FIELD OF THE INVENTION

The present disclosure discloses a fluid jet polishing technique. Particularly, the present disclosure is about an acoustophoresis-assisted fluid jet polishing/machining device. BACKGROUND

Fluid Jet Polishing (FJP) is a versatile procedure of impinging a surface with abrasive particles using a carrier fluid jet, where the kinetic energy of abrasive particles removes material from the required area. The process is easily controllable and leads to the development of a stable footprint. Different materials like glasses, ceramics, and metals can be efficiently polished using the FJP. In this procedure, pressurized carrier fluid with the abrasive particles is issued from a nozzle and impacted on a workpiece to polish or generate desired patterns on it. This procedure produces sub-millimetre footprints and is free from external influences, such as tool contact. Thus, it is convenient to obtain proper surface patterns without increasing the surface roughness.

The procedure is easily controllable to have material removal rates in the order of a few nanometres per minute, making it suitable for polishing optical components made of glass. In order to optimally attain such benefits, it is essential to understand the influence of various parameters that affect the procedure. Generally, it is known that the surface roughness of the workpiece is independent of the incident angle of the FJP. However, the material removal rate from the workpiece depends on the incident angle as the developed pressure field on the workpiece is not the same for all angles.

Interestingly, the abrasive particle sizes also govern the material removal rate. Larger particles deviate from the trajectory of the carrier fluid jet, thereby causing a straight-line impact, whereas the smaller particles faithfully follow the fluid jet. In addition, the hardness of the abrasive particles also affects the surface finish of the workpiece. For example, silicon carbide, having higher hardness than cerium oxide, has a greater tendency to produce pits on the surface of the workpiece. Thus, particles with lower hardness and smaller size help generate a better surface finish on the workpiece. However, the trajectory of the smaller particles is governed by the unpredictable nature of the impinging carrier fluid jet. This poses a serious problem in arriving at an optimal nozzle path to remove material from the workpiece to ensure polishing of the surface, as the material removal rate varies with the movement of the FJP nozzle. Further, the impinging jet has a stagnation zone. The stagnation zone is devoid of impact by the abrasive particles and hence, the material removal process becomes spatially inhomogeneous. Further, the trajectory of the abrasive particles typically adheres to flow streamlines. Thus, most abrasive particles escape without impacting/interacting with the target area, resulting in a low material removal rate. Another problem associated with the conventional FJP is that the impact of abrasive particles is random on the workpiece, mainly owing to the turbulent nature of the carrier fluid jet. This leads to inhomogeneous material removal and produces undesired patterns on the workpiece. Moreover, this also creates a problem of nozzle wall erosion which ultimately affects the repeatability of the machining/poli shing process.

One can improve the machining rate by increasing the nozzle's inlet pressure and the abrasive particles' size. However, this decreases the surface finish of the targeted area. In this regard, many solutions have been proposed, for instance, utilization of multiple jets, air ventilation, pulsating water jet, etc. However, the water jet machining is unsuitable for precision polishing because of the instability of the carrier fluid jet, which makes the impact asymmetric and the material removal inhomogeneous.

Another known art discloses 'an air-driving fluid jet polishing' system, which uses an air/water mixer to draw a slurry/mixture of the abrasive particles and the carrier fluid. Compressed air improves the abrasive particles' kinetic energy, making it more efficient in material removal. However, this system has disadvantages as the compressed air may break the carrier jet plume which results in a loss of process stability and poor surface finish.

Another known art discloses an air-assisted FJP. The main issue with air-assisted FJP is the lack of control over the size and number of bubbles to be injected into a stream of the carrier fluid jet. To overcome the problem associated with the air-assisted FJP, an ultrasonic cavitation-assisted FJP has been suggested. In the ultrasonic cavitation-assisted FJP, the size and the number of micro-bubbles are controlled through the frequency and the intensity of the ultrasonic generator. Ultrasonic assistance is provided to make the jet pulsatile, this helps in enhancing the impact force due to the water hammer effect. Similarly, ultrasonic vibration of the nozzle enhances the mixing of the abrasive particles to improve the material removal rate. One can also vibrate the target surface using ultrasonics to alter the particle impact process in the stagnation zone, which results in a better material removal rate and a smoother surface. However, the above-mentioned ultrasonic-assisted FJPs also have limitations, i.e., they do not improve the controllability of the overall process. Hence, there is a need to provide a Fluid Jet Polishing (FJP) device that ensures homogeneous material removal from a workpiece while overcoming the abovementioned problems.

