A flexible force control clamping device and method for adaptive complex curved surface aluminum castings

Abstract

The application discloses a flexible force control clamping device and method for adaptive complex curved surface aluminum castings. The device comprises a base assembly, a phase change rigidity adjusting assembly, an array profiling assembly and a grating force control feedback assembly. The magnetorheological fluid of the phase change rigidity adjusting assembly is filled in the accommodating cavity of the base assembly, and the excitation coil is arranged along the inner wall of the accommodating cavity. The lower part of the column pin of the array profiling assembly is inserted into the magnetorheological fluid, and the upper part is connected with the metal rod body, and the annular micro groove is arranged at the connection position. The fiber Bragg grating sensor of the grating force control feedback assembly is packaged in the annular micro groove and connected with the photoelectric demodulator. When the contact force exceeds the preset thin wall deformation threshold, the industrial computer reduces the output current of the corresponding excitation coil. The application can realize the shape and pressure fitting, high-precision clamping and positioning, and dynamic retreat and vibration absorption effect in the machining.

Description

Technical Field

[0001] This invention relates to the field of machine tool fixture technology, specifically to a flexible force-controlled clamping device and method for adaptive complex curved aluminum castings used in five-axis CNC machine tool machining of thin-walled aluminum alloy curved surface castings. Background Technology

[0002] In the field of new energy vehicle manufacturing, aluminum alloy die-cast parts such as motor housings and steering knuckles extensively employ complex free-form surface and thin-walled structure designs. During precision milling on five-axis CNC machine tools, the clamping and positioning of these thin-walled aluminum castings face significant physical challenges. Currently, industrial sites primarily rely on traditional rigid fixtures for workpiece clamping, such as conventional vises or custom-made cast iron jigs for specific parts. These rigid fixtures generally employ a hard-point contact positioning method.

[0003] Due to the unavoidable microscopic surface contour tolerances inherent in aluminum castings during cooling and shrinkage, rigid clamping points cannot perfectly conform to the actual microscopic curved surfaces of each workpiece. This limitation in contact area leads to severe stress concentration in localized areas of the workpiece when clamping force is applied. For thin-walled areas, this concentrated stress can easily induce elastic deformation of the material, even leaving irreversible indentations on the workpiece surface. After machining is completed and the clamping force is released, the elastic potential energy stored in the workpiece causes it to elastically recover. This release process directly results in out-of-tolerance dimensional and positional tolerances on the machined precision mating surfaces.

[0004] Furthermore, during the dynamic process of CNC milling, the interaction between the tool and the workpiece generates continuous high-frequency cutting vibrations. Currently, the industry uses array-type contour jigs locked by mechanical wedges or cylinders. However, after the locking action is completed, the entire support system of these jigs exhibits a completely rigid state. Rigid structures cannot effectively dissipate and absorb the vibration energy from high-frequency cutting, causing the peak cutting force to be directly and undampedly transmitted to the weak areas of the workpiece. This not only causes obvious chatter marks on the machined surface, but in extreme conditions, it can even lead to the scrapping of the entire workpiece due to microscopic tearing. Currently, it is difficult to find a comprehensive clamping solution that can simultaneously achieve adaptive fitting of complex curved surfaces, high-precision clamping and positioning, and dynamic yielding and vibration absorption during machining. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a flexible force-controlled clamping device and method to overcome the defects of existing rigid clamps that easily cause deformation of thin-walled aluminum castings and cannot absorb cutting vibrations.

[0006] To address the aforementioned technical problems, this invention provides a flexible force-controlled clamping device for adaptive complex curved aluminum castings, comprising a base assembly with an internal receiving cavity, and a guide perforated plate made of non-magnetic material connected to the top of the base assembly; a phase change stiffness adjustment assembly including a magnetorheological fluid filled in the receiving cavity and excitation coils arranged along the inner wall of the receiving cavity; and an array contouring assembly including multiple pins, the lower parts of which pass through the guide perforated plate and are inserted into the magnetorheological fluid in the receiving cavity. Each pin includes a lower metal rod and an upper polymer ball head. An annular microgroove is formed at the connection between the polymer ball head and the metal rod; the grating force control feedback component includes a fiber Bragg grating sensor, a photoelectric demodulator, and an industrial computer; the fiber Bragg grating sensor is encapsulated inside the annular microgroove and connected to the photoelectric demodulator via a pigtail; the photoelectric demodulator is connected to the industrial computer; the industrial computer is connected to the excitation coil; the photoelectric demodulator is configured to calculate the contact force based on the reflected light signal; the industrial computer is configured to reduce the output current of the excitation coil in the corresponding area when the contact force borne by the local pin exceeds a preset thin-wall deformation threshold.

