Metal additive and subtractive material non-contact process parameter regulation and control system based on directional energy deposition

Abstract

The invention relates to the technical field of metal 3D printing, and particularly discloses a non-contact process parameter regulation and control system for metal additive and subtractive materials based on directional energy deposition, which can be used for the non-contact process parameter regulation and control system for additive and subtractive materials. Comprising a non-contact measurement unit, a DED printing execution unit, a central control unit and an auxiliary function module in signal connection with the central control unit. The central control unit is used for performing non-contact real-time observation on a workpiece in machining through the non-contact measurement unit, and generating a feedback signal based on the deviation between a measured value and a design value; the DED printing execution unit is controlled through the central control unit, the mechanical arm drives the DED printing execution unit, the galvanometer and the laser device, the machining path of the laser device is adjusted, and closed-loop adjustment of the printing process and the subtractive machining process is achieved. According to the method, real-time compensation in layers and intelligent defect identification and repair are realized, accumulative errors are effectively eliminated, defects such as over-accumulation, under-fusion and over-cutting are reduced, and reworking treatment is not needed.

Description

Technical Field

[0001] This invention relates to the field of metal 3D printing technology, and in particular to a non-contact process parameter control system for metal additive and subtractive manufacturing based on Directed Energy Deposition (DED). The system utilizes DED equipment for 3D metal additive and subtractive manufacturing, employing a coaxial confocal rangefinder, optical coherence tomography (OCT) system, or laser interferometry rangefinder to achieve non-contact feedback control of the printed layer and dynamically adjust process parameters. This solution is suitable for DED-based 3D metal printing subtractive manufacturing scenarios such as rapid manufacturing of large components, damage repair, and preparation of graded functional materials. Background Technology

[0002] Directed energy deposition (DED) technology melts synchronously transported metal powder or filaments with a high-energy beam (laser / arc / plasma) to achieve near-net-shape forming layer by layer. It has shown significant advantages in aerospace, mold repair and other fields, with features such as fast forming speed, high material utilization and the ability to repair large components.

[0003] However, traditional DED technology is essentially an "open-loop additive manufacturing" process. Affected by factors such as unstable melt pool dynamics, powder feeding fluctuations, thermal stress deformation, and cumulative errors of the robotic arm, the formed parts generally exhibit cumulative Z-axis height errors, easily leading to defects such as incomplete fusion between layers, excessive build-up, localized spatter, and spheroidization. To correct these defects, subtractive processing is required to remove burrs and residual support components. However, existing subtractive processing technologies have the following shortcomings: 1. Near real-time interlayer Z-axis height feedback can only "suppress error accumulation" and cannot actively correct existing geometric defects (such as local protrusions, collapses, and burrs), making it difficult to adapt to the precision requirements of subtractive processing.

[0004] 2. Traditional methods rely on offline coordinate measuring machines or structured light scanning. The laser melting process needs to be stopped during inspection, and the inspection cycle can take several hours. They cannot respond to real-time deformation during the printing process and lack a complete closed loop between "measurement, decision-making, and execution". The subtractive process is only a post-processing remedy rather than an embedded part of the process. Contact probes are easily damaged by the high temperature environment during laser melting and have a slow scanning speed. Single-point laser ranging cannot obtain contour information and is severely affected by the light from the molten pool.

[0005] Therefore, there is an urgent need for a high-speed, high-precision, and interference-resistant non-contact process parameter adjustment scheme to achieve closed-loop quality control when defects are detected during additive manufacturing using DED, by using newly added pulsed lasers and galvanometers to perform subtractive processing. This would solve the problems of error accumulation and detection lag in existing technologies, and allow for periodic subtractive finishing during additive manufacturing. This is especially suitable for complex structural parts such as internal tubes that are difficult to reshape after additive manufacturing. Summary of the Invention

[0006] The core objective of this invention is to overcome the shortcomings of existing DED-based 3D metal printing subtractive processing technology and provide a non-contact process parameter adjustment system based on 3D sensing to obtain the workpiece morphology. Specific objectives include: 1. Solve the problem of stable measurement under high temperature and strong interference environment, realize the online measurement accuracy of Z-axis height ≤ ±0.05mm, and form a real-time control system with closed loop feedback cycle <50ms; 2. Eliminate accumulated errors in multi-layer deposition and subtractive processing, and improve Z-axis forming accuracy to within ±0.1mm; 3. Enables automatic identification and precise removal of non-design feature protrusions (burrs, spatter, support residue), as well as effective repair of overcut areas; 4. Adaptable to special scenarios such as grafting printing and multi-material gradient printing, ensuring processing accuracy and interface bonding quality in different application scenarios.

[0007] To achieve the above objectives, this invention provides a non-contact process parameter control system for metal additive and subtractive manufacturing based on directional energy deposition (DED), comprising a non-contact measurement unit, a DED printing execution unit, an auxiliary function module connected to a central control unit via signal connection, and is executed according to the following steps: S01. The central control unit performs non-contact real-time observation of the workpiece during processing through a non-contact measurement unit, and generates a feedback signal based on the deviation between the measured value and the design value; S02. The generated feedback signal is used to control the DED printing execution unit through the central control unit. The DED printing execution unit includes a robotic arm of a multi-axis processing unit, a DED printing nozzle, a galvanometer, and a pulsed laser. The galvanometer and pulsed laser are installed at the off-axis position of the DED printing nozzle. The robotic arm drives the DED printing nozzle, galvanometer, and laser, thereby adjusting the processing path of the laser. S03. The process parameters of the laser pulse time, power and scanning speed are dynamically adjusted by the central control unit and auxiliary function modules to achieve closed-loop regulation of the printing process.

