Sphericity Detection Technology of High Quality 3D Printing Powder

Author: Ivy Li, Bill Tang, Will Wang 2017-03-14

Abstract: The paper introduces a method to analysis the degree of sphericity of 3D metal powder by SEM image and IPP software

Key word: Roundness, Particle Shape, SEM Image, IPP Software

3D printing requires high flowability metal powders with particle spherical shape which will effects the metal powder flowability and bulk property. Recently, the main analysis method to measure degree of sphericity is by SEM, but it is hard to be quantification. So the quantification is must during the analysis of degree of sphericity.

1. Theory

1.1 Definition

The degree of sphericity is the ratio between the equivalent diameter of particle perimeter and equivalent diameter of particle area. This definition is 2-dimention description.

                                                                     （1）

d1 is the equivalent diameter of particle perimeter, set the perimeter as l, then l = 2πd1

da is the equivalent diameter of particle area, set the area as A, then A = πda^2

1.2 SEM for Sample Particle

The SEM theory, an electron beam with diameter between 20µm to 30µm is emitted from an electron gun. Then the beam is accelerated by the voltage to be focused by condenser lenses to a spot about 0.4 to 5 nm in diameter. The beam passes through scanning coils of deflector plates so that it scans in a raster fashion of the sample surface and activate many electronic signals. These signals are amplified by various types of electronic amplifiers and displayed as variations in brightness on the computer monitor.  Each pixel of computer video memory is synchronized with the position of the beam on the specimen in the microscope, and the resulting image is therefore a distribution map of the intensity of the signal being emitted from the scanned area of the sample.

Use SME can get the surface characters of different particles with different magnification times.

1.3 IPP Software

The full name of IPP software is Image-Pro Plus, which is widely used in medical science, medical treatment, pharmacy and bioscience areas. With the functions of counting and measuring, the software can divide the SEM with light and shade, then measure them to get the sorting and statistics automatically, which improves the efficiency greatly. This method can realize the rapid division of SEM particles, exclusion of incomplete particles, and calculation of equivalent diameters of complete particles based on their area and perimeter. Then we get the degree of particle sphericity by formula (1).

2.   The Methods of Measuring and Data Analysis

2.1 Method of Measuring

According to formula (1), the degree of sphericity can be calculated based on the particle perimeter and area, furthermore, the whole SEM degree of particle can be calculated.

Below provides 2 SEMs, they locates different positions with the same magnification times. It is likely that B is better than A before quantitation analysis.

Use the IPP software to divide the SEM and get the pictures below:

Calculate the ratio between equivalent diameter of particle perimeter and equivalent diameter of particle area by the software. Image 3-a and 3-b show the average sphericity of degree and average deviation for A and B. And we can find that the sphericity of degree for A is better than B due to the quantitative index.

3. Conclusion

This articleis based on the theory of 2D degree of sphericity, and combined with SEM and IPP software, to represent the degree of particle sphericity. This method has provided a way to quantitate the particle sphericity, so it is valuable for popularized application.

References:

1. Image-Pro+Plus+6.0+Official Chinese Reference Manual

2. Allen T， Particle Size Measurement(4^th)[M], New York: Chapman & Hall, 1990.127-179