Micro-/Nano-texturing by Ultrasonic-Assisted Grinding
In this chapter, a novel ultrasonic-assisted micro-/nano-texturing method was proposed and developed. A new 3D ultrasonic vibration spindle was developed for carrying out the proposed processes. The texturing mechanisms were analyzed by mathematically calculating the cutting loci and establishing the surface generation modeling processes. Finally, the tool design principles were proposed and experimentally verified. The experimental results and theoretical analysis proved that the proposed method can rapidly and precisely fabricate tailored surface textures at micrometer and nanometer scales.
KeywordsMicro-/nano-texturing Ultrasonic assisted grinding Texured surface Functional surface
1.1 Micro-/Nano-texturing Technologies
Methods for fabricating textured surfaces comprising micro-/nanostructures have been exploited in many industries (Masuzawa 2000).
Conventional diamond machining processes, including turning, cutting, milling, microgrinding, and fly cutting, produce surface textures by removing the material using mechanical forces. These methods are capable of machining ultraprecise microstructures (Brinksmeier et al. 2012; Denkena et al. 2010), which are usually fabricated on mold inserts when replicating structures on polymer or glass materials or are directly fabricated on engineering components. There are no specific material requirements for the machining objects because diamond has the highest hardness in nature. On the other hand, tool wear can be an issue, especially when machining ferrous metals. The reason for this is that the high machining temperature usually results in graphitization of the diamond by the ferrous metals (Shimada et al. 2004), which greatly accelerates tool wear and deteriorates surface quality. Surface textures at the submicrometer scale are also difficult to obtain using conventional diamond machining because the radius of the cutting edge is limited and cutting burrs on the edges of the microstructures are usually difficult to prevent or remove (Yan et al. 2009).
Besides using mechanical energy, optical energy and electrical energy are popularly utilized in the current industry, for example, laser beam machining (LBM) (Dubey and Yadava 2008) and electrical discharge machining (EDM) (Ho and Newman 2003; Abbas et al. 2007). Both methods provide optical or electrical energy to the work material, which is locally removed via melting and evaporation. Laser beam or electrical discharge can easily provide heat that exceeds the boiling point of any material. However, in practice, certain materials with low optical absorbance or low electrical conductivity cannot be processed by such methods; therefore, it is very difficult to obtain highly precise structures and surfaces using these methods. The heat-affected zone on the machined surface is also an inevitable problem. However, with the development of the excimer laser and femtosecond laser, ultrashort laser pulses can be used to remove the material by vaporization; this mitigates the melting phase, which can help in obtaining high dimensional accuracy and fewer heat defects (Liu et al. 1997; Cheng et al. 2013). On the other hand, the machining efficiency is usually lower than that of LBM or EDM.
The micro-fabrication methods used in the microelectromechanical system (MEMS) field, including lithography, chemical etching, plasma etching, electron (or ion) beam etching, and oxidation, are capable of the fabrication of very complex structures at the micrometer and nanometer scales (Lyshevski 2002); these are widely used in the semiconductor industry. However, these methods do exhibit certain problems, such as the limitations of the machinable materials, complicated fabrication processes, and costly equipment. In addition, the fabrication processes are usually carried out in a direction perpendicular to the workpiece surfaces, which also restricts the machinable structures.
Replication processes (Hansen et al. 2011), including molding and embossing (or imprinting), can be used to fabricate microstructures at a relatively low cost and high efficiency. The textural patterns are directly reproduced from those of a die or a mold. However, the materials used for the dies must possess high-temperature strength, thus limiting the range of potential materials. A molding process is typically used when fabricating textures on glass, polymeric, or metal materials, which are melted and then solidified into a mold to replicate the structure. Only metals that exhibit good ductility and are softer than the die/mold materials can be used for the embossing process. A major problem with replication processes is the loss of shape accuracy.
Self-assembling methods like chemical vapor deposition (CVD) and physical vapor deposition (PVD) can be used for producing structures at micrometer and nanometer scales (e.g., nanotubes and nanowire) (Stupp et al. 1997; Shimomura and Sawadaishi 2001). However, these methods are limited to specific materials and are usually time-consuming and costly.