[0008] Optionally, the non-contact measurement unit is a galvanometer-driven optical coherence tomography (OCT) system or a 3D line structured light camera.

[0009] Optionally, the non-contact measurement unit is a coaxial confocal rangefinder, which includes a light source, a dispersive objective lens, a spectral receiving unit, and a coaxial beam splitter. The light source illuminates the processing area of ​​the workpiece through a dispersive objective lens and a coaxial beam splitter. The spectral receiving unit collects the light signal from the processing area and stitches the depth information obtained by one-dimensional line scanning into depth information containing two-dimensional coordinates. The laser fringe triangulation method is used to calculate the height distribution data of the substrate surface.

[0010] The central control unit is connected to a non-contact sensing module. The central control unit and the non-contact sensing module form a closed-loop control system. The coaxial sensing module includes a line scan camera. The optical path of the line scan camera is coupled to the return optical path of the galvanometer during scanning via a beam splitter.

[0011] The central control unit controls the scanning time of the pulsed laser used for subtractive processing, scans multiple times according to the processing depth and detects the processing depth in stages. During the additive processing, it periodically performs non-contact observation according to the set time. When over-accumulation is detected, the pulsed laser is called to perform subtractive fine-tuning.

[0012] The system also includes an overcut region repair method, which is performed according to the following steps: S1. Identify the boundary of the overcut region using surface data acquired by the non-contact measurement unit, generate a closed compensation profile, and define the Z-axis height to be compensated for the overcut region as |ΔZremain|; S2. Switch the DED printing execution unit to the coaxial powder feeding DED mode and deposit micro-protrusions in the overcut area. The thickness of the micro-protrusions is |ΔZremain|+100μm. S3. After the micro-protrusion cools down, the DED printing execution unit switches back to laser subtractive processing mode and performs closed-loop finishing on the micro-protrusion until the |ΔZ| of the processed area is ≤50μm.

[0013] The auxiliary function module is connected to the central control unit and the non-contact measurement unit via signals. The auxiliary function module includes an automatic identification module and a laser subtractive material removal module, and its working logic is as follows: S011. Register and map the surface point cloud data Pscan={(xi,yi,zi)} acquired in real time by the non-contact measurement unit with the theoretical surface model SCAD(x,y) of the original CAD model at the corresponding printing layer. S012. Calculate the normal deviation at each point: di = zi - SCAD(xi, yi); If a region simultaneously meets the following criteria, it is determined to be a non-design feature protrusion (including burrs, spatter, or support residue): di > δupper (δupper = 10-200μm, the specific value depends on the printing material and process parameters). The area of ​​this region is A < Amax (Amax = 5-50 mm)2 (Specific values ​​depend on the printing material and process parameters). The gradient of d values ​​around this region >Gthr (Gthr=0.5mm) -1 (Specific values ​​depend on the printing material and process parameters). S013. For the identified non-design feature protrusion areas, automatically generate selective ablation paths and configure the following laser parameters: Spot diameter: 30-150μm (matching the protrusion size); Energy density: 0.2-18 mJ per pulse, average power 100-2000 W, pulse width 10-800 μs, cutoff rate 10-200 mm 3 / min; Pulse overlap rate: 60-85%; Target removal depth: di-ε (ε=2-5μm, used to retain a small safety margin to avoid overcutting); S014. After performing a single or multiple laser scanning ablation, trigger a secondary scanning verification to ensure that di ≤ δupper in the region.

[0014] The non-contact measurement unit performs measurements using a scanning galvanometer and an f-theta field lens. The non-contact measurement unit and the laser share the same scanning galvanometer and f-theta field lens, achieving concentric overlap of the measurement spot and the processing spot on the workpiece surface, with a positional deviation between the measurement spot and the processing spot ≤10μm. The non-contact measurement unit is a type of coaxial confocal distance meter and OCT system.

[0015] The system is suitable for grafting printing scenarios, and the central control unit is configured as follows: S001. Before the additive manufacturing process begins, control the non-contact measurement unit to perform a pre-scan model of the existing substrate surface and obtain the three-dimensional topography point cloud Pbase of the substrate. S002. Based on the spatial Boolean operation between Pbase and the newly added geometric CAD model, automatically generate the dynamic starting Z-plane Zstart(x,y)=Zbase(x,y)+t0, where: t0 is the theoretical first layer thickness, Zbase(x,y) is the corresponding height function of the grafted part in two-dimensional space, and Zstart(x,y) is the corresponding height function of the starting Z-plane in two-dimensional space; S003. During the first layer deposition process, the measured first layer height Zactual(x,y) and Zstart(x,y) are compared in real time. If the local deviation ΔZ < -0.05mm, the continuous laser power of the irradiated area is immediately increased by ≥10% and the scanning speed is reduced by ≥15% to ensure the metallurgical bonding quality of the interface.

