Abrading – Abrading process – Glass or stone abrading
Patent
1995-08-10
1998-06-02
Rose, Robert A.
Abrading
Abrading process
Glass or stone abrading
451269, 451291, B24B 100
Patent
active
057590885
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The invention relates to machining precision components, in particular, to processes of machining components made of brittle materials and devices for carrying out the same.
PRIOR ART
When machining precision components using the method of free lapping there are obtained high accuracies of the form of the surface, whose deviation from the given one may constitute 0,1 to 0,01 of the wavelength. However, producing accurate surfaces is guaranteed for components with a relative thickness (the relationship of thickness and diameter, or the diagonal of a component machined), not affecting the deformation during machining, being h/D>1/5. In so doing, productivity of grinding and polishing operations is inversely proportional to the accuracy of the surface obtained.
Yet, in a number of the fields of the present-day engineering there is an extensive range of articles from glass, quartz, ceramics and other materials, for which the above-mentioned restrictions are not applicable. Among them there may be glass and quartz blanks for masks, glass and glass ceramic blanks for magneto-optical and magnetic disks, plates for liquid crystal indicators, screens, to mention a few. The relative thickness of said components is 0,01 and less. At the same time, fairly rigid requirements are set to the working surfaces and geometric dimensions of these articles.
Machining of the above-identified class of articles is effected with the use of a loose abrasive, providing, compared to a coupled diamond tool the reduction of unit loads in the zone of machining. Among the basic drawbacks of such technology are: requires long polishing useful utilization; small degree of mechanization and automation of processes owing to the foregoing reasons.
As glass and other brittle materials are ground, the transition from a loose abrasive to a coupled diamond tool spells out a qualitatively novel level of technology, featuring a dramatic growth of machining productivity, high wear-resistance of the tool and better culture of production. However, there are no cases of using the coupled diamond tool for precision finished grinding of thin large-size articles with a relative thickness of h/D.apprxeq.1/50 and less with high requirements to the accuracy of the form of the surface to be machined, which may be due to higher specific pressures during diamond grinding.
In addition to high requirements set to the geometry and finish of the working surfaces of the above-mentioned articles, the latter should meet strict requirements as to the accuracy of their overall dimensions. Therefore, the conventional technology of manufacturing articles in question provides for an initial phase of diamond machining and chamfering of the edges of the articles and subsequent machining of their surfaces. The grinding operation is the last one in the technological cycle of machining precision articles. This fact allows for the availability of nonworking/idle zones on the working surface of precision articles, which are arranged along the edges of the components, stipulated by "rounding" of the edges during polishing. For articles, such as magnetic or magneto-optical disks, this shortcoming brings about a dramatic reduction of the effective area of an article and, consequently, a lesser memory of the disk.
Known in the art is a process of machining components, whereby the force is applied on the components, pressing them to the tool and the components and the tool move relative to each other in the plane of machining (USSR Inventor's Certificate No. 1237387). In this process as the forced grinding is performed under loads of 1200 to 4000N there is achieved a higher accuracy of forming a flat surface due to the use of a diamond-abrasive tool with a concave working surface, compensating for deformation of the tool body.
However, these modes of machining are absolutely unacceptable for precise machining of parts with a relative thickness of h/D<1/10.
Known in the art is a process of unilateral polishing the components between two tools, in which
REFERENCES:
patent: 2963830 (1960-12-01), Hook
patent: 4962616 (1990-10-01), Wittstock
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