Accurately-centered high-speed drilling surface residual stress testing method

Abstract

The invention relates to the technical field of component residual stress testing, in particular to an accurately-centered high-speed drilling surface residual stress testing method which comprises the following steps: grinding the surface of a target sample in a crossed manner by using 180Cw and 600Cw abrasive paper, cleaning the surface of the target sample by using absolute ethyl alcohol, drawing a reference line on the surface of the target sample by using a pencil to calibrate a testing point, and measuring the residual stress of the surface of the target sample by using the reference line. A strain gauge and a terminal are pasted on the surface of a target sample through 502 glue, the target sample is clamped to a machining center table top, a centering clamp and a drill bit are clamped, the drill bit is perpendicular to a testing face of the machining center table top, a microscope and the centering clamp are assembled, the center of the microscope is aligned with a ring core of the strain gauge in a cross mode, and the position of a cutter is adjusted. Enabling the center of the drill bit to directly face the ring core of the strain gauge, fixing the strain gauge and one end of the electric wire on the terminal through tin soldering, and connecting the other end of the electric wire to the static strain gauge, and realizing efficient and high-precision measurement of the surface residual stress through combination of high-speed drilling and precise centering technologies.

Description

Technical Field

[0001] The present invention relates to the technical field of component residual stress testing, and in particular to a method for accurately centering high-speed drilling surface residual stress testing. Background Art

[0002] With the advancement of science and technology in my country and the increasing complexity of the international landscape, the requirements for residual stress in components in fields such as aerospace, defense, and precision machining have risen to a level of importance equal to mechanical properties and corrosion resistance. Residual stress refers to the internal stress that persists within a material or component even when not subjected to external loading. In most cases, residual stress can negatively impact various component performance indicators, such as causing deformation that affects component dimensional accuracy, reducing fatigue life and affecting component performance, and inducing cracks and fractures that lead to structural failure. Therefore, accurate measurement of residual stress in components is key to achieving residual stress reduction and control.

[0003] The drilling method is widely used to measure residual stress on sample surfaces. Traditional low-speed drilling involves using a hand drill to create a small hole. Due to its low rotational speed, the drilling process generates high cutting heat. The drill requires manual pressure, making feed speed difficult to control and prone to overloading. Furthermore, manual alignment of the drill bit and strain gauges is difficult to ensure, making it difficult to ensure drill verticality and accurate hole insertion. These drawbacks result in significant errors in test results from this method, making it difficult to accurately determine residual stress in components. Summary of the Invention

[0004] In view of this, the present invention addresses the deficiencies in the prior art and proposes a method for accurately centered high-speed drilling surface residual stress testing, aiming to solve at least one of the problems raised in the above background technology.

[0005] The present invention provides a method for testing residual stress on the surface of a precisely centered high-speed drilled hole, comprising the following steps:

[0006] S1. Use 180Cw and 600Cw sandpaper to cross-grind the surface of the target sample, clean the surface of the target sample with anhydrous ethanol, draw reference lines on the surface of the target sample with a pencil to calibrate the test points, and adhere the strain gauge and terminals to the surface of the target sample with 502 glue;

[0007] S2. Clamp the target sample onto a machining center table, and install a centering fixture and a drill bit, wherein the drill bit is perpendicular to the test surface of the machining center table;

[0008] S3. Assemble the microscope and the centering fixture, adjust the microscope, align the center of the microscope with the strain gauge ring core, obtain the tool coordinates based on the positional relationship between the microscope and the drill bit, and adjust the position of the tool so that the center of the drill bit is aligned with the strain gauge ring core;

[0009] S4, fixing the strain gauge and one end of the wire to the terminal by soldering, and connecting the other end of the wire to the static strain gauge;

[0010] S5. Turn on the static strain gauge, set the spindle speed of the machining center table machine tool to >50,000 r / min, set the drill feed rate to 1-2 mm, set the tool feed speed to 1 μm / s, and start drilling;

[0011] S6. After drilling is completed, the tool is retracted at a speed of 0.5 mm / s. The drill bit is retracted to more than 2 mm above the strain gauge, and the spindle is stopped. When the fluctuation of the static strain gauge data is less than or equal to the preset threshold, the data is read and recorded. After completion, the component is disassembled and the test is completed.

[0012] In some embodiments, the distance between the centering fixture and the test point is greater than 50 mm.

[0013] In some embodiments, the drill bit is a carbide drill bit, and the drill bit diameter is 1.5 mm.

