WO2015018551A1

WO2015018551A1 - Method for generating a weld seam and component

Info

Publication number: WO2015018551A1
Application number: PCT/EP2014/062675
Authority: WO
Inventors: Jens Theis; Mario Matic
Original assignee: Robert Bosch Gmbh
Priority date: 2013-08-06
Filing date: 2014-06-17
Publication date: 2015-02-12
Also published as: DE102013215421A1

Abstract

The invention relates to a method for generating a weld seam (10), in which a laser beam (101) generated by means of a laser beam device (100) heats the material of at least one workpiece (1, 2) on a partial region of the at least one workpiece (1, 2) within a molten bath (15) down to a base (16) of the molten mass to a melting temperature, wherein, after the action of the laser beam (101), the molten material solidifies in a subsequent cooling phase from the marginal region of the molten bath (15) toward the workpiece (1, 2) in the direction of the centre (20) of the molten bath.

Description

description

Method of producing a weld and component

PRIOR ART The invention relates to a method for producing a weld seam after

Preamble of claim 1. Furthermore, the invention relates to a component which has been produced by means of the method according to the invention.

A method according to the preamble of claim 1 is already known from practice. It is carried out by means of a laser beam device, the one

Laser beam for welding, for example, generated by two components, wherein the two components made of metallic material, in particular the same material exist. In this case, in a joining zone, the material of at least one component is melted over a partial region of its depth or thickness. The molten bath thus produced has a rounded melting base on the side facing away from the laser beam to the non-liquefied material. Upon solidification of the molten material, this solidifies from the walls of the at least one workpiece delimiting the molten bath towards the center of the molten bath, where the greatest temperatures still prevail at the end. In practice, it has been found that when forming such welds the

Welds tend to cause hot cracks, which increases the strength and thus

Impair component safety. In practice, these hot cracks extend approximately from the middle of the weld seam and reach close to the melting point, but do not reach it.

To solve the problem of hot cracks have been different

Solutions described. On the one hand, it is possible to use a material that is less critical with respect to hot cracks by changing the base material for the at least one workpiece. However, this presupposes that the (changed) base material is applicable for the respective application and, for example, also justified for cost reasons. Another known Measure relates to the addition of filler materials, which should reduce the tendency to hot cracking during the solidification of the weld. However, such an addition of filler material is a relatively complicated

Process technology that must also be monitored or logged.

DISCLOSURE OF THE INVENTION Starting from the illustrated prior art, the invention is the

It is an object of the invention to develop a method for producing a weld according to the preamble of claim 1 such that the tendency toward hot cracking is reduced without the additional measures mentioned, as known from the prior art. This task will

According to the invention in a method for producing a weld with the

Characteristics of claim 1, characterized in that by temporally successively running over the same area of the at least one workpiece by the laser beam in each case a molten bath in the last generated, already solidified weld is generated, the depth of the molten bath compared to the last molten pool of the already solidified

Weld is reduced, and wherein the depth of the molten bath is selected such that the molten bath extends into a range of below the respective molten bath, already solidified weld in which no solidification line is formed.

The invention makes use of the observation that hot cracks usually do not reach the melting point. This behavior can be explained by the fact that in the area of the melt base, which is usually curved or rounded in cross-section, during the solidification of the molten material, the solidification of the individual metal crystals of the

Wall of the molten bath is carried out in a direction perpendicular to the wall. As a result of the rounding or curvature in the area of the melt base, the material solidifies, at least approximately, last in a point which lies approximately in the region of the midpoint of a radius in the cross section of the melt pool in the melt base. In contrast, the solidification above the

Melting ground from the two sides of the walls of the molten bath in the direction towards the center of the molten bath, whereby the material of the molten bath is finally solidified in the middle of the molten bath in the form of a continuous line which is potentially prone to hot cracks. By repeated driving over in the claimed manner according to the invention, in contrast, a plurality of superimposed welds are generated, wherein after the solidification of the respective weld, the individual solidified areas can each be regarded as solidified melt reason, not due to the above-mentioned solidification behavior tend to crack. Such a method according to the invention requires only a repeated overrunning of the area of the weld, but for example none

Additives. It only has to be ensured that the respectively last-generated molten bath has a reduced depth compared to the molten bath produced by suitable parameters. Advantageous developments of the method according to the invention are in the

Subclaims listed.

There are various possibilities for producing the next melting bath with the reduced depth. In the context of the invention, it is provided that with each generation of a new melt the performance of the

Laser beam is reduced and / or a feed rate of the

Laser beam is increased and / or an exposure time of the laser beam is reduced. The measures mentioned, both individually and in combination, ensure that the introduced power is reduced to the melting zone, so that a melting zone reduced in depth can be generated.

