Powder evaluation method, powder evaluation system and program

Abstract

Acquire the technology to evaluate the adhesion of powders. This method is a powder evaluation method using the critical state line (CSL) and powder bed failure envelope (PYL) defined in JIS-Z8835, and calculates the integrated value of shear stress indicated by the powder bed failure envelope in the range of normal stress indicated by the powder bed failure envelope as A. PYL , the integrated value of the shear stress indicated by the limit state line in the range of the normal stress is A CSL As a parameter for evaluating the adhesion of the powder, (A PYL -A CSL ) / A PYL Calculate.

Description

[Technical Field]

[0001] The present invention relates to a technique for evaluating the physical properties of powder. [Background technology]

[0002] Non-Patent Document 1 describes that a highly adhesive powder has a powder yield locus (PYL) that is an upwardly convex curve. It also describes that measuring the adhesive force of a powder is difficult. Patent Document 2 describes how the flowability of a powder is evaluated using the adhesive force of the powder calculated from the fracture envelope obtained by a shear test. [Prior art documents] [Non-patent literature]

[0003] [Non-Patent Document 1] J. Soc. Powder Technol. Japan.44 732-741(2007) [Patent documents]

[0004] [Patent Document 1] WO2019 / 038909 publication Summary of the Invention [Problem to be solved by the invention]

[0005] PYL provides insight into the adhesive strength of powders. However, the adhesive strength of powders obtained by conventional methods is not sufficient as a parameter for evaluating the adhesiveness of powders. In this context, the present invention aims to provide a new technology for evaluating the adhesiveness of powders. [Means for solving the problem]

[0006] The present invention is a powder evaluation method using the critical state line (CSL) and powder bed failure envelope (PYL) defined in JIS-Z8835, and is a method for evaluating a powder by calculating the integrated value of the shear stress indicated by the powder bed failure envelope in the range of normal stress indicated by the powder bed failure envelope as A. PYL , the integrated value of the shear stress indicated by the limit state line in the range of the normal stress is A CSL As a parameter for evaluating the adhesion of the powder, (A PYL -A CSL ) / A PYL This is a powder evaluation method that calculates the

[0007] The present invention provides a method for evaluating powder using a prediction model obtained by machine learning, the prediction model being used to estimate the particle size distribution (D 10 ,D 50 ,D 90 ), convexity, circularity, linearity, aspect ratio, and the relationship between surface features and specific parameters are obtained by machine learning, and the specific parameters are calculated by calculating the integrated value of shear stress indicated by the powder bed failure envelope in the range of normal stress indicated by the powder bed failure envelope in the limit state line (CSL) and powder bed failure envelope (PYL) specified in JIS-Z8835. PYL , the integrated value of the shear stress indicated by the limit state line in the range of the normal stress is A CSL As, (A PYL -A CSL ) / A PYL This is a powder evaluation method defined by:

[0008] The present invention is a powder evaluation system that uses the critical state line (CSL) and powder bed failure envelope (PYL) defined in JIS-Z8835, and calculates the integrated value of shear stress indicated by the powder bed failure envelope in the range of normal stress indicated by the powder bed failure envelope as A. PYL , the integrated value of the shear stress indicated by the limit state line in the range of the normal stress is A CSL As a parameter for evaluating the adhesion of the powder, (A PYL -A CSL ) / APYL The powder evaluation system is provided with a calculation unit that calculates the

[0009] The present invention is a program for causing a computer to execute evaluation of powder using the critical state line (CSL) and powder bed failure envelope (PYL) defined in JIS-Z8835, and for a target powder, the program calculates an integrated value of shear stress indicated by the powder bed failure envelope in the range of normal stress indicated by the powder bed failure envelope as A. PYL , the integrated value of the shear stress indicated by the limit state line in the range of the normal stress is A CSL As a parameter for evaluating the adhesion of the powder, (A PYL -A CSL ) / A PYL It is a program that causes a computer to execute a process of calculating [Effects of the Invention]

