Device and method for measuring friction coefficient of powder for additive manufacturing

Abstract

The invention relates to a device and a method for measuring a friction coefficient of powder for additive manufacturing, in particular to measurement of a powder-powder substrate friction coefficient and measurement of a powder-substrate friction coefficient. The device comprises a shell, a funnel, an electric control valve, a laser emitting device, a laser receiving device, a powder scraping device, a powder laying device, a mechanical claw, a telescopic arm, a tension meter, an electric control translation table, a measuring platform and a powder collecting barrel. According to the invention, the components such as the electric control valve, the laser emitting and receiving device and the powder scraping device are adopted to measure the repose angle of the powder to be measured, so that automatic measurement of the powder-powder friction coefficient is realized; by controlling the mechanical claw to place the substrate, the powder laying device to lay the powder bed and utilizing the tension meter to measure the friction force, automatic measurement of the powder-substrate friction coefficient is realized, so that manual intervention is reduced, the measurement precision is improved, the two measuring devices are integrated into a whole through the hydraulic device, and the device is simplified.

Description

Technical Field

[0001] The present application relates to the technical field of powder friction coefficient measurement, and specifically to a device and method for measuring the friction coefficient of powder for additive manufacturing. Background Art

[0002] Existing methods for determining the powder-powder friction coefficient mainly include the shear method and the angle of repose method. Since the pre-compression and consolidation process of the shear method changes the initial state of the powder, it is quite different from the actual additive manufacturing process, resulting in significant deviations in the measurement results. Although the angle of repose method is easy to operate, existing patent documents, such as the patent document with publication number CN108240949A, need to rely on complex image processing systems, which are costly and complex to operate; the patent document with publication number CN102445403A relies on manual visual judgment and has low accuracy; and the patent document with announcement number CN217359491U has problems such as many manual operations and easy introduction of errors, which are difficult to meet the needs of the additive manufacturing field for high-precision and automated measurements.

[0003] The existing powder-substrate friction coefficient determination methods mainly include the inclined plane method and the flat plate method. For the inclined plane method, the existing technology, such as the patent document with the announcement number CN210626293U, relies on manual judgment of the material sliding moment, which has the defects of strong subjectivity and low precision; although the patent document with the publication number CN114965257A uses a displacement detection sensor to monitor the material sliding, it has the advantages of faster response and lower error probability compared to manual observation, and the sliding friction coefficient obtained is more accurate, but due to the monitoring principle of the displacement detection sensor, the device can only measure some larger bulk materials. Although the flat plate method can be automated, the existing technology is difficult to apply to tiny powders, and it is quite different from the powder-substrate interaction mechanism in the actual additive manufacturing process. In addition, although the existing friction coefficient measuring instrument can measure the friction coefficient of a variety of materials, its principle and test method are not applicable to tiny powders, and it is impossible to measure the powder-powder and powder-substrate friction coefficients at the same time. Summary of the invention

[0004] The purpose of the present invention is to provide a device and method for measuring the friction coefficient of powder for additive manufacturing, which can overcome the defects of the prior art, such as many manual operations, easy introduction of errors, difficulty in meeting the needs of the additive manufacturing field for high-precision and automated measurement, reliance on manual judgment of the material sliding moment, strong subjectivity, low precision and limited measurement range, and inability to meet the requirements of the additive manufacturing process, and can simultaneously measure the powder-powder friction coefficient and the powder-substrate friction coefficient.

[0005] The first technical solution adopted by the present invention is: a device for measuring the friction coefficient of powder for additive manufacturing, comprising a shell, a funnel, an electrically controlled valve, a laser emitting device, a laser receiving device, a powder scraping device, a powder spreading device, a mechanical claw, a telescopic arm, a dynamometer, an electrically controlled translation stage, a measuring platform and a powder collecting bucket; a transparent observation window is arranged on the panel of the shell, a display screen and buttons are arranged under the panel, and a single-chip microcomputer is built in the display screen; the funnel is arranged on the top of the shell, and the electrically controlled valve is arranged at the discharge port of the funnel; the laser emitting device and the laser receiving device are arranged on both sides of the inner wall of the shell relative to each other, and the powder scraping device is arranged on the inner wall of the laser between the light emitting device and the laser receiving device, and the bottom of the powder scraping device is at the same height as the lower vertex of the laser; the powder spreading device is arranged directly below the powder scraping device, the measuring platform is arranged directly below the powder spreading device, and the powder collecting bucket is arranged at the bottom of the shell and is located directly below the measuring platform; the telescopic arm and the electric-controlled translation platform are arranged on the side wall of the shell, the mechanical claw is arranged at one end of the telescopic arm, the dynamometer is arranged on the electric-controlled translation platform, a wire is arranged at one end of the dynamometer, and a tooling fixture is arranged at the other end of the wire; the electric-controlled valve, laser emitting device, laser receiving device, telescopic arm, electric-controlled translation platform and buttons are all connected to the single-chip microcomputer.

