Method for cutting a bandage comprising a carbon fiber reinforced plastic

Abstract

The invention relates to a method (1000) for cutting a bandage (16) comprising a carbon fiber reinforced plastic, wherein the bandage is a bandage (16) for a rotor of an electric motor. It is provided that the bandage (16) is cut by laser cutting using a laser cutting device (10) in several passes, with the temperature of the bandage (16) being measured after each pass. The invention further relates to a laser cutting device (10). It enables the bandage (16) to be cut in a material-friendly manner.

Description

[0001] The present invention relates to a method for cutting a bandage comprising a carbon fiber reinforced plastic, hereinafter referred to as CFRP. State of the art

[0002] From EP 4 050 770 A1 it is known to cut a CFRP-containing bandage into smaller rings.

[0003] EP 4 050 770 A1 describes a rotor of an electric motor which includes a bandage made of a fiber winding.

[0004] EP 2 517 818 A1 describes a laser-based cutting device for a fiber-reinforced resin.

[0005] ES 2 302 418 A1 describes a laser processing method for carbon fiber reinforced epoxy resin composites.

[0006] DE 10 2014 109 281 A1 relates to a method for cutting fiber-reinforced plastic with a laser.

[0007] CN 1 15 740 782 A describes a laser cutting process for a carbon fiber product.

[0008] DE 40 03 031 A1 describes a hand-held power tool with a high-speed, internally ventilated electric motor.

[0009] EP 4 119 284 A1 discloses a calibration of a quality estimator for a laser cutting process and a laser cutting device. Disclosure of the invention

[0010] For example, in the production of rotors for electric motors, such as those used in battery-electric vehicles, a bandage is pressed onto the rotor being manufactured. After pressing, the bandage must be cut to size.

[0011] To withstand the expected stresses at high speeds of the electric motor, the bandages are made, for example, from a carbon fiber reinforced material.

[0012] Up to now, bandages have typically been cut mechanically by sawing. This results in damage to the bandage material in the area of ​​the saw cut edges.

[0013] The object of the present invention is therefore to offer a method and a laser cutting device that enable the shortening of bandages in the most material-friendly way possible.

[0014] The problem is solved by a method for cutting a bandage comprising a carbon fiber reinforced plastic, wherein the bandage is a bandage for a rotor of an electric motor, wherein the bandage is cut by laser cutting using a laser cutting device in several passes, wherein a temperature of the bandage is measured after each pass.

[0015] A key idea of ​​the invention is that a matrix-shaped composite material, such as carbon fiber reinforced plastic, can exhibit complex temperature behavior.

[0016] In previous attempts to separate the bandage using laser cutting, certain components of the matrix could melt, vaporize, or burn, while other components, such as carbon fibers, remained solid. Therefore, uncontrolled laser cutting can lead to changes in individual matrix components, particularly at the cut edges, disrupting the matrix as a whole, especially in the cut area. Damage to the cut edges can result.

[0017] This is where the invention comes into play, in that the bandage is cut in several passes.

[0018] Therefore, on each pass it is sufficient to remove only a portion of the bandage along the planned cutting line with a shallow cutting depth.

[0019] This allows the cutting process to be carried out with a lower laser beam power. The energy input into the rest of the bandage, especially along the cut edges, is thus reduced. This alone helps to minimize damage to the material.

[0020] Furthermore, the plan is to measure the temperature of the bandage after each pass. In particular, the temperature in the area of ​​the cut edges can be measured. This allows the thermal effect of the laser beam to be precisely monitored.

[0021] Overall, the bandage can be shortened, causing less damage to the bandage material than, for example, the mechanical sawing of the bandage mentioned at the beginning.

[0022] In comparison to mechanical sawing, laser cutting offers the further advantage of producing significantly fewer dust particles. Therefore, this method can considerably reduce the workload at the workplace where the bandage is being shortened compared to mechanical sawing.

[0023] Laser cutting can be stopped if the temperature reaches or exceeds a damage threshold of the bandage. This prevents heat stress that could lead to temperatures above the damage threshold and thus to extensive damage to the bandage, especially in the area of ​​the cut edges.

[0024] Temperature can be measured using pyrometry. For example, two-quotient pyrometry can be used. This makes it possible to measure the temperature without contact, especially from a distance.

[0025] After a pass, the focus position of the laser beam of the laser cutting device can be adjusted. This allows the focus position to be adapted to the cutting depth, thus further improving the cut and achieving a clean cut edge.

[0026] The focus position of the laser beam can be determined using optical coherence tomography measurement, hereinafter referred to as OCT measurement.

[0027] Preferably, the focus should lie in the plane of the section. The focus can be continuously and / or as needed adjusted to achieve this.

[0028] Electric motors, especially those used in battery-electric vehicles, are designed to have high power ratings, which necessitates high rotational speeds. Therefore, even minor damage, particularly to a rapidly rotating rotor, can negatively impact the functionality and, in particular, the lifespan of the electric motor.

[0029] The method, which, as described above, reduces or completely avoids such damage, is therefore particularly suitable for shortening bandages made of carbon fiber reinforced material for a rotor of an electric motor.

[0030] Furthermore, the method is particularly suitable for cutting thick materials, especially thick bandages. For example, it can be advantageous to cut a bandage with a thickness of at least 1 mm, particularly at least 0.8 mm, using this method.

[0031] The issue here is that attempting to completely cut through such thick material in a single pass would require a particularly high laser beam power. This would also result in a particularly high heat input into the bandage material at the cut edge, leading to extensive damage. However, such extensive damage can be avoided or at least significantly reduced by the method described here, particularly due to the reduced heat input.

