Papers by Keyword: Diamond Turning

Abstract: The most important goal of advanced diamond machining is to improve precision and product integrity. Cutting force could have a strong effect on diamond machining performance and hence, it can be used as an indicator for monitoring tool condition for achieving successful machining. Moreover, diamond machining process parameters such as cutting speed, depth of cut and feed rate may strongly influence the process outcomes in terms of surface roughness and tool failure. Diamond machining parameters have a significant role on the cutting force values, and machine-tool stability during ultra-high precision machining that makes use of a natural diamond cutting tool. The main objective of this research work is to investigate the effect of cutting speed, feed rate, depth of cut and nose radius on the cutting force generated during diamond turning of a rapidly solidified aluminum alloy grade called RSA 6061. The effect of nose radius and cutting parameters on cutting force during the ultra-high precision diamond turning process was monitored. The study shows that low speed, low depth of cut and an increase in feed rate at large nose radius consequently results in increase in the cutting force.

Abstract: In the globally competitive environment, surface roughness and finer tolerances are becoming stringent and certainly most critical for optical components. The aim of this study is to determine the effects of diamond turning process parameters on surface finish when diamond turning RSA 443 alloy having high silicon content. This alloy is a new grade of aluminum that has a potential to be used for production of various optical components. The experiments were conducted based on the Box-Behnken design with three diamond-turning parameters varied at three levels. A mathematical regression model was developed for predicting surface roughness. Further, the analysis of variance was used to analyze the influence of cutting parameters and their interaction in machining. The developed prediction model reveals that cutting speed and feed rate are the most dominant diamond turning factors influencing surface roughness.

Abstract: Optical free-form surfaces are becoming more and more popular in the industry application, which can be fabricated by diamond turning based on fast tool servo (FTS). It is an efficient, precise and low-cost processing method. In order to use diamond turning to fabricate the freeform optics, this paper develops a novel long range fast tool servo which is actuated by voice coil motor. The total range can reach up to 30 mm. The important parts of the FTS have been simulated and analyzed. The transfer function model identification of the FTS has been accomplished. Since the desired tool trajectories are approximately periodic signals in freeform surfaces turning, and the adaptive feedforward cancellation (AFC) control can achieve perfect tracking and disturbance rejection of periodic signals, the AFC control is designed to be added on the IMC-PID controller.

Abstract: This study describes the non-rotationally symmetric diamond turning (XZC turning) for producing large-size precision freeform mirror. This is a high speed machining method as compared with the traditional XYZ diamond milling or fly-cutting. Moreover, the application of this method is a key factor in the development of the ultra-precision light-weight freeform mirror for outer space use. This report introduces these cutting-edge approaches.

Abstract: The optical properties of micro-structure surface mold roller in the field of optics, machinery and electronics, biomedical and defense sectors are showing an increasingly important application value and broad application prospects. There is still no more mature method to machining ultra-precision large-size optical V-groove mold roller, and the roller surface treatment technology cant meet the technical requirements of the field of optical applications. This article takes advantage of ultra-precision diamond turning to machining V-groove structure on nickel-phosphorus plating steel roller by spiral cutting method. The helix angle of the mold roller was designed 0.9", which meet the requirements of the experimental error, while using a nickel-phosphorus alloy coating can eliminate the secondary polishing process and achieve a cost-efficient ultra-precision machining. Analyzed the processed tool wear, high-temperature graphitization and micro-chipping were the main reason for tool wear.

