the chip away from the cutting zone and direct it into the nearest main chip removal groove inlet, realizing "generation as guidance"; Staged independent cooling: Each cutting edge has its own dedicated jet hole to serve it, ensuring that every cutting area from the drill tip to the maximum diameter can receive direct and sufficient cooling and lubrication, solving the problem of traditional internal cooling not being able to keep up with both ends.

[0009] On the other hand, the present invention provides an adaptive pulsating drilling method using the above-mentioned drill bit. This method needs to be executed on a CNC machine tool with real-time spindle load monitoring function, and its control logic is as follows: The system presets a safety load threshold L_th related to the tool material and diameter (usually set to 70%-80% of the normal breaking torque of the tool). During the drilling process, the spindle current or axial thrust signal is monitored in real time and converted into a real-time load L_real. This conversion can be achieved through a built-in or external power / torque sensor in the machine tool numerical control system and a preset conversion algorithm, which is a mature existing technology.

[0010] When L_real < 80% L_th, the system performs continuous drilling at a constant feed rate F0 to pursue the best machining efficiency.

[0011] When 80% L_th ≤ L_real < L_th, the system intelligently judges that the chip removal resistance increases and there is a potential risk of chip jamming, and immediately triggers the high-frequency pulsating feed mode; in this mode, the feed rate F is no longer constant, but fluctuates periodically between (0.3-1.2) F0 according to an asymmetric waveform (such as a sawtooth wave or a modified sine wave), and the fluctuation frequency is set to 20-50Hz.

[0012] The core principle of this pulsation control lies in its cooperation with the above-mentioned drill bit structure: the periodic pulsation of the mechanical feed makes the cutting thickness change slightly and rapidly, which not only promotes the regular fracture of the chip itself, but more importantly, it produces a fluid-mechanical coupling effect with the radially directed jet and the unequal-lead spiral groove; the slight fluctuation of the cutting force caused by the pulsation changes the boundary conditions of the interaction between the jet and the chip, and forms a periodic pressure fluctuation in the limited space of the spiral groove. This excitation effect can effectively break the adhesion state of the chip, make the coolant jet penetrate and carry debris more easily, and form a chip removal dynamics similar to "pulse pumping" in the groove, thereby dynamically and actively dredging the chip removal path instead of waiting passively for blockage to occur.

[0013] Compared with the existing technology, the beneficial effects of the present invention are: In this small-diameter deep-hole stepped drilling method and drill bit, when machining a deep hole with a Φ3mm aperture (stepped to Φ5mm) of TC4 titanium alloy and a total depth of 60mm, continuous drilling without retracting the tool can be achieved throughout the process, eliminating the problems of tool chipping, breaking and workpiece burning caused by chip jamming. Tests show that compared with traditional integral stepped drills, under the same processing conditions, the early tool failure rate caused by chip removal problems is zero.

[0014] Secondly, the present invention completes multi-stage stepped machining at one time, ensuring extremely high coaxiality; actual measurements show that the coaxiality error between each step can be stably controlled within 0.012mm, which is more than 70% higher than the step-by-step machining method; the Ra value of the hole wall surface roughness is reduced by more than 50%, and there are no scratches and vibration marks.

[0015] Because there is no need for periodic tool retraction for chip removal, and the average feed rate can be increased by 30%-50% (thanks to stable machining conditions), the overall machining efficiency is 2-3 times that of traditional step-by-step machining methods. Staged directional jet ensures effective cooling of each cutting edge, and adaptive pulsation controls peak loads, resulting in uniform and slow drill wear under extreme conditions. When machining Inconel 718 high-temperature alloy, the average wear on the tool flank (VB value) is reduced by more than 40%, and the number of holes that can be machined with a single drill bit is increased by 2-3 times.

