Layered precision molding process for 3D printing of complex thin-walled sand molds

Abstract

This invention relates to the field of casting molding technology and discloses a layered precision molding process for 3D printed sand molds of complex thin-walled parts. The process includes: dividing the mold cavity into an outer structural layer and an interface buffer layer based on the three-dimensional geometry of the part to be cast; using a sand mold 3D inkjet printing device to gradient-spray resin binder to bond the original sand, forming a loose structure within the interface buffer layer containing 30% to 40% by mass of uncured original sand and uncrosslinked resin; pre-embedding a carbon fiber damping preform or layered pre-embedding carbon fiber material within this layer; injecting molten metal under vacuum negative pressure and monitoring the acceleration signal; switching the excitation frequency band according to the decrease in response amplitude; constructing a dynamic gas film using the gas phase components of resin pyrolysis; and dissipating strain energy through particle friction. This invention effectively resolves the thermal mismatch contradiction at heterogeneous interfaces by constructing a thermal buffer structure in situ inside the sand mold, thereby improving the molding accuracy and comprehensive mechanical properties of thin-walled composite castings.

Description

Technical Field

[0001] This invention belongs to the field of casting molding technology, and in particular relates to a layered precision molding process for 3D printing sand molds of complex thin-walled parts. Background Technology

[0002] Improving the dynamic mechanical properties of basic castings is currently key to ensuring the machining limits of the entire machine. This is usually achieved by embedding carbon fiber composite damping material preforms in situ into the metal matrix to construct a multi-component composite structure. The damping characteristics of the heterogeneous materials complement each other to achieve structural vibration reduction. Currently, additive manufacturing technology is used to stack coated sand layer by layer to construct cavities, which can produce complex thin-walled topological structures that are difficult to achieve with traditional molding processes, providing a flexible path for the overall molding of high-performance composite castings.

[0003] However, when faced with the molding and pouring conditions of complex thin-walled composite castings, conventional sand molds, due to their uniform sand layer structure, struggle to provide customized thermal barrier channels within the cavity for damping preforms with low heat resistance limits. The leading-edge thermal radiation generated by the pouring of molten metal easily causes pyrolysis and carbonization of the preform, thereby damaging the carbon fiber coating structure and leading to mechanical debonding at the interface. Furthermore, when the molten metal enters the solid-liquid two-phase region, the precipitated primary dendritic network causes the system to exhibit a high apparent viscosity. If linear improvement methods such as increasing macroscopic pressure or increasing excitation amplitude are used to allow the residual liquid phase to penetrate into the micropores of the preform, the resulting mechanical strain often easily exceeds the yield limit of the thin-walled sand mold, leading to cavity collapse or fracture and instability of the built-in preform. This fundamental constraint between macroscopic structural mold preservation and microscopic interface wetting dynamics becomes a technical bottleneck restricting the precision manufacturing of high-performance composite thin-walled castings. In addition to the aforementioned physical structural constraints, there are also limitations at the process control level.

[0004] Therefore, the technical problem to be solved by this invention is how to achieve the coordinated solution of thermal damage protection of heterogeneous composite interfaces and interface wetting dynamic supply during the semi-solid phase transition stage while ensuring the macroscopic topological integrity of complex thin-walled sand molds. Summary of the Invention

[0005] This invention proposes a layered precision molding process for 3D printing sand molds of complex thin-walled parts, including:

[0006] Step 101, Cavity Division: Based on the three-dimensional geometry of the complex thin-walled part to be cast, the cavity area of ​​the sand mold is determined, and the cavity area of ​​the sand mold is divided into an outer structural layer and an interface buffer layer.

[0007] Step 102, gradient curing: The original sand is laid out using a sand mold 3D inkjet printing device. When spraying the outer structural layer, a second spray droplet is output to completely cure the resin binder in the original sand. When spraying the interface buffer layer, a first spray droplet is output. The first spray droplet is lower than the spray droplet threshold for complete resin curing, so that a loose structure containing 30% to 40% by mass of uncured free original sand and uncrosslinked resin components is formed in the interface buffer layer.

[0008] Step 103, Precast Placement: While laying the original sand for the interface buffer layer in 3D printing, simultaneously lay the precast carbon fiber composite damping material in situ between layers or pre-embed carbon fiber material in layers, and complete the sand mold assembly.

[0009] Step 104, Negative Pressure Vibration Filling: In a vacuum negative pressure environment of -0.05MPa to -0.06MPa, molten metal is injected into the cavity area of ​​the sand mold, and pulse excitation of the first frequency band of 10Hz to 50Hz is applied. Simultaneously, the acceleration sensor on the periphery of the sand mold is monitored to obtain the vibration acceleration signal. When the low-frequency response amplitude of the monitored vibration acceleration signal drops to 50% of the initial stable value, the frequency is switched to the second frequency band of 300Hz to 1000Hz for high-frequency micro-vibration. The gas phase component generated by the thermal pyrolysis of the uncrosslinked resin component in the interface buffer layer is used to construct a dynamic gas film on the surface of the carbon fiber composite damping material preform. The interparticle frictional slip generated by the uncured free original sand dissipates the strain energy, so that the metal flow front in the solid-liquid two-phase region can penetrate into the carbon fiber composite damping material preform under the action of acceleration.

[0010] Preferably, step 102 includes: controlling the first spray droplet amount to be 60% to 80% of the second spray droplet amount, so that the original sand in the interface buffer layer forms a discontinuous network skeleton composed of cured resin, and the network skeleton provides a spatial constraint network for the uncured free original sand.

