Method for controlling curing shrinkage deformation of 3D printing green body

Abstract

A 3D printing green body curing shrinkage deformation control method comprises the following steps that forming is conducted, specifically, powder is laid layer by layer through an adhesive spraying 3D printing technology, and an adhesive is selectively sprayed through a slicing pattern of a part till a 3D printing model is completed; cleaning is conducted, specifically, the printed model is subjected to powder cleaning, and a 3D printing green body is obtained; and curing: putting the green body into a curing furnace, firstly carrying out heating and heat preservation, then carrying out rapid cooling, and then carrying out tempering curing. A green body which is subjected to bonding jet printing is firstly heated and then rapidly cooled in the thermocuring process, the temperature of the material is rapidly reduced through rapid cooling at a certain temperature, and thermal strain caused by temperature change is reduced; and then tempering and curing are carried out. And the continuity of the curing reaction is kept, the curing process is completed at low temperature, and the bonding temperature between the binder and the powder can be reduced, so that the shrinkage deformation problem caused by mismatching of thermal expansion coefficients is reduced.

Description

Technical Field

[0001] The present invention relates to the field of additive manufacturing, and in particular to a method for reducing thermal curing shrinkage deformation of a 3D printed green body. Background Art

[0002] Binder jet 3D printing is an advanced additive manufacturing technology that builds three-dimensional objects layer by layer by selectively spraying a binder onto powdered materials. This technology has significant advantages in high precision and manufacturing complex geometries and is applicable to a variety of materials. Due to its fast printing speed and excellent material utilization, binder jet 3D printing is particularly popular in mass production and rapid prototyping.

[0003] In the process of binder jetting 3D printing green body, thermosetting polymers are usually used as binders. However, in the subsequent heat curing stage, due to the difference in thermal expansion coefficients between the powder and the binder, the green body may expand or shrink locally. In addition, the heat curing process may also cause uneven heating, resulting in a temperature gradient inside the green body. That is, there are differences in the rate of temperature change in different regions. These factors may cause shrinkage deformation of the green body after heat curing, thereby seriously affecting the mechanical properties, structural integrity and reliability of the molded parts. Therefore, it is urgent to propose an effective method to solve the problem of shrinkage deformation of binder jetting 3D printing green body during heat curing. Summary of the invention

[0004] Based on this, the present invention proposes a method for controlling the shrinkage deformation of 3D printed green body during curing. By introducing a method of rapid cooling and tempering curing during the thermal curing process of the printed green body, the temperature of the material inside the green body is quickly reduced, the thermal strain caused by temperature change is reduced, and the shrinkage deformation of the green body during the thermal curing process is controlled.

[0005] A method for controlling the solidification shrinkage deformation of a 3D printed green body, comprising the following steps:

[0006] Molding: Use the binder jetting 3D printing process to apply powder layer by layer and selectively spray binder through the slice pattern of the part until the 3D printed model is completed;

[0007] Cleaning: Clean the powder of the printed model to obtain the 3D printed green body;

[0008] Curing: Place the green body into a curing furnace to first heat and keep it warm, then cool it rapidly, and then temper and cure it.

[0009] The green body printed by binder jetting is first heated up and then cooled rapidly during the thermal curing process. Rapid cooling at a certain temperature allows the material temperature to drop rapidly, reducing the thermal strain caused by temperature changes; followed by tempering and curing. This not only maintains the continuity of the curing reaction, but also completes the curing process at a low temperature, which can also reduce the bonding temperature between the binder and the powder, thereby reducing the shrinkage deformation problem caused by the mismatch of thermal expansion coefficients.

[0010] In one embodiment, in the solidification step, heating and holding and rapid cooling are performed at least once.

[0011] According to the precision requirement of green body size shrinkage, in the solidification step, the heating and heat preservation and rapid cooling steps or processes can be performed once or cyclically for multiple times.

[0012] In one embodiment, the process of heating and holding in the curing step is as follows:

[0013] The green body is placed in a curing furnace and heated from room temperature to 100-250°C, and kept warm for 20-60 minutes.

[0014] In one embodiment, the rapid cooling process in the solidification step is as follows:

[0015] The green body after heating and heat preservation is moved from the curing furnace to a refrigerator and cooled to room temperature.

[0016] In one embodiment, the average cooling rate of the rapid cooling is 5-80° C. / min.

[0017] In one embodiment, the temperature range of the freezer is -80 to 0°C.

[0018] In one embodiment, the process of tempering curing in the curing step is as follows:

[0019] The rapidly cooled green body is put back into the curing furnace and cured at a temperature of 100 to 250° C. for 120 to 360 minutes.

[0020] In one embodiment, the binder used for binder jet printing is one of furan resin, phenolic resin, polyvinyl alcohol, polyvinyl pyrrolidone, and polyacrylic acid.

[0021] In one embodiment, the powder used for binder jet printing is one of silicon carbide, graphite, and aluminum oxide.

[0022] In one embodiment, in the cleaning step, the 3D printed model is first pre-cured and then the powder is cleaned.