For the generation of geometrically defined surface textures, diamond machining methods have strong merits, including high form accuracy, high flexibility, and high productivity (Denkena et al. 2010). In recent decades, hybrid diamond machining processes, such as laser-assisted machining and ultrasonic-assisted machining, have been developed for improving diamond machining performance. For example, the laser-assisted turning process has been proved to have a higher material removal rate (Rozzi et al. 2000a, b) and to potentially suppress the generation of cutting burrs. The elliptical vibration-assisted cutting process has been proved applicable to machine brittle materials in the ductile regime, helping to decrease tool wear and improve surface quality (Shamoto and Moriwaki 1994; Moriwaki and Shamoto 1995).
1.2 Rotary Ultrasonic Texturing
Rotary ultrasonic machining has been widely used in grinding, drilling, and milling operations to fabricate flat surfaces, holes, and various surface structures (Brehl and Dow 2008). To study the effect of ultrasonic vibration on improvements in surface quality in the 1D ultrasonic-assisted grinding process, K. Shimada (2012) established a theoretical calculation model for predicting the grinding forces and roughness of finished surfaces and found that some micro- and nanostructures could be fabricated using the ultrasonic-assisted slant-feed grinding (UASG) method.
The combination of ultrasonic vibration, tool rotation, and workpiece feed motion can lead to a high-frequency periodic change of the cutting locus of every cutting edge on the grinding wheel. The texturing principle is to fabricate surface textures at the micrometer/nanometer scale by intentionally controlling the cutting locus; the periodic features of the cutting locus can be of micrometer or submicrometer dimensions under appropriate experimental conditions. Until now, only one paper has reported the fabrication of micro-textures using 1D rotary ultrasonic machining with the principle mentioned above – D. Xing (2013) (Xing et al. 2013) studied the kinematics of cutting edges in a 1D ultrasonic-assisted milling process and fabricated a micrometer-scale scaly textured surface on aluminum alloy by controlling the high-frequency periodic change of the cutting locus. There has been no report on the fabrication of surface textures using a 3D rotary ultrasonic machining process, except for the previous work reported by the authors of the present dissertation (Xu et al. 2013, 2014).
In this chapter, a novel ultrasonic-assisted micro-/nano-texturing method that uses diamond grinding wheels or one-point diamond tools, referred to as the rotary ultrasonic texturing (RUT) method, is proposed and developed. A new 3D ultrasonic vibration spindle was firstly developed for carrying out the RUT processes. The surface generation processes were analyzed by mathematically calculating the cutting loci under different vibration modes. The material removal mechanisms were studied by analyzing the relationship between the geometry of the cutting edges and the related textural features. Then, the geometrically defined diamond tools were designed and manufactured for the RUT process, and surface generation models for the use of these tools were established for predicting the 3D surface textures.
2 Development of Equipment for Rotary Ultrasonic Texturing
The vibration mode depends on the structure of the ultrasonic vibrator. There are typically two types of ultrasonic vibrator, magnetostrictive and piezoelectric (Thoe et al. 1998). The resonant piezoelectric vibrator was selected for manufacturing the 3D ultrasonic vibration spindle in the present study. The vibrator is resonated by exciting several combined piezoelectric plates, which are sandwiched between metal cylindrical horns, with high-frequency electrical signals; this system is generally referred to as a bolt-clamped Langevin-type transducer (BLT) (Kurosawa et al. 1998). The high-frequency electrical energy is converted into mechanical vibration via the resonant piezoelectric transducer (PZT). The horn/tool assembly is used to amplify the vibration amplitude of the tool because the oscillation amplitude at the face of the piezoelectric transducer is too small to achieve a reasonable cutting rate.
Specifications of the 3D ultrasonic vibration spindle
3D ultrasonic vibration spindle (SC-450SP-H24)
0–4000 rpm (stable at 0–3000 rpm)
Bolt-clamped Langevin-type transducer (BLT)
Microcomputer-controlled phased-locked loop-type automatic synchronization system
Protruding length of tools/total tool length
Clamping torque of bolt
Vibration frequency (LV mode)
25.0 ± 3.0 kHz
Vibration frequency (CV mode)
19.0 ± 2.0 kHz
Vibration amplitude (LV mode)
1.5 μm (L)
3 μm (H)
Vibration amplitude (CV mode)
10 × 10 μm2 (L)
15 × 15 μm2 (H)
3 Proposed UASG Method
3.1 The Calculation of the Cutting Loci
To determine the texturing mechanisms of the UASG technique, the kinematic motion of the diamond cutting abrasives should first be analyzed. The vibration loci in the LV, CV, and HV modes can be calculated by Eqs. (1), (2), and (3), respectively, as follows.