[0011] Preferably, the thickness of the interface buffer layer is spatially gradient-distributed with the change of surface curvature of the sand mold cavity region, and at the abrupt change in curvature of the sand mold cavity region, the thickness of the interface buffer layer is greater than that of the flat part of the sand mold cavity region.

[0012] Preferably, in step 104, the gaseous components generated by vacuum negative pressure induced pyrolysis permeate to the metal flow front, maintaining a dynamic gas film on the surface of the carbon fiber composite damping material preform.

[0013] Preferably, step 104 further includes: step 1041: extracting the high-frequency component in the vibration acceleration signal; step 1042: determining the contact area between the molten metal and the carbon fiber composite damping material preform based on the amplitude change of the high-frequency component.

[0014] Preferably, in step 104, in the solid-liquid coexistence zone of the molten metal, the shear thinning effect of the uncured free sand in the interface buffer layer is enhanced by increasing the excitation frequency of the second frequency band high-frequency micro-vibration.

[0015] Preferably, the coated sand includes raw sand and thermosetting resin with a mass fraction of 1.8% to 2.5%, and the local curing effect of the thermosetting resin under the first spray droplet volume forms microporous venting channels in the interface buffer layer.

[0016] Preferably, before step 103, the carbon fiber composite damping material preform is preheated at a temperature of 150°C to 180°C.

[0017] Preferably, after the molten metal solidifies, the temperature difference between the interface buffer layer and the outer structural layer is stabilized within a preset temperature difference range by adjusting the circulation rate of the cooling medium.

[0018] Compared with existing technologies, the layered precision molding process of 3D printing sand molds for complex thin-walled parts in this invention has the following advantages:

[0019] 1. In the layered precision modeling of 3D printed sand molds, the gradient distribution of the jetting droplets during the 3D inkjet printing process of sand molds is utilized to enable the sand mold cavity to have spatial topological thermal resistance differences during the forming stage. By forming a network pore structure in the interface thermal control zone and retaining a specific proportion of uncrosslinked free original sand, a small amount of volatile gas is induced to expand and absorb heat under vacuum negative pressure to form a dynamic cold gas film. This mechanism enables an adaptive thermal barrier to be generated between the built-in carbon fiber composite damping material preform and the high-temperature molten metal. Under the premise of ensuring the integrity of the preform's covering structure, the thermal radiation at the forefront of the molten metal is blocked from causing pyrolysis damage to the damping network. This solves the contradiction of thermal stability of the heterogeneous material composite interface from the boundary control dimension of casting modeling.

[0020] 2. By retaining 30% to 40% of uncrosslinked free sand within the low thermal conductivity buffer sand layer, an acoustic impedance matching layer with mechanical filtering characteristics is constructed. During vibration, the free sand particles generate interparticle frictional slippage, and physical dissipation may lead to large-amplitude mechanical strain in the macroscopic collapse of complex thin-walled sand molds. At the same time, the free sand is used as a rigid medium to transmit high-frequency micro-acceleration to the solid-liquid phase interface. This mechanism preserves the macroscopic topology of the fragile thin-walled sand mold while providing microscopic wetting dynamics for the phase interface, thus resolving the physical mutual exclusion between macroscopic stress damage and microscopic filling requirements in conventional molding processes.

[0021] 3. By simultaneously laying carbon fiber composite damping material preforms or pre-embedding carbon fiber materials in situ between layers during the 3D printing of the interface buffer layer, the precise fit between the damping preforms and the complex thin-walled sand mold spatial topology is achieved. This ensures the overall mold closing accuracy of the sand mold while significantly improving the comprehensive mechanical properties and service life of the complex thin-walled parts. Attached Figure Description

[0022] Figure 1 This is a complete process diagram of the precision sand molding and frequency conversion control logic for 3D printing of complex thin-walled parts according to the present invention;

[0023] Figure 2 This is a schematic diagram illustrating the system architecture and physical evolution principle of the digital precision modeling process of this invention. Detailed Implementation

[0024] The technical solutions of the embodiments of this application will be clearly described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of this application are within the scope of protection of this application.

[0025] It should be noted that all directional and positional terms used in this invention, such as: up, down, left, right, front, back, vertical, horizontal, inner, outer, top, bottom, transverse, longitudinal, center, etc., are only used to explain the relative positional relationship and connection between components in a specific state (as shown in the accompanying drawings). They are only for the convenience of describing this invention and do not require that this invention be constructed and operated in a specific orientation. Therefore, they should not be construed as limiting this invention. In addition, the descriptions of "first," "second," etc., in this invention are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated.

[0026] In the description of this invention, unless otherwise explicitly specified and limited, the terms installation, connection, and linking should be interpreted broadly. For example, they can refer to fixed connections, detachable connections, or integral connections; they can refer to mechanical connections; they can refer to direct connections or indirect connections through an intermediate medium; they can refer to the internal connection of two components. For those skilled in the art, the specific meaning of the above terms in this invention can be understood according to the specific circumstances.

[0027] In the description of this specification, references to the terms "an embodiment," "some embodiments," "illustrative embodiments," "examples," "specific examples," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example, and the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0028] A layered precision molding process for 3D printing sand molds of complex thin-walled parts includes:

[0029] Step 101, Cavity Division: Based on the three-dimensional geometry of the complex thin-walled part to be cast, the cavity area of ​​the sand mold is determined, and the cavity area of ​​the sand mold is divided into an outer structural layer and an interface buffer layer.

