Thai Nguyen

An assessment of the applicability of cold air and oil mist in surface grinding

Abstract This paper discusses the application of an eco-grinding system using a mixture of compressed cold air and vegetable oil. The feasibility of the system was assessed using the surface grinding of plain carbon steel 1045 with a BWA60MVA1 wheel. The investigation showed that cold air can be used to suppress surface burning under certain material removal rates and has an advantage of reduced grinding forces. With the addition of very small amount of vegetable oil, a larger depth of cut can be performed without burning while keeping a good grinding quality. Grinding chips were of lamellar and leafy shapes, indicating a shearing mechanism of chip formation. There was no significant difference in subsurface hardness of the components ground with coolant or with cold air and oil mist (CAOM), although the latter showed a stronger dependence of surface residual stresses on the depth of cut due to the limited cooling capacity of CAOM.

Effect of temperature and stress on plastic deformation in monocrystalline silicon induced by scratching

Dry air, coolant, and liquid nitrogen were applied, respectively, to study the effect of temperature and stress on plastic deformation in scratching monocrystalline silicon. Phases generated in surface deformation were characterized by means of the transmission electron microscopy. It was shown that the size of the amorphous transformation zone and the depth of slip penetration in sample subsurface were mainly dependent on the stress field applied. The influence of the temperature variation to −196 °C was surprisingly small and the low temperature did not suppress the phase transformation and dislocation activity.

Machining of Micro-Channels on Brittle Glass Using an Abrasive Slurry Jet

This paper presents a study of using an abrasive slurry jet for the machining of micro channels on brittle glasses. The machined surface morphology and channel dimensions are used to assess the technology. Surface morphology was found featuring with two types of wave patterns; one was along the channels with large wave lengths as a result of the jet deflection during the motion of nozzle, and the other was due to viscous flow that resulted in smooth surface eroded predominantly by ductile mode. The investigation showed that using higher jet pressure and higher particle concentration enables to create channels with higher depth, although these widened the channels and degraded the surface quality in some cases by inducing a larger number of pit fragments on the surface. With proper control of the operating parameters, this technology can be used for machining micro channels on brittle materials with high quality of surface finish.

A Preliminary Study of the Erosion Process in Micro-Machining of Glasses with a Low Pressure Slurry Jet

The erosion process in micro-machining of brittle glasses using a low pressure slurry jet is discussed. The process capability of the technique is assessed by examining the machined surface integrity in relation to fluid flow dynamics in micro-hole generations. The holes produced are characterised by a “W” shape in the cross section, while the surface morphology is distinguished by three zones associated with the fluid flow behaviour, i.e. a direct impact zone, a wavy zone and an accumulation zone. The surfaces appear to be smooth and without cracks, indicating a predominance of the ductile mode erosion process. With the increase of pressure, the erosion rates can be enhanced as a result of the expending of the accumulation zone while the outer diameter of the holes remains unchanged. This study shows that this technique can be used for micro-machining with high surface quality, and provides an essential understanding for further research in the avenue.

Characterizing the Mechanical Properties of the Hardened Layer Induced by Grinding-Hardening

A grinding-hardening process uses the grinding heat to initiate the phase transformation in a workpiece made of quenchable steel and hence to generate its surface hardening. This paper investigates this phase transformation process and the mechanical properties of such hardened layers with the aid of experiments and the finite element analysis. It was found that the phase transformation followed a diffusionless martensitic kinetics in which the external stresses caused by the mechanical loading of the grinding wheel on the workpiece played an important role. The top hardened layer appeared to be a plastically deformed zone of uniform thickness. A metallurgical examination revealed that this layer contained refined martensitic laths, as compared with the ordinary martensite obtained by a conventional quenching method. The microstructural evolution has led to a hardness increase by 1.4 times the ordinary martensite. In addition, the grinding-hardening can promote compressive residual stresses in the ground surface, about 17% higher than the yield strength of the parent ferrite-pearlite material.

A STUDY OF MICRO-CHANNELING ON GLASSES USING AN ABRASIVE SLURRY JET

A study of micro-channeling on glasses using an abrasive slurry jet is presented. The mechanism of channel formation is discussed. It is found that the cross section of the channel is characterized by a V-shape, where the maximum channel width is larger than the nozzle inner diameter. The surface morphology features with two types of major and minor wave patterns. The major wave patterns with large wavelength developed along the channel are caused by the jet deflection during nozzle traverse motion. The minor wave patterns are a result of the secondary viscous flow that is induced by the impact of jet on the target. Material was eroded predominantly by the ductile mode, resulting in a smooth surface. The depth of the channel is mainly affected by the jet kinetic energy transferring to material via abrasive particles. In contrast, the viscous flow plays a main role in the formation of the channel width. The turbulent flow that drives the moving particles accumulated at the bottom of the channel contributes to the formation of channel wall inclination. With a proper control of the operating parameters, this technology can be used for machining micro-channel on brittle materials to achieve high surface quality.

Color image enhancement using correlated intensity and saturation adjustments

The enhancement of digital color images needs to be performed in accordance with human perception in terms of hue, saturation, and intensity attributes instead of improving only the contrast. Two approaches were developed in this work, which use a correlated adjustment mechanism incorporating intensity and saturation attributes and provide contrast and saturation enhancements together with brightness consistency. In these algorithms, object edges are emphasized for contrast, and image saturation is increased by boosting the salient regions. Furthermore, intensity and saturation enhancements are carried out in a lattice structure where adjustments are made inter-related for better performance. Experiments were conducted with benchmark and real-world images. Results had shown improvements in image qualities both qualitatively and quantitatively.

An Investigation of the Grinding-Hardening Induced by Traverse Cylindrical Grinding

This study investigates the formation of the layer hardened on a cylindrical workpiece by grinding-hardening using the traverse grinding method. A finite element heat transfer model, that took into account the helical trajectory of the of the grinding heat source movement, was developed. The hardened layer was found featuring a wavy profile as a result of the heat conduction from an adiabatic plane crossing the middle of the trajectory pitch. The accumulation of the grinding heat within a small pitch can lead to the welding of the molten material with the base material. Enlarging the pitch by reducing the workpiece speed will increase the time of heating, allowing the heat to penetrate deeper and to expand wider in the workpiece, thus thickening the hardened layer. [DOI: 10.1115/1.4028058]

Temperature Fields in Workpieces during Grinding-Hardening with Dry Air and Liquid Nitrogen as the Cooling Media

This paper presents a temperature-dependent finite element heat transfer model, incorporating a triangular moving heat source and various cooling conditions, to predict the three-dimensional temperature field in plunge surface grinding. The model was applied to analyse the grinding-hardening of quenchable steel 1045 using dry air and liquid nitrogen as the cooling media. The temperature field variation under such grinding conditions was also measured experimentally. It was found that the temperature history predicted by the model agrees well with the measured results. The model provides a fundamental study as a first step in optimisation and control of the hardened layer thickness and its compositions in grinding-hardening technology.

Prediction of the Hardened Layer in Traverse Cylindrical Grinding-Hardening

A finite element heat transfer model incorporating a moving heat source has been developed to predict the temperature field in traverse cylindrical grinding. The model was then applied to analyse the grinding-hardening of quenchable steel 1045. It was found that in the region where the grinding wheel had an entire contact with the workpiece, material would experience a heating-cooling cycle, enabling the generation of a uniform hardened layer. In the transient regions at the two ends of the workpiece where the wheel-workpiece contacts were partial, the material was not hardened but experienced an annealing process. The results were in good agreement with the experimental observations.