Wenlong Chang

Fabrication of periodic nanostructures by single-point diamond turning with focused ion beam built tool tips

Periodic nanostructures have been widely used on emerging nano-products such as plasmonic solar cell and nano-optics. However, lack of cost-effective fabrication techniques has become the bottleneck for commercialization of these nano-products. In this work, we develop a scale up approach to fabricate high-precision nanostructures in large area. In this method, a nano-scale single crystal diamond (SCD) tool is produced by focused ion beam (FIB) machining. The nano SCD tool is then further applied to cut periodic nanostructures using single-point diamond turning (SPDT). A divergence compensation method and surface topography generation model forms a deterministic FIB fabrication approach. It has been used to generate four periods of the required periodic nano-grating structures (with a minimal dimension of 150 nm) on a normal SCD tool tip and achieves 10 nm form accuracy. The contribution of the beam tail effect has also been evaluated by using the surface topography simulation method. The fabricated diamond tool is then applied to obtain nano-grating on an electroless nickel substrate in a total area of 5 × 2 mm2 through SPDT. The whole SPDT machine process only takes 2 min (with a material removal rate up to 1.8 × 104 μm3 s−1). Due to the elastic recovery that occurred upon the workpiece material, the practical cutting width is 13 nm smaller than the tool tip. The machining trial shows it is very promising to apply this scale up nanofabrication approach for commercialization of nano-products which possess period nanostructures.

Laser assisted micro grinding of high strength materials

This paper aims to develop a laser assisted grinding process capable of manufacturing micro features in high strength materials. A diode laser with wavelength 808 nm was set on a precision grinding machine. Micro grooves were fabricated on high strength materials including silicon nitride and aluminium oxide by using the laser assisted grinding process, i.e. laser pre-heat workpiece flowed by micro grinding. The experimental results showed that the laser assisted grinding process resulted in deeper grooves due to thermal expansion of workpiece materials caused by laser heating. However, the machined surface roughness was more consistently better than that obtained using solo grinding process and applying coolant. No subsurface damage was observed in the SEM images of cross sections of the machined workpieces when laser assisted grinding process was used.

Single Point Diamond Turning of Calcium Fluoride Optics

This paper aims to develop a cost-effective diamond turning process to obtain nanosmooth CaF2 optics. Diamond tool wear was also carried out through a number of cutting trials. Three CaF2 specimens (diameter of 50 mm and thickness of 5 mm, crystal orientation of (111)) were diamond turned on an ultra precision lathe (Moore Nanotech 350UPL) by a number of facing cuts. In the cutting trials feed rate varied from 1 μm/rev to 10 μm/rev. White spirit mist was used as the coolant. Cutting forces were measured by a dynamometer (Kistler BA9256). Surface roughness of the CaF2 optics and tool flank wear were measured by a white light interferometer (Zygo Newview 5000) and a scanning electron microscope (FEI Quanta 3D FEG), respectively. It was found that using a feed rate of 1 μm/rev surface roughness Ra of 2 nm could be obtained. When the ratio of the normal cutting force to the tangential cutting force was lower than 1 tool wear would initiate. In diamond turning of calcium fluoride abrasive wear was the main tool wear mechanism. Using white spirit mist as thecoolant could avoid generation of thermal type brittle fracture on the machined CaF2 surfaces.

Fabrication of microfluidic injection moulds by a hybrid micromachining process

In this paper a hybrid micromachining approach was developed for the fabrication of microfluidic injection moulds. A micro injection mould with 500μm wide and 200μm high channels was machined by high-speed micromilling. The microchannels inside the mould were then processed by a Nd:YAG laser to remove the burrs generated in the micromilling process. The measurement results confirmed the effectiveness of this hybrid micromachining process in obtaining high-quality microproducts.

Design of compliant parallel grippers using the position space concept for manipulating sub-millimeter objects

The structure or configuration of compliant mechanisms can be reconfigured through changing the positions of each compliant module thereof within their position spaces. A number of 1-DOF 2-PRRP compliant parallel grippers (CPGs) can be obtained using the structure re-configurability for manipulating sub-millimeter objects. Even with the geometrical parameters for the systems pseudo-rigid-body model (PRBM) and each compliant module kept at the same values, the position of each compliant joint can be anywhere within its position space. The performance of the resulting CPG varies with the position of the compliant joint. In this paper two typical CPG designs are presented and analyzed. Comparisons between FEA simulaiton resutls and analytical models show that the input-output kinematic relationship of the non-compact design agrees better with that of the PRBM due to its better load transmissibility. One can design different structures based on specific design requirements.