[0006] Furthermore, the powder scraping device includes a scraper and a first swinging device, the first swinging device is fixed on the housing and connected to the scraper, the first swinging device is connected to the single chip microcomputer, and the single chip microcomputer controls the first swinging device to swing left and right.

[0007] Furthermore, the powder spreading device includes a powder scraper, a powder spreading knife, a motor and a second swinging device, the second swinging device is fixed on the shell and connected to the motor, the motor is also connected to the powder scraper and the powder spreading knife, the powder scraper and the powder spreading knife are arranged back to back, the blade of the powder scraper coincides with the upper plane of the measuring platform, and there is a gap between the blade of the powder spreading knife and the upper plane of the measuring platform; the motor and the second swinging device are connected to the single-chip microcomputer, and the single-chip microcomputer controls the rotation of the motor and the left and right swing of the second swinging device.

[0008] Furthermore, the measuring platform includes a powder-powder friction coefficient measuring platform, a powder-substrate friction coefficient measuring platform, a hydraulic rod and a powder collecting funnel. One end of the hydraulic rod is connected to the bottom of the shell, and the other end is connected to the powder-powder friction coefficient measuring platform. The powder-substrate friction coefficient measuring platform is connected to the outer shell of the hydraulic rod through a support rod and is sleeved on the outside of the powder-powder friction coefficient measuring platform. The powder collecting funnel is sleeved on the outside of the hydraulic rod, and the outlet of the powder collecting funnel is aligned with the powder collecting barrel; the hydraulic rod is also connected to the single-chip microcomputer.

[0009] Furthermore, a base is provided at the bottom of the shell, and the base is provided at four corners of the bottom of the shell, and a rubber pad is provided at the bottom of the base.

[0010] The second technical solution adopted by the present invention is: a method for measuring the friction coefficient of powder for additive manufacturing, using the device as described in the first technical solution for measurement, comprising the following steps: S1: Add the powder to be tested into the funnel, fix the substrate to be tested on the fixture, place the substrate to be tested on the mechanical claw, and close the transparent observation window; S2: Use the button to input the number of times the powder-powder friction coefficient is measured, and start measuring the powder-powder friction coefficient. The specific steps are as follows: S201: The single chip microcomputer controls the extension of the hydraulic rod to raise the powder-powder friction coefficient measurement platform until the upper plane coincides with the blade surface of the scraper; S202: The single chip microcomputer controls the electronically controlled valve to open, and the powder to be tested begins to flow out from the discharge port of the funnel, falls to the powder-powder friction coefficient measurement platform, and accumulates into a cone shape; S203: The single chip microcomputer controls the electric control valve to close, and controls the laser emitting device to emit a horizontal linear laser with a width of L0, wherein a part of the laser is blocked by the accumulated powder to be tested, and another part of the laser is received by the laser receiving device, and the laser receiving device transmits the received laser width L to the single chip microcomputer and calculates the powder-powder friction coefficient; S204: After the data is transmitted and the calculation is completed, the single chip microcomputer controls the laser emitting device and the laser receiving device to stop working, and controls the powder scraping device to scrape off the powder to be tested on the powder-powder friction coefficient measurement platform, completing a powder-powder friction coefficient measurement; S205: Repeat steps S202 to S204 according to the input number of measurements, and take the average value of the powder-powder friction coefficient calculated each time as the final measurement result; S3: Use the operation button to input the number of times the friction coefficient between the powder and the substrate is measured, and start measuring the friction coefficient between the powder and the substrate. The specific steps are as follows: S301: the single chip computer first controls the hydraulic rod to retract, so that the upper surface of the powder-powder friction coefficient measuring platform drops to coincide with the upper plane of the powder-substrate friction coefficient measuring platform; S302: The single chip microcomputer controls the electronically controlled valve to open, and the powder to be tested begins to flow out from the discharge port of the funnel, falls to the powder-substrate friction coefficient measurement platform, and accumulates into a cone. At this time, the single chip microcomputer controls the electronically controlled valve to close; S303: The single chip microcomputer controls the powder spreading device to spread the powder to be tested, and the fallen powder to be tested falls into the powder collecting funnel and finally flows into the powder collecting bucket for collection; S304: repeating steps S302 to S303 at least three times to ensure that the powder to be tested is evenly spread on the powder-substrate friction coefficient measurement platform; S305: After the powder spreading is completed, the single chip microcomputer controls the mechanical claw to clamp the substrate to be tested, and then turns the substrate to be tested counterclockwise so that the upper surface of the substrate to be tested is initially facing downward and parallel to the horizontal plane, and then controls the telescopic arm and the mechanical claw to move the substrate to be tested to a position where the lower surface is 1 mm away from the upper surface of the powder to be tested on the powder-substrate friction coefficient measurement platform, and controls the mechanical claw to open so that the substrate to be tested is placed on the upper surface of the powder to be tested; then the single chip microcomputer controls the mechanical claw and the telescopic arm to return to the initial position; S306: The single-chip microcomputer controls the electric control translation stage to drive the dynamometer to move rightward at a uniform speed. The dynamometer pulls the substrate to be tested on the powder to be tested to move rightward at a uniform speed through the wire. The dynamometer measures the friction force F at the pulling moment, and transmits the data to the single-chip microcomputer in real time to calculate the powder-substrate friction coefficient. S307: The single chip microcomputer controls the mechanical claw to flip counterclockwise and controls the telescopic arm to extend to the specified position, controls the mechanical claw to clamp the substrate to be tested and move to the specified position and then flip 90 degrees clockwise, and then controls the telescopic arm and the electric control translation stage to return to the initial position, completing a measurement of the powder-substrate friction coefficient; S308: After data transmission and calculation are completed, the single chip microcomputer controls the powder spreading device to clean the powder to be tested on the powder-substrate friction coefficient measuring platform, and the scraped powder to be tested falls into the powder collecting funnel and flows into the powder collecting bucket for collection; S309: Repeat steps S302 to S308 according to the input number of measurements, and take the average value of the powder-substrate friction coefficient calculated each time as the final measurement result.

