WO2011124627A9

WO2011124627A9 - Method for fracture splitting workpieces, workpiece and laser unit

Info

Publication number: WO2011124627A9
Application number: PCT/EP2011/055384
Authority: WO
Inventors: Siegfried Gruhler; Horst SCHÖLLHAMMER; Willi Breithaupt; Joachim Klein
Original assignee: Mauser-Werke Oberndorf Maschinenbau Gmbh
Priority date: 2010-04-06
Filing date: 2011-04-06
Publication date: 2012-03-29
Also published as: KR20130055592A; DE102010014085B4; MX2012011690A; WO2011124627A1; MX2013011618A; CN102939182B; DE102010014085A1; KR101609654B1; EP2555904A1; CN102939182A; BR112012025493A2; DE102023104504A1

Abstract

The invention relates to a method for fracture splitting workpieces (1) and to a workpiece produced in accordance with such a method. According to the invention, for example the laser type, the pulse rate, the pulse duration, the workpiece material and/or the laser power are selected such that the distance of the notch sections (6) is considerably larger than the notch distance (K) that would be computationally obtained from the feed rate (V) of the laser beam (12) and/or of the workpiece (1) and the pulse rate of the laser. The described feed modulation also enables the formation of oblique laser notches for rolling surfaces, as they occur, for example, in ball or roller guides. According to the invention, the feed rate is also modulated during laser machining depending on the workpiece geometry and/or periodically.

Description

description

Process for fracture separation of workpieces, workpiece and laser unit

The invention relates to a method for fracture separation of workpieces according to the preamble of patent claim 1, a workpiece produced by such a method and a laser unit.

EP 0 808 228 B2 of the Applicant describes a generic fracture separation method in which a notch which predetermines the fracture plane is formed in a connecting rod eye to be fractured by means of laser energy. This notch consists of a plurality of notch sections, the distance of which is essentially based on the pulse rate of the laser and the feed rate of the laser beam with respect to

Connecting rod eye yields. It has been found that the notch impact number can be increased quite considerably compared to through notches by these notch sections, so that formation of a notch with comparatively low laser power is made possible. Due to this low laser power and the associated low introduced heat energy an undesirable, profound structural change in the notch area is avoided, with only certain edge zones of the notch undergo a microstructure transformation and thus improve the fracture separation behavior.

In the applicant's DE 2005 031 335 A1, an improved method is described in which the notch is formed not straight but sinusoidal with straight end sections. It was found, surprisingly, that the fracture separation behavior can be further improved by such a notch design.

A certain disadvantage of the above-described procedure is that - as explained - the feed rate and the pulse rate must be coordinated so that form the notch behavior improving notch sections. Furthermore, it has been found that, especially in the case of the formation of sinusoidal notches or of connecting rods with a large axial length, the laser beam must be refocused, because the depth of field is not sufficient to perform the notch sections (perforation) with the required precision.

On the other hand, the object of the invention is to provide a method which enables the creation of notch sections of a fracture separation notch with little effort. The object of the invention is furthermore to provide a workpiece produced by such a method and a laser unit for carrying out the method.

This object is achieved by a method having the combination of features of claim 1, by a workpiece having the features of independent patent claim 12 and a laser unit having the features of patent claim 14.

In the method according to the invention-similar to conventional procedures-a laser notch is formed by means of laser energy, this notch having a plurality of notch sections. According to the laser type, the pulse rate, the workpiece material and the average laser power are coordinated so that the distance of the notch portions is substantially greater than the notch spacing, which results arithmetically from the feed rate, the relative movement and the pulse rate (frequency) of the laser.

The coupling of the laser beam is preferably carried out obliquely to the longitudinal axis Kerbl.

Surprisingly, it has been found that by suitable selection of the above-mentioned criteria, even with a very high pulse rate and fast feed, a notch provided with a perforation can be produced, whereby this notch spacing is then significantly greater than the notched notch spacing. This procedure has the advantage that a high-frequency laser with a very high feed rate can be used, so that the formation of the laser notch can be done much faster and with less heat input than conventional solutions.