[0007] In one optional embodiment, the metal rod and the polymer ball head are connected by threads; the annular microgroove is disposed at the root position where the lower end face of the polymer ball head and the upper end face of the metal rod are spliced ​​together; the fiber Bragg grating sensor is equidistantly wound around the annular microgroove and sealed and fixed in the annular microgroove with epoxy resin adhesive.

[0008] In one optional embodiment, the outer wall of the metal rod is provided with a fiber guide groove extending through the annular microgroove along the axial direction; the depth of the fiber guide groove is greater than the outer diameter of the fiber; the fiber extends from the annular microgroove along the trajectory of the fiber guide groove to the outside of the receiving cavity; the fiber guide groove is filled with a flexible sealant layer, which is flush with the outer surface of the metal rod.

[0009] In one optional embodiment, the excitation coil includes multiple independent annular electromagnetic windings stacked along the depth direction of the receiving cavity; the receiving cavity is also provided with multiple non-magnetic isolation rings, and two adjacent independent annular electromagnetic windings are separated by one of the non-magnetic isolation rings, forming multiple magnetic field distribution layers independently arranged along the axial direction.

[0010] In one optional embodiment, a magnetic energy-concentrating ring is embedded on the inner sidewall surface of the guide perforated plate corresponding to the magnetic circuit penetration area of ​​the independent annular electromagnetic winding; the magnetic energy-concentrating ring is made of silicon steel; the thickness of the magnetic energy-concentrating ring gradually decreases from the middle to both ends.

[0011] In one optional embodiment, the polymer ball head is made of polyetheretherketone material; the guide porous plate has guide through holes corresponding to a plurality of the pins, and the metal rod is slidably inserted into the guide through holes.

[0012] This invention also provides a clamping control method for adaptive complex curved surface aluminum castings, applied to the aforementioned flexible force-controlled clamping device for adaptive complex curved surface aluminum castings. The method includes acquiring the reflected light wavelength signal detected by the fiber Bragg grating sensor; calculating the contact force borne by the polymer ball head based on the reflected light wavelength signal; and, in response to the contact force exceeding a preset thin-wall deformation threshold, reducing the output current of the excitation coil in the corresponding region, weakening the yield stress of the magnetorheological fluid in the corresponding region, and causing the compressed pin to axially retract.

[0013] In one optional implementation, the step of reducing the output current of the excitation coil in the corresponding region in response to the contact force being greater than a preset thin-wall deformation threshold includes obtaining the difference between the contact force and the preset thin-wall deformation threshold; inputting the difference to an incremental proportional-integral-derivative (PID) controller; calculating a target current attenuation based on the output result of the IPD controller; and controlling the output current of the excitation coil in the corresponding region to decrease in a stepwise manner according to the target current attenuation.

[0014] In an optional embodiment, the method further includes continuously monitoring the contact force after the pin undergoes axial retraction; and initiating a relocking process in response to the contact force falling below a safety threshold; the relocking process includes acquiring the current residual current value of the excitation coil and controlling the output current of the excitation coil to linearly increase from the residual current value to the initial operating current value according to a preset current recovery slope; wherein the safety threshold is set to 80% to 90% of the preset thin-wall deformation threshold, and the current recovery slope is dynamically configured according to the rotational speed frequency of the cutting spindle.

[0015] The present invention also provides a control device, including a microprocessor and a memory storing computer instructions, wherein the microprocessor, when executing the computer instructions, implements the above-described adaptive clamping control method for complex curved aluminum castings. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the overall structure of the flexible force-controlled clamping device provided in an embodiment of the present invention.

[0017] Figure 2 This is a three-dimensional sectional view of the flexible force-controlled clamping device provided in an embodiment of the present invention.

[0018] Figure 3This is a partially enlarged view of the pin and grating force control feedback component provided in an embodiment of the present invention.

[0019] Figure 4 This is a block diagram of the logic structure of the control system provided in an embodiment of the present invention.

[0020] Figure 5 This is a flowchart of the clamping control method provided in the embodiment of the present invention.

