DE10322449B3 - Laser welding method for superimposed coated sheets used in automotive industry with laser beam used for pre-cutting of slit in at least one coated sheet - Google Patents

Abstract

The laser welding method has a laser beam used for cutting a slit in at least one of the superimposed coated sheets in a first step, before laser welding of the superimposed sheets via the obtained slit in a second step. The laser beam can be moved across the surface of the superimposed sheets via a scanning device, a transversal movement component superimposed of the laser beam movement during the second step.

Description

The invention relates to a method for laser welding coated plates according to the preamble of claim 1. Such a method is already known from US 2001 0047 983 A1 or the JP 2002 316 281 A known. Similar methods are known from JP 2001-162389 or the DE 100 47 807 A1 known.

For many coated plates, especially in zinc and organically coated sheets such as used in the automotive industry, has the coating material a much lower boiling point than the melting point of the sheet material. This results in laser welding with zero gap of such sheets in the overlap burst to explosive Evaporation of coating material containing molten sheet metal thrill and the quality strongly affect the connection.

To improve the quality of the connection has already been proposed to create spacers by means of narrow gaps between the sheets, in which the evaporated coating material can escape. Suitable crater-shaped spacers can according to the JP 11-047967 be generated by laser bombardment of the surface.

The disadvantage here is on the one hand the required relatively long preparation and processing time, which causes considerable costs, especially in series production.

On the other hand, becoming part of the molten sheet material during the manufacture of the welded joint between the sheets also in the gap (gap) flow, which is why this material volume is then missing in the region of the weld seam outer surface and surface defects causes in a seam lowering.

That is why already in the DE 100 47 807 A1 proposed not to provide a gap between the sheets, but to position them as close to each other and then to weld by means of a defocused laser. Due to the defocusing, a larger processing area with lower power per unit area is processed at the same laser power and thus melted more slowly and more uniformly. This should avoid both the eruption-like evaporations of the coating and the seam lowering of the weld. The experiment shows, however, that eruptions occur, albeit to a lesser extent, that carry away the sheet material and thus lead to holes in the weld. However, the decisive disadvantage is the significantly lower feed rate due to the lower power per unit area.

According to the JP 2001-162389 The sheets are also positioned without gap together and then welded together in a first processing step at the expense of eruptive evaporation. In this case, a hole or a channel is to be created in the weld, which is at least partially closed at the top by (over the surface protruding) eruption material. In a second processing step, this eruption material is remelted and then should fill up the hole / gutter evenly. Experience has shown, however, that at best a part of the eruption material remains in the vicinity of the first weld and is thus available for reflow, while a substantial proportion is distributed over a wide area by the eruption. As a result, here again material is missing and there are holes in the weld.

The object of the present invention is therefore the required processing time for production the weld to reduce and at least maintain the quality of preferably to improve.

The invention is in relation to the to be created by the features of claim 1 played. The other claims contain advantageous Embodiments and developments of the method according to the invention (claims 2 to 5).

The task is related to the to be created process according to the invention solved in that during a first method step by means of the laser beam first Gap cut through at least one or all plates and after that while a second process step, the at least two plates above the Gap welded become. For the split generation is the laser beam to the plane between the Focus plates.

At the first step (laser cutting) should have a gap with as possible small width can be generated. This is the laser beam on the Layer between the plates as possible strong with a suitable optics to focus. This is the result Laser power per unit area very high, so not only the coating of the plates evaporates, but also the plate material As a result, no eruptions of molten plate material occur on.

For This first step is a suitable processing time until Pretending passage or also providing a penetration sensor, which regulates the processing speed.

In the second step (laser welding), the laser beam is at least defocused so far that the plate is not vaporized by the impact. Although the coating continues to evaporate, its vapor can escape through the gap produced in the first process step, so that no Vapor pressure is built up, which could lead to eruptions.

The proportion of the gap generation evaporated plate material is relatively low, so it only to minimal incidence of the weld comes.

Compared to the introduction of spacers, e.g. Nubs, the process of the invention has advantages with respect to. Time and cost as well as accuracy.

In an advantageous embodiment the method according to the invention The laser beam is directed by means of a scanner device on the surface. A scanner setup is a particularly fast and flexible one Beam deflecting device, such as a mirror system (off at least one single or multi-axis controllable pivotable Mirrors) or acousto-optic modulators.

