CZ296864B6 - Process for making precise shear surface during progressive cold forming and apparatus for making the same - Google Patents

Abstract

In the present invention, there is disclosed an apparatus having a pre-cut punch (2) for preliminary cut with material (1) allowance (1a) within the range of 0.5 to 1.0 mm on a corresponding surface having a cutting clearance within the range of 6 to 12 percent of the material (1) thickness (t) being cut relative to its shear plate (3) and a trimming punch (4) for trimming said allowance (1a), having a one-side clearance (V2) within the range of 0.01 to 0.05 mm relative to its shear plate (5). Said pre-cut punch (2) and the trimming punch (4) are arranged in a transfer-forming tool. First, a precut with allowance (1a) of 0.5 to 1.0 mm on the corresponding surface is carried out by said pre-cut punch and subsequently trimming is carried out by said trimming punch (4) removing thus said allowance (1a). So formed shear surface exhibits properties of a precise shear surface.

Description

Technical field

The present invention relates to the field of cold forming, in particular to a process for producing an accurate shear surface in a cold forming process and to an apparatus for carrying out the process.

BACKGROUND OF THE INVENTION

As part of the cold forming process by means of merged process tools on the crank or eccentric presses of the column construction, shearing is also performed. This is accomplished by a punch and a cutting plate which are incorporated in the merged transfer tools, and there must be a shear clearance between the cutting plate and the punch which is in the range of 6 to 12% of the thickness of the material to be cut. However, the resulting cutting surface is not accurate, ie. it does not have the same roughness throughout the thickness, it does not reach perpendicularity and flatness, it shows tearing. All this is due to the aforementioned necessary shear clearance between the cutting plate and the punch, during which the shearing is first cut and then torn off. Such shear surfaces are then adversely affected by subsequent bending, whereby cracks are formed in the shear surface which adversely affect, in particular, the strength properties of the molded part. An example of such a component may be the combined cold-formed brake pedal transfer tools, which, after shearing, undergo an irregular U-shape. The cracks described cause a reduction in its strength properties, which is undesirable.

Shear surfaces without the above-mentioned shortcomings, i.e. precision shear surfaces, can be made by precision cutting, but this method, where the clearance between the cutting plate and the punch is minimized to several hundredths of a millimeter, is only feasible on precision cutting machines with a hydraulic system. It cannot be used in cold rolling on crank or eccentric presses of the column construction.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an accurate shear surface during cold forming which has the properties of a shear surface created by the precision shear method, thereby avoiding cracks during subsequent bending.

This object is achieved by a process for forming an accurate shear surface in a cold forming process and by an apparatus for carrying out the process according to the invention.

The essence of the process is that first, a pre-shear punch having a shear clearance of 6-12% of the thickness of the material to be cut with its shear plate is sheared with an addition in the range of 0.5 to 1.0 mm on the respective surface and then with a blanking punch having a one-sided clearance in the range of 0.01 to 0.05 mm with respect to its shear plate, the blank is cut to cut off said addition.

The principle of the apparatus for carrying out said process is that the apparatus has a pre-shear punch with a material addition in the range of 0.5 to 1.0 mm on the respective surface, which has a shear clearance of 6 to 12% of the shear thickness relative to its shear plate. material and a blanking punch for cutting said addition having a one-sided clearance with respect to its shear plate in the range of 0.01 to 0.05 mm, both punches being included in a transfer forming tool.

-1 CZ 296864 B6

The process and apparatus according to the invention make it possible to create a precise shear surface by means of a progressive forming tool on crank or eccentric presses of the column construction.

BRIEF DESCRIPTION OF THE DRAWINGS

An exemplary embodiment of the invention is shown in the accompanying drawings, in which Fig. 1 shows schematically a device for producing an accurate shear surface and Fig. 2 is a section A-A according to Fig. 1.

DETAILED DESCRIPTION OF THE INVENTION

The apparatus for forming an accurate shear surface in a cold progressive forming is arranged in a merged advancing tool at two successive work stations. On the first one there is a pre-punch 2 and its associated shear plate 3, between which the shear clearance is in the range of 6 to 12% of the thickness t of the material to be cut 1. In this example, a thickness t equal to 3 mm, there is a one-sided clearance VI of 0.15 mm between the pre-punch 2 and its associated cutting plate 3. The additive and the material 1 in the range of 0.5 to 1.0 mm are determined on the respective surface. The shear punch 4 and its associated shear plate 5 are arranged at the next work station. The one-sided clearance V2 between the shear plate 5 and the shear punch 4 is in the range of 0.01 to 0.05 mm regardless of the material thickness t, in this case in particular 0.05 mm. This one-sided clearance V2 is provided with a one-sided clearance of 0.15 mm in relation to its shear plate 5 in other areas where an exact cutting surface is not required. The cutting punch 4 has a radius R in the range of 0.1 to 0.2 mm at the cutting edge. The contour of the blank, in this case the brake pedal, is indicated by a thin line in FIG.

The process of forming an accurate shear surface thus proceeds in two successive cold forming operations at two successive work stations. In the first, said pre-punch 2, which has the aforementioned one-sided clearance VI with respect to its shear plate 3, is pre-preloaded with the addition of Ia of material 1 in the range of 0.5 to 1.0 mm on the respective surface. The resulting cutting surface is inaccurate and shows all the drawbacks of the cutting surfaces created by this classic cut. At the second workstation, the punch 4 is cut, in which only the additive and material L are cut. As a result, and due to said minimum unilateral play V2 between the cutting plate 5 and the punch 4, an accurate cutting surface is produced.

Industrial applicability

The invention is useful in the cold forming of parts that need to be precisely cut to prevent cracks on the surface during subsequent bending, for example in the cold forming of the brake pedal.

Claims (2)

PATENT CLAIMS Method for producing a precision cutting surface in a cold forming process, characterized in that first, a pre-punch (2) having a shear clearance in the range of 6 to 12% of the material to be cut (t) relative to its cutting plate (3) 1), cuts with an addition (1a) in the range of 0.5 to 1.0 mm on the respective surface and subsequently with a cutting punch (4) which has a one-sided clearance (V2) with respect to its cutting plate (5), 01 to 0.05 mm, cuts to cut said addition (1a). Device for carrying out the process according to claim 1, characterized in that it has a pre-shear punch (2) with an addition (1a) of material (1) in the range of 0.5 to 1.0 mm on a respective surface which has a shear plate (3) a shear clearance in the range of 6 to 12% of the thickness (t) of the material to be cut (1) and a shear punch (4) for shearing said addition (1a) having unilateral play (V2) relative to its shear plate (5) in the range of 0.01 to 0.05 mm, both punches being engaged in a transfer forming tool.