[0021] In the picture: 101-Base assembly, 102-Guide perforated plate, 103-Pin, 104-Corrugated dust cover, 201-Receiving cavity, 202-Magnetorheological fluid, 203-Excitation coil, 204-Independent toroidal electromagnetic winding, 205-Non-magnetic isolation ring, 206-Magnetic energy-concentrating ring, 207-Limiting ring, 301-Metal rod, 302-Polymer ball head, 303-Threaded connection, 304-Annular microgroove, 305-Fiber Bragg grating sensor, 306-Fiber pigtail, 307-Fiber pigtail guide groove, 308-Flexible sealing layer, 309-Epoxy resin adhesive, 401-Photoelectric demodulator, 402-Industrial computer, 403-External power supply module, 404-Adjustable current drive circuit module, 405-Communication interface module. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0023] This application provides a flexible force-controlled clamping device for adaptive complex curved aluminum castings. For example... Figure 1 As shown, the device mainly comprises a base assembly 101, a phase change stiffening assembly, an array contouring assembly, and a grating force control feedback assembly for acquiring stress data, all housed within the base assembly 101 and associated with it. The base assembly 101 is a shell structure with a closed bottom, and its exterior is provided with flange edges and locating pin holes for fastening to the worktable of a five-axis CNC machine tool. The base assembly 101 is made of high-strength cast iron or alloy steel to ensure that it will not undergo structural yielding or deformation under high-frequency cutting vibration. A guide perforated plate 102 is connected to the top of the base assembly 101, and this guide perforated plate 102 is rigidly connected to the top edge of the base assembly 101 by circumferentially distributed high-strength fastening screws.

[0024] Specifically, to prevent the magnetic field generated during clamping from leaking to the machine tool end or interfering with the movement of the pins 103, the guide perforated plate 102 is made of a non-magnetic material. In this embodiment, the guide perforated plate 102 is specifically made of brass. Brass not only possesses excellent non-magnetic properties, effectively cutting off the upward escape path of magnetic lines of force, but also has good self-lubricating properties, reducing frictional losses of subsequent inserting components. The array contouring assembly includes multiple matrix-arranged pins 103. All pins 103 are arranged vertically and distributed in a dot matrix above the guide perforated plate 102 for direct physical contact with the thin-walled aluminum casting placed above. To prevent coolant and aluminum dust from entering the device during processing, the base assembly 101 also includes a corrugated dust cover 104 fitted over the pins 103. By using a combination of an integral housing and a brass perforated plate, a robust and magnetically controlled foundation support platform can be provided for the device.

[0025] like Figure 2 As shown, the base assembly 101 has a sealed receiving cavity 201 inside. The receiving cavity 201 is a one-piece blind hole structure, and its inner wall surface is precision bored to ensure cylindricity. The phase change stiffening assembly includes magnetorheological fluid 202 filled inside the receiving cavity 201, and excitation coils 203 arranged in a circumferential array along the inner wall of the receiving cavity 201. The magnetorheological fluid 202 is mainly composed of micron-sized magnetic particles, a base fluid, and surface-active additives to prevent particle sedimentation. Under normal conditions without an applied external magnetic field, the magnetorheological fluid 202 exhibits Newtonian fluid characteristics with a certain degree of fluidity, extremely low yield stress, and internal particles in a disordered free state. The excitation coils 203 are embedded in an annular groove reserved in the side wall of the receiving cavity 201, and are physically isolated from the magnetorheological fluid 202 by a thin-walled non-magnetic insulating sleeve to prevent the coil insulation layer from being eroded by the fluid.

[0026] In the sidewall structure of the receiving cavity 201, the excitation coil 203 includes multiple independent annular electromagnetic windings 204 stacked along the depth direction of the receiving cavity 201. Multiple non-magnetic isolation rings 205 are also provided inside the receiving cavity 201, with each adjacent independent annular electromagnetic winding 204 separated by a non-magnetic isolation ring 205. The non-magnetic isolation rings 205 can be made of epoxy fiberglass board. A magnetically conductive energy-concentrating ring 206 is embedded on the inner sidewall surface of the guide perforated plate 102 corresponding to the magnetic circuit penetration area of ​​the independent annular electromagnetic windings 204. This magnetically conductive energy-concentrating ring 206 is made of cold-rolled grain-oriented silicon steel, which has extremely high permeability and low hysteresis loss. By setting the independent annular electromagnetic windings 204 and the magnetically conductive energy-concentrating ring 206, multiple axially independently arranged magnetic field distribution layers can be formed. More importantly, the axial cross-sectional thickness of the magnetic concentrating ring 206 exhibits a geometric feature that gradually decreases from the middle to both ends, i.e., a wedge-shaped structure that is thicker in the middle and thinner at the edges. This gradually varying thickness structure forces magnetic field lines to converge when penetrating the silicon steel layer, eliminating magnetic flux leakage caused by edge effects and guiding high-density magnetic field lines orthogonally through the gaps in the magnetorheological fluid 202. Through the magnetic focusing effect of the magnetic concentrating ring 206, the phase transition response speed of the local magnetorheological fluid 202 can be improved, enabling it to complete the liquid-solid conversion within milliseconds.

[0027] Under the influence of the magnetic field generated by the excitation coil 203 after the magnetorheological fluid 202 is energized, its internal rheological properties will change drastically. Specifically, the nonlinear relationship between the yield shear stress of the local magnetorheological fluid 202 and the magnetic field strength follows the physical laws of the system.

