Papers by Keyword: Diamond Tool Wear

Abstract: Rapid solidification of molten metals has been recently used to generate a new group of alloys having ultra-fine microstructures and high end mechanical properties. Therefore, such alloys can be successfully used in the optics industry to produce diamond machined mirrors and mould inserts for plastic lens injection. Rapidly solidified aluminium grades characterised by their ultra-fine grains can be used to replace traditional optical aluminium such as 6061-T6 which has coarse microstructure when making optics. However, there is currently no data available on the performance of these new grades in terms of diamond tool wear when machined in single-point diamond turning operation. This paper reports on the wear mechanisms of natural diamond tools when turning RSA 443 which is a new aluminium grade produced by rapid cooling process. Although this new aluminium grade enjoys fine microstructure, it is harder than traditional optical aluminium because of its increased content of silicon (about 40%). Therefore, there is a need to establish a deeper understanding of diamond tool performance when using diamond turning of optical components from this material. In this study, three machining parameters, namely cutting speed, feed rate, and depth of cut, were varied at three levels and the edge wear of the diamond inserts was observed using scanning electron microscopy after 4 km of cutting distance. The first observations from this preliminary study show that tool wear of diamond is more sensitive to the change in cutting speed than it is for other cutting parameters. Wear is relatively high (12 µm) at the lowest cutting speed (500 rpm). However, at high cutting speed (3000 rpm) the edge wear was small (3 µm). This could be attributed to the increased impacts of cut the material on the cutting edge. The study also reports on the surface finish obtained at the different combinations of cutting parameters.

Abstract: In this paper, cutting force and its power spectrum analysis at different tool wear levels are explored. A dynamic model is established to simulate the measured cutting force compositions, and a series of cutting experiments have been conducted to investigate the cutting force evolution with the tool wear progress. Research results reveal that in the time domain, the cutting force in UPRM is characterized as a force pulse follows by a damped vibration signals, the vibration can be modeled by a second order impulse response of the measurement system. While in the frequency domain, it is found that the power spectrum density at the natural frequency of dynamometer increases with the progress of tool wear, which therefore can be utilized to monitor diamond tool wear in UPRM.

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: Tool wear reduction is very important in cutting of ultra hard and brittle materials. In this paper, a tool-swinging cutting method was applied to reduce the wear of round-nosed diamond tools in cutting of tungsten carbide (WC). In this method, the geometrical center of the cutting edge was adjusted to be in coincidence with the rotation center of the B-axis table, and thus the cutting point could be changed along the cutting edge by swinging the tool about the B-axis center. Experimental results showed that the width of the flank wear land was greatly reduced compared to that in the conventional cutting. This work can shed light on ultraprecision machining WC parts without or with less need for subsequent polishing process.

Abstract: This paper presents results for the machining of materials typically applied in ultra precision machining in comparison to a nitrocarburized tool steel. Analyzing and evaluating the machining results regarding surface integrity lead to recommendations for the ultra precision machining of this new mold material. The influence of feed, depth of cut and cutting speed on surface quality, resulting cutting forces and tool wear have been investigated. The results show that the decisive factor for the ultra precision machining of nitrocarburized tool steel are the significantly higher cutting forces. In some cases the high cutting forces lead to vibrations during the turning process deteriorating the surface integrity. Therefore, tool nose radius and depth of cut have to be reduced to minimize the cutting forces and avoid the vibrations.

Abstract: As is well known, excessive chemical tool wear occurs when steel alloys are machined with monocrystalline diamond tools prevents many important applications. In order to reduce this catastrophic tool wear, certain process modifications have been proposed in the literature, e.g. cryogenic cutting and elliptical vibration cutting. Another approach for realizing precision machining of steel is coating the diamond with a TiN layer or using ceramic tools. However, only elliptical vibration cutting has proven to be ready for industrial use, but a large amount of auxiliary equipment is needed. The basic idea of the new approach is to avoid chemical reactions between the carbon of the diamond tool and the iron of the substrate by establishing a chemical bond between the iron and other chemical elements in the workpiece's subsurface layer. Using a custom-made thermo-chemical process for altering the chemical composition of the boundary layer of the workpiece the diamond tool wear can be reduced by more than two orders of magnitude. The surface roughness obtained in single point diamond turning of carbon steel was approximately 10 nm Ra and 6 nm Ra for raster milling processes.