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Magnetorheological finishing of an irregular-shaped small-bore complex component using a small ball-end permanent-magnet polishing head
NPE-00033; No of Pages 5 Nanotechnology and Precision Engineering xxx (xxxx) xxx
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Magnetorheological finishing of an irregular-shaped small-bore complex component using a small ball-end permanent-magnet polishing head Henan Liu, Jian Cheng, Tingzhang Wang, Mingjun Chen ⁎ School of Mechatronics Engineering, Harbin Institute of Technology, Harbin 150000, China
a r t i c l e
i n f o
Available online xxxx Keywords: Complex component Magnetorheological finishing Magnetostatic simulation Small curvature radius
a b s t r a c t A novel magnetorheological finishing (MRF) process using a small ball-end permanent-magnet polishing head is proposed, and a four-axes linkage dedicated MRF machine tool is fabricated to achieve the nanofinishing of an irregular ψ-shaped small-bore complex component with concave surfaces of a curvature radius less than 3 mm. The processing method of the complex component is introduced. Magnetostatic simulation during the entire finishing path is carried out to analyze the material removal characteristics. A typical ψ-shaped small-bore complex component is polished on the developed device, and a fine surface quality is obtained with surface roughness Ra of 0.0107 μm and surface accuracy of the finished spherical surfaces of 0.3320 μm (PV). These findings indicate that the proposed MRF process can perform the nanofinishing of a kind of small-bore complex component with small-curvature-radius concave surfaces. Copyright © 2019 Tianjin University. Publishing Service by Elsevier B.V. on behalf of KeAi Communications Co., Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
1. Introduction Magnetorheological (MR) finishing (MRF) is a computer-controlled deterministic polishing technique developed by Kordonski based on previous works on intelligent fluids.1 To date, this process is widely used in the fabrication of high-quality optical components with freeform surfaces. Many researchers have developed a number of new MRF processes and experimental setups for finishing of different sizes and shapes of complicated components. Salzman et al. investigated the effect of chemical composition and pH of MR fluid on the material removal and surface quality for the MRF of infrared polycrystalline materials.2,3 Sidpara et al. developed a MR fluid based finishing tool mounted on the three-axes CNC milling machine for finishing knee joint implants with complex freeform surfaces, and the best final surface roughness value obtained was 28 nm.4–6 They also proposed a rotational–MR abrasive flow finishing process for finishing of this freeform surface component, and a surface roughness ranging from 35 nm to 78 nm was achieved at various locations.7 Singh et al. developed a MRF device using an electromagnetic finishing tool for finishing flat and 3D workpiece surfaces, and the roughness of flat ground surface was reduced to as low as 19.7 nm after 120 min of finishing.8,9 Nanofinishing of the BK7 glass specimen was carried out, and surface roughness value Ra was reduced from 41 nm to 17 nm after 90 min of finishing.10 Then, a newly MR fluid based honing process was developed for internal surface finishing of ferromagnetic cylindrical workpiece.11,12 ⁎ Corresponding author. E-mail address: [email protected] (M. Chen).
For the finishing complex components of concave surfaces with small curvature radius, a MRF process using small ball-end permanent-magnet (SBEPM) polishing head and a four-axes linkage dedicated polishing device were developed. In the present work, the proposed MRF process is employed for the nanofinishing of an irregular ψ-shaped small-bore complex component with curved surfaces. Magnetostatic simulation during the entire finishing path is carried out to analyze the material removal characteristics and used as a basis for surface finishing.
2. MRF process using SBEPM polishing head A MRF process using a small ball-end polishing head is proposed to finish the complex component with small-curvature-radius concave surfaces. The polishing head comprises rare-earth permanent magnet to generate a gradient magnetic field in the polishing area, and the MR fluid forms a solid-like flexible polishing film adhering to the polishing head surface (Fig. 1). The carbonyl iron particles (CIPs) contained in the MR fluid become polarized and form a series of CIP chains along the direction of external magnetic field. Then, the nonmagnetic abrasive particles are firmly gripped by the CIP chain structure and shoved toward the workpiece surface to produce a shear squeeze and wear out the peaks due to relative motions on the finishing surface. The stiffened MR fluid driven by high-speed rotating polishing head generates a hydrodynamic flow at the polishing gap to apply hydrodynamic pressure and shear stress on the workpiece surface to achieve material removal. Fig. 2(a) shows the surface topography of a typical polishing spot created by the proposed MRF process.