[0028]

[0029] The physical parameters in the formula are defined as follows: This represents the macroscopic yield shear stress exhibited by magnetorheological fluid 202 in the direction perpendicular to the magnetic field lines; B This represents the magnetic flux density generated in a local region by the independent toroidal electromagnetic winding 204; k This represents the medium constant related to the magnetorheological fluid ratio and ambient temperature. In this embodiment, B The operating value range is generally between 0.2T and 0.8T, while k The reference value is approximately 120 kPa / T². According to this formula, by changing the excitation current input to the excitation coil 203, a quadratic amplification control of the fluid shear yield stress can be achieved, which macroscopically manifests as stepless stiffness adjustment of the immersed pin 103 from "free sliding" to "rigid locking". It should be noted that the above medium constant is only an example; those skilled in the art can calibrate the constant according to the specific fluid type selected.

[0030] The lower half of the pin 103 is inserted into the receiving cavity 201 through a guide hole in the guide perforated plate 102 and is immersed in the magnetorheological fluid 202. A limiting ring 207 is provided on the lower end face of the pin 103. The outer diameter of the limiting ring 207 is larger than the inner diameter of the guide hole. This ring is used to prevent the pin 103 from being pulled out of the base by interfering with the bottom surface of the guide perforated plate 102 when the pin 103 is subjected to an upward pull-out force. When the aluminum casting is placed above the array of pins 103 and an initial downward clamping pressure is applied, the magnetorheological fluid 202 is in a liquid state because the excitation coil 203 is not energized at this time. Under the pressure of the complex curved surface of the aluminum casting, each pin 103 can freely generate axial displacement of different heights along the guide hole. The excess magnetorheological fluid 202 flows freely in the connecting gap in the receiving cavity 201 to compensate for the volume, thereby passively realizing the conformal fit of the entire array of pins 103 to the three-dimensional contour of the workpiece. Once the fit is complete, the system outputs current to the excitation coil 203, exciting the magnetic field to complete the rigid locking of the entire array.

[0031] like Figure 3 As shown, the pin 103 is not a single-material monolithic cylinder in its physical structure, but rather adopts a split splicing structure to accommodate different engineering needs. The pin 103 includes a lower metal rod 301 and an upper polymer ball head 302. The metal rod 301 is made of 304 stainless steel to ensure sufficient rigidity and fatigue strength when subjected to repeated axial cutting pressure. The guide through-hole on the guide perforated plate 102 and the metal rod 301 are fitted with a clearance fit, allowing the metal rod 301 to slide through the guide through-hole. The polymer ball head 302 is made of polyetheretherketone (PEEK). The elastic modulus of PEEK is between that of conventional metals and elastic rubber. This special mechanical property allows it to provide stable rigid positioning support when in contact with thin-walled aluminum castings, while also preventing hard scratches or indentations on the smooth surface of the aluminum castings. The upper end of the corrugated dust cover 104 mentioned above is sealed and fixed to the lower edge of the polymer ball head 302 with a clamp, while its lower end is sealed and fixed to the top surface of the guide perforated plate 102 with adhesive. The metal rod 301 and the polymer ball head 302 are fastened together by a threaded connection 303. By combining the flexible polymer ball head 302 with the rigid metal rod 301, a first line of mechanical flexible defense against surface damage can be built at the workpiece contact interface.

[0032] A deep annular microgroove 304 is formed at the neck position where the polymer ball head 302 and the metal rod 301 are joined. Specifically, the annular microgroove 304 is located at the root of the joint between the lower end face of the polymer ball head 302 and the upper end face of the metal rod 301. To ensure structural strength while accommodating the sensing element, the axial depth of the annular microgroove 304 is precisely controlled at 2 mm. The device is also equipped with a grating force control feedback assembly, the core of which is a fiber Bragg grating sensor 305 encapsulated inside the annular microgroove 304. The fiber Bragg grating sensor 305 reflects a specific wavelength spectrum by periodically modulating the refractive index of the fiber core. When the end of the pin 103 is subjected to external pressure, causing a slight deformation in its neck, the period of the grating changes, thereby causing a drift in the reflected wavelength. The fiber Bragg grating sensor 305 is wound multiple times equidistantly around the annular microgroove 304 to enhance the sensitivity to strain. To ensure the survival rate of the sensor in harsh processing environments, the fiber Bragg grating sensor 305 is sealed and fixed within the annular microgroove 304 using a dedicated epoxy resin adhesive 309. After curing, the epoxy resin adhesive 309 firmly bonds the grating fiber to the groove wall, thus achieving complete physical isolation of the fiber Bragg grating sensor 305 from external cutting fluid, aluminum chips, and strong magnetic field environments.