[0016] This method and drill bit design are particularly suitable for the step machining of small-diameter deep holes in difficult-to-machine materials such as titanium alloys, high-temperature alloys, and stainless steel, which have high viscosity and poor thermal conductivity. It provides a stable, reliable, and efficient solution for high-end manufacturing fields such as aerospace and precision medicine. Attached Figure Description

[0017] Figure 1 This is a flowchart of the adaptive pulsating drilling process of Embodiment 1 of the present invention. Detailed Implementation

[0018] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0019] Example 1: A composite drill bit and method for deep hole step machining of TC4 titanium alloy This embodiment provides a composite drill bit and adaptive drilling method suitable for machining deep holes in TC4 titanium alloy workpieces with a hole diameter ranging from Φ3.0mm (first stage) to Φ5.0mm (second stage) and a total depth of 60mm (depth-to-diameter ratio 20:1). The steps are as follows: Step S1: Fabrication of the composite drill bit 1. Matrix material: Ultra-fine grain cemented carbide bar material is selected. In this embodiment, grade GU25UF is used, with bending strength ≥4500MPa and hardness ≥93.0 HRA.

[0020] 2. Macroscopic structure: The drill bit is integrally ground using a five-axis precision grinding machine. The total length of the drill bit is 120mm, and the structure from the drill tip is as follows: Guide centering part: 5mm in length, Φ2.995mm in diameter (0 to -0.005mm tolerance), with a slight positive taper of 1° and a standard 140° apex angle at the front end for initial centering.

[0021] First step cutting section: diameter Φ3.0mm, length 35mm, this section is responsible for machining small diameter deep hole sections; The second step cutting section has a diameter of Φ5.0mm and a length of 10mm. This section is widened into a step after drilling to the predetermined depth. Reinforced handle section: Φ6mm in diameter, for clamping.

[0022] 3. Key feature processing: Unequal lead double helical groove: Two helical grooves are ground on the cutting parts of Φ3mm and Φ5mm and part of the tool body; Main chip removal groove: lead P1=30mm (10 times the maximum diameter D=Φ3mm), groove width accounts for 60% of the circumference, responsible for the main chip collection and removal; Auxiliary shear groove: lead P2=12mm (4 times D), groove width occupies 25% of the circumference, and the helixes of the two helical grooves have a phase difference of 120° on the circumference; Graded radial jet holes: using micro-hole electrical discharge machining technology; A Φ0.8mm axial internal cooling channel is machined at the center of the drill bit.

[0023] First-stage jet orifice: Located in the first step cutting section (Φ3mm segment), 15mm from the drill tip. Orifice diameter Φ0.2mm, exit direction at a 20° sweep angle to the drill bit rotation tangent, axis at an 85° angle to the drill bit axis (nearly radial).

[0024] Second-stage jet orifice: located at the starting end of the second-step cutting section (Φ5mm segment), with a diameter of Φ0.25mm and a sweep angle of 20°.

[0025] Coating: The blade surface is coated with a multi-layer composite coating (AlTiN / Si3N4) with a thickness of about 3μm to reduce the coefficient of friction and improve wear resistance.

[0026] Step S2: Adaptive pulsating drilling process flow, see Figure 1 It is performed on a high-precision CNC machining center equipped with a real-time spindle load monitoring system.

[0027] 1. Workpiece and clamping: TC4 titanium alloy plate, 65mm thick. The workpiece is securely clamped, with sufficient space below for chip removal.

[0028] 2. Preset processing parameters: Spindle speed: N=3180rpm (cutting speed Vc≈30m / min for Φ3mm); Initial feed rate: F0 = 38 mm / min (feed per revolution f ≈ 0.012 mm / r); Coolant: Special high-pressure water-based cutting fluid, pressure P_cool=6MPa, delivered through the internal cooling channels of the machine tool spindle and drill bit; Safe load threshold L_th setting: Based on the tool material and diameter, the torque threshold is set to 0.45 N·m (approximately 75% of the drill bit's breaking torque) through pre-testing.