[0016] The system is suitable for printing scenarios with multiple material gradients. The central control unit is configured to perform closed-loop control of interface morphology and composition. The specific process is as follows: S04. Before the deposition of the interface layer when switching from material A to material B, control the non-contact measurement unit to complete the scanning of the final layer of material A and construct the actual surface critical morphology SactualA of the final layer of material A; S05. Calculate the height deviation field ΔZinterface(x,y) of SactualA relative to the ideal interface plane Sdesigninterface(x,y); S06. Spatially variable parameter deposition strategy for generating the first layer of material B based on ΔZinterface(x,y): If ΔZinterface > +δup (δup = 0.05 mm), then reduce the powder feeding rate / filament feeding rate of material B in the corresponding area. The adjustment formula is FB = FB * (1 - α * ΔZinterface) (α = 20 mm). -1 ); If ΔZinterface < -δlow (δlow = 0.03 mm), then increase the powder / filament feeding rate and laser power in the corresponding area, and increase local reciprocating scanning; the deposition strategy ensures that the first layer of material B has the dual functions of geometric correction and compositional transition.

[0017] Compared with the prior art, the beneficial effects of the present invention are: 1. By adopting a non-contact measurement unit and coaxial optical path design, the strong light interference from the molten pool is avoided. Combined with an anti-interference algorithm, the online Z-axis height measurement accuracy is ≤ ±0.05mm, and the closed-loop feedback cycle is <50ms, which meets the stable measurement requirements under high temperature and strong interference environment.

[0018] 2. Through strategies such as real-time compensation within layers and intelligent defect identification and repair, the cumulative error is effectively eliminated, and the Z-axis forming accuracy is improved to within ±0.1mm, reducing defects such as over-accumulation, under-fusion, and over-cutting, without the need for offline rework.

[0019] 3. Personalized control strategies are provided for different scenarios such as conventional subtractive processing, grafting printing, and multi-material gradient printing to ensure interface bonding quality, composition transition accuracy, and geometric dimension accuracy, thereby expanding the application scope of DED-based 3D metal printing technology.

[0020] 4. It achieves fully closed-loop automatic control between "measurement, calculation, and correction", eliminating the need for manual intervention to adjust process parameters, reducing operational difficulty, improving processing efficiency and product consistency, and providing technical support for the industrial application of DED-based 3D metal printing subtractive processing. Attached Figure Description

[0021] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0022] Figure 1 This is a schematic diagram of the structure of each module of the system in this invention.

[0023] Figure 2 This is a flowchart illustrating the 3D printing closed-loop control method of this invention.

[0024] Figure 3 This is a schematic diagram of the system architecture for closed-loop control of 3D printing in this invention.

[0025] Figure 4 This is a schematic diagram of the near real-time (interlayer) closed-loop control of 3D printing based on DED in this invention.

[0026] Figure 5 This is a schematic diagram of the real-time control principle within the layer in this invention.

[0027] Figure 6 This is a schematic diagram comparing the real-time intra-layer control effects in this invention.

[0028] Figure 7 This is a schematic diagram illustrating the control principle of the present invention during subtractive processing.

[0029] Figure 8 This is a side view of the actual structure of the device for implementing the present invention.

[0030] Figure 9 yes Figure 8 A frontal view of the actual structure of the device being implemented. Detailed Implementation

[0031] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0032] The components of the embodiments of the invention described and shown in the accompanying drawings can typically be arranged and designed in a variety of different configurations. Therefore, the following detailed description of the embodiments of the invention provided in the drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention.

[0033] Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0034] Please refer to Figures 1-9 ,in, Figure 8 In the section controlled by the robotic arm, the left side contains a line scan camera for ranging, the middle contains a nozzle and laser head, and the right side contains a galvanometer.

[0035] This invention provides a non-contact process parameter control system for metal additive and subtractive manufacturing based on directional energy deposition. The system acquires surface data of the workpiece in real time through a non-contact measurement unit. The central control unit generates a feedback signal based on the deviation between the measured value and the design value, dynamically adjusts the processing path and process parameters, and combines auxiliary function modules to complete defect handling and special scenario adaptation, forming a complete closed-loop control method.

[0036] The system includes a non-contact measurement unit, a DED printing execution unit, a central control unit, and auxiliary function modules connected to the central control unit. These units work together to achieve precise control of the processing. The non-contact measurement unit is used for non-contact real-time observation of the workpiece during processing. It can be selected from a coaxial confocal rangefinder, optical coherence tomography (OCT) system or laser interferometer. It shares the same scanning galvanometer and f-theta field lens with the laser to achieve concentric coincidence of the measurement spot and the processing spot on the workpiece surface, with a positional deviation of ≤10μm, ensuring the coordination between measurement accuracy and processing action.

[0037] OCT configuration: OGS850-50 / 100, 840nm laser, bandwidth 50-60nm, imaging depth 8mm, scanning line frequency 130KHz, detector pixel 2048 linear array, spectral resolution 0.02nm.

[0038] Line scan camera configuration: MECH MIND LNX-8000, 4096 contour points, X-axis field of view: near side: 76mm, reference: 89mm, far side: 96mm; reference distance: 250mm, z-axis detection distance: 100mm.

[0039] A custom-designed coaxial confocal rangefinder is fixed to the DED printhead housing via a precision bracket. The measurement optical path is at an angle of 18°±3° to the processing laser optical path. This angle design ensures that the measurement field of view covers the critical area of ​​the deposition layer and completely avoids the strong light interference area of ​​the molten pool. The dispersive objective lens is equipped with an active cooling protection window at the front end and adopts a double-layer quartz glass structure. The beam splitter has a transmittance of ≥99.5% for 1064 / 1070nm laser wavelength, a reflectance of ≥98% for the measurement band (400-700nm), and extremely low reflectance (≤0.5%) at 532nm to avoid laser frequency doubling interference. The surface of the beam splitter is coated with a high-temperature resistant dielectric film (capable of withstanding 300℃) and is installed at an angle of 45° to the horizontal plane in the optical path to reduce back reflection interference.

