Geometrical instruments – Gauge – Surface plate or gauge block
Patent
1990-07-24
1992-05-19
Will, Thomas B.
Geometrical instruments
Gauge
Surface plate or gauge block
33605, 33545, 33567, G01B 330
Patent
active
051135922
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The invention relates to a master part with a plurality of reference or datum zones for determined workpieces, these zones including precision machined surfaces having pre-established mutual spatial arrangements.
The invention also relates to a process for manufacturing said master part.
BACKGROUND ART
As it is known, the processes for manufacturing and inspecting workpieces involve the use of master parts adapted to provide datums or references for the critical features or surfaces of the workpieces, in particular for linear dimensions, shape and geometry features, etc.
In particular, these master parts are necessary for zero-setting devices and machines used for checking, through comparative measurements, said features of the workpieces during the different steps and at the end of the mechanical machining operations relating to the same workpieces.
The known master parts are manufactured through precision, chip-forming machining operations, on blocks of special steel for master parts, at least as far as the surfaces corresponding to the critical surfaces of the workpieces are concerned. After the mechanical machinings, the master part undergoes hardening and annealing heat treatments.
The material of the conventional master pats is characterized by very high hardness and stability and therefore this material is "special" for both intrinsic chemical features and the hardening and annealing treatments.
These master parts have conceptually monolithic, i.e. integral structure, even if sometimes--due to accessibility problems or other practical difficulties--, especially in the case of very complex master parts, this structure is comprised of a plurality of blocks.
In order to preserve the master parts from corrosion, often on them there are applied, before the finishing machinings and the final heat treatments, chromium or nickel platings, or platings with other anticorrosive materials. This renders the finishing (grinding, lapping, etc.) machinings more difficult and expensive, in particular with regard to the reference surfaces, where consequently these platings are not always applied. In this case, the reference surfaces must periodically be greased.
Moreover, the master parts are subjected to a certification procedure in a metrology department, by means of measuring apparatuses having a very high accuracy. This procedure is basically distinct from the manufacturing process.
The manufacturing of a conventional master part is very complex and expensive, since, among other things, a machining error may cause the rejection of the entire master part or of a substantial part of it. Besides, the manufacturing process has a very poor or null flexibility, because the major part of it is specific for a determined workpiece.
Usually, the shape of the master parts is rather similar to that of the relevant workpieces, especially as far as the critical surfaces of the workpieces are concerned.
As it is known, even if the workpieces have to be dynamically checked (for example, in the case of shafts, during rotation about their geometrical axis), the master parts are used in a static way, by using as references only a minor portion of the precision machined surfaces or zones. Thus, for example, when cylindrical surfaces providing references or datums for corresponding workpiece surfaces are concerned, two or four points or zones of these surfaces of the master part are used, to define one or, respectively, two diameters.
DISCLOSURE OF INVENTION
Object of the invention is to simplify the manufacturing method used for the known master parts by obtaining, through cheaper processes and materials, master parts that eliminate many drawbacks, while guaranteeing high accuracies and stability.
The invention, as characterized in the claims, makes it possible to diminish the intrinsic cost of the materials and to reduce, even for very complex master parts, the precision machinings and the hardening and stabilization treatments.
The support structure or body of the master part can be made of cheap materials h
REFERENCES:
patent: 1308493 (1919-07-01), Jaques, Jr.
patent: 1362726 (1920-12-01), Mason
patent: 2039141 (1936-04-01), Brault
patent: 2537340 (1951-01-01), Fonda
patent: 2725636 (1955-12-01), Green
patent: 2831256 (1958-04-01), Werle
patent: 3845560 (1974-11-01), Sommer
patent: 3861049 (1975-01-01), Muller
patent: 4578875 (1986-04-01), Vertin
MARPOSS Societa' per Azioni
Will Thomas B.
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