Micro-abrasive Jet Research Articles

Multi-criteria optimization of micro-hole on glass using developed µ-abrasive jet machine set-up

In non-traditional machining, micro-abrasive jet machining (MAJM) is a cost-effective machining process. MAJM has been used for fabricating electronic devices and microfluidic channels. This work has made an effort to utilize MAJM for glass. A new design and fabrication of the Laval type of nozzle have been proposed to improve machining accuracy. A nozzle is conceived to ensure specific characteristics of the mixture (compressed air and abrasive particles) pass through it. The abrasive particle force is converted to kinetic energy, increasing the mixture’s velocity. The cross-sectional area of the nozzle can be circular, rectangular, square, or oval. A circular cross-sectional nozzle has been developed for high velocity, precise etching, and patterning on difficult-to-machine materials such as steel alloys. A circular cross-sectional micro-nozzle with a large aspect ratio is proposed, and the flow characteristics and cutting performance are examined precisely by the experiment. Efforts are being made to make machining processes sustainable, productive, and efficient. Here, the Taguchi-grey relational analysis integration approach has been used to analyze the machining parameters such as air pressure, stand-off distance, and abrasive mesh size (AMS). The top hole diameter, bottom hole diameter, material removal rate, and radial overcut are the response variables in this investigation. Analysis of variance (ANOVA) results showed that the AMS was the most efficient parameter, which followed the processing condition on the total input of the multi-purpose function. The reported optimized process parameters are air pressure of 8 bar, stand-off distance of 2 mm, and AMS mix (50%+100%) micron, which significantly affects the top and bottom micro-hole diameters.

Performance Improvement of Micro-Abrasive Jet Blasting Process for Al 6061

Aluminum 6061 is a precipitation-hardened alloy, containing magnesium and silicon as its major alloying element, and it is widely used in industries due to its remarkable mechanical properties and weld ability. Several types of machining manners are researched for aluminum 6061 alloys, and micro-abrasive jet blasting (μ-AJM) is one of the most developed processes for improving surface roughness. When operating μ-AJM on aluminum alloys, sufficient consideration of environmental variables such as particle types, nozzle diameter, pressure, standoff distance, and injection time is a prerequisite for the appropriate degree of roughness. To find the optimal conditions, a statistical method of analysis of variables was used to investigate the maximum value for depth, diameter, width, etc., of the blasting surface. According to experimental results, multiple factors have a great influence on the condition of surface roughness. The blasting processes were conducted as square and cylindrical experiments, and the parameters for optimal conditions have been derived from a surface roughness measurement system.

Study of micro-dimples fabricated on alumina-based ceramics using micro-abrasive jet machining

• Micro-texturing with desired morphology characteristics was firstly explored on ceramics using micro-air jet machining. • The model of abrasive velocity distribution was amended and found to be a good indicator to present the micro-texturing performance. • Introducing micro-patterns on ceramics using micro-AJM is verified to be an effective way to enhance wear resistance in a lubricant system. This paper presents a study of fabricating micro-dimples with desired morphology characteristics using micro-abrasive jet machining. Experiments are conducted under different processing conditions so that blasted dimples with various sizes and geometries could be obtained and analysed. The results indicated that among all the processing factors used in this study, changing processing time and air pressure is found to be the most efficient and controllable way to vary dimple dimension. On the other hand, nozzle stand-off distance and air pressure both play a pivotal role in determining dimple geometry. The results indicate that a variety of desired morphologies on the blasted area could be obtained by optimizing parameter combination. To further reveal the mechanism of shape variation, an amended model of cross-sectional particle velocity distribution is proposed. By correlating the working conditions and the final form of machined micro-structures, the model is confirmed to be an effective indicator to present the machining performance. In the end, friction tests and wear characterization are conducted to verify the positive effect of the introduced micro-texture on improving the lifespan of ceramic-based workpieces.

