WO1991018705A1

WO1991018705A1 - Process for treating the surfaces of workpieces with laser radiation

Info

Publication number: WO1991018705A1
Application number: PCT/DE1991/000489
Authority: WO
Inventors: Axel Zwick; Kurt Wissenbach; Andres Gasser
Original assignee: Fraunhofer-Gesellschaft zur Förderung der angewandten Forschung e.V.
Priority date: 1990-06-08
Filing date: 1991-06-07
Publication date: 1991-12-12
Also published as: DE4042349A1

Abstract

Described is a process for treating the surfaces of workpieces (12) by using laser radiation (10) to heat edge zones, in particular for treating shafts for motor vehicles. The process calls for a laser beam to strike the surface (13) of the workpiece at an angle of incidence which is other than zero, producing an oval light spot (14), the beam being moved at right angles to it. In order to be able to work at high speed and produce products of high quality, linearly polarized laser radiation (10) is used and, to optimize the transfer of energy into the workpiece (12), the angle of incidence (α2) in at least one sector (15) of the light spot (14) differs from the angle of incidence (α3) in the other sectors (e.g. 16) of the light spot (14).

Description

Fraunhofer Society for the Promotion of Applied Research e .V. , Leonrodstr. 54, 8000 Munich 19

Process for surface treatment of workpieces with laser radiation

TECHNICAL FIELD The invention relates to a method for the surface treatment of cams for shafts of motor vehicles, in which a laser beam with an angle of incidence deviating from zero hits the workpiece surface with an elongated beam spot and is moved relative to it transversely. Surface treatment means, for example, tempering, hardening or remelting. The shafts of motor vehicles mentioned are, for example, camshafts or crankshafts whose cams or. Bearing seats are treated.

State of the art

The industrial use of high-power lasers, such as, for example, carbon dioxide lasers, for surface finishing of workpieces often fails because the absorption of the laser radiation is not sufficiently great. In order to increase the energy coupling, it is generally known to use laser radiation that is linearly polarized in parallel and to apply this with an angle of incidence of close to 90 ° to the surface of the surface to be processed

SPARE BLADE Of the workpiece. As a result, there is increased energy absorption or coupling. As a result, increased process speeds are possible, which results in an improvement in the economy of the treatment process. However, it has been shown that the processing quality leaves something to be desired, for example melting on the edges of treated workpiece surfaces is to be observed, or the heating is insufficient in the areas lying transversely to the relative movement direction of the laser beam into the deep. Presentation of the invention

The invention is therefore based on the object of improving a process with the features mentioned at the outset, which is generally known as a process for surface treatment with laser radiation, in such a way that a high process speed is linked to an improvement in the processing quality.

This object is achieved in that linearly polarized laser radiation is used and its angle of incidence is adjusted to adapt the energy coupling into the cams in at least a partial area of the beam spot, deviating from the angle of incidence of the remaining areas of the beam spot.

The adaptation of the absorption to the geometry of the cam to be machined is of crucial importance for the optimization of the process speed in connection with an increase in the machining quality. This adaptation is achieved by influencing the laser beam depending on the workpiece shape present. At least a portion of a beam spot of the laser radiation is selected in which the angle of incidence of the laser radiation is set differently from the angles of incidence of the remaining areas of the beam spot. As a result, the absorption of the energy differs in the areas of the beam spot mentioned. By choosing the angle of incidence according to the known dependence between absorption and this angle of incidence for linearly parallel polarized laser radiation, the workpiece can be heated in such a way that Different heat quantities are supplied to workpiece areas. For example, edge melting on a cam can be avoided by

E _RS ATZBLATT sufficient less energy is supplied without the heat supply having to be removed from areas away from the edge. There is an improvement in quality at high process speed.

Various process steps are possible for setting the angle of incidence of the laser radiation. A ^"we¬ sentliche possibility is | it if the shape of the beam spot is tuned surface to be machined to the geometry _ The influence on the shape of the beam spot makes it on different horizontal levels located Oberflächenab¬ sections of the workpiece to irradiate this results.. In the case of curved workpiece surfaces, it is possible to allow different angles of incidence to take effect. It goes without saying that the shape of the beam spot must be individually matched to the surface of the workpiece. A one-off adjustment is sufficient if the surface to be machined is always If this is not the case, the shape of the beam spot has to be continuously changed, for example, depending on the changes in the relative position of the workpiece.

A moon crescent-shaped beam spot is advantageously used parallel to the cylinder axis in the case of a workpiece with a cylindrically curved surface. Workpieces with a cylindrically curved surface have a jacket region with a constant curvature, so that a moon-crescent-shaped beam spot, which is used parallel to the cylinder axis, covers surface areas at its ends which have a different height level with respect to the beam direction than the central areas of this beam spot . As a result, the laser radiation strikes the surface to be processed at the ends at a different angle, so that the energy absorption is correspondingly different than in the mitrel regions of the beam spot.