[0029] 3. Drilling process control: Start the machine tool and activate the high-pressure cooling system; The drill bit drills continuously at a speed of F0, and the monitoring system collects the spindle current in real time and calculates the real-time load L_real. When the drilling depth reaches about 25 mm (entering the stable deep hole drilling stage), L_real begins to approach 0.36 N·m (80% L_th). The control system automatically switches to the pulsed feed mode: the feed speed F is between 15 mm / min (≈0.4F0) and 45 mm / min (≈1.2F0), and changes periodically with a sawtooth waveform at a frequency of 35 Hz; In this mode, the drill bit continued to feed to a total depth of 60mm, during which L_real fluctuated between 0.36-0.43 N·m without triggering the upper limit alarm; Once the machining is complete, the drill bit retracts quickly.

[0030] In this embodiment, throughout the entire 60mm continuous drilling process, the discharged chips consistently appear as silver "C"-shaped or short spiral chips no longer than 5mm. The edges of the auxiliary shear groove periodically mechanically interfere with the chips in the main groove, while the minute pulsations of the feed alter the instantaneous cutting thickness. Together, these actions break up the easily formed, entangled, long, ribbon-like chips of TC4 material into easily discharged forms in their early stages. The high-pressure radial jet (6MPa) was observed to rapidly "purge" the chip roots away from the cutting edge and guide them directionally to the main chip removal groove inlet, completely eliminating chip adhesion and secondary cutting phenomena on the cutting edge and working surface.

[0031] Ten machined samples were inspected using a coordinate measuring machine (CMM). The results showed that the average cylindricity of the Φ3.0mm segment was 0.008mm, and that of the Φ5.0mm segment was 0.010mm. Most importantly, the coaxiality error between the two stepped holes remained stable between 0.008mm and 0.012mm, with an average of 0.010mm. This result represents a more than 75% improvement in accuracy compared to traditional step-by-step machining (where coaxiality is typically >0.05mm), with extremely high consistency. This is entirely due to the one-time integral forming process, which eliminates errors from multiple tool changes and tool setting, and the stable, interference-free drilling process that ensures the rigidity consistency of the tool system. The surface roughness Ra of the hole walls, as measured by a profilometer, ranged from 1.4μm to 1.8μm, with no macroscopically visible periodic vibration marks or tool retraction scratches, and a uniform surface texture.

[0032] After machining, scanning electron microscopy (SEM) revealed no chipping, microcracks, or other damage on the two main cutting edges and at the stepped transition of the drill bit. The flank wear band (VB) was uniform, with a maximum width of only 0.05 mm. This indicates that the staged radially oriented jet provided effective cooling for each cutting area, suppressing built-up edge and thermal diffusion wear common in titanium alloy machining; while adaptive pulsation control avoided continuous high loads, protecting the tool.

[0033] Example 2: Aspect Ratio Enhanced Composite Drill Bit and Method This embodiment is for a deeper diameter ratio hole made of Inconel 718 material, which requires machining a Φ2.5mm stepped diameter to Φ4.0mm diameter hole with a total depth of 50mm (depth-to-diameter ratio of 20:1, with the smaller diameter section having a depth-to-diameter ratio of 20:1).

[0034] The difference between this embodiment and Embodiment 1 is that: 1. Drill bit structure reinforcement: Increased core diameter: The core thickness ratio (core diameter / drill bit diameter) of the first step (Φ2.5mm) is increased to 0.4 (normally about 0.3) to enhance rigidity; Spiral groove optimization: The lead of the main chip removal groove P1=28mm and the lead of the auxiliary shearing groove P2=10mm. The difference between the two leads is larger to enhance the shearing and crushing ability of tough chips. Jet hole enhancement: Two radial jet holes are set in the Φ2.5mm section, located at 10mm and 25mm from the drill tip respectively, forming a dual cooling and chip removal auxiliary.

[0035] 2. Adjustment of process parameters: Rotational speed: N = 3820 rpm (Vc ≈ 30 m / min); Initial feed: F0 = 30 mm / min (f ≈ 0.0078 mm / r), which is more conservative; Pulsation parameters: feed rate between 10-40 mm / min, pulsating at a frequency of 40 Hz; The cooling pressure was increased to 8 MPa.