https://doi.org/10.1016/j.npe.2019.10.001 2589-5540/Copyright © 2019 Tianjin University. Publishing Service by Elsevier B.V. on behalf of KeAi Communications Co., Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
Please cite this article as: H. Liu, J. Cheng, T. Wang, et al., Magnetorheological finishing of an irregular-shaped small-bore complex component using a small ball-..., , https://doi.org/10.1016/j.npe.2019.10.001
2
H. Liu et al. / Nanotechnology and Precision Engineering xxx (xxxx) xxx
Fig. 1. Developed MRF process using a SBEPM polishing head. (a) Schematic of the proposed MRF process; (b) stiffened MR fluid adhering to the polishing head; (c) photo of the polishing tool.
Compared with conventional wheeled MRF process, the proposed MRF process using a considerably smaller polishing head is provided with more complicated material removal characteristic. The magnetic flux density generated by the permanent magnetic polishing head is unevenly distributed around the hemispherical head. The inhomogeneous magnetic field results in the different material removal characteristics on the polishing head due to variation in the finishing angle γ between the normal line of the workpiece surface and axis of the polishing tool. A series of polishing spots is created by the proposed MRF process under different finishing angles, and the surface topography of the MRF spots is measured by interference microscope to acquire the material removal rate. Based on the experimental research, the relationship between the material removal rate and finishing angle γ is exhibited, as presented in Fig. 2(b). The material removal rate depends on the relative processing velocity and magnetic flux density in the polishing gap, which affects the shear yield stress of the MR fluid. Thus, the machining posture of the MR finishing tool should be controlled during processing.
device is set up (Fig. 3). The polishing tool using a SBEPM polishing head with a diameter of 4 mm is installed on the vertical Z-axis movement system. The polishing spindle is mounted below a C-axis rotary table and is tilted horizontally to achieve an inclined-axis process. This process can avoid interference when finishing the irregularly shaped complex component. The ψ-shaped small-bore component is fitted into the workpiece spindle mounted on the X–Y linear movement slides. MR fluid is delivered to the processing area by a peristaltic pump. The MR fluid adsorbed on the surface of polishing head generates a high apparent viscosity and produces relative motion between with the workpiece surface to apply hydrodynamic pressure and shear stress on the workpiece surface. The material removal amount and polishing force can be controlled by adjusting the process parameters, such as the rotation speed of polishing tool and workpiece, polishing gap, feed speed, and space angle of the polishing tool, to guarantee the polishing accuracy and surface quality.
3. MF finishing of a ψ-shaped component
3.2. MF finishing of the Ψ-shaped component
3.1. Experimental setup
Fig. 3(b) shows the ψ-shaped rotary workpiece whose material includes fused silica. The minimal transition fillet curvature radius of the curved surfaces is less than 3 mm. The structure of the component is a thin-walled hemisphere shell with a central shaft. To achieve the
According to the requirements of the MRF processing of a typical ψshaped small-bore complex component, a four-axes linkage polishing
Fig. 2. Material removal characteristic of the proposed MRF process. (a) Surface topography of a typical polishing spot created by the SBEPM MRF process; (b) relationship between the material removal rate and finishing angle γ.
Please cite this article as: H. Liu, J. Cheng, T. Wang, et al., Magnetorheological finishing of an irregular-shaped small-bore complex component using a small ball-..., , https://doi.org/10.1016/j.npe.2019.10.001
H. Liu et al. / Nanotechnology and Precision Engineering xxx (xxxx) xxx
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Fig. 3. Experimental setup for finishing of a ψ-shaped component. (a) Photo of the device; (b) the ψ-shaped component; (c) machining principle.