The great advantage of this embodiment of the method according to the invention over the in JP 2001-162389 proposed is that the scanner device is uniformly rela tively moved to the surface of a plate while the scanner device directs the laser beam for a short processing period on a processing line for gap generation and then very quickly redirects the laser beam to the beginning again to to start the welding process. This eliminates the time required for the repositioning of the laser beam, in particular the defocusing time, almost completely. Thus, a very high utilization of the laser system is possible. In contrast, in a conventional laser system, such as in the JP 2001-162389 a laser beam is directed over the processing line by means of a rigid lens system. For the return to its beginning for the second welding step, the lens system must be moved relative to the component, while the laser must be turned off. As a result, this embodiment of the invention requires only a fraction of the processing time compared to the subject matter of JP 2001-162389 and is due to the much higher feed speed many times faster than the subject of the DE 100 47 807 A1 ,

In a further advantageous embodiment the method according to the invention the laser beam is during of the second process step not on a surface of focused at least two plates. Preferably, the is Focus at such a distance from the surface of the beam side plate, that the irradiation area of the Lasers on the surface its focus area around at least 50 percent, better 200 percent.

Alternatively or in addition thereto a further broadening of the processing surface by movement of the irradiation surface by means of minimal deflection of the laser beam (superposition of a transversal Movement component in the main feed direction; so-called beam spinning) be achieved.

Such surface heating even out Melting process of coating and plates and favors the Training a uniform weld. Farther receives an enlarged connection cross section, which bridges the cutting gap.

In a further advantageous embodiment the method according to the invention is The relationship from gap width to weld width 1 to x, with x ε [3; 30], preferably [5; 10]. This ensures the training of a high quality weld in very short processing time.

The following is based on two figures and two embodiments the inventive method explained in more detail:

Show

1 : Laser beam cutting of two plates positioned without a gap on top of each other

2 : Laser beam welding of the plates positioned without a gap on top of each other

According to the first embodiment, two coated sheets (as are common in the automotive industry) are aligned without a gap on top of each other, a scanner device is moved evenly over it and directs a laser beam successively on multiple processing surfaces. The scanner device consists of a two-dimensionally swiveling computer-controlled mirror system. The scanner device has for the first process step of the laser cutting about 300 mm distance from the surface of the first sheet, the laser beam is focused on the plane between the two sheets. The focused laser beam has sufficient power to vaporize the coating and sheet material and cuts a thin gap through both sheets (see FIG. 1 ). In a second process step - the laser welding (see. 2 ) - the laser beam is defocused, ie the focus is now about 20 mm in front of the surface of the first sheet. The irradiation area is about 200 percent larger than the focus area. The defocused laser beam is passed over the previously generated column. The defocusing of the laser beam results in a planar and uniform heating of the processing surfaces, which extend on both sides beyond the gap due to the defocusing. This results in a uniform evaporation of the coating, which can escape eruption through the gap and a uniform melting and welding of the sheets. The ratio of gap width to weld width is 1 to 3.

In a second embodiment, the degree of defocusing is reduced. The focus The laser beam is only about 5 mm above the surface of the first sheet. As a result, the processing area is smaller (the irradiation area is approximately 50 percent larger than the focus area) and the intensity is higher for the same laser power. The laser beam is passed over the column again. However, this feed motion is superimposed on a transverse movement component in the main feed direction (so-called beam spinning). The beam makes a spiral or sinusoidal movement about the split line. Thus, with high laser power per unit area still a uniform processing of a wide processing surface can be guaranteed. The ratio of gap width to weld width is 1 to 5.

The inventive method proves in the embodiments of the examples described above are particularly suitable for laser welding Sheets in the automotive industry.

In particular, such significant advantages in terms of Processing time can be achieved. But also the corrosion protection is improved by the missing gap, where otherwise moisture could collect.

The invention is not limited to the previously described embodiments limited, but rather transferable to others.

For example, it is conceivable that the scanner device rather than through a mirror system by acousto-optic modulators train. Furthermore, it is possible instead of the laser scanner over the component surface respectively, to move the components under a stationary scanner. Possibly can Scanner and component perform a mutually coordinated movement.

Also, the distance of the scanner device from Sheet metal and the degree of defocusing are not mandatory and can at Demand, for example, to the laser power or to the material of Sheet metal and / or coating to be adapted.

In addition, it can be beneficial be the laser power during the irradiation in a suitable manner.

Furthermore, the method is not on welding coated metallic sheets, but also on the welding of plastic sheets applicable.

Claims (5)

Method for laser welding of at least two coated plates, the gap between each other as possible be positioned during a first method step by means of a laser beam first Gap is cut through at least one of the panels,  thereby in  that after that while a second process step, the at least two plates above the Gap welded become. Method according to claim 1, characterized in that that the Laser beam directed by means of a scanner device to the surface becomes. Method according to one of the preceding claims, characterized characterized in that Laser beam during of the second process step not on a surface of at least two plates is focused. Method according to one of the preceding claims, characterized characterized in that Laser beam during the second step is performed such that its Main feed direction is superimposed on a transverse component of motion (so-called beam spinning). Method according to one of the preceding claims, characterized characterized in that relationship from gap width to weld width 1 to x, with x ε [3; 30], preferably [5; 10].