Prediction of erosion volume of PDMS by cryogenic micro-abrasive jet machining based on dimensional analysis method and experimental verification

The polymer polydimethylsiloxane (PDMS) is used widely in microfluidic chips. At room temperature, when PDMS is machined by micro-abrasive jet machining (MAJM), its high elasticity means that it often suffers from processing defects such as abrasive embedding and a surface deterioration layer. Cryogenic micro-abrasive jet machining (CMAJM) based on the glass transition has been proposed, but a model for predicting the volume of material removed is yet to be established. In this study, orthogonal experiments are used to investigate how different processing parameters influence the material removal volume. The results show that the material removal volume is largest when the jet pressure is 0.6 MPa, the erosion angle is 60°, the erosion distance is 3.5 mm, and the scanning speed is 0.2 mm/s. A model is established to predict the material removal volume during the CMAJM of PDMS, and single-factor experiments are used to assess the model qualitatively. The results show that the model offers good predictions of how the material removal volume changes with the scanning speed and jet pressure.

Tool performance on micro-abrasive post-treatment coated carbide

The cutting performance of coated tools can be significantly improved by appropriate post-treatment of coated surface. To determine the effects of micro-abrasive slurry jet (MASJ) and micro-abrasive air jet (MAAJ) on the performance of coated tools, single-factor tests were conducted to investigate the effects of micro-abrasive jet processing parameters on surface roughness of coated tools and thickness of coating removed. Based on the single-factor results, multi-process tests were designed, and two types of coated tools were obtained after micro-abrasive jet post-treatment. Based on the results of wear tests and the effect of cutting parameters on the surface roughness of the turning workpiece, the cutting performance of the three different tools on hardened die steel was evaluated. Turning tests showed that the micro-abrasive jet post-treatments effectively improved the surface morphology of the coating and the surface quality of the coated tools. Under the same machining parameters, the coated tools treated with the MASJ show better cutting performance than the tools post-treated by MAAJ.

Fabrication of micro-channels on Co–Cr–Mo joints by micro-abrasive jet direct writing

Hectares of tribological micro-texture must be machined per year to reduce friction and wear in artificial articular joints. Productive and cost-effective tribo-texturing of freeform surfaces consisting of hard-to-machine materials is a current manufacturing challenge. This study evaluates the accuracy and productivity of micro abrasive jet machining when fabricating micro-channels on metal in a mask-less way. The influence of micro abrasive jet process parameters on micro-channel’s geometry and fabrication speed is in focus in this study. We blast 27-μm alumina powder through Ø0.5 mm nozzle at Co-Cr-Mo substrate under 0.1 – 0.8 MPa of air pressure, 30° – 90° of nozzle angles and 0.5 – 3.5 mm of stand-off distance. Measurements show that the micro-channels can be as narrow as 110% of the nozzle diameter and have V-, U- or W-shaped bottom at the particular stand-off distance and air pressure. The fabrication speed of 550 μm × 5 μm channels (width × depth) reaches 260 mm/min and allows to texture the femoral head of a hip joint within several minutes using a single nozzle and a few grams of abrasives. Overall, the accuracy, productivity and cost-effectiveness of micro abrasive jet machining are highly suitable for tribological surface texturing of artificial joints.

Theoretical study on particle velocity in micro-abrasive jet machining

Micro-abrasive jet machining (AJM) is an advanced subtractive machining technology with ample opportunities to form regular micro-patterns on freeform surfaces. AJM removes material mainly through erosion and abrasion, which transform kinetic energy to fracture and deform substrates. The kinetic energy of a solid particle is tightly connected to its velocity, which is the most significant source of error in precise prediction of a machined feature. The present study involves both theoretical analysis and two-dimensional axisymmetric numerical simulation of particle velocity fields at the lower end of the micro-scale. The developed model represents the finest particles in a cylindrical nozzle down to an inner diameter of 100 μm. The computed results agree well with the experimental data. It is shown that, due to viscous friction, such nozzles are significantly less efficient in terms of particle saturation with kinetic energy. The study highlights the effects of nozzle diameter and length, air pressure, particle size and density on particle velocity development through the jet field. Finally, practical recommendations and multiple regression models of maximum particle velocity, location from the nozzle exit and simplex velocity profile approximation are offered for management of particle kinetic energy.