[0036] In this embodiment, Inconel 718 exhibits worse machinability than TC4, and its high strength, high work hardening tendency, and low thermal conductivity pose a severe challenge to the cutting tool. Using the solution in this embodiment, a full-depth 50mm drilling operation was achieved in a single pass. The discharged chips were short, dark purple fragments, indicating that the cutting temperature was controlled. The dual-jet orifice design creates a "relay zone" for cooling and lubrication in the first step (Φ2.5mm), ensuring sufficient coolant coverage in the cutting zone even with increased drilling depth, effectively mitigating heat buildup caused by poor material thermal conductivity.

[0037] Post-machining measurements showed coaxiality remained within 0.015 mm. Despite the more challenging material to machine, the tool failure mode shifted from severe abnormal chipping (caused by chip clogging) to gradual, normal flank wear due to a systematic solution to chip removal and cooling issues. Under the same wear standard as Example 1 (VB = 0.15 mm), this drill bit could machine 15 holes consecutively, while commercially available step drills of the same material had an average lifespan of less than 5 holes (often due to early failure caused by chip entanglement and thermal cracking). This represents a tool life improvement of over 200%, demonstrating the superior reliability and economy of this invention under extreme materials and operating conditions.

[0038] Example 3: Micro-diameter composite drill bit and method This embodiment is for medical cobalt-chromium alloy workpieces, which are machined with micro-holes ranging from Φ1.2mm to Φ2.0mm and with a total depth of 24mm.

[0039] The difference between this embodiment and Embodiment 1 is that: 1. Miniaturized and precision-manufactured drill bits: Micro-grinding technology was employed. The guide section diameter is Φ1.198mm. Unequal lead double spiral groove: Due to the small diameter, the auxiliary shearing groove is designed as "intermittent", that is, a pit is ground at a certain interval on the spiral path, which can play a shearing role without excessively weakening the tool body. Staged radial jet: Axial internal cooling channel diameter Φ0.3mm. The jet holes are laser-machined with a diameter of Φ0.08mm, requiring extremely high manufacturing precision.

[0040] 2. Adjustment of process parameters: Ultra-high speed: N=12000rpm (using a high-speed spindle); Minimal feed: F0 = 24 mm / min (f ≈ 0.002 mm / r); High-frequency micro-amplitude pulsation: The feed is between 7-30 mm / min, pulsating at a frequency of 50 Hz, with small fluctuation amplitude to prevent micro-drill bit breakage; The coolant is an oil-based mist that serves both cooling and lubrication purposes.

[0041] This embodiment successfully applies the core principles of the present invention to the Φ1.2mm micro-drilling scale. The machining process is stable, without chatter or tool breakage. The intermittent auxiliary shearing groove, while ensuring the strength of the tool body, still plays the role of disturbing the chip flow and preventing long chips from entangled. The Φ0.08mm micro-jet hole processed by laser precisely guides the atomized cooling oil to the cutting tip.

[0042] Ultra-high precision measurements were performed on the machined micro-stepped holes, revealing a coaxiality of 0.008 mm, an extremely high level of precision for micromachining. Electron microscopy revealed no material tearing or obvious recast layer on the hole walls, and the edges were clearly defined, meeting the stringent quality requirements of precision medical devices. This demonstrates the invention's excellent dimensional adaptability, overcoming the fundamental contradictions of poorer rigidity and extremely limited chip space in micro-drills.

[0043] Experiment 1: Chip removal performance comparison test, the purpose of which is to verify the synergistic chip removal effect of unequal lead double helical groove and adaptive pulsation control.

[0044] Control group: Traditional single straight-lead (P=30mm) step drill, without radial jet orifice, using constant feed (F=38mm / min) and conventional cooling.

