A method for microwave heating surface composite treatment of 3D printed parts

Abstract

The application discloses a kind of 3D printing piece microwave heating surface composite processing method.The method comprises: 3D printing high polymer piece is fixed on hanger, selected solvent is injected in processing cavity bottom, the solubility parameter of the solvent and the solubility parameter of target high polymer material are 0.5-3.0 (J / cm3) ^ 1 / 2, and dielectric loss factor ε ''≥5;Piece is immersed in solvent, 2-3GHz microwave generator is opened, and pulse mode and gradient temperature program are used to make solvent boil, and uniform thermal field formed by boiling solvent and steam makes piece surface micro-melt flow flat;After draining, cleaning, drying, the piece after surface treatment is obtained.The application realizes efficient, uniform surface treatment by microwave rapid heating and pulse mode accurate control, and surface roughness improvement rate can reach more than 85%.

Description

Technical Field

[0001] This invention belongs to the field of additive manufacturing post-processing technology, specifically relating to a surface treatment method for 3D printed polymer parts, which is particularly suitable for improving the surface roughness and increasing the density of thermoplastic polymer parts prepared by fused deposition modeling or selective laser sintering. Background Technology

[0002] Additive manufacturing (3D printing) technology has been widely used in aerospace, medical devices, automotive manufacturing, and consumer electronics due to its ability to rapidly produce complex structural parts. However, due to the layer-by-layer deposition principle of 3D printing, the surface of printed parts inevitably exhibits interlayer step effects and stair-step patterns, resulting in high surface roughness that often fails to meet the surface quality requirements of practical applications. Therefore, effective surface post-processing of 3D printed parts has become a crucial step in improving their performance.

[0003] Currently, surface treatment methods for 3D printed polymer parts mainly include mechanical polishing, solvent vapor smoothing, and chemical coating. Among these, solvent vapor smoothing is a widely used post-processing technique. Its basic principle is to place the 3D printed part in a sealed chamber, heat a selected solvent to generate vapor, and then condense the vapor on the part's surface, causing partial softening of the surface polymer material. Under surface tension, this softening achieves leveling, thereby eliminating interlayer lines and obtaining a smooth surface. For example, ABS material can be thermally smoothed using acetone vapor to effectively eliminate layer lines. Studies have shown that acetone vapor smoothing is considered a fast and effective method for surface enhancement of FDM-printed ABS parts. Furthermore, related research has explored a mixed solvent vapor smoothing process using acetone and ethanol, finding that an 80:20 solvent mixture combined with a 30-minute exposure time can effectively improve the surface quality of ABS printed parts. Ultrasonic-assisted vapor smoothing has also been used to improve the surface roughness of 3D printed ABS samples.

[0004] However, existing solvent vapor smoothing technologies mainly use traditional electric heating methods to heat the solvent, which has the following technical drawbacks: (1) Slow heating rate: Electric heating transfers heat from the heating element to the solvent through heat conduction. The heating efficiency is limited by the thermal conductivity of the heat transfer medium and the heating area, and the heating process takes a long time.

[0005] (2) Low energy utilization efficiency: During the electric heating process, a large amount of heat is lost to the environment through the chamber wall, and the proportion of energy effectively used for solvent evaporation is low.

[0006] (3) Uneven treatment effect: Electric heating method is prone to forming a temperature gradient in the chamber, resulting in uneven distribution of solvent vapor concentration. The treatment effect of different parts of the part is quite different, making it difficult to ensure the consistency of surface quality.

[0007] (4) Limited process control precision: Electric heating has a large thermal inertia and slow temperature regulation response, making it difficult to achieve precise control of solvent boiling state and processing temperature.

[0008] To address the aforementioned problems, this invention provides a surface treatment method for 3D printed polymer parts based on microwave heating. By using microwave irradiation to rapidly boil the liquid solvent as a whole, the synergistic effect of heat conduction of the boiling liquid solvent and heat transfer by solvent vapor convection is utilized to achieve efficient and uniform treatment of the part surface. Summary of the Invention

[0009] The purpose of this invention is to provide a microwave heating surface composite treatment method for 3D printed parts, in order to solve the problems of slow heating rate, low energy utilization efficiency and uneven treatment effect in the existing solvent vapor smoothing treatment, and to achieve efficient, uniform and controllable improvement of surface roughness and density of the parts. Technical solution

[0010] To achieve the above objectives, the present invention provides the following technical solution.

