BLANKING MACHINE AND METHOD FOR PRODUCING BLANKS

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims foreign priority benefits under 35 U.S.C. § 119(a)-(d) to DE Application 102024131275.0 filed Oct. 25, 2024, which is hereby incorporated by reference in its entirety.

TECHNICAL FIELD

Blanking machines and methods that separate a blank from a main body of an electrical sheet using punch and die.

BACKGROUND

The welding of two components using a capacitor impulse welding method is known from DE 25 26 588 C3.

U.S. Pat. No. 9,745,641 B2 deals with the forming of metallic glasses, i.e. bulk metallic glasses (BMG). In this method, the discharge of electrical energy stored in a capacitor is used to heat a sample or batch of a metallic glass alloy comprehensively, i.e. fully and rapidly, to a predetermined process temperature between the glass transition temperature of the amorphous material and the equilibrium melting point of the alloy, in a time scale of a few milliseconds or less. Once the sample is fully heated, such that the entire sample block has a sufficiently low process viscosity, it can be formed into high-quality amorphous bulk articles by any number of methods in a time frame of less than one second, for example by injection molding, dynamic forging, die forging and blow molding.

The demand for electric motors that are compact, highly efficient and powerful has increased significantly in recent years due to the ever-increasing fuel economy requirements for electrified vehicles (for example, hybrid, plug-in hybrid and all-electric vehicles). As a result, there is an increased demand for high-performance rotor and stator laminations, which are used in electric vehicle motor cores and can convert energy in an efficient and effective manner. These laminations are composed of electrical sheet.

Electrical sheet is a particular type of steel that has special electromagnetic properties. Electrical sheet is normally produced in strips less than 2 mm thick. For example, extremely thin electrical sheets with thicknesses of 100-350 μm are known. These strips are cut to size to form the laminated cores of transformers and the stator, as well as the rotor of electric motors. The electrical sheet is often cut to size by blanking. In this process, the electrical sheet is placed in the blanking machine, between the punch and the die, such that the required portion is cut out from the main body. While conventional machining methods such as blanking are commonly used to profile metal sheets, this approach can cause residual stresses that can have a negative effect on the magnetic properties of electrical steels. Moreover, it can result in the formation of burrs, which can cause problems during the winding process. However, some electrical sheets made of high-silicon iron-based alloy known for excellent soft magnetic properties, such as high electrical resistivity, low iron losses, and near-zero magnetostriction such as, for example, high-alloy Fe6.5Si, are also too brittle to undergo blanking. Yet other electrical sheets such as, for example, cobalt-iron alloys (FeCo), require upstream heat treatment if they are supplied as a semi-finished product. Otherwise, these electrical sheets cannot be blanked either.

Also already known is the method of separating, i.e. cutting out, the laminations from the electrical sheet by means of wire erosion or a laser. With wire erosion, a high-quality result is achieved. However, this is much slower than blanking in terms of the speed of production of the laminations. Laser cutting, on the other hand, is somewhat faster in the production of the laminations, but is not as accurate and requires a high energy input, and is also much slower than blanking. Laser cutting is also mainly used for the production of prototypes.

In view of the prior art mentioned above, there is still room for improvement in the production of blanks, especially laminations made from an electrical sheet.

SUMMARY

A blanking machine and a method for producing blanks according to one or more configurations, in particular from an electrical sheet, by means of such a blanking machine, produce, by simple means, high-quality blanks, in particular laminations for electric motors, from the main body, in particular from electrical sheets, with low energy input while avoiding the need for reworking.

It should be pointed out that the features and measures listed individually in the following description may be combined with one another in any technically appropriate manner and disclose further configurations, aspects, or embodiments of the claimed subject matter. The description additionally characterizes and specifies the claimed subject matter, in particular in conjunction with the figures.

As described herein, a blanking machine is configured for separating at least one blank from a main body, having a punch and a die between which the main body, in particular made from an electrical sheet, is arranged. An energy storage arrangement is electrically connected both to the punch and to the die to provide a rapid discharge of the energy storage arrangement that heats the main body in the region of a blanking edge.

According to various aspects, a blanking machine mechanically separates the blank from the main body and also heats the blanking edge via the rapid discharge of the energy storage arrangement. The energy storage arrangement may be a capacitor arrangement configured to discharge capacitively, i.e. discharge very rapidly. In the following, the energy storage arrangement is referred to as a capacitor arrangement, which is not intended to be limiting. The energy storage unit may be implemented by any element that is suitable for storing energy, in particular electrical energy, and releasing it again rapidly, or for generating it rapidly, such that a locally delimited region is heated or softened briefly by means of the rapidly released high current. The very brief capacitive discharge of the energy storage unit generates the heat that is sufficient to soften the blanking edge, with temperatures of 600° C. to 1200° C. being generated in a locally delimited manner at the blanking edge. Since the capacitor arrangement also discharges very briefly, which in this case may also be referred to as a discharge current that lasts less than a few milliseconds, in particular 50 ms, a locally delimited thermal influence zone is also generated.

