Shear-thickening Polishing Research Articles

High Efficiency Preparation of Microdrill Edge by Shear Thickening Polishing

High Efficiency Preparation of Microdrill Edge by Shear Thickening Polishing

Parameters Optimization of Active Flexible Tool‐Assisted Shear Thickening Polishing Method for Concave Surface

An innovative approach, active flexible tool‐assisted shear thickening polishing (AFT‐STP), is introduced to overcome the limitations of low efficiency involved in the STP process of the concave surface. The principle and characteristics of AFT‐STP are presented, accompanied by the design of a flexible tool structure and the creation of an experimental setup. Utilizing the Taguchi method, experiments are planned and results are assessed via the signal‐to‐noise ratio to optimize process parameters. A variance analysis is then used to ascertain the relative influence of four key parameters—polishing speed, polishing gap, abrasive particle size, and abrasive concentration on the polishing performance of quartz glass in STP. Under the optimal parameters, a concave quartz glass workpiece with diameter Ø 20 mm and curvature radius 488 mm is polished, the average surface roughness Sa of the five measuring points on the surface decreases from 142.18 ± 8.63 (Avg. ± Std.) nm to 5.34 ± 1.16 nm in 45 min with MRR 57.3 nm min−1, and the surface defects of the processing area are completely removed, leaving only minor pits. The results show that the AFT‐STP is an effective method for high‐quality polishing of concave surfaces.

Effect of chemical action on shear thickening polishing of YAG

The shear-thickening polishing (STP) method, a flexible polishing technique developed in recent years, was utilized to obtain high surface quality of yttrium aluminum garnet (YAG) crystal effectively. The effect of polishing slurry pH value, which characterizes the chemical action between slurry and YAG crystal, on the material removal rate and surface roughness of YAG crystal was investigated, and the mechanism of the chemical action between YAG and slurry in STP process was revealed through X-ray photoelectron spectroscopy (XPS) analysis. The influence of polishing speed and abrasive concentration, which were relating with mechanical action, on the polishing effects was also studied. The experimental results show that when the pH value of the polishing slurry is lower than 11, the dissociation of chemical bonds and the formation of new bonds on the surface of the YAG crystal are predominantly found, resulting in a lower material removal rate. While the pH value of polishing slurry reaches 13, a reaction layer consisting of Al2SiO5 and Y2SiO5, which has lower hardness than abrasive, is formed on the surface, and this reaction layer can be removed by mechanical action efficiently. The surface roughness Sa decreases from 60 ± 10 nm to 0.38 ± 0.06 nm in 15 min with MRR reaches 117.30 nm/min, which is 4.3 times higher than that of chemical mechanical polishing. Based on the results of XPS analysis, the material removal mechanism of YAG polished by STP is proposed. As revealed by the results, STP with chemical action provide a high efficiency polishing method for the high surface quality YAG crystal.

Research on the shear thickening polishing CaF2 with textured hollow polishing tool

Due to its excellent precision and surface quality, ultra-precision polishing has become a necessary machining technology for obtaining ultra-smooth surface. Shear thickening polishing (STP) uses the non-Newtonian shear thickening mechanisms to achieve high-precision and low-cost polishing. A kind of textured hollow polishing tool for shear thickening polishing was proposed in our work to improve the renewal rate and utilization rate of STP slurry, and the high-performance polishing to achieve the STP of Calcium fluoride (CaF2). Firstly, the preparation process of STP slurry was explored, and the influence of abrasive concentration on its rheological properties was analyzed, resulting in the determination of the optimal concentration. And on this basis, combined the computational fluid dynamics (CFD) simulation analysis, the design of textured hollow polishing tool was analyzed to study the influence of different texture structures on the flow velocity field and pressure field of the STP slurry. Secondly, the experimental platform was set up and its kinematics and material removal mechanism were analyzed. The material removal mathematical model was constructed based on Preston equation, which was then experimentally validated. The relative error between the experimental and theoretical values was 8.36 %. Finally, the interactive experiment was designed and the optimal process parameters were obtained based on response surface method (RSM) analysis. The experimental results indicated that the surface roughness of CaF2 converged to 5.9 nm, which proved the potential of the proposed textured hollow polishing tool as a promising polishing method for STP.