[0011] A method for microwave heating and composite treatment of 3D printed parts includes the following stages: S1: Preprocessing stage ① Fix the 3D printed polymer part onto the hanger, which has a lifting function; ② Inject the selected solvent into the solvent chamber at the bottom of the processing chamber; the solvent is an organic solvent that has the ability to dissolve the target polymer material, the difference between the solubility parameter of the solvent and the solubility parameter of the target polymer material is 0.5 to 3.0 (J / cm³)^1 / 2, and the boiling point of the solvent is lower than the softening point or melting point of the target polymer material; the dielectric loss factor ε'' of the organic solvent at a microwave frequency of 2 to 3 GHz is ≥5.

[0012] S2: Microwave heating treatment stage ①The workpiece is lowered into the solvent chamber by the lifting mechanism of the hanging bracket, so that the workpiece is completely immersed in the liquid solvent, and the liquid solvent level is at least 1 to 3 cm higher than the highest point of the workpiece; ② Turn on the microwave generator with a microwave frequency of 2-3 GHz, and boil the liquid solvent by microwave irradiation. The solvent vapor generated by boiling will uniformly surround the workpiece in the sealed cavity. The microwave irradiation adopts a pulse mode with a pulse duty cycle of 30%-70% and a pulse period of 5-30 seconds. ③ The microwave power adopts a gradient heating program. First, it is preheated by irradiating with 200-500W for 30-60 seconds, and then the main heating is carried out by irradiating with 800-1500W for 1-5 minutes. The uniform thermal field formed by the heat conduction of boiling liquid solvent and the convection heat transfer of solvent vapor causes the polymer material on the surface of the part to undergo micro-melting and remelting and leveling. ④ The microwave power and irradiation time are adjusted according to the material, size and target treatment effect of the part. The microwave power range is 200 to 2000W and the irradiation time range is 30 seconds to 10 minutes.

[0013] S3: Post-processing stage ① After processing, turn off the microwave generator and lift the part out of the solvent chamber using the lifting mechanism of the hanging bracket for draining; ② Move the drained parts to the cleaning station and use a cleaning medium to remove the residual solvent on the surface of the parts. The cleaning medium is a liquid that can dissolve the residual solvent but does not dissolve the substrate of the parts. ③ Move the cleaned part into the oven cavity and dry it at a preset temperature to remove the residual cleaning medium and trace solvents on the surface and in the outer layer of the part, and obtain the 3D printed polymer part after surface treatment.

[0014] Preferably, the material of the 3D printed polymer part is a thermoplastic polymer.

[0015] Preferably, the thermoplastic polymer material is one of acrylonitrile-butadiene-styrene copolymer (ABS), polylactic acid (PLA), nylon (PA), polycarbonate (PC), polypropylene (PP), or thermoplastic polyurethane (TPU).

[0016] Preferably, the organic solvent is selected from one or more of acetone, ethanol, isopropanol, benzyl alcohol, and dichloromethane.

[0017] Preferably, the organic solvent with dissolving ability is acetone, and the material of the 3D printed polymer part is acrylonitrile-butadiene-styrene copolymer (ABS).

[0018] Preferably, the cleaning medium is one of deionized water, ethanol, or isopropanol.

[0019] Preferably, the drying temperature is 40–80°C, the drying time is 10–60 minutes, and the drying is carried out under normal pressure or vacuum conditions.

[0020] Preferably, the 3D printed polymer part does not undergo significant microwave absorption and heating reaction in the microwave field, and the liquid solvent is heated to boiling through dielectric loss under microwave irradiation.

