Method for detecting mechanical properties of a binder forming blank for 3D printing

Abstract

The present application relates to the field of binder jetting 3D printing technology, and particularly relates to a method for detecting mechanical properties of a binder forming blank for 3D printing. The present application provides a method for detecting mechanical properties of a binder forming blank for 3D printing, which can accurately test the strength of different binder saturation degree blanks without a binder jetting (BJ) printer, quickly and accurately test the strength of different binder saturation degree blanks between different binders and powders, establish a binder printing performance database, reduce the binder development cycle, reduce the waste of printing materials in the process of testing the strength of the blank, and further correct the binder saturation degree based on the microstructure of the blank, so as to correct the difference between the dispersion characteristics of the binder in the blank under the mold forming condition and the dispersion characteristics of the binder in the powder after printing in the process of testing without a printer.

Description

Technical Field

[0001] This invention relates to the field of binder jetting 3D printing technology, and more specifically to a method for testing the mechanical properties of binder-molded preforms for 3D printing. Background Technology

[0002] Binder Jetting (BJ) 3D printing technology is an indirect 3D printing technology. Its forming process is mainly divided into two parts: the layer-by-layer forming part, which is mainly based on blank forming, and the post-processing part, which is mainly based on debinding and sintering. The main process flow of the blank forming part is as follows: (1) build a CAD model, (2) slice, (3) spread powder, (4) spray the binder to print the pattern. Repeat steps (3) and (4) until all layers are printed. Then, the blank is placed in an oven for curing treatment, the cured blank is de-powdered, and finally the blank is placed in a sintering furnace for debinding and sintering treatment to obtain a complete printed part. Due to its layer-by-layer forming process, BJ forming process has the advantages of short production cycle, ability to form complex shapes, and high material utilization.

[0003] Compared to other 3D printing methods, the biggest characteristic of the BJ (Brush-Joint) process is that it involves minimal energy input during the forming process. The strength of the BJ preform primarily comes from the bonding force between the powder particles after curing. This also means that BJ preforms are relatively weak, and lower preform strength translates to poor resistance to external disturbances (forces generated by movement during the preform forming process, external forces generated during powder removal, etc.). If the preform strength is low, it often becomes difficult to complete subsequent post-processing and is damaged. Therefore, preform strength is a crucial factor in evaluating the printability of the binder used in BJ printing.

[0004] Currently, to determine the strength of a cured binder preform, researchers typically print the binder directly, followed by curing, and then test the mechanical properties of the cured preform. While direct printing tests can objectively reflect the binder's printing performance, the printing process requires spreading the powder bed. To achieve good powder spreading, a large amount of molding powder is often needed to fill the powder cylinder. Powder recovery and the cleaning of the ink system after printing prolong the binder's testing cycle. After printing and curing, the preform needs to undergo powder removal. Differences in human operation during the powder removal process can lead to variations in the preform's mechanical properties. Furthermore, different printing saturations (the volume ratio of binder to powder voids) significantly affect the preform's mechanical properties.

[0005] Currently, existing methods for judging the strength of developed binder preforms after molding and curing only allow for one printing saturation level per printing process, resulting in a long data collection cycle for the mechanical properties of binder preforms at different saturations. Summary of the Invention

[0006] The purpose of this invention is to solve the problem of long collection cycles for mechanical property data of binder preforms at different saturations in the current BJ (Browser-based) industry. This invention provides a method for testing the mechanical properties of binder-molded preforms for 3D printing. This invention can obtain relatively accurate mechanical property data of preforms under different saturation conditions without the need for printing on a printer, using only a relatively small amount of powder, thus providing a reference for the development of binders for BJ.

[0007] The technical solution of this application is:

[0008] A method for testing the mechanical properties of binder-molded preforms for 3D printing includes the following steps:

[0009] A1: The mold used to make the binder blank is ultrasonically cleaned with alcohol and dried. The overall weight of the mold after drying is measured. Printing powder that has been ultrasonically cleaned and dried with alcohol is filled into the mold. The change in the overall weight of the mold after the powder is poured into the mold is the mass of the powder.

[0010] A2: The powder in the mold is compacted to obtain the height h0 of the compacted powder and the relative density ρ of the compacted powder.