[0040] The DED printing execution unit includes a robotic arm, a galvanometer, and a laser. The robotic arm drives the galvanometer and laser to adjust the processing path. It can switch to the coaxial powder feeding DED mode to achieve the deposition function, or switch to the laser subtractive mode to perform the removal process, meeting the dual needs of additive repair and subtractive finishing.

[0041] The central control unit, as the core of the system, connects the non-contact measurement unit, the DED printing execution unit, and auxiliary function modules. It receives measurement data, calculates deviations, generates control commands, and realizes processing path adjustment, dynamic control of process parameters, real-time compensation, and strategy execution for special scenarios.

[0042] The auxiliary function modules include an automatic identification module and a laser subtractive material removal module, which are used to identify non-design feature protrusions and perform selective ablation to help improve the quality of the processed surface.

[0043] When the non-contact measuring unit is a coaxial confocal distance meter, it includes: Broadband or supercontinuum light source with an output wavelength range of 400-700 nm; A dispersive objective lens whose axial dispersion relation satisfies Z=a*λ+b (where a<0, unit: μm / nm); The spectral receiving unit is a linear array spectrometer or a CMOS sensor with a beam splitter, with a spectral resolution ≤2nm; The coaxial beam splitter has a transmittance of ≥99% for the processing laser wavelength (1064nm or 1070nm) and a reflectance of ≥95% for the measurement wavelength.

[0044] When the non-contact measurement unit is used in an optical coherence tomography (OCT) system, it includes: Near-infrared broadband light source with a center wavelength of 1100nm±40nm and a bandwidth of ≥100nm; The interference optical path shares the same objective lens, and the optical path difference between the reference arm and the sample arm is adjustable in the range of 0-2 mm; The interference signal is acquired by a high-speed linear scanning camera with an A-scan rate ≥50kHz. The Z-coordinate of the surface peak was extracted by the envelope detection algorithm, with a sampling interval ≤0.1mm.

[0045] A coaxial sensing module is connected to the central control unit, forming a closed-loop control system. The coaxial sensing module includes a line scan camera, whose optical path is coupled to the return optical path of the galvanometer scanning system via a coaxial beam splitter. The central control unit is configured to: control the galvanometer to drive the laser beam to scan at a uniform speed along the Y direction, and synchronously trigger the line scan camera to acquire a one-dimensional image sequence in the X direction at a line frequency fs; stitch the image sequence into a two-dimensional surface image, and calculate the height distribution data of the substrate surface based on the laser stripe triangulation method.

[0046] The automatic identification module registers and maps the surface point cloud data Pscan={(xi,yi,zi)} acquired in real time by the non-contact measurement unit with the theoretical surface model SCAD(x,y) of the original CAD model at the corresponding printing layer, and calculates the normal deviation di=zi-SCAD(xi,yi) for each point.

[0047] When the surface point cloud is found to be tilted relative to the processing module, and side processing is required, the tilt angle x is calculated according to the normal direction. The input laser power is adjusted according to the projection energy. When x is 90 degrees, there is no tilt between the processing surface and the incident laser. The laser power at this time is y. When x is greater than 100 degrees or less than 80 degrees, the power is adjusted to y / sin(x) to compensate for the increased spot irradiation area and decreased energy density caused by the tilted incident light, so as to ensure that the cutting depth remains unchanged.

[0048] If a region simultaneously meets the following criteria, it is determined to be a non-design feature protrusion (including burrs, spatter, or support residue): di > δupper (δupper = 10-200μm, specific value depends on printing material and process parameters); the area of ​​this region A < Amax (Amax = 5-50mm) 2 The specific value depends on the printing material and process parameters; the d-value gradient around this area is greater than Gthr (Gthr=0.5mm, the specific value depends on the printing material and process parameters).

[0049] The laser subtractive material removal module automatically generates selective ablation paths for identified non-designed protruding feature areas and configures the following laser parameters: The spot diameter is 30-150μm (matching the protrusion size); Energy density: 0.2-18 mJ per pulse, average power 100-2000 W, pulse width 10-800 μs, cutoff rate 10-200 mm 3 / min; pulse overlap rate 60-85%; The target removal depth is di-ε (ε = 2-5 μm, used to retain a small safety margin to avoid overcutting).

[0050] After performing a single or multiple laser scanning ablation operations, a secondary scanning verification is triggered to ensure that di ≤ δupper in the region.

[0051] The central control unit is equipped with a dedicated timing control module to achieve precise timing synchronization between the measurement system and laser processing. This module receives the laser's operating status signal, analyzes the molten pool light intensity change cycle in real time through the FPGA, and generates a synchronization trigger signal for the measurement unit. Specifically, the measurement is started during the interval of the pulsed laser (i.e., the "dark period"), and the exposure window is strictly limited to the middle 70% of the laser pulse interval to avoid the peak plasma radiation period before and after the laser pulse. For continuous laser processing mode, a high-frequency modulated measurement light source (modulation frequency of 200kHz) is used, and the synchronization signal is extracted through lock-in amplification technology to effectively suppress background noise.

