A kind of unsupported inclined 3D printing mode and process parameter optimization method

Abstract

The application discloses a kind of unsupported tilt 3D printing mode and process parameter optimization method.The method is first based on material rheological characteristics to construct heat-force coupling model, the theoretical critical stable angle threshold of material is predicted.In path planning stage, the geometric collapse node of model is identified, and with less than the theoretical threshold as constraint condition, the actual cutting tilt angle of model overhanging part is determined.Subsequently, based on the actual cutting angle, through the preset "angle-parameter" adaptive mapping mechanism, the optimal printing speed, extrusion temperature and cooling strategy are matched for overhanging part;The closer the cutting angle is to the critical threshold, the more conservative and precise the process control is.In addition, high-temperature remelting connection process is used at the cutting interface.The application realizes "process parameter dynamic response based on actual tilt working condition", maximizes printing efficiency and interlayer bonding strength under the premise of ensuring forming stability.

Description

Technical Field

[0001] This invention relates to the field of additive manufacturing (3D printing) technology, specifically to a method for supportless printing path planning and process control of fused deposition modeling (FDM) based on a multi-degree-of-freedom robotic arm or a multi-axis linkage platform. Background Technology

[0002] When manufacturing complex cantilever beams or large-angle overhanging structures, fused deposition modeling (FDM) technology typically requires the addition of support structures. However, removing these support structures is not only time-consuming and labor-intensive but also easily damages the surface quality of the model. In recent years, tilt printing (i.e., supportless printing) technology based on multi-degree-of-freedom robotic arms has become a research hotspot. Its core idea is to rotate the printing platform or nozzle to transform the overhanging part into an "upright" or "slightly tilted" state for printing.

[0003] However, existing technologies have the following drawbacks when implementing tilt printing: (1) Model segmentation relies on experience: often simple segmentation is carried out based solely on geometry, without considering the rheological properties of the material under different temperatures and gravitational fields, which may result in the tilt angle after segmentation still exceeding the self-support limit of the material.

[0004] (2) Rigid and fixed process parameters: Once it is determined to perform tilt printing, extremely low printing speed and strong cooling measures are usually used throughout the process to prevent collapse. This "one-size-fits-all" strategy results in extremely low printing efficiency and heat accumulation in small-angle tilt areas, which affects the molding accuracy.

[0005] (3) Weak interlayer bonding: Model segmentation printing inevitably introduces physical interfaces. Simple layer printing cannot guarantee the mechanical strength at the interface, which can easily lead to the breakage of the printed parts at the joint.

[0006] Therefore, a method is needed that can scientifically predict the critical angle based on the thermodynamic properties of materials and adaptively adjust process parameters according to actual working conditions. Summary of the Invention

[0007] The purpose of this invention is to provide a supportless tilting 3D printing method and a process parameter optimization method. By predicting the physical limits of materials through theoretical modeling, and using this as a constraint to guide the gradient matching of model segmentation and process parameters, printing efficiency and interface strength are maximized while ensuring printing success rate.

[0008] This invention is achieved through the following technical solution: (1) Theoretical threshold prediction: Obtain the thermophysical parameters of the printing material, construct a critical stability angle prediction model for the material based on a non-isothermal rheological model, and calculate the theoretical critical stability angle threshold of the material under a specific printing environment. (2) Simulation and collapse node identification: Simulation conditions are set in the simulation model, and the Nakamura-Weibull non-isothermal crystallization dynamics model coupled with the finite element method is used to calculate the thermal stress evolution and local deformation during the printing process, and extract the warping displacement field in the Z-axis direction; the area where the displacement exceeds the preset safety value is marked as the overhang area, and its starting point is defined as the geometric collapse node; (3) Cutting angle determination: Traverse the geometric collapse nodes to determine the dividing plane that separates the overhang feature from the matrix; the determination of the dividing plane must meet the constraint condition: the actual cutting tilt angle (4) Adaptive matching of process parameters: Based on the determined actual cutting tilt angle Through the preset "tilt angle-process parameter" nonlinear mapping model, a set of exclusive printing process parameters for the overhang feature area is generated; (5) Mapping model logic setting: The logic of the mapping model is: when the actual cutting tilt angle The closer to the theoretical critical stability angle threshold At that time, the printing speed decreases non-linearly, and the cooling fan speed increases non-linearly; (6) Cooperative printing and interface enhancement: First, the substrate area is printed using conventional parameters; at the physical separation interface between the substrate and the overhang feature, a high-temperature remelting connection process is performed; then the printing platform or nozzle posture is adjusted to the angle. Using the exclusive process parameter set generated in step (4), the tilted unsupported printing of the overhang feature area is completed.