In particular, the method comprises a molten bath in which the

Melting base of the respective molten bath has a rounding or curvature with a radius, wherein the depth of a melt bath subsequently produced corresponds to the depth of the molten bath previously generated, reduced by a maximum of the radius. By this measure, it is particularly ensured that in the last solidified area the solidification of the material of

Schmelzbads in the Schmelzbadmitte not in the form of the mentioned

Solidification line has taken place. Often tend components that have a weld through

different heat input or cross sections for delay. In order to avoid or reduce the inclination of the at least one workpiece for delay, it is provided in a particularly preferred embodiment of the invention that the laser beam of the laser beam device to the at least one

Aligned workpiece is that every time you drive over to create a new melt pool, an offset of the laser beam to the last generated

Melting bath takes place. This makes it possible to equalize or compensate for a last generated distortion in the at least one workpiece by generating a "counter-delay" in a renewed driving over the at least one workpiece.

In a first embodiment of the last-mentioned method with an offset, it is proposed that the offset be designed as a lateral offset in relation to the respective last weld center. However, it may additionally or alternatively be provided that the contour of the weld is formed closed, and that the offset is an offset along the contour of the

Weld is. The process according to the invention preferably takes place in a dendritic

Solidification behavior of the respective molten bath Use. The dendritic solidification behavior can be influenced or produced by a corresponding temperature gradient and the solidification rate. The invention also includes a component which is according to an inventive

Process is made. This is in particular a component made of metal, in a particularly preferred embodiment or use of a component which is at least approximately in the region of the weld

is formed rotationally symmetrical. Such a typical application example, the manufacture of housings in automotive applications, such as housings of injectors or the like, is.

Further advantages, features and details of the invention will become apparent from the following description of preferred embodiments and from the drawing. This shows in:

Fig. 1 in a simplified representation of a device for generating a

Weld seam on two workpieces to be joined together and

Fig. 2

to

Fig. 5 respectively the region of the weld in the components of FIG. 1 in a longitudinal section

The same elements or elements with the same function are provided in the figures with the same reference numerals.

In Fig. 1 is an arrangement for producing a weld 10 in

Connecting area of two, made of the same metallic material

Workpieces 1, 2 shown. The workpieces 1, 2 are shown in the

Embodiment rotationally symmetrical and have in the region of the weld 10 on the same diameter. Here, the two workpieces 1, 2 abut each other at a respective front end, forming a weld seam plane 1 1. The weld 10, the only one

Part of the depth or thickness of the workpieces 1, 2 is formed, is generated by means of a laser beam device 100, preferably one

produced alternatively, a pulsed laser beam 101, wherein the laser beam 101 in the illustrated embodiment in the region of

Weld 10 perpendicular to the surface of the workpieces 1, 2 meets.

Between the laser beam 101 and the workpieces 1, 2 takes place in the region of the weld 10, a relative movement by, for example, the two workpieces 1, 2 are rotated about their common longitudinal axis 12 in the direction of the arrow 13 by means not shown. Alternatively, it is of course also conceivable, the two workpieces 1, 2 rigid

to arrange or clamp and by a corresponding optical

Device for moving the laser beam 101 along the

Component surfaces or the weld 10 to provide. The production of the weld 10 is carried out according to the invention by forming and

Solidification of a plurality of at least substantially aligned with Welding plane 1 1 arranged one above the other welds 10a to 10d, wherein the welds are produced 10a to 10d successively in time, and wherein each time subsequent weld 10b to 10d is generated when the time previously generated weld 10a to 10c at least in

Essentially completely frozen.

In FIG. 2, it can be seen that after activation of the laser beam device 100 by means of the laser beam 101, a first molten bath 15a has been produced, which in cross-section has an approximately rounded or grounded melting base 16. At the melting base 16, a closes in the

Cross-section in approximately rectangular area 17, which on the

Meltdown 16 opposite side in a flared area 18 passes. After the first molten bath 15a has been produced, the laser beam device 100 is switched off so that the material of the molten bath 15a solidifies. The solidification of the material of the molten bath 15 a is carried out by the

(not melted) edge of the molten bath 15a in the direction of

Schmelzbadmitte out, which should be illustrated by the arrows 19. In this case, the arrows 19 are each perpendicular to the boundary or to the edge of the

Melting bath 15a aligned. In particular, it can be seen that the material of the molten bath 15a finally solidifies in a common solidification point 21 in the area of the melt base 16. In contrast, the material solidified in the regions 17, 18 forms a multiplicity of solidification points, which form in the form of a continuous solidification line 22. The solidification line 22, which is located approximately in the weld level 1 1, joins the solidification point 21 at. This solidification line 22 represents a potential starting point for hot cracks.

After the material of the molten bath 15a, which has a depth t-ι, is substantially completely solidified, the laser beam 101 is again introduced into the same region of the last or first generated molten bath 15a, as shown in FIG. It is essential that by a variation of the parameters of the laser beam device 100 generated during the second crossing of the molten bath 15a and the weld 10a

Melting bath 15b has a depth t ₂ , which is less than the melt bath depth ti. In particular, the glass bath is t ₂ slightly larger than the glass bath t-ι, reduced by the radius r. Thereby, the material of the weld 10a in Height of the solidification point 21 and the solidification line 22 completely melted. After the second molten bath 15b has been produced and the laser-jet device 100 has been switched off, solidification of the molten bath 15b to generate the weld 10b takes place once again. Here, a new form

Freezing point 21 a and a solidification line 22a.