[0014] In some embodiments, when the fluctuation of the static strain gauge data is less than or equal to a predetermined threshold, the method includes:

[0015] The pre-threshold value is 1 με.

[0016] In some embodiments, the positioning accuracy of the machining center table is greater than or equal to 2 μm.

[0017] Compared with existing technologies, the present invention offers the following advantages: Residual stress testing can be performed using a machining center, eliminating the need for specialized equipment to measure surface residual stress on large and geometrically complex components. High rotational speeds reduce the effects of cutting forces and heat on residual stress at component test points, thereby improving the accuracy of surface residual stress test results. CNC-controlled alignment of the drill bit center and strain gauge ring core reduces the errors caused by traditional manual alignment methods, effectively improving residual stress test accuracy.

[0018] The foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the present disclosure.

[0019] Other features and aspects of the present disclosure will become more apparent from the following detailed description of exemplary embodiments with reference to the attached drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the specific embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0021] Figure 1 A comparison chart of the residual test error of the high-speed drilling surface residual stress test method with the precise centering provided by an embodiment of the present invention and the residual stress test error of the traditional low-speed drilling method. DETAILED DESCRIPTION

[0022] The following will be combined with the drawings in the embodiments of this application to clearly and completely describe the technical solutions in the embodiments of this application. Obviously, the embodiments described are only part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0023] In the description of this application, it should be understood that the terms "center", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc., indicating the orientation or position relationship, are based on the orientation or position relationship shown in the accompanying drawings, and are 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, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on this application.

[0024] The terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of the technical features being referred to. Thus, a feature specified as "first" or "second" may explicitly or implicitly include one or more of such features. Throughout this application, unless otherwise specified, "plurality" means two or more.

[0025] In the description of this application, it should be noted that, unless otherwise expressly specified or limited, the terms "mounted," "connected," and "connected" should be understood in a broad sense. For example, they can refer to fixed, detachable, or integral connections; mechanical or electrical connections; direct or indirect connections through an intermediate medium; and internal communication between two components. Those skilled in the art will understand the specific meanings of the above terms in this application based on the specific circumstances.

[0026] See Figure 1 As shown, a method for testing residual stress on a surface of a high-speed drilled hole with precise centering according to an embodiment of the present application includes the following steps:

[0027] S1. Use 180Cw and 600Cw sandpaper to cross-grind the surface of the target sample, clean the surface of the target sample with anhydrous ethanol, draw reference lines on the surface of the target sample with a pencil to calibrate the test points, and adhere the strain gauge and terminals to the surface of the target sample with 502 glue;

[0028] S2. Clamp the target sample onto a machining center table, and install a centering fixture and a drill bit, wherein the drill bit is perpendicular to the test surface of the machining center table;

[0029] S3. Assemble the microscope and the centering fixture, adjust the microscope, align the center of the microscope with the strain gauge ring core, obtain the tool coordinates based on the positional relationship between the microscope and the drill bit, and adjust the position of the tool so that the center of the drill bit is aligned with the strain gauge ring core;

[0030] S4, fixing the strain gauge and one end of the wire to the terminal by soldering, and connecting the other end of the wire to the static strain gauge;

[0031] S5. Turn on the static strain gauge, set the spindle speed of the machining center table machine tool to >50,000 r / min, set the drill feed rate to 1-2 mm, set the tool feed speed to 1 μm / s, and start drilling;

[0032] S6. After drilling is completed, the tool is retracted at a speed of 0.5 mm / s. The drill bit is retracted to more than 2 mm above the strain gauge, and the spindle is stopped. When the fluctuation of the static strain gauge data is less than or equal to the preset threshold, the data is read and recorded. After completion, the component is disassembled and the test is completed.

[0033] It should be understood that the grit of 180Cw and 600Cw sandpapers is gradually refined, and cross-grinding can evenly remove machining marks on the sample surface to prevent surface roughness from interfering with strain measurement. The cross-grinding direction (such as horizontal first and then vertical) can eliminate the surface texture orientation caused by single-direction grinding, ensure the isotropy of the sample surface, and reduce stress concentration or measurement deviation. The surface finish of the sample after fine grinding is higher, which helps the strain gauge to fit closely to the sample surface, avoid strain transmission loss due to gaps or unevenness, and thus improve measurement sensitivity. Grinding can remove surface oxide layers, scratches or contamination to prevent these defects from inducing local stress mutations during subsequent drilling or loading, affecting the accuracy of residual stress testing.