[0023] After printing, the powder bed work box and the formed model are moved to the blast curing furnace for drying and pre-curing. Whether to perform drying and pre-curing depends on the selected binder system. After pre-curing, the surface and interior of the model are cleaned to obtain a green body.

[0024] In one embodiment, the pre-curing temperature is 80-240° C., and the pre-curing time is 120-720 min.

[0025] By introducing an optimized process of rapid cooling of the gel point during the green body curing process, the material temperature is quickly reduced, reducing the thermal strain caused by temperature changes. The uniformity of dimensional shrinkage of the binder jet 3D printed products after thermal curing is improved, and the problem of product shrinkage and deformation is alleviated, so that it meets the needs of production and application. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 Schematic diagram of the process flow for this application DETAILED DESCRIPTION

[0027] In order to facilitate the understanding of the present invention, a plurality of embodiments will be given below to describe the present invention in a more comprehensive manner. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the disclosure of the present invention more thoroughly and comprehensively understood. The binder jet 3D printing (3DP or BJ) herein works on the principle that a powder spreader lays a layer of powder, and then the print head sprays the binder at the position where the molding is required according to the slice pattern of the three-dimensional model, and prints layer by layer to finally form a three-dimensional printed blank. The uncured green body in the table herein refers to the green body after the 3D printing is completed and the powder is cleared. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those generally understood by technicians in the technical field of the present invention. The terms used in the specification of the present invention herein are only for the purpose of describing specific embodiments and are not intended to limit the present invention. The term "and / or" used herein includes any and all combinations of one or more related listed items.

[0028] A method for controlling the solidification shrinkage deformation of a 3D printed green body, comprising the following steps:

[0029] Molding: Use the binder jetting 3D printing process to apply powder layer by layer and selectively spray binder through the slice pattern of the part until the 3D printed model is completed;

[0030] Cleaning: Clean the powder of the printed model to obtain the 3D printed green body;

[0031] Curing: Place the green body into a curing furnace to first heat and keep it warm, then cool it rapidly, and then temper and cure it.

[0032] The green body printed by binder jetting is first heated up and then cooled rapidly during the thermal curing process. Rapid cooling at a certain temperature allows the material temperature to drop rapidly, reducing the thermal strain and residual stress caused by temperature changes; followed by tempering and curing. Maintaining the continuity of the curing reaction not only improves the strength of the green body, but also completes the curing process at a low temperature, which can also reduce the bonding temperature between the binder and the powder, thereby reducing the shrinkage deformation problem caused by the mismatch of thermal expansion coefficients.

[0033] The method for controlling the solidification shrinkage deformation of a 3D printed green body is described below in conjunction with a specific embodiment. In order to further illustrate the advancement and practical effectiveness of the technical solution of the present application, a specific embodiment is now given to further understand the concept of the method for controlling the solidification shrinkage deformation of a 3D printed green body.

[0034] Embodiment 1

[0035] A method for controlling the solidification shrinkage deformation of a 3D printed green body, comprising the following steps:

[0036] Molding: Use 3D drawing software to draw a barrel-shaped model. The barrel-shaped model has an outer diameter of 94mm, an inner diameter of 88mm, a height of 120mm, and a bottom thickness of 20mm; use slicing software to slice the 3D model and then import it into the printer system.

[0037] Then the graphite powder is passed into the powder spreader of the 3D printer for binder jetting 3D printing. The powder is spread layer by layer, and the binder is selectively sprayed on each layer of the preset slice map, and the cycle is repeated until the three-dimensional model is printed (green).

[0038] During the printing process, polyvinyl pyrrolidone was selected as the binder, the powder layer thickness was set to 90 microns, and the binder saturation was 60%.

[0039] Cleaning: After printing, move the powder bed work box to the blast curing furnace for drying and pre-curing. The pre-curing temperature is 100°C and the pre-curing time is 120 minutes. After pre-curing, transfer the printed powder bed to the powder cleaning station to remove excess powder on the surface and inside of the green body to obtain a complete green body, and measure the outer diameter of the top and middle of the green body.

[0040] Curing: Place the cleaned green body on a high temperature resistant plate covered with graphene paper, and then move it to a blast curing furnace for rapid cooling, tempering and curing. The specific steps are as follows:

[0041] Heating and heat preservation: The curing temperature of the green body placed in the curing oven is raised from room temperature to 160°C and maintained at this temperature for 20 minutes.

[0042] Rapid cooling: The green body with a certain temperature in the curing furnace is quickly moved to a walk-in freezer with a temperature of -20 degrees Celsius to cool to room temperature. In order to ensure the effect, the average cooling rate in this step is 30°C / min.

[0043] It should be noted that the above-mentioned steps of heating, heat preservation and rapid cooling can be repeated three times to meet the precision requirement of shrinkage of green body size.

[0044] Tempering and curing: The green body cooled to room temperature is put back into the curing furnace and cured at 160°C for 240 minutes to complete the remaining curing process. After curing, the green body is taken out and the outer diameter of the top and middle of the green body is measured.

[0045] It can be seen from the test data in Table 1 that the shrinkage size of the green body after curing in this embodiment is very small and the shrinkage consistency is good.

