METHOD OF PREPARING A SHEET-METAL WORKPIECE FOR COATING

Abstract

A sheet-metal workpiece is prepared for coating by first trimming or punching a sheet-metal workpiece to give it an edge with sharp corners. Then the edge is rounded such that the corners are no longer sharp and merge into adjacent faces of the workpiece. Finally, and coating at least the rounded edge of the workpiece with an anticorrosive agent with a matrix of organic binders or with predominantly organic components.

Claims

1. A method of preparing a sheet-metal workpiece for a coating, the method comprising the steps of: trimming or punching a sheet-metal workpiece to give it an edge with sharp corners; rounding the edge such that the corners are no longer sharp and merge into adjacent faces of the workpiece; and coating at least the rounded edge of the workpiece with an anticorrosive agent with a matrix of organic binders or with predominantly organic components.

2. The method defined in claim 1, further comprising after rounding the edge the step of: roughening the rounded edge to improve adherence of the coating.

3. The method defined in claim 1, wherein the rounding is done by a laser beam.

4. The method defined in claim 1, wherein the laser beam is pulsed by a short-pulse laser.

5. The method defined in claim 1, further comprising the step, after the trimming or punching, of: cleaning the edge of oxides or other contaminants before the rounding or synchronously therewith.

6. The method defined in claim 5, wherein the cleaning is done by a laser beam.

7. The method defined in claim 1, wherein the edge is rounded so as to merge steplessly into adjacent faces of the sheet-metal workpiece.

8. The method defined in claim 1, wherein the sheet-metal workpiece has a wall thickness of less than or equal to 5 mm.

9. The method defined in claim 1, wherein the coating is applied in a thickness of less than or equal to 35 m.

10. The method defined in claim 1, further comprising the step of: roughening the rounded edge in the form of an irregular or regular geometry.

Description

BRIEF DESCRIPTION OF THE DRAWING

[0025] The above and other objects, features, and advantages will become more readily apparent from the following description, reference being made to the accompanying drawing in which:

[0026] FIG. 1 is a sectional view of an outer edge of a sheet-metal workpiece according to the invention;

[0027] FIGS. 2 and 3 show alternative forms of the outer edge after appropriate processing.

[0028] FIG. 4 shows and explains the prior art;

[0029] FIGS. 5A, 5B, and 5C are a small-scale schematic views illustrating the method of the invention.

SPECIFIC DESCRIPTION OF THE INVENTION

[0030] In FIG. 4, one can see the sharp outer edge of a punched or trimmed sheet-metal workpiece 1. The outer edge is shown at 2. If a cathodic E-coating 3 is applied to such a finished workpiece 1, then a configuration is produced after subsequent processing in a furnace (heating to about 180 to 190 C.) such that, as a result of the surface tension due to the molecular forces of the coating, the region 4 on the edge of the workpiece 1 gets insufficient coating. Such a thin coating at an edge can result from other physical effects as well. The invention is intended to prevent this effect.

[0031] FIG. 5 shows the method of this invention. First, as shown in FIG. 5, an edge piece 1 is trimmed off the workpiece leaving a square edge 2 (FIG. 4) with two sharp corners 4. Then as shown in FIG. 5B, a laser 9 is aimed at the corners 4 to round the edge into a part-cylindrical shape 5 so they are no longer sharp and merge smoothly into the adjacent planar faces of the workpiece 2. Finally the entire workpiece 1 and in particular the edge region that was rounded in FIG. 5B are electrophoretically coated by applying a negative or positive charge to the workpiece from a power supply 11 and an opposite charge to a spray head 10 emitting charged particles of a coating material that stick to the oppositely charged workpiece 1 and form a smooth coating 3 of uniform thickness thereon, including the entire rounded edge.

[0032] To this end, the invention proposes a method of the following type. In order to prepare a sheet-metal workpiece 1, which actually cut as shown in FIG. 5A has a trimmed edge as shown in FIG. 4, for coating with an anticorrosive agent 3 in the form of a matrix of organic binder or predominantly organic components, particularly in the form of a cathodic E-coating, the trimmed edge 2 of the workpiece 1 is rounded. The rounding structure 5 is illustrated in FIGS. 1 and 5B. Instead of the rounding structure or in addition to the rounding structure, a slightly roughened structure 6 with an irregular geometry or a roughening structure 7 with a regular geometry can be applied. The rounding and/or the roughening 5, 6, 7 is performed by a laser beam. In particular, the processing is performed here by a pulsing laser beam, particularly by short-pulse laser. In this way, unnecessarily high energy input into the workpiece 1 is avoided. What is more, the treatment with the laser beam enables any contaminants on the trimmed edge 2 to be removed simultaneously or beforehand or afterward.

[0033] Preferably, the rounded edge 5 merges steplessly into the adjacent surface of the sheet-metal workpiece, as can be seen particularly well in FIGS. 1, 5B, and 5C. Such a sheet-metal workpiece 1 usually and preferably has a wall thickness of 1 mm to 5 mm. The coating 3 preferably has a thickness of 20 to 35 m.

[0034] What is achieved by the rounding 5 and/or by the roughening with the roughening structures 6 or 7 is that the coating material 3 can also be applied to the edge region with a sufficient layer thickness, with the maintaining of the layer thickness in the edge region also being ensured through the appropriate configuration and application of the method, so that the finished workpiece is insensitive to edge corrosion.

[0035] The invention is not limited to the illustrated embodiments, but rather can be varied in many respects within the framework of the disclosure.

[0036] All of the individual and combined features disclosed in the description and/or drawing are regarded as essential to the invention.