[0033] The fiber Bragg grating sensor 305 transmits optical signals outward via an extremely fine pigtail 306. A pigtail guide groove 307, extending through an annular microgroove 304, is formed along the outer wall of the metal rod 301, running axially downwards. Due to the relatively fragile material of the pigtail 306, the processing depth of the pigtail guide groove 307 must be greater than the outer diameter of the pigtail 306 to ensure that the pigtail 306 sinks into the groove and does not protrude from the surface of the metal rod 301. After being led out from the annular microgroove 304, the pigtail 306 extends downwards along the trajectory of the pigtail guide groove 307, eventually passing through the guide porous plate 102 and extending to the outside of the receiving cavity 201. To prevent leakage and seepage of the magnetorheological fluid 202 or external impurities through the groove, a flexible sealant layer 308 is filled into the fiber optic guide groove 307. After leveling during construction, the outer surface of the flexible sealant layer 308 is completely flush with the outer cylindrical surface of the metal rod 301, thus not affecting the sliding fit of the metal rod 301 within the guide hole. The design of the fiber optic guide groove 307 and the flexible sealant layer 308 provides a safe, concealed, and leak-proof physical channel for fragile pure optical signal transmission lines.

[0034] like Figure 4As shown, at the system control level, the grating force control feedback component also includes an opto-demodulator 401 and an industrial computer 402 located outside the clamping device. The end of the pigtail 306 is connected to the optical interface of the opto-demodulator 401. The opto-demodulator 401 internally contains a broadband light source and a high-precision spectral analysis module, configured to emit a light beam in real time and receive reflected light signals from the fiber Bragg grating sensor 305. The opto-demodulator 401 is connected to the industrial computer 402 via a high-speed Ethernet bus, and the industrial computer 402, as the core computing unit, is responsible for issuing commands.

[0035] In addition, to support the closed-loop operation of the entire device, the system is also equipped with an external power supply module 403, an adjustable current drive circuit module 404, and a communication interface module 405. The external power supply module 403 is connected to the industrial power grid and performs transformer rectification to power the photoelectric demodulator 401 and the industrial control computer 402. The signal input terminal of the adjustable current drive circuit module 404 is connected to the control port of the industrial control computer 402, and its high-power output terminal is connected to the independent ring electromagnetic windings 204 of each area. The communication interface module 405 connects the industrial control computer 402 and the CNC system of the machine tool host to synchronize the spindle speed and feed status of the machine tool. The industrial control computer 402 is configured to execute the core adaptive logic, that is, when the cutting contact force borne by the pin 103 in a local area exceeds the preset thin-wall deformation threshold, it sends an attenuation command to the adjustable current drive circuit module 404 to instantly reduce the output current of the excitation coil 203 in the corresponding area.

[0036] The photoelectric demodulator 401 extracts the wavelength drift data of the reflected light signal and calculates the equivalent contact force borne by the end face of the polymer ball head 302 based on physical principles. The specific mapping law between wavelength drift and axial strain can be expressed by the following relationship.

[0037]

[0038] The physical parameters in the formula are defined as follows: This indicates the real-time drift of the center wavelength reflected by the fiber Bragg grating sensor 305. This indicates the initial center wavelength of the sensor under stress-free conditions, typically around 1550nm. P e This represents the effective elastic-optical coefficient of the optical fiber core material; for silica optical fiber, its typical reference value is 0.22. This represents the microscopic axial strain generated at the installation location; This represents the coefficient of thermal expansion of the optical fiber; This represents the thermo-optic coefficient of the optical fiber; This represents the amount of temperature change relative to an environmental reference. In constant-temperature workshops or scenarios where processing temperatures change slowly, the spectral drift caused by temperature fluctuations is extremely small. Therefore, the photoelectric demodulator 401 will include the amount of temperature change. The compensation term was eliminated as a constant for simplification. Subsequently, the system directly extracted the pure axial strain based on the wavelength shift. By combining the cross-sectional area and elastic modulus of the neck of the metal rod 301, the strain is linearly converted into a real-time clamping contact force value. It should be noted that the above formula fully elucidates the coupling mechanism of opto-mechanical conversion, and those skilled in the art can use high-frequency sampling demodulation algorithms to improve the refresh frequency of the contact force.