finishing of this irregularly shaped component, a polishing tool with SBEPM polishing head has to be employed to make effective contact with the small-curvature-radius concave surfaces. The machining principle of this ψ-shaped complex component is that the polishing head, which is set at the middle section of the specimen, moves along the central rod and internal and external spherical surfaces of the workpiece. Both surfaces rotate around their revolving axes, as shown in Fig. 3(c). The machining trajectory is established by the linear motion of X–Y axes units cooperating with the C-axis movement of the polishing tool. Fig. 4 illustrates a schematic of the processing of internal and external spherical surfaces of the component surface. Given the avoidance of interference and the change in material removal rate, the space angle α of the polishing tool changes twice during processing of the internal spherical surfaces, whereas three changes occur when processing the external spherical surface. Thus, the characteristics of material removal in the polishing area vary at different angular positions θ of the polishing trajectory. To realize the deterministic removal of surface material to maintain the surface accuracy, material removal characteristics during the entire polishing trajectory should be analyzed.
4. Analysis of magnetic field in the polishing area The present SBEPM MRF process uses flexible polishing mold formed on surface of polishing head to remove material from the workpiece surface by shearing action. As the magnetic flux density is one of the most important factors affecting the process performance, magnetostatic finite element simulation is carried out to analyze the distribution of magnetic field in the polishing area for 0.1 mm working gap when processing both the internal and external spherical surfaces under different angular positions θ. Figs. 5 and 6 show the results of the magnetostatic simulation for finishing of the internal and external spherical surfaces under a typical angular position. The findings show that the distribution of magnetic flux density is influenced by the specimen and forms a local stronger magnetic gradient field in the polishing gap. Therefore, MR polishing fluid could be retained more strongly around the polishing head, and the magnetic flux lines from the polishing gap gradually become parallel to the workpiece surface. As a result, higher magnetic shear forces can be produced to shear the materials from the peaks of the workpiece surface by shear forces.
Fig. 4. Processing of spherical surfaces. (a) Internal surface; (b) external surface.
Please cite this article as: H. Liu, J. Cheng, T. Wang, et al., Magnetorheological finishing of an irregular-shaped small-bore complex component using a small ball-..., , https://doi.org/10.1016/j.npe.2019.10.001
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H. Liu et al. / Nanotechnology and Precision Engineering xxx (xxxx) xxx Table 1 Processing parameters for surface finishing of the small-bore complex component.
Fig. 5. Typical result of magnetostatic simulation for finishing the internal surface. (a) Distribution of magnetic flux density; (b) polishing gap area; (c) curve of magnetic flux density.
Polishing spindle speed (rpm)
Workpiece spindle speed (rpm)
Polishing gap (mm)
C-axis Feed Processing angular speed time position α (mm/min) (min) (°)
6000
250
0.1
−30–80
1.8
540
Figs. 5(b) and 6(b) show the distribution of local magnetic flux density in the polishing gap with a width range of 1.5 mm centered at the minimum interspace. Figs. 5(c) and 6(c) plot the curve of magnetic flux intensity changes on the finishing surface. Simulation results show the maximum value of magnetic flux intensity achieved on the finishing surface. Further simulation analyses reveal that the position of this peak intensity of magnetic field gradually changes from one side of the minimum processing interspace to gradually away from the interspace on the other side under different angular positions θ. Fig. 7 displays the magnetic flux density at the position of minimum processing interspace under different angular positions. As depicted in the illustration, the variation in magnetic flux density at the minimum polishing gap is comparative less during the finishing of external spherical surface. However, magnetic field is relatively low when processing the internal spherical surface on the interior, where the angular position θ is between 50° and 63°. As the characteristics of material removal change based on the variation of magnetic flux density on finishing surface, the parameters for component finishing process should be regulated accordingly to ensure the surface accuracy. 5. Experiment on the MRF of the small-bore complex component
Fig. 6. Typical result of magnetostatic simulation for finishing the external surface. (a) Distribution of magnetic flux density; (b) polishing gap area; (c) curve of magnetic flux density.