SUMMARY

This summary is provided to introduce a selection of concepts in a simplified manner. Further information is provided in the ‘detailed description’ section of this document. This summary is neither intended to identify key/essential inventive concepts of the invention nor is it intended for determining the scope of the invention.

The present disclosure aims to provide a Fluid Jet Polishing device that ensures homogeneous material removal from a workpiece by using abrasive particles mixed with carrier fluids under the influence of an acoustophoresis.

The present disclosure relates to a Fluid Jet Polishing (FJP) device for a workpiece. The FJP includes a mixer, a nozzle, and an acoustic transducer. The mixer is adapted to mix a carrier fluid with abrasive particles. The nozzle is connected with the mixer and adapted to create a jet stream of the mixture. The acoustic transducer is disposed around a radius of the nozzle. The acoustic transducer is adapted to generate standing acoustic waves perpendicular to a path of mixture flow within the nozzle to align the abrasive particles along a centerline of the jet stream.

In an embodiment, the present disclosure relates to a nozzle unit including a nozzle and an acoustic transducer. The nozzle is connected to a mixer and adapted to create a jet stream of a mixture of a carrier fluid with abrasive particles. The acoustic transducer is disposed around a radius of the nozzle. The acoustic transducer is adapted to generate standing acoustic waves perpendicular to a path of mixture flow within the nozzle to align the abrasive particles along a centerline of the jet stream.

According to the present disclosure, the operation of the acoustophoresis-assisted FJP device reduces the machining/polishing footprints to the order of abrasive particles’ size. Since the abrasive particles are actively pushed away from a nozzle wall, the erosion-related damages, generally seen in the nozzles, are minimized. Also, acoustophoresis provides an additional means of controlling the machining/polishing process, i.e., it brings in the ability to attain any erosion profile ranging between W-shape and U-shape. Transient control of the acoustophoresis also helps in developing desired surface patterns. In the current technique of acoustophoresis-assisted FJP, the impedance contrast between the abrasive particles and the carrier fluid is used to migrate the abrasive particles without modifying the dynamics of an impinging fluid jet. This essentially distinguishes the present disclosure from a known art involving ultrasonic-assisted FJP, where the ultrasound vibrations were directly imposed on the nozzle wall, and the intention was not to redistribute the abrasive particles within the fluid jet.

To further clarify the advantages and features of the present disclosure, a more particular description of the invention will be provided with reference to specific embodiments thereof, which is illustrated in the appended drawings. It is understood that these drawings depict only typical embodiments of the invention and are therefore not to be considered limiting of its scope. The invention will be described and explained with additional specificity and detail with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features, aspects, and advantages of the present disclosure will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein:

Figure 1A illustrates an assembled view of a conventional Fluid Jet Polishing (FJP) device;

Figure IB illustrates particle tracks obtained from a simulation of the conventional FJP device;

Figure 1C illustrates a distribution of material removal rate in the conventional FJP device;

Figure 2A illustrates an assembled view of an FJP device with an acoustic transducer, in accordance with an embodiment of the present disclosure;

Figure 2B illustrates particle tracks obtained from a simulation of the FJP device, in accordance with an embodiment of the present disclosure;

Figure 2C illustrates a spatial distribution of material erosion rate, in accordance with an embodiment of the present disclosure; and

Figure 2D illustrates a prediction of the material erosion rate, in accordance with an embodiment of the present disclosure.

