Dongming Guo

Optimization of cutting conditions for single pass turning operations using a deterministic approach

Abstract An optimization analysis, strategy and CAM software for the selection of economic cutting conditions in single pass turning operations are presented using a deterministic approach. The optimization is based on criteria typified by the maximum production rate and includes a host of practical constraints. It is shown that the deterministic optimization approach involving mathematical analyses of constrained economic trends and graphical representation on the feed-speed domain provides a clearly defined strategy that not only provides a unique global optimum solution, but also the software that is suitable for on-line CAM applications. A numerical study has verified the developed optimization strategies and software and has shown the economic benefits of using optimization.

A Variable-Diameter Capsule Robot Based on Multiple Wedge Effects

Based on multiple wedge effects, this paper describes an innovative variable-diameter capsule robot with radial clearance compensation for active locomotion inside the gastrointestinal (GI) tract using an outer rotating magnetic field. The surface of the capsule robot, encapsulated by a thin latex sleeve for protecting the GI tract from any injuries, is composed of four copper tiles, on which four separated spiral blades are wound respectively. When the capsule robot rotates, its four copper tiles are extended synchronously under the action of their centrifugal forces, achieving reduced clearance between the surface of the capsule robot and the pipe inner wall, and a convergent wedge-like gap between the surface of each of four copper tiles and the pipe inner wall is formed, resulting in multiple wedge effects when fluid travels through the four convergent wedge-like gaps. The radial dynamic balance equation and kinematics equation of the capsule robot are derived according to fluid dynamics. To investigate multiple wedge effects, the capsule robot prototype with clearance compensation has been designed, manufactured, and tested. Simulations and experiments have demonstrated that the propulsion and swimming speed of the capsule robot are significantly improved, and the innovative capsule robot is capable of swimming vertically inside a pigs intestine; thus, it has a promising prospect for medical applications.

Chemical mechanical polishing and nanomechanics of semiconductor CdZnTe single crystals

(1 1 1), (1 1 0) Cd0.96Zn0.04Te and (1 1 1) Cd0.9Zn0.1Te semiconductor wafers grown by the modified vertical Bridgman method with dimensions of 10 mm × 10 mm × 2.5 mm were lapped with a 2–5 µm polygonal Al2O3 powder solution, and then chemically mechanically polished by an acid solution having nanoparticles with a diameter of around 5 nm, corresponding to the surface roughnesses Ra of 2.135 nm, 1.968 nm and 1.856 nm. The hardness and elastic modulus of (1 1 1), (1 1 0) Cd0.96Zn0.04Te and (1 1 1) Cd0.9Zn0.1Te single crystals are 1.21 GPa, 42.5 GPa; 1.02 GPa, 44.0 GPa; and 1.19 GPa, 43.4 GPa, respectively. After nanocutting is performed by the Berkovich nanoindenter, the surface roughness Ra of the (1 1 1) Cd0.9Zn0.1Te single crystal attains a 0.215 nm ultra-smooth surface. The hardness and elastic modulus of three kinds of CdZnTe single crystals decrease with the increase of indentation load. When the nanoindenter departs the surface of the crystals, the adherence effects are obvious for the three kinds of single crystals. This is attributed to the plastic sticking behavior of CdZnTe material at a nanoscale level. When the indentation load of the three kinds of CdZnTe single crystals is in the range of 4000–12 000 µN, the adhered CdZnTe material on the nanoindenter falls onto the surface and accumulates around the nanoindentation.

A novel approach of high speed scratching on silicon wafers at nanoscale depths of cut

In this study, a novel approach of high speed scratching is carried out on silicon (Si) wafers at nanoscale depths of cut to investigate the fundamental mechanisms in wafering of solar cells. The scratching is conducted on a Si wafer of 150 mm diameter with an ultraprecision grinder at a speed of 8.4 to 15 m/s. Single-point diamonds of a tip radius of 174, 324, and 786 nm, respectively, are used in the study. The study finds that at the onset of chip formation, an amorphous layer is formed at the topmost of the residual scratch, followed by the pristine crystalline lattice beneath. This is different from the previous findings in low speed scratching and high speed grinding, in which there is an amorphous layer at the top and a damaged layer underneath. The final width and depth of the residual scratch at the onset of chip formation measured vary from 288 to 316 nm, and from 49 to 62 nm, respectively. High pressure phases are absent from the scratch at the onset of either chip or crack formation.

A novel approach of chemical mechanical polishing for cadmium zinc telluride wafers

A novel approach of chemical mechanical polishing (CMP) is developed for cadmium zinc telluride (CdZnTe or CZT) wafers. The approach uses environment-friendly slurry that consists of mainly silica, hydrogen peroxide, and citric acid. This is different from the previously reported slurries that are usually composed of strong acid, alkali, and bromine methanol, and are detrimental to the environment and operators. Surface roughness 0.5 nm and 4.7 nm are achieved for Ra and peak-to-valley (PV) values respectively in a measurement area of 70 × 50 μm2, using the developed novel approach. Fundamental polishing mechanisms are also investigated in terms of X-ray photoelectron spectroscopy (XPS) and electrochemical measurements. Hydrogen peroxide dominates the passivating process during the CMP of CZT wafers, indicating by the lowest passivation current density among silica, citric acid and hydrogen peroxide solution. Chemical reaction equations are proposed during CMP according to the XPS and electrochemical measurements.