Simulation and Experimental Study on the Effect of Edge Radius on the Cutting Condition of Carbide Inserts

Carbide tools are extensively used in the automotive, aerospace, and marine industries. However, an unsuitable tool-edge treatment can affect the cutting performance of carbide tools. In the tool-cutting process, the cutting edge radius is one of the major factors that affect the cutting force, temperature, and quality. In this study, a cutting simulation model of carbide inserts was used to analyze the effect of the cutting edge radius on the cutting performance. The cutting edge radii of the inserts were prepared using shear-thickening polishing methods, followed by cutting experiments. The accuracy of the cutting simulation model was verified through cutting experiments. The simulation results showed that under low-speed cutting conditions, the cutting force and temperature tended to increase with an increase in the cutting edge radius, and the cutting temperature was less affected by the cutting edge radius. The results of the cutting force and cutting temperature obtained from the experiment and simulation were consistent; therefore, the cutting simulation model was verified to be reliable. The results indicate that modeling cutting simulation is a promising research method for predicting the cutting performance of tools.

Surface and subsurface damage of fused quartz glass induced by shear-thickening polishing

Fused quartz glass is widely used in the civil and national defense fields. Shear-thickening polishing (STP) technology is highly efficient for processing quartz glass. However, the surface and subsurface damage (SSD) caused by STP have yet to be studied. In this study, the SSD characteristics of quartz glass after STP were examined using chemical etching and nanoindentation tests. The Sa (average roughness) of the fused quartz glass after 30 min of STP was 1.6 nm and the embedded depth of impurities was approximately 30 nm. The 3D morphology of the Beilby layer was sensitive to the chemical etching time, disappearing when the etching time was 120 s (at which point the Beilby layer with a depth ranging from 97 to 144 nm was completely removed). From various analysis methods, it can be inferred that the SSD depth was between 4.8–6.7 μm. To confirm that the above SSD came from the grinding or STP process, the polished fused silica glass was etched for 150 min to remove the SSD, after which it was polished for 30 min to regain its smooth surface; the workpieces were then etched again and the Sa and 3D morphology were compared with the workpiece which had no damage removal. The results showed that STP did not introduce new SSD and was a near-lossless polishing technique under the conditions used in this study. STP can achieve an extremely low surface roughness, efficiently; however, the depth of material removal is insufficient, and the SSD caused by the grinding process remains.

Ultra-precision machining process of inner surface considering shear-thickening polishing method

Shear-thickening polishing (STP) is a non-traditional flexible ultra-precision processing method that exploits the polishing fluid’s shear-thickening properties to create a shear rate between the workpiece surface and the potential flow. This increases viscosity and achieves material removal. In the past, the shear-thickening polishing method was mostly employed for the outer surface of rotating bodies. Nevertheless, to apply the STP method to ultra-precision processing of the workpiece’s inner surface, this paper proposes an active formed shear-thickening layer polishing method based on a numerical calculation model. Additionally, the main parameters affecting the machining efficiency were identified, orthogonal experiments were performed on the process parameter levels, and optimal machining conditions were derived. The optimized process was adopted to machine the inner surface of the large-size bearing ring, and the surface roughness in terms of Ra was reduced from the original 131.27 to 27.14 nm in 30 min and further to 19.52 nm in 60 min. The validation experiments highlight that the numerical model can predict the experimental results accurately, demonstrating the proposed method’s feasibility for ultra-precision machining on the inner surface with the STP method.

Theoretical and Experimental Investigation of Material Removal Rate in Magnetorheological Shear Thickening Polishing of Ti–6Al–4V Alloy