[0030] Step 102, gradient curing: The original sand is laid out using a sand mold 3D inkjet printing device. When spraying the outer structural layer, a second spray droplet is output to completely cure the resin binder in the original sand. When spraying the interface buffer layer, a first spray droplet is output. The first spray droplet is lower than the spray droplet threshold for complete resin curing, so that a loose structure containing 30% to 40% by mass of uncured free original sand and uncrosslinked resin components is formed in the interface buffer layer.

[0031] Step 103, Precast Placement: While laying the original sand for the interface buffer layer in 3D printing, simultaneously lay the precast carbon fiber composite damping material in situ between layers or pre-embed carbon fiber material in layers, and complete the sand mold assembly.

[0032] Step 104, Negative Pressure Vibration Filling: In a vacuum negative pressure environment of -0.05MPa to -0.06MPa, molten metal is injected into the cavity area of ​​the sand mold, and pulse excitation of the first frequency band of 10Hz to 50Hz is applied. Simultaneously, the acceleration sensor on the periphery of the sand mold is monitored to obtain the vibration acceleration signal. When the low-frequency response amplitude of the monitored vibration acceleration signal drops to 50% of the initial stable value, the frequency is switched to the second frequency band of 300Hz to 1000Hz for high-frequency micro-vibration. The gas phase component generated by the thermal pyrolysis of the uncrosslinked resin component in the interface buffer layer is used to construct a dynamic gas film on the surface of the carbon fiber composite damping material preform. The interparticle frictional slip generated by the uncured free original sand dissipates the strain energy, so that the metal flow front in the solid-liquid two-phase region can penetrate into the carbon fiber composite damping material preform under the action of acceleration.

[0033] Preferably, step 102 includes: controlling the first spray droplet amount to be 60% to 80% of the second spray droplet amount, so that the original sand in the interface buffer layer forms a discontinuous network skeleton composed of cured resin, and the network skeleton provides a spatial constraint network for the uncured free original sand.

[0034] Preferably, the thickness of the interface buffer layer is spatially gradient-distributed with the change of surface curvature of the sand mold cavity region, and at the abrupt change in curvature of the sand mold cavity region, the thickness of the interface buffer layer is greater than that of the flat part of the sand mold cavity region.

[0035] Preferably, in step 104, the gaseous components generated by vacuum negative pressure induced pyrolysis permeate to the metal flow front, maintaining a dynamic gas film on the surface of the carbon fiber composite damping material preform.

[0036] Preferably, step 104 further includes: step 1041: extracting the high-frequency component in the vibration acceleration signal; step 1042: determining the contact area between the molten metal and the carbon fiber composite damping material preform based on the amplitude change of the high-frequency component.

[0037] Preferably, in step 104, in the solid-liquid coexistence zone of the molten metal, the shear thinning effect of the uncured free sand in the interface buffer layer is enhanced by increasing the excitation frequency of the second frequency band high-frequency micro-vibration.

[0038] Preferably, the coated sand includes raw sand and thermosetting resin with a mass fraction of 1.8% to 2.5%, and the local curing effect of the thermosetting resin under the first spray droplet volume forms microporous venting channels in the interface buffer layer.

[0039] Preferably, before step 103, the carbon fiber composite damping material preform is preheated at a temperature of 150°C to 180°C.

[0040] Preferably, after the molten metal solidifies, the temperature difference between the interface buffer layer and the outer structural layer is stabilized within a preset temperature difference range by adjusting the circulation rate of the cooling medium.

[0041] Example 1: In the scenario of integral molding of a basic structural component for a precision compressor, the component has a thin-walled topology with a wall thickness of 5mm to 8mm. A carbon fiber composite damping material preform is in-situ laid at a predetermined position inside the cavity. During the molten metal filling process, the homogeneous coated sand mold struggles to maintain the integrity of the cavity structure while providing thermal insulation for the polymer damping network with a heat resistance limit below 300℃. Furthermore, when the molten metal enters the solid-liquid two-phase region, the precipitated primary dendrites form a network skeleton, leading to an increase in the apparent viscosity of the melt. This makes it difficult for the residual liquid phase to penetrate the micropores of the damping preform under negative pressure, resulting in the risk of interfacial mechanical debonding and dimensional accuracy degradation in large castings. Based on the components to be cast... The three-dimensional geometry of the thin-walled part is determined by defining the sand mold cavity area. This cavity area is divided into an outer structural layer and an interface buffer layer. Raw sand is laid using a sand mold 3D inkjet printer. During the spraying of the outer structural layer, a second spray droplet is output to completely cure the resin in the raw sand. Simultaneously, a first spray droplet is output during the scanning of the interface buffer layer. This results in a loose structure within the interface buffer layer, consisting of 30% to 40% by mass of uncured free raw sand and uncrosslinked resin components. The first spray droplet volume is lower than the resin-curing spray droplet threshold. A preform is anchored to a predetermined surface within the interface buffer layer cavity. The mold is then closed and sealed, and a vacuum source is used to maintain a pressure of -0.05 MPa to -0.06 MPa within the cavity area. A negative pressure environment of MPa is created by injecting molten metal into the casting system. The temperature of the molten steel is 1500-1550℃. Simultaneously, a vibration table is started and pulse excitation at a frequency of 10Hz to 50Hz is applied. Accelerometers mounted on the rigid support of the precast preform are continuously monitored. As the temperature of the molten metal tip drops to the solid-liquid two-phase region, primary dendrites precipitated in the melt rigidly interfere with the inner wall of the sand mold, increasing system damping. When the low-frequency response amplitude detected by the acceleration sensor drops to 50% of the initial stable value, the vibration table is switched to a high-frequency micro-vibration at a frequency of 300Hz to 1000Hz. At the instant of this frequency switch, the interface buffer layer... The mechanical properties of the medium undergo a crucial cross-scale physical transformation. The loose, slippery sand, exhibiting loose characteristics under low-frequency pulses, is excited by a high-frequency micro-vibration field of 300Hz to 1000Hz. Because the high-frequency oscillation period is shorter than the mechanical displacement relaxation time of the particle group, a dynamic self-locking and acoustic hardening effect is instantly triggered in the particle system. This high-frequency dynamic self-locking mechanism causes the originally loose sand particles to instantly form a tightly interlocked force chain network. Thus, without increasing the macroscopic static structural stiffness, it is temporarily transformed into a rigid waveguide medium capable of transmitting high-frequency stress waves without damage and with high efficiency at the microscopic transmission scale, eliminating the interference and mutual exclusion between the macroscopic buffering and dissipation requirements and the microscopic wave transmission requirements.