[0011] A3: Select a saturation level S, and calculate the required adhesive mass m corresponding to that saturation level S. s ;

[0012] A4: Measure the mass as m s The adhesive is measured and slowly dripped into the surface of the compacted powder inside the mold in A3;

[0013] A5: After adding the binder in A4, slowly drip low-boiling-point solvent onto the powder surface inside the mold. Stop dripping the low-boiling-point solvent when it is about to submerge the compacted powder material, and let the mold stand after dripping the low-boiling-point solvent.

[0014] A6: After the mold in A5 has been left to stand, move the whole mold into the oven for curing. After curing, demold the blank.

[0015] A7: Scanning electron microscopy (SEM) tests were performed on random parts of the preform after A6 curing. The proportion of binder that provides mechanical properties to that that does not provide mechanical properties was statistically analyzed from the images obtained by SEM tests, and the proportion k of binder that provides mechanical properties to the total binder content was calculated.

[0016] A8: Based on the binder ratio k obtained in A7, correct the saturation S to the effective saturation S. i Effective saturation S i The corrected formula is as follows:

[0017] S i =Sk

[0018] Select multiple different effective saturation S i And A1 to A6 were repeated to obtain different effective saturation S. i The corresponding cured preform was prepared, and its mechanical properties were tested after curing.

[0019] Compared with the prior art, this application has the following advantages:

[0020] This invention provides a method for testing the mechanical properties of 3D printed preforms made with binders. It can accurately test the strength of preforms with different binder saturation levels without the need for a BJ printer. It can quickly and accurately test the strength of preforms with different saturation levels between different binders and powders, establish a binder printing performance database, reduce the binder development cycle, and reduce the waste of printing materials during preform strength testing.

[0021] Meanwhile, this invention corrects the binder saturation based on microscopic images of the preform, solving the problem of the difference between the dispersion characteristics of the binder within the preform under mold forming conditions and the dispersion of the printed binder among powders during printer-free testing of the mechanical properties of the preform. This allows for an effective evaluation of the mechanical properties of the binder-formed preform, providing a more accurate reference for the printability of the binder. Attached Figure Description

[0022] Figure 1 A schematic diagram of the process for testing the mechanical properties of 3D printing binder-molded preforms provided by the present invention;

[0023] Figure 2 This is a scanning electron microscope image of the A7 cured preform in this invention;

[0024] Figure 3 This is a comparison chart of the strength of the cured preform of the present invention and the strength of the cured preform tested by a 3D printer;

[0025] Figure 4 This is a schematic diagram of the mold used in this invention to manufacture the adhesive preform.

[0026] Figure 5 This is a schematic diagram of the detachable mold assembly of the present invention. Detailed Implementation

[0027] Specific implementation method one: Combining Figure 1 , Figure 4 This embodiment describes a method for testing the mechanical properties of a 3D printing binder preform, comprising the following steps:

[0028] A1: The mold used to make the binder blank is ultrasonically cleaned with alcohol and dried. The overall weight of the mold after drying is measured. Printing powder that has been ultrasonically cleaned and dried with alcohol is filled into the mold. The change in the overall weight of the mold after the powder is poured into the mold is the mass of the powder.

[0029] A2: The powder in the mold is compacted to obtain the height h0 of the compacted powder and the relative density ρ of the compacted powder.

[0030] A3: Select a saturation degree S, where S is the volume fraction of the adhesive in the voids, ranging from 0 to 1. Calculate the required adhesive mass m corresponding to this saturation degree S. s ;

[0031] A4: Measure the mass as m s The adhesive is measured and slowly dripped into the surface of the compacted powder inside the mold in A3;

[0032] A5: After adding the binder in A4, slowly drip low-boiling-point solvent onto the powder surface inside the mold. Stop dripping the low-boiling-point solvent when it is about to submerge the compacted powder material, and let the mold stand after dripping the low-boiling-point solvent.

[0033] A6: After the mold in A5 has been left to stand, move the whole mold into the oven for curing. After curing, demold the blank.