[0011] Furthermore, the specific formula for calculating the powder-powder friction coefficient is: μ1= tanθ = h / r; h = L0– L; Wherein, μ1 represents the powder-powder friction coefficient, θ represents the angle of repose, h represents the height of the piled-up powder to be tested, and r represents the radius of the powder-powder friction coefficient measurement platform.

[0012] Furthermore, the specific formula for calculating the powder-substrate friction coefficient is: μ2 = F / N; Where μ2 represents the powder-substrate friction coefficient and N represents the normal pressure of the substrate.

[0013] The beneficial effects of the present invention are as follows: the present invention can measure both the powder-powder friction coefficient and the powder-substrate friction coefficient, thereby saving equipment costs; the present invention has a simple structure, is easy to operate, can carry out repeated experiments, and has a high degree of automation, does not require excessive manual intervention during the measurement process, effectively prevents operational errors introduced by manual operation, improves measurement accuracy, and saves the labor of researchers; the present invention adopts a closed design, which is conducive to reducing external interference and improving the accuracy of the results, while also avoiding the risk of fine powder flying into the air being inhaled by the human body, thereby protecting the health of personnel. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0015] Figure 1 It is a front view of an embodiment of the present invention; Figure 2 It is a schematic diagram of the structure of the wire and the fixture in the embodiment of the present invention; Figure 3 This is a schematic diagram of the structure of a powder spreading device in an embodiment of the present invention; Figure 4 It is a structural schematic diagram of a measurement platform in an embodiment of the present invention; Figure 5 Schematic diagram of the working state when measuring the powder-powder friction coefficient in an embodiment of the present invention Figure 1 ; Figure 6 Schematic diagram of the working state when measuring the powder-powder friction coefficient in an embodiment of the present invention Figure 2 ; Figure 7 The figure is a schematic diagram of the working state when measuring the powder-substrate friction coefficient according to an embodiment of the present invention.

[0016] Explanation of the accompanying drawings: 1-shell, 2-funnel, 3-electrically controlled valve, 4-laser emitting device, 5-laser receiving device, 6-mechanical claw, 7-telescopic arm, 8-tensile meter, 9-electrically controlled translation stage, 10-powder collecting bucket, 11-transparent observation window, 12-display screen, 13-button, 14-wire, 15-tool fixture, 16-scraper, 17-first swinging device, 18-powder scraping knife, 19-powder spreading knife, 20-motor, 21-second swinging device, 22-powder-powder friction coefficient measuring platform, 23-powder-substrate friction coefficient measuring platform, 24-hydraulic rod, 25-powder collecting funnel, 26-base, 27-powder to be tested, 28-substrate to be tested. DETAILED DESCRIPTION

[0017] In order to more clearly understand the above-mentioned purpose, features and advantages of the present invention, the present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments. In the following description, many specific details are set forth to facilitate a full understanding of the present invention, but the present invention can also be implemented in other ways different from those described herein, and therefore, the present invention is not limited to the limitations of the specific embodiments disclosed below.