[0052] The core control process is as follows: S01: The central control unit performs non-contact real-time observation of the workpiece during processing through a non-contact measurement unit, and generates a feedback signal based on the deviation between the measured value and the design value; S02: The feedback signal controls the DED printing execution unit through the central control unit. The robotic arm drives the DED printing nozzle, galvanometer and laser, and adjusts the processing path of the laser. S03: The process parameters such as laser pulse time, power, powder / filament feeding rate and scanning speed are dynamically adjusted through the central control unit and auxiliary function modules to achieve closed-loop regulation of the printing process.

[0053] The central control unit of the real-time compensation process within the layer controls the DED printing execution unit through real-time compensation. The specific process is as follows: 1. In the single-channel laser subtraction path of the laser, Z-value sampling is triggered once every time the movement distance d≤1.0mm; 2. Calculate the local remaining removal depth ΔZremain=Zcurrent-Ztarget, where Zcurrent is the current measured Z-axis height and Ztarget is the designed Z-axis height; 3. If the current processing depth of the pulsed laser is insufficient, continue to use the pulsed laser for subtractive processing until the expected Z-axis height Ztarget is reached at each point on the workpiece.

[0054] The overcut region repair process system also includes an overcut region repair method, the specific steps of which are as follows: S1: Identify the boundary of the overcut area using surface data acquired by the non-contact measurement unit, and generate a closed compensation profile; S2: Switch the DED printing execution unit to the coaxial powder feeding DED mode, and deposit micro-protrusions in the overcut area. The thickness of the micro-protrusions is |ΔZremain|+100μm. S3: After the micro-protrusion cools down, the DED printing execution unit switches back to the pulsed laser subtractive mode and performs closed-loop finishing on the micro-protrusion until the |ΔZ| of the processed area is ≤50μm.

[0055] Special scenario adaptation processes include grafting printing scenarios and multi-material gradient printing scenarios, among which: 1) Grafting printing scenario: S001: Before the additive manufacturing process begins, the central control unit controls the non-contact measurement unit to perform a pre-scan model of the existing substrate surface and obtain the three-dimensional topography point cloud Pbase of the substrate. S002: Based on the spatial Boolean operation between Pbase and the newly added geometric CAD model, automatically generate the dynamic starting Z-plane Zstart(x,y)=Zbase(x,y)+t0, where t0 is the theoretical first layer thickness, Zbase(x,y) is the corresponding height function of the grafted part in two-dimensional space, and Zstart(x,y) is the corresponding height function of the starting Z-plane in two-dimensional space; S003: During the first layer deposition process, the measured first layer height Zactual(x,y) and Zstart(x,y) are compared in real time. If the local deviation ΔZ < -0.05mm, the laser power in that area is immediately increased by ≥10% and the scanning speed is reduced by ≥15% to ensure the metallurgical bonding quality of the interface.

[0056] 2) Multi-material gradient printing scenario: The non-contact measurement unit integrates component detection functions (such as a spectral analysis module), and the central control unit is configured to perform collaborative closed-loop control of interface morphology and composition. The specific process is as follows: S04: Before the deposition of the interface layer when switching from material A to material B, control the non-contact measurement unit to complete the scanning of the final layer of material A and construct the actual surface critical morphology SactualA of the final layer of material A; S05: Calculate the height deviation field ΔZinterface(x,y) of SactualA relative to the ideal interface plane Sdesigninterface(x,y); S06: Spatially variable parameter deposition strategy for generating the first layer of material B based on ΔZinterface(x,y): If ΔZinterface > +δup (δup = 0.05 mm), then reduce the powder feeding rate / filament feeding rate of material B in the corresponding area. The adjustment formula is FB = FB * (1 - α * ΔZinterface) (α = 20 mm). -1 ); If ΔZinterface < -δlow (δlow = 0.03 mm), then increase the powder / filament feeding rate and laser power in the corresponding area, and increase local reciprocating scanning; the deposition strategy ensures that the first layer of material B has the dual functions of geometric correction and compositional transition.

[0057] Example 1: Closed-loop control of conventional DED-based 3D metal printing process The system hardware includes: The DED printing execution unit adopts a coaxial powder-feeding printhead, which integrates powder nozzles and laser focusing lens group. The laser is a high-power fiber laser with a power range of 1kW-6kW and a wavelength of 1070nm. The motion mechanism adopts a five-axis linkage CNC machine tool, with the printhead fixed on the Z-axis and the substrate fixed on the XY platform. It is equipped with a high-precision carrier gas powder feeder to ensure stable and continuous powder delivery.

[0058] The non-contact measurement unit uses a coaxial confocal rangefinder, fixed on the print head at a 15-30° angle to the vertical direction. The measurement line is perpendicular to the scanning direction, covering an area of ​​0.5-3mm behind the molten pool. A narrow-band filter (FWHM≤10nm) is used in conjunction with the exposure window for synchronous exposure, selectively exposing within the bright and dark cycles of the molten pool, resulting in a signal-to-noise ratio improvement of >20dB.

[0059] The central control unit includes an industrial computer (IPC), an image acquisition card, a motion control card, and software modules. The software modules integrate an image processing module, an altitude calculation module, a path planning module, and a real-time control module, and run an adaptive PID controller (PID + fuzzy logic).

[0060] The software control process includes: 1. The camera's intrinsic and extrinsic parameters are calibrated using a checkerboard calibration board; a laser line is projected onto the substrate, and the zero height point (Z=0) is set; the offset of the printhead nozzle center point from the center point of the laser line scanning measurement area in the X, Y, and Z directions is accurately measured and recorded for subsequent coordinate alignment.