In the tool-in-hand coordinate system shown in Fig. 8, the cutting locus of every diamond abrasive in the UASG process can be mathematically calculated using Eqs. (4), (5), and (6) in the LV, CV, and HV modes, respectively, where v fy and v fz are the feed speeds in the y and z directions, D is the tool diameter, h p is the protrusion height of the diamond cutting abrasive, n t is the rotational frequency of the diamond tool, and φ r is the initial phase of the rotational motion.
3.2 Conventional Grinding and Slant-Feed Grinding
In contrast, during the SG process, the cut track produced during each rotation period is individually duplicated on the surface of the workpiece with no (or minimal) overlap along the slanted feed direction. Only diamond abrasives with a larger protrusion height than that of adjacent diamond abrasives (e.g., the diamond abrasives labeled 1, 2, 3, and 4 in Fig. 13b) will leave obvious effective cut tracks on the finished surface. Therefore, the surface textures shown in Fig. 13d were generated using the SG method. The length of each cut track along the slant feed direction is determined by the protrusion height and distribution of the diamond cutting abrasives.
3.3 Surface Texturing Mechanisms
4 Experimental Verification and Discussion
4.1 Experimental Conditions
Diameter of grinding wheel (mm)
Diamond grit mesh
#600, #1000, #3000
ZrO2 ceramics (13 × 14 × 17 mm3)
Rotation frequency (rpm)
Feed speed along Y axis (mm/min)
Feed speed along Z axis (mm/min)
Grinding depth (μm)
Vibration frequency (LV) (kHz)
Vibration frequency (CV) (kHz)
Vibration amplitude (LV) (peak-to-peak) (μm)
Vibration amplitude (CV) (peak-to-peak) μm2
10 × 10
4.2 Experimental Results
4.3 Limitations of the UASG Technique
The experimental results reveal that the UASG method can be used for fabricating different periodic micro-/nano-textures in the LV and CV modes or random-like surfaces in the HV mode. The irregular shapes of the diamond cutting abrasives also provided various machined structures in the UASG method. If the textural pattern must be controlled, the shapes and distribution of the diamond abrasives must be tailored. In addition, it is virtually impossible to determine the relationship between the shapes of the diamond cutting abrasives and the textural features. Therefore, it is preferable to use another tool to determine the mechanisms of material removal during the micro-/nano-texturing process. To fully control the texturing process, the cutting edges should be geometrically designed and regularly distributed on the surface of the tool. As such, the next section describes the design and manufacture of diamond tools with only one cutting tip. These are referred to as one-point diamond tools, and these were produced using electroplating in the RUT process.
5 Rotary Ultrasonic Texturing Using One-Point Diamond Tools
5.1 Theories of Texturing Mechanisms
5.1.1 Surface Generation Mechanisms in the LV Mode
5.1.2 Surface Generation Mechanisms in the CV Mode
If 0 < a p < h c *, the depth of the textured patterns (h c ) is equal to a p , and the width of the textured patterns (w c ) is smaller than w c *; thus, discontinuous textured patterns will be generated. If a p ≥ h c *, the depth of the textured patterns (h c ) is equal to h c *, and the width of the textured patterns (w c ) is equal to w c *; thus, continuous textured patterns will be fabricated.
5.2 Texturing Procedures and Corresponding Cutting Loci
In Fig. 30a, the parameter (w g ), the width of a machined area at a certain cutting depth (a p ) in one rotation period, has to be considered; this can be calculated using Eq. (16). If w g is smaller than d y , each machined surface along the Y axis will be disconnected. In contrast, if w g is bigger than d y , the machined surface areas along the Y axis will be connected. In the LV mode, sinusoidal cutting loci (as shown in Fig. 30b) can be generated, whereas in the CV mode, 2D cutting loci (as shown in Fig. 30c) can be generated.