A novel approach to produce holes with high degree of cylindricity through Micro-Abrasive Jet Machining (μ-AJM)

The current research work proposes a novel approach to produce holes with high degree of cylindricity on brittle materials using Micro-Abrasive Jet Machining (μ-AJM) technique. Cylindrical micro holes are used as fluid reservoir in microfluidics application such as lab on chip and organ on chip systems. The shape of the holes produced using μ-AJM is observed to be conical due to its tapered sidewalls. It is difficult to achieve cylindrical holes through the μ-AJM process at present. The novel approach presents a hypothesis that by maintaining nozzle stand-off distance (NSD) constant during machining to a value set at the beginning of machining, the taper angle of the holes can be reduced resulting in holes with higher degree of cylindricity. Geometrical characteristics of the machined holes such as their dimension and form error have been examined using coordinate measuring machine (CMM). The obtained results showed significant reduction of 56% in the taper angle and improvement of 57% in the cylindricity of machined holes.

Experimental Investigations on the Influence of Mixing Chamber Design in Micro – Abrasive Jet Machining of Borosilicate Glass

Borosilicate glass finds applications in micro-fluidic devices, micro-electro mechanical devices (MEMS) due to its bio-compatibility, optical transparency and anodic bonding capability with silicon wafer. Abrasive jet machining (AJM) is a potential process to machine low machinability brittle materials like borosilicate glass and ceramics with low specific power consumption and high material rates. This paper presents the details of developed micro-abrasive jet machine prototype and the experimental investigations on the influence of mixing chamber design on material removal rate in machining of borosilicate glass. Pressure, stand-off-distance, nozzle diameter, abrasive type (Al2O3 and SiC) and abrasive size were used as control factors. Experiments were conducted based on L16 orthogonal array and optimized with Taguchi’s method. ANOVA was performed to find the significant control factors and their percentage contribution. A multilayer perceptron artificial neural network (ANN) model was used with back-propagation algorithm to predict and validate experimental results. Experimental values of material removal rate with both the fixed and oscillating mixing chamber were compared with the predicted values. It was found that the oscillating mixing chamber has resulted good material removal rate and less spread for the given control factor combination due to uniform mixing of abrasive particles with compressed air

Surface texturing on SiC by multiphase jet machining with microdiamond abrasives

ABSTRACT The multiphase microabrasive jet machining is a new type of surface texturing technique using compressed air to accelerate the mixtures of abrasive and water to remove material. It is effective for surface texturing on different materials, and can also reduce the pollution and cost by recycling the microabrasive particles easily. Basing on this technique and using the micro synthetic diamond as the abrasive, a multiphase jet technique is developed for machining on silicon carbide (SiC) surfaces. The processing results are compared to other abrasives, and influences of the processing parameters such as jet distance, jet pressure, abrasive concentration, particle size, and jet angle are investigated experimentally. The improvement on machining quality and efficiency are confirmed.

A multi-phase micro-abrasive jet machining technique for the surface texturing of mechanical seals

The surface texture such as micro-dimples or micro-grooves on the surface of mechanical seals can help to improve the tribological and sealing properties. A technique of multi-phase micro-abrasive jet machining is proposed to fabricate micro-grooves on the surface of mechanical seals. This technique takes the advantages of the current micro-abrasive jet machining and can recycle the abrasive particles easily to avoid the pollution on the environments by accelerating the mixture of abrasives and water with compressed air. The machining effects on three typical materials for mechanical seals are investigated and compared. The influences of machining times, abrasive flow rate, jet pressure, and jet distance on machining quality are studied and optimized through experiments.