[0018] Unless otherwise defined, the technical or scientific terms used herein shall have the usual meanings understood by persons of ordinary skill in the field described in this application. The words "first", "second" and similar terms used in this patent application specification and claims do not indicate any order, quantity or importance, but are only used to distinguish different components. Similarly, words such as "one" or "an" do not indicate a quantity limitation, but rather indicate the existence of at least one. Words such as "connected" or "connected" are not limited to physical or mechanical connections, but may include electrical connections, whether direct or indirect. "Up", "down", "left", "right" and the like are only used to indicate relative positional relationships. When the absolute position of the object being described changes, the relative positional relationship also changes accordingly.

[0019] like Figure 1~Figure 4 As shown, a device for measuring the friction coefficient of powder for additive manufacturing includes a housing 1, a funnel 2, an electrically controlled valve 3, a laser emitting device 4, a laser receiving device 5, a powder scraping device, a powder spreading device, a mechanical claw 6, a telescopic arm 7, a dynamometer 8, an electrically controlled translation stage 9, a measuring platform and a powder collecting bucket 10. A transparent observation window 11 is provided on the panel of the housing 1, and a display screen 12 and a button 13 are provided under the panel. The display screen 12 has a built-in single-chip microcomputer (not shown in the figure); the transparent observation window 11 can provide an observation field for the operator, and the operator can perform human-computer interaction through the display screen 12, read the measurement results, and send operation instructions through the button 13.

[0020] The funnel 2 is arranged at the top of the shell 1, and the electric control valve 3 is arranged at the discharge port of the funnel 2. The discharge of the funnel 2 can be controlled by the electric control valve 3. The laser emitting device 4 and the laser receiving device 5 are relatively arranged on both sides of the inner wall of the shell 1. The laser emitting device 4 and the laser receiving device 5 are both rectangular structures and can emit a linear laser beam of a certain width. The powder scraping device is arranged between the laser emitting device 4 and the laser receiving device 5, and the bottom of the powder scraping device is at the same height as the lower vertex of the laser; the powder spreading device is arranged directly below the powder scraping device, the measuring platform is arranged directly below the powder spreading device, and the powder collecting barrel 10 is arranged at the bottom of the shell 1 and is located directly below the measuring platform. The telescopic arm 7 and the electrically controlled translation platform 9 are arranged on the side wall of the shell 1, the mechanical claw 6 is arranged at one end of the telescopic arm 7, the dynamometer 8 is arranged on the electrically controlled translation platform 9, a wire 14 is arranged at one end of the dynamometer 8, and a fixture 15 is arranged at the other end of the wire 14, and the substrate 28 to be tested is clamped by the fixture 15 for measurement; the electrically controlled valve 3, the laser emitting device 4, the laser receiving device 5, the telescopic arm 7, the electrically controlled translation platform 9 and the button 13 are all connected to the single chip microcomputer, and the single chip microcomputer realizes automatic control.

[0021] In an embodiment of the present invention, the powder scraping device includes a scraper 16 and a first swinging device 17. The first swinging device 17 is fixed on the shell 1 and connected to the scraper 16. The first swinging device 17 is connected to the single-chip microcomputer, and the single-chip microcomputer controls the first swinging device 17 to swing left and right, thereby driving the scraper 16 to swing to perform powder scraping operations. The powder spreading device includes a powder scraper 18, a powder spreading knife 19, a motor 20 and a second swinging device 21. The second swinging device 21 is fixed on the shell 1 and connected to the motor 20. The motor 20 is also connected to the powder scraper 18 and the powder spreading knife 19. The powder scraper 18 and the powder spreading knife 19 are arranged back to back. The blade surface of the powder scraper 18 coincides with the upper plane of the measuring platform to ensure that the powder scraper 18 can fully scrape off the powder 27 to be tested on the surface of the measuring platform, and there is a gap between the blade surface of the powder spreading knife 19 and the upper plane of the measuring platform. In the embodiment of the present invention, the width of the gap is 5 mm, that is, the powder spreading knife 19 can be used to spread 5 mm thick powder 27 to be tested on the surface of the measuring platform. The motor 20 and the second swinging device 21 are connected to the single chip microcomputer, and the single chip microcomputer controls the motor 20 to rotate and the second swinging device 21 to swing left and right, thereby driving the scraping knife 18 and the powder spreading knife 19 to swing, and perform powder scraping or powder spreading operations; the rotation of the motor 20 can adjust the position of the scraping knife 18 and the powder spreading knife 19, and adjust the tool to be used to the position below for operation.

