Ductile Grinding Research Articles

Loose abrasive line-contact machining of aspherical optical surfaces of revolution

A new fabrication technique for the generation of optical aspherical surfaces of revolution is presented. This fabrication technique combines the characteristics of conventional loose abrasive machining with features of high-precision machining tools. A prototype of the machine tool based on this fabrication technique is currently being developed. We describe the characteristics of this method. Fabrication of aspherical ultraprecise surfaces using a tube is a line-contact method for the generation of both on- and off-axis, convex and concave, aspherical surfaces of revolution. It employs a self-correcting process and enables the use of loose-abrasive ductile grinding [Appl. Opt. 30, 2761-2777 (1991)] and subsequent bowl-feed polishing [Appl. Opt. 26, 696-703 (1987); Opt. Eng. 31, 1086-1092 (1992); Appl. Opt. 33, 89-95 (1994)] for the generation of aspherical surfaces.

Ductile regime grinding of ferrite with variation of grain size by a piezoelectric-driven micropositioning grinding table

A mirror-like grinding of brittle materials is required in many precision engineering regions. Ductile regime grinding, a new grinding technology for brittle materials, is considered as a solution of this difficult-to-cut materials grinding. It is known that a fracture mechanism of brittle materials is transient to plastic deformation in the region of extremely small depth of grinding or removal rates. In this paper, the ductile regime grinding experiment of ferrite with variation of grain size has been performed using a micropositioning grinding table.

Nanoscale grinding of ceramics using diamond fibres

Abstract Diamond fibres have been manufactured by CVD on to W wires. The fibers were used to grind optical glass and alumina. The surfaces were studied using Talysurf, SEM, and atomic force microscopy. Nanoscale surface roughness values have been obtained and ductile grinding was produced on glass. The results suggest that the shallow depth of cut produced by the surface diamond facets will lead to reduced surface damage, and the high density of cutting sites will allow high rates of material removal.

Nanoscale ductile grinding of glass by diamond fibres

Chemical vapour-deposited diamond fibres have been used to grind soda glass. The surface topography was studied using scanning electron microscopy and atomic force microscopy techniques. The diamond surface facets and edges led to grinding without surface cracking and to surface roughness, Ra, values in the range 3–50 nm. The grinding mechanism involved the formation by ductile flow of glass ribbons adjacent to the grinding grooves. This grinding mechanism was similar to that reported for single-point diamond machining. The potential for ductile grinding with diamond fibres is discussed.

Ductile Regime Mirror Finish Grinding of Ceramics with Electrolytic In-process Dressing (ELED) Grinding

Abstract Advanced structural ceramics, such as silicon nitride based materials, are of interest owing to their unique physical and mechanical properties. However the cost of grinding these ceramics, which is an integral part of their fabrication, is very high. Moreover, grinding can result in surface and sub-surface damage in the material and these defects can significantly reduce the strength and reliability of the finished components. Grinding damage is sensitive to grinding parameters. Two types of silicon nitride based ceramic materials were ground with Electrolytic In-Process Dressing (ELID) using different grit sized metal bonded diamond grinding wheels. With the application of ELID technology, mirror surface finish was realized with a #4000 mesh size wheel (average grain size = 4μm). Differences in ground surface topography caused by wheel grain size were analyzed using scanning electron microscopy (SEM) and atomic force microscopy (AFM). The SEM and AFM studies reveal that material was predominant...

Semi-Ductile Grinding and Polishing of Ophthalmic Aspherics and Spherics*

Ductile grinding yields surfaces whose precision is far beyond that expected of ophthalmic requirements. This process requires machine tools and cutting tools that are manufactured to sub micron tolerances and which require clean rooms, thus making its cost prohibitive. While fracture mode grinding, followed by lapping and polishing have been successful, this paper presents results of semi-ductile grinding that is followed by reduced polishing time without an intervening lapping operation. Using conventional CNC machining centres and/or dedicated machines, silicon, germanium and glass were ground by metal bonded and/or diamond bonded diamond wheels followed by conventional polishing techniques.

Observations on Polishing and Ultraprecision Machining of Semiconductor Substrate Materials

Among the polishing techniques used for semi-conductor materials that are hard and brittle (Si), chemical-mechanical polishing (CMP) has many advantages and a few serious disadvantages too. For materials that are soft and brittle like GaAs, GaP, and InP, which have a very promising future, the CMP technique is now possible without the use of toxic agents. The elimination of the polishing process altogether, or a substantial reduction in polishing time is another strategy that has been successfully established by the use of electroyltic in-process dressing techniques (ELID). At the same time there are applications where profile requirements are not stringent like inexpensive night vision lenses, where partial ductile grinding and simple mechanical polishing are highly economical. Finally a simulated model for ultra precision grinding is presented here.