Measurements and modeling of instantaneous particle orientation within abrasive air jets and implications for particle embedding

Previous theoretical studies indicate that the material removal mechanism and the likelihood of particle embedding in solid particle erosion processes strongly depend on instantaneous particle orientation at impact. The present study utilized pulsed laser shadowgraphy to measure the size, shape, and instantaneous orientation distributions of particles within a micro-abrasive jet at various pressures, particle sizes, and nozzle standoff distances. A particle orientation angle was defined as the angle between the particle linear velocity vector (approximately parallel to the jet centerline axis) and the line connecting the center of mass to the furthest downstream particle vertex. Particles were considered to be ‘oriented’, i.e. in a configuration favorable to embedding, if this angle was between 0 and 10°. The measurements revealed that, at all pressures (i) between 24% and 29.5% of the particles were oriented at the nozzle exit; (ii) the percentage of oriented particles increased slowly with standoff distance; (iii) larger particles had a stronger tendency to orient than smaller ones; (iv) particles having larger aspect ratios had a stronger tendency to aerodynamically align with the jet, and (v) although not all particles that were oriented actually embedded, the measured percentage of embedded particles on Al 6061-T6 surfaces nevertheless correlated with the percentage of oriented particles. A model capable of predicting the instantaneous particle orientation and velocity within and downstream of the nozzle was presented and shown to agree well with measurements. To the knowledge of the authors, these are the first measurements of the instantaneous orientation of abrasive particles under conditions that are typical of abrasive air jets. The results may have important implications for optimizing solid particle erosion tests and in abrasive jet machining applications.

Introduction of Premixed Micro-Abrasive Water Jet Technology for Deburring

Micro-abrasive water jet technology for deburring is a new type of removing burrs technics with advantages of high productivity, high flexibility, no cutter damage and less residual damage etc, which is applied more and more extensively. This paper introduces the difference of premixed micro-abrasive water jet and post-mixed micro-abrasive water jet on jet formation, the difference of system principles and applications. This paper also provides the formula that how to quantitatively calculate the impact force of water jet. The principles and factors which influence on deburring and some application examples are also described in this paper.

Optimal conditions of SU-8 mask for micro-abrasive jet machining of 3-D freeform brittle materials

Micro-abrasive jet machining (AJM), also called micro-blasting, is a mainstream machining process that uses abrasive particles for difficult-to-cut workpieces such as glass, carbides, and ceramics. During the micro-blasting process, non-machined areas are covered by a protective mask. Today, either mask fabrication practice or micro-blasting process is well suited and optimized for producing micro-features on planar workpieces. However, the demand for micro-features on three-dimensional (3-D) freeform substrates in micro electro-mechanical systems (MEMS) and lab-on-a-chip devices requires more refined non-planar micro-manufacturing techniques. We focused on devising an appropriate photoresist mask required by micro-AJM processes on the surface of a 3-D freeform workpiece. Fundamental erosion mechanisms based on SU-8 mask properties (hardness, surface roughness, and thickness) were investigated. The optimal conditions were found at an ultraviolet (UV) energy of 12.0752 μJ/μm, focus ratio of 4.8341, and hard baking time of 8.4974 min. Under these settings, the mask hardness and surface roughness were 25.04 HV and 1.14 μm, respectively. The reliability of the fabricated mask was verified through a micro-AJM process. With existing plant conditions, the engraved microfeature dimensions on the surface of a 3-D freeform workpiece were 535.3 μm (width) and 11.6 μm (depth).

Research of Micro-Abrasive Suspension Jet Erosion Morphology and Material Removal Mechanism

This paper introduces the micro-abrasive suspension jet polishing technology in precision machining technology. In order to understand the micro-abrasive suspension jet erosion morphology and material removal mechanism, the erosion experiments of micro-abrasive suspension jet on 40CrMnMo7 special steel work-piece were taken. We found that when the incident angles are 90°, 60°, 30°, the polishing area is respectively annular shape, horseshoe shape and blade shape. During the erosion process, as the incident angle becomes smaller, most amounts of abrasive particles impact angles will also be small, and these cause more material removal. When the particles impact the work-piece with small angles, most particles play shearing action on the work-piece and leave the work-piece nanoscale scratches; while the particles impact the work-piece at large angles, extrusion and blow are formed by the majority of the particles on the work-piece, leaving different small size pits.