[0046] Table 1 Comparison table of dimensions of a blank before and after solidification in Example 1

[0047]

[0048] Note: Uncured green body refers to the green body after printing is completed and cleaned; cured green body refers to the green body after heating, insulation, rapid cooling and tempering.

[0049] Embodiment 2

[0050] A method for controlling the solidification shrinkage deformation of a 3D printed green body, comprising the following steps:

[0051] Molding: Use 3D drawing software to draw a barrel-shaped model. The barrel-shaped model has an outer diameter of 94mm, an inner diameter of 88mm, a height of 120mm, and a bottom thickness of 20mm; then use slicing software to slice the 3D model and pour it into the printer system.

[0052] Then, the aluminum oxide powder is passed into the powder spreader of the 3D printer for binder jetting 3D printing. The powder is spread layer by layer, and the binder is selectively sprayed on each layer of the preset slice map, and the cycle is repeated until the three-dimensional model is printed (green).

[0053] During the printing process, polyvinyl alcohol was selected as the binder, the powder layer thickness was set to 80 microns, and the binder saturation was 65%.

[0054] Cleaning: After printing, move the powder bed workbox to the powder cleaning station to remove excess powder on the surface and inside of the green body to obtain a complete green body, and measure the outer diameter of the top and middle of the green body.

[0055] Curing: Place the cleaned green body on a high temperature resistant plate covered with graphene paper, and then move it to a blast curing furnace for rapid cooling, tempering and curing. The specific steps are as follows:

[0056] Heating and heat preservation: The curing temperature of the green body placed in the curing oven is raised from room temperature to 120°C and maintained at this temperature for 35 minutes.

[0057] Rapid cooling: The green body with a certain temperature in the curing furnace is quickly moved to a walk-in freezer with a temperature of -15 degrees Celsius to cool to room temperature. In order to ensure the effect, the average cooling rate in this step is 25°C / min.

[0058] It should be noted that the above-mentioned steps of heating, heat preservation and rapid cooling can be repeated three times to meet the precision requirement of shrinkage of green body size.

[0059] Tempering and curing: The green body cooled to room temperature is put back into the curing furnace and cured at 120°C for 180 minutes to complete the remaining curing process. After curing, the green body is taken out and the outer diameter of the top and middle of the green body is measured.

[0060] It can be seen from the experimental data in Table 2 that the shrinkage size of the green body after curing in this embodiment is very small and the shrinkage consistency is good.

[0061] Table 2 Comparison table of dimensions of green body before and after solidification in Example 2

[0062]

[0063] It can be seen from the above embodiments that, by adopting the technical solution of the present application, the copper alloy parts have very high strength after sintering (without subsequent treatment), and the density of the parts is significantly improved.

[0064] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0065] The above-mentioned embodiments only express several implementation methods of the present invention, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. A method for controlling the solidification shrinkage deformation of a 3D printed green body, characterized in that: The following steps are involved: Molding: Use the binder jetting 3D printing process to apply powder layer by layer and selectively spray binder through the slice pattern of the part until the 3D printed model is completed; Cleaning: Clean the powder of the printed model to obtain the 3D printed green body; Curing: Place the green body into a curing furnace to first heat and keep it warm, then cool it rapidly, and then temper and cure it.

2. The method for controlling the solidification shrinkage deformation of a 3D printed green body according to claim 1, characterized in that: In the solidification step, the heating and heat preservation and rapid cooling steps are performed at least once.

3. The method for controlling the solidification shrinkage deformation of a 3D printed green body according to claim 1, characterized in that: In the curing step, the heating and insulation process is as follows: The green body is placed in a curing furnace and heated from room temperature to 100-250°C, and kept warm for 20-60 minutes.

4. The method for controlling the solidification shrinkage deformation of a 3D printed green body according to claim 1, characterized in that: During the curing step, the rapid cooling process is as follows: The green body after heating and heat preservation is moved from the curing furnace to a refrigerator and cooled to room temperature.

5. The method for controlling the solidification shrinkage deformation of a 3D printed green body according to claim 4, characterized in that: The average cooling rate of rapid cooling is 5 to 80°C / min.

6. The method for controlling the solidification shrinkage deformation of a 3D printed green body according to claim 4, characterized in that: The temperature range of the freezer is -80 to 0°C.

7. The method for controlling the solidification shrinkage deformation of a 3D printed green body according to claim 1, characterized in that: In the curing step, the tempering curing process is as follows: The rapidly cooled green body is put back into the curing furnace and cured at a temperature of 100 to 250° C. for 120 to 360 minutes.

8. The method for controlling the solidification shrinkage deformation of a 3D printed green body according to claim 1, characterized in that: The powder used for binder jet printing is one of silicon carbide, graphite, and alumina.

9. The method for controlling the solidification shrinkage deformation of a 3D printed green body according to claim 1, characterized in that: In the cleaning step, the 3D printed model is pre-cured and then the powder is removed.

10. The method for controlling the solidification shrinkage deformation of a 3D printed green body according to claim 9, characterized in that: The pre-curing temperature is 80-240°C, and the pre-curing time is 120-720 minutes.

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