[0022] The measuring platform includes a powder-powder friction coefficient measuring platform 22, a powder-substrate friction coefficient measuring platform 23, a hydraulic rod 24 and a powder collecting funnel 25. One end of the hydraulic rod 24 is connected to the bottom of the housing 1, and the other end is connected to the powder-powder friction coefficient measuring platform 22. The powder-substrate friction coefficient measuring platform 23 is connected to the outer shell of the hydraulic rod 24 through a support rod and is sleeved on the outside of the powder-powder friction coefficient measuring platform 22. The powder collecting funnel 25 is sleeved on the outside of the hydraulic rod 24, and the outlet of the powder collecting funnel 25 is aligned with the powder collecting barrel 10. The hydraulic rod 24 is also connected to the single-chip microcomputer, and the single-chip microcomputer controls the hydraulic rod 24 to rise and fall, so as to adjust the embodiment of the present invention to enter the powder-powder friction coefficient measuring mode or the powder-substrate friction coefficient measuring mode. The powder collecting funnel 25 can collect the fallen powder 27 to be measured to the powder collecting barrel 10 for collection, so as to facilitate the recovery of the powder 27 to be measured. In order to keep the device stable, the embodiment of the present invention further provides a base 26 at the bottom of the shell 1. The base 26 is provided at the four corners of the bottom of the shell. A rubber pad is provided at the bottom of the base 26 to alleviate vibration and reduce interference with the experiment.

[0023] The method for measuring the friction coefficient of powder for additive manufacturing according to the embodiment of the present invention specifically comprises the following steps: S1: Add the powder 27 to be tested into the funnel 2, fix the substrate 28 to be tested on the fixture 15, place the substrate 28 to be tested on the mechanical claw 6, and close the transparent observation window 11. The size of the substrate 28 to be tested used in the measurement process is 150 mm long, 50 mm wide, and 5 mm high.

[0024] S2: operate button 13 to input the number of times the powder-powder friction coefficient is measured, and start measuring the powder-powder friction coefficient. The specific steps are as follows: S201: Figure 5 As shown, the single chip microcomputer controls the hydraulic rod 24 to extend, so that the powder-powder friction coefficient measuring platform 22 rises until the upper plane of the powder-powder friction coefficient measuring platform 22 coincides with the blade surface of the scraper 16 .

[0025] S202: The single chip microcomputer controls the electric control valve 3 to open, and the powder 27 to be tested begins to flow out from the discharge port of the funnel 2, falls to the powder-powder friction coefficient measurement platform 22, and accumulates into a cone.

[0026] S203: Figure 6As shown, when the powder 27 to be tested piles up a conical powder pile on the plane of the powder-powder friction coefficient measuring platform 22, the single chip microcomputer controls the electric control valve 3 to close, the powder 27 to be tested stops falling, and the single chip microcomputer controls the laser emitting device 4 to emit a horizontal linear laser with a width of L0, part of which is blocked by the piled powder 27 to be tested, and the other part of the laser is received by the laser receiving device 5. The laser receiving device 5 transmits the received laser width L to the single chip microcomputer and calculates the powder-powder friction coefficient. The specific formula for calculating the powder-powder friction coefficient is: μ1= tanθ = h / r; h = L0– L; Here, μ1 represents the powder-powder friction coefficient, θ represents the angle of repose, h represents the height of the piled-up powder 27 to be tested, and r represents the radius of the powder-powder friction coefficient measuring platform 22 .

[0027] S204: After data transmission and calculation, the single chip microcomputer controls the laser emitting device 4 and the laser receiving device 5 to stop working, and then controls the powder scraping device to swing back and forth to scrape off the powder 27 to be tested on the powder-powder friction coefficient measuring platform 22. The swing angle of the first swing device 17 in the embodiment of the present invention is -60°~60°. The scraped powder 27 to be tested falls on the upper plane of the powder-substrate friction coefficient measuring platform 23. When the powder scraping device scrapes off all the powder 27 to be tested on the upper plane of the powder-powder friction coefficient measuring platform 22, the single chip microcomputer controls the powder scraping device to stop working. At this time, the powder-powder friction coefficient is completed once.

[0028] S205: Repeat steps S202 to S204 according to the input number of measurements, and take the average value of the powder-powder friction coefficient calculated each time as the final measurement result.

[0029] S3: operate button 13 to input the number of times the friction coefficient between powder and substrate is measured, and start measuring the friction coefficient between powder and substrate. The specific steps are as follows: S301 : the single chip microcomputer first controls the hydraulic rod 24 to retract, so that the upper surface of the powder-powder friction coefficient measuring platform 22 drops to coincide with the upper plane of the powder-substrate friction coefficient measuring platform 23 .