[0034] Anhydrous ethanol (purity ≥99.7%) is highly volatile and highly soluble, effectively removing contaminants such as grease, dust, and fingerprints from sample surfaces, preventing these impurities from interfering with strain gauge bonding or measuring signals. Compared to aqueous cleaners, anhydrous ethanol leaves no residual water, preventing oxidation and corrosion reactions with metal surfaces. It also prevents traces of water left after evaporation, which can affect surface quality. Anhydrous ethanol evaporates quickly, eliminating the need for additional drying after cleaning, allowing subsequent operations (such as drawing lines and attaching strain gauges) to proceed directly, improving experimental efficiency.

[0035] Pencil markings clearly mark reference lines and test point locations on the specimen surface, providing a benchmark for subsequent drilling alignment and preventing measurement errors due to misalignment. Pencil marks remain on the surface only, without damaging the specimen material or introducing additional stress. They are easily wiped clean, ensuring no interference with subsequent repeat tests. The reference lines serve as a visual aid for microscope alignment, helping the operator quickly adjust the drill bit position and ensure precise alignment between the drill bit center and the strain gauge ring core.

[0036] Terminals connect the strain gauge leads to the conductors through soldering or mechanical crimping, completing the circuit and transmitting the strain gauge's resistance change signal to the static strain gauge. Terminals, typically small metal blocks (such as silver-plated copper), securely hold the wire ends in place, preventing loosening or breakage due to pulling or vibration. Terminals shield against external electromagnetic interference, reducing the coupling of noise signals into the measurement circuit. Standardized interfaces (such as plug-in designs) also facilitate replacement or repair.

[0037] Maintaining the drill bit perpendicular to the test surface (specimen surface) is a key requirement for residual stress testing. A tilted drill bit will generate additional lateral forces during drilling, leading to uneven localized deformation of the specimen and interfering with strain gauge measurements. Vertical drilling ensures stress release is limited to the thickness direction, eliminating the introduction of errors. The tabletop must be precision ground or scraped to a flatness tolerance of ≤2μm to provide uniform support and prevent specimen warping or stress concentration caused by uneven surfaces.

[0038] The machining center can be a high-precision machining center (such as a three-axis or five-axis CNC machine tool), with a table equipped with locating pins, T-slots, or a vacuum adsorption system for quickly securing specimens and fixtures. The centering fixture, such as the Newport 462 series, uses a spiral fine-tuning mechanism or linear guides to achieve submicron adjustment of the drill bit's X / Y / Z axes, ensuring alignment between the drill bit center and the strain gauge ring core. The fixture has a built-in angle sensor or laser calibration device to monitor the perpendicularity of the drill bit axis to the table in real time, with an error of ≤0.1°. This can be an autocollimator (such as the Taylor Hobson Talyvel) or an infrared verticality measurement system.

[0039] The microscope's magnification and positioning functions allow direct observation of the relative position of the strain gauge ring core (typically only 1-2 mm in diameter) and the drill bit center, limiting alignment errors to within ±2 μm and preventing uneven stress release due to eccentric drilling. Traditional alignment methods, which rely on the naked eye or mechanical scales, are susceptible to operator experience. However, a microscope combined with a digital imaging system (such as a CCD camera) provides real-time visual feedback and automatically calculates deviations using image recognition algorithms, improving alignment consistency.

[0040] When the drill bit verticality requirement is extremely high (error ≤ 0.1°) and the rotation speed is >50,000 r / min, the microscope can monitor the drill bit position in real time and dynamically adjust it based on machine tool parameters (such as tool displacement coordinates) to avoid deviation caused by vibration or thermal deformation during high-speed rotation.