This is followed by a crossing of the weld 10b recently generated, again the power of the laser beam device 100 is reduced and the parameters are adjusted such that the depth t ₃ of the molten now generated 15c is less than the glass bath generated last t ₂ of the molten last generated 15b. Here, the relationship holds that the melt bath depth t _{3 is} slightly larger than the melt bath depth t ₂ , reduced by the radius r. The solidification direction of the material of the molten bath 15 c is indicated by the arrows 24. It form a new solidification point 21 b and a solidification line 22b.

Finally, the production of a fourth molten bath 15d takes place by again passing over the last produced weld 10c. Again, the processes are repeated as described above, wherein it is essential that in the now subsequent solidification process of the molten bath 15d

according to the arrows 25 no crack line 22 is formed more. Thus, after solidification of the molten bath 15d, at which the weld seam 10d forms, the weld seam 10 thus formed, formed from the individual, superposed welds 10a to 10d, completely free of hot cracking prone areas or solidification lines 22, 22a, 22b ,

The method described so far for the production of a weld 10 can be modified or modified in many ways, without departing from the spirit of the invention. Thus, it can be provided in particular that when generating the respective next or subsequent weld seam 10b to 10d, the respective weld seam 10b to 10d is arranged by a lateral offset in relation to the last produced weld seam 10a to 10c. The offset takes place either by an offset perpendicular to the plane of the welding plane 1 1 instead and / or in that takes place according to the illustration of FIG. 1, an offset in the circumferential direction of the respective weld 10b to 10d. It can also be provided that only individual Weld seams 10a to 10a or portions of the individual welds 10a to 10d are free from tear lines 22, 22a, 22b. Even in such a case, the tendency to (continuous) hot cracks in the components 1, 2 is reduced. Also, the total number of weld pools 15a to 15d depends on the geometry of the workpiece 1, 2 or its thickness. The in the previously described

Embodiment formed number of four weld pools 15a to 15d is therefore only exemplary.

Claims

claims

1 . Method for producing a weld seam (10), in which a laser beam (101) produced by means of a laser beam device (101) covers the material of at least one workpiece (1, 2) on a partial region of the at least one workpiece (1, 2) within a molten bath (15 heated to a melting point (16) to a melting temperature, the molten material after the action of the laser beam (101) in a subsequent cooling phase from the edge region of the molten bath (15) to the workpiece (1, 2) in the direction of the molten bath center (20) towards solidified, characterized in that by temporally successive running over the same area of the at least one workpiece (1, 2) by the laser beam (101) each have a molten bath (15b to 15d) in the last generated, already solidified weld seam (15a to 15c ), wherein the depth (ti to t ₃ ) of the molten bath (15b to 15d) relative to the last-generated molten bath (15a to 15c) of already solidified weld (15a to 15c) is reduced, and wherein the depth (t-ι to t ₃ ) of the molten bath (15b to 15d) is selected such that the molten bath (15b to 15d) into a range below the respective Melting bath (15a to 15d) arranged, already solidified weld (10a to 10c) is sufficient, in the no

Solidification line (22, 22a 22b) is formed.

2. The method according to claim 1,

characterized,

each time a new molten bath (15b to 15d) is produced, the power of the laser beam (101) is reduced and / or a

Feed rate of the laser beam (101) is increased and / or an exposure time of the laser beam (101) is reduced. Method according to claim 1 or 2,

characterized,

that the melting base (16) of the respective molten bath (15a to 15d) has a rounding or curvature with a radius (r), and that depth (ti to t ₃ ) of a subsequently produced molten bath (15b to 15d) of depth {to t ₃ ) corresponds to the previously generated molten bath (15a to 15c), reduced by a maximum of the radius (r).

Method according to one of claims 1 to 3,

characterized,

the laser beam (101) of the laser beam device (100) is aligned with the at least one workpiece (1, 2) in such a way that at each

Moving over to produce a new molten bath (15b, 15c, 15d), an offset of the laser beam (101) to the last-generated molten bath (15a, 15b, 15c) takes place.

Method according to claim 4,

characterized,

that the offset is a lateral offset relative to the last one

Welding center (20) is formed.

Method according to one of claims 1 to 4,

characterized,

in that the weld seam (10) has a closed contour, and that the offset is an offset along the contour of the weld seam (10).

Method according to one of claims 1 to 6,

characterized,

the solidification of the respective molten bath (15a to 15d) takes place dendritically.

Component (1, 2), produced by a method according to one of claims 1 to 7. Component according to claim 8,

characterized,

that the component (1, 2) consists of metal.

Component according to claim 8 or 9,

characterized,

the component (1, 2) is designed to be at least approximately rotationally symmetrical in the region of the weld seam (10).