In a particularly preferred variant of the method, the feed rate during laser processing is varied so that a notch with different lent deep notch sections is formed. In addition, the depth of a continuous region, referred to as the notch base in the following, can be varied by the variation of the feed rate Such a notch has a further improved notch effect number and thus improved fracture mechanics.

According to the invention, it is preferred if the variation of the feed rate takes place according to a periodic function, for example a sine function or depending on the component geometry.

The feed rate during laser processing can vary in the range between 100mm / min and 1500mm / min.

In the current claim 1 is claimed that the machining parameters and the laser type are chosen such that sets a greater notching than the notched notch spacing. The Applicant reserves the right to pursue an independent claim, for example in the context of a divisional application, with which, regardless of the choice of machining parameters and the laser type, the variation of the feed rate during laser processing is claimed. That is, such an independent claim would then be directed to the laser processing of a fracture separation notch with varying feed rate (features of claim 3 without recourse to claim 1).

In this case, the laser beam can be moved relative to the stationary workpiece, in kinematic reversal, however, the workpiece can be moved relative to the stationary laser, mixed forms are advantageous. The laser beam can be radial, d. h., Are coupled perpendicular to the fracture separation notch or obliquely to the fracture separation notch.

In a radial coupling the notch portions are thus perpendicular to the notch axis, while they are employed at an oblique coupling obliquely to the notch axis. The coupling is preferably carried out at an angle of <45 ° (with respect to the plane perpendicular to the longitudinal axis Kerblängsachse (in a connecting rod that is the radial plane of the Connecting rod)). In the case of a horizontal connecting rod and perpendicularly extending feed direction (notch axis), the angle would thus be, for example, 30 ° to the horizontal and 60 ° to the vertical (see FIG. 11).

In a variant of the invention, the actual kerf spacing, which is established on the basis of the choice of the parameters, is more than 1 (times the arithmetic notch spacing, which results from the pulse rate and the feed rate.

With a suitable choice, it is even possible to achieve a notch spacing that is 50 times greater.

According to the invention, it is preferred if a so-called fiber laser is used as the laser. Such fiber lasers are known from the prior art, so that detailed descriptions of the structure can be dispensed with.

In a variant of the invention, a laser with an average power of less than 50 watts and a pulse rate of substantially more than 1 KHz, preferably more than 10 kHz is used, wherein the feed may be more than 1000 mm / min. On the other hand, the pulse rate in conventional methods is about the same

Magnitude, the pulse frequency is significantly longer, for example, 50 to 140Hz.

In a preferred embodiment of the invention, the notch portions extend out of a continuous notch base.

The workpiece produced by the method may be, for example, a connecting rod or a crankcase or other workpiece in which a bearing eye or other area to be separated by a fracture separation process.

The workpiece produced by the method can have notch portions of varying depth by varying the feed rate of the laser. It is particularly preferred if these variations are repeated periodically along the notch portion. A laser unit for carrying out the method has a laser module, a laser head for focusing the laser beam emitted via the laser module onto a workpiece to be machined and an feed axis which is effective in the feed direction. This can be controlled by a control unit such that the feed is varied periodically during the laser processing.

In this case, a highly dynamic feed axis is preferred, with which the feed rate changes with an acceleration of more than 0.5 g, preferably in the range of 1 to 2g can be carried out. That is, the feed rate profiles can be sinusoidally performed with high precision, in the limit, even almost rectangular.