MR finishing of the ψ-shaped small-bore complex component is conducted. The initial surface of the experimental component is obtained by precision grinding using a small diamond wheel, and the MRF process is used to improve the surface quality and maintain the structural surface accuracy. The processing procedure applied for the experiment is designed as a repeated cycle of operation, and the processing parameters are listed in Table 1. The MR fluid used in the analysis and experiments is self-made in laboratory, and it is formulated by a waterbased fluid with proper amount of cerium oxide abrasive particles and CIPs. The average particle size of cerium oxide abrasive particles is 3 μm, while that of the CIPs is 4 μm. And the composition of synthesized MR fluid is shown in Table 2. Fig. 8(a) shows a photograph of the finishing process. The surface profile of the component after polishing is measured by Taylor Hobson roughness profiler PGI 1240. The experimental results in Fig. 8 show that the finished surface roughness Ra is improved from 0.0538 μm to 0.0107 μm, and the surface accuracy of the spherical surfaces equals 0.3320 μm (PV). A higher quality surface finish can be produced by further optimizing process parameters. These findings indicate that the proposed SBEPM MRF process can perform the nanofinishing of a kind of small-bore complex component with small-curvature-radius concave surfaces. 6. Conclusions According to the requirements of the processing of a typical ψshaped small-bore complex component, a four-axes linkage polishing
Table 2 Composition of synthesized MR fluid.
Fig. 7. Curve of magnetic flux density at the minimum polishing gap on finishing surfaces.
Constituent
% Volume concentration
Water-based fluid medium Carbonyl iron particles Cerium oxide abrasive particles Stabilizing agent
57 36 6 1
Please cite this article as: H. Liu, J. Cheng, T. Wang, et al., Magnetorheological finishing of an irregular-shaped small-bore complex component using a small ball-..., , https://doi.org/10.1016/j.npe.2019.10.001
H. Liu et al. / Nanotechnology and Precision Engineering xxx (xxxx) xxx
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Fig. 8. MR finishing of small-bore complex component. (a) Finishing in process; (b) measurement result of finished surface roughness; (c) surface accuracy measured by Taylor Hobson surface profiler.
device is fabricated using the SBEPM MRF process. The processing method of the ψ-shaped complex component is introduced. During the polishing process, the machining posture of a polishing tool is controlled to rotate several different angular positions to avoid interference and collision. Magnetostatic finite element simulation is carried out, and the magnetic flux density at the position of minimum processing interspace under different angular positions during the entire finishing path is analyzed. MR finishing of the ψ-shaped small-bore complex component is conducted, and a fine surface quality is obtained.
Acknowledgments This work was supported by the National Key Research and Development Program of China [grant number 2018YFB1107600].
8. Singh AK, Jha S, Pandey PM. Nanofinishing of a typical 3D ferromagnetic workpiece using ball end magnetorheological finishing process. Int J Mach Tool Manu 2012;63 (4):21-31. https://doi.org/10.1016/j.ijmachtools.2012.07.002. 9. Singh AK, Jha S, Pandey PM. Performance analysis of ball end magnetorheological finishing process with MR polishing fluid. Mater Manuf Process 2015;30(12): 1482-9. https://doi.org/10.1080/10426914.2015.1019098. 10. Kumar S, Singh AK. Nanofinishing of BK7 glass using a magnetorheological solid rotating core tool. Appl Opt 2018;57(4):942-51. https://doi.org/10.1364/AO.57.000942. 11. Paswan SK, Bedi TS, Singh AK. Modeling and simulation of surface roughness in magnetorheological fluid based honing process. Wear 2017;376:1207-21. https:// doi.org/10.1016/j.wear.2016.11.025. 12. Bedi TS, Singh AK. Development of magnetorheological fluid-based process for finishing of ferromagnetic cylindrical workpiece. Mach Sci Technol 2018;22(1): 120-46. https://doi.org/10.1080/10910344.2017.1336631. Henan Liu is currently a Ph.D. candidate in Harbin Institute of technology, China. His research interest includes magnetorheological finishing for precision optics manufacturing.