[0041] Alignment process: Move the drill bit using the handwheel or servo motor on the machining center so that the image of the strain gauge ring core appears in the microscope field of view. Adjust the drill bit position so that the microscope crosshairs roughly cover the edge of the strain gauge ring core. Switch to high-magnification mode to observe the details of the strain gauge ring core. Fine-tune the drill bit's X / Y axis position so that the center of the microscope crosshairs completely coincides with the geometric center of the strain gauge ring core. Observe the contact between the drill bit edge and the specimen surface through a microscope. Adjust the drill bit inclination angle to ensure that the drill bit axis is perpendicular to the specimen surface. Some systems use laser projection or autocollimators to assist in verifying verticality. Use the center of the microscope crosshairs as the origin to establish the machine tool coordinate system (XY plane) and the drill bit feed coordinate (Z axis). Use a microscope calibration plate (such as a grid plate) or a standard part of known size to convert the pixel position in the microscope field of view into actual coordinates (such as 1 pixel = 0.1 μm). When the drill bit center is aligned with the strain gauge ring core, the machine tool's X / Y coordinates (e.g., X = 10.002 mm, Y = 5.001 mm) are recorded and used as the tool's reference position. If drilling is required at different measurement points, the alignment process can be repeated using a coordinate offset (e.g., ΔX = 0.5 mm, ΔY = 0 mm). During drilling, if the drill bit deviates due to thermal deformation or vibration, the microscope monitors the deviation in real time and automatically compensates for the displacement using the machine tool's closed-loop control system (e.g., a PID algorithm). For example, if the microscope detects a drill bit center offset ≥1 μm, the machine tool pauses drilling, adjusts the X / Y axis position, and resumes feeding. Coaxial light or ring-shaped LED illumination is used to reduce shadow interference and ensure clear visibility of the strain gauge ring core edge. Some systems use ultraviolet light to excite fluorescent markers (e.g., fluorescent spots on the strain gauge) to improve contrast. Edge detection algorithms (e.g., the Canny operator) automatically extract the strain gauge ring core outline and calculate the geometric center coordinates. Machine learning (e.g., template matching) is combined to accommodate strain gauges of varying shapes or colors. The microscope coordinate data is transmitted to the machine tool control system via RS-232 or Ethernet interface to achieve automatic adjustment of the drill position.

[0042] At extremely high speeds, the drill bit's contact time with the material is extremely short (on the order of milliseconds). Frictional heat generated by the specimen is limited to a microscopic surface area, preventing localized temperature rise that could lead to material softening or phase transformation. This ensures that the stress release process occurs within the elastic deformation phase, conforming to the linear assumption of residual stress testing. Compared to low-speed drilling, high-speed cutting reduces the perturbation of the specimen caused by mechanical loads and avoids the introduction of additional stress fields due to plastic deformation. A feed rate of 1-2 mm covers the residual stress gradient from the surface to the subsurface, capturing both surface residual stresses due to work hardening and the true stress state in the deeper layers of the material. This parameter, aligned with the strain gauge core size (typically 1-2 mm in diameter), ensures that the strain relief region fully overlaps with the strain gauge sensitive area during drilling, preventing data loss. A feed rate that is too small (e.g., <1 mm) may result in insufficient stress release, while a feed rate that is too large (e.g., >2 mm) may penetrate the specimen or introduce excessive perturbation. A setting of 1-2 mm ensures sufficient stress release while avoiding irreversible damage to the specimen substrate.

[0043] The ultra-low feed rate (1 μm / s) allows the drilling process to approach quasi-static loading, allowing strain gauges to capture stress gradient changes in real time, preventing dynamic effects (such as inertial forces or stress waves) from interfering with the measurement results. This speed matches the sampling frequency of the static strain gauge (typically ≥100 Hz), ensuring that strain data for every micron feed step is fully recorded, providing high-density data support for subsequent integral calculations of residual stresses.

[0044] The combination of high speed and low feed rate ensures instantaneous stress release while avoiding dynamic errors. This results in a smooth and continuous strain-depth curve measured by the strain gauge, making it easier to fit and calculate residual stress. For example, for every 1μm of drill penetration, the strain gauge captures the corresponding linear segment of ε change, preventing computational model failure due to nonlinear response.

[0045] In some specific embodiments, the distance between the centering fixture and the test point is greater than 50 mm.

[0046] In some specific embodiments, the drill bit is a carbide drill bit, and the diameter of the drill bit is 1.5 mm.

[0047] In some specific embodiments, the method of waiting for the static strain gauge data fluctuation to be less than or equal to a predetermined threshold value includes:

[0048] The pre-threshold value is 1 με.

[0049] In some specific embodiments, the positioning accuracy of the machining center table is greater than or equal to 2 μm.

[0050] The distance between the fixture and the test point is >50mm, which can effectively isolate the stress field transmitted from the clamping force to the specimen. According to the stress attenuation law (generally, the stress decays to 1 / 4 for every doubling of the distance from the clamping point), a spacing of 50mm can reduce the clamping stress to a negligible level (<1με), preventing it from superimposing on the residual stress and causing measurement deviation. When the machining center is running, the fixture may produce slight vibrations due to the high-speed rotation of the spindle (>50,000r / min). A distance of >50mm can reduce the transmission of vibrations through the specimen to the test point, ensuring the stability of the strain gauge signal. For special-shaped or small specimens, the fixture is far away from the test point to avoid structural interference and provide spatial redundancy for the layout of multiple measuring points. For example, when drilling multiple holes on a pipe or curved specimen, the fixture position does not affect the positioning of other measuring points.