Abstract Magnetorheological shear thickening polishing (MRSTP) is a novel hybrid polishing method that combines the magnetorheological effect and the shear thickening effect. It has great potential for ultra-precision machining of complex surfaces. However, the absence of a correlation between material removal and the rheological properties of the polishing media has posed difficulties for further improvements in polishing efficiency and quality in MRSTP. In this work, a material removal model for MRSTP was established based on the principles of magneto-hydrodynamics, non-Newtonian fluid kinematics, and microscopic contact mechanics. This model combines the material removal model for a single abrasive particle with a statistical model of active grits. When comparing the experimental and theoretical results, it became evident that the developed material removal model can accurately predict the material removal depth of the workpiece under different processing parameters such as rotational speed of the rotary table and magnetic field strength. The average prediction error was found to be less than 5.0%. Furthermore, the analysis of the rheological behavior and fluid dynamic pressure of the polishing media reveals the coupling effects between the magnetic, stress, and flow fields. This provides theoretical guidance for the actual processing of MRSTP. Finally, the maximum material removal rate of 3.3 μm/h was achieved on the cylindrical surface of the Ti–6Al–4V workpiece using the MRSTP method. These results demonstrate that the MRSTP method holds great potential in the field of ultra-precision machining of difficult-to-machine materials.

Modeling and prediction of surface topography and surface roughness in magnetic-field-enhanced shear-thickening polishing of SiC mold

To fill the gap in the research on the surface morphology formation theory of small aspheric magnetic-field-enhanced shear-thickening polishing (MESTP), a theoretical framework for surface morphology formation during the MESTP process was proposed for the first time. Based on the macroscopic computational fluid dynamics and convolution iteration theory, a multiscale surface morphology prediction model was established. This model considers the mechanical mechanism of the ductile-brittle transition of hard and brittle materials and effective cutting abrasive distribution law. Through a series of experiments and simulations, the maximum relative error between the measured Sa data and theoretical prediction data was 9.1%, and the accuracy of the model was analyzed based on RMSE. The proposed model can predict the microsurface morphology in MESTP.

Surface polishing and modification of Ti-6Al-4V alloy by shear thickening polishing

In this study, a comparison of three newly developed polishing techniques namely, shear thickening polishing (STP), Chemistry enhanced STP (C-STP) and Electrolysis enhanced STP (E-STP) was made to investigate their suitability to Ti-6Al-4V biomaterials polishing and modification, which can produce Beilby layer after polishing and enhance mechanical and biological performance. The surface roughness Sa after STP was about 13.8 nm with a material removal rate of 54.3 nm/min. The C-STP showed the lowest surface roughness of 7.2 nm which was almost half that of STP and the MRR during C-STP was almost 2.1 times that of the conventional STP. The STP did not lead to any change of the surface composition, whereas a 136 nm thick Beilby layer was observed to form during the C-STP which revealed a lower friction coefficient of 0.04 as well as improved osteoblast cell activity. The E-STP showed an intermittent improvement as it provided a surface roughness of 10.2 nm and 1.6 times MRR than that obtained from conventional STP. Due to the dense oxide film of about 60 nm, the E-STP processed surface showed the best wettability and corrosion resistance. Overall, we reveal an important pathway for achieving scalable finishing on Ti-6Al-4V with desirable surface characteristics.

Experimental Study on Flexible Fiber Assisted Shear Thickening Polishing for Cutting Edge Preparation of Core Drill

To improve the cutting performance of the core drill, the flexible fiber assisted shear-thickening polishing (FF-STP) for cutting edge preparation was proposed to eliminate the microscopic defect and obtain proper radius of the cutting edge of the core drill. The flexible fiber was introduced into the shear-thickening polishing process to break the thickened agglomerates and improve the efficiency of cutting edge preparation. The influence of the polishing speed, abrasive concentration and the flexible fiber contact length with the core drill on the cutting edge radius r and surface morphology of the core drill edge was analyzed, and the drilling experiments were carried out after preparation, the cutting heat and drilled holes’ roughness were employed as evaluation indexes to evaluate the performance of the core drill. The results show that the cutting edge radius increases with the increase of polishing speed, abrasive concentration and contact length. However, too high a polishing speed and contact length reduce the abrasive particles involved in the polishing process, and then lead to a decline in preparation efficiency. Under the selected processing conditions, the cutting edge radius increases from the initial 5 μm to 14 μm and 27 μm with 4 min of treatment and 6 min of treatment preparation, respectively. The sharp cutting edge becomes rounded, the burrs and chipping on the cutting edge are eliminated, and the average roughness (Ra) of the flank face decreases from 110.4 ± 10 nm to 8.0 ± 3 nm. Nine holes were drilled consecutively by core drills after cutting edge preparation, and the cutting temperature and drilled holes’ roughness were recorded. The maximum cutting temperature (122.4 °C) in the process with the prepared core drill (radius r = 14 μm) is about 20 °C lower than that with untreated one, and the roughness of the drilled hole (Ra 510.5 nm) about 189.9 nm lower. The results indicates that FF-STP is a promising method for high consistency preparation of the core drill cutting edge.