[0061] 2. The central control unit controls the motion platform and print head to perform deposition according to the preset printing path. At the same time, the non-contact measurement unit scans synchronously, and the high-speed camera continuously acquires the laser line image modulated by the surface of the deposited layer (the scanning area is located behind the molten pool to ensure that the measurement has solidified the deposited layer).

[0062] 3. The acquired images are filtered and denoised, and the laser line center is extracted. Based on the principle of laser triangulation, the two-dimensional pixel coordinates are converted into three-dimensional point cloud coordinates and transformed to the printing coordinate system. The actual height model Zactual(X,Y) of the current layer is constructed by interpolation algorithm and compared with the theoretical design height Zdesign of the preset CAD slice model. The error ΔZ=Zactual-Zdesign is calculated.

[0063] 4. Real-time compensation execution: If ΔZ > 100μm (over-stacking), reduce the laser power of the next layer by 10-30%, and simultaneously slightly reduce the powder feeding rate or increase the printing speed; If 0 < ΔZ ≤ 100 μm, use the nominal pulse energy; If -50μm≤ΔZ≤0, reduce the pulse energy to 50% of the nominal value or skip this point; If |ΔZ|>1mm, trigger an alarm and pause printing.

[0064] 5. After completing the printing and compensation of the current layer, raise the print head by one theoretical layer thickness and repeat the above steps until the part is printed.

[0065] Example 2: Overcut Region Repair and Removal of Undesigned Feature Protrusions The system hardware is based on Example 1, ensuring that the DED printing execution unit supports rapid switching between coaxial powder feeding DED mode and laser subtractive lithography mode, and that the automatic identification module and laser subtractive lithography removal module of the auxiliary function modules are enabled normally.

[0066] The processing flow is as follows: 1. During printing and scanning, the automatic identification module calculates the normal deviation di in real time. For protruding areas that meet the judgment criteria, the laser subtractive removal module generates a selective ablation path (spot diameter 30-150μm, energy density 0.2-18mJ per pulse, average power 100-1000W, 10-200mm). 3 ( / min, pulse overlap rate 60-85%), perform a second scan after ablation to verify that di≤δupper.

[0067] 2. When an overcut region (ΔZremain < -50μm) is detected, the boundary of the overcut region is first identified and a closed compensation profile is generated; switch to coaxial powder feeding DED mode and deposit a micro-protrusion with a thickness of |ΔZremain| + 100μm; after the micro-protrusion cools down, switch back to laser subtractive processing mode and perform closed-loop finishing on the micro-protrusion. Subtractive processing is performed on each point step by step by pulsed laser. After each point is irradiated with 3 pulsed lasers, observation is performed until |ΔZ| ≤ 50μm.

[0068] Example 3: Application of Grafting Printing Scenarios The non-contact measurement unit uses an optical coherence tomography (OCT) system, and the central control unit is loaded with printing-specific control logic to support substrate pre-scan modeling and dynamic initial Z-plane generation.

[0069] The control process is as follows: 1. The printhead does not start the laser / toner feeding. The control motion system scans 5mm outward along the boundary of the repair area. The OCT system collects the point cloud Pbase and generates the base digital elevation model Zbase(x,y) through the moving least squares (MLS) algorithm. The dynamic starting Z-plane Zstart(x,y) = Zbase(x,y) + t0 (t0 is the theoretical first layer thickness) is automatically generated.

[0070] 2. Compare Pbase with the ideal repair boundary. If burrs or oxide protrusions are detected (zi > Zbasefit + 30μm), trigger the laser subtraction unit (spot diameter 80μm, energy density 0.2-18mJ per pulse, average power 100-1000W, 10-200mm). 3 ( / min), the protrusions were removed by spiral scanning path, and a second scan confirmed that the surface |zi-Zbasefit|≤10μm.

[0071] 3. The printhead is raised to Zstart(x,y) to begin the first layer deposition, and scanning is simultaneously activated to obtain Zactual(x,y). The error ΔZ is calculated as Zactual - [Zbase(x,y) + t0]; If ΔZ < -0.05mm, increase the power locally by 15% and decrease the speed by 20%; If ΔZ > +0.10mm, reduce the powder feeding rate locally by 10% and mark the high stress warning zone.

[0072] 4. After each layer is scanned, Zactual(n) is obtained. A thermal accumulation factor H(x,y) is introduced, and the morphology and thermal history are fused to calculate the compensation amount for the next layer. When RMS(ΔZ(n))≤0.08mm and max|ΔZ(n)|≤0.15mm, the final surface finishing mode is started, and the out-of-tolerance points are reduced layer by layer with a step size of 5μm until max|ΔZ|≤0.05mm.

[0073] Example 4: Application of Multi-Material Gradient Printing Based on Example 1, the system is equipped with at least two independent high-precision powder feeders (loaded with material A and material B respectively). The powder feeding pipeline is connected to the print head through a powder feeding switching valve, supporting millisecond-level powder switching and mixing ratio control. The non-contact measurement unit integrates a spectral analysis module, and the central control unit software module is upgraded with "multi-material interface control logic".

[0074] The control process is as follows: 1. Print Material A to the layer before the interface: Print layer by layer according to the optimized process parameters of Material A, and use inter-layer closed-loop control to ensure geometric accuracy until the layer before the material switching surface is printed.

[0075] 2. After the final layer of material A is printed, the print head is removed, and the non-contact measurement unit is activated to perform a full-coverage scan, constructing the actual surface morphology Sactual (A-final), and obtaining the composition distribution through the spectral analysis module.