Laser deburring process for structured edges on precision moulds

In this paper a laser deburring process is developed to remove micro burrs generated by micromilling processes in order to obtain high quality micro fluidic injection mould. A two-temperature model (TTM) is used to determine the critical laser machining parameters such as the laser energy density and laser power. The laser deburring experiment is carried on by using an Nd:YAG nanosecond laser source with frequency of 15 Hz and a spot size of 5 μm. The edge quality and the machined surface of micro channels in the micro fluidic mould are measured by a SEM and a white light interferometer. The measurement results show that the micro burrs on the micro channels in the micro fluidic mould have been completely removed. The average surface roughness (Ra) was only 0.114 μm after the laser deburring process. Therefore, laser deburring process cannot only remove micro burrs on the micro fluidic channel but also help to achieve good surface finish on the mould.

A new grinding force model for micro grinding RB-SiC ceramics with grinding wheel topography as an input

The ability to predict the grinding force for hard and brittle materials is important to optimize and control the grinding process. However, it is a difficult task to establish a comprehensive grinding force model that takes into account the brittle fracture, grinding conditions, and random distribution of the grinding wheel topography. Therefore, this study developed a new grinding force model for micro-grinding of reaction-bonded silicon carbide (RB-SiC) ceramics. First, the grinding force components and grinding trajectory were analysed based on the critical depth of rubbing, ploughing, and brittle fracture. Afterwards, the corresponding individual grain force were established and the total grinding force was derived through incorporating the single grain force with dynamic cutting grains. Finally, a series of calibration and validation experiments were conducted to obtain the empirical coefficient and verify the accuracy of the model. It was found that ploughing and fracture were the dominate removal modes, which illustrate that the force components decomposed are correct. Furthermore, the values predicted according to the proposed model are consistent with the experimental data, with the average deviation of 6.793% and 8.926% for the normal and tangential force, respectively. This suggests that the proposed model is acceptable and can be used to simulate the grinding force for RB-SiC ceramics in practice.

A generic control architecture for hybrid micro-machines

Hybrid micro-machining, which integrates several micro-manufacturing processes on one platform, has emerged as a solution to utilize the so-called “1 + 1 = 3” effect to tackle the manufacturing challenges for high value-added 3D micro-products. Hybrid micro-machines tend to integrate multiple functional modules from different vendors for the best value and performance. However, the lack of plug-and-play solutions leads to tremendous difficulty in system integration. This paper proposes a novel three-layer control architecture for the first time for the system integration of hybrid micro-machines. The interaction of hardware is encapsulated into software components, while the data flow among different components is standardized. The proposed control architecture enhances the flexibility of the computer numerical control (CNC) system to accommodate a broad range of functional modules. The component design also improves the scalability and maintainability of the whole system. The effectiveness of the proposed control architecture has been successfully verified through the integration of a six-axis hybrid micro-machine. Thus, it provides invaluable guidelines for the development of next-generation CNC systems for hybrid micro-machines.

Superhydrophobicity of micro-structured surfaces on zirconia by nanosecond pulsed laser

Abstract This article presents a systematic approach to improve the hydrophobicity of microstructured surfaces. It includes a contact angle prediction model for microstructures obtained by nanosecond pulsed laser. Combining with the theoretical constraints for stable Cassie–Baxter state, this approach can be used to optimize microstructures dimensions for maximizing surface hydrophobicity. Laser machining experiments were conducted to evaluate the prediction model. It shows that the proposed systematic approach can accurately predict the contact angle and obtain microstructures dimensions for maximizing surface hydrophobicity. The results also indicate that the contact angle increases with the decrease of pitch of the microstructures. Superhydrophobicity with maximum contact angle of 155.7° is obtained, for the first time, on a microstructured surface (P030) of zirconia with a pitch of 30 µm machined under a laser power at 8W.

Fabrication of hydrophobic structures by nanosecond pulse laser

In this paper, a feasibility study of manufacturing anti-bacteria surface on stainless steel 7C27Mo2 used for surgical tools by using nanosecond pulse laser is presented. The effect of laser power on the depth of groove was studied through laser cutting experiment. Micro-pillar arrays of different dimensions and spacing were generated by laser cutting. The wetting characteristics of micro-structured surfaces were assessed by using the static contact angle measurement approach. The measurement results show that the original hydrophilic stainless steel surface can be converted into a hydrophobic surface by using laser structuring as the contact angle can be doubled. This research shows that it is feasible to manufacture hydrophobic microstructures with a laser cutting process.