[0042] Vibrational energy is conducted from the outer structural layer to the interface buffer layer. The uncured free sand encased within this layer undergoes high-frequency frictional slippage between particles under high-frequency micro-vibrations in the second frequency band. This slippage mechanism dissipates mechanical strain leading to the overall collapse of the sand mold, preserving the overall topology of the thin-walled sand mold. Simultaneously, the uncured free sand, acting as rigid media particles, transmits high-frequency micro-acceleration to the semi-solid metal melt phase interface, applying localized mechanical shear to the overlapping primary dendrite network and inducing a thixotropic effect to reduce the apparent viscosity of the residual liquid phase. The gaseous components generated by the thermal pyrolysis of the uncrosslinked resin component in the interface buffer layer permeate towards the metal flow front under vacuum negative pressure, constructing a dynamic gas film on the surface of the carbon fiber composite damping material preform. This dynamic gas film utilizes the expansion and absorption of trace amounts of volatile gases... The thermal effect creates a thermal barrier, preventing the high-temperature melt from pyrolyzing and carbonizing the damping network while ensuring the integrity of the preform's covering structure. This allows the low-viscosity residual liquid phase to infiltrate the porous surface of the carbon fiber composite damping material preform under the drive of high-frequency micro-acceleration, resulting in interfacial micro-leakage and physical fusion. The establishment of this physical fusion process depends on the dynamic collapse mechanism of the interfacial gas film. When the front end of the molten metal cools down due to heat transfer and enters the solid-liquid two-phase region, its outward radiated heat energy density decreases significantly, causing the rate of gas production from the pyrolysis of the underlying resin to drop sharply and momentarily fall below the directional suction rate of the external vacuum source. At this time, the high-pressure dynamic gas film originally covering the surface of the damping preform rapidly ruptures and collapses due to the loss of continuous internal gas phase pressure replenishment. The constructed thermal resistance isolation layer disappears, and the porous surface of the carbon fiber composite damping material preform is exposed again. This allows the thixotropically treated semi-solid metal fluid to penetrate and fully wet the microporous network of the preform at the interface physical boundary without any gas phase obstruction. After cooling and solidification, the composite thin-walled casting is removed. This casting maintains a tensile strength of not less than 600 MPa while achieving a damping loss factor of over 0.35. By utilizing the differences in the physical phase distribution of the molding materials to construct a mechanical filtering mechanism, the physical constraint between the overall structural shape preservation requirements and the local interface-scale wetting dynamic requirements is resolved. After completing the above filling process and entering the solidification and cooling stage, in order to stabilize the temperature difference between the interface buffer layer and the outer structural layer within the preset temperature difference range... To achieve the intended purpose, this invention employs a hardware and fluid collaborative control path based on dual-source monitoring. During the initial 3D inkjet printing of the outer structural layer using a sand mold, a conformal cooling medium circulation micro-pipeline network covering the periphery of the cavity is simultaneously and integrally formed. Miniature thermocouple nodes are pre-embedded at the critical depth close to the interface buffer layer. The control system reads the internal deep transient temperature data fed back by these thermocouples in real time and compares it with the cooling medium status monitored by the external fluid flow meter. A closed-loop PID algorithm is used to dynamically adjust the output speed of the external variable frequency fluid pump connected to the micro-pipeline network, thereby changing the instantaneous circulation velocity of the cooling water. By adjusting the macroscopic heat exchange rate, precise targeted feedback control of the cross-interface temperature gradient in the deep cavity is achieved.

[0043] Example 2: In a sand mold physical test platform equipped with a vacuum negative pressure maintenance unit and a variable frequency electromagnetic vibration worktable, a piezoelectric accelerometer with a measurement accuracy better than 0.01g, deployed on the outer wall of the sand mold, is used to collect vibration characteristic signals. The sampling frequency of the accelerometer is set to 5000Hz, and Gaussian white noise with a signal-to-noise ratio of 20dB is actively superimposed at the signal input end to restore the mechanical background noise of the industrial production environment. The setting of the first spray droplet volume E1 is determined based on the critical cross-linking spray droplet volume threshold Ethresh of the resin in the original sand. By pre-measuring the relationship curve of the resin cross-linking degree with the spray volume, the spray droplet volume identifies the characteristic inflection point with the largest change in the curvature of the cross-linking degree as the process setting benchmark, so as to balance the initial shaping strength of the sand mold interface and the permeability requirements of subsequent pyrolysis gas production, ensuring that the mass fraction of uncured free original sand formed in the interface buffer layer is in the range of 30% to 40%. At the same time, the center frequency of the first frequency band pulse excitation is based on the first resonant frequency of the sand mold system. It is determined that this frequency was selected to ensure a larger ripple range in the early stages of molten metal filling, thereby preventing premature solidification at the molten metal front.