[0009] The thermophysical properties of the printing material in step (1) include at least the material density. Melt viscosity Glass transition temperature and shear strength .

[0010] The theoretical critical stability angle mentioned in step (1) The prediction criterion is: the shear component generated by gravity along the tangential direction during the relaxation time t after material extrusion. It must always be less than the material's temperature variation. and relative crystallinity Evolution of instantaneous static yield stress The critical criterion formula is expressed as: Where h is the thickness of a single-layer slice. Let be the temperature decay function over time. The relative crystallinity is calculated using the Nakamura-Weibull model.

[0011] In step (2), the relative crystallinity at different cooling rates is calculated using the Nakamura-Weibull model. And map crystallinity to the instantaneous elastic modulus of the material. Substitute the values ​​into the finite element mesh to calculate the strain state and printing collapse displacement of each printing point.

[0012] The "tilt angle-process parameter" nonlinear mapping model mentioned in steps (4) and (5) specifically involves setting a safety reference angle. (usually taken) ); When the actual cutting angle When the condition is determined to be low-risk, the high-efficiency mode is selected, and the rated high speed allowed by the equipment is adopted. and standard extrusion temperature ; when Time: Determined as a high-risk working condition, printing speed Follow The increase of follows the following decay function: in, For material viscosity sensitivity index ( ).

[0013] The high-temperature remelting bonding process described in step (6) includes: after completing the printing of the top layer of the substrate region, the extrusion temperature is instantly increased to [temperature value missing]. .

[0014] and with At low speed, 1-2 transition layers are extruded at the interface, and the excess enthalpy is used to cause deep diffusion and re-entanglement of polymer chain segments at the interface of new and old materials.

[0015] Compared with the prior art, the present invention has the following advantages: (1) The present invention proposes a supportless tilting 3D printing method and process parameter optimization method, which provides a solution for printing overhanging structures, and does not require additional support material, saving printing raw materials, improving printing efficiency, and eliminating the subsequent support removal process.

[0016] (2) This invention abandons the conservative "one-cut" process strategy in existing supportless printing and establishes an adaptive mapping mechanism for process parameters based on the deviation between the actual cutting angle and the theoretical critical threshold. In the low-risk tilt region far from the critical threshold, the high-speed printing potential of the equipment is fully released; in the high-risk region approaching the critical threshold, precise conservative parameters are automatically matched. This dynamic response mechanism maximizes overall manufacturing efficiency while ensuring that complex overhanging structures do not flow and collapse.

[0017] (3) This invention improves the scientific rigor of critical feature identification and segmentation. Unlike traditional segmentation methods that rely solely on geometric shapes or static empirical formulas, this invention constructs a thermo-mechanical coupling model based on the non-isothermal rheological properties and crystallization kinetics of materials, accurately predicting the theoretical critical stability angle threshold of materials under specific printing environments. Using this physical limit as a constraint guides the identification of geometric collapse nodes and the planning of cutting planes, effectively avoiding printing failures caused by prediction deviations and reducing the trial-and-error costs of developing new material processes.