Further, skilled artisans will appreciate that elements in the drawings are illustrated for simplicity and may not have necessarily been drawn to scale. Furthermore, in terms of the construction of the device, one or more components of the device may have been represented in the drawings by conventional symbols. The drawings may show only those specific details pertinent to understanding the embodiments of the present disclosure so as not to obscure the drawings with details that will be readily apparent to those of ordinary skill in the art having the benefit of the description herein.

DETAILED DESCRIPTION OF THE FIGURES

For the purpose of promoting an understanding of the principles of the invention, reference will now be made to the embodiment illustrated in the drawings, and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended, such alterations and further modifications in the illustrated system, and such further applications of the principles of the invention as illustrated therein being contemplated as would normally occur to one skilled in the art to which the invention relates. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skilled in the art to which invention belongs. The system and examples provided herein are illustrative only and not intended to be limiting.

It should be appreciated by a person skilled in the art that the terminology and structure employed herein are for describing, teaching, and illuminating some embodiments and their specific features and elements and, therefore, should not be construed to limit, restrict or reduce the spirit and scope of the present disclosure in any way.

For example, any terms used herein such as “includes,” “comprises,” “has,” “consists,” and similar grammatical variants do not specify an exact limitation or restriction and certainly do not exclude the possible addition of one or more features or elements, unless otherwise stated. Further, such terms must not be taken to exclude the possible removal of one or more of the listed features and elements unless otherwise stated, for example, by using the limiting language including, but not limited to, “must comprise” or “needs to include.”

Whether or not a certain feature or element was limited to being used only once, it may still be referred to as “one or more features” or “one or more elements” or “at least one feature” or “at least one element.” Furthermore, the use of the terms “one or more” or “at least one” feature or element does not preclude there being none of that feature or element unless otherwise specified by limiting language including, but not limited to, “there needs to be one or more...” or “one or more elements is required.”

Unless otherwise defined, all terms, especially any technical and/or scientific terms used herein, may be taken to have the same meaning as commonly understood by a person ordinarily skilled in the art. Reference is made herein to some “embodiments.” It should be understood that as per one embodiment is an example of a possible implementation of any features and/or elements of the present disclosure. Some embodiments have been described for the purpose of explaining one or more of the potential ways in which the specific features and/or elements of the proposed disclosure fulfill the requirements of uniqueness, utility, and nonobviousness.

Use of the phrases and/or terms including, but not limited to, “a first embodiment,” “a further embodiment,” “an alternate embodiment,” “one embodiment,” “an embodiment,” “multiple embodiments,” “some embodiments,” “other embodiments,” “a further embodiment,” “furthermore embodiment,” “additional embodiment” or other variants thereof do not necessarily refer to the same embodiments. Unless otherwise specified, one or more particular features and/or elements described in connection with one or more embodiments may be found in one embodiment, or may be found in more than one embodiment, or may be found in all embodiments, or may be found in no embodiments. Although one or more features and/or elements may be described herein in the context of only a single embodiment, or in the context of more than one embodiment, or in the context of all embodiments, the features and/or elements may instead be provided separately or in any appropriate combination or not at all. Conversely, any features and/or elements described in the context of separate embodiments may alternatively be realized as existing together in the context of a single embodiment.

Any particular and all details set forth herein are used in the context of some embodiments and, therefore, should not necessarily be taken as limiting factors to the proposed disclosure.

Embodiments of the present disclosure will be described below in detail with reference to the accompanying drawings.

For the sake of clarity, the first digit of a reference numeral of each component of the present disclosure is indicative of the Figure number, in which the corresponding component is shown. For example, reference numerals starting with the digit “1” are shown at least in Figure 1. Similarly, reference numerals starting with the digit “2” are shown at least in Figure 2.

Figure 1A illustrates an assembled view of a conventional Fluid Jet Polishing (FJP) device 100. Figure IB illustrates particle tracks obtained from a simulation of the conventional FJP device 100. Figure 1C illustrates a distribution of material erosion rate obtained in the conventional FJP device.