Preparation of Cemented Carbide Insert Cutting Edge by Flexible Fiber-Assisted Shear Thickening Polishing Method.

Reasonable cutting edge preparation can eliminate microscopic defects and improve the performance of a cutting tool. The flexible fiber-assisted shear thickening polishing method was used for the preparation of cemented carbide insert cutting edge. The influences of the polishing angle and polishing speed on the cutting edge preparation process were investigated, and the cutting edge radius and K-factor were employed as evaluation indexes to evaluate the edge shape. A prediction model of the cutting edge radius was also established using the mathematical regression method. The results show that the polishing angle has a more significant effect on the cutting edge radius. The cutting edge preparation efficiency is the highest under the polishing angle of 10°, and the cutting edge radius increased from the 15 ± 2 μm to 110 ± 5 μm in 5 min. The cutting edge shape can be controlled by adjusting the polishing angle, and the K-factor varies from 0.14 ± 0.03 to 0.56 ± 0.05 under the polishing angle (from −20° to 20°). The polishing speed has a less effect on the cutting edge radius and shape, but increasing the polishing speed within a certain range can improve the efficiency of cutting edge preparation. The flank face roughness decreased from the initial Ra 163.1 ± 10 nm to Ra 5.2 ± 2 nm at the polishing angle of −20°, which is the best polishing angle for the flank face surface roughness. The ANOVA method was employed to evaluate the effective weight of the polishing angle and polishing speed on preparation efficiency. The polishing angle (86.79%) has the more significant influence than polishing speed (13.21%) on the cutting edge preparation efficiency. The mathematical regression method was used to establish the model of the prediction of the cutting edge radius with polishing angle and speed, and the models were proved rationally. The results indicate that the FF-STP is an effective method for the high consistency preparation of cemented carbide insert cutting edge.

Shear-thickening polishing of inner raceway surface of bearing and suppression of edge effect

Shear-thickening polishing is a non-traditional finishing method that uses the shear thickening effect by impacting the non-Newtonian fluid over the machining surface. As a result, it forms a velocity gradient that increases viscosity sharply, producing a flexible fixed abrasive tool to remove the material. Shear-thickening polishing is applied for finishing the outer surface of the rotary workpiece in previous work. The material removal distribution on the inner surface is completely different from those on the outer surface due to the different structures. The thickened slurry tends to form a relatively dense boundary layer on the surface, resulting in a decrease in the polishing quality and efficiency. The present study investigates the effect of the impact angle of slurry and polishing velocity on polishing quality to obtain the uniform surface morphology of the ring’s inner surface by the shear-thickening polishing process. The inner raceway of the outer ring of the tapered roller bearing 30203 was taken as the machining object. The numerical material removal model of the raceway surface was built according to the rheological performance of the shear-thickening slurry. A mathematical geometric model is used to explore the real impact angle of slurry. The model was able to accurately predict the experimental conditions, and the results of the simulation were in good agreement with the model’s predictions. In the fixture, a guide block was introduced to guide the flow of the slurry, ensuring consistent material removal across the whole surface. The optimal experimental results show that the average surface roughness measured by Ra reduces from 300 to 42.9 nm in 30 min, which further drops to 11.16 nm in 90 min with a variance of 0.58 nm2. The conclusion could be drawn from the studies of this paper that a uniform inner raceway surface of the bearing is achievable through a properly designed STP process.

Shear Thickening Polishing of Quartz Glass.