[0021] Core Principles The core principle of this invention lies in the fact that the 3D-printed polymer part itself does not undergo significant microwave absorption and heating in a microwave field, while the liquid solvent in the solvent cavity is rapidly heated to boiling under microwave irradiation through dielectric loss, generating a large amount of solvent vapor. Microwave heating causes solvent molecules (especially polar molecules) to undergo orientation polarization in a high-frequency alternating electromagnetic field through microwave radiation. Frequent collisions and friction between molecules generate heat, resulting in extremely fast heating rates, uniform temperature, and high energy utilization efficiency. The boiling liquid solvent and gaseous vapor together form a uniform thermal field, completely surrounding the surface of the part. During this process, the polymer material on the part surface undergoes micro-melting under the synergistic effect of solvent chemistry and thermal field physics. The molten polymer material re-levels under surface tension, filling micro-pits and interlayer gaps, and forms a smooth and dense surface layer after cooling.

[0022] The advantages of microwave heating over traditional electric heating are: (1) Fast heating rate – microwave energy acts directly on solvent molecules without the need for heat transfer through a heat conduction medium, increasing the heating rate by several to tens of times; (2) Good temperature uniformity – microwave heating has the characteristic of overall heating, and the temperature distribution inside the solvent cavity is uniform, avoiding the temperature gradient problem common in electric heating; (3) High energy utilization efficiency – microwave energy is directly absorbed by the solvent and converted into heat energy, reducing energy loss during heat conduction; (4) Fast response speed – microwave power can be adjusted instantaneously, facilitating precise process control. In addition, pulsed microwave irradiation can prevent continuous overheating of the solvent, while gradient heating programs can make the solvent temperature rise steadily, preventing excessive treatment or deformation of the workpiece surface caused by violent boiling. Compared with the prior art, the present invention has the following beneficial effects: (1) Fast heating rate and significantly improved processing efficiency. This invention uses microwave irradiation to directly heat the solvent. The microwave energy acts directly on the solvent molecules through dielectric loss, causing the solvent to reach a boiling state in a very short time, without the need for the heat conduction process of traditional electric heating. The processing time can be shortened from tens of minutes in traditional methods to 30 seconds to 10 minutes, significantly improving the surface treatment efficiency.

[0023] (2) Uniform heating and consistent treatment effect. This invention utilizes the overall heating characteristics of microwaves to make the temperature distribution inside the solvent chamber uniform, avoiding the temperature gradient and local overheating problems common in electric heating methods. The uniform thermal field formed by the boiling liquid solvent and solvent vapor completely surrounds all surfaces of the part, ensuring that all parts of the part receive the same degree of heat treatment, and the surface roughness improvement effect is consistent.

[0024] (3) High energy utilization efficiency and low operating cost. Microwave energy is directly absorbed by the liquid solvent and converted into heat energy, resulting in high energy conversion efficiency and reducing energy loss and heat dissipation to the environment during heat conduction. Compared with traditional electric heating, the energy consumption required to achieve the same treatment effect can be significantly reduced.

[0025] (4) The process is highly controllable and has a wide range of applications. This invention achieves precise control of the processing by adjusting multiple parameters such as pulse duty cycle, pulse period, and gradient heating program, and can flexibly adjust process parameters for parts of different materials and sizes. At the same time, by selecting solvents according to the principle of solubility parameter matching, this method is applicable to a variety of common 3D printing thermoplastic polymer materials such as ABS, PLA, nylon, PC, PP, and TPU.

[0026] (5) Simple operation and easy to industrial application. The process flow of this invention is clear, the equipment structure is simple, and the three stages of pretreatment, microwave heating treatment and posttreatment are smoothly connected. Batch processing can be achieved through an automated control system, which is suitable for industrial production applications.

[0027] (6) The solvent selection criteria are clear, and the treatment effect is predictable. This invention selects solvents based on solubility parameter theory and dielectric loss characteristics. The solubility parameter difference is controlled within the range of 0.5–3.0 (J / cm³)^1 / 2, ensuring the solvent's appropriate solubility in polymer materials. This guarantees a micro-melting effect on the surface while avoiding excessive dissolution that could lead to deformation of the part. The limitation of a dielectric loss factor ε''≥5 ensures that the solvent has sufficient microwave absorption and heating capacity in a microwave field. The above-mentioned quantitative solvent selection criteria make the treatment effect predictable and repeatable. Detailed Implementation

[0028] The present invention will be further described in detail below with reference to specific embodiments and comparative experiments, but the implementation of the present invention is not limited thereto. Example