[0010] According to the present invention, a new technique for evaluating the adhesiveness of powder is provided. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a conceptual diagram showing the collapse behavior of a powder layer. [Figure 2] FIG. 10 is a diagram showing the measured values ​​of the powder layer failure envelope of a powder sample. [Figure 3] FIG. 10 is a diagram showing the measured values ​​of the powder layer failure envelope of a powder sample. [Figure 4] FIG. 1 is a diagram illustrating a method for calculating the convexity ratio (APC) of the powder layer fracture envelope (PYL). [Figure 5] This is the APC value of the powder sample. [Figure 6] FIG. 1 is a diagram showing the relationship between the initial normal load and the convexity ratio (APC) in a shear test, and the relationship between the initial normal load and shear adhesive strength. [Figure 7] FIG. 1 is a conceptual diagram of a powder bed shear force measuring device. [Figure 8] FIG. 1 is a diagram showing definitions of convexity, circularity, linearity, and aspect ratio of powder particles. [Figure 9] FIG. 10 is a diagram showing the relationship between the predicted and measured values ​​of the convexity ratio (APC) of the powder bed fracture envelope (PYL). DETAILED DESCRIPTION OF THE INVENTION

[0012] 1. First embodiment (definition) The powder bed failure envelope and its measurement method are described in JIS-Z8835. The following explains the terms used in this specification based on the above JIS standard. Figure 1 is a conceptual diagram showing the relationship between the normal stress σ (horizontal axis) and shear stress τ (vertical axis) applied to a powder layer, which is related to the collapse behavior of the powder layer when a shear force is applied to the powder layer.

[0013] (Fracture envelope: YL (Yield locus)) Figure 1 shows the failure envelope (YL). The failure envelope (YL) can be understood as being divided into the powder bed failure envelope (PYL) and the consolidation collapse line (CYL). The YL (PYL, CYL) is a line that shows the relationship between τ and σ when a vertical stress σ is applied to any surface in a stationary powder bed with a certain void ratio, and a shear stress τ is gradually applied horizontally to that surface, reaching the critical stress state at which the bed just begins to collapse.

[0014] The angle between the tangent to YL and the normal stress axis (horizontal axis in Figure 1) is called the internal friction angle φi, and its gradient is called the internal friction coefficient. Also, the shear stress value C (the intercept of YL) at the intersection of YL and the shear stress axis (vertical axis in Figure 1) is the shear adhesion force.

[0015] (CSL (critical state line)) In the collapse of a powder bed, a straight line passing through the origin shows the relationship between the shear stress τ when a load is applied to the powder bed and the normal stress σ acting on the shear surface when the shear stress τ reaches a constant value.

[0016] (Powder dynamic friction angle: φ CSL (angle of critical state line) It is defined as the angle between the CSL and the normal stress axis.

[0017] (Powder yield locus, PYL) It is the envelope of the region where normal stress is small from the intersection of the failure envelope (YL) and the limit state line (CSL). In other words, the value of σ at the intersection of YL and CSL is σ CSL Let the value of τ be τ CSL When YL is 0≦σ≦σ CSL The range of PYL is the range in which the powder layer expands and collapses during the shear process. PYL represents the relationship between the maximum static friction stress and normal stress of the powder layer, and CSL represents the relationship between the maximum static friction stress and normal stress of the powder layer.

[0018] (Consolidation yield locus: CYL) It is defined as the envelope of the region of high normal stress from the intersection of the failure envelope (YL) and the critical state line (CSL). That is, σ of YL CSL The range of <σ is defined as CYL. CYL is the YL when the powder layer collapses due to consolidation during the shear process.

[0019] (overview) In this embodiment, the adhesiveness of the powder is evaluated by quantitatively evaluating the shape of the powder layer failure envelope (PYL). Here, the shape of the powder layer failure envelope (PYL) is quantitatively evaluated by the convexity ratio, which will be described below.

[0020] An example of measured data for the powder layer failure envelope (PYL) is shown in Figures 2 and 3. In Figures 2 and 3, the convex portion of the PYL that protrudes upward from the straight line of the CSL correlates with the adhesive force of the powder.

[0021] Here, the ratio of upward convex area of ​​PYL curve (APC) is introduced as a parameter to quantitatively evaluate the part of the CSL that protrudes upward from the straight line. Figure 4 shows how to calculate the ratio of upward convex area of ​​PYL curve. Figure 4 shows an example of measured data of the PYL (fracture envelope) of a powder layer.

[0022] The convexity ratio is defined as follows: First, the value of σ (value on the horizontal axis) at the intersection of YL and CSL in FIG. CSL Let the value of τ (value on the vertical axis) be τ CSL And, 0≦σ≦σ CSL Let PYL be the YL in the range of τ, and let A be the integrated value of τ indicated by YL (PYL) in that range. PYL Here, the area of ​​the waveform indicated by YL (PYL) in the range is A PYL Calculated as follows: 0≦σ≦σ CSL The range of normal stress (value of σ on the horizontal axis) is the range in which the shear stress value (value of τ on the vertical axis) indicated by the powder bed failure envelope (PYL) is equal to or greater than the shear stress value (value of τ on the vertical axis) indicated by the critical state line (CSL). A PYL is calculated by the following equation 1.