Preferred embodiments of the invention are explained in more detail below with reference to schematic drawings. Show it:

Figure 1 is a schematic diagram of a laser unit for producing a fracture separation notch in a large connecting rod;

FIG. 2 shows a greatly enlarged illustration of a fracture separation notch produced by the method according to the invention;

FIG. 3 a corresponding representation with modified laser power and / or pulse rate;

FIG. 4 shows fracture separation notches depending on the feed;

FIG. 5 shows fracture separation notches as a function of the mean laser power;

Figure 6 is a diagram illustrating the dependence of a notch depth of a feed of the laser beam;

FIG. 7 shows a diagram for illustrating feed rate modulation as a function of time;

FIG. 8 shows a diagram and an illustration to illustrate the resulting notch depth as a function of the average feed rate in feed rate modulation; FIG. 9 shows fracture separation notches under comparable conditions with and without feed rate modulation;

FIG. 10 shows a schematic illustration of a laser unit that can be used in a feed rate modulation laser method, and

1 1 is a schematic diagram of a laser head of the laser unit according to FIG. 10.

Figure 1 shows a sectional view of a large connecting rod 1, which is to be separated by fracture separation in a bearing shell and a connecting rod side part. The course of this fracture separation plane 2 is predetermined by two diametrical fracture separation notches 4 (only one shown in FIG. 1), which is preferably formed in the form of a perforation with a multiplicity of notch sections 6. As explained in the prior art described above, after forming the fracture separation notches 4 in Figure 1 left and right wall of the connecting rod 1 an expanding mandrel inserted into the connecting rod and then by suitable spreading of the expanding mandrel and supporting the connecting rod, the bearing shell of the rod-side part of Pleuels separated, the resulting fracture separation plane geometry due to the microstructure simplifies the precise assembly of the two parts.

For the embodiment of the fracture separation notch 4, a fiber laser according to the invention is used, whose laser head 8 is shown schematically in FIG. Such fiber lasers may in principle be diode-pumped solid-state lasers, with a core of a glass fiber forming the active medium. The radiation of the solid-state laser is introduced via a coupling into the fiber, in which then takes place the actual laser gain. The beam properties and beam quality of the laser can be adjusted via the geometry of the fiber (glass fiber), so that the laser remains largely independent of external influences and shows a very simple structure.

After emerging from said active fiber, the laser beam is introduced into a glass fiber, via which the radiation is then directed to the laser head 8 shown in FIG. 1 and directed onto the workpiece 1 to be machined via its focusing optics 10. In the illustrated embodiment, a laser beam 12 impinges in the radial direction, ie, perpendicular to the notch axis (vertical in FIG. 1). This arrangement may have the disadvantage that the focusing optics 10 are damaged by the melting material. is dirty, because due to the 90 ° coupling reflections and possibly residual melt directly go back the beam path. If coupling takes place at an angle, for example at 30 ° or 45 °, any reflections and residual melt that occur are reduced below the angle of failure (see Figure 1: 12 "") so that no contamination occurs. A laser unit with oblique coupling is described with reference to FIGS. 10 and 11.

Another disadvantage of the 90 ° coupling is that no sluggish or piercing beam guidance is possible. In an inclined position, the notch geometry can additionally be influenced by the trailing (upwards in FIG. 11) or piercing (downward in FIG. 11) beam guidance. The notch geometry can additionally be influenced by the air flow acting through the nozzle through the melt. Also on the two aforementioned aspects, a subclaim can be addressed.

These fiber lasers are characterized by very good electrical-optical efficiencies and outstanding beam quality with great depth of field in a very compact structure, so that less costly solutions can be created with a small space than with conventional lasers. Due to the high peak power and the good focusability of fiber lasers, the power density is relatively high, so that vaporized material content outweighs. However, as part of the energy is converted into heat, there is still melting and heat influence of the environment. In this case, the residual heat can accumulate, so that one obtains pronounced melting phenomena that could lead to the arithmetic notch spacing being significantly smaller than the notch spacing actually occurring and this notching distance is also comparatively stable with variation of the other parameters.

After processing the left in Figure 1 Pleuelwandung the laser head is rotated by 180 ° and edited the right Pleuelwandung. In principle, however, also crossheads can be used in which both wall sections are processed simultaneously.