In Fig. 31a, the parameters l y and h g must be considered. The term l y can be calculated using Eq. (17), and h g is given by Eq. (18); δ is the solution of Eq. (19). It can be found that the rotational speed and the feed speed along the Y axis determine l y and h g . If a p is smaller than h g , each machined surface area along the Y axis will be disconnected. In contrast, if a p is no smaller than h g , the machined surface areas along the Y axis will be connected. The specific shapes of the cutting loci depend on the tool parameters and experimental conditions. The radial motion of the tool changes the cutting depth from 0 to the maximum value (a p ) and then back to 0 during each rotation period; this must be considered in the RUT process.
5.3 Design of Geometrically Defined One-Point Diamond Tools
The diamond cutting tip shown in Fig. 32 was used for preliminary testing of the RUT process in the LV and CV modes. A square pyramid cutting tip is fixed at the bottom of the tool shank. The included angle of two opposite faces (e.g., face ABE and face CDE) is about 70.5°, and the nose radius is approximately 200 nm.
Figure 33 shows the diamond tool with a triangular pyramid cutting tip, which was used for micro-/nano-texturing in the LV mode. The cutting edge AD (or BD) acts as the advance cutting edge when the tool feeds along the negative (or positive) Z axis. The faces ACD and BCD are the two rake faces when the tool vibrates downward and upward, respectively. The cutting corner D has a radius of approximately 200 nm.
Figure 34 shows the one-point diamond tool designed for the RUT process in the CV mode. The turning diameter is 3.6 mm. A two-level flank face was designed with clearance angles of 15° and 30° to ensure the strength of the cutting edge and reduce the interference between the rake face and workpiece. The major cutting edge has an included angle of 5° to the Z axis, and the minor cutting edge has an included angle of 10° to the Y axis. The nose radius is approximately 20 μm.
5.4 Modeling of the Surface Generation Process
The final research objective of the work described in this chapter was to fabricate different surface micro-/nano-textures using the RUT method. Therefore, before conducting practical experiments, it was necessary to predict the machinable structures based on the cutting locus and the diamond cutting tip’s geometry, which can also be used to guide the design of cutting tip geometries and texturing parameters. There have been many approaches reported (Ehmann and Hong 1994; Lin and Chang 1998; Lee and Cheung 2001; Kim et al. 2002) for predicting surface topography in the diamond machining processes. However, most of these studies only report the resultant surface profiles, and they focus on changes in surface roughness. In this chapter, the textural features of the finished surface at the micrometer/nanometer scale are of greater interest. The material removal process during each vibration period must also be visualized in order to determine the material removal mechanisms. Therefore, a new modeling method applicable to surface generation in the RUT process is proposed. This method can be used to simulate the 3D surface profiles of finished surfaces and visualize the cutting process in each vibration period.
5.4.1 Assumptions in the Modeling Process
In the RUT process, each tool rotation fabricates a cut track on the surface of the workpiece at a certain cutting depth. The feed rate along the Z axis is usually set at 0 or a value much lower than the peripheral velocity of the rotating tool. Thus, the included angle between each cutting path on the machined area and the Y axis is maintained at 0 or a very small value, which can be ignored. Therefore, in the modeling process, the direction of each cutting path along the workpiece should be horizontal along the Y axis. The instantaneous cutting depth is also assumed to be constant along each cutting path and equal to the cutting depth. Mechanical deformation of the workpiece is not considered, and the workpiece material is assumed to be fully removed when the rake face contacts the workpiece. The interference between the flank face and workpiece is taken into account.
