Method for producing a friction brake body

Abstract

A method is disclosed for producing a friction brake body, in particular a brake disc, which has a main part with a frictional contact region. A wear protection layer is produced on the frictional contact region by way of laser cladding using a laser beam oriented towards the frictional contact region. The wear protection layer is produced by at least one pulverulent additive during the laser cladding. At least two pulverulent additives are added simultaneously such that the dwell time thereof in the laser beam differs.

Claims

1. A method for producing a friction brake body which has a base body with a frictional contact region, comprising: producing a wear protection layer on the frictional contact region by way of laser cladding using a laser beam directed onto the frictional contact region, wherein the wear protection layer is produced with at least two powdered additives during the laser cladding, wherein the at least two powdered additives enter the laser beam simultaneously, wherein a dwell time in the laser beam of each additive of the at least two additives is of different lengths, wherein each additive of the at least two additives is blown separately into the laser beam by at least one corresponding nozzle as a corresponding material jet, such that each of the additives enters the laser beam before reaching the base body, wherein all material jets of the at least two additives (i) meet at one meeting point in the laser beam, (ii) are mixed with one another at the one meeting point in the laser beam, and wherein the one meeting point is spaced apart from the base body, and wherein the at least two additives are blown into the laser beam at different angles relative to a longitudinal axis of the laser beam.

2. The method according to claim 1, wherein the at least two additives are blown into the laser beam (i) at equal or different radial distances from a longitudinal axis of the laser beam, and (ii) at equal or different axial heights relative to the base body.

3. The method according to claim 1, wherein the angles are selected such that each additive of the at least two additives is melted by the laser beam at the one meeting point.

4. The method according to claim 1, wherein each additive of the at least two additives is blown in from the at least one corresponding nozzle in a manner diametrically opposite relative to the laser beam.

5. The method according to claim 1, wherein: two groups are used as the at least two additives, and the two groups are alloys.

6. The method according to claim 1, wherein the friction brake body is a brake disc.

7. The method according to claim 1, wherein the angles are selected such that each additive of the at least two additives is melted by the laser as completely as possible.

8. The method according to claim 1, wherein the angles are selected such that each additive of the at least two additives is melted by the laser beam as incompletely as possible.

9. The method according to claim 1, wherein: two groups are used as the at least two additives, the two groups are iron-based alloys and hard materials, and the hard materials are compounds of one type including carbides, nitrides, or borides.

10. The method according to claim 1, wherein the one meeting point is a point located on a central longitudinal axis of the laser beam.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The disclosure is explained in more detail below with reference to the drawings.

(2) FIG. 1 shows an advantageous friction brake body in a simplified perspective illustration, and

(3) FIGS. 2 and 3 show advantageous exemplary embodiments of a device and of a method for producing the friction brake body.

DETAILED DESCRIPTION

(4) FIG. 1 shows a simplified perspective illustration of a friction brake body, designed as a brake disk 1, of a friction brake 2 (not shown in greater detail here) of a motor vehicle. The brake disk 1 is designed in the shape of a circular ring and serves to work together with a movable brake pad of the friction brake 2, which brake pad can be pressed against at least one of the end faces of the brake disk 1. An optionally present brake disk pot is not shown in FIG. 1.

(5) The brake disk 1 has a base body 3 which is designed in the shape of a circular ring and, on both of its faces, has a frictional contact surface 4 in each case which serves to work together with the brake pad of the friction brake 2. The base body 3 is preferably made of gray cast iron. The friction contact surfaces 4 are preferably formed by a wear protection layer 5 formed on the base body 3.

(6) According to the present exemplary embodiment, the wear protection layer 5 is produced by laser cladding. FIG. 2 shows, in a simplified illustration, an advantageous device 6 for carrying out the laser cladding method. The device 6 has a working head 7 which bears a laser beam source 8 for generating a laser beam 9, and a unit 10 for blowing out different powdered additives.

(7) The unit 10 has, by way of example, a plurality of nozzles 11, 12, 13 and 14 which are held on the working head 7. In this case, the nozzle pairs 13 and 14 or 11 and 12 are arranged rotationally symmetrically around the laser beam and are only shown as a pair for illustrative reasons. In particular, at least three nozzles are advantageous for each rotational symmetry. When three nozzles are used, they are arranged offset at an angle of 120; when four nozzles are used, an angular offset of 90 is preferred.

(8) When distributing the nozzles 11 to 14, the rotational symmetry along the laser beam 9 is to be maximized. When 23 nozzles are used, the nozzles are alternately offset by 60.

(9) As an alternative to discrete nozzles (injectors), annular gap nozzles may be used which enable continuous conveying (analogous to the lateral surface of a pyramid that has a round base area and stands on the tip). The nozzles 11 to 14 are oriented at a particular angle to the laser beam 9 so that a material jet S11 to S14 leaving the respective nozzle 11 to 14 is oriented at a predetermined angle 11, 12, or 13 and 14, to the laser beam 9 or its central longitudinal axis 9.