In particular, if electrical sheets of a thickness of less than 2 mm, preferably of 100-350 μm, are used to produce the blanks, i.e. for example the laminations, only a very narrow and thin blanking edge is heated to initiate the actual blanking process. In this respect, the machine and method utilize a very low energy input despite the use of electricity, because there is no need to heat the entire main body and/or blank, with only a locally delimited region, namely only the blanking edge, which may also be referred to as the cutting edge, being heated and softened.

In particular, if the main body is formed from an electrical sheet, there are further positive effects, for example the microstructure of the electrical steels remains unchanged, which is advantageous for achieving better magnetic properties. This is because only a very small cutting or blanking edge is heated, such that the main properties of the electrical sheet remain virtually unaffected by the small thermal influence zone.

A further advantage can be seen in the introduction of tensile stresses into the cutting or blanking edge due to the rapid heating and subsequent cooling during/after the blanking process. Tensile stresses in soft magnetic materials have a positive effect on the magnetic properties of electrical steels (lower core losses).

In particular, a blanking machine according to the disclosure also makes it possible to process super-hard materials such as, for example, boron-alloyed steels, i.e. to produce blanks.

The main body, particularly in the form of an electrical sheet, may have an electrical insulation, for example a so-called C5 coating. Such a C5 coating is used on electrical sheet to reduce thermal losses due to eddy currents in electrical machines. This is taken into account in the blanking machine or method according to the disclosure in that the electrical current for heating the cutting or blanking edge is to be of such a rating as to overcome the insulation. It is considered in this regard that the surface resistance of electrical sheet that has C5 coating may be approximately ˜5 Ohm/cm². Amperages of 1000 A, but also significantly higher, may be required. This depends on the developed length of the blanking or cutting edge that needs to be heated.

The capacitor arrangement, which is electrically connected both to the punch and to the blanking edge, serves to provide the currents required for heating, i.e. for softening the cutting or blanking edge. In one design, the capacitor arrangement is in the form of a single capacitor that is configured accordingly. As already mentioned above, amperages of 1000 A or significantly more may be required. Capacitances may therefore range from 0.05 to 0.1 F. In an alternative design, the capacitor arrangement may have a plurality of capacitors, i.e. two or more capacitors, which are interconnected. In particular, the individual capacitors may be interconnected in parallel to increase the capacitance.

The main body may be fed into the blanking machine in a variety of ways. On the one hand, the main body may be a pre-blanked element that in each case is inserted separately into the blanking machine. This design increases the customization of the blank. In a further possible design, the main body may be in the form of a sheet to be unwound from a coil, which is fed continuously into the blanking machine. This design increases the throughput of the blanking machine.

In particular, it is provided that the punch and/or the die is/are made of a material that has good electrical conductivity but still has the necessary resistance to separate the blank, i.e. the lamination, from the main body, especially in the form of an electrical sheet. As such, the punch and/or the die are made of a copper material. Alternatively, the punch and/or the die are made of a hard metal material.

As already mentioned, the capacitor arrangement has a capacitance such that the amperage generated by the capacitive discharge is such that the blanking edge is heated in a manner that permits blanking, with only the narrowly delimited local region being warmed, i.e. heated.

In particular, the punch and the die are designed to match each other in such a way that, when the blanking machine is in the preloaded state, i.e. when the punch and the die are in contact with respectively opposite surfaces of the main body, they form the blanking edge, with an outer diameter of the punch corresponding to the inner diameter of the die. In particular, the current path for the current generated by the capacitive discharge is formed by the outer wall of the punch and the inner wall of the die, which are adjacently positioned when the blanking machine is in the closed state, such that only the blanking edge is heated by the briefly flowing high current.

Alternatively or additionally, an electrical insulation (e.g. pad, ceramic inlay, etc.) is arranged on the punch and/or the die to optimally guide the electrical current only along the blanking or cutting edge. The electrical insulation would be arranged over a large area, for example on the punch, and leave a peripheral region uninsulated, such that the current can flow here in a targeted manner and heat the blanking or cutting edge.

A blanking machine according to the disclosure is advantageously combined with a capacitor arrangement that heats the blanking edge to a temperature of from 600° C. to 1200° C. by a brief capacitive discharge, this temperature value being dependent on the capacitance of the capacitor arrangement, which in turn is selected to suit the material used and its resistance, including surface resistance.

Conventional blanking tools for electrical steels are usually progressive tools comprising a multiplicity of stages, sometimes thirteen or more stages. With the blanking machine according to the disclosure, which for example is combined with a capacitor arrangement, the length of such tools can be reduced by integrating a plurality of blanking steps into one step, which shortens the tool length and results in smaller blanking machines, which may also be referred to as presses. Moreover, blanking of the heated blanking or cutting edge also makes it possible to reduce the blanking forces required.