[0039] The hardware system of this application embodiment solves the detection blind zone problem in strong magnetic field environments by introducing a fiber Bragg grating sensor 305. In previous technologies, if conventional piezoelectric ceramic sensors or resistance strain gauges were used to measure the force state, the phase change stiffness adjustment of the magnetorheological fluid 202 required frequent changes in the current of the excitation coil 203. This dynamic process would generate strong alternating electromagnetic pulses around the receiving cavity 201. According to Faraday's law of electromagnetic induction, these pulses would induce a huge induced electromotive force in the metal circuit of conventional electrical sensors, causing the feedback electrical signal to be completely submerged by magnetic field interference noise, resulting in serious misjudgments by the industrial control computer 402. This device utilizes the purely optical, non-electrical physical nature of the fiber Bragg grating, enabling the sensing signal to be transmitted in the form of photons in silica fibers. This physical mechanism blocks the coupling interference of the external Maxwell alternating electromagnetic field on the detection circuit. Based on this, extremely weak mechanical deformation forces can be accurately captured in magnetic field storms of tens of thousands of gauss, providing a unique and reliable closed-loop data source for subsequent dynamic flexible force control based on the magnetorheological fluid 202.

[0040] Based on the aforementioned physical platform, this application further implements a clamping control method. For example... Figure 5 As shown, the adaptive complex curved surface aluminum casting clamping control method provided in this application embodiment provides ordered time sequence actions, which are mainly automatically executed by the industrial control computer 402 in the control system in coordination with various modules.

[0041] Step S1: Acquire the reflected light wavelength signal detected by the fiber Bragg grating sensor 305. The system acquires the reflected light wavelength signal detected by the fiber Bragg grating sensor 305 through the photoelectric demodulator 401. The photoelectric demodulator 401 performs digital discrete sampling on the captured spectral information.

[0042] Step S2: Calculate the contact force borne by the polymer ball head 302 based on the reflected light wavelength signal. Based on the analyzed reflected light wavelength shift, calculate the current contact force value borne by the polymer ball head 302 according to the aforementioned conversion model. This contact force reflects the instantaneous impact load generated when the machine tool tool presses against the thin-walled surface of the aluminum casting.

[0043] In step S3, in response to the contact force exceeding a preset thin-wall deformation threshold, the industrial control computer 402 reduces the output current of the excitation coil 203 in the corresponding area, weakening the yield stress of the magnetorheological fluid 202 in the corresponding area, causing the compressed pin 103 to axially retract. After acquiring a continuous contact force data stream, the logic judgment unit inside the industrial control computer 402 continuously compares the contact force with the pre-stored preset thin-wall deformation threshold. This preset thin-wall deformation threshold is the critical elastic deformation force obtained through finite element simulation or experimentation, based on the currently processed aluminum alloy grade and its wall thickness characteristics. When a sudden surge in contact force at a certain local location is detected, exceeding the preset thin-wall deformation threshold, the industrial control computer 402 immediately responds, reducing the output current of the excitation coil 203 in the impacted area through the adjustable current drive circuit module 404. The decrease in current weakens the magnetic field strength in that area, and according to the aforementioned yield stress formula, the yield stress of the magnetorheological fluid 202 in the corresponding area is significantly reduced. At the instant the shear stress decreases, the previously rigidly locked pin 103, under external overload pressure exceeding the threshold, breaks through the locking resistance of the magnetorheological fluid 202, resulting in a slight downward axial displacement. This microscopic axial yielding action instantly inserts a high-damping hydraulic spring at the bottom of the workpiece, converting the destructive peak energy from tool cutting into fluid frictional heat energy for dissipation, thereby achieving dynamic vibration absorption and protecting the thin-walled area from being crushed.

[0044] To achieve precise and overshoot-free yield control, in one optional implementation, the process of the industrial control computer 402 reducing the output current of the excitation coil 203 in the corresponding area incorporates a closed-loop regulation algorithm. The industrial control computer 402 acquires the numerical difference between the actual contact force at the current instant and the preset thin-wall deformation threshold. To convert this error signal into a control command, the industrial control computer 402 inputs the difference to a built-in incremental proportional-integral-derivative (PID) controller. This controller outputs a smooth regulation command by proportionally amplifying, accumulating integrals, and performing differential prediction calculations on the deviation sequence. Subsequently, based on the output of the IPD controller, the system accurately calculates the current required target current attenuation. The industrial control computer 402 controls the output current of the excitation coil 203 in the corresponding area to decrease rapidly in a step-like manner according to the target current attenuation. In this embodiment, the proportional gain parameter of the IPD controller can be configured to be between 0.4 and 0.8, and the preset thin-wall deformation threshold is typically set between 300N and 500N. By introducing an incremental controller algorithm, response hysteresis caused by integral depth saturation can be prevented, ensuring that the current drop is proportional to the actual overload impact. This allows the retraction distance of pin 103 to be controlled at the micrometer level, absorbing vibration without affecting the overall machining positioning reference. It should be noted that the above parameters are only preferred ranges for machining specific aluminum parts in this embodiment. Those skilled in the art can adjust the control parameters appropriately according to the stiffness characteristics of the actual material.