[0076] 3. Compare Sactual (A-final) with the ideal interface design plane Sdesign (interface) to generate the height deviation field ΔZinterface(x,y); If ΔZinterface > +0.05mm, reduce the powder feeding rate / filament feeding rate of material B in the corresponding area (FB = FB * (1 - 20 * ΔZinterface)). If ΔZinterface < -0.03mm, increase the powder / filament feeding rate and laser power in the corresponding area, and increase local reciprocating scanning.

[0077] 4. The powder feeding system switches to material B and performs initial layer printing according to the generated variable parameter set. After printing, it scans again to verify the surface flatness. If the error exceeds the threshold, it continues to make slight compensation in the second layer of material B until the interface is flat, and then switches to the standard interlayer closed-loop control mode of material B.

[0078] 5. Error Calculation: Generate height error mapping ΔZinterface(X,Y)=Sactual(A-final)-Sdesign(interface).

[0079] If ΔZinterface>0, it means that the last layer of material A is too high, forming a "protrusion".

[0080] If ΔZinterface < 0, it means that the last layer of material A is too low, forming a "pit".

[0081] For "protrusions": the initial layer of material B needs to be "shaving peaks and filling valleys"; the system uses the ΔZinterface error map as input to dynamically generate the non-uniform printing path and parameters of the initial layer of material B; in the protruding area (ΔZinterface>0): the laser power and powder feed rate of the local area are significantly reduced, and the highest point can even be skipped in the path planning to achieve the "milling" effect; in the normal or concave area (ΔZinterface≤0), normal or slightly higher parameters are used for deposition to fill the depressions.

[0082] For “pits”: the initial layer of material B needs to be “filled”; significantly increase the laser power and powder feed rate in the depressed area (ΔZinterface<0) and may reduce the scanning speed to ensure sufficient material fusion to fill the pits; additional, localized reciprocating scans can be performed on the depressed area.

[0083] The advantages of this invention are as follows: 1. The non-contact measurement unit shares the same scanning galvanometer and f-theta field lens with the laser. The measurement spot and the processing spot are concentric and coincident. The observation equipment is at a specific angle to the DED laser beam path, ensuring that the measurement field of view covers the key area of ​​the deposition layer and avoids the strong light interference area of ​​the molten pool, thereby improving the measurement stability and accuracy under high temperature and strong interference environment.

[0084] 2. Based on the high-frequency sampling data of the non-contact measurement unit, combined with the laser stripe triangulation method and envelope detection algorithm to solve the surface height distribution, the sampling and parameter adjustment are triggered once every 1.0 mm of movement through the in-layer real-time compensation strategy, which quickly corrects the processing error and avoids the accumulation of defects. At the same time, the overlapping shoulder feature points of the printed adjacent trajectories are used to fit the local reference plane in real time to eliminate the workpiece tilt error.

[0085] 3. The auxiliary function module automatically identifies non-design feature protrusions through multi-dimensional judgment criteria and generates targeted ablation paths; for overcut areas, it adopts an integrated solution of "deposition repair + finishing processing" to achieve precise removal and effective repair of defects without the need for additional offline processing procedures.

[0086] 4. To address the substrate adaptation requirements of grafting printing, a dynamic starting Z-plane is generated and the first layer deposition parameters are optimized; to address the interface adaptation requirements of multi-material gradient printing, collaborative closed-loop control of morphology and composition is achieved to adapt to the personalized needs of different application scenarios and improve process robustness.

[0087] This embodiment does not impose any limitation on the shape, material, structure, etc. of the present invention. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention shall fall within the protection scope of the technical solution of the present invention.

Claims

1. A non-contact process parameter control system for metal additive and subtractive manufacturing based on directional energy deposition, characterized in that, It includes a non-contact measurement unit, a DED (Dual Addition / Subtraction) material execution unit, an auxiliary function module for signal connection to the central control unit, and is executed according to the following steps: S01. The central control unit performs non-contact real-time observation of the workpiece during processing through a non-contact measurement unit, and generates a feedback signal based on the deviation between the measured value and the design value; S02. The generated feedback signal is used to control the DED additive and subtractive manufacturing execution unit through the central control unit. The DED additive and subtractive manufacturing execution unit includes a robotic arm of a multi-axis machining unit, a DED printing nozzle, a galvanometer, and a pulsed laser. The galvanometer laser output system is installed at the off-axis position of the DED printing nozzle. The robotic arm drives the DED printing nozzle and the galvanometer, thereby adjusting the processing path of the printing deposition and the galvanometer laser. S03. By combining the central control unit and auxiliary function modules, the process parameters of the laser pulse time, power and scanning speed are dynamically adjusted to achieve closed-loop regulation of the printing process.

2. The non-contact process parameter control system for metal additive and subtractive manufacturing based on directional energy deposition according to claim 1, characterized in that, The non-contact measurement unit is a galvanometer-driven optical coherence tomography (OCT) system or a 3D line structured light camera.

3. The non-contact process parameter control system for metal additive and subtractive manufacturing based on directional energy deposition according to claim 1, characterized in that, The non-contact measurement unit is a coaxial confocal rangefinder, which includes a light source, a dispersive objective lens, a spectral receiving unit, a depth reconstruction unit, and a coaxial beam splitter. The light source illuminates the workpiece's processing area through a dispersive objective lens and a coaxial beam splitter. The depth reconstruction unit receives the light signal from the processing area collected by the spectral receiving unit, calculates the depth, and stitches the one-dimensional image sequence into a two-dimensional surface image.