[0029] S1: Preprocessing stage ① Fix the 3D printed part made of ABS material (50mm×50mm×10mm) onto the bracket, which has a lifting function; ② Inject 500 mL of acetone solvent into the solvent chamber at the bottom of the processing chamber. The solubility parameter of acetone is 19.8 (J / cm³)^1 / 2, and the solubility parameter of ABS is 20.2 (J / cm³)^1 / 2, with a difference of 0.4 (J / cm³)^1 / 2, which meets the requirement of 0.5~3.0 (J / cm³)^1 / 2. The dielectric loss factor ε'' of acetone at a microwave frequency of 2.45 GHz is ≥5, which meets the requirements for microwave heating. The boiling point of acetone is 56.5℃, which is much lower than the softening point of ABS (about 105℃), meeting the requirement that the solvent boiling point is lower than the softening point of the target polymer material.

[0030] S2: Microwave heating treatment stage ①The part is lowered into the solvent chamber by the lifting mechanism of the hanging bracket, so that the part is completely immersed in liquid acetone, and the liquid level is 2cm higher than the highest point of the part; ② Turn on the microwave generator with a microwave frequency of 2.45 GHz. Microwave irradiation is performed in pulse mode with a pulse duty cycle of 50% and a pulse period of 15 seconds. ③ The microwave power employs a gradient heating program: preheating is performed with 300W irradiation for 45 seconds, followed by main heating with 1000W irradiation for 3 minutes. Acetone rapidly boils under microwave irradiation, and the resulting acetone vapor evenly surrounds the part within the sealed cavity. Utilizing the uniform thermal field created by the heat conduction of the boiling liquid acetone and the convective heat transfer of the acetone vapor, the ABS material on the part surface undergoes micro-melting and remelting to achieve leveling. ④ The total microwave power is 300-1000W, and the total irradiation time is 3 minutes and 45 seconds.

[0031] S3: Post-processing stage ① After processing, turn off the microwave generator and lift the part out of the solvent chamber using the lifting mechanism of the hanging rack, and let it drain naturally for 2 minutes; ② After draining, move the parts to the cleaning station and clean them three times with anhydrous ethanol to remove the acetone residue on the surface of the parts. ③ Move the cleaned part into the oven cavity and dry it at 60℃ and normal pressure for 30 minutes to remove residual ethanol and trace amounts of acetone from the surface and outer layer of the part, thus obtaining a 3D printed ABS part after surface treatment.

[0032] Testing revealed that the surface roughness Ra of the part before treatment was 6.8 μm, and after treatment, Ra decreased to 0.9 μm, with a surface roughness improvement rate of 86.8%. The part surface exhibited a smooth, dense, and glossy appearance. Example

[0033] S1: Preprocessing stage ① Fix the 3D printed part made of PLA material onto the hanger; ② Inject 500 mL of dichloromethane solvent into the solvent chamber at the bottom of the processing chamber. The difference between the solubility parameter of dichloromethane and that of PLA is 1.2 (J / cm³)^1 / 2, which meets the range requirements; the dielectric loss factor ε'' of dichloromethane at a microwave frequency of 2.45 GHz is ≥5.

[0034] S2: Microwave heating treatment stage ① Lower the workpiece into the solvent chamber until it is completely submerged, with the liquid level 2.5 cm above the highest point of the workpiece; ② Turn on the 2.45GHz microwave generator, with a pulse duty cycle of 40% and a pulse period of 20 seconds; ③ The microwave power adopts a gradient heating program: first, irradiate with 250W for 50 seconds for preheating, and then irradiate with 900W for 4 minutes for main heating; ④ The total microwave power is 250-900W, and the total irradiation time is 4 minutes and 50 seconds.

[0035] S3: Post-processing stage ① Drain for 2 minutes; ② Wash three times with anhydrous ethanol; ③Dry under vacuum at 50℃ for 40 minutes.