Disclosed in a further aspect of the invention is a method for producing a blank from a main body, in particular formed from an electrical sheet, comprising a blanking machine, in particular according to any one of the designs described above, having a punch and a corresponding die between which the main body is inserted. When the punch is inserted into the die, a blanking edge, which may also be referred to as a cutting edge, is heated by means of a rapid discharge of an energy storage arrangement that is electrically connected to the blanking machine.

The advantages mentioned above in relation to the blanking machine described above can be achieved in a similar manner with the method. As before, the energy storage arrangement is referred to as a capacitor arrangement and is connected both to the punch and to the die.

The method may comprise a plurality of successive steps.

In one step, the main body is inserted into the blanking machine, i.e. into a gap between the punch and the die. At the same time, the capacitor arrangement is charged.

The capacitor arrangement may have a single capacitor or a plurality of capacitors. If a plurality of capacitors is provided, these may be connected in parallel to increase the capacitance of the capacitor arrangement. The charging of the capacitor is known and is therefore not described in detail.

Once the main body is inserted into the blanking machine and the capacitor arrangement is charged, the blanking machine is preloaded, which means that the punch and the die are moved towards each other. In one configuration, the punch is movable relative to the stationary die. Alternatively, the die is movable relative to the stationary punch. The punch and the die may also be guided in a movable manner. In any case, both the punch and the die are in contact with the main body, which means that, when the blanking machine is in the preloaded state, the punch and the die are in contact with opposite surfaces of the main body. The main body can then bend very slightly, such that there is a better flow of current between the punch, the main body and the die, since the current is then conducted only at the blanking or cutting edge. Bending in the μm range is sufficient. This type of clamping of the main body in the blanking machine facilitates the subsequent heating of only the locally delimited region along the blanking edge, such that a clean blanking edge is also produced that requires little or no post-processing. The main body is, in particular, an electrical sheet of a thickness of less than 2 mm, in particular of a thickness of 100-350 μm.

When the blanking machine is in the preloaded state, an outer diameter of the punch is positioned adjacent to an inner wall of the die. This creates a current path, such that only the blanking edge of the main body undergoes heating.

Once the blanking machine is preloaded, a circuit of the capacitor arrangement is closed by means a closed-loop control unit that is located either in the connection of the capacitor arrangement to the punch or in the connection of the capacitor arrangement to the die. This allows the capacitor arrangement to discharge. A high current, for example of 1000 A or more, then flows through the punch to the die, causing the blanking edge to heat up. This takes a few milliseconds, such as 50 ms as an example. In this short period of time, the main body is heated to a temperature of from 600 to 1200° C. at its blanking edge. At the same time, the punch is inserted into the die.

It is of course within the concept of the claimed subject matter that the current is not simply switched on or off. Rather, the discharge may be controlled in a precise manner in accordance with the required heating profile and the material. For this purpose, a control device may be provided, which is communicatively connected to the blanking machine and the capacitor arrangement, and which controls the application and level of current, voltage and process force, depending on the desired and given parameters. This allows the process to be controlled and information on quality to be obtained. The control unit or controller, which may also be referred to as a central control unit, may comprise stored software, an integrated input unit and an output device for checking the parameters.

Following the capacitive discharge, i.e. after a few milliseconds, in particular after 50 ms or even after 10 ms, the capacitor arrangement circuit is subsequently opened again as a result of being actuated accordingly by the closed-loop control unit. However, the punch is moved further into the die, causing the blank to be fully separated from the main body, along its heated blanking edge.

The process can recommence.

Since, with the procedure according to the disclosure, no material has to be melted or vaporized, but only a capacitive discharge of the capacitor arrangement is used, and only the blanking edge of the main body, i.e. of the blank, is heated, i.e. softened, the blanking process according to the invention requires less energy than, for example, laser cutting. It is also advantageous that, due to the softening of the material, the process forces are lower, and this is beneficial in terms of the energy consumption and wear of the blanking machine. Moreover, as no wire, electrolyte or process gases are required and reworking of the accurately cut-out blanks is at least largely avoided, the associated resources are reduced. Also, only electrical energy is consumed, which may also be generated as green electricity (solar power, wind energy), such that, in the production of the blanks, in particular the laminations formed from electrical sheet, the blanking machine and process reduces CO₂ emissions.

According to one aspect of the invention, only the blanking edge is heated. This has a number of advantages: on the one hand, significantly less energy is required than if the entire electrical sheet, for example, has to be heated; furthermore, the cycle time of a possible production is much lower resulting in higher throughput; furthermore, it is possible to work in a narrower tolerance field because there is virtually no thermal linear expansion of the blank, in particular of the