[0051] Carbide drill bits have high hardness (HRA89-92) and strong wear resistance, which can maintain the sharpness of the cutting edge. Even at a small diameter of 1.5mm, they can still achieve smooth hole walls (roughness Ra ≤ 0.8μm), avoiding the introduction of additional stress fields due to burrs or microcracks on the hole edge. Carbide has better toughness than ceramic or diamond tools. Under high-speed rotation (>50,000r / min) and low-speed feed (1μm / s), it can withstand drilling torque without breaking. It is especially suitable for hard materials (such as hardened steel) or composite materials. Carbide has a low thermal expansion coefficient (about 7×10 -6 / °C), which better matches the sample material (such as steel with a similar thermal expansion coefficient), reduces aperture deviation caused by temperature changes, and ensures consistent drilling dimensions. Data fluctuations ≤ 1με (microstrain) indicate that the strain gauge signal has entered a steady state, eliminating the influence of environmental noise (such as temperature fluctuations, electromagnetic interference) or machine tool vibration. Starting drilling at this time ensures accurate initial strain values, providing a reliable benchmark for subsequent stress release calculations. The residual stress calculation formula for the blind hole method relies on the slope of the strain-depth curve (dε / dz). If the data fluctuations exceed 1με, the fitting error will increase and even the stress direction (tensile stress / compressive stress) will be misjudged. Fluctuations ≤ 1με ensure that the slope calculation error is less than 5%, meeting engineering precision requirements.

[0052] A positioning accuracy of 2μm or greater ensures alignment error between the drill bit center and the strain gauge ring core of 2μm or less, preventing asymmetric stress release due to positional offset. For example, a 2μm offset on a 1.5mm diameter drill bit can cause a difference of more than 10% in strain distribution around the hole edge, directly affecting calculation results.

[0053] Obviously, those skilled in the art may make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if such changes and modifications fall within the scope of the claims and their equivalents, the present invention is intended to include such changes and modifications.

Claims

1. A method for testing residual stress on the surface of a precisely centered high-speed drilled hole, characterized in that: The following steps are involved: S1. Use 180Cw and 600Cw sandpaper to cross-grind the surface of the target sample, clean the surface of the target sample with anhydrous ethanol, draw reference lines on the surface of the target sample with a pencil to calibrate the test points, and adhere the strain gauge and terminals to the surface of the target sample with 502 glue; S2. Clamp the target sample onto a machining center table, and install a centering fixture and a drill bit, wherein the drill bit is perpendicular to the test surface of the machining center table; S3. Assemble the microscope and the centering fixture, adjust the microscope, align the center of the microscope with the strain gauge ring core, obtain the tool coordinates based on the positional relationship between the microscope and the drill bit, and adjust the position of the tool so that the center of the drill bit is aligned with the strain gauge ring core; S4, fixing the strain gauge and one end of the wire to the terminal by soldering, and connecting the other end of the wire to the static strain gauge; S5. Turn on the static strain gauge, set the spindle speed of the machining center table machine tool to >50,000 r / min, set the drill feed rate to 1-2 mm, set the tool feed speed to 1 μm / s, and start drilling; S6. After drilling is completed, the tool is retracted at a speed of 0.5 mm / s. The drill bit is retracted to more than 2 mm above the strain gauge, and the spindle is stopped. When the fluctuation of the static strain gauge data is less than or equal to the preset threshold, the data is read and recorded. After completion, the component is disassembled and the test is completed.

2. The method for testing surface residual stress of a precisely centered high-speed drilling hole according to claim 1, characterized in that: The distance between the centering fixture and the test point is greater than 50 mm.

3. The method for testing surface residual stress of a precisely centered high-speed drilling hole according to claim 1, characterized in that: The drill bit is a carbide drill bit, and the diameter of the drill bit is 1.5 mm.

4. The method for testing surface residual stress of a precisely centered high-speed drilling hole according to claim 1, characterized in that: When the fluctuation of the static strain gauge data is less than or equal to a preset threshold, the method includes: The pre-threshold value is 1 με.

5. The method for testing surface residual stress of high-speed drilling with precise centering according to claim 1, characterized in that: The positioning accuracy of the machining center table is greater than or equal to 2 μm.

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