[0044] A control group with 0% uncured free sand and an experimental group with 35% uncured free sand were compared under the same molten metal filling environment. In the control group, the response amplitude recorded by the accelerometer showed a linear and slow decrease as the filling process progressed, indicating a gentle change in system damping. In the experimental group, after the melt front temperature dropped to the solid-liquid two-phase region, based on a single-degree-of-freedom forced vibration physical model, the fundamental response amplitude of the forced vibration was inversely proportional to the equivalent mass. Before obtaining the real-time low-frequency response amplitude, the control unit calculated the real-time cumulative loading mass of the molten metal according to the product of the pre-calibrated pouring flow rate and filling time. A mass feedback compensation operator was used to smooth and filter out the measured total acceleration amplitude in real time, eliminating the interference from the molten metal's own gravity loading during filling and extracting the pure damping attenuation component caused only by primary dendrite network interference. The specific internal execution logic of this mass feedback compensation operator is as follows: In the system control... The control unit pre-stores a lookup table corresponding to the unloaded cavity mass and vibration amplitude response obtained from experimental calibration. During the actual liquid injection and filling process, the control unit continuously inputs the theoretical cumulative injection mass calculated based on the flow rate into this lookup table to extract the expected basic amplitude offset that should be generated at the current moment solely due to the increase in the static mass of the molten metal. In the data cleaning process of the sliding sampling root mean square calculation module, differential subtraction is used to subtract the above-mentioned expected basic amplitude offset point by point from the total acceleration feature envelope signal obtained by the sensor. Through this data cleaning action, the macroscopic low-frequency suppression effect on the vibration response caused by the increase in the overall inertia of the system due to the continuous increase in the casting mass is filtered out, ensuring that the attenuation feature signal that finally enters the judgment program is 100% derived from the intrinsic damping mutation of the system induced by the cross-linking and overlapping of the microscopic primary dendrite network. Due to the mechanical interference between the precipitated primary dendrites and the interface buffer layer, the low-frequency response amplitude monitored by the sensor is reduced. From the initial stable value 5.25 It rapidly decreased to 2.63. When the attenuation ratio reaches the 50% logical criterion, the excitation source is switched to the second frequency band high-frequency micro-vibration with a frequency of 650Hz. Under the drive of this high-frequency field, the interfacial thixotropic index recorded by the experimental group increases from 0.15 to 0.87, and the apparent viscosity of the semi-solid metal melt decreases abruptly. The pyrolysis gas phase component generated by the uncrosslinked resin in the interfacial buffer layer penetrates into the metal flow front under vacuum negative pressure, and a dynamic gas film is constructed on the surface of the carbon fiber composite damping material preform. The measured depth of the heat-affected zone of the preform in the experimental group is 0.48mm, which is lower than the 3.52mm of the control group.

[0045] To determine the process window and verify parameter boundaries, gradient sample groups containing uncured free sand at mass fractions of 25%, 35%, and 45% were set up for comparison. Measured data showed that when the uncured free sand mass fraction was 25%, the mechanical filtering effect caused by particle slippage was insufficient, resulting in a residual stress measurement value of 152 MPa in the casting of complex thin-walled sections, with a damping loss factor of only 0.21. When the mass fraction was 35%, the tensile strength of the casting was 618 MPa, and the damping loss factor increased to 0.39, demonstrating a synergistic state of interfacial micro-leakage and physical integration. However, when the mass fraction increased to 45%, due to the decrease in the stiffness of the sand mold structure, local deformation occurred under the hydrostatic pressure of the molten metal, leading to the thin-walled part... The wall thickness deviation suddenly increased from 0.3 mm to over 1.2 mm. This deterioration phenomenon confirms that the 30% to 40% component ratio is the physical limit for ensuring the balance between the geometric accuracy of the sand mold and the wetting dynamics of the interface. Through correlation analysis of the performance data of different components, it is confirmed that the method of the present invention utilizes the spatial distribution differences of the physical phases of the molding materials to construct a mechanical energy conversion mechanism. It utilizes the dynamic friction characteristics of the uncured components in the interface buffer layer at a specific frequency band to dissipate strain energy and simultaneously converts the resin pyrolysis products into an interface protective medium. Without changing the basic alloy composition, it achieves the simultaneous improvement of high strength and high damping performance of complex thin-walled castings, and completes the full-process verification of the effectiveness of the layered precision molding process under real complex working conditions.