Fixed abrasive grinding of CVD SiC mirrors

A strategy for machining ceramic (silicon carbide) mirrors is described. By taking advantage of the relative ductility of ceramics compared with that of glass, it is shown that fixed-abrasive, ultraprecision grinding is a viable fabrication process for high-performance aspheric mirrors. Also, it is shown that ductile grinding of ceramic substrates can produce optical quality surfaces, particularly in infrared applications. Laboratory-scale ductile-regime grinding of chemically vapor deposited silicon carbide is described, as is a scale-up of the technology to a commercially available ultraprecision machine tool that has been retrofitted for grinding aspheric ceramic components.

Neutral ion figuring of chemical vapor deposited SiC

Ion figuring of optical components is a relatively new technology that can alleviate some of the problems associated with traditional contact polishing. Because the technique is noncontacting, edge distortions and rib structure print through do not occur. This investigation was aimed at determining the effect of ion figuring on surface roughness of previously polished or ductile ground ceramic optical samples. This is the first step in research directed toward the combination of a prefinishing process (ductile grinding or polishing) with ion figuring to produce finished ceramic mirrors. Multiple, chemical vapor deposited silicon carbide (CVD SiC) samples were polished or ductile ground to specular or near-specular roughness. These samples were then characterized to determine topographic surface information. The surface evaluation consisted of stylus profilometry, interferometry, and optical and scanning electron microscopy. The surfaces were then ion machined to depths from 0 to 5 micron. The finished surfaces were characterized to evaluate the effects of the ion-machining process with respect to the previous processing methods and the preexisting subsurface damage. This study provides some of the information required to effectively utilize a combined ductile grinding or polishing with ion machining as a procedure for figuring optical components.

Grinding Mode Identification by Means of Surface Characterization

A new method was developed to characterize ground ceramic surfaces. The method is based on the evaluation of planar areas caused by ductile mode conditions. The necessary three-dimensional topography data of the surfaces were obtained by SEM. Applying the evaluation method, surfaces ground by the two opposite grinding modes, ductile grinding and brittle fracture grinding, can be distinguished. Moreover, the percentage of ductile regime ground surface in mixed mode surfaces can be determined. The method was verified using ceramic samples of different material, machined applying different mesh numbers of grinding wheel and increase of depth of cut respectively.

Generation of Parabolic and Toroidal Surfaces on Silicon and Silicon-Based Compounds Using Diamond Cup Grinding Wheels

This paper presents the methods and experimental results using diamond cup wheels and CNC machining centers for grinding parabolic and toroidal surfaces made of Si and SiC, the former for use as a thermal imaging lens and the latter for synchrotron radiation facilities. Generation of aspheric surfaces, by zonal material removal, on Si using cup grinding wheels and a 5-axis machining center was investigated. Theoretical and experimental investigation of the grinding and material parameters that influence ductile grinding are discussed. Ductile grinding is possible with wheels having small grit size and with proper combination of feed and unit normal load; a resinoid bonded wheel promotes this more easily than a metal bonded wheel, though at the expense of profile accuracy. Profile analysis, surface integrity, and examination of grinding swarf using digital imaging are discussed. Also, generation of toroidal surfaces on SiC using metal-bonded cup wheels, a 3-axis machining center and a micro-displacement table with piezoelectric actuators was studied. Toroidal SiC mirrors were ground with good shape accuracy, mirror finish, and low surface roughness. The time consumed in the process is very short. The machines used are inexpensive and not specially designed for ultra-precision grinding.

斜入射Ｘ線ミラー用超精密研削加工機の開発

In order to fabricate grazing incidence X-ray mirrors made of hard and brittle CVD-SiC, a large 5 axis control ultra-precision grinding machine has been developed. The machine must be capable of generating non-axisymmetric aspheric surfaces by ductile grinding. So as to obtain precise profile accuracy, new mechanisms such as flexible coupling, guide rails with fine deformation mechanism and leveling blocks for correcting warp of guide rails are applied to hydrostatic linear slideways. As experimental results, excellent straightness of X axis slide of 0.05 μm in a 500mm traverse is obtained on the grinding machine. Non-axisymmetric aspheric mirrors have been ground within a profile error of 0.9μm with the machine.

Specific grinding energy as an in-process control variable for ductile-regime grinding

This article addresses the problem of monitoring the material removal regime (ductile versus brittle) that occurs during the grinding of brittle materials. Often a ductile grinding regime is desired, but currently there is no way to measure the grinding ductility “in process.” A model is developed to describe the dependence of the specific grinding energy on the material removal regime. It is found that the specific grinding energy will remain relatively constant for ductile-regime grinding but will decrease in a power-law relationship with an increasing material removal rate for brittle-regime grinding. Experimental confirmation of the proposed model is presented. The potential for using measurements of specific grinding energy to control the grinding ductility is established, and the benefits of such a closed-loop feedback system in ductile-regime grinding are explained.