[0045] After vibration absorption is completed, the fixture must quickly return to its rigid state to support subsequent milling paths. In one alternative embodiment, after the pin 103 undergoes axial retraction, the industrial computer 402 continuously monitors the grating contact force in that local area. In response to the contact force gradually decreasing to below a set safety threshold due to the retraction action, the system formally initiates the relocking process. This relocking process is initiated by the industrial computer 402 acquiring the residual current value maintained by the current excitation coil 203. Based on a current recovery slope preset in the memory of the industrial computer 402, the adjustable current drive circuit module 404 controls the output current of the excitation coil 203 to gradually and linearly increase from the residual current value according to the set slope until it returns to the initial operating current value.

[0046] In this recovery control logic, the definition of parameters directly affects the smoothness of machining. The safety judgment threshold is set to 80% to 90% of the preset thin-wall deformation threshold (for example, if the deformation threshold is 400N, the safety judgment threshold is set between 320N and 360N). The residual current value is typically maintained at around 0.5A during retraction, and the initial working current value is generally set between 2.0A and 3.0A. Furthermore, the current recovery slope is dynamically configured based on the spindle speed frequency. If the spindle speed is high, a steeper slope is configured to achieve rapid locking; if the speed is low and the feed is slow, a gentler slope is configured to prevent secondary oscillations caused by sudden current surges. By setting hysteresis judgment within the threshold range and linear slope recovery based on the spindle frequency, high-frequency vibrations in the fixture between rigid and flexible states can be avoided, ensuring a smooth transition of the cutting edge and eliminating wavy chatter marks on the machined surface.

[0047] Based on the synergy of the aforementioned hardware structure and software algorithm, the working principle of this application in actual operation can be summarized as follows: During the preparation stage, in the unpowered state, the thin-walled aluminum casting is placed on the polymer ball head 302. Gravity and initial mechanical clamping force cause each pin 103 to automatically slide along the guide hole, completing the conformal fitting of the complex curved surface blank contour. Subsequently, the industrial control computer 402 outputs the initial working current, and the magnetorheological fluid 202 undergoes phase change solidification, firmly locking the workpiece. During the cutting stage, once the tool travels to the thin-walled, weak-stiffness region and generates high-frequency vibration impact, the fiber Bragg grating sensor 305 ignores the surrounding magnetic field interference and rapidly transmits the strain light wave back. Once the industrial control computer 402 determines that the force exceeds the red line, it immediately reduces the local coil excitation through incremental control. Within one-hundredth of a second, the fluid in the impacted area softens, and the pins 103 undergo nanometer to micrometer-level micro-yield, absorbing and dissipating excess cutting peaks. Once the dangerous peak has passed, the system controls the current to gradually increase based on the spindle frequency, and the magnetorheological fluid 202 hardens again to continue providing rigid support.

[0048] In summary, this application, by combining a magnetorheological phase-change hydraulic support array with purely optical internal sensor feedback, not only solves the problem of stress concentration deformation caused by the inability to fit complex micro-contours, but also utilizes a transient local current reduction and yielding mechanism to balance high-precision rigid positioning and dynamic anti-vibration buffering, ultimately achieving high yield and high surface quality in the machining of thin-walled curved aluminum castings.

[0049] At the control level, this application embodiment also provides a control device. This control device constitutes the core hardware carrier of the aforementioned industrial control computer 402. The control device includes a microprocessor connected via an internal bus and a memory storing computer instructions. The microprocessor is selected from industrial-grade chips or digital signal processing chips with high-speed floating-point arithmetic capabilities. The memory contains the aforementioned control program based on an incremental algorithm and threshold parameter tables for each level. When the microprocessor is powered on and wakes up to execute the computer instructions in the memory, it can completely schedule the photoelectric demodulator 401 for data interaction and calculate and control the adjustable current drive circuit module 404, thereby realizing all the above-mentioned adaptive complex curved aluminum casting clamping control method processes. Through the high-frequency instruction execution of the dedicated microprocessor, extremely low latency from stress sensing to phase transition yielding is ensured.

