A compensation approach based on the on-machine measurement was developed for the grinding of tungsten carbide aspheric moulds. In this approach, the on-machine measurement was employed to eliminate the profile error caused by the re-installation of the workpiece. A new method was proposed to reconstruct the actual ground profile based on the measured profile data. The overall profile error after grinding was obtained by subtracting the target profile from the actual ground profile along normal direction and was then used to generate a new tool path for compensation grinding. The experimental results showed that after three compensation grinding cycles the aspheric surface had a profile accuracy of 177 nm (in PV) with a roughness of 1.7 nm (in Ra). The on-machine measurement was in excellent agreement with the off-machine measurement by commercially available profilometers.

Profile error compensation in ultra-precision grinding of aspheric surfaces with on-machine measurement

Numerical and experimental analysis of surface roughness generated by shot peening

Emerging trends in surface metrology

Surface roughness can significantly influence the fluid dynamics and heat transfer in convective flows by inducing perturbations in the velocity profile which affect surface drag, turbulent mixing and heat transfer. While surface roughness can often negatively affect the performance of systems, it can also lead to performance improvements, such as in convective flows where roughness elements have been shown to enhance heat transfer. Turbulent flows over rough surfaces have been studied for about a century leading to significant developments in this field. Direct Numerical Simulation (DNS) has made significant contributions to the knowledge of turbulent flows over rough surfaces as well as evaluation of the developed theories. Moreover, the turbulent closures model has seen wide use for simulation of rough-wall turbulent flows in practical applications where DNS is hindered by its complexity and computational resources. Despite a significant number of experimental and CFD studies and the latest advances in this field, a recent review was not available. Therefore, this review surveys the past and recent experimental and numerical studies to address the fundamentals and theories related to the structure of turbulent flows over rough walls. This study chiefly investigates the structure of mean flow profile over rough surfaces, and its correlation with smooth wall mean flow profile. This review study can contribute to prospective experimental and CFD work, and for characterising rough-wall turbulent flows and heat transfer in different academic and engineering applications such as aerodynamics, hydraulics, meteorology, and manufacturing. The review concludes that despite significant progress, the structure of turbulent flow is still not fully understood. This is mainly due to a lack of systematic studies on the structure of turbulent flow and also due to the variety of roughness which influence the dynamics of the flow in the roughness sublayers. The current roughness scale (sand-grain roughness height) fails to completely characterise roughness in many cases. Therefore, there is a need for a universal roughness scale that can describe every type of roughness and be used in any rough-flow regimes, including fully rough and transitionally rough regimes.

A review on turbulent flow over rough surfaces: Fundamentals and theories

Multi-frequency weak signal detection based on wavelet transform and parameter compensation band-pass multi-stable stochastic resonance

Engineering surfaces are comprised of a range of spatial wavelengths. Filtering techniques are commonly adopted to separate the different wavelength components into well-defined bandwidths. Filtering is done prior to numerical characterization and it is also essential for extracting information needed to provide process feedback and establish functional correlation. This paper reviews commonly used filters in surface metrology like the 2RC, Gaussian and several new ones currently under research such as the spline, morphological, wavelets, regression filters and robust regression filters. The need for these new filters and examples illustrating the features of these filters are also presented.

Recent advances in separation of roughness, waviness and form

This paper describes the development of an inexpensive, portable three-dimensional (3-D) stylus-based surface profiler with a scan range of 4.5 mm × 5.5 mm and a maximum vertical range of 150 μm (limited by signal conditioning electronic range) with a resolution of better than 0.9 μm and a range of 30 μm with a resolution of better than 30 nm at the highest vertical sensitivity. The instrument occupies a volume with dimensions of approximately 75 × 75 × 40 mm (L × B × H) with scan speeds up to 0.5 mm s −1 . Construction of instrument components from similar material results in a thermally balanced design with a reasonably low thermal coefficient of 0.27 μm K −1 and a first-order time constant of approximately 40 min. The stylus probe sensor has a free resonant frequency of 49 Hz and a low damping ratio of 0.006. When in stationary contact with a steel surface, this increases to above the transducer bandwidth of 900 Hz. Calibration of the probe sensor is achieved through direct comparison against a standard stylus gauge. Lateral calibration of the specimen carriage position has been assessed by the measurement of standard gratings and laser interferometry. Planar errors caused by the motion of the carriage have been assessed by measuring an optical flat and inferring deviation from a perfect plane as an indication of the worst-case error, which in this case, was 0.2 μm (P-V). The design and construction of the internal datum and the portability of the instrument to facilitate in situ measurement of components are emphasized. Images illustrating the surface mapping capabilities of the profiler are presented.

J. Raja

Papers

Recent advances in separation of roughness, waviness and form

A portable three-dimensional stylus profile measuring instrument