In the described embodiment, the workpiece, ie, the connecting rod is firmly clamped and the laser head 8 is at a feed rate V in Axialrich- tion or axis-parallel moves, the laser power at about 50 W and the pulse frequency of the laser in the illustrated embodiment is approximately 20KHz. The spot diameter is about 30 μιτι, the feed V is about 1500mm / min. With these parameters, a notch spacing of approximately 0.00125 mm would be calculated. In fact, the notch spacing K (here at 45 ° obliquely coupled laser beam) is about 0.1 mm.

Figure 2 shows a greatly enlarged view of a concretely processed by the method according to the invention with the above parameters Pleuelauges, in this embodiment, the laser beam obliquely (45 °) is coupled. The average laser power is about 50 W and the pulse power at about 8 kW. The distance between the perforation (notch spacing) K is about 0.1 mm, resulting in a continuous notch base (G), out of which the individual, the perforation forming notch portions 6 extend out. The depth of the notch root G in the embodiment according to FIG. 2 is about 0.51 mm, while the depth P (seen in the radial direction) of the notch sections 6 is about 0.78 mm (measured from the circumferential wall 14 of the connecting-end eye 1).

Figure 3 shows a similar embodiment with reduced laser power (40 W) and steeper coupling (30 °) of the laser beam 12 - it can be seen that the notch K results in no significant change, the depth G of the notch base and the depth P of the notch sections are at the steeper coupling and reduced laser power (40 W) slightly larger. With the somewhat steeper coupling, a notch improving the fracture behavior can thus be formed with even less power than in the previously described embodiment.

FIG. 4 shows the dependence of the fracture separation notch on the set feed rate V (see FIG. 1) with which the laser beam is moved in the kerf longitudinal direction.

It can be seen clearly that at different feed rates

(500mm / min, 1000m m / m in, 1500mm / min) the notch distance remains almost unchanged. It is clear, however, that at lower feed speeds on the one hand, the depth G of the notch base is larger and also the axial length of the notch portions (PG) behaves inversely proportional to the feed, the differences between the

500mm / min and 1000mm / min are comparatively low.

FIG. 5 shows the dependence of the fracture separation notch on the laser power. In the figure above, an average laser power of 50 W was set. The fracture separation notch shown below results from an average laser power of 100 W, the other parameters being unchanged. It can be seen clearly that with reduced laser power a somewhat finer notch structure with longer notch sections is formed, the notch spacing, however, remaining approximately unchanged, as already indicated above. With the reduced laser power, as expected, a continuous notch bottom with a slightly smaller depth G is formed than at a higher laser power. With regard to fracture mechanics, the use of a laser with comparatively low laser power (50 W and less) at an average feed rate in the range between 500 and 1500 mm / min should therefore be optimal.

The beam quality can be improved by a so-called Q-switch. Such a Q-switch is an optical device which, in a pulsed laser, delays the pulse, reduces the pulse duration, and increases the pulse height (peak power) to give a very sharp laser pulse which increases rapidly and after reaching a sharp maximum quickly drops again. Without such a Q-switch, the pulse is significantly wider and flatter.

FIG. 6 shows the dependence of the occurring notch depth on the feed, which is varied between 100 and 3000 mm / min. The dimension S2 corresponds to the above-described dimension G (depth of the notch base) and the dimension S1 of the total depth P (see FIGS. 2 and 3) of the notch, so that the length of the notch portions corresponds to the difference (GP). The upper curve shows the course of the total depth S1 of the notch, while the lower curve shows the course of the depth of the notch base S2. It can be clearly seen that at comparatively low feed rates in the range of up to about 800 mm / min, there is a comparatively strong dependence of the notch depth (S1, S2) on the feed rate. At higher feed rates (about 800 - 3000mm / nnin), the dependence is much less pronounced. These experiments were carried out at a pulse frequency of 50kHz and a mean pulse power of 50W. The dependence of the notch geometry on the feed rate explained with reference to the above-described figures was thus confirmed by the experiments shown in FIG.