Referring to Figures 1 A to 1C, in the conventional FJP device 100, the mixer 101 mixes the abrasive particles with the carrier fluid and is transmitted to the nozzle 102. The nozzle 102 issues the carrier fluid jet with abrasive particles towards a target surface of the workpiece 103. This results in a randomly distributed manner of issuing the abrasive particles from the nozzle 102 of the conventional FJP device 100 on a desired/targeted surface of the workpiece 103. Hence, there is an inhomogeneous material removal from the surface of the workpiece 103. Apart from this, the contact of the abrasive particle with a wall of the nozzle 102 leads to its erosion and subsequent damage.

Figure 2A illustrates an assembled view of an FJP device 200 with an acoustic transducer 202a, in accordance with an embodiment of the present disclosure. Figure 2B illustrates particle tracks obtained from a simulation of the FJP device 200, in accordance with an embodiment of the present disclosure. Figure 2C illustrates a spatial distribution of material erosion rate in accordance with an embodiment of the present disclosure. Figure 2D illustrates a prediction of the material erosion rate data in accordance with an embodiment of the present disclosure. The FJP device 200 disclosed in the present disclosure ensures targeted removal of material from the required surface of a workpiece 203 by manipulating the abrasive particles using the acoustic transducer 202a.

The FJP device 200 for a workpiece 203 may include but is not limited to a mixer 201, a nozzle 202, and the acoustic transducer 202a, details of which will be provided in subsequent paragraphs.

Referring to Figure 2A, the mixer 201 may be adapted to mix the abrasive particles with the carrier fluid and is transmitted to a nozzle unit. The nozzle unit may include a nozzle 202 and the acoustic transducer 202a. The nozzle 202 may be connected with the mixer 201. The nozzle 202 may be adapted to create a jet stream of a mixture of the carrier fluid and the abrasive particles. The nozzle 202 may include a first end 202b and a second end 202c. In an embodiment, the first end 202b may be connected with the mixer 201. The first end 202b receives the mixture in the nozzle 202. Further, the second end 202c may be openable towards the workpiece 203. The second end 202c may be adapted to transfer the abrasive particles, provided in a controlled and pointed manner by the acoustic transducer 202a, to a targeted surface of the workpiece 203. In an embodiment, the workpiece 203 may be one of a wooden block, a tile, a marble, steel etc., without departing from the scope of the present disclosure. In one example, the acoustic transducer 202a may be disposed around a radius of the nozzle 202. The acoustic transducer 202a may be adapted to generate standing acoustic waves, which are perpendicular to a path of mixture flow within the nozzle 202. In an embodiment, the acoustic transducer 202a may be a single transducer, without departing from the scope of the present disclosure. In another embodiment, the acoustic transducer 202a may be multiple transducers, without departing from the scope of the present disclosure. In an embodiment, the standing acoustic waves may be generated across a bore of the nozzle 202, without departing from the scope of the present disclosure. In another embodiment, the standing acoustic waves may be generated parallelly across a length of the nozzle 202, without departing from the scope of the present disclosure. The standing acoustic wave helps in the migration of the abrasive particles to a desired location within the nozzle 202. For instance, the standing acoustic wave helps to align the abrasive particles along a centre line of the jet stream. Further, the acoustic transducer 202a aligns the abrasive particles to push radially inwardly and away from an inner surface of the nozzle 202. Further, the acoustic transducer 202a also aligns the abrasive particles in the controlled and pointed manner towards the desired/targeted surface of the workpiece 203.

In one example, in the nozzle 202, the abrasive particles are redistributed within the carrier fluid using an acoustic radiation pressure acting on the particles. For instance, the abrasive particles are redistributed owing to the difference in the acoustic impedance value between the abrasive particles and the carrier fluid. In the presence of the standing acoustic wave, the impedance mismatch results in the generation of an acoustic radiation pressure/force on the surface of the abrasive particles. Thus, an unbalanced acoustic force may be exerted on the surface of the abrasive particles that helps focus the abrasive particles at desired locations within the nozzle 202. This results in enhancing the local material removal rate from the workpiece 203 and ensuring a focussed process from the FJP device 200. In contrast, as shown in Figure la (prior art), the particle issued from the nozzle 102 simply follows the flow streamlines in the conventional FJP device 100 and owing to the presence of stagnation zone leads to spatial inhomogeneity in material removal from the targeted surface 103.