[0045] Experimental Group: Drill Bit and Method of Embodiment 1 of the Invention Conditions: Machining TC4 titanium alloy, with the same hole pattern as in Example 1. The standard deviation of spindle load fluctuation (reflecting cutting smoothness) and whether forced tool retraction or chip clogging occurred during each machining operation were monitored and recorded; the results are shown in Table 1.

[0046] Table 1 Group Average torque (N·m) Torque ripple standard deviation Number of times chip clogging / tool ​​retraction occurred Hole wall quality control group 0.52 0.15 Three times (at depths of 18, 35, and 48 mm). Scratches and vibration marks experimental group 0.40 0.05 0 times smooth As shown in Table 1, the average torque of the control group was as high as 0.52 N·m and fluctuated drastically (standard deviation 0.15). This indicates that its machining process continuously experienced a vicious cycle of "chip clogging, load surge, chip clogging being broken or forced tool retraction, and load sudden drop". Each torque peak corresponds to a potential tool damage and hole wall scratch.

[0047] In contrast, the experimental group (the present invention) showed a 23% reduction in average torque, and more importantly, a significant 67% reduction in the standard deviation of torque fluctuation, with a smooth curve. This directly demonstrates that the chip removal environment of the present invention is extremely smooth, and the cutting process changes from an "intermittent, unstable impact state" to a "continuous, stable shearing state." This stability is the dynamic basis for achieving high precision and long tool life.

[0048] The control group exhibited three instances of chip clogging / retraction at depths of 18mm, 35mm, and 48mm, a typical "chip clogging cycle phenomenon" in traditional deep hole drilling. In contrast, the experimental group showed uninterrupted chip flow throughout the entire process, with chips continuously flowing out in a controlled, short, fragmented manner. This stark difference is not due to a single improvement, but rather a direct result of three technologies: pulsating feed and unequal lead grooves actively manage chip morphology; radial jets then flush and directionally transport the chips. This forms a preventative, proactive chip management system, rather than a passive response to clogging.

[0049] Test Example 2: Machining accuracy and tool life verification test, the purpose of which is to evaluate the improvement of machining accuracy and tool durability of the present invention.

[0050] Method: Using the drill bit from Example 1, identical stepped holes (a total of 10 holes) were continuously machined on 10 TC4 titanium alloy test plates. After each hole was machined, the coaxiality was measured, and the width of the wear band (VB value) on the drill bit's flank was observed under a microscope.

[0051] Comparative example: Using a commercially available high-end solid carbide internal cooling stepped drill (single spiral groove), machining was performed under the same parameters (except for no pulsation). The machining was terminated due to excessive torque alarm when machining the 4th hole; the results are shown in Table 2.

[0052] Table 2 Tools / Methods Number of holes processed continuously Coaxiality variation range (mm) Final VB value (mm) Failure Mode Commercially available step drill 4 (Incomplete) 0.018~0.035 0.25 Chip clogging leads to severe wear and chipping of the flank face. Drill bit and method of the present invention 10 (All Completed) 0.009~0.013 0.12 Uniform normal wear As shown in Table 2, the coaxiality of commercially available comparative drill bits rapidly deteriorated from 0.018 mm to 0.035 mm, which is related to rapid tool wear and slight wobble caused by each retraction and re-entry. In contrast, the coaxiality of the solution proposed in this invention was kept within an extremely narrow range of 0.009 mm to 0.013 mm throughout the entire process, demonstrating better stability. This illustrates that ensuring accuracy through one-time machining, and that a stable, low-temperature, and interference-free cutting process are key to maintaining consistent accuracy. The VB value after wear was only 0.12 mm, and the wear morphology was uniform, indicating that the tool was in an ideal progressive wear state, rather than a catastrophic failure caused by abnormal working conditions.

[0053] Commercially available drill bits fail before the fourth hole is completed, resulting in an actual effective output of 3.5 qualified holes. The drill bit of this invention completes all 10 holes and remains usable. Based on the cost-sharing of the tooling cost per qualified product, this invention reduces the tooling cost per hole by over 70%. Combined with the 152% efficiency improvement observed in Example 1, this invention achieves simultaneous and significant optimization in three manufacturing indicators: efficiency, accuracy, and cost.