As will be explained in more detail below, it was found at very low feed speeds (less than 200 mm / min) that the notch quality due to thermal overheating in the region of the notch base was insufficient. It created charred areas that made the laser machined workpiece practically useless. These charred areas are shown for example in FIG. 9 above, which will be discussed in more detail later.

Care should therefore be taken in laser processing to control the feed rate so as to avoid such quality losses in the formation of the fracture separation notch.

It has been found that such phenomena can be avoided by varying the feed rate during laser processing, in which case a fracture separation notch is produced which on the one hand has a sufficient notch depth and on the other hand can be formed at high feed rates and thus in a short time no loss of quality is to be expected, resulting in a deterioration of the fracture mechanics.

FIG. 7 shows examples of a feed rate modulation, which takes place according to a sine function. Of course, the speed modulation can also be carried out according to other, preferably periodic functions. Shown is the course of the feed rates within a certain feed range, which does not correspond to the entire length of the traction fracture notch to be formed as a function of time. Specifically shown here is the feed range between 67.5 and 69.5mm, that is, there are only 2mm of the entire fracture separation notch shown, the velocity modulation in the non-illustrated areas of the fracture separation notch, however, takes place accordingly. The slightly wavy from top left to bottom right shown Curves (top dashed curve / bottom continuous curve) show the actual feed toward the fracture separation notch as a function of time t. During this slightly wavy feed, the feed rate is varied according to the sine functions drawn, the sine function being associated with a larger amplitude of the dashed laser path, while the sine function having a smaller amplitude is assigned to the solid laser motion path. It can be seen that the feed rate is changed relatively high frequency, so that the laser head 8 has to be greatly accelerated and decelerated within a short time in order to adjust the motion profile along the traction fracture notch to be formed.

In the graph according to FIG. 7, the respective set feedrate actual values are shown on the right. Accordingly, the velocity was varied in the range between 117 and 1157 mm / min in the case of the above-defined blur modulation. In the formation of the fracture separation notch with such a velocity modulation results in a fracture separation notch geometry, as shown by way of example in Figures 8 and 9. Figure 8 shows a diagram in which the self-adjusting notch depth depending on the average feed V _m , that is, the average value of the above-described speed modulation adjusts. In FIG. 8 it can be seen that, for example, at a mean feed rate of 800 mm / min (in fact, the feed rate varies according to the sine function according to FIG. 7), a fracture separation notch adjusts with the progression shown in FIG. It can be seen clearly that different notch sections are formed from a notch base with the dimension S2 (G) corresponding to the sine period. The portions indicated by S3 are formed in the regions in which the feed rate is comparatively low. The notch portions marked S1 are formed in the regions in which the laser speed moves at a comparatively high speed.

The course of the characteristic quantities S1 (P), S2 (G), S3 (P) as a function of the average feed is shown in the diagram according to FIG. The curve above shows the course of the total notch depth (S3) at low feed rate, the curve S1 the course of the notch depth at a comparatively high feed rate (always during the speed modulation) and the curve S2 the course of the depth of the notch base again. It can be seen that the notch depth increases with

ADJUSTED SHEET (RULE 91)

ISA / EP reduced the average feed rate. It is clearly visible, however, that notch sections with varying notch depths can be formed with appropriate speed modulation. It was found that such a notch has a significantly improved fracture mechanics compared to the aforementioned notches. In other words, the feed rate modulation makes it possible to form comparatively deep, and sharp starting notches which significantly improve the initiation fracture toughness and the arrest fracture toughness against continuous perforation score scores without the feed rate modulation.

It is thus possible to crack even complex components, wherein the modulation of the feed rate can also be done in dependence on the component geometry. That is, for very complex components, such as breakthroughs in the fracture separation notch, the feed rate can be adapted to the geometry of the component, so that in unproblematic areas with a comparatively high feed rate or amplitude of the feed rate modulation is driven, while in more critical areas, the speed modulation accordingly is withdrawn, so that sets a lower average feed rate or a constant feed rate.