Further, the present disclosure also discloses that the abrasive particles are focused on desired locations within the nozzle 202 due to acoustic transducer 202a, thus ensuring that most abrasive particles are aligned along the centerline. This impacts the target surface precisely at the desired location, thereby enhancing the local material removal rate. This configuration helps in reducing machining/polishing footprints to that of the particle size. Since the abrasive particles are actively pushed away from the wall of the nozzle 202, the procedure significantly minimizes erosion-related damage generally occurring in the nozzle 202. Also, acoustic transducer 202a provides an additional means of controlling the machining/ polishing process, i.e., this brings in the ability to attain any erosion profile ranging between W-shape and U-shape. Transient control of the acoustic transducer 202a can also help develop desired surface patterns.

Further, many numerical simulations using ANSYS FLUENT have been performed to validate the efficiency of the FJP device 200 with the acoustic transducer 202a. Two sets of numerical simulations have been carried out: the first set is the case involving the conventional FJP device 100, and the second set is the case considering the additional influence of the acoustic transducer 202a on the FJP device 200 in accordance with the present disclosure. The numerical modelling essentially consists of three parts. The first part involves a continuous phase to model the carrier fluid jet dynamics and impingement on the target surface of the workpiece. The second part may be for modelling discrete phase dynamics of the abrasive particles. The third part involves the estimation of the erosion process at the surface.

It is assumed that the mixture used in the present simulation is dilute, thus, there is no particle-particle interaction and no influence of particle dynamics on the carrier fluid flow. The evolution of the continuous phase (jet flow) is modelled by solving Navier-Stokes equations in the Eulerian reference frame using the finite volume method. Steady-state three- dimensional mass and momentum conservation equations are solved to compute the velocity and pressure fields. The turbulence effects are modelled using the standard k-e model with scalable wall function. The Semi-Implicit Method for Pressure-Linked Equation (SIMPLE) algorithm is used to solve the pressure-velocity coupling in the equations. The convective and diffusion terms are discretized using the second-order upwind and central-differencing schemes, respectively.

Further, in the present simulation, a one-way particle-fluid interaction is used, implying that only the forward influence of carrier fluid flow on the abrasive particles is considered. The reverse influence of the abrasive particles on the flow is neglected. The trajectories of motion of the abrasive particles are simulated using the discrete phase model (DPM). The abrasive particle motion is simulated by integrating the Lagrangian transport equation with time. Different constituent forces such as drag, gravity, Saffman lift, virtual mass, pressure gradient, etc., are appropriately modelled. The turbulence effects on the particles are estimated using the discrete random walk (DRW) model. Like the above one-way coupling, the flow of the carrier fluid is considered to be unperturbed by the acoustic standing wave set up in the nozzle 202. The various acoustic forces acting on the abrasive particles, such as the acoustic radiation pressure force, the asymmetric drift force, etc., are modelled using appropriate relationships. Once the trajectory of the abrasive particles is obtained, impact characteristics of the abrasive particles like the angle of impingement, particle impingement velocity, etc., are used to estimate the local erosion rate/material removal at the target surface. Further, other necessary information, for example, the size of the abrasive particles, shape, material, etc., and the target material characteristics are required to estimate the material removal rate from the workpiece 203.

In one example, for the present proof-of-concept simulations, a simple submerged FJP scenario is considered. The mixture is issued from the nozzle 202 of inner diameter, d = approx. 8 mm, and length, L ^:=: approx. 80 mm. The workpiece 203 is placed at s = approx 12.7 mm from the outlet of the nozzle 202. The target surface diameter is ten times the diameter of the issuing pipe. The solid abrasive particles have a nominal size of approximately 300 pm, a density of approximately 2650 kg/m3, and a sphericity value of approximately 1.0. The material of the workpiece is steel with a density of approximately 8000 kg/m3. The acoustophoresis assistance is effectuated by considering the formation of an acoustic standing wave perpendicular to the flow within the nozzle 202. The shape of the standing wave formed is controlled by varying the frequency and amplitude of the acoustics wave. The numerical value of dimensions in the present disclosure is considered only for illustration purposes. However, the invention disclosed in the present disclosure can be implemented on any other surface having different dimensional values.