Deformation twinning evolution from a single crystal in a face-centered-cubic ternary alloy

Deformation twinning evolution from a single crystal is conducted by molecular dynamics simulations, to elucidate a twinned face-centered-cubic alloy in an experiment with hardness up to 100 times as that of single crystals, and with ductility simultaneously. Critical twinning stress of cadmium zinc telluride (CdZnTe or CZT) calculated is 1.38 GPa. All the twin boundaries are along the (11-1) orientation, except the one with the (-111) plane that supports the indentation, interpreting the unidirectional and boundary-free characteristics, confirmed in the experiment. Three twin thicknesses after unloading are 3.2, 3.5, and 16 nm, which is consistent with the experimentally repeated pattern of a lamellar twin with thickness larger than 12.7 nm, followed by one or several twins with thicknesses smaller than 12.7 nm. An inverse triangle of a twin combining with three twins generate a synergistic strengthening effect through the hardening and softening functions, illuminating the ultrahigh hardness demonstrated in the experiment. Twinning takes place in loading, and detwinning occurs in unloading, which expounds the high ductility observed in the experiment.

Design and evaluation of soft abrasive grinding wheels for silicon wafers

The objective of this study is to design and evaluate soft abrasive wheels for silicon wafer grinding. In this study, CeO2, SiO2, Fe2O3 and MgO soft abrasives are used in the design of soft abrasive grinding wheels. The soft abrasive grinding wheels are then used to grind silicon wafers and compared with diamond wheel grinding and chemomechanical polishing. This study demonstrates that the newly designed soft abrasive grinding wheels are generally superior to diamond wheel grinding or chemomechanical polishing in terms of wafer surface/subsurface quality, wheel dressability, grinding ratio and material removal rate. This study further identifies the MgO soft abrasive grinding wheel as the best of the four soft abrasive grinding wheels. Discussion is provided to explore material removal mechanisms, wheel dressing characteristics and wafer surface finish and quality of the newly designed soft abrasive grinding wheels.

Electrochemical Mechanical Polishing of Copper with High Permittivity Abrasives

Electro-Chemical Mechanical Polishing (ECMP) is a promising low-pressure copper planarization method for the interconnection containing low-k material. ECMP utilizes anodic dissolution of copper to raise the material removal rate. However, the surface roughness is usually not acceptable in ECMP because the selective removal ability of electrochemical dissolution is poor. Different permittivity abrasives have different influence on surface quality in ECMP. High permittivity abrasives can enhance selective removal ability to get better polishing results through aggrandizing the potential drop in electrode/electrolyte interface. In this article, three abrasives with different permittivity are compared using polishing experiments. The results show that rutile TiO2, permittivity of which is larger than anatase TiO2 and SiO2, gets the best surface quality among the three abrasives. The composition of electrolyte with rutile TiO2 was also optimized to improve polishing performance. The chosen electrolyte contains 0.5 mol/L glycine, 0.1 mol/L TSA, 1 wt% rutile TiO2. The material removal rate got by using this electrolyte is 0.06 mg/min and the surface roughness is Ra8.9 nm.

Pulsed Laser Welding of Hastelloy C-276: High-Temperature Mechanical Properties and Microstructure

Based on the welding requirement during the coolant pump manufacture in the nuclear industry, the pulsed laser welding of 0.5 mm thickness Hastelloy C-276 was investigated, and the well defect-free weld joint of less than 1 mm width was obtained. According to the using temperature request of welding structure, the tensile test of as-welded samples at the high-temperature (200°C, 300°C, and 400°C) and the scanning electron microscope (SEM) observation of fracture were conducted. It was found that some tensile samples were broken in the base metal and others were broken in the weld joint. The results indicated that the high-temperature yield strength, ultimate tensile strength and elongation of as-welded sample satisfied the demand compared to those of base metal. Also, the plastic deformation behavior of pulsed laser weld joint was not obviously changed, and just the plastic instability in the weld joint was restrained to some extent. In addition, the high-temperature fracture morphology in the weld joint indicated the weld joint fracture type belonged to the ductile fracture. At elevated temperature, the dislocation movement and reinforced element segregation resulted in the larger size of voids at the fracture, and the same voids characteristic between 200°C and 400°C indicated that the influence of the temperature on the dislocation movement and element segregation was not important.

Nanogrinding of SiC wafers with high flatness and low subsurface damage

Abstract Nanogrinding of SiC wafers with high flatness and low subsurface damage was proposed and nanogrinding experiments were carried out on an ultra precision grinding machine with fine diamond wheels. Experimental results show that nanogrinding can produce flatness less than 1.0 μm and a surface roughness Ra of 0.42 nm. It is found that nanogrinding is capable of producing much flatter SiC wafers with a lower damage than double side lapping and mechanical polishing in much less time and it can replace double side lapping and mechanical polishing and reduce the removal amount of chemical mechanical polishing.