A method for detecting electrical properties of metal powder based on capacitance

Abstract

The present invention discloses a method for detecting the electrical properties of metal powder based on capacitance. It mainly solves the technical problem that the performance changes of metal powder recycled and reused in additive manufacturing are difficult to detect accurately and online; the key points of its technical solution are: utilizing the characteristic that the electrical properties of metal powder change with different times of use, the dielectric constant and conductivity of the metal powder are detected based on the capacitance effect. In this method, a capacitor is placed in the metal powder circulation path, and the capacitor's plates are connected to the capacitance measurement circuit; when the metal powder passes through the capacitor, a voltage signal is generated in the capacitance measurement circuit, and the capacitance generated when the metal powder acts as the dielectric of the capacitor can be calculated based on the signal; then, based on the relationship between the capacitance and the dielectric spectrum of the medium, the dielectric spectrum of the metal powder ε=ε′‑jε″ is obtained, where ε′ is the dielectric constant; finally, the conductivity σ of the metal powder can be calculated from the conductivity relationship σ=ωε0ε″.

Description

Technical Field

[0001] The invention relates to a capacitance-based metal powder electrical property detection method, belonging to the technical field of metal powder electrical parameter testing. Background Art

[0002] Additive manufacturing, as an emerging technology, can produce a wide range of high-value metal parts while shortening development cycles, holding great promise for future applications in the manufacturing sector. Metal powder, the raw material for additive manufacturing, is recycled and reused during the manufacturing process. After one or more printing cycles, different types of powder exhibit varying performance changes. To ensure that part performance matches production standards, it is essential to monitor these changes in the recycled powder.

[0003] To address these issues, metal powders have been tested using a variety of methods, including chemical and mechanical methods. For example, the invention patent application with publication number CN213103175U discloses a metal powder detection device for 3D printed parts. This invention uses a mechanical device to screen the powder particle size. However, this contact detection method has a complex structure and can only detect the particle size of metal powders, but not other parameters.

[0004] At present, the metal powder detection method is still mainly based on contact detection. The laser induction method is a non-contact detection method. Compared with traditional mechanical detection, it can avoid the problem of filter clogging during the detection process of the detection instrument. For example, the invention patent application with publication number CN105136752A discloses an online powder detection device based on laser-induced breakdown spectroscopy. The invention uses laser to break down the powder sample to form a plasma. The plasma emission spectral line signal is collected by the collection lens and optical fiber through the sample chamber window lens. After being introduced into the spectrometer, the powder type and concentration characteristics are obtained through spectral analysis. However, this method requires sampling and testing in the laboratory, which makes it difficult to achieve online detection and the detection cost is high.

[0005] Conductivity and dielectric constant, as electrical properties of metal powder, will change during the repeated use of metal powder. By taking advantage of the characteristics of metal powder's electrical properties changing during repeated use, the quality of metal powder in the additive manufacturing process can be monitored online. However, during the additive manufacturing process, there are large gaps between the particles of metal powder in the circulation path, and the volume and mass of metal powder passing through the circulation path per unit time are also different. Therefore, conventional detection methods based on voltage, resistance, etc. cannot effectively detect the electrical properties of metal powder. For this reason, people urgently need a low-cost method that can quickly detect the electrical properties of metal powder online. Summary of the Invention

[0006] One purpose of the present invention is to overcome the above-mentioned shortcomings of the method for detecting the electrical properties of metal powder in the additive manufacturing process, and to provide a capacitance-based method for detecting the electrical properties of metal powder. The method has the following advantages: the detection process is online detection, which improves the detection efficiency; the conductivity and dielectric constant of the metal powder in the additive manufacturing process can be detected simultaneously, and the detection data is comprehensive; the system requires less software and hardware and has a higher degree of integration.

[0007] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0008] A method for detecting the electrical properties of metal powder based on capacitance includes the following specific steps:

[0009] Step 1: Place a capacitor in the metal powder circulation path and connect the two plates of the capacitor to an AC capacitance measurement circuit.

[0010] Step 2: The host computer controls the signal generator to generate an excitation signal U with a radial frequency of ω i (t) = sin(ωt), connected to the input of the capacitance measurement circuit. When the metal powder passes through the capacitor, a voltage signal U is generated in the capacitance measurement circuit. o (t);

[0011] Step 3: Perform data calculation in the host computer. 测 =kU o (t), and the measured capacitance C related to the electrical properties of the metal powder is obtained 测 , where k is the gain of the capacitance measurement circuit. Get the edge capacitance C of the capacitor 边 , where: D is the diameter of the capacitor plate, in meters; t is the thickness of the capacitor plate, in meters; d is the distance between the capacitor plates, in meters; ε0 is the dielectric constant of vacuum, which is equal to 8.854187817×10 - 12 F / m. According to Get the actual capacitance C of the capacitor 实 , where: j is the imaginary unit; θ is the capacitor impedance phase angle, in rad. Finally, according to The dielectric spectrum of the metal powder is obtained as ε = ε'-jε";

[0012] The calculation steps for the capacitor impedance phase angle θ are as follows:

[0013] In the capacitance measurement circuit integrated with the phase angle detection circuit, the acquisition card simultaneously collects the voltage signal U(t) and current signal I(t) at both ends of the capacitor plate. The host computer calculates the voltage signal U(t) and current signal I(t) according to the formula Obtain the impedance phase angle θ;

[0014] Step 4: Analyze the dielectric spectrum ε in the host computer to obtain the real part ε′ and the imaginary part -ε″. ε′ is the dielectric constant of the metal powder, in F / m. Then, according to σ=ωε0ε″, the conductivity σ of the metal powder can be calculated, in S / m;

[0015] Step 5: Based on the calculation results, the host computer displays the values ​​of dielectric constant and conductivity, which are the test results of the electrical properties of the metal powder.