The method can be carried out in such a way that, in the case of a workpiece width approximately corresponding to the length of the beam spot, a beam spot with a bend is used which extends transversely to the beam direction in the direction of surface portions of the workpiece which are located deeper when the cylinder is cylindrical Workpiece surface is convex, otherwise

REPLACEMENT LEAF returns. In this method, the angle of incidence of the radiation at the ends of the beam spot is smaller than in the remaining areas of this beam spot in between. As a result, the energy coupling at the ends of the beam spot is reduced. This method is particularly suitable for workpieces with a width that essentially corresponds to the beam spot length. Depending on the treatment method, melting, deformation or melting can be avoided.

The method can also be carried out in such a way that, in the case of a workpiece width which substantially exceeds the length of the beam spot, a beam spot with a bend is used which extends transversely to the beam direction in the direction of surface portions of the workpiece which are higher in the beam when the cylindrical workpiece surface is convexly curved , otherwise vice versa. The angles of incidence of the laser radiation at the ends of the beam spot are larger than the angles of incidence in the remaining central regions, so that at the. Ends of the beam spot is absorbed to an increased extent. The method is suitable for producing a machining track over its entire width with the same machining geometry and the same quality. As a result, there is no need for overlapping of machining tracks, for example, if larger workpiece surfaces have to be treated.

In order that the method can be used flexibly, that is to say for workpieces of different dimensions, a beam spot with an adjustable length and / or with an adjustable width is used. The method according to the invention is flexible insofar as it does not necessarily require the shaping of the beam spot. Rather, conventional beam spots can be used which have the areas of different angles of incidence of the laser radiation. The generation of the laser radiation must be produced with transverse to the laser beam correspondingly shaped optics then most to the desired angle of incidence to ensu ^¬.

Brief description of the drawings

The invention is explained with reference to the drawing. It shows:

REPLACEMENT LEAF 1 to 3 different workpiece geometries with cylindrical, curved surfaces which are treated with curved beam spots, 7, 8 are schematic representations of a device for generating crescent-shaped curved beam geometries, and FIG. 9 shows the dependence of the absorption of the energy of laser radiation on the angle of incidence α. Best way to carry out the invention

The workpiece 12 shown in FIG. 1 is a circular cylinder with projections 20 shown in section. As a result, edges 21 are present, on which heat would build up if the workpiece were simultaneously irradiated with laser radiation over its entire width B, whereby it is assumed that the beam spot is arranged elongated and parallel to the cylinder axis 17 and has an intensity distribution that is uniform over its length. Since the entire workpiece surface 13 is to be heated with laser radiation, it is necessary to rotate it relative to the laser radiation 10, in which case the desired heating of all peripheral layers 11 takes place. -

The beam spot 14 shown schematically in FIG. 1 is approximately as long as the workpiece 12 is wide. The beam spot 14 can look approximately as shown in FIG. 4, from which it can be seen that the beam spot is approximately crescent-shaped, its width b being considerably smaller than its length 1.

From Fig.l it can further be deduced that the laser radiation 10, due to the curved shape of the beam spot 14, strikes a partial area 15 of the beam spot 14 which is located transversely to the beam direction 18 than the central area 16. That is ~ to be traced back to the illustrated bend of the beam spot 14 parallel to the cylinder axis 17 transverse to the beam direction 18. In this higher-lying partial area 15, the angle of incidence 0: _{2 of} the laser radiation 10 is smaller than in the area

SPARE BLADE 16. As a result, there is less absorption in sub-area 15, as can be derived from FIG. 9. The absorption in the range of angles of incidence of size 0 ₃ is twice as large as at angles of incidence 0 ₃ when laser radiation that is linearly polarized in parallel is used. Linearly polarized laser radiation is understood in the usual way to mean laser radiation which vibrates only in the plane of incidence, that is to say in the plane defined by the incident beam 10 and the reflected beam 10 '.

With respect to FIG. 1, there is a considerably lower heating of the partial areas 15 and thus a reduction in the risk of unwanted melting, deforming or melting of these partial areas 15 or the edge 21.

In FIG. 2, the workpiece 12 is also formed with a cylindrically curved surface 13, but in the region of the radiation from the beam spot 14, however, it is not curved convexly, but concavely curved. As a result, for the laser radiation 10 incident in the direction 18 there are greater angles of incidence 0 ₂ in the edge regions 15 than the angles of incidence 0 _{3 of} the central regions 16, since the workpiece surface 13 here is already flatter than in the areas as a result of the concave curvature ¬ range 15. In the latter, there is an increased absorption. This is undesirable if it is assumed that the edge areas of the workpiece 12 anyway heat accumulate laterally, that is to say transversely to the relative movement direction 22 between the laser radiation 10 and the workpiece 12, due to the lateral limitation. To avoid this, the bend shown in FIG. 2 would have to be arranged exactly opposite, that is to say as in FIG. 3.