4. The non-contact process parameter control system for metal additive and subtractive manufacturing based on directional energy deposition according to any one of claims 2-3, characterized in that, The central control unit controls the scanning time of the pulsed laser to scan multiple times and detect the processing depth in stages according to the processing depth.

5. The non-contact process parameter control system for metal additive and subtractive manufacturing based on directional energy deposition according to claim 4, characterized in that, The system also includes an overcut region repair method, which is performed according to the following steps: S1. Identify the boundary of the overcut region using surface data acquired by the non-contact measurement unit, generate a closed compensation profile, and define the Z-axis height to be compensated for the overcut region as |ΔZremain|; S2. Switch the DED printing execution unit to the coaxial powder feeding DED mode, deposit micro-protrusions in the overcut area, and the thickness of the micro-protrusions is |ΔZremain|+100um to compensate for the overcut area. S3. After the micro-protrusion cools down, the DED printing execution unit switches back to the laser subtractive mode and performs closed-loop finishing on the micro-protrusion until the deviation between the actual value of the Z-axis of the processing area and the design value is less than 50um.

6. The non-contact process parameter control system for metal additive and subtractive manufacturing based on directional energy deposition according to claim 1, characterized in that, The auxiliary function module is connected to the central control unit and the non-contact measurement unit via signals. The auxiliary function module includes an automatic identification module and a laser subtractive material removal module, and its working logic is as follows: S011. Register and map the surface point cloud data Pscan={(xi,yi,zi)} acquired in real time by the non-contact measurement unit with the theoretical surface model SCAD(x,y) of the original CAD model at the corresponding printing layer. S012. Calculate the normal deviation at each point: di = zi - SCAD(xi, yi); If a region simultaneously meets the following criteria, it is determined to be a non-design feature protrusion (including burrs, spatter, or support residue): di > δupper (δupper = 10-200μm, the specific value depends on the printing material and process parameters). The area of ​​this region is A < Amax (Amax = 5-50 mm) 2 (Specific values ​​depend on the printing material and process parameters). The gradient of d values ​​around this region >Gthr (Gthr=0.5mm) -1 (Specific values ​​depend on the printing material and process parameters). S013. For the identified non-design feature protrusion areas, automatically generate selective ablation paths and configure the following laser parameters: Spot diameter: 30-150μm; Energy density: 0.2-18 mJ per pulse, average power 100-2000 W, pulse width 10-800 μs, cutoff rate 10-200 mm 3 / min; Pulse overlap rate: 60-85%; Target removal depth: di-ε (ε=2-5μm, used to retain a small safety margin to avoid overcutting); S014. After performing a single or multiple laser scanning ablation, trigger a secondary scanning verification to ensure that di ≤ δupper in the region.

7. The non-contact process parameter control system for metal additive and subtractive manufacturing based on directional energy deposition according to claim 4, characterized in that, The non-contact measurement unit is calibrated with the scanning galvanometer optical path to achieve concentric alignment of the measurement coordinate system and the processing spot on the workpiece surface, and the positional deviation between the measurement coordinate system and the processing spot is ≤10μm.

8. The non-contact process parameter control system for metal additive and subtractive manufacturing based on directional energy deposition according to claim 1, characterized in that, The system is suitable for grafting printing scenarios, and the central control unit is configured as follows: S001. Before the additive manufacturing process begins, control the non-contact measurement unit to perform a pre-scan model of the existing substrate surface and obtain the three-dimensional topography point cloud Pbase of the substrate. S002. Based on the spatial Boolean operation between Pbase and the newly added geometric CAD model, automatically generate the dynamic starting Z-plane Zstart(x,y)=Zbase(x,y)+t0, where: t0 is the theoretical first layer thickness, Zbase(x,y) is the corresponding height function of the grafted part in two-dimensional space, and Zstart(x,y) is the corresponding height function of the starting Z-plane in two-dimensional space; S003. During the first layer deposition process, the measured first layer height Zactual(x,y) and Zstart(x,y) are compared in real time. If the local deviation ΔZ < -0.05mm, the continuous laser power of the irradiated area is immediately increased by ≥10% and the scanning speed is reduced by ≥15% to ensure the metallurgical bonding quality of the interface.

9. The non-contact process parameter control system for metal additive and subtractive manufacturing based on directional energy deposition according to claim 1, characterized in that, The system is suitable for printing scenarios with multiple material gradients. The central control unit is configured to perform closed-loop control of interface morphology and composition. The specific process is as follows: S04. Before the deposition of the interface layer when switching from material A to material B, control the non-contact measurement unit to complete the scanning of the final layer of material A and construct the actual surface critical morphology SactualA of the final layer of material A; S05. Calculate the height deviation field ΔZinterface(x,y) of SactualA relative to the ideal interface plane Sdesigninterface(x,y); S06. Spatially variable parameter deposition strategy for generating the first layer of material B based on ΔZinterface(x,y): If ΔZinterface > +δup (δup = 0.05 mm), then reduce the powder feeding rate / filament feeding rate of material B in the corresponding area. The adjustment formula is FB = FB * (1 - α * ΔZinterface) (α = 20 mm). -1 ); If ΔZinterface < -δlow (δlow = 0.03 mm), then increase the powder / filament feeding rate and laser power in the corresponding area, and increase local reciprocating scanning; the deposition strategy ensures that the first layer of material B has the dual functions of geometric correction and compositional transition.

Images