[0023]

number

[0024] In addition to the calculation method shown in Equation 1, the equation of the curve of τ = f(σ) that fits the plot points (measurement points) of the PYL is found, and the equation of this curve is set to 0≦σ≦σ CSL By integrating over the range of A PYL There is also a way to calculate

[0025] On the other hand, 0≦σ≦σ CSL The integrated value of τ indicated by CSL in the range of is calculated. CSL Here, 0≦σ≦σ CSL The area of ​​the CSL waveform in the range of A CSL ACSL is calculated by the following equation 2.

[0026]

number

[0027] The convexity ratio (APC) is defined by the following formula:

[0028]

number

[0029] The convexity ratio (APC) in Equation 3 is the area of ​​the convex part of the PYL that protrudes upward from the CSL line (A PYL -A CSL ) and the area A of PYL in the corresponding range of σ PYL That is, the convexity ratio (APC) is 0≦σ≦σ CSL The area of ​​the convex part of the PYL in the range (A PYL -A CSL ) PYL area A CSL It is calculated as a ratio to

[0030] Even if the initial normal load (the load applied from above) is the same, the normal stress σ at the limit state (point CS: the rightmost point of the PYL) will be different due to stress relaxation and wall friction. CSL varies depending on the sample. Therefore, the greater the stress at the CS point, the greater the A PYL -A CSL Therefore, by taking the ratio of the convex portion to the whole, it is possible to quantitatively compare the degree (degree) of convexity above the CSL between different powders.

[0031] For powders with low adhesiveness, the convexity ratio (APC = (A PYL -A CSL ) / A PYL For example, the data for sample 4 in Figure 2 is for a powder with low adhesiveness. In this case, A PYL The value of ACSL Therefore, the APC of a powder with low adhesiveness will be a relatively small value. Conversely, the APC of a powder with high adhesiveness will be a relatively large value.

[0032] (APC effectiveness) Figure 5 shows the APC values ​​for the samples shown in Figures 2 and 3. Sample 4 is a powder with low adhesion and high flowability. Figure 5 clearly shows the low adhesion of the powder in Sample 4.

[0033] Figure 6 shows the relationship between the initial normal load and APC in a shear test of a certain sample, as well as the relationship between the initial normal load and shear adhesion (the value of C in Figure 1). The shear adhesion increases as the initial normal load increases (as the void ratio decreases and the filling rate increases). On the other hand, the APC shows the opposite trend.

[0034] As the name "shear" suggests, shear adhesion is affected by friction in addition to adhesion. As the initial normal load increases, the void ratio decreases and the packing ratio increases, increasing the influence of friction on the behavior of the powder. Therefore, as the initial normal load increases, the shear adhesion increases.

[0035] In contrast, APC tends to decrease as the initial normal load increases, as shown in Figure 6. This means that APC shows the dominance of adhesion force among the effects of adhesion and friction forces.

[0036] In other words, as the initial normal load increases, the influence of frictional force increases, so the proportion of adhesive force that dominates decreases relatively, and therefore the APC value tends to decrease. Conversely, when the initial normal load is small, the influence of frictional force is small, so the proportion of adhesive force that dominates relatively increases, and the APC value increases.

[0037] In this way, APC can be used to evaluate the proportion of adhesive force that is dominant in the physical properties of powder. That is, if the APC is large, adhesive force is dominant, and if the APC is small, the influence of adhesive force is reduced and friction force is dominant.

[0038] In this way, APC can be used to estimate whether adhesion or friction is dominant in the behavior of a powder. Furthermore, because APC is defined as a ratio, it is highly reliable for comparison between different samples.

[0039] (measurement system) 7 conceptually shows a powder bed shear force measurement system 100 utilizing the present invention. The powder bed shear force measurement system 100 comprises a measurement device main body 110, a control unit 120, a UI (user interface), and a PC (personal computer) 130 that functions as a calculation unit for calculating the PYL convexity ratio (APC).

[0040] The powder bed shear force measurement system 100 performs measurements in accordance with JIS-Z8835 and calculates the various evaluation data and the APC of the present invention as described in relation to Fig. 1. The measurement device main body 110, control unit 120, and PC 130 are connected by a signal cable.