[0046] Example 3: In the manufacturing scenario of a high-end compressor housing, the housing has a thin-walled structure with a thickness of 6.5mm and complex irregular flow channels. The material is set to high-strength alloy steel. The sand mold cavity area consists of an outer structural layer made of high-strength coated sand and an interface buffer layer with gradient porosity. To eliminate signal interference caused by system frequency drift during the initial filling of the molten metal, a benchmark calibration program is started before casting. A frequency sweep excitation with an amplitude of 0.5g is applied in advance using a variable frequency electromagnetic vibration table, and an accelerometer continuously collects data within a 30s sampling period. A periodic signal, according to the formula Calculate the initial stable value of the system, where, Refers to the initial stable value, Refers to the first The instantaneous amplitude at each sampling point The total number of samples is selected as 5000 in this example. Alloy steel melt at 1500℃ to 1550℃ is injected into the mold cavity. When the melt contacts the interface buffer layer, the gaseous components generated by the resin, driven by a vacuum negative pressure of -0.055MPa, penetrate into the center of the cavity through the micron-level gaps between the uncured free sand. The flow rate is controlled by the increasing porosity gradient of the interface buffer layer from the inside out, generating a dynamic gas film with a thickness of 0.25mm to 0.45mm on the surface of the pre-embedded carbon fiber composite damping material preform. As the melt tip enters the solid-liquid two-phase region, the primary dendrite network mechanically anchors to the sand mold wall, causing a change in the dynamic response characteristics of the sand mold system. An acceleration sensor installed on the rigid support of the preform surrounding the sand mold monitors the low-frequency response amplitude in real time. The control unit uses a sliding sampling window of 20ms to perform root mean square calculation on the monitored signal and compares it with the initial stable value. Perform a logical comparison, and when a judgment is made... The value remained below the initial stable value for three consecutive sampling periods. When the frequency reaches 50%, the excitation frequency switching command is triggered. To avoid mechanical shock caused by frequency abrupt changes, the control unit uses a frequency compensation operator to perform exponential slope frequency adjustment during the process of excitation frequency conversion from 50Hz to 800Hz, so that the excitation energy acts on the semi-solid melt front with a smooth power spectrum.

[0047] Based on the principle of acoustic impedance energy transmission, the high-frequency vibration energy transmittance at the interface between two-phase fluids has a direct linear relationship with the physical wetting area between the solid and liquid phases. The state sensing system separates the high-frequency acceleration characteristic component of the center frequency through a bandpass filter, extracts the root mean square amplitude of five consecutive vibration cycles, and uses the calculation formula... Determine the current interface wetting contact state, where, This represents the actual contact area between the molten metal and the carbon fiber damping preform. This indicates the real-time extraction of the root mean square amplitude of high-frequency features. The no-load calibration process of the value acquisition system records the reference amplitude at the same frequency. As the interfacial transfer coefficient constrained by apparent viscosity is fixed at 120 at the standard filling temperature of this alloy system, in actual operation, the complex microscopic solid-liquid contact mechanics is successfully reduced to a single high-frequency acceleration amplitude change. The physical transformation is based on the rigid monotonic mapping relationship between the actual wetting area ratio of the solid-liquid interface and the local transmission acoustic impedance of the system. As the residual liquid phase gradually fills and weds into the microporous network on the surface of the preform, the mechanical coupling stiffness of the two-phase interface increases proportionally, resulting in a corresponding proportional increase in the root mean square amplitude of the specific high-frequency transmitted wave. Energy decay, and the constant term 120 in the formula, originates from the offline physical calibration program before the system was put into production: by pre-pouring standard-temperature steel alloy melt at the same grade into a series of stepped damping precast samples with known precise surface area coefficients, the steady-state amplitude decay rate before and after reaching a fully wetted stable state was measured. The inverse of the slope obtained after linear regression fitting is the interface transfer coefficient of the specific alloy system. This constructs an accurate conversion data channel from macroscopic one-dimensional sensor signals to microscopic two-dimensional contact area. The control unit calculates the actual contact area based on this data. Whether the pre-loaded structural parameter threshold is exceeded to generate a hardware cut-off command to terminate the second frequency band high-frequency micro-vibration closed loop.

[0048] Uncured free sand within the interface buffer layer, driven by an 800Hz high-frequency micro-vibration field, generates a localized fluidized layer between the carbon fiber composite damping material preform and the melt. This utilizes the physical dissipation of interparticle sliding friction to dissipate the interfacial shear stress caused by thermal contraction, preserving the geometric accuracy of the thin-walled sections of the compressor housing. Simultaneously, the thermal resistance generated by the dynamic gas film maintains the transient temperature of the preform surface below 278.6℃, preventing thermal decomposition of the polymer components. After the alloy steel melt completely solidifies and cools to room temperature, the casting is removed. The wall thickness deviation of the thin-walled sections of the compressor housing is controlled within 0.3mm, and a continuous, pore-free fusion interface is formed between the carbon fiber composite damping material preform and the alloy steel matrix. The measured tensile strength is 625.4MPa. By quantitatively describing the adaptive control logic and the gas phase transport path, the thermal field control problem during the molding process of the thin-walled composite component is solved.

[0049] Example 4: When the system encounters different batches of coated sand materials arriving on site, the offline calibration unit is used to determine the threshold for the amount of sprayed droplets for complete resin curing. This unit uses a stepped injection method to prepare a sample block with a side length of 10 mm and a thickness of 2 mm on a reference base plate. The wavelength of the sample block is monitored using a Fourier transform infrared spectrometer. The intensity of the characteristic absorption peak at the point was used to calculate the degree of resin crosslinking under different droplet inputs. Establish a correlation mapping curve between the amount of sprayed droplets and the degree of crosslinking to identify the degree of crosslinking. The minimum spray droplet volume value that reaches 95% is used as the second spray droplet volume. Select the slope of the curve The point at which the spray droplet volume is maximized is used as the spray droplet volume threshold for complete resin curing. The process determines the first jet droplet volume based on the intrinsic reaction characteristics of the material. The boundary values ​​of .