[0018] (4) This invention significantly improves the interfacial bonding strength of layered printing. For the physical segmentation interfaces that inevitably exist in multi-axis printing, this invention innovatively introduces a high-temperature remelting bonding process. By using excess enthalpy, the polymer chain segments at the interface of the new and old materials undergo deep diffusion and re-entanglement, effectively overcoming the "cold seam" defect that is easily generated at the joint in traditional segmented printing, so that the Z-axis mechanical properties of the printed parts are close to the level of integral molding. Attached Figure Description

[0019] Figure 1 Overall process flow diagram Figure 2 Simulation graphs of Nakamura-Weibull crystallinity evolution, where (a) is offset by 0.1 mm, (b) by 0.2 mm, (c) by 0.3 mm, and (d) by 0.4 mm. Figure 3 Schematic diagram of critical collapse test Figure 4 Schematic diagram of geometric collapse node identification and cutting Figure 5 "Tilting Angle - Process Parameter" Mapping Curve Figure 6 Schematic diagram of substrate printing implementation Figure 7 Schematic diagram of hanging printing implementation Detailed Implementation Plan This example uses polylactic acid (PLA) material to print a model with large-angle overhang features.

[0020] The overall process flow is as follows Figure 1As shown, the adaptive variable parameter unsupported printing method of the present invention mainly includes four core stages: theoretical threshold prediction, geometric segmentation planning, adaptive matching of process parameters, and variable posture collaborative printing. The present invention includes a "parameter adaptive calculation" stage after model segmentation, ensuring an optimal balance between efficiency and stability in the subsequent printing process.

[0021] Theoretical prediction and calibration of the critical stability angle of materials: First, obtain the thermophysical parameters (density) of the PLA printing material. Glass transition temperature Simulation prediction: such as Figure 2 As shown, the temperature drop curve of the material after extrusion from the nozzle was calculated using the Nakamura-Weibull non-isothermal crystallization kinetic model. Figure 2 The curve T in the middle and the curve of relative crystallinity evolution ( Figure 2 (Curve X). Simulation results show that, under standard cooling conditions, the material reaches a crystallinity sufficient to resist gravitational flow within approximately 1.5 seconds after extrusion. Based on this thermo-mechanical coupling model, the theoretical critical stability angle threshold of the material is calculated. Experimental verification: such as Figure 3 As shown, to correct the deviation of the theoretical model, a single-line offset printing experiment was used for verification. This was achieved by progressively increasing the horizontal offset of the printed lines. This continues until the line collapses due to gravity. The measured results match the simulation results, confirming... This represents the safety constraint boundary in this embodiment.

[0022] Geometric collapse node identification and cutting planning: Import the T-shaped pipe model into the path planning system for geometric topology analysis. For example... Figure 4 As shown, the system identifies the model as containing a vertical, non-overhanging matrix region (Zone A) and an inclined, overhanging feature region (Zone B). At the branch junction, the system detects a sharp increase in the tangent angle of the geometric surface, identifying it as a geometric collapse node (e.g., Figure 4 (As shown in the middle circle). Establish the dividing plane based on this node. To completely eliminate the overhang of Zone B, geometric calculations indicate that Zone B needs to be rotated relative to the Z-axis by an angle of... Constraint verification: The system automatically compared and found that the required actual cutting tilt angle... Less than the theoretical threshold Therefore, the segmentation scheme is deemed feasible, and the determination is made. These serve as input variables for subsequent process calculations.

[0023] Adaptive matching of process parameters: based on a determined actual cutting angle The system calls a preset "tilt-process parameter" mapping model to generate custom G-code. For example... Figure 5 As shown, this mapping model exhibits an "inverse S-shaped" nonlinear curve characteristic: in The safe zone maintains the printing speed at [the specified speed]. High position; in The transition and risk zones are characterized by a sharp decrease in velocity as the angle increases. Parameter generation: [The remaining text appears to be a fragment and requires further context for accurate translation.] Substitution Figure 5 The curve model shown is used to calculate the corresponding optimal printing speed. Simultaneously, the system automatically adjusts the cooling strategy, setting the fan speed to 100% and reducing the extrusion temperature from the standard... Fine-tuning to To increase the viscosity of the melt.