The advantage of the described feed rate modulation is illustrated with reference to FIG. This shows above a fracture separation notch, as they would be at a comparatively low constant feed rate of 200mm / min. It can be clearly seen the comparatively large notch depth and the burns / charring, which can occur due to the high heat input at low feed rate. Such a fracture separation notch is virtually unusable.

On the other hand, in the figure below, a notch made according to the feed rate modulation method according to the invention is shown, wherein the feed rate modulation is in the range of 1 17 to 17

1 157mm / min. It can be clearly seen that burns in the region of the notch base can be reliably avoided by this modulation. Furthermore, one recognizes the trained by appropriate speed modulation notch sections greater or lesser depth, the depth also depending on the angle of attack of the laser. In the illustrated exemplary embodiments, the angle of attack, that is to say the coupling-in angle, was approximately 30 ° with respect to the horizontal in FIG. 9.

A laser unit is described with reference to FIGS. 10 and 11, which is particularly well suited for carrying out the method with feed rate modulation described above. According to FIG. 10, the laser unit has a laser module 16 which contains, for example, a fiber laser and the control of this fiber laser. The control of the laser unit 16 is designed so that the feed rate of the laser beam can be modulated in the manner described above.

The laser beam 12 generated by the laser module 16 is guided via optical fibers 18 to a recollimator 20, which is merely indicated in FIG. In this, the laser beam is converted into a parallel beam, with the beam diameter in the range of about 6mm. This parallel beam is then guided via the light guide 18 to the laser head 8, via which a laser beam is then directed onto the workpiece to be machined, in the present case a connecting rod eye 1 of a connecting rod. The focused laser beam is coupled at an angle of 30 ° to the horizontal in FIG. The laser head 8 is designed with a Z-feed axis 22, via which the feed takes place in the longitudinal groove axis. This feed axis is designed as a highly dynamic axis, with the extremely high accelerations at a high loop gain and a large jerk are feasible, so that an extremely precise control of the modulation is required. The accelerations may be, for example, in the range between 1 to 2 g, the loop gain in the range of 10 n / min / mm (166.71 / s) and the jerk greater than 400 m / s ³ . For two-sided processing of the connecting rod 1 of the laser head 8 is still with a

Swivel axis 24 executed, via which the laser head 8 about the Z-feed axis 22 is pivotable. The laser unit further has an X-adjusting axis 26, via which the entire laser head 8 can be moved in the X-direction (radially to the connecting-rod eye 1). With such a device can also form sinusoidal fracture separation notches.

FIG. 11 shows the basic structure of the beam guidance in the laser head 8. The optical fiber 18 coupled to the fiber laser (laser module 16) is shown. The laser beam is converted in the recollimator 20 into a parallel beam with a diameter of approximately 6 mm. converted and then deflected by a deflecting mirror 28 by 90 ° in the direction of the Pleuelaugenachse. The deflected laser beam 12 is then focused on the Pleuelaugenwandung via an optical system with a focal length of, for example, 100mm, wherein an alignment to Pleuelumfangswandung via a further deflection mirror 32, which is employed in the illustrated embodiment at an angle of 60 ° to the horizontal, so that the Laser beam resulting in a coupling angle of 30 ° to the horizontal or in an angle of attack of 60 ° to the incident on the deflection mirror 32 vertical part of the laser beam 12 (deflection 60 °) impinges on the Pleuelumfangswandung. The laser beam exits via a nozzle 34 and is focused so that the laser spot is located approximately 3 mm in front of the exit plane of the nozzle 34. To avoid contamination of the optics 30 and the mirrors 28, 32, a protective glass 34 is provided in the beam path between the nozzle 34 and deflecting mirror 32. In the illustration according to FIG. 11, the pivot axis 24 can also be seen; in this case, the laser head 8 is rotatably mounted via a rotary bearing 38 and can be pivoted about the Z-feed axis 22 via a motor, not shown, so that practically every peripheral wall area of the connecting rod is pivoted is reachable.