[0050] In the modeling of novel, complex, thin-walled structural components, to eliminate the impact of sand mold compaction fluctuations on acceleration signal transmission efficiency, a sensor benchmark calibration process is initiated after mold closing and before casting. The vibration table is controlled to apply a sweeping excitation signal within the 10Hz to 1500Hz range, and the frequency response function of the sand mold under no-load conditions is obtained through an accelerometer. According to the peak bandwidth of the frequency response function Calculate the reference damping ratio of the sand mold structure When the moisture content of the production environment fluctuates, the reference damping ratio is affected. When the deviation from the preset reference value is 10%, the system automatically corrects the amplitude ratio threshold for triggering the switching of the excitation frequency band, so that the determination of the amplitude reduction ratio is anchored within the dynamic linear response range of the sand mold structure.

[0051] Example 5: Establishing the interface buffer layer thickness in a large-scale precision manufacturing scenario for compressor housing design. With complex thin-walled component design wall thickness The geometric dimension calibration procedure was used to determine the interface buffer layer thickness to satisfy the calculation formula through offline controlled experiments. ,in, Refers to the thickness of the interface buffer layer. Refers to the wall thickness in the design of complex thin-walled components. Refers to the geometric shape factor, with a selection range of 1.2 to 1.5; This refers to the heat-affected margin constant, which is selected as 0.5mm in this example. The material density detection unit integrated in the laying equipment collects sand layer compaction data in real time. When the detected bulk density deviates from the preset benchmark value by more than 3%, the system automatically corrects the equipment output of the first spray droplet amount according to the pre-stored mapping function, so that the mass fraction of uncured free sand in the interface buffer layer is stably controlled within the range of 30% to 40%. When the molding system encounters an unsteady filling condition caused by vacuum source negative pressure fluctuations, the control unit starts the online fault-tolerant correction program, extracts the vibration acceleration signal obtained by the acceleration sensor in real time, and calculates the real-time root mean square amplitude of the signal. Through calculation First derivative with time To determine the physical moment when the melt enters the solid-liquid two-phase region, when the vacuum negative pressure fluctuates from -0.06MPa to -0.045MPa and the absolute value of the slope of the decrease in the acceleration response amplitude exceeds 20% of the preset reference slope, the system uses a frequency compensation operator. Smoothing compensation is performed on the starting frequency of the high-frequency micro-vibrations in the second frequency band, wherein, Refers to the real-time root mean square amplitude. Referring to time, Refers to the frequency compensation operator, which characterizes the nonlinear correction effect of vacuum pressure changes on the system stiffness. The frequency compensation operator is selected... Satisfy the calculation formula ,in, This is the real-time vacuum pressure value. Using the reference vacuum pressure value, this correction logic enables the high-frequency micro-vibration field in the second frequency band to still induce the interfacial thixotropic effect under the environment of weakened filling power, driving the residual liquid phase to penetrate into the micropores on the surface of the carbon fiber composite damping material preform. The measured thickness distribution of the interfacial fusion layer of the complex thin-walled casting is less than 0.02 mm.

[0052] In precision modeling scenarios involving complex thin-walled components with high curvature topological features, the thickness of the interface buffer layer is established. Normal thickness of the complex thin-walled part to be cast The quantitative mapping relationship is used to determine the transient temperature field distribution after the molten metal is filled using a heat conduction analysis model, based on the pyrolysis rate of the resin. With vacuum negative pressure Pressure gradient distribution identifies the effective diffusion radius of pyrolysis gas phase components. The thickness of the interface buffer layer Set as effective diffusion radius The expansion boundary of the dynamic gas film is 1.1 to 1.3 times that of the original material. Based on Darcy's law in porous media fluid mechanics, the microscopic permeation direction of the fluid is controlled by the local three-dimensional media permeability gradient rather than a single macroscopic negative pressure. The outer structural layer is fully cross-linked and solidified to construct a dense flow resistance boundary. This causes the uncross-linked resin in the interface buffer layer to generate high-pressure gas phase components that overcome the directional suction of the vacuum source. Driven by local positive vapor pressure, directional Knudsen diffusion occurs along the loose pore grid towards the preform interface. In the actual physical process, the establishment of this Knudsen diffusion mechanism relies on the dynamic thermal shrinkage effect of the porous media channel size. When the uncross-linked resin in the interface buffer layer is instantaneously subjected to the strong thermal radiation of the high-temperature molten metal... Incomplete transient pyrolysis occurs, resulting in the in-situ precipitation of amorphous carbon meshes with nanoscale pore structures. These newly generated nanoscale carbon structures rapidly fill and bridge the gaps between the original free sand particles, which were originally at the micrometer level. This physically divides and refines the macroscopic gas exhaust channels between sand particles into a submicrometer to nanometer-scale micropore network with characteristic scales smaller than the mean free path of gas phase molecules. Consequently, the macroscopic seepage that originally followed conventional viscous fluid dynamics is forcibly transformed into microscopic Knudsen diffusion dominated by the probability of collisions between molecules and pore walls. This ensures that high-pressure steam achieves low-speed and uniform seepage on surfaces with complex geometric curvatures. Based on the Darcy seepage principle and the radial pressure decay integral model in cylindrical coordinates, a geometric adjustment operator is selected. Dimensional corrections were made for different curvature sections, among which... Refers to the thickness of the interface buffer layer. Refers to the normal thickness of the part to be cast. Refers to the pyrolysis rate Refers to the effective diffusion radius. Refers to the geometric adjustment operator, which is used to correct the effect of curvature on gas phase osmotic pressure. The geometric adjustment operator is selected accordingly. Satisfy the calculation formula ,in, This specification defines the local radius of curvature for this location. It enables the layered precision molding process to maintain thermal resistance balance at the phase interface even when facing sudden changes in component wall thickness. When the molding system encounters fluctuations in the flowability of the coated sand caused by varying environmental humidity, a standardized pre-calibration is performed using the sand-laying torque feedback unit built into the sand mold 3D inkjet printer. This is achieved by continuously laying three 0.1mm thick test layers on a reference base plate and recording the resistance torque of the sand-laying roller. Based on the proportional coefficient of the drag torque deviating from the reference value Real-time fine-tuning of nozzle overlap Select the proportionality coefficient Satisfy the calculation formula ,in, To monitor torque values ​​in real time, Using the reference torque value, this correction process eliminates the random interference of material physical state differences on the porosity of the loose structure of the interface buffer layer, ensuring that the thickness distribution difference of the dynamic air film on the surface of the carbon fiber composite damping material preform is controlled within 0.05 mm.

