Method of feeding powder material in laser powder cladding and device implementing it

Abstract

FIELD: laser technology.SUBSTANCE: group of inventions is proposed, comprising a method for feeding powder material during laser powder cladding and a device for implementing the proposed method. The gravitational flow of powder into the laser impact zone is activated through a nozzle attachment that forms a flow of outflowing powder and is connected to a container with powder. Said activation is carried out by means of vibrations of the nozzle attachment and the container along the axis of the nozzle attachment. The vibrations are caused by an ultrasonic piezoceramic activator, excited by applying electrical oscillations to it at its resonant frequency, modulated in amplitude by a low-frequency periodic rectangular signal. The frequency of the modulating signal is within the audio range of 20 Hz - 15 kHz. Said device for feeding powder material includes a powder container connected to said nozzle, an ultrasonic piezoelectric activator and a holder for securing said device to the transfer system. An ultrasonic piezoceramic activator is installed between said holder and the powder container and is designed to create ultrasonic vibrations of said nozzle attachment and container along the axis of the nozzle attachment.EFFECT: increase in the stability of the powder flow in ultrasonic powder feed devices by its gravitational flow without the use of additional low-frequency vibrators and without scattering the powder jet at the nozzle outlet.2 cl, 3 dwg

Description

[0001] The invention relates to the field of powder metallurgy and additive technologies and can be used in laser powder cladding, including in the additive manufacturing of products from powder materials.

[0002] There are several known methods for feeding powder materials into the laser action zone during laser powder cladding: side feed, multi-jet and coaxial powder feed [Zlenko M.A. Additive technologies in mechanical engineering / M.V. Nagaytsev, V.M. Dovbysh / / manual for engineers. - M. SRC RF FSUE "NAMI" 2015. 220 p.]. Powder is fed into the cladding zone in multi-jet nozzle attachments by a flow of transport gas propagating in internal transport channels, and in coaxial nozzle attachments - in the gap between the guide cones. For precision powder feed, the diameter of the internal transport channels and the width of the gap between the cones are made as small as possible. However, after exiting the nozzle, the gas-powder submerged jet gradually becomes turbulent, which leads to dispersion of the powder flow and, ultimately, to a decrease in the material utilization rate, accuracy and productivity of powder surfacing.An additional contribution to the dispersion of the powder flow is made by the different aerodynamics of non-spherical powder particles, which leads to a deviation of their trajectory from the flow lines of the transport gas.

[0003] A known method of vibrational feeding of powder material into the laser cladding zone [W. Wang and L. Li High-quality high-material-usage multiple-layer laser deposition of nickel alloys using sonic or ultrasonic vibration powder feeding / / Proc. IMechE Vol. 225 Part B: J. Engineering Manufacture P.130-139], which uses the gravitational flow of powder through a nozzle activated by vibrations of the container with powder in the sonic or ultrasonic (US) frequency range. When using piezoceramic activators (ultrasonic oscillators) as a source of ultrasonic vibrations, it is necessary to keep in mind that they operate effectively only in a narrow frequency range near their natural resonant frequency. When the frequency of the exciting electrical oscillation shifts from resonance, the efficiency of the emitter decreases sharply. Therefore, such oscillation sources are predominantly single-frequency (in some cases, dual-frequency) and do not allow a smooth change in the radiation frequency.

[0004] A powder dosing system for laser cladding [Wei C., Gu H., Zhang X., Chueh Y., Li L. Hybrid ultrasonic and mini-motor vibration-induced irregularly shaped powder delivery for multiple materials additive manufacturing / / Additive Manufacturing. – 2020. – Vol. 33. – 101138] is known, implementing a dual effect on the powder – ultrasonic and sonic vibrations. An ultrasonic generator ensured the unimpeded gravitational flow of powder through the nozzle capillary. An additional vibration source generated by a miniature vibration motor was used to break up agglomerated powder particles near the transition between the powder hopper and the capillary inlet. It was found that the hybrid dual-frequency action on the powder in the ultrasonic and sonic range provides a more stable feed than that caused by ultrasonic action alone and avoids interruption of the powder flow.A disadvantage of this dual-action powder dosing system is the need for two emitters—one for the ultrasonic and one for the audio frequency ranges. Furthermore, the use of a vibration motor, which generates low-frequency vibrations in the dosing system housing, can lead to transverse vibrations of the free end of the powder feed capillary, increasing dispersion of the powder jet at the capillary outlet and reducing deposition accuracy.

[0005] It is known [Handbook of theoretical foundations of radio electronics edited by B.Kh. Krivitsky, Moscow: Energy, 1977, Vol. 2, p. 128] that in the frequency spectrum of a high-frequency oscillation, amplitude-modulated (AM) by a periodic low-frequency rectangular signal, there is both the frequency of the carrier high-frequency oscillation, and the frequency of the modulating signal and their combined frequencies.

[0006] The technical task, which the proposed technical solution is aimed at, is to increase the stability of the powder flow in ultrasonic powder feed devices by means of its gravitational flow without the use of additional low-frequency vibrators and without scattering the powder jet at the nozzle outlet.

[0007] The technical result of the proposed method for feeding powder material during laser powder cladding consists of the gravitational flow of powder into the laser action zone through a capillary connected to a container with powder, the flow of powder is activated by vibrations of the capillary and container caused by an ultrasonic activator excited by the supply of electrical oscillations to it at its resonant frequency, which are modulated in amplitude by a low-frequency periodic rectangular signal, wherein the frequency of the modulating signal can vary within the audio range of 20 Hz - 15 kHz.