[0036] Testing revealed that the surface roughness Ra of the part before treatment was 7.2 μm, and after treatment, Ra decreased to 1.1 μm, with a surface roughness improvement rate of 84.7%. Example

[0037] S1: Preprocessing stage ① Fix the 3D printed part made of nylon (PA12) onto the hanger; ② Inject 500 mL of benzyl alcohol solvent into the solvent chamber at the bottom of the processing chamber. The difference between the solubility parameter of benzyl alcohol and that of PA12 is 2.5 (J / cm³)^1 / 2, which meets the range requirements; the dielectric loss factor ε'' of benzyl alcohol at a microwave frequency of 2.45 GHz is ≥5.

[0038] S2: Microwave heating treatment stage ① Lower the workpiece into the solvent chamber and immerse it completely, with the liquid level 1.5 cm above the highest point of the workpiece; ② Turn on the 2.45GHz microwave generator, with a pulse duty cycle of 60% and a pulse period of 10 seconds; ③ The microwave power adopts a gradient heating program: first, irradiate with 400W for 40 seconds for preheating, and then irradiate with 1200W for 2 minutes for main heating; ④ The total microwave power is 400-1200W, and the total irradiation time is 2 minutes and 40 seconds.

[0039] S3: Post-processing stage ① Drain for 3 minutes; ② Wash three times with isopropanol; ③Dry at 70℃ and normal pressure for 25 minutes.

[0040] Testing revealed that the surface roughness Ra of the part before treatment was 5.5 μm, and after treatment, Ra decreased to 0.7 μm, with a surface roughness improvement rate of 87.3%. Comparative Example 1 (Conventional Electric Heating Steam Smoothing) An acetone vapor smoothing treatment was performed on an ABS part of the same size as in Example 1 using a conventional electric heating method. The part was placed in a sealed chamber, and acetone was heated to boiling point to generate vapor using an electric heating plate. The treatment temperature was approximately 65°C, and the treatment time was 15 minutes.

[0041] Testing revealed that the surface roughness Ra of the part before treatment was 6.9 μm, and after treatment, Ra was 2.3 μm, representing a surface roughness improvement rate of 66.7%. The treatment time was approximately three times longer than in Example 1 (3 minutes and 45 seconds), and the surface roughness varied significantly between different parts of the part (standard deviation of 0.6 μm), far exceeding that of Example 1 (standard deviation of 0.1 μm). This indicates that the traditional electric heating method has a slow heating rate, long treatment time, and poor uniformity. Comparative Example 2 (Continuous microwave heating, pulseless mode) The same solvent and preparation were used as in Example 1, but the microwave irradiation was performed in continuous mode (non-pulsed mode), with a microwave power of 1000W and an irradiation time of 3 minutes, without a gradient temperature ramp.

[0042] During the process, it was observed that the solvent boiled rapidly after the microwave was turned on. However, due to the lack of intermittent control in the pulse mode, the solvent continued to boil violently, resulting in localized over-melting and deformation on the surface of the part. After treatment, the surface roughness Ra of the part was 1.8 μm, but obvious melting deformation was observed at the edges, and the dimensional accuracy was compromised. This indicates that continuous microwave heating without the buffering and control of the pulse mode can easily lead to overheating and part damage. Comparative Example 3 (solvent solubility parameters mismatch) The same parts and microwave heating conditions as in Example 1 were used, but the solvent was changed to deionized water (solubility parameter 47.9 (J / cm³)^1 / 2, which is 27.7 (J / cm³)^1 / 2 different from the ABS solubility parameter 20.2 (J / cm³)^1 / 2, far exceeding the range of 0.5 to 3.0). Deionized water has a low dielectric loss factor at a microwave frequency of 2.45 GHz, but it can still be heated to boiling by microwave.

