A study of real-time spindle error compensation in single-point diamond turning of optical micro-structured patterns on precision rollers

Micro-structured patterns are widely used in optics since the optical performance can be significantly improved in many applications [1]. One of the most common methods to fabricate the micro-structure is using Single-Point Diamond Turning on Precision Rollers [2]. The accuracy requirement of the Precision Rollers is stringent because the dimension of the microstructure is very small (pitch lengths and depths 10-100μm) and surface finishing is ultra-smooth (Ra<3nm) [2]. In order to achieve this level of accuracy, the manufacturing errors of the machine tool are required to be reduced while error compensation methods are needed to be developed. Spindle errors can be classified as synchronous error and asynchronous error [3]. Synchronous error occurs at integer times of spindle rotation frequency and can be represented as repeatable error while asynchronous error occurs at noninteger times of spindle rotation frequency and can be represented as non-repeatable error. Most of the existing error compensation techniques are based on offline error compensation methods (OECM) which can only compensate the synchronous error [4,5]. The asynchronous error is fluctuating without a predictable value and it is different from the synchronous error so it cannot be eliminated using OECM. One of the most promising methods to compensate the asynchronous error is real-time error compensation method (RECM). Some researchers have studied the RECM and their results showed that it was effective to enhance the machine accuracy [6,7]. However, most of the previous research work is focused on the machine tools with a relatively low accuracy and there is relatively few studies focused on the Single-Point Diamond Turning. Kim and Kim developed a feed-forward control of fast tool servo system for real-time correction of spindle error for diamond turning of flat surfaces [8]. A capacitive displacement sensor was used to measurement the spindle axial error motion and the motion error was compensated using a fast tool servo. A flatness of 0.1μm was achieved with a 100mm diameter aluminum specimen. However, the study only considered the axial error, when it is diamond turned on precision rollers, both the radial error and axial error have to be compensated. This paper attempts to investigate the RECM in Single-Point Diamond Turning of Optical Microstructured Patterns on Precision Rollers. The radial error and axial error were simulated and the compensated results of OECM and RECM were presented considering both synchronous errors and asynchronous errors in radial and axial directions. The results of OECM and RECM were also compared and discussed. Furthermore, the effects of time delay in RECM were studied. An adaptive time-series modeling method was also proposed to predict the realtime error to reduce the time delay effect of RECM. The results show that the RECM is effective and promising to further improve the accuracy of the Single-Point Diamond Turning Precision Rollers

Modelling and analysis of uncertainty in the form characterization of ultra-precision freeform surfaces on coordinate measuring machines

This paper presents an uncertainty analysis model for the form characterization of ultra-precision freeform surfaces on coordinate measuring machines (CMM). The model is developed by incorporating the effect of the CMM, the sampling plan, and the evaluation method taking into account workpiece form deviations. It allows the analysis of the uncertainty of evaluated surface parameters with respect to the magnitude of the workpiece form deviation based on Monte Carlo simulation. The effectiveness of the model was successfully verified using a designed freeform artefact on a precision CMM. The model should make the reliable form characterization of ultra-precision freeform surfaces possible

Magnesium application in railway rolling stocks: A new challenge and opportunity for lightweighting

Magnesium (Mg) and their alloys show potential in railway rolling stock applications due to their attractive mechanical properties, developed manufacturing processes, cost efficiency, and affluent resource reserve. In particular, high-strength Mg alloy components are important to lightweighting efforts in the railroad industry. In this review, Mg alloy processing technology for railroad vehicles is discussed with emphasis on energy savings, manipulation convenience, and reduction in friction/wear, vibration, and fatigue damage. It is shown that a Mg alloy train has a theoretical 8.6–12.6% comprehensive weight reduction potential in the equal-strength and equal-stiffness condition, where low-speed trains (metro, light rail train, tram/trolley car, monorail car, suspension train/schwebebahn etc..) exhibit a larger energy-savings than high speed trains. It is evident that the regulations of fabrication, processing, post treatment, assembly/installation, protection, and maintenance/replacement of Mg alloy components for the railroad industry all need further research and development. Keywords: Mg alloys, Lightweight train, Energy saving

Effect of Graphene Nanoplatelets Content on the Mechanical and Wear Properties of AZ31 Alloy

Graphene, as a rising-star materials, has attracted interest in fabricating lightweight self-lubricating metal matrix composites with superior mechanical and wear properties. In this work, graphene nanoplatelets (GNPs) reinforced AZ31 alloy composites were fabricated by a powder metallurgy technique and then a hot extrusion. The effects of GNPs content (0.5, 1.0, and 2.0 wt.%) on the microstructures, mechanical properties, and wear performance of the extruded GNPs/AZ31 composites were studied. It was found that the addition of GNPs resulted in a weakened basal plane texture and grain refinement of the AZ31 matrix metal. Less than 1.0 wt.% GNPs in GNPs/AZ31 composites resulted in the enhancement in both Vickers hardness and tensile yield strength with acceptable elongation. The Vickers hardness and tensile yield strength of 1.0GNPs/AZ31 composite increased by 4.9% and 9.5% respectively, compared with the unreinforced AZ31. Moreover, the elongation of the composites was about the same as the AZ31 base alloy. Both the friction coefficient and the wear mass loss continuously decreased with the increasing GNPs content, which exhibited a self-lubricating effect. The relationship of the friction coefficient and wear mass loss with the GNPs content could be modeled in terms of the Holliday model and the exponential decay model, respectively. The worn surface morphology revealed that adhesive wear and abrasive wear simultaneously acted in AZ31 alloy. Nevertheless, abrasive wear became the dominant wear mechanism in the GNPs/AZ31 composites

The Effects of Carbon Nanotubes on the Mechanical and Wear Properties of AZ31 Alloy

Carbon nanotube (CNT)-reinforced AZ31 matrix nanocomposites were successfully fabricated using a powder metallurgy method followed by hot extrusion. The influence of CNTs on microstructures, mechanical properties, and wear properties were systematically investigated by optical microscope (OM), scanning electron microscope (SEM), X-ray diffraction (XRD), hardness test, tensile test, and wear test. The results revealed that the nanocomposites showed a slightly smaller grain size compared with the matrix and uniform distribution that CNTs could achieve at proper content. As a result, the addition of CNTs could weaken basal plane texture. However, the yield strength and ultimate tensile strength of the composites were enhanced as the amount of CNTs increased up to 2.0 wt. %, reaching maximum values of 241 MPa (+28.2%) and 297 MPa (+6.1%), respectively. The load transfer mechanism, Orowan mechanism, and thermal mismatch mechanism played important roles in the enhancement of the yield strength, and several classical models were employed to predict the theoretical values. The effect of CNT content on the friction coefficient and weight loss of the nanocomposites was also studied. The relationships between the amount of CNTs, the friction coefficient, and weight loss could be described by the exponential decay model and the Boltzmann model, respectively

Generalized form characterization of ultra-precision freeform surfaces

2012-2013 > Academic research: refereed > Publication in refereed journa