References 1. Jacobs SD, Golini D, Hsu Y, et al. Magnetorheological finishing: a deterministic process for optics manufacturing. Proc SPIE 1995;2576:372-82. https://doi.org/10. 1117/12.215617. 2. Salzman S, Romanofsky HJ, West G, et al. Acidic magnetorheological finishing of infrared polycrystalline materials. Appl Opt 2016;55(30):8448-56. https://doi.org/10. 1364/AO.55.008448. 3. Salzman S, Romanofsky HJ, Giannechini LJ, et al. Magnetorheological finishing of chemical-vapor deposited zinc sulfide via chemically and mechanically modified fluids. Appl Opt 2016;55(6):1481-9. https://doi.org/10.1364/AO.55.001481. 4. Sidpara AM, Jain VK. Nanofinishing of freeform surfaces of prosthetic knee joint implant. Proc Inst Mech Eng B J Eng Manuf 2012;226(A11):1833-46. https://doi.org/10. 1177/0954405412460452. 5. Sidpara A, Jain VK. Analysis of forces on the freeform surface in magnetorheological fluid based finishing process. Int J Mach Tool Manu 2013;69:1-10. https://doi.org/ 10.1016/j.ijmachtools.2013.02.004. 6. Sidpara A, Jain VK. Rheological properties and their correlation with surface finish quality in MR fluid-based finishing process. Mach Sci Technol 2014;18(3):367-85. https://doi.org/10.1080/10910344.2014.925372. 7. Kumar S, Jain VK, Sidpara A. Nanofinishing of freeform surfaces (knee joint implant) by rotational-magnetorheological abrasive flow finishing (R-MRAFF) process. Precis Eng 2015;42:165-78. https://doi.org/10.1016/j.precisioneng.2015.04.014.
Mingjun Chen received his Ph.D. degree in Mechanical Engineering from Harbin Institute of technology, China, in 2001. He is currently a professor and Ph.D. candidate supervisor in Harbin Institute of technology, China. His research interests include precision and ultra-precision machining, micro machining and biomaterial compatibility evaluation.
Please cite this article as: H. Liu, J. Cheng, T. Wang, et al., Magnetorheological finishing of an irregular-shaped small-bore complex component using a small ball-..., , https://doi.org/10.1016/j.npe.2019.10.001
Contents lists available at ScienceDirect
Nanotechnology and Precision Engineering journal homepage: http://www.keaipublishing.com/en/journals/nanotechnologyand-precision-engineering/
Magnetorheological finishing of an irregular-shaped small-bore complex component using a small ball-end permanent-magnet polishing head Henan Liu, Jian Cheng, Tingzhang Wang, Mingjun Chen ⁎ School of Mechatronics Engineering, Harbin Institute of Technology, Harbin 150000, China
a r t i c l e
i n f o
Available online xxxx Keywords: Complex component Magnetorheological finishing Magnetostatic simulation Small curvature radius
a b s t r a c t A novel magnetorheological finishing (MRF) process using a small ball-end permanent-magnet polishing head is proposed, and a four-axes linkage dedicated MRF machine tool is fabricated to achieve the nanofinishing of an irregular ψ-shaped small-bore complex component with concave surfaces of a curvature radius less than 3 mm. The processing method of the complex component is introduced. Magnetostatic simulation during the entire finishing path is carried out to analyze the material removal characteristics. A typical ψ-shaped small-bore complex component is polished on the developed device, and a fine surface quality is obtained with surface roughness Ra of 0.0107 μm and surface accuracy of the finished spherical surfaces of 0.3320 μm (PV). These findings indicate that the proposed MRF process can perform the nanofinishing of a kind of small-bore complex component with small-curvature-radius concave surfaces. Copyright © 2019 Tianjin University. Publishing Service by Elsevier B.V. on behalf of KeAi Communications Co., Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
1. Introduction Magnetorheological (MR) finishing (MRF) is a computer-controlled deterministic polishing technique developed by Kordonski based on previous works on intelligent fluids.1 To date, this process is widely used in the fabrication of high-quality optical components with freeform surfaces. Many researchers have developed a number of new MRF processes and experimental setups for finishing of different sizes and shapes of complicated components. Salzman et al. investigated the effect of chemical composition and pH of MR fluid on the material removal and surface quality for the MRF of infrared polycrystalline materials.2,3 Sidpara et al. developed a MR fluid based finishing tool mounted on the three-axes CNC milling machine for finishing knee joint implants with complex freeform surfaces, and the best final surface roughness value obtained was 28 nm.4–6 They also proposed a rotational–MR abrasive flow finishing process for finishing of this freeform surface component, and a surface roughness ranging from 35 nm to 78 nm was achieved at various locations.7 Singh et al. developed a MRF device using an electromagnetic finishing tool for finishing flat and 3D workpiece surfaces, and the roughness of flat ground surface was reduced to as low as 19.7 nm after 120 min of finishing.8,9 Nanofinishing of the BK7 glass specimen was carried out, and surface roughness value Ra was reduced from 41 nm to 17 nm after 90 min of finishing.10 Then, a newly MR fluid based honing process was developed for internal surface finishing of ferromagnetic cylindrical workpiece.11,12 ⁎ Corresponding author. E-mail address: [email protected] (M. Chen).
