On-machine and in-process surface metrology for precision manufacturing

Micro-structured functional surfaces have achieved widespread applications in various advanced scientific, technological, industrial, and engineered fields due to their excellent performances, which are vitally limited by their feasible fabrication. Currently, ultra-precision machining, typically including ultra-precision diamond turning, ultra-precision diamond milling, ultra-precision diamond scratching, ultra-precision grinding, and ultra-precision polishing, is developed as a very-promising solution for the micro-structured functional surface fabrication with high quality, high efficiency, high flexibility, and low cost. Therefore, this paper aims to briefly review the current state of the art in the investigation into ultra-precision machining characteristics of micro-structured functional surfaces with a focus on their typical advanced applications as the significant achievements of their ultra-precision machining fabrication, discuss the key challenges, and further provide new insights into ultra-precision machining of micro-structured functional surfaces for the future research and their further advanced applications.

Advances in ultra-precision machining of micro-structured functional surfaces and their typical applications

Traditional fluid jet polishing (FJP) is limited by its low material removal rate and its applicability to medium-large size surfaces. This paper presents a novel multi-jet polishing (MJP) process and tools based on FJP which can implement high-efficiency polishing on large-scale surfaces or lens array surfaces. The MJP makes use of a purposely designed nozzle which possesses many regularly distributed holes, whose number can be a few to several hundred. Moreover, each hole can spray out a high-energy fluid jet leading to a dramatic increase of material removal. Its feasibility is firstly analyzed through a Computational Fluid Dynamics (CFD) simulation. Hence, its surface generation mechanisms in the integrated polishing mode and discrete polishing mode are studied. After that, a series of polishing experiments on different materials are conducted to validate its polishing performance as compared to single jet polishing (SJP). The experimental results show that the MJP tool can realize a much higher material removal rate, together with compatible surface roughness to SJP. Hence, the MJP tool has the potential to implement high-efficiency polishing on medium-large size surfaces and lens array surfaces.

A novel multi-jet polishing process and tool for high-efficiency polishing

Waterjet machining has attracted great attention in the conditions of hard-to-machine materials, microstructures, or complicated industrial components, and it has become well-established in all major areas of theoretical researches and already been found across the broad spectrum of technical application areas especially in the specific sectors of scientific frontiers, including the mechanical precision component, advanced functional material, intelligent automotive engineering, aerospace equipment, renewable energy science, leading medical instruments, etc. This paper reviews the historical and latest research developments and integrated applications of waterjet machining in the domains of mechanism and performances, which covers a lot of key aspects such as waterjet machining optimization, dynamic simulation and process monitoring of machining process, and the influence mechanism of waterjet machining as well. Its machining mechanism, performance capability, functional advantages, and inherent disadvantages are characterized and assessed in detail, so that the integrated applications of multifield-assisted waterjet machining can be introduced and focused thereafter. Finally, various future development prospects in all the abovementioned aspects of waterjet machining are discussed systematically and explored subsequently, which contribute to the acquirement of a series of comprehensive conclusions. This review can be used as suitable and effective tools to study and summarize the complicated correlations between waterjet machining mechanism and its actual working performances in different environmental conditions; therefore, this proposed investigation facilitates the precision manufacture or characteristic improvements of industrial product with higher efficiency and better quality in return.

Waterjet machining and research developments: a review

Although coherence scanning interferometry (CSI) is capable of measuring surface topography with sub-nanometre precision, it is well known that the performance of measuring instruments depends strongly on the local tilt and curvature of the sample surface. Based on 3D linear systems theory, however, a recent analysis of fringe generation in CSI provides a method to characterize the performance of surface measuring instruments and offers considerable insight into the origins of these errors. Furthermore, from the measurement of a precision sphere, a process to calibrate and partially correct instruments has been proposed. This paper presents, for the first time, a critical look at the calibration and correction process. Computational techniques are used to investigate the effects of radius error and measurement noise introduced during the calibration process for the measurement of spherical and sinusoidal profiles. Care is taken to illustrate the residual tilt and curvature dependent errors in a manner that will allow users to estimate measurement uncertainty. It is shown that by calibrating the instrument correctly and using appropriate methods to extract phase from the resulting fringes (such as frequency domain analysis), CSI is capable of measuring the topography of surfaces with varying tilt with sub-nanometre accuracy.