[0034] A7: Scanning electron microscopy (SEM) tests were performed on random parts of the preform after A6 curing. The proportion of binder that provides mechanical properties to that that does not provide mechanical properties was statistically analyzed from the images obtained by SEM tests, and the proportion k of binder that provides mechanical properties to the total binder content was calculated.

[0035] A8: Based on the binder ratio k obtained in A7, correct the saturation S to the effective saturation S. i Effective saturation S i The corrected formula is as follows:

[0036] S i =Sk

[0037] Select multiple different effective saturation S i And A1 to A6 were repeated to obtain different effective saturation S. i The corresponding cured preform was prepared, and its mechanical properties were tested after curing.

[0038] Those skilled in the art can use the steps of this invention to accurately test the strength of preforms with different binder saturation levels without the need for a BJ printer. This allows for rapid and accurate testing of the strength of preforms with different saturation levels between different binders and powders, the establishment of a binder printing performance database, reduction of binder development cycle, and reduction of printing material waste during preform strength testing.

[0039] Specific Implementation Method Two: Combining Figure 1 , Figure 4 and Figure 5 This embodiment describes a method for testing the mechanical properties of a 3D printing binder-molded preform: the mold described in A1 is a mold that is easy to remove from the mold, the structure of the mold is a detachable structure, the mold cavity described in A1 is a cylinder, which facilitates demolding after the preform has solidified, and at the same time, it is necessary to ensure that the binder does not leak before and after disassembly. Other steps are the same as any one of the specific embodiments one or two.

[0040] Specific implementation method three: Combining Figure 1 This embodiment describes a method for testing the mechanical properties of a 3D printing binder-molded preform: the mold material mentioned in A1 is polytetrafluoroethylene, and the powder material mentioned in A1 is a 3D metal printing material. The 3D metal printing material includes: iron-based alloys, titanium and titanium-based alloys, nickel-based alloys, cobalt-chromium alloys, aluminum alloys, copper alloys, and precious metals. To ensure the test results, its particle size should be consistent with the particle size of the printing powder. Other steps are the same as any one of the specific embodiments one to three.

[0041] Specific implementation method four: Combination Figure 1 This embodiment describes a method for testing the mechanical properties of a 3D printing binder preform: The height h0 of the compacted powder described in A2 is calculated using the following formula:

[0042] h0 = h - h1

[0043] In the formula: h is the distance from the bottom to the top of the mold cavity;

[0044] h1 is the height of the powder surface after compaction from the top of the cavity;

[0045] The relative density ρ of the compacted powder mentioned in A2 is calculated by the mass ratio between the powder added in A1 and the powder material of the same volume after compaction. The other steps are the same as any one of the specific embodiments one to four.

[0046] Specific Implementation Method Five: Combining Figure 1 This embodiment describes a method for testing the mechanical properties of a 3D printing binder preform: the saturation S mentioned in A3 corresponds to the required binder mass m. sIt is calculated using the following formula:

[0047] V = S x h0

[0048] m s =VS(1-ρ)ρ binder

[0049] In the formula: V is the volume of the powder after compaction;

[0050] S x The area of ​​the cavity bottom;

[0051] h0 is the height of the powder after compaction;

[0052] S represents saturation;

[0053] ρ is the relative density of the powder after compaction;

[0054] ρ binder This represents the density of the adhesive.

[0055] Specific Implementation Method Six: Combination Figure 1 This embodiment describes a method for testing the mechanical properties of a 3D printing binder preform: the slow dripping described in A4 refers to multiple drippings using a pipette, with each dripping volume being less than 200 μL, to prevent excessively rapid dripping from generating air bubbles that could damage the internal pore structure of the preform. The other steps are the same as any one of the specific embodiments one to five.

[0056] Specific implementation method seven: Combination Figure 1 This embodiment describes a method for testing the mechanical properties of a 3D printing binder-molded preform: Before slowly adding a low-boiling-point solvent to the powder surface inside the mold after adding the binder as described in A5, the low-boiling-point solvent is first placed into the container used to measure the binder in A4 to reduce the influence of the binder residue on the container surface in A4 on the binder saturation; the low-boiling-point solvent refers to a solvent with a boiling point more than 10°C lower than the boiling point of the binder that can dissolve the binder, usually isopropanol and alcohol, etc. Other steps are the same as any one of the specific embodiments one to six.