5.4.2 Surface Generation Model Under the LV Mode
5.4.3 Surface Generation Model for the CV Mode
5.5 Fabrication of Micro-/Nano-textures
5.5.1 Micro-/Nano-texturing in the LV Mode
Workpiece (Ni-P plating)
Rotational frequency (rpm)
Feed speed along Z axis (mm/min)
Cutting depth (μm)
Ultrasonic vibration spindle (SD-100)
Vibration frequency (kHz)
Vibration amplitude (peak to peak) (μm)
Ultrasonic vibration spindle (SC-450SP-H24)
Vibration frequency (kHz)
Vibration amplitude (peak to peak) (μm)
5.5.2 Micro-/Nano-texturing in the CV Mode
Experimental conditions in the CV mode
Phosphorous content: 10 wt.%
Rotational frequency (rpm)
500, 1000, 3000
Feed speed along Z axis (mm/min)
2, 4, 40, 120
Cutting depth (μm)
Ultrasonic vibration spindle (SC-450SP-H24)
Vibration frequency (kHz)
Vibration amplitude (peak to peak) (μm2)
10 × 10
5.6.1 Effect of Cutting Loci Shape
The surface condition that occurs in most machining operations is a result of the cutting edge exiting the workpiece (Boothroyd and Knight 2006). The ultrasonic vibration makes the tool periodically vibrate at a very high frequency; thus, the cutting edge contacts and exits the workpiece at the same frequency along the cutting locus. Specifically, the sinusoidal cutting locus in the LV mode in the RUT process makes the cutting edge remove the material and exit the workpiece at each peak point of the sinusoidal locus, which results in the formation of cutting debris and the generation of burrs around the peak points on the textured surfaces. The cutting loci in the CV mode, as described in the modeling process, make the cutting edge intermittently or continuously remove the material. The relationship between the shape of the cutting edge and the shape of the cutting loci determines the interference between the flank face and the workpiece. It also determines the instantaneous rake angle, which results in different material removal mechanisms. The large interference volume and large negative rake angle could be prevented by an improved design of the shape of the cutting loci. The work material is sheared and removed in an ultrasonic periodical manner, which is fundamentally different from that of the conventional cutting process. Therefore, the geometry of the tool cutting tip should be carefully designed to control the generation and removal of cutting chips along the cutting loci, thus allowing for efficient chip removal and the fabrication of surfaces with fewer cutting burrs.
5.6.2 Effect of Cutting Edge Geometry
The geometry of the cutting edges should be designed to more efficiently remove cutting chips and decrease cutting burrs on the edges of textural patterns. This would increase the stability and capability of the micro-/nano-texturing technique.
The radial motion of the diamond cutting tip makes the instantaneous cutting depth change periodically when fabricating textures on flat surfaces. The advance cutting edge could be designed to control the instantaneous cutting depth along the feed direction, i.e., by modulating the amount of the work material removed by the cutting tip in each vibration period, thus making the texturing process more stable.
When the LV mode is employed, the design of the triangular pyramid cutting tip can be used to efficiently remove the cutting chips. As shown in Fig. 36b, the cutting chips and cutting burrs generated in one vibration period can be removed by the cutting process in the next vibration period along the sinusoidal cutting locus. In the case shown in Fig. 36c, the cutting chips and cutting burrs generated by the upper rake face or lower rake face in a half vibration period can be immediately removed by the same rake face in the next half vibration period. Therefore, the adverse effect of the high-frequency tool-exit-workpiece motion can be largely eliminated. Ultimately, the micro-/nano-textures were successfully fabricated.
When the CV mode is employed, the large interference volume between the flank face and workpiece should be avoided. Continuous textural patterns are required to eliminate the adverse effect of the high-frequency tool-exit-workpiece motion. Therefore, the tool flank angle should be designed based on a consideration of the shapes of the applied cutting loci.
6 Summary and Outlook
The newly proposed ultrasonic-assisted texturing method provides designers with additional freedom to fabricate precisely controlled micro-/nano-textured surfaces at relatively high speed. The geometrically defined one-point diamond tools enrich tool design principles in the diamond machining field, and they also enlarge the range of machinable structures possible using diamond machining techniques. Theoretically, various surface textures other than those discussed in the present dissertation can be fabricated using the RUT method if the diamond tools are designed with cutting edges of appropriate geometry. To further develop the RUT technique, diamond tools should be designed and optimized so as to be capable of fabricating the textural patterns required in practical application fields.
In a future work, a more robust and flexible ultrasonic-assisted texturing method should be developed based on the rotary ultrasonic spindle. Moreover, the scientific principles applicable to the design of textural patterns for functional performance should be given greater attention.
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