[0054] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely preferred examples and are not intended to limit the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for step drilling of small-diameter deep holes, characterized in that, It includes the following steps: S1. Preset a safety load threshold L_th related to the tool material and diameter, and set L_th to 70% - 80% of the normal breaking torque of the tool; S2. Start drilling, and monitor the spindle current or axial thrust signal in real time, and convert it into a real-time load L_real through a sensor and a conversion algorithm; S3. Compare L_real with L_th, and dynamically adjust the feed mode according to the comparison result: When L_real < 80% L_th, continuous drilling is carried out at a constant initial feed rate F0; When 80% L_th ≤ L_real < L_th, a high-frequency pulsating feed mode is triggered, and the feed rate F fluctuates periodically between 0.3F0 and 1.2F0 according to a preset asymmetric waveform, and the fluctuation frequency is 20 - 50Hz; S4: Continuously execute S3 until the drilling reaches a predetermined depth.

2. The method for step drilling of small-diameter deep holes according to claim 1, characterized in that, The asymmetric waveform in S3 is a sawtooth wave or a modified sine wave.

3. The method for step drilling of small-diameter deep holes according to claim 1, characterized in that, In the high-frequency pulsating feed mode, the fluctuation amplitude and frequency of the feed rate F are adjusted according to the drill bit diameter and the workpiece material.

4. A drill bit applied to the stepped drilling method for small-diameter deep holes according to any one of claims 1-3, the drill bit being integrally formed coaxially from the drill tip to the tool holder, and sequentially comprising a guide centering portion, at least two stages of stepped cutting portions with increasing diameters, and a reinforced tool holder portion, characterized in that... Two independent spiral grooves are provided on the cylindrical surface of the tool body of the drill bit: One is the main chip fluting groove, and its lead P1 is 8 to 12 times the maximum diameter D of the drill bit; The other is the auxiliary shearing groove, and its lead P2 is 3 to 6 times the drill bit diameter D, and P2 < P1; The main chip fluting groove and the auxiliary shearing groove are staggered in the spatial phase; A high-pressure internal cooling channel is provided along the axis in the center of the drill bit, and at least one micro radial jet hole is opened near the flank face of each step cutting part, and the jet hole connects the internal cooling channel with the outer surface of the tool; the outlet direction of the jet hole has a rake angle of 15° - 25° with the drill bit rotation direction.

5. The drill bit for the small-diameter deep hole stepped drilling method according to claim 4, characterized in that, The phase difference between the main chip fluting groove and the auxiliary shearing groove in the circumferential direction is 100° - 140°.

6. The drill bit for the small-diameter deep-hole stepped drilling method according to claim 4, characterized in that, The aperture of the micro radial jet hole is Φ0.08mm to Φ0.3mm.

7. The drill bit for the small-diameter deep-hole stepped drilling method according to claim 4, characterized in that, For the small-diameter section in the step cutting part, at least two of the micro radial jet holes are axially provided.

8. The drill bit for the small-diameter deep hole stepped drilling method according to claim 4, characterized in that, For a micro drill bit with a diameter ≤ Φ1.5mm, the auxiliary shearing groove is a discontinuous spiral groove, which is composed of pits or short grooves distributed at intervals along the spiral path.

9. The drill bit for the small-diameter deep hole stepped drilling method according to claim 4, characterized in that, The matrix material of the drill bit is ultrafine grain cemented carbide, and the surface is coated with a composite coating for reducing friction and improving wear resistance.

10. A stepped machining system for small-diameter deep holes, characterized in that, A drill bit including the small-diameter deep-hole step drilling method according to any one of claims 4 - 9; And a numerical control machine tool configured to execute the small-diameter deep-hole step drilling method according to any one of claims 1 - 3.

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