(10) The nozzles 11, 12 serve to blow out a first additive. The nozzles 13 and 14 serve to blow out a second additive. As shown in FIG. 2, the additives are blown into the laser beam 9 at the predetermined angles 11 to 14. The blow-in angles of the nozzles 11 and 12 correspond to one another and differ from the blow-in angles 13 and 14 of the nozzles 13 and 14, which are likewise equal (11=1213=14). The nozzles 11 and 12 are arranged on different sides or diametrically opposite one another on the working head 7, as are the nozzles 13 and 14 with respect to one another. As a result, the material jets S11, S12, S13, S14 of the nozzles 11, 12, 13, 14 meet in the laser beam 9 at a meeting point TP1. The nozzles 11, 12 are arranged at a further radial distance from the laser beam or the laser beam source 8 on the working head 7 than are the nozzles 13, 14. Due to the different blow-in angles 11, 12 on the one hand and 13, 14 on the other hand, it is ensured that the material jets S11 to S14 nevertheless meet at the meeting point TP1 within the laser beam 9 at an axial distance from the base body 3.

(11) Due to the advantageous arrangement and orientation of the nozzles 11 to 14, it is achieved that the two additives dwell in the laser beam 9 for different lengths of time. Due to the smaller angle 13, 14 and due to the lateral distance from the laser beam source 8, it is achieved that the second additive blown out by the nozzles 13, 14 dwells longer in the laser beam 9 than does the first additive blown out by the nozzles 11, 12. The meeting point TP1 is selected such that the material jets S11 to S14 meet on the base body 3 within the laser beam 9 so that the additives are melted, and an advantageous substance-to-substance bond of the blown in additives to the melted region of the base body 3 is ensured. As a first additive in the present case, an additive is thus used which requires a shorter dwell time in the laser beam in order to be melted in comparison to the second additive. Conversely, the principle can also be used if, for example, an additive is not to melt. When processing an iron-based alloy with chromium carbide, for example, the iron-based alloy is to melt completely, while it is advantageous for chromium carbide if the degree of melting is as low as possible. In this case, chromium carbide is preferably blown in such that the interaction time (dwell time) with the laser beam 9 is as short as possible.

(12) In the event that particularly high thermophysical differences of the additives exist, a separate meeting point is respectively set for the two additives by means of the blow-in angle and the blow-in position of the nozzles 11 to 14. In this respect, FIG. 3 shows a further exemplary embodiment in a simplified illustration, wherein identical elements are provided with identical reference signs, and reference is made in this respect to the above description. Below, basically only the differences will be discussed.

(13) As in the preceding exemplary embodiment, the material jets S13 and S14 meet in the aforementioned meeting point TP1 at a distance from the base body 3. In contrast, the material jets S11 and S12 meet at a second meeting point TP2 which is located at an axial distance, or a distance in the beam direction of the laser beam 9, from the meeting point TP1. In the present case, the meeting point TP2 is located in the beam direction of the laser beam 9 but within the base body 3. For this purpose, the blow-in angles 11 and 12 are selected to be smaller than in the preceding exemplary embodiment. This allows the second additive to have a significantly longer dwell time in the laser beam 9 than the first additive which is blown out by the nozzles 11 and 12.

(14) According to a further exemplary embodiment, the wear protection layer has niobium carbide (NbC) and stainless steel (e.g., a Cr or CrNi steel). Due to the higher thermal stability of NbC compared to stainless steel, a longer interaction time with the laser is to be sought for NbC. By adapting the dwell time of niobium carbide and stainless steel above the base body 3 in the laser beam 9, effective melting of the two additives up to complete melting is ensured. The molten portion of the niobium carbide is finely distributed as NbC in the stainless steel matrix during solidification, and thus causes a homogeneous hardness distribution within the coating. In addition, the melting of the surface of the remaining portion of the carbides enables a substance-to-substance bond between matrix and hard materials, whereby the hard materials or carbides can be prevented from detaching during thermomechanical stress on the friction brake body. Thus, according to the present exemplary embodiment, it is provided that niobium carbide is used as the second additive and is subjected to a longer dwell time in the laser beam 9 until complete melting.

(15) According to a further exemplary embodiment, the wear protection layer is formed from silicon carbide and stainless steel. Due to the high thermal conductivity of the silicon carbide, advantageous heat conduction from the wear protection layer into the base body is ensured, whereby the thermal strength of the friction brake body is increased. By adapting the meeting point TP2 for the silicon carbide used as the first additive according to FIG. 3, the thermal energy fed into the silicon carbide during laser cladding is reduced, whereby dissociation of SiC is reduced, and formation of undesired FeSi compounds in the wear protection layer 5 is largely prevented so that, in particular, embrittlement of the wear protection layer 5 is prevented.