Quartz glass is a typical optical material. In this research, colloidal silica (SiO2) and colloidal cerium oxide (CeO2) are used as abrasive grains to polish quartz glass in the shear thickening polishing (STP) process. The STP method employs the shear-thickening mechanism of non-Newtonian power-law fluid to achieve high-efficiency and high-quality polishing. The different performance in material removal and surface roughness between SiO2 and CeO2 slurries was analyzed. The influence of the main factors including polishing speed, abrasive concentration, and pH value on the MRR, workpiece surface roughness, and the surface topography was discussed. Two different slurries can both achieve fine quartz surface in shear thickening polishing with the polishing speed 100 rpm, and pH value 8. The quartz glass surface roughness Ra decreases from 120 ± 10 to 2.3 nm in 14 minutes’ polishing with 8 wt% 80 nm SiO2 slurry, and the MRR reaches 121.6 nm/min. The quartz glass surface roughness Ra decreases from 120 ± 10 to 2.1 nm in 12 minutes polishing by 6 wt% 100 nm CeO2 slurry and the MRR reaches 126.2 nm/min.

Experimental study on the brush tool–assisted shear-thickening polishing of cemented carbide insert

To obtain uniform surface roughness of the complex cutting edge of the cemented carbide insert in the polishing process, a novel method, brush tool–assisted shear-thickening polishing (B-STP), was proposed in this study. This method introduces the flexible brush tool into the shear thickening polishing process to improve the surface roughness consistency of the complex cutting edge. The influence of the fiber-density of the brush tool and its contact length with insert on the B-STP performance was firstly investigated, and then the effects of four main processing parameters including polishing speed, diamond abrasive concentration, abrasive size, and inclination angle on the surface roughness and its consistency of the cutting edge were analyzed by Taguchi method. The ANOVA method was employed to evaluate the effective weight of the four factors and optimize the polishing conditions. The polishing experiment under optimum processing parameters combination with polishing speed 70 rpm, abrasive concentration 6 wt%, abrasive size no. 5000, and inclination angle 2°. The average surface roughness Ra of the seven measuring points on the cutting edge decreases from 118.01 to 8.13 nm in 10 min polishing, while the standard deviation decreases from 7.40 to only 0.3 nm. The comprehensive performance of surface quality obtained by the B-STP method is improved by 9.47 times and 3.67 times, respectively, compared with the STP method and the non-optimized B-STP method. The results show that the B-STP is an effective method for high consistency polishing of the cemented carbide insert cutting edge with complex shape.

Shear thickening polishing of the concave surface of high-temperature nickel-based alloy turbine blade

High-temperature nickel-based alloy, which is a valuable crucial material for fabricating functional components, is commonly used to fabricate turbine blades. However, the concave surface of the turbine blade is much difficult to be polished. In this work, shear-thickening polishing (STP), which employed the shear-thickening mechanism of non-Newtonian power-law fluid, was utilized to achieve high efficiency and high-quality polishing of the concave surface of the high-temperature nickel-based alloy turbine blade. The finite element simulation of the pressure and velocity distribution on the concave surface during STP process was carried out by ANSYS, and the effects of different polishing angles, polishing velocities, pH values of polishing slurry and Fenton's reagent on the surface morphology and roughness of the workpiece were investigated by experiment. The comparison between simulation and experimental results indicated that the suitable polishing angle is 45°. The best surface can be obtained with a pH value of 6.5. With the increase of the polishing speed, polishing efficiency improved gradually. The workpiece surface was improved by adding 0.5% hydrogen peroxide (H2O2) and 0.15% FeSO4 in the polishing slurry. In the final, surface roughness of the turbine blade was reduced rapidly from Ra = 72.3 nm to Ra = 4.2 nm after 9 min polishing under the appropriate conditions. The research results provide reference and basis for high-temperature nickel-based alloy turbine blade polishing.

Anhydrous based shear-thickening polishing of KDP crystal

Based on the special physical–chemical characteristics of optical crystal in the field of aeronautics, a new anhydrous based shear-thickening polishing (ASTP) method has been proposed to restrain deliquescence and to improve physical properties for KDP machining. The ultra-precision polishing of KDP crystal is completed by ASTP. A kind of anhydrous based thickening polishing slurry (ATPS) was proposed in our work, and high-performance rheological properties were determined to achieve the ASTP of KDP crystal. A material removal model of ASTP in KDP machining is established, followed by the verification experiment of the prediction model. The maximum error of the predictive model is only 9.8%, which proves the validity of the material removal model for KDP polishing. The polishing experiments were carried out on the polishing platform developed by ourselves. The results show that the new polishing method can polish 20 mm × 20 mm × 5 mm KDP crystal and obtain a super-smooth surface with a surface roughness of 1.37 nm and high shape accuracy. The surface accuracy of polished KDP crystal reaches up to 0.68λ (RMS). The experimental results show that the ASTP is a potential ultra-precision machining method for KDP crystal.