[0041] In this embodiment, the various parameters shown in Fig. 1 and the convexity ratio (APC) of the PYL are calculated in the PC 130. Here, the powder bed shear force measurement system 100 is an NS-S500 manufactured by Nano Seeds Corporation, and an operating program for calculating the convexity ratio (APC) of the PYL is installed in the part corresponding to the PC 130 (a dedicated PC attached to the product).

[0042] The measuring device main body 110 includes a servo cylinder 111 that applies a pressing load to the powder bed, a pressing load detection load cell 112 that detects the pressing load, a pestle (piston) 113 that presses the powder bed from above, an upper fixed cell 114 that contains the powder, a lower movable cell 115 that contains the powder and moves horizontally, a bottom load detection load cell 116 that detects the vertical load applied to the powder bed, a shear force detection load cell 117 that detects the shear force applied to the powder bed from the force pressing the lower movable cell 115 horizontally, and a linear actuator 118 for moving the lower movable cell 115 horizontally.

[0043] A servo cylinder 111 applies a vertical load to the powder filled in an upper fixed cell 114 and a lower movable cell 115, and the lower movable cell 115 is moved horizontally to shear the powder bed. The normal stress σ applied to the powder bed is detected by a load cell 112 for detecting the indentation load and / or a load cell 116 for detecting the bottom load. The shear stress τ applied to the powder bed is detected by a load cell 117 for detecting the shear force. YL (PYL, CYL) and CSL are measured by changing the normal stress.

[0044] (Example of operation procedure) First, the shear force of the powder to be measured is measured in the measurement device main body 110. This measurement is performed in accordance with the contents specified in JIS-Z8835. The operation of each part during this measurement is controlled by the control unit 120.

[0045] The measurement data obtained by the shear test is sent to the PC 130. Based on this measurement data, the PC 130 processes the data to obtain the various evaluation data (PYL, CSL, etc.) described in relation to Fig. 1. Furthermore, the PC 130 performs the calculation described in relation to Fig. 4 to calculate the PYL convexity ratio (APC).

[0046] (Conclusion) In this embodiment, a powder evaluation method using a limit state line (CSL) and a powder bed failure envelope (PYL) defined in JIS-Z8835 is used, and in the target powder, the integrated value of the shear stress indicated by the powder bed failure envelope (PYL) in the range of the normal stress indicated by the powder bed failure envelope (PYL) is calculated as A PYL , the integrated value of the shear stress indicated by the critical state line (CSL) in the range of the normal stress is A CSL As a parameter for evaluating the adhesion of the powder, the convexity of PYL (APC) = (A PYL -A CSL ) / A PYL According to this embodiment, a new technique for evaluating the adhesiveness of powder is provided.

[0047] 2. Second embodiment The APC of PYL can also be predicted from photographed images of the particles that make up the powder. Here, we use Partial Least Squares Regression (PLS regression), a linear regression method, to predict the APC of PYL from photographed images of the particles that make up the powder.

[0048] Specifically, the procedure is as follows: First, an SEM image (scanning electron microscope photograph) of the target powder is obtained. This SEM image is analyzed using image analysis software to determine the particle size distribution (D 10 ,D 50 ,D 90 ), convexity, circularity, linearity, aspect ratio, and surface features are calculated.

[0049] Figure 8 shows the definitions of convexity, circularity, linearity, and aspect ratio. Surface feature values ​​are parameters that indicate the degree of unevenness on the surface of the particles that make up the powder. If there are fine irregularities on the surface of a particle, the image will have a fine pattern. Surface feature values ​​are a quantitative evaluation of the fineness of this pattern.

[0050] For example, consider the pixels that make up a captured image of a particle. Images with fine patterns often have small variations in shading. Therefore, the gradation of the pixel is quantified as a pixel value, and the degree of variation depending on the location is measured to obtain a surface feature amount. The more fine irregularities there are on the surface of the particle, the larger the value of the surface feature amount. Surface feature amounts are described in detail, for example, in JP 2023-111351 A.

[0051] Surface feature quantities may be measured by extracting feature points in an image using image analysis software, where the surface feature quantity is defined as the number of feature points per unit area.

[0052] Here, we consider the particle size distribution (D 10 ,D 50 ,D 90 ), convexity, circularity, linearity, aspect ratio, and surface features are used as input variables, and machine learning is performed using training data with the actual measured values ​​of APC as output, to create a predictive model using PLS regression.