[0030] S302: The single chip microcomputer controls the electronically controlled valve 3 to open, and the powder 27 to be tested begins to flow out from the discharge port of the funnel 2, falls to the powder-substrate friction coefficient measuring platform 23, and accumulates into a cone. At this time, the single chip microcomputer controls the electronically controlled valve 3 to close.

[0031] S303: The single chip microcomputer controls the swing device of the powder spreading device to start working, driving the powder spreading knife 19 to swing back and forth to spread the powder 27 to be tested. The swing angle of the second swing device 21 in the embodiment of the present invention is also -60°~60°. The fallen powder 27 to be tested falls into the powder collecting funnel 25 and finally flows into the powder collecting barrel 10 for collection.

[0032] S304: Repeat steps S302 to S303 at least three times to ensure that the powder 27 to be tested is evenly spread on the powder-substrate friction coefficient measuring platform 23.

[0033] S305: Figure 7 As shown, after the powder spreading is completed, the single chip microcomputer controls the mechanical claw 6 to clamp the substrate 28 to be tested, and then flips the substrate 28 to be tested counterclockwise so that the upper surface of the substrate 28 to be tested is facing downward and parallel to the horizontal plane at the beginning, and then controls the telescopic arm 7 and the mechanical claw 6 to move the substrate 28 to be tested to a position where the lower surface is 1 mm away from the upper surface of the powder 27 to be tested on the powder-substrate friction coefficient measurement platform 23, and controls the mechanical claw 6 to open so that the substrate 28 to be tested is placed on the upper surface of the powder 27 to be tested; then the single chip microcomputer controls the mechanical claw 6 and the telescopic arm 7 to return to the initial position.

[0034] S306: The single-chip microcomputer controls the electric control translation stage 9 to drive the dynamometer 8 to move rightward at a uniform speed. The dynamometer 8 pulls the substrate 28 to be tested on the powder 27 to be tested to move rightward at a uniform speed through the wire 14. The dynamometer 8 measures the friction force F at the pulling moment, and transmits the data to the single-chip microcomputer in real time and calculates the powder-substrate friction coefficient. The specific formula for calculating the powder-substrate friction coefficient is: μ2 = F / N; Where μ2 represents the powder-substrate friction coefficient and N represents the normal pressure of the substrate.

[0035] S307: The single chip microcomputer controls the mechanical claw 6 to flip counterclockwise and controls the telescopic arm 7 to extend to the specified position, controls the mechanical claw 6 to clamp the substrate 28 to be tested and move to the specified position and then flip 90 degrees clockwise, and then controls the telescopic arm 7 and the electric control translation stage 9 to return to the initial position, completing a measurement of the powder-substrate friction coefficient; S308: After the data is transmitted and the calculation is completed, the single chip microcomputer controls the motor 20 of the powder spreading device to work, so that the blade surface of the powder scraper 18 coincides with the plane on the powder-substrate friction coefficient measuring platform 23, and then controls the swing device to drive the powder scraper 18 to swing back and forth to clean the powder 27 to be tested on the powder-substrate friction coefficient measuring platform 23. The scraped powder 27 to be tested falls into the powder collecting funnel 25 and flows into the powder collecting bucket 10 for collection; S309: Repeat steps S302 to S308 according to the input number of measurements, and take the average value of the powder-substrate friction coefficient calculated each time as the final measurement result.

[0036] The embodiment of the present invention uses a high-precision laser emitting device 4 and a laser receiving device 5 to measure the height of the powder to be measured, and can emit and receive a linear laser beam with a width accuracy of 4 to 132 microns, which is better than the 1mm accuracy achieved by the length measuring ruler and the 0.1 degree accuracy achieved by the angle measuring ruler in the prior art. By adopting the above-mentioned high-precision laser measurement system, the embodiment of the present invention greatly improves the accuracy of the measurement results. In the process of measuring the friction coefficient between the powder and the substrate, the tensile gauge used in the embodiment of the present invention has a full-scale accuracy of ±0.5%, which further ensures the accuracy and stability of the tensile measurement.

[0037] In the embodiment of the present invention, 316L stainless steel powder is used as the test object. In the process of measuring the powder-powder friction coefficient, the width of the laser emitted by the laser emitting device 4 is about 30mm, and the width of the laser received by the laser receiving device 5 is about 22~23mm. The stacking height of the powder to be tested on the platform is 7~8mm, and the radius is 25mm. According to the formula, the powder-powder friction coefficient is 0.28~0.32. In the process of measuring the powder-substrate friction coefficient, for a 316L stainless steel substrate with a size of 150mm long, 50mm wide and 5mm high, its density is 7.98g / cm 3 , the normal pressure N of the substrate is calculated to be 2.93265N; the friction force F measured by the dynamometer 8 ranges from 0.58653N to 1.466325N. According to the formula, the powder-substrate friction coefficient ranges from 0.2 to 0.5.