Shear Thickening Polishing of Black Lithium Tantalite Substrate

To achieve high efficiency in the polishing process to obtain a high surface quality of black LT substrate (a kind of soft brittle material), shear thickening polishing (STP),which is a “gentle” finishing process developed in recent years, was employed in this study. The influence of three key parameters in the STP process including polishing speed, diamond abrasive size and diamond abrasive concentration were analyzed. To investigate the potential mechanical effect of the nanometre abrasive, nano-SiO2 abrasive particles were added in the slurry, and the concentration of SiO2 abrasive was also taken as a factor. Taguchi method was utilized to evaluate the influence of the four factors and optimize the polishing conditions. The surface roughness (Ra/Rz) was used as the evaluation index, and the optimized polishing conditions were verified through experiments. Diamond abrasive size has the most significant effect on Ra/Rz, followed by diamond abrasive concentration and then SiO2 concentration, as the polishing speed has been selected and limited in a small variation rang according to the previous study. Based on the S/N average response analysis, the surface quality is the best under the conditions with 8000# diamond abrasive, 5 wt% diamond abrasive concentration, 90 rpm polishing speed and 10 wt% SiO2 concentration. After 4 min polishing, the surface roughness Ra/Rz is reduced rapidly from 200.5/1374.6 to 4.2/22.1 nm without embedded abrasive particles on the surface of the black LT substrate. It also shows that the mechanical effect plays a dominant role in the material removal. A certain amount (10 wt% in this study) of nano-SiO2 can reduce friction between solid colloidal and workpiece, and helps to improve surface quality.

Experimental study on shear thickening polishing of cemented carbide insert with complex shape

Shear thickening polishing (STP), an emerging polishing method, is used to polish the cemented carbide insert with complex shape in this study. The principle and performance of STP were introduced. Four parameters having significant influence on the STP process, including polishing speed, abrasive concentration, abrasive size, and inclination angle of fixture, were experimentally investigated. The influence of the four parameters on the surface quality of cemented carbide insert was analyzed by orthogonal experiment method, and the optimal processing parameter combination for the STP of cemented carbide insert was determined. Although the influence degree of the processing parameter on the left cutting edge PA, the top cutting edge PB, the root cutting edge PD, and the right cutting edge PK was different, the optimal processing parameter combination for each position was the same: polishing speed of 90 rpm, abrasive concentration of 9 wt%, abrasive size of #8000, and inclination angle of 4°. Under the optimal processing parameter combination, the surface roughness of cemented carbide insert at the left cutting edge PA was reduced from 121.8 to 7.1 nm after 15 min polishing. The scanning electron microscopy (SEM) and the white light interferometer confirmed the effectiveness of the STP process in the polishing of cemented carbide insert. The experimental results show that STP was a promising and feasible processing method in the polishing of cemented carbide insert with complex shape.

Surface integrity of bearing steel element with a new high-efficiency shear thickening polishing technique

The bearing steel elements with high quality surface are required to improve the performance of bearings. A new high-efficiency shear-thickening polishing (STP) technology was used on bearing steel element ultraprecision machining. A kind of high efficiency shear thickening polishing slurry (HE-STPS) was prepared by mechanical mixing and ultrasonic dispersion method. The polishing experiments were carried out on a new intelligent polishing machine (HE-STP-II). The surface integrity of bearing steel element was studied by scanning electron microscopy (SEM), laser profilometer and some micro-scale test devices, then surface roughness and profile accuracy from sample surface were measured. Surface roughness decreases slightly as SiO2 size reaches nanoscale, which is related to the cutting depth of individual abrasive. The HE-STP would be a continuous process of wear, whose complex machining mechanism including micro-cutting, adhesive wear and other machining mechanism, which could reduce machining scratches and other micro defects, and achieve “flexible polishing” on the bearing steel element surface. The studies indicated that high surface integrity of bearing steel element could be obtained by this new high-efficiency polishing method.