[0024] Variable orientation collaborative printing and interface enhancement: such as Figure 6 As shown, the multi-degree-of-freedom robotic arm performs the final printing task: substrate printing (Zone A): the robotic arm maintains a vertical orientation, according to... Figure 5 The high-efficiency zone parameters allow for rapid printing of the substrate area at a speed of 60mm / s. High-temperature interfacial remelting: When printing reaches the "interfacial high-temperature remelting point," the robotic arm pauses, and the printhead temperature instantly increases to [temperature value missing]. (Above printing temperature) The nozzle extrudes two transition layers at the interface at a low speed of 10 mm / s. The high-temperature heat flow causes deep molecular diffusion at the interface between the new and old materials. Overhang printing (Zone B) is an example. Figure 7 As shown: Rotation of the robotic arm's end effector (i.e., angle) This aligns the printhead perpendicular to the cross-section of Zone B. At this point, the system automatically executes the precise process parameters generated in step three, completing the printing of the overhanging branches at a speed of 24 mm / s.

Claims

1. A supportless tilting 3D printing method and process parameter optimization method, characterized in that, The process includes the following steps: (1) Theoretical threshold prediction: Obtain the thermophysical parameters of the printing material, construct a critical stability angle prediction model for the material based on a non-isothermal rheological model, and calculate the theoretical critical stability angle threshold of the material under a specific printing environment. Its critical criterion formula is expressed as: Where h is the thickness of a single-layer slice. Let be the temperature decay function over time. (2) Simulation and collapse node identification: Set simulation conditions in the simulation model, use the Nakamura-Weibull non-isothermal crystallization dynamics model coupled with the finite element method to calculate the thermal stress evolution and local deformation during the printing process, and extract the warping displacement field in the Z-axis direction; mark the area where the displacement exceeds the preset safety value as the overhang area, and define its starting point as the geometric collapse node; (3) Cutting angle determination: traverse the geometric collapse nodes to determine the dividing plane that separates the overhang feature from the matrix; the determination of the dividing plane must meet the constraint conditions: actual cutting tilt angle (4) Adaptive matching of process parameters: based on the determined actual cutting tilt angle By using a preset "tilt angle - process parameter" nonlinear mapping model, a set of exclusive printing process parameters for this overhang feature area is generated, specifically: setting a safety reference angle. (usually taken) ); when the actual cutting angle When the condition is determined to be low-risk, the high-efficiency mode is selected, and the rated high speed allowed by the equipment is adopted. and standard extrusion temperature ;when Time: Determined as a high-risk working condition, printing speed Follow The increase of follows the following decay function: in, For material viscosity sensitivity index ( (5) Mapping model logic setting: The logic of the mapping model is: when the actual cutting tilt angle The closer to the theoretical critical stability angle threshold At that time, the printing speed decreases non-linearly, and the cooling fan speed increases non-linearly; (6) Cooperative printing and interface enhancement: First, the substrate area is printed using conventional parameters; at the physical separation interface between the substrate and the overhang feature, a high-temperature remelting connection process is performed; then the printing platform or nozzle posture is adjusted to the angle. Using the exclusive process parameter set generated in step (4), the tilted unsupported printing of the overhang feature area is completed.

2. The method according to claim 1, characterized in that, The thermophysical properties of the printing material in step (1) include at least the material density. Melt viscosity Glass transition temperature and shear strength .

3. The method according to claim 1, characterized in that, The theoretical critical stability angle mentioned in step (1) The prediction criterion is: during the relaxation time t after material extrusion, the shear component generated by gravity along the tangential direction must always be less than the material's shear component with temperature change. and relative crystallinity Evolution of instantaneous static yield stress .

4. The method according to claim 1, characterized in that, In step (2), the relative crystallinity at different cooling rates is calculated using the Nakamura-Weibull model. And map crystallinity to the instantaneous elastic modulus of the material. Substitute the values ​​into the finite element mesh to calculate the strain state and printing collapse displacement of each printing point.

5. The method according to claim 1, characterized in that, The high-temperature remelting bonding process described in step (6) includes: after completing the printing of the top layer of the substrate region, the extrusion temperature is instantly increased to [temperature value missing]. ; and with At low speed, 1-2 transition layers are extruded at the interface, and the excess enthalpy is used to cause deep diffusion and re-entanglement of polymer chain segments at the interface of new and old materials.

Images