3D tool path generation for micro-abrasive jet machining on 3D curved surface

Micro-patterns can be carved by jetting fine particles onto the surface of a workpiece. A mask structure is required to classify the surface regions to be machined. This mask is a plate with a hole that corresponds to the pattern to be carved. Abrasive particles are used to erode the workpiece through the hole in the mask. Recently, abrasive jet machining technology has been applied to workpieces with three-dimensional curved surfaces. To utilize the technology for a three-dimensional workpiece, a mask structure needs to be built on the workpiece. Microstereolithography can be used to build this three-dimensional mask for the workpiece. Consequently, process planning technology for the movement of the abrasive jet nozzle should be developed. It should follow the three-dimensional mask and workpiece at a specific distance to achieve uniform machining and a better surface finish. This paper introduces a process planning technique that can automatically generate a three-dimensional machining path for a three-dimensional mask and workpiece. A verification example and an application example are also shown.

Process analysis of abrasive jet micromachining for brittle materials

Abrasive jet micromachining (AJM) is a non-traditional machining process based on the erosion of substrates by an abrasive-laden air jet. It is a promising machining technique for the cost effective fabrication of micro-devices from brittle and hard materials. For the machining process to be more efficient and better predictable, mathematical models for the AJM process are necessary. This paper presented an analysis of the AJM process for brittle materials. The analysis is based on a fundamental erosion model of solid particle impact for brittle materials, and a recently developed model for the particle velocity in micro-abrasive jet, to form a mathematical basis for AJM process modelling and optimisation. Experimental study on the flow characteristics and the effects of some important process parameters are also given.

Direct 3D mask modeling for nonplanar workpieces in microabrasive jet machining

Recently, a new microengraving technology, microabrasive jet machining, has been studied as a machining technology for highly brittle materials. The technology implements the machining by using an abrasive jet and it uses mask structures to achieve microscale geometrical accuracy. The mask structure selectively blocks the abrasive jet at the portions of the surface that are not to be machined. Modeling and fabrication of the mask structure are thus key processes in microabrasive jet machining. Microstereolithography is believed to be a better means of mask fabrication for general planar and nonplanar workpieces. However, it is not easy to model a precise 3D mask structure from a given pattern image. Because of inconsistencies between the computer-aided design (CAD) model and the actual workpiece, mask structures modeled from workpiece CAD models often fall off. We therefore propose an automated modeling algorithm for the corresponding 3D nonplanar mask structure by using measured geometry directly. The algorithm takes the workpiece geometry as section images acquired from computer tomography and generates the CAD mask model directly from the section and mask images. Application software was developed to verify the algorithm and was tested by verification and actual cases.

Measurement of the particle spatial and velocity distributions in micro-abrasive jets

Novel experimental techniques for obtaining the particle spatial distribution and the velocity distribution across a micro-abrasive jet were presented and tested. The spatial distribution of particles within the jet was found by using a direct particle capture technique, and was found to depend on the nozzle diameter, following either a Weibull or a piecewise Weibull distribution. In general, the jet was found to be more focused when more particles were present across the nozzle opening. It was demonstrated how the measured particle spatial distribution could be used with a measurement of the eroded profile to extract an estimate of the non-dimensional particle velocity distribution within the jet. Using this technique, a linear or nonlinear velocity distribution was obtained, depending on the particle type and the nozzle diameter used. The results for the velocity distribution were compared to particle tracking velocimetry (PTV) results and were found to be within the acceptable measurement error ranges.

Development of rapid mask fabrication technology for micro-abrasive jet machining

Micro-machining of a brittle material such as glass or silicon is important in micro fabrication. Particularly, micro-abrasive jet machining (μ-AJM) has become a useful technique for micro-machining of such materials. The μ-AJM process is mainly based on the erosion of a mask which protects brittle substrate against high velocity of micro-particles. Therefore, fabrication of an adequate mask is very important. Generally, for the fabrication of a mask in the μ-AJM process, a photomask based on the semi-conductor fabrication process was used. In this research a rapid mask fabrication technology has been developed for the μ-AJM. By scanning the focused UV laser beam, a micro-mask pattern was fabricated directly without photolithography process and photomask. Therefore, rapid and economic mask fabrication can be possible for the micro-abrasive jet machining. Two kinds of mask patterns were fabricated by using SU-8 and photopolymer (Watershed 11110). Using fabricated mask patterns, abrasive-jet machining of Si wafer was conducted successfully.