Claims

1. A flexible force-controlled clamping device for adaptive complex curved aluminum castings, characterized in that, include: A base assembly, wherein the base assembly has an internal receiving cavity and a guide perforated plate made of non-magnetic material is connected to the top of the base assembly; A phase change stiffening assembly includes a magnetorheological fluid filled in the cavity and excitation coils arranged along the inner wall of the cavity; The array contouring component includes multiple pins, the lower part of which passes through the guide porous plate and is inserted into the magnetorheological fluid in the receiving cavity. The pin includes a lower metal rod and an upper polymer ball head, and an annular microgroove is formed at the connection between the polymer ball head and the metal rod. The grating force control feedback component includes a fiber Bragg grating sensor, a photoelectric demodulator, and an industrial computer; the fiber Bragg grating sensor is encapsulated inside the annular microgroove and connected to the photoelectric demodulator via a pigtail; the photoelectric demodulator is connected to the industrial computer; the industrial computer is connected to the excitation coil; The photoelectric demodulator is configured to calculate the contact force based on the reflected light signal; the industrial control computer is configured to reduce the output current of the excitation coil in the corresponding area when the contact force borne by the local column pin exceeds a preset thin-wall deformation threshold.

2. The flexible force-controlled clamping device for adaptive complex curved surface aluminum castings as described in claim 1, characterized in that, The metal rod and the polymer ball head are connected by threads; the annular microgroove is located at the root position where the lower end face of the polymer ball head and the upper end face of the metal rod are joined; the fiber Bragg grating sensor is equidistantly wound around the annular microgroove and sealed and fixed in the annular microgroove with epoxy resin adhesive.

3. The flexible force-controlled clamping device for adaptive complex curved surface aluminum castings as described in claim 2, characterized in that, The outer wall of the metal rod is provided with a axially extending fiber guide groove that penetrates the annular microgroove; the depth of the fiber guide groove is greater than the outer diameter of the fiber; the fiber extends from the annular microgroove along the trajectory of the fiber guide groove to the outside of the receiving cavity; the fiber guide groove is filled with a flexible sealant layer, which is flush with the outer surface of the metal rod.

4. The flexible force-controlled clamping device for adaptive complex curved surface aluminum castings as described in claim 1, characterized in that, The excitation coil includes multiple independent annular electromagnetic windings stacked along the depth direction of the receiving cavity; multiple non-magnetic isolation rings are also provided inside the receiving cavity, and two adjacent independent annular electromagnetic windings are separated by one of the non-magnetic isolation rings, forming multiple magnetic field distribution layers arranged independently along the axial direction.

5. The flexible force-controlled clamping device for adaptive complex curved surface aluminum castings as described in claim 4, characterized in that, The inner wall surface of the guide perforated plate is embedded with a magnetic energy-concentrating ring corresponding to the magnetic circuit penetration area of ​​the independent annular electromagnetic winding; the magnetic energy-concentrating ring is made of silicon steel; the thickness of the magnetic energy-concentrating ring gradually decreases from the middle to both ends.

6. The flexible force-controlled clamping device for adaptive complex curved surface aluminum castings as described in claim 1, characterized in that, The polymer ball head is made of polyetheretherketone material; the guide porous plate has guide through holes corresponding to multiple pins, and the metal rod slides through the guide through holes.

7. A clamping control method for adaptive complex curved surface aluminum castings, applied to the flexible force-controlled clamping device for adaptive complex curved surface aluminum castings as described in any one of claims 1 to 6, characterized in that, include: Acquire the reflected light wavelength signal detected by the fiber Bragg grating sensor; The contact force borne by the polymer ball head is calculated based on the reflected light wavelength signal; In response to the contact force being greater than a preset thin-wall deformation threshold, the output current of the excitation coil in the corresponding region is reduced, the yield stress of the magnetorheological fluid in the corresponding region is weakened, and the pressurized pin undergoes axial retraction.

8. The clamping control method for adaptive complex curved surface aluminum castings as described in claim 7, characterized in that, The step of reducing the output current of the excitation coil in the corresponding region in response to the contact force exceeding a preset thin-wall deformation threshold includes: Obtain the difference between the contact force and the preset thin-wall deformation threshold; The difference is input to an incremental proportional-integral-derivative controller. The target current attenuation is calculated based on the output of the incremental proportional-integral-derivative controller. The output current of the excitation coil in the corresponding region is controlled to decrease in a step manner according to the target current decay amount.

9. The clamping control method for adaptive complex curved surface aluminum castings as described in claim 8, characterized in that, Also includes: The contact force is continuously monitored after the pin undergoes axial retraction. In response to the contact force falling below the safety threshold, a relocking process is initiated. The restart and relocking process includes obtaining the residual current value of the current excitation coil and controlling the output current of the excitation coil to linearly increase from the residual current value to the initial operating current value according to a preset current recovery slope; wherein, the safety judgment threshold is set to 80% to 90% of the preset thin-wall deformation threshold, and the current recovery slope is dynamically configured according to the rotational speed frequency of the cutting spindle.

10. A control device, characterized in that, It includes a microprocessor and a memory storing computer instructions, wherein the microprocessor, when executing the computer instructions, implements the adaptive clamping control method for complex curved surface aluminum castings as described in any one of claims 7 to 9.

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