[0053] The embodiments of this application have been described above with reference to the accompanying drawings. Unless otherwise specified, the embodiments and features in the embodiments of this application can be combined with each other. This application is not limited to the specific embodiments described above. The specific embodiments described above are merely illustrative and not restrictive. Those skilled in the art can make many other forms under the guidance of this application without departing from the spirit of this application and the scope of protection of this invention, and all of these forms are within the protection scope of this application.

Claims

1. A layered precision molding process for 3D printing sand molds of complex thin-walled parts, characterized in that, include: Step 101, Cavity Division: Based on the three-dimensional geometry of the complex thin-walled part to be cast, the cavity area of ​​the sand mold is determined, and the cavity area of ​​the sand mold is divided into an outer structural layer and an interface buffer layer. Step 102, gradient curing: The original sand is laid out using a sand mold 3D inkjet printing device. When spraying the outer structural layer, a second spray droplet is output to completely cure the resin binder in the original sand. When spraying the interface buffer layer, a first spray droplet is output. The first spray droplet is lower than the spray droplet threshold for complete resin curing, so that a loose structure containing 30% to 40% by mass of uncured free original sand and uncrosslinked resin components is formed in the interface buffer layer. Step 103, Precast Placement: While laying the original sand for the interface buffer layer in 3D printing, simultaneously lay the precast carbon fiber composite damping material in situ between layers or pre-embed carbon fiber material in layers, and complete the sand mold assembly. Step 104, Negative Pressure Vibration Filling: In a vacuum negative pressure environment of -0.05MPa to -0.06MPa, molten metal is injected into the cavity area of ​​the sand mold, and pulse excitation of the first frequency band of 10Hz to 50Hz is applied. Simultaneously, the acceleration sensor on the periphery of the sand mold is monitored to obtain the vibration acceleration signal. When the low-frequency response amplitude of the monitored vibration acceleration signal drops to 50% of the initial stable value, the frequency is switched to the second frequency band of 300Hz to 1000Hz for high-frequency micro-vibration. The gas phase component generated by the thermal pyrolysis of the uncrosslinked resin component in the interface buffer layer is used to construct a dynamic gas film on the surface of the carbon fiber composite damping material preform. The interparticle frictional slip generated by the uncured free original sand dissipates the strain energy, so that the metal flow front in the solid-liquid two-phase region can penetrate into the carbon fiber composite damping material preform under the action of acceleration.

2. The layered precision molding process for 3D printing sand molds of complex thin-walled parts according to claim 1, characterized in that, Step 102 includes: controlling the first spray droplet amount to be 60% to 80% of the second spray droplet amount, so that the original sand in the interface buffer layer forms a discontinuous network skeleton composed of cured resin, and the network skeleton provides a spatial constraint network for the uncured free original sand.

3. The layered precision molding process for 3D printing sand molds of complex thin-walled parts according to claim 1, characterized in that, The thickness of the interface buffer layer varies spatially with the surface curvature of the sand mold cavity region, and the thickness of the interface buffer layer is greater than that of the flat parts of the sand mold cavity region at the abrupt change in curvature.

4. The layered precision molding process for 3D printing sand molds of complex thin-walled parts according to claim 1, characterized in that, In step 104, the gaseous components generated by vacuum negative pressure induced pyrolysis permeate into the metal flow front, maintaining a dynamic gas film on the surface of the carbon fiber composite damping material preform.

5. The layered precision molding process for 3D printing sand molds of complex thin-walled parts according to claim 1, characterized in that, Step 104 also includes: Step 1041: Extracting the high-frequency component from the vibration acceleration signal; Step 1042: Determining the contact area between the molten metal and the carbon fiber composite damping material preform based on the amplitude change of the high-frequency component.

6. The layered precision molding process for 3D printing sand molds of complex thin-walled parts according to claim 1, characterized in that, In step 104, in the solid-liquid coexistence zone of the molten metal, the shear thinning effect of the uncured free sand in the interface buffer layer is enhanced by increasing the excitation frequency of the second frequency band high-frequency micro-vibration.

7. The layered precision molding process for 3D printing sand molds of complex thin-walled parts according to claim 1, characterized in that, The coated sand includes raw sand and thermosetting resin with a mass fraction of 1.8% to 2.5%. The local curing effect of the thermosetting resin under the first spray droplet volume forms microporous venting channels in the interface buffer layer.

8. The layered precision molding process for 3D printing sand molds of complex thin-walled parts according to claim 1, characterized in that, Before step 103, the carbon fiber composite damping material preform is preheated at a temperature of 150°C to 180°C.

9. The layered precision molding process for 3D printing sand molds of complex thin-walled parts according to claim 1, characterized in that, After the molten metal solidifies, the temperature difference between the interface buffer layer and the outer structural layer is stabilized within a preset temperature difference range by adjusting the circulation rate of the cooling medium.

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