[0053] This prediction model is based on the particle size distribution (D 10 ,D 50 ,D 90 ), convexity, circularity, linearity, aspect ratio, and surface feature data are input to predict the APC of the powder.

[0054] Figure 9 is a graph showing the relationship between the predicted APC values ​​(horizontal axis) and the measured APC values ​​(vertical axis) for various powders. In addition to the PLS regression described above, various machine learning methods can be used to obtain a prediction model for predicting APC values ​​using the results of image analysis.

[0055] When this embodiment is used, the APC value can be predicted using a magnified image of the powder bed without conducting a shear test. This method is effective when the amount of sample powder is small, when the sample powder is rare, or when the sample powder is expensive.

[0056] An example of implementing this embodiment will be described below. Here, an operating program for causing a computer to execute the above prediction model and a powder particle size distribution (D 10 ,D 50 ,D 90 ), convexity, circularity, linearity, aspect ratio, and surface feature quantities are acquired. A computer is installed with the image analysis program.

[0057] Then, an SEM image of the target powder is taken, and the data of this SEM image is sent to the computer. The computer uses the installed image analysis software to calculate the particle size distribution (D 10 ,D 50 ,D 90 ), convexity, circularity, linearity, aspect ratio, and surface feature values ​​are calculated, and these parameters are input into the prediction model to obtain a predicted APC value.

[0058] 3. Third embodiment APC can also be calculated in the following way. PYL is 0≦σ≦σ CSL The PYL value is sampled at multiple sampling points within the range of A and calculated as the integrated value. CSL is 0≦σ≦σ CSL The CSL values ​​are sampled at the same sampling points as above in the range and calculated as the integrated value. Then, APC = (A PYL -A CSL ) / A PYL The APC is calculated by: Narrowing the sampling intervals can improve accuracy. It is preferable to have equal sampling intervals.

Claims

1. A powder evaluation method using the critical state line (CSL) and powder bed failure envelope (PYL) defined in JIS-Z8835, In the target powder, The integrated value of the shear stress indicated by the powder bed failure envelope in the range of the normal stress indicated by the powder bed failure envelope is defined as A ＰＹＬ , The integrated value of the shear stress indicated by the limit state line in the range of the normal stress is A ＣＳＬ As, As a parameter for evaluating the adhesion of the powder, (A ＰＹＬ -A ＣＳＬ ) / A ＰＹＬ A powder evaluation method that calculates the

2. A powder evaluation method using a prediction model obtained by machine learning, The prediction model is based on the particle size distribution (D １０ , D ５０ , D ９０ ), convexity, circularity, linearity, aspect ratio, and the relationship between surface features and specific parameters are obtained by machine learning. The specific parameters are: In the critical state line (CSL) and powder bed failure envelope (PYL) specified in JIS-Z8835, The integrated value of the shear stress indicated by the powder bed failure envelope in the range of the normal stress indicated by the powder bed failure envelope is defined as A ＰＹＬ , The integrated value of the shear stress indicated by the limit state line in the range of the normal stress is A ＣＳＬ As, (A ＰＹＬ -A ＣＳＬ ) / A ＰＹＬ A powder evaluation method defined by

3. A powder evaluation system using the critical state line (CSL) and powder bed failure envelope (PYL) defined in JIS-Z8835, In the target powder, The integrated value of the shear stress indicated by the powder bed failure envelope in the range of the normal stress indicated by the powder bed failure envelope is defined as A ＰＹＬ , The integrated value of the shear stress indicated by the limit state line in the range of the normal stress is A ＣＳＬ As, As a parameter for evaluating the adhesion of the powder, (A ＰＹＬ -A ＣＳＬ ) / A ＰＹＬ A powder evaluation system comprising a calculation unit that calculates:

4. A program for causing a computer to execute evaluation of powder using the critical state line (CSL) and powder bed failure envelope (PYL) defined in JIS-Z8835, In the target powder, The integrated value of the shear stress indicated by the powder bed failure envelope in the range of the normal stress indicated by the powder bed failure envelope is defined as A ＰＹＬ , The integrated value of the shear stress indicated by the limit state line in the range of the normal stress is A ＣＳＬ As, As a parameter for evaluating the adhesion of the powder, (A ＰＹＬ -A ＣＳＬ ) / A ＰＹＬ A program that causes a computer to execute a process to calculate

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