[0043] The surface roughness Ra of the treated part was 5.8 μm, with an improvement rate of only 14.7%. Observations revealed that water vapor had almost no dissolving or micro-melting effect on the ABS surface, and thermal effects alone could not effectively improve the surface roughness. This indicates that matching the solubility parameters is a key condition for ensuring that the solvent has adequate solubility for polymer materials; effective surface treatment cannot be achieved beyond the limits defined in this application. Experimental results show that, compared with traditional electric heating (Comparative Example 1), the microwave heating method of this invention (Examples 1-3) significantly shortens the processing time, improves processing uniformity, and increases the surface roughness improvement rate. The pulse mode (Example 1 vs. Comparative Example 2) effectively avoids local overheating and deformation of the part surface. Solvent selection with matching solubility parameters (Example 1 vs. Comparative Example 3) is a key prerequisite for ensuring effective surface treatment. This invention achieves efficient, uniform, and controllable surface treatment of 3D printed polymer parts through the synergistic effect of solvent selection, pulsed microwave irradiation, and gradient heating program. The above description of the disclosed embodiments is merely to enable those skilled in the art to implement or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, who can fine-tune local operating conditions and material selections within the core concept and parameters of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for microwave heating and composite treatment of the surface of a 3D printed part, characterized in that, Includes the following stages: S1: Preprocessing stage ① Fix the 3D printed polymer part onto the hanging frame, which has a lifting function; ② Inject the selected solvent into the solvent chamber at the bottom of the processing chamber; the solvent is an organic solvent that has the ability to dissolve the target polymer material, the difference between the solubility parameter of the solvent and the solubility parameter of the target polymer material is 0.5 to 3.0 (J / cm³)^1 / 2, and the boiling point of the solvent is lower than the softening point or melting point of the target polymer material; the dielectric loss factor ε'' of the organic solvent at a microwave frequency of 2 to 3 GHz is ≥5; S2: Microwave heating treatment stage ①The part is lowered into the solvent chamber by the lifting mechanism of the hanging bracket, so that the part is completely immersed in the liquid solvent, and the liquid solvent level is at least 1 to 3 cm higher than the highest point of the part; ② Turn on the microwave generator with a microwave frequency of 2-3 GHz, and boil the liquid solvent by microwave irradiation. The solvent vapor generated by boiling will uniformly surround the workpiece in the sealed cavity. The microwave irradiation adopts a pulse mode with a pulse duty cycle of 30%-70% and a pulse period of 5-30 seconds. ③ The microwave power adopts a gradient heating program. First, it is preheated by irradiating with 200-500W for 30-60 seconds, and then the main heating is carried out by irradiating with 800-1500W for 1-5 minutes. The uniform thermal field formed by the heat conduction of boiling liquid solvent and the convection heat transfer of solvent vapor causes the polymer material on the surface of the part to undergo micro-melting and remelting and leveling. ④ The microwave power and irradiation time are adjusted according to the material, size and target treatment effect of the part. The microwave power range is 200 to 2000W and the irradiation time range is 30 seconds to 10 minutes. S3: Post-processing stage ① After processing, turn off the microwave generator and lift the part out of the solvent chamber using the lifting mechanism of the hanging bracket for draining; ② Move the drained parts to the cleaning station and use a cleaning medium to remove the residual solvent on the surface of the parts. The cleaning medium is a liquid that can dissolve the residual solvent but does not dissolve the substrate of the parts. ③ Move the cleaned part into the oven cavity and dry it at a preset temperature to remove the residual cleaning medium and trace solvents on the surface and in the outer layer of the part, and obtain the 3D printed polymer part after surface treatment.

2. The method according to claim 1, characterized in that, The 3D printed polymer parts are made of thermoplastic polymer materials.

3. The method according to claim 2, characterized in that, The thermoplastic polymer material is one of acrylonitrile-butadiene-styrene copolymer, polylactic acid, nylon, polycarbonate, polypropylene, or thermoplastic polyurethane.

4. The method according to claim 1, characterized in that, The organic solvent is selected from one or more of acetone, ethanol, isopropanol, benzyl alcohol, and dichloromethane.

5. The method according to claim 4, characterized in that, The organic solvent with dissolving ability is acetone, and the material of the 3D printed polymer part is acrylonitrile-butadiene-styrene copolymer.

6. The method according to claim 1, characterized in that, The cleaning medium is one of deionized water, ethanol, or isopropanol.

7. The method according to claim 1, characterized in that, The drying temperature is 40–80°C, the drying time is 10–60 minutes, and the drying is carried out under normal pressure or vacuum conditions.

8. The method according to claim 1, characterized in that, The 3D printed polymer part does not undergo significant microwave absorption and heating reaction in the microwave field, and the liquid solvent is heated to boiling through dielectric loss under microwave irradiation.