Papers by Keyword: Single-Point Diamond Turning

Abstract: Acoustic emission signal-based prediction of surface roughness has been utilized widely, yet little work has been done in this regard on RSA443. This paper seeks to study the correlation between acoustic emission (AE) signal parameters and surface roughness. Estimation of surface roughness using AE signal parameters and subsequent examination of the influence of AE signal parameters (root mean square, peak rate and prominent frequency) on the accuracy of the RSM model in surface roughness prediction are carried out. The experiment is designed using the Taguchi L9 orthogonal array to minimize the number of experiments. Emitted acoustic signals are captured using a Piezotron sensor. Three RSM models are formulated and compared in this study: a model that uses only critical machining parameters (cutting speed, depth of cut and feed rate), a model that uses only AE signal parameters (root mean square, peak rate and prominent frequency) and a model that uses both critical machining parameters and AE signal parameters. An assessment based on the models’ mean absolute percentage error (MAPE) is made to see if AE signal parameters have any contribution towards surface roughness prediction accuracy. The order of parameter significance in the most accurate model is investigated in this paper. The mean absolute percentage error results for the models indicate that the model in which AE signal parameters are utilized in conjunction with critical machining parameters has the highest prediction accuracy of 97.32%. The model that utilizes only critical machining parameters has a prediction accuracy of 96.35% while the one that utilizes only AE signal parameters has a prediction accuracy of 84.43%. It is observed that the order of parameter significance from the most to the least significant is as follows: feed rate, cutting speed, peak rate, AErms, depth of cut and prominent frequency.

Abstract: Single-point diamond turning (SPDT) is a machining process making use of a monocrystal diamond tool which possesses nanometric edge sharpness, form reproducibility and wear resistance. The process is capable of producing components with micrometre to submicrometre form accuracy and surface roughness in the nanometre range. The cutting parameters that can make an effect on surface finish and form accuracy of SPDT such as spindle speedfeed ratedepth of cut and so on.

Abstract: In recent years, plastic lenses have been widely adopted for optical components in consumer products because of the significant improvement in microelectronics technology. Currently, plastic lenses are mass produced for applications in 3G/4G smart mobile phones, digital still/motion cameras, and micro-projectors. During mass production, one of the key factors in costs reduction is to enhance lifetime of the molding tools. Electroless nickel phosphorus plating (Ni-P) is the most popular mold and die surface treatment process because of its excellent machinability in single-point diamond turning process. However, Ni-P plated molds cannot sustain satisfactory tool life under the adhesion forces between the mold surface and the molten plastic. In this study, a novel material made of a nickel-phosphorus-polytetrafluoroethylene (Ni-P-PTFE) compound was plated electrolessly on experimental dies to study relevant properties. Since Ni-P-PTFE exhibits strong anti-adhesion properties, it is noted to improve the lifetime of the dies. After machining of the dies, the surface roughness was measured by confocal microscopy together with the particle size being measured by scanning electron microscopy (SEM). In conclusion, the adhesion phenomenon is interpreted via hydrophobic contact angles showing that hydrophobic contact angle of Ni-P-PTFE surfaces is smaller when compared to Ni-P surfaces which infers the anti-adhesion properties of Ni-P-PTFE materials.

Abstract: The swelling effect is an important factor to affect surface generation in SPDT. Face cutting experiments are conducted for copper, aluminum alloy and electroless nickel phosphorus to analyze the swelling effect including the relationship between it and cutting parameters as well as effect of material property. How the material swelling affects surface roughness is also studied in this paper. The results indicate that the swelling effect is influenced by spindle speed and material property more remarkably when compared to feed rate and depth of cut. In addition, a softer and more ductile material will lead to a stronger material recovery, a lower swelling proportion, a lower tool mark height and a smoother machined surface. The result reveals that the swelling effect must be considered when predicting surface roughness in SPDT

Abstract: Experimental results indicate the previous theoretical model cannot predict well the surface roughness in single-point diamond turning on a precision lathe. In solving that, an improved model was presented in this paper. The difference between the previous model and the improved model is that the relative tool-workpiece vibration is measured before cutting operation using a capacitive displacement sensor in the previous model whilst the vibration is extracted from the measured surface profile in the improved model. The relative vibration was first studied under various cutting conditions to establish the vibration modes under corresponding cutting conditions. Then the surface roughness was predicted based on the vibration modes. The results prove that there is good agreement between the predicted values and measured values and the improved model is useful and reliable.

Abstract: Grazing incidence optics used in soft X-ray microscopes require supersmooth surface and highly accurate figure. We considered the fabrication of a Wolter type I mirror, one of grazing incidence optics, with axial-symmetric inner reflecting surfaces using single-point diamond turning. Electroless nickel was chosen as reflecting material Cutting conditions for machining the inner reflecting surface were restricted because of long arm of a single-crystal diamond tool. The machined Wolter type I mirror had approximately 270 nm P-V in figure error and 3 nm Ra in surface roughness. The direct-machined Wolter type I mirror could be successfully used in a soft Xray microscope based on laser-produced X-ray source.