3 shows the arrangement of a crescent-shaped beam spot 14 on a cylindrical workpiece 12 with a convex curvature in the event that the extension given in the direction of the cylinder axis 17 is substantially greater than the length of the beam spot 14. In this case there is a heat outflow in the direction of the cylinder axis 17, so that increased absorption is desired in the partial areas 15 of the beam spot 14 in order to heat the edge layers 11 of the workpiece 12 uniformly deep over its entire width. The bend of the beam spot 14 thus extends transversely to the beam direction 18

E _RS ATZBLATT in the direction of higher-lying surface sections 19 ′, in order to bring about the larger angles of incidence c_2 in the edge regions than in region 16.

5, 6 show curvature-free, flat surfaces 13. The workpiece 12 in FIG. 5 is approximately as long as the beam spot (not shown), so that when the laser radiation 10 and workpiece 12 move relative to one another in the direction 22, they move transversely thereto a heat build-up results. As a result, the procedure is such that a comparatively large angle of incidence 03 is selected in the areas 16 located in the center of the workpiece 12, whereas the angle of incidence 02 of the areas 15 located on the edge is smaller. Accordingly, the energy coupling in the areas 15 is lower. Conversely, the inclination of the laser radiation 10 is in the central region 16 of the workpiece 12 of FIG. 6, which is laterally unlimited with respect to the length of the beam spot, not shown. The angle of incidence 0: 3 is thus smaller than the angle of incidence <2 on the edge, which leads to a uniformly deep heating of the workpiece 12 over the entire length of the beam spot.

The shape of the beam spot of the laser radiation 10 is of comparatively little importance for the workpieces 12 in FIGS. 5, 6. A crescent-shaped beam spot formation is indicated by the arrangement of the arrows symbolizing the laser radiation 10. However, the same treatment effect can be obtained when a linear beam spot formation is used, only the angle of incidence of the laser radiation 10 0. ₃ provided in the regions 16 as shown respectively in relation to the angles of incidence are 02.

7, 8 show the spatial arrangement of an optic with which sickle-shaped beam spots can be generated. The optics 23 consists of a plane mirror 24 arranged in a housing 28, which deflects the laser radiation 10 in the direction of a line focusing mirror 25 by 90 °. An elliptical mirror 26 is arranged at an adjustable distance L from this line focusing mirror 25, which deflects the radiation 10 by 90 ° and points it at the workpiece 12 to be irradiated, which is in a distance A. The shape of the beam spot corresponds to Fig. 4.

REPLACEMENT LEAF With the aid of the above-described methods, processing can be carried out at high process speeds with optimum processing quality. Possible processing methods are: tempering, transformation hardening, remelting, alloying, dispersing or coating of outer layers or. Edge layers of the cam. Incorrect machining can be avoided, such as edge rounding due to melting or. Evaporation of material or uneven machining geometries. The workpieces that come into question are primarily those that are not arched in at least one direction, that is to say workpieces with flat surfaces and workpieces with cylindrical curved surfaces. In these, for example, with beam spots in the width of, for example. 30 to 40mm are machined.

Commercial recycling

The process for the surface treatment of workpieces by means of laser radiation is used to achieve a high process speed with simultaneous improvement in the processing quality.

REPLACEMENT LEAF

Claims

Expectations :

1. A method for the surface treatment of cams for shafts of motor vehicles with laser radiation by heating peripheral layers, in which a laser beam with an incidence angle deviating from zero strikes the workpiece surface with an elongated beam spot and is moved transversely thereto, characterized in that linearly polarized laser radiation ( 10) and their angle of incidence (c_2) for adapting the energy coupling into the cams in at least one partial area (15) of the beam spot (14) deviating from the angles of incidence (C-.3) of the remaining areas (for example 16) of the Beam spot (14) is set.

2. The method according to claim 1, characterized in that the shape of the beam spot (14) is matched to the geometry of the surface to be machined (13).

3. The method according to claim 1 or 2, characterized gekennzeich¬ net that a moon crescent-shaped beam spot (14) is used parallel to the cylinder axis (17) in a workpiece (12) with a cylindrical vaulted surface (13).

- Method according to claim 3, characterized in that in the case of a workpiece width (B) approximately corresponding to the length (1) of the beam spot (14), a beam spot (14) with a bend is used which extends transversely to the beam direction (18) in the direction Surface sections (19) of the workpiece (12) which are located deeper in the beam, if the cylindrical workpiece surface (13) is convex, otherwise vice versa.

REPLACEMENT LEAF A method according to claim 3, characterized in that in the case of a workpiece width (B) substantially exceeding the length (1) of the beam spot (14), a beam spot (14) with a bend is used which is transverse to the beam direction (18) in Extends in the direction of surface sections (19 ') of the workpiece (12) which are located at a higher beam if the cylindrical workpiece surface (13) is convexly curved, otherwise vice versa.

Method according to one of Claims 1 to 5, characterized in that a beam spot (14) with an adjustable length (1) and / or with an adjustable width (b) is used.

REPLACEMENT LEAF