When using a fiber laser and by a suitable choice of a feed rate modulation and a comparatively (compared to conventional solutions) high pulse rate can thus be formed a perforation, which has an optimal notch efficiency, but can be formed with much lower energy input and at significantly faster feed rates, than at conventional systems is the case.

The tests carried out show that, for example, in the case of a fiber laser with a power of 50 watts at a pulse frequency of 20 kHz, a fracture separation notch 4 can be formed, in which the notch sections 6 are spaced in 1/1 Omm range, preferably in the range of 0.1 to Have 0.3mm. It was found that even when using a laser with a power of only 30 watts, a highly effective perforated fracture separation notch 4 can be formed.

Disclosed are a method for fracture separation of workpieces and a workpiece produced by such a method. According to the invention, for example example, the laser type, the pulse rate, the pulse duration, the workpiece material and / or the laser power selected so that the distance between the notched portions is substantially greater than the notch spacing, which is calculated from the feed rate of the laser beam and / or the workpiece and the pulse rate of the laser would result. The feed modulation described also allows the formation of oblique laser notches for runways, as they occur for example in ball or roller guides.

According to the invention further discloses that the feed rate during laser processing in response to the workpiece geometry and / or periodically modulated.

connecting rod

fracture plane

Fracture splitting notch

notch portions

laser head

focusing optics

laser beam

peripheral

laser module

optical fiber

Rekollimator

feed axis

swivel axis

adjusting axis

deflecting

optics

Deflection mirror nozzle

Protective glass pivot bearing

Claims

claims

1 . Method for fracture separation of workpieces (1) by means of laser energy, wherein by relative displacement between a laser beam (12) and the workpiece (1) a fracture separation plane predetermining fracture separation notch (4) is formed, which is in the form of a perforation with notch portions (6) , characterized in that the processing parameters, such as the laser type, the pulse rate, the pulse duration, the workpiece material and the laser power are chosen so that the distance of the notch portions (6) is substantially greater than the notch spacing (K), which is calculated from the Feed rate (V) of the laser beam (12) and / or the workpiece (1) and the pulse rate of the laser results.

2. The method according to claim 1, wherein the laser beam (12) is coupled obliquely to the longitudinal axis Kerbl.

3. The method according to claim 1 or 2, wherein the feed rate (V) is varied during processing.

4. The method according to claim 3, wherein the feed rate (V) is varied according to a periodic function, such as a sine function.

5. The method according to claims 3 or 4, wherein the feed rate between 100mm / min and 1500mm / min is varied.

6. The method according to any one of the preceding claims, wherein the actual notch spacing (K) by 1 (Mache is greater than the notched notch gap.

7. The method according to claim 6, wherein the notch spacing (K) by more than 50 times greater than the notched notch spacing.

8. The method according to any one of the preceding claims, wherein a fiber laser is used as a laser.

A method according to any one of the preceding claims, wherein the average power of the laser is 50 watts and less at a pulse rate of more than 1 KHz, preferably more than 10KHz.

10. The method according to any one of the preceding claims, wherein the Einkoppelwinkel is about 30 °.

1 1. Method according to one of the preceding claims, wherein the fracture separation notch (4) has a continuous notch base from which the notch portions (6) extend.

12. workpiece, in particular a connecting rod or a crankcase, produced by a method according to claims 1 to 1 1st

13. A workpiece according to claim 12, wherein this has approximately periodically repeating sequences of one or more notch portions (6) with shallow depth and one or more notch portions (6) with greater depth or depending on the workpiece geometry different notch depths (P).

14. Laser unit for carrying out the method according to one of claims 1 to 1 1, comprising a laser, a laser head (8) for focusing a laser beam (12) on a workpiece to be machined, with at least one feed axis acting in the feed direction (22) and a control unit (16) for varying the feed rate during the laser processing.

15. The laser unit according to claim 14, wherein the feed axis (22) is designed such that feed rate changes with an acceleration of> 0.5g, preferably up to 2g are possible.