Abstract: Ultra-precision diamond turning can deliver very accurate form, often less than 100nm P-V. A possible manufacturing method for thin Wolter type-1 mirrors in hard X-ray space telescopes thus involves generating electroless nickel plated mandrels by diamond turning, before coating them with a reflective film and substrate. However, the surface texture after turning falls far short from the requirements of X-ray and EUV applications. The machining marks need to be removed, with hand polishing still widely employed. There is thus a compelling need for automated finishing of turned dies. A two step finishing method is presented that combines fluid jet and precessed bonnet polishing on a common 7-axis CNC platform. This method is capable of finishing diamond turned electroless nickel plated dies down to 0.28nm rms roughness, while deterministically improving form error down to 30nm P-V. The fluid jet polishing process, which consists of pressurizing water and abrasive particles for delivery through a nozzle, has been specially optimized with a newly designed slurry delivery unit and computer simulations, to remove diamond turning marks without introducing another waviness signature. The precessed bonnet polishing method, which consists of an inflated membrane rotated at an angle from the local normal to the surface and controlled by geometrical position relative to the work-piece, is subsequently employed with a novel control algorithm to deliver scratch-free surface roughness down to 0.28 nm rms. The combination of these two deterministic processes to finish aspheric and freeform dies promises to unlock new frontiers in X-ray and EUV optics fabrication.

Abstract: This publication focuses on the ultra precision manufacturing of hardened steel parts with single crystal diamond tools for optical applications such as injection moulding. Nowadays optical steel moulds are nickel plated, in order to be able to machine the surface with single crystalline diamond tools. One technology that has proven its potential for replacing this procedure is the ultrasonic assisted diamond turning technique. This process allows direct machining of hardened steel with single crystal diamond tools, which is conventionally not possible due to the high tool wear. The ultrasonic assisted diamond turning process is applied in order to machine different steel alloys that are conventionally used for mould manufacturing in injection moulding. The goal is to analyze the influence of the steel alloy and the material microstructure on the machining results. The presented analysis show the capabilities of this new technology and opens the door for it to compete with established manufacturing processes, such as the manufacturing of nickel plated mold inserts.

Abstract: Diamond turning of steel parts is conventionally not possible due to the high tool wear. However this process would enable several different applications with high economical innovative potential. One technology that enables the direct manufacturing of steel components with monocrystalline diamond is the ultrasonic assisted diamond turning process. This technology has been investigated over the years within the Fraunhofer IPT and is now commercialized by its spin-off company son-x. Surface roughness in the range of Ra < 5 nm can be achieved and the diamond tool wear is reduced by a factor of 100 or higher. In order to prove the industrial suitability of the process, two aspherical shapes and one large spherical geometry have been manufactured. The possible form accuracies and surface roughness values will be described in this paper, as well as the tool wear. The goal was to achieve optical surface roughness and a shape accuracy below 300 nm.

Abstract: This paper aims to develop a cost-effective diamond turning process to obtain nanosmooth CaF₂ optics. Diamond tool wear was also carried out through a number of cutting trials. Three CaF₂ specimens (diameter of 50 mm and thickness of 5 mm, crystal orientation of (111)) were diamond turned on an ultra precision lathe (Moore Nanotech 350UPL) by a number of facing cuts. In the cutting trials feed rate varied from 1 μm/rev to 10 μm/rev. White spirit mist was used as the coolant. Cutting forces were measured by a dynamometer (Kistler BA9256). Surface roughness of the CaF₂ optics and tool flank wear were measured by a white light interferometer (Zygo Newview 5000) and a scanning electron microscope (FEI Quanta 3D FEG), respectively. It was found that using a feed rate of 1 μm/rev surface roughness Ra of 2 nm could be obtained. When the ratio of the normal cutting force to the tangential cutting force was lower than 1 tool wear would initiate. In diamond turning of calcium fluoride abrasive wear was the main tool wear mechanism. Using white spirit mist as thecoolant could avoid generation of thermal type brittle fracture on the machined CaF₂ surfaces.

Abstract: Micro-structured surfaces on brittle materials, e.g. ceramic and glass, are gaining increasing application in a range of areas. In this paper, fast tool servo (FTS) diamond turning has been applied to machine micro-structured surfaces on brittle materials and the machined surfaces has been observed to study its machining mechanism. A machining model is presented to enable ductile-regime machining of the brittle material. Based on the model, machining characteristics can be predicted for given cutting conditions. Experimental investigation on machining of a micro-structured surface verified that ductile-regime machining can be ensured on the entire surface through path planning simulation based on the machining model.