Referring to Figure 2B, the abrasive particles, because of the standing acoustic wave generated by the acoustic transducer 202a, get focused along the centerline of the jet stream in the nozzle 202 of the FJP device 200. Thus, the interaction between the wall of the nozzl e 202 and the abrasive particles decreases, thereby decreasing the problem of the erosion of the wall of the nozzl e 202 and leading to focused material removal from the targeted surface of the workpiece 203. In contrast, in Figure IB (prior art), the abrasive particles are scattered inside nozzle 102. They interact with the wall of the nozzle 102, thereby increasing the problem of the erosion of the wall of the nozzle and inhomogeneous material removal from the surface of the workpiece 103.

Referring to Figure 2C, the peak erosion rate by the FJP device 200 having acoustic transducer 202a is at the center of the workpiece 203. This peak erosion rate of the present disclosure reduces the erosion of the nozzle wall and leads to homogeneous removal of the material from the targeted surface of the workpiece 203. Further, the new peak value is approx. 30 times higher than the previous peak value. In contrast, as shown in Figure lC (prior art), the peak erosion rate is away from the center line, thereby leading to inhomogeneous material removal from the targeted surface of the workpiece 103.

Referring to Figure 2D, radially averaged material removal rates from workpiece 203 are predicted by the Oka erosion model for different acoustic signal parameters. Further, the erosion profile at 150 kHz and 260 dB is no longer the W-shape as observed for the conventional process. There is a substantial downward spike at the impingement center. Thus, the overall erosion pattern can be conveniently modified in the present case by simply altering the frequency and the wavelength of the imposed acoustic wave provided by the acoustic transducer 202a.

As would be gathered, the FJP device 200 disclosed in the present disclosure offers a comprehensive approach for ensuring focused material removal from the surface of the workpiece 203 while maintaining the jet stream. The FJP device 200 as disclosed provides an easy means to generate diverse patterns by effortlessly varying the wavelength and the amplitude of the imposed acoustic wave. The FJP device 200 as disclosed provides better control and repeatability of the surface finish is obtained. Further, the machining/polishing process is highly targeted/focused, hence, the local material removal rate is much higher.

The FJP device 200 as disclosed ensures better abrasive particle utilization as most abrasive particles can be made to impact the surface of the workpiece 203. This reduces the number of abrasive particles required for machining/polishing. Since the abrasive particles are essentially focused along the centreline of the carrier fluid jet, there is little interaction between the particles and the issuing nozzle wall. This helps in increasing the nozzle life and ensuring the repeatability of the machining/polishing process. The machining/polishing process can be made insensitive to the nozzle standoff distance, hence, reducing power consumption. Further, the FJP device 200 as disclosed ensures that different types of abrasive material may be used unlike magneto-rheological fluid polishing. The FJP device 200 as disclosed improves the process performance without having the need to change the underlying process parameters like nozzle pressure, standoff distance, etc.

Further, the present disclosure may be used in various industrial applications, for example, general FJP of metals, machining/polishing of brittle materials like glass, ceramics, etc., machining/polishing of heat sensitive materials such as silicon, gallium, polishing of optical components, microfabrication of channels and patterned surfaces for bio-medical applications, fabrication of bio-inspired surfaces with varied surface topography at different scales for better tribological applications, transportation of unrefined crude in oil and gas industries.

While specific language has been used to describe the present disclosure, any limitations arising on account thereto, are not intended. As would be apparent to a person in the art, various working modifications may be made to the method in order to implement the inventive concept as taught herein. The drawings and the foregoing description give examples of embodiments. Those skilled in the art will appreciate that one or more of the described elements may well be combined into a single functional element. Alternatively, certain elements may be split into multiple functional elements. Elements from one embodiment may be added to another embodiment.