[0057] Specific implementation method eight: Combination Figure 1 This embodiment describes a method for testing the mechanical properties of a 3D printing binder preform: the standing treatment described in A5 is determined based on the compatibility between the binder and the low-boiling-point solvent, and the standing time is 2-30 minutes. Other steps are the same as any one of the specific embodiments one to seven.

[0058] Specific Implementation Method Nine: Combining Figure 1This embodiment describes a method for testing the mechanical properties of a 3D printing binder-molded preform: The A7 statistical method involves scanning the preform and statistically analyzing the area ratio of the binder between powder particles and the binder on the powder surface that does not provide strength to the preform. The proportion k of the binder that provides mechanical properties between powder particles is calculated. The binder providing mechanical properties mentioned in A7 refers to the binder that connects powder particles. The binder that does not provide mechanical properties mentioned in A7 refers to the binder on the surface of a single powder particle. Other steps are the same as in any of the specific embodiments one to eight.

[0059] Specific Implementation Method Ten: Combining Figures 1 to 3 This embodiment describes a method for testing the mechanical properties of a 3D printing binder-molded preform: In this embodiment, the mechanical property test mentioned in A8 refers to testing the compressive strength of the cured preform.

[0060] A mold structure for easy demolding was designed, and a corresponding cylindrical PTFE mold with a diameter d of 10 mm and a height h of 12 mm was fabricated. The mold and spherical pure copper powder with a particle size of 38 micrometers were ultrasonically cleaned with alcohol and dried in an oven at 60℃ for 30 minutes. The powder was poured into the mold, and the change in the overall weight of the mold before and after the powder was poured in was measured. The mass of the powder was recorded as 3.85 g. The powder was compacted, and the height h1 of the powder surface from the upper surface of the mold after compaction was measured to be approximately 2 mm. The relative density ρ of the compacted powder was calculated to be 0.55. A saturation degree S of 0.3 was selected, and the mass m of the binder corresponding to a saturation degree S of 0.3 was calculated. s 0.116g of triethylene glycol dimethacrylate (TGD) binder was dropped into the mold and the powder was compacted. Isopropanol solvent was added to the container used to measure the binder mass in A4 to reduce the influence of binder residue on the container surface on binder saturation. A certain amount of low-boiling-point solvent was slowly added dropwise to the powder surface in the mold using a pipette, 100μL at a time. After each addition, the mold was allowed to stand for 10 minutes to ensure thorough mixing of the binder and solvent. The PTFE mold was then placed in an oven for curing at 140℃ for 4 hours. After curing, the mold was removed, and the green body was demolded. Scanning electron microscopy (SEM) tests were performed on the cured green bodies. The ratio of binder providing mechanical properties (binder that connects powder particles) to binder not providing mechanical properties (binder only on the surface of individual powder particles) was approximately 39:61, and k was calculated to be 0.39. Repeat steps A1 to A6, varying the required amount of adhesive added in A3, and adjusting the effective saturation S of the adhesive based on the ratio k = 0.39 calculated in A7.i Calculations were performed, and the effective saturation S was tested separately. i The mechanical properties of the billet corresponding to values ​​of 0.15, 0.2, and 0.25 are determined by... Figure 3 As can be seen, the present invention corrects the binder saturation based on the microscopic image of the preform, solving the problem of the difference between the dispersion characteristics of the binder in the preform under mold forming conditions and the dispersion of the printed binder among powders in the mechanical property test of the preform without a printer. This enables an effective evaluation of the mechanical properties of the binder-formed preform, providing a more accurate reference for the printing performance of the binder. The strength of preforms with different binder saturations without a BJ printer is essentially consistent with the strength of the binder ligand printed with a BJ printer. Other steps are the same as any one of the specific embodiments one to nine.

[0061] The above description is merely of preferred embodiments of the present invention. It should be understood that the present invention is not limited to the specific embodiments described above. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent substitutions, and improvements made to the above embodiments without departing from the scope of the present invention, based on the technical essence of the present invention, and within the spirit and principles of the present invention, shall still fall within the protection scope of the present invention.