On tilt and curvature dependent errors and the calibration of coherence scanning interferometry

Fluid Jet Polishing (FJP) has the advantages of localized force and cooling of the debris, and of a stable and controllable material removal function with very little tool wear. Due to the complex machining mechanism, it is still difficult to model the material removal characteristics and simulate the surface generation for FJP. In the present study, an attempt has been made to better understand the material removal and surface generation mechanisms in the FJP process. Hence, a theoretical model is built for predicting and characterizing the material removal characteristics and surface generation in FJP based on computational fluid dynamic modelling. A series of spot and pattern polishing tests, as well as simulation experiments by the theoretical model, were conducted. The results show that the theoretical model satisfactorily predicts the surface generation under different polishing conditions and enables a better understanding of the polishing process in FJP.

Modelling and characterization of surface generation in fluid jet polishing

Ultraprecision freeform surfaces (UPFSs) are increasingly being used in advanced optical systems due to their superior optical properties. However, current research on the measurement of machined UPFSs is still hindered by lack of efficient and robust form characterization techniques which can characterize the form error of measured freeform surfaces with submicrometer accuracy. This paper presents an invariant-feature-pattern-based form characterization (IFPFC) method. IFPFC makes use of intrinsic surface features (e.g., Gaussian curvature) to map the surface into an orientation-independent feature pattern to represent the surface geometry. Surface matching and comparison are then undertaken in terms of feature pattern registration. Compared with conventional methods, the IFPFC is not only robust to the initial position of the measured surface relative to the design template but also computationally efficient since it does not involve much iteration. A series of computer simulations and actual measurement are conducted to demonstrate the performance and the validity of the IFPFC method in the measurement and characterization of UPFSs with submicrometer form accuracy.

Invariant-Feature-Pattern-Based Form Characterization for the Measurement of Ultraprecision Freeform Surfaces

Traditional off-line measuring systems find it difficult to measure micro-structured workpieces which have a large volume and heavy weight, such as micro-structured patterned precision roller drums. This paper proposes an autostereoscopy-based three-dimensional (3D) measuring method and develops an innovative measuring system for the 3D on-machine measurement of the micro-structured surfaces, an Autostereoscopy-based Three-Dimensional On-machine Measuring (ATDOM) system. The ATDOM system is compact and capable of fast data acquisition and high accuracy in 3D computational reconstruction of complex surfaces under different measuring environments. A prototype ATDOM system is experimentally verified through a series of measurement experiments conducted on a precision machine tool. The results indicate that the ATDOM system provides an important means for efficient and reliable on-machine measurement of micro-structured surfaces.

Autostereoscopy-based three-dimensional on-machine measuring system for micro-structured surfaces

Although the scanning white light interferometer can provide measurement results with subnanometer resolution, the measurement accuracy is far from perfect. The surface roughness and surface gradient have significant influence on the measurement uncertainty since the corresponding height differences within a single CCD pixel cannot be resolved. This paper presents an uncertainty estimation method for estimating the measurement uncertainty due to the surface gradient of the workpiece. The method is developed based on the mathematical expression of an uncertainty estimation model which is derived and verified through a series of experiments. The results show that there is a notable similarity between the predicted uncertainty from the uncertainty estimation model and the experimental measurement uncertainty, which demonstrates the effectiveness of the method. With the establishment of the proposed uncertainty estimation method, the uncertainty associated with the measurement result can be determined conveniently.

Mingjun Ren

Papers

Modelling and characterization of surface generation in fluid jet polishing

Invariant-Feature-Pattern-Based Form Characterization for the Measurement of Ultraprecision Freeform Surfaces

Autostereoscopy-based three-dimensional on-machine measuring system for micro-structured surfaces

Estimation of measurement uncertainty caused by surface gradient for a white light interferometer.

Generalized form characterization of ultra-precision freeform surfaces