[0038] After the measurement is completed, the operator can read the measurement result from the display screen 12. The embodiment of the present invention can measure both the powder-powder friction coefficient and the powder-substrate friction coefficient, saving equipment costs; the present invention has a simple structure, is easy to operate, can perform repeated experiments, and has a high degree of automation. There is no need for excessive manual intervention during the measurement process, which effectively prevents operational errors introduced by manual operation, improves measurement accuracy, and saves the labor of researchers; the present invention adopts a closed design, which is conducive to reducing external interference and improving the accuracy of the results. At the same time, it also avoids the risk of fine powder flying into the air being inhaled by the human body, protecting the health of personnel.

[0039] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A device for measuring the friction coefficient of powder for additive manufacturing, characterized in that: It includes a shell, a funnel, an electric control valve, a laser emitting device, a laser receiving device, a powder scraping device, a powder spreading device, a mechanical claw, a telescopic arm, a dynamometer, an electric control translation platform, a measuring platform and a powder collecting bucket; a transparent observation window is arranged on the panel of the shell, a display screen and buttons are arranged under the panel, and a single chip microcomputer is built in the display screen; the funnel is arranged on the top of the shell, and the electric control valve is arranged at the discharge port of the funnel; the laser emitting device and the laser receiving device are arranged on both sides of the inner wall of the shell, and the powder scraping device is arranged between the laser emitting device and the laser receiving device, and The bottom of the powder scraping device is at the same height as the lower vertex of the laser; the powder spreading device is arranged directly below the powder scraping device, the measuring platform is arranged directly below the powder spreading device, and the powder collecting bucket is arranged at the bottom of the shell and is located directly below the measuring platform; the telescopic arm and the electric control translation platform are arranged on the side wall of the shell, the mechanical claw is arranged at one end of the telescopic arm, the dynamometer is arranged on the electric control translation platform, a wire is arranged at one end of the dynamometer, and a tooling fixture is arranged at the other end of the wire; the electric control valve, laser emitting device, laser receiving device, telescopic arm, electric control translation platform and buttons are all connected to the single chip microcomputer.

2. The device for measuring the friction coefficient of powder for additive manufacturing according to claim 1, characterized in that: The powder scraping device comprises a scraper and a first swinging device, wherein the first swinging device is fixed on the housing and connected to the scraper, and the first swinging device is connected to the single chip microcomputer, and the single chip microcomputer controls the first swinging device to swing left and right.

3. The device for measuring the friction coefficient of powder for additive manufacturing according to claim 1, characterized in that: The powder spreading device includes a powder scraper, a powder spreading knife, a motor and a second swinging device. The second swinging device is fixed on the shell and connected to the motor. The motor is also connected to the powder scraper and the powder spreading knife. The powder scraper and the powder spreading knife are arranged back to back. The blade of the powder scraper coincides with the upper plane of the measuring platform, and there is a gap between the blade of the powder spreading knife and the upper plane of the measuring platform. The motor and the second swinging device are connected to the single-chip microcomputer, and the single-chip microcomputer controls the rotation of the motor and the left and right swing of the second swinging device.

4. The device for measuring the friction coefficient of powder for additive manufacturing according to claim 1, characterized in that: The measuring platform includes a powder-powder friction coefficient measuring platform, a powder-substrate friction coefficient measuring platform, a hydraulic rod and a powder collecting funnel. One end of the hydraulic rod is connected to the bottom of the shell, and the other end is connected to the powder-powder friction coefficient measuring platform. The powder-substrate friction coefficient measuring platform is connected to the outer shell of the hydraulic rod through a supporting rod and is sleeved on the outside of the powder-powder friction coefficient measuring platform. The powder collecting funnel is sleeved on the outside of the hydraulic rod, and the outlet of the powder collecting funnel is aligned with the powder collecting barrel; the hydraulic rod is also connected to the single-chip microcomputer.

5. The device for measuring the friction coefficient of powder for additive manufacturing according to claim 1, characterized in that: The bottom of the shell is also provided with a base, which is arranged at four corners of the bottom of the shell, and the bottom of the base is provided with a rubber pad.