For the finishing complex components of concave surfaces with small curvature radius, a MRF process using small ball-end permanent-magnet (SBEPM) polishing head and a four-axes linkage dedicated polishing device were developed. In the present work, the proposed MRF process is employed for the nanofinishing of an irregular ψ-shaped small-bore complex component with curved surfaces. Magnetostatic simulation during the entire finishing path is carried out to analyze the material removal characteristics and used as a basis for surface finishing.
2. MRF process using SBEPM polishing head A MRF process using a small ball-end polishing head is proposed to finish the complex component with small-curvature-radius concave surfaces. The polishing head comprises rare-earth permanent magnet to generate a gradient magnetic field in the polishing area, and the MR fluid forms a solid-like flexible polishing film adhering to the polishing head surface (Fig. 1). The carbonyl iron particles (CIPs) contained in the MR fluid become polarized and form a series of CIP chains along the direction of external magnetic field. Then, the nonmagnetic abrasive particles are firmly gripped by the CIP chain structure and shoved toward the workpiece surface to produce a shear squeeze and wear out the peaks due to relative motions on the finishing surface. The stiffened MR fluid driven by high-speed rotating polishing head generates a hydrodynamic flow at the polishing gap to apply hydrodynamic pressure and shear stress on the workpiece surface to achieve material removal. Fig. 2(a) shows the surface topography of a typical polishing spot created by the proposed MRF process.
https://doi.org/10.1016/j.npe.2019.10.001 2589-5540/Copyright © 2019 Tianjin University. Publishing Service by Elsevier B.V. on behalf of KeAi Communications Co., Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
Please cite this article as: H. Liu, J. Cheng, T. Wang, et al., Magnetorheological finishing of an irregular-shaped small-bore complex component using a small ball-..., , https://doi.org/10.1016/j.npe.2019.10.001
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H. Liu et al. / Nanotechnology and Precision Engineering xxx (xxxx) xxx
Fig. 1. Developed MRF process using a SBEPM polishing head. (a) Schematic of the proposed MRF process; (b) stiffened MR fluid adhering to the polishing head; (c) photo of the polishing tool.
Compared with conventional wheeled MRF process, the proposed MRF process using a considerably smaller polishing head is provided with more complicated material removal characteristic. The magnetic flux density generated by the permanent magnetic polishing head is unevenly distributed around the hemispherical head. The inhomogeneous magnetic field results in the different material removal characteristics on the polishing head due to variation in the finishing angle γ between the normal line of the workpiece surface and axis of the polishing tool. A series of polishing spots is created by the proposed MRF process under different finishing angles, and the surface topography of the MRF spots is measured by interference microscope to acquire the material removal rate. Based on the experimental research, the relationship between the material removal rate and finishing angle γ is exhibited, as presented in Fig. 2(b). The material removal rate depends on the relative processing velocity and magnetic flux density in the polishing gap, which affects the shear yield stress of the MR fluid. Thus, the machining posture of the MR finishing tool should be controlled during processing.
device is set up (Fig. 3). The polishing tool using a SBEPM polishing head with a diameter of 4 mm is installed on the vertical Z-axis movement system. The polishing spindle is mounted below a C-axis rotary table and is tilted horizontally to achieve an inclined-axis process. This process can avoid interference when finishing the irregularly shaped complex component. The ψ-shaped small-bore component is fitted into the workpiece spindle mounted on the X–Y linear movement slides. MR fluid is delivered to the processing area by a peristaltic pump. The MR fluid adsorbed on the surface of polishing head generates a high apparent viscosity and produces relative motion between with the workpiece surface to apply hydrodynamic pressure and shear stress on the workpiece surface. The material removal amount and polishing force can be controlled by adjusting the process parameters, such as the rotation speed of polishing tool and workpiece, polishing gap, feed speed, and space angle of the polishing tool, to guarantee the polishing accuracy and surface quality.