[0016] Compared with the prior art, the present invention adopts the above technical solution and has the following technical effects:

[0017] (1) The detection process is online, which is more efficient than traditional mechanical methods;

[0018] (2) The electrical conductivity and dielectric constant of metal powders in the additive manufacturing process can be detected simultaneously. Unlike general detection methods, the detection parameters of the present invention are more comprehensive;

[0019] (3) Compared with the laser induction method for detecting powder quality, this system requires less hardware and software and has a higher degree of integration; BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 Flow chart of the method of the present invention.

[0021] Figure 2 It is a schematic diagram of the structure of the device of the present invention. DETAILED DESCRIPTION

[0022] The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments:

[0023] The electrical properties of metal powder are tested, and the schematic diagram of the device is shown as follows: Figure 2 As shown, it includes: host computer 1, signal generator 2, capacitance measurement circuit 3, acquisition card 4, circular plate capacitor 5 and metal powder 6. The measurement steps are as follows Figure 1 As shown, the following specific steps are included:

[0024] Step 1: Place the circular plate capacitor 5 of the system in the circulation path of the metal powder 6, and connect the two circular plates of the capacitor to the capacitance measurement circuit 3;

[0025] Step 2: The host computer 1 controls the signal generator 2 to generate an excitation signal U with a radial frequency of ω i (t) = sin(ωt), which is connected to the input of the capacitance measurement circuit 3. When the metal powder 6 passes through the circular plate capacitor 5, a voltage signal U is generated in the capacitance measurement circuit 3. o (t);

[0026] Step 3: Perform data calculation in host computer 1. 测 =kU o (t), and obtain the measured capacitance C related to the electrical characteristics of the metal powder 6 测 , where k is the gain of the capacitance measurement circuit 3. Get the edge capacitance C of the capacitor 边 , where: D is the diameter of the capacitor plate, in meters; t is the thickness of the capacitor plate, in meters; d is the distance between the capacitor plates, in meters; ε0 is the dielectric constant of vacuum, which is equal to 8.854187817×10 -12 F / m. According to Get the actual capacitance C of the capacitor 实 , where: j is the imaginary unit; θ is the capacitor impedance phase angle, in rad. Finally, according to The dielectric spectrum of the metal powder is obtained as ε = ε'-jε";

[0027] The calculation steps for the capacitor impedance phase angle θ are as follows:

[0028] In the capacitance measurement circuit 3 integrated with the phase angle detection circuit, the acquisition card simultaneously collects the voltage signal U(t) and current signal I(t) at both ends of the capacitor plate. The host computer uses the formula: Obtain the impedance phase angle θ;

[0029] Step 4: Analyze the dielectric spectrum ε in the host computer 1 to obtain the real part ε′ and the imaginary part -ε″. ε′ is the dielectric constant of the metal powder 6, in F / m. Then, according to σ=ωε0ε″, the electrical conductivity σ of the metal powder 6 can be calculated, in S / m;

[0030] Step 5: The host computer 1 displays the values ​​of the dielectric constant and the conductivity based on the calculation results, which are the detection results of the electrical characteristics of the metal powder 6.

[0031] The above description is only a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any person familiar with the technology can understand and think of any changes or replacements within the technical scope disclosed by the present invention, which should be included in the scope of the present invention. Therefore, the scope of protection of the present invention should be based on the scope of protection of the claims.

Claims

1. A method for detecting the electrical properties of metal powder based on capacitance, characterized in that: The specific steps include: Step 1: Place a capacitor in the metal powder circulation path and connect the two plates of the capacitor to an AC capacitance measurement circuit. Step 2: The host computer controls the signal generator to generate an excitation signal U with a radial frequency of ω i (t) = sin(ωt), connected to the input of the capacitance measurement circuit; when the metal powder passes through the capacitor, a voltage signal U is generated in the capacitance measurement circuit o (t); Step 3: Perform data calculation in the host computer; according to C 测 =kU o (t), and the measured capacitance C related to the electrical properties of the metal powder is obtained 测 , where k is the gain of the capacitance measurement circuit; according to Get the edge capacitance C of the capacitor 边 , where: D is the diameter of the capacitor plate, in meters; t is the thickness of the capacitor plate, in meters; d is the distance between the capacitor plates, in meters; ε0 is the dielectric constant of vacuum, which is equal to 8.854187817×10 - 12 F / m; according to Get the actual capacitance C of the capacitor 实 , where: θ is the capacitor impedance phase angle, in rad; j is the imaginary unit; finally, according to The dielectric spectrum of the metal powder is obtained as ε = ε'-jε"; Step 4: Analyze the dielectric spectrum ε in the host computer to obtain the real part ε′ and the imaginary part -ε″; ε′ is the dielectric constant of the metal powder, in F / m; then, according to σ=ωε0ε″, calculate the conductivity σ of the metal powder, in S / m; Step 5: Based on the calculation results, the host computer displays the values ​​of dielectric constant and conductivity, which are the test results of the electrical properties of the metal powder.

2. The method for detecting electrical properties of metal powder based on capacitance according to claim 1, characterized in that: The capacitor plates in step 1 are circular plates.

3. The method for detecting electrical properties of metal powder based on capacitance according to claim 1, characterized in that: The excitation signal in step 2 is a sinusoidal voltage signal.

Images