6. A method for measuring the friction coefficient of powder for additive manufacturing, using the device as claimed in claim 1 for measurement, characterized in that: The steps include: S1: Add the powder to be tested into the funnel, fix the substrate to be tested on the fixture, place the substrate to be tested on the mechanical claw, and close the transparent observation window; S2: Use the button to input the number of times the powder-powder friction coefficient is measured, and start measuring the powder-powder friction coefficient. The specific steps are as follows: S201: The single chip microcomputer controls the extension of the hydraulic rod to raise the powder-powder friction coefficient measurement platform until the upper plane coincides with the blade surface of the scraper; S202: The single chip microcomputer controls the electronically controlled valve to open, and the powder to be tested begins to flow out from the discharge port of the funnel, falls to the powder-powder friction coefficient measurement platform, and accumulates into a cone shape; S203: The single chip microcomputer controls the electric control valve to close, and controls the laser emitting device to emit a horizontal linear laser with a width of L0, wherein a part of the laser is blocked by the accumulated powder to be tested, and another part of the laser is received by the laser receiving device, and the laser receiving device transmits the received laser width L to the single chip microcomputer and calculates the powder-powder friction coefficient; S204: After the data is transmitted and the calculation is completed, the single chip microcomputer controls the laser emitting device and the laser receiving device to stop working, and controls the powder scraping device to scrape off the powder to be tested on the powder-powder friction coefficient measurement platform, completing a powder-powder friction coefficient measurement; S205: repeating steps S202 to S204 according to the input number of measurements, taking the average value of the powder-powder friction coefficient calculated each time as the final measurement result; S3: Use the operation button to input the number of times the friction coefficient between the powder and the substrate is measured, and start measuring the friction coefficient between the powder and the substrate. The specific steps are as follows: S301: the single chip computer first controls the hydraulic rod to retract, so that the upper surface of the powder-powder friction coefficient measuring platform drops to coincide with the upper plane of the powder-substrate friction coefficient measuring platform; S302: The single chip microcomputer controls the electronically controlled valve to open, and the powder to be tested begins to flow out from the discharge port of the funnel, falls to the powder-substrate friction coefficient measurement platform, and accumulates into a cone. At this time, the single chip microcomputer controls the electronically controlled valve to close; S303: The single chip microcomputer controls the powder spreading device to spread the powder to be tested, and the fallen powder to be tested falls into the powder collecting funnel and finally flows into the powder collecting bucket for collection; S304: repeating steps S302 to S303 at least three times to ensure that the powder to be tested is evenly spread on the powder-substrate friction coefficient measurement platform; S305: After the powder spreading is completed, the single chip microcomputer controls the mechanical claw to clamp the substrate to be tested, and then turns the substrate to be tested counterclockwise so that the upper surface of the substrate to be tested is initially facing downward and parallel to the horizontal plane, and then controls the telescopic arm and the mechanical claw to move the substrate to be tested to a position where the lower surface is 1 mm away from the upper surface of the powder to be tested on the powder-substrate friction coefficient measurement platform, and controls the mechanical claw to open so that the substrate to be tested is placed on the upper surface of the powder to be tested; then the single chip microcomputer controls the mechanical claw and the telescopic arm to return to the initial position; S306: The single-chip microcomputer controls the electric control translation stage to drive the dynamometer to move rightward at a uniform speed. The dynamometer pulls the substrate to be tested on the powder to be tested to move rightward at a uniform speed through the wire. The dynamometer measures the friction force F at the pulling moment, and transmits the data to the single-chip microcomputer in real time to calculate the powder-substrate friction coefficient. S307: The single chip microcomputer controls the mechanical claw to flip counterclockwise and controls the telescopic arm to extend to the specified position, controls the mechanical claw to clamp the substrate to be tested and move to the specified position and then flip 90 degrees clockwise, and then controls the telescopic arm and the electric control translation stage to return to the initial position, completing a measurement of the powder-substrate friction coefficient; S308: After data transmission and calculation are completed, the single chip microcomputer controls the powder spreading device to clean the powder to be tested on the powder-substrate friction coefficient measuring platform, and the scraped powder to be tested falls into the powder collecting funnel and flows into the powder collecting bucket for collection; S309: Repeat steps S302 to S308 according to the input number of measurements, and take the average value of the powder-substrate friction coefficient calculated each time as the final measurement result.

7. A method for determining the friction coefficient of powder for additive manufacturing according to claim 6, characterized in that: The specific formula for calculating the powder-powder friction coefficient is: μ1 = tanθ = h / r; h = L0 – L; Wherein, μ1 represents the powder-powder friction coefficient, θ represents the angle of repose, h represents the height of the piled-up powder to be tested, and r represents the radius of the powder-powder friction coefficient measurement platform.

8. A method for determining the friction coefficient of powder for additive manufacturing according to claim 6, characterized in that: The specific formula for calculating the powder-substrate friction coefficient is: μ2 = F / N; Where μ2 represents the powder-substrate friction coefficient and N represents the normal pressure of the substrate.

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