Technological background of the invention According to the prior art, the biahkingof metai parts in a press, also known as punching, is an operation which brings about the detachment of a portion from a semi-finished product along an outline corresponding to the cross-section of a blanking tool, that is the punch, and of a respective die.

The cutting takes place owing to the pressure exerted by the punch during its working stroke on the semi-finished product disposed on the die.

Blanking is widely used in various fields by virtue of the low costs and fast production that are typical of this process. However, it has some disadvantages such as, for example, poor surface finishing of at least a portion of the detachment region. In fact a portion of the surface resulting from blanking has imperfections such as signs of tearing and the like which are not acceptable in the finished product in some cases. Generally, about 1/3 of the surface produced during blanking is cut and the remaining 2/3 is torn so'that the part has to be reprocessed'by further finishing processes, for example, bevelling or polishing, to attenuate the above-mentioned surface imperfections. However, these operations lead to a considerable increase in processing costs.

Description of the invention The problem underlying the present invention is that of providing a method of processing metal parts by blanking that is designed to overcome the limitations discussed above with reference to the prior art mentioned.

This problem is solved by the present invention by means of a method of processing parts by blanking in accordance with the appended claims.

Brief description of the drawings The characteristics and the advantages of the invention will become clearer from the following detailed description of a preferred embodiment

thereof which is described by way of non-limiting example with reference to the appended drawings, in which: - Figure 1 is a perspective, view of a : semi-finished metal product. to _be procebbu))) accordance with the method of the invention, - Figure 2 is a perspective view of the semi-finished product of Figure 1 after a first processing step, - Figure 3 is a perspective view of the semi-finished product of Figure 2 after a further processing step, - Figure 4 is a perspective view of the semi-finished product of Figure 3 after a further processing step, - Figure 5 is a perspective view of the semi-finished product of Figure 4 after a further processing step, and - Figure 6 is a schematic view of a detail of the semi-finished product of Figure 3, in section and on an enlarged scale.

Preferred embodiment of the invention With reference first of all to Figure 1, a semi-finished product made of metal such as, preferably, brass, nickel silver, aluminium, precious metals, or the like, prepared for processing according to the method of the invention, is indicated 1.

The drawings show a semi-finished product for the production of a spectacle frame; however, the method according to the invention is directed towards the processing of semi-finished products irrespective of their final purpose and can therefore be used in various technical fields, such as goldsmithery, precision mechanics, spectacle production, etc.

According to the method of the invention, the semi-finished product 1, which has a predetermined shape produced by conventional blanking or by stamping, is first of all processed by coining to produce a coined semi-finished product 10, on one surface 2 of which an imprint 3 of the shape of the finished product to be produced is coined. The imprint 3 is preferably formed in high relief.

The coined semi-finished product 10 is shaped as a portion of a spectacle frame and, in particular, comprises two upper portions of lens- holding rims 5 connected by a bridge 7, and two shoulders 6.

A plurality of projections is also formed on the surface 2 of the coined semi-finished product 10 by the coining step; in this preferred example, a first and a second pair of appendages 4a, 4b are formed for locating the coined semi-finished product 10 on a die (not shown) for the subsequent blanking step.

The coined semi-finished product 10 is then subjected to a first blanking step by means of a conventional die and punch, so as to produce a blanked semi-finished product 20 having the characteristics described below.

During this first blanking step, the coined semi-finished product 10 is blanked, leaving an allowance which affects its entire blanking profile or at least the surfaces that are visible in the finished product. In practice, the die and the punch are larger than is necessary for blanking to finished dimensions, by an amount equal to the preselected allowance. According to a principal characteristic of the invention, the thickness S of the allowance is between 0.1 and 1 mm and preferably between 0.2 and 0.25 mm.

Moreover, during the first blanking step, the first pair 4a of locating appendages of the coined semi-finished product 10 is removed.

The surface blanked in this first blanking step, in which the blanked semi-finished product 20 is produced, has the typical imperfections due to blanking, that is, a generally major portion of the thickness bears signs of tearing.

The blanked semi-finished product 20 is then blanked for a second time so as to produce a final product 30 of the desired dimensions. In this second blanking step, the allowance remaining after the first blanking and also the second pair of locating appendages 4b are removed.

Surprisingly, it has been found that the number and density of imperfections of the surface of the final product 30 that is involved in the second blanking are greatly reduced in comparison with the semi-finished product 20 produced by the first blanking step so that the blanked surface is homogeneous and substantially free of signs of tearing.

It is pointed out that the second pair of appendages 4b is preferably formed in surfaces of the semi-finished product that can be processed further after the second blanking step and/or which are not in view in the finished

product; in the example described, which relates to a product that is intended to constitute the front portion of a spectacle frame, the second pair of appendages 4b is formed on the inside of the lens-holding rim portions 5. In the region of these projections, the blanked surface portion of the final product 30 bears signs of tearing and more marked imperfections than the remaining surface since it is subjected to a single blanking step, but a chamfering step is subsequently performed on the inside of the lens-holding rim 5 for the fixing of the lenses to the spectacle frame and the surface portion affected by the,. locating appendages. 4b is therefore reprocessed.

In order also to remove the remaining irregularities, the final product 30 may be polished, for example, by tumbling until the desired surface uniformity is achieved, as shown, for example, in Figure 5 in which a final polished product is indicated 40.

The invention thus solves the problem posed, affording many advantages over the prior art mentioned.

A first advantage consists of the fact that, by virtue of the method of the invention, the final product has a surface finish which is considerably improved in comparison with a semi-finished product conventionally blanked only once. In particular, the surface portion which may bear signs of tearing is considerably smaller.

Moreover, the method of the invention permits production with limited costs, lower than those of production by other methods which give an equally homogeneous surface.