3. MF finishing of a ψ-shaped component
3.2. MF finishing of the Ψ-shaped component
3.1. Experimental setup
Fig. 3(b) shows the ψ-shaped rotary workpiece whose material includes fused silica. The minimal transition fillet curvature radius of the curved surfaces is less than 3 mm. The structure of the component is a thin-walled hemisphere shell with a central shaft. To achieve the
According to the requirements of the MRF processing of a typical ψshaped small-bore complex component, a four-axes linkage polishing
Fig. 2. Material removal characteristic of the proposed MRF process. (a) Surface topography of a typical polishing spot created by the SBEPM MRF process; (b) relationship between the material removal rate and finishing angle γ.
Please cite this article as: H. Liu, J. Cheng, T. Wang, et al., Magnetorheological finishing of an irregular-shaped small-bore complex component using a small ball-..., , https://doi.org/10.1016/j.npe.2019.10.001
H. Liu et al. / Nanotechnology and Precision Engineering xxx (xxxx) xxx
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Fig. 3. Experimental setup for finishing of a ψ-shaped component. (a) Photo of the device; (b) the ψ-shaped component; (c) machining principle.
finishing of this irregularly shaped component, a polishing tool with SBEPM polishing head has to be employed to make effective contact with the small-curvature-radius concave surfaces. The machining principle of this ψ-shaped complex component is that the polishing head, which is set at the middle section of the specimen, moves along the central rod and internal and external spherical surfaces of the workpiece. Both surfaces rotate around their revolving axes, as shown in Fig. 3(c). The machining trajectory is established by the linear motion of X–Y axes units cooperating with the C-axis movement of the polishing tool. Fig. 4 illustrates a schematic of the processing of internal and external spherical surfaces of the component surface. Given the avoidance of interference and the change in material removal rate, the space angle α of the polishing tool changes twice during processing of the internal spherical surfaces, whereas three changes occur when processing the external spherical surface. Thus, the characteristics of material removal in the polishing area vary at different angular positions θ of the polishing trajectory. To realize the deterministic removal of surface material to maintain the surface accuracy, material removal characteristics during the entire polishing trajectory should be analyzed.
4. Analysis of magnetic field in the polishing area The present SBEPM MRF process uses flexible polishing mold formed on surface of polishing head to remove material from the workpiece surface by shearing action. As the magnetic flux density is one of the most important factors affecting the process performance, magnetostatic finite element simulation is carried out to analyze the distribution of magnetic field in the polishing area for 0.1 mm working gap when processing both the internal and external spherical surfaces under different angular positions θ. Figs. 5 and 6 show the results of the magnetostatic simulation for finishing of the internal and external spherical surfaces under a typical angular position. The findings show that the distribution of magnetic flux density is influenced by the specimen and forms a local stronger magnetic gradient field in the polishing gap. Therefore, MR polishing fluid could be retained more strongly around the polishing head, and the magnetic flux lines from the polishing gap gradually become parallel to the workpiece surface. As a result, higher magnetic shear forces can be produced to shear the materials from the peaks of the workpiece surface by shear forces.
Fig. 4. Processing of spherical surfaces. (a) Internal surface; (b) external surface.
Please cite this article as: H. Liu, J. Cheng, T. Wang, et al., Magnetorheological finishing of an irregular-shaped small-bore complex component using a small ball-..., , https://doi.org/10.1016/j.npe.2019.10.001
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H. Liu et al. / Nanotechnology and Precision Engineering xxx (xxxx) xxx Table 1 Processing parameters for surface finishing of the small-bore complex component.
Fig. 5. Typical result of magnetostatic simulation for finishing the internal surface. (a) Distribution of magnetic flux density; (b) polishing gap area; (c) curve of magnetic flux density.