[0008] The technical result of the proposed device for feeding powder material during laser powder cladding, including a capillary connected to a container with powder, a piezoelectric vibrator that creates ultrasonic vibrations of the capillary and container along the axis of the capillary, characterized in that electrical vibrations are fed to the piezoelectric vibrator at its resonant frequency, which are modulated in amplitude by a low-frequency periodic rectangular signal, wherein the frequency of the modulating signal can vary within the audio range of 20 Hz - 15 kHz.

[0009] Figure 1 schematically illustrates the essence of the proposed method for feeding powder material during laser powder cladding. Capillary 1, forming a flow of freely flowing powder 2, is connected to container 3 for powder material 4. Between holder 5, securing the powder material feeding device to the movement system (not shown in the figure) and container 3, an ultrasonic activator (for example, in the form of piezoceramic plates) 6 is installed, oscillating along the axis of nozzle attachment 1. An AM signal 7 is fed to ultrasonic activator 6, with a carrier frequency Fp corresponding to the resonant frequency of the activator and modulated by rectangular pulses with an audio frequency Fz in the range from 20 Hz to 15 kHz, wherein the modulation frequency can be varied.

[0010] Let us consider the operation of a device for feeding powder material during laser powder cladding. The device is fixed with a holder 5 on a three-coordinate movement system in such a way that the axis of the capillary 1 is oriented vertically. Container 3 is filled with powder material 4. The positioning device positions the capillary 1 above the starting point of the cladding trajectory, an AM signal 7 is supplied to the ultrasonic activator 6, as a result of which the powder in the container 3 passes into a fluidized state and begins to flow out of the end of the capillary 1 under the action of gravity, forming a powder jet 2. If we perform a Fourier transform of the AM signal 7 (Fig. 1) supplied to the ultrasonic activator 6, then its frequency spectrum is obtained. As an example, Fig. 2b shows the frequency spectrum of the AM signal for a carrier frequency of Fp = 33 kHz and a modulation frequency of Fz = 500 Hz. It is obtained by Fourier transforming the AM signal shown in Fig. 2a.It contains oscillations with a carrier frequency corresponding to the resonant frequency Fр of ultrasonic activator 6, as well as a modulation frequency Fз, the sum Fр + Fр and difference Fр - Fр frequencies, as well as harmonics of the modulation frequency. When the modulation frequency Fз changes, the frequency of ultrasonic oscillations (carrier frequency Fр) will not change; only the frequency of the sound impact and its harmonics will change. This guarantees maximum efficiency of ultrasonic vibration emission at the resonant frequency of ultrasonic activator 6. Thus, it is possible to select the most optimal frequency of sound impact on the powder located in container 3 and in the transition zone between container 3 and capillary 1, without degrading the efficiency of ultrasonic impact on the powder in capillary 1.

[0011] The result of the powder feed device operation during laser powder cladding is shown in Fig. 3, which shows images of powder flow 2 gravitationally flowing out of capillary 1, with ultrasonic activation of the powder flow at the resonant frequency of the piezoceramic activator of 33 kHz without modulation (a) and with amplitude modulation of ultrasonic oscillations of a frequency of 33 kHz by rectangular pulses with an audio frequency of 500 Hz (b). Fig. 3a shows that the powder is fed into the capillary non-uniformly, in portions, which indicates that the powder is stuck in the transition zone from container 3 to capillary 4. Single-frequency ultrasonic action does not allow for the destruction of powder particle agglomerates in the transition zone and ensures uniform powder feed into the capillary.When amplitude-modulated oscillations are applied to the ultrasonic activator, the powder flow becomes stable, the powder particle flow density increases threefold, and the powder flow has clear spatial boundaries. Thus, the presence of audio-frequency oscillations in the ultrasonic activator's frequency spectrum effectively prevents powder agglomeration in the transition zone between the powder container and the capillary, thereby ensuring stable gravitational powder flow from the capillary. The proposed method and the device implementing it simplify the powder feed system compared to the prototype, eliminating the vibration motors for low-frequency powder activation.Since the ultrasonic activator, unlike the vibration motor, generates vibrations of the powder container and capillary only in the direction along the axis of the capillary, additional low-frequency vibrations in the sound range will not cause transverse vibrations of the free end of the capillary and, thus, will not lead to a broadening of the powder flow.

Claims

1. A method for feeding powder material during laser powder cladding, which includes activating the gravitational flow of powder into the laser action zone through a nozzle attachment that forms a flow of outflowing powder and is connected to a container with the powder, characterized in that said activation is carried out by means of vibrations of the nozzle attachment and the container along the axis of the nozzle attachment, caused by an ultrasonic piezoceramic activator excited by feeding it electrical oscillations at its resonant frequency, modulated in amplitude by a low-frequency periodic rectangular signal, wherein the frequency of the modulating signal is within the audio range of 20 Hz - 15 kHz.

2. A device for feeding powder material during laser powder cladding, comprising a powder container connected to a nozzle attachment that forms a flow of outflowing powder, an ultrasonic piezoelectric activator and a holder for securing said device on a movement system, characterized in that the ultrasonic piezoceramic activator is installed between said holder and the powder container and is designed to create ultrasonic vibrations of said nozzle attachment and container along the axis of the nozzle attachment when electrical vibrations are fed to said ultrasonic piezoceramic activator at its resonant frequency, which are modulated in amplitude by a low-frequency periodic rectangular signal, wherein the frequency of the modulating signal is within the audio range of 20 Hz - 15 kHz.

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