[0032] The application also includes a laser cutting device that is set up to implement the method described above.

[0033] The laser cutting device can be set up to adjust the focus position as needed and / or continuously so that it lies in a cutting plane of the laser cutting device.

[0034] The laser cutting device can include a cutting laser, an OCT unit, and a pyrometer. The previously described method can be implemented with such a laser cutting device. In particular, the temperature can be measured using the pyrometer. The OCT unit can be configured for optical coherence tomography measurements. The OCT unit can thus determine the focus position of a laser beam from the laser cutting device. The focus position can then be adjusted to the respective cutting depth for each pass.

[0035] A measuring beam from the OCT unit can be aligned along the laser beam of the cutting laser. This allows the ablation depth to be precisely determined along the cutting line traversed by the passes.

[0036] The application also covers a rotor for an electric machine of the type described above for driving a motor vehicle.

[0037] Further features and advantages of the invention will become apparent from the following detailed description of an embodiment of the invention with reference to the figures of the drawing, which show details essential to the invention, as well as from the claims.

[0038] The individual features can be implemented individually or in any combination in various versions of the invention. The schematic drawing illustrates exemplary embodiments of the invention, which are explained in more detail in the following description. Brief description of the drawings

[0039] They show: Fig. 1 a laser cutting device and Fig. 2 a method for cutting a bandage comprising a carbon fiber reinforced plastic.

[0040] To facilitate understanding of the invention, the same reference numerals are used for corresponding elements in the following description of the figures. Embodiments of the invention

[0041] Fig. Figure 1 shows a schematic representation of a laser cutting device 10 with a cutting laser 12.

[0042] The cutting laser 12 generates a laser beam 14, which is used to process a bandage 16.

[0043] For processing, the bandage 16 can be rotated so that the laser beam 14 can effectively pass over the bandage 16 in a multitude of passes.

[0044] A pyrometer 18 is set up to measure a temperature in the area of ​​the point of impact of the laser beam 14 on the bandage 16.

[0045] For this purpose, the pyrometer 18 is set up to measure the temperature using two-quotient pyrometry.

[0046] The cutting laser 12 generates the laser beam 14 with an adjustable focus position.

[0047] In particular, the cutting laser 12 is controlled by an OCT unit 20 such that the focus of the laser beam 14 is set on a surface of the bandage 16. For measurement, the OCT unit 20 can use a measuring beam 22. The measuring beam 22 runs along the laser beam 14.

[0048] According to the ablation depth of the laser beam 14 during each pass over the bandage 16, the OCT unit 20 can thus gradually shift the focus position into the bandage 16 until the bandage 16 is finally completely cut through.

[0049] Fig. Figure 2 shows a method 1000 for cutting a bandage comprising a carbon fiber reinforced material.

[0050] Method 1000 is exemplified by the cutting of the bandage 16 using a laser cutting device 16, as previously described in connection with Fig. As described in section 1, it is explained.

[0051] In an OCT phase 1010, the ablation depth is determined with the help of the OCT unit 20 during each pass of the laser beam 14 over the bandage 16 and the focus position of the laser beam 14 is adjusted accordingly.

[0052] In a pyrometry phase 1020, a temperature in the area of ​​the cutting line, i.e. in the area of ​​the focus of the laser beam 14, is measured after each passage of the laser beam 14 over the bandage 16 using the pyrometer 18 by two-quotient pyrometry.

[0053] In a cutting phase 1030, the laser beam 14 passes over the bandage 16 and thus cuts it, as long as the temperature is below a predefined damage threshold.

[0054] If the measured temperature exceeds the damage threshold, a subsequent crossing of the intersection line is delayed until the temperature has dropped back to a permissible value. The permissible value can be chosen so that the damage threshold is never exceeded. In particular, it can be chosen so that the damage threshold is not immediately exceeded again even after several subsequent crossings.

[0055] Phases 1010, 1020 and / or 1030 can be executed simultaneously. However, they can also be executed alternatively, as shown in the [document / section]. Fig. The flowchart shown symbolizes the steps to be executed sequentially.

[0056] In such a consecutive execution of phases 1010, 1020 and / or 1030, after a cutting according to phase 1030, a new cycle can begin with the OCT phase 1010, until finally the bandage 16 is completely cut through. Reference symbol list 10 Laser cutting device 12 cutting lasers 14 Laser beam 16 Bandage 18 pyrometers 20 OCT units 22 Measuring beam 1000 procedures 1010 OCT phase 1020 Pyrometry phase 1030 Cutting phase

Claims

[1] Method (1000) for cutting a bandage (16) comprising a carbon fiber reinforced plastic, wherein the bandage (16) is a bandage for a rotor of an electric motor, wherein the bandage (16) is cut by laser cutting using a laser cutting device (10) in several passes, wherein after each pass a temperature of the bandage (16) is measured. [2] Method according to the preceding claim, characterized by , that if the temperature reaches or exceeds a damage threshold of the bandage (16), the laser cutting is suspended. [3] Method according to any of the preceding claims, characterized by that the temperature is measured using pyrometry. [4] Method according to any of the preceding claims, characterized by , that after a pass a focus position of a laser beam (14) of the laser cutting device (10) is adjusted. [5] Method according to the preceding claim, characterized by , that the focus position of the laser beam (14) is adjusted using OCT. [6] Method according to any of the preceding claims, characterized by , that the bandage (16) has a thickness of approximately at least 1 mm.

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