Polishing spindle speed (rpm)
Workpiece spindle speed (rpm)
Polishing gap (mm)
C-axis Feed Processing angular speed time position α (mm/min) (min) (°)
6000
250
0.1
−30–80
1.8
540
Figs. 5(b) and 6(b) show the distribution of local magnetic flux density in the polishing gap with a width range of 1.5 mm centered at the minimum interspace. Figs. 5(c) and 6(c) plot the curve of magnetic flux intensity changes on the finishing surface. Simulation results show the maximum value of magnetic flux intensity achieved on the finishing surface. Further simulation analyses reveal that the position of this peak intensity of magnetic field gradually changes from one side of the minimum processing interspace to gradually away from the interspace on the other side under different angular positions θ. Fig. 7 displays the magnetic flux density at the position of minimum processing interspace under different angular positions. As depicted in the illustration, the variation in magnetic flux density at the minimum polishing gap is comparative less during the finishing of external spherical surface. However, magnetic field is relatively low when processing the internal spherical surface on the interior, where the angular position θ is between 50° and 63°. As the characteristics of material removal change based on the variation of magnetic flux density on finishing surface, the parameters for component finishing process should be regulated accordingly to ensure the surface accuracy. 5. Experiment on the MRF of the small-bore complex component
Fig. 6. Typical result of magnetostatic simulation for finishing the external surface. (a) Distribution of magnetic flux density; (b) polishing gap area; (c) curve of magnetic flux density.
MR finishing of the ψ-shaped small-bore complex component is conducted. The initial surface of the experimental component is obtained by precision grinding using a small diamond wheel, and the MRF process is used to improve the surface quality and maintain the structural surface accuracy. The processing procedure applied for the experiment is designed as a repeated cycle of operation, and the processing parameters are listed in Table 1. The MR fluid used in the analysis and experiments is self-made in laboratory, and it is formulated by a waterbased fluid with proper amount of cerium oxide abrasive particles and CIPs. The average particle size of cerium oxide abrasive particles is 3 μm, while that of the CIPs is 4 μm. And the composition of synthesized MR fluid is shown in Table 2. Fig. 8(a) shows a photograph of the finishing process. The surface profile of the component after polishing is measured by Taylor Hobson roughness profiler PGI 1240. The experimental results in Fig. 8 show that the finished surface roughness Ra is improved from 0.0538 μm to 0.0107 μm, and the surface accuracy of the spherical surfaces equals 0.3320 μm (PV). A higher quality surface finish can be produced by further optimizing process parameters. These findings indicate that the proposed SBEPM MRF process can perform the nanofinishing of a kind of small-bore complex component with small-curvature-radius concave surfaces. 6. Conclusions According to the requirements of the processing of a typical ψshaped small-bore complex component, a four-axes linkage polishing
Table 2 Composition of synthesized MR fluid.
Fig. 7. Curve of magnetic flux density at the minimum polishing gap on finishing surfaces.
Constituent
% Volume concentration
Water-based fluid medium Carbonyl iron particles Cerium oxide abrasive particles Stabilizing agent
57 36 6 1
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Fig. 8. MR finishing of small-bore complex component. (a) Finishing in process; (b) measurement result of finished surface roughness; (c) surface accuracy measured by Taylor Hobson surface profiler.
device is fabricated using the SBEPM MRF process. The processing method of the ψ-shaped complex component is introduced. During the polishing process, the machining posture of a polishing tool is controlled to rotate several different angular positions to avoid interference and collision. Magnetostatic finite element simulation is carried out, and the magnetic flux density at the position of minimum processing interspace under different angular positions during the entire finishing path is analyzed. MR finishing of the ψ-shaped small-bore complex component is conducted, and a fine surface quality is obtained.
Acknowledgments This work was supported by the National Key Research and Development Program of China [grant number 2018YFB1107600].
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Mingjun Chen received his Ph.D. degree in Mechanical Engineering from Harbin Institute of technology, China, in 2001. He is currently a professor and Ph.D. candidate supervisor in Harbin Institute of technology, China. His research interests include precision and ultra-precision machining, micro machining and biomaterial compatibility evaluation.
Please cite this article as: H. Liu, J. Cheng, T. Wang, et al., Magnetorheological finishing of an irregular-shaped small-bore complex component using a small ball-..., , https://doi.org/10.1016/j.npe.2019.10.001