Claims

1. A method for testing the mechanical properties of binder-molded preforms for 3D printing, characterized in that, Includes the following steps: A1: The mold used to make the binder blank is ultrasonically cleaned with alcohol and dried. The overall weight of the mold after drying is measured. Printing powder that has been ultrasonically cleaned and dried with alcohol is filled into the mold. The change in the overall weight of the mold after the powder is poured into the mold is the mass of the powder. A2: Compact the powder inside the mold to obtain the height of the compacted powder. And to obtain the relative density ρ of the compacted powder; the height of the compacted powder It is calculated using the following formula: In the formula: h is the distance from the bottom to the top of the mold cavity; This refers to the height of the powder surface from the top of the cavity after compaction. The relative density ρ of the compacted powder is calculated by the mass ratio between the powder added in A1 and the powder of the same volume after compaction. A3: Select a saturation level S, and calculate the required amount of adhesive corresponding to that saturation level S. The saturation S corresponds to the required adhesive mass m. s It is calculated using the following formula: In the formula: V is the volume of the powder after compaction; The area of ​​the cavity bottom; The height of the powder after compaction; S represents saturation; The relative density of the powder after compaction; The density of the adhesive; A4: Measure the mass as The adhesive is measured and slowly dripped onto the surface of the compacted powder inside the mold in A2; A5: After adding the binder in A4, slowly drip low-boiling-point solvent onto the powder surface inside the mold. Stop dripping the low-boiling-point solvent when it is about to submerge the compacted powder material, and let the mold stand after dripping the low-boiling-point solvent. A6: After the mold in A5 has been left to stand, move the whole mold into the oven for curing. After curing, demold the blank. A7: Scanning electron microscopy (SEM) tests were performed on random parts of the preform after A6 curing. The proportion of binder that provides mechanical properties to that that does not provide mechanical properties was statistically analyzed from the images obtained by SEM tests, and the proportion k of binder that provides mechanical properties to the total binder content was calculated. A8: Based on the binder ratio k obtained in A7, correct the saturation S to the effective saturation. Effective saturation The corrected formula is as follows: Select multiple different effective saturations Then, A1 through A6 were repeated to obtain different effective saturation levels. The corresponding cured preform was prepared, and its mechanical properties were tested after curing.

2. The method for testing the mechanical properties of a 3D printing binder-molded preform according to claim 1, characterized in that: The mold described in A1 is a mold that is easy to remove from the mold. The mold has a detachable structure, and the mold cavity described in A1 is a cylinder.

3. A method for testing the mechanical properties of a 3D printing binder-molded preform according to claim 1 or 2: characterized in that: The mold material described in A1 is polytetrafluoroethylene, and the powder material described in A1 is a 3D metal printing material. The 3D metal printing material includes: iron-based alloys, titanium and titanium-based alloys, nickel-based alloys, cobalt-chromium alloys, aluminum alloys, copper alloys, and precious metals.

4. A method for testing the mechanical properties of a 3D printing binder-molded preform according to claim 1 or 3, characterized in that: The slow dripping method described in A4 refers to multiple drippings using a pipette, with each dripping volume being less than 200 μL.

5. The method for testing the mechanical properties of a 3D printing binder-molded preform according to claim 4, characterized in that: Before slowly adding a low-boiling-point solvent to the powder surface inside the mold after adding the binder as described in A5, the low-boiling-point solvent is first placed into the container used to measure the binder in A4; the low-boiling-point solvent refers to a solvent whose boiling point is more than 10°C lower than the boiling point of the binder and can dissolve the binder.

6. The method for testing the mechanical properties of a 3D printing binder-molded preform according to claim 5, characterized in that: The settling process described in A5 is determined based on the compatibility between the binder and the low-boiling-point solvent, and the settling time is 2-30 minutes.

7. The method for testing the mechanical properties of a 3D printing binder-molded preform according to claim 1, characterized in that: The binder that provides mechanical properties as described in A7 refers to a binder that acts as a bond between powder particles; the binder that does not provide mechanical properties as described in A7 refers to a binder that is only present on the surface of a single powder particle.

8. The method for testing the mechanical properties of a 3D printing binder-molded preform according to claim 1, characterized in that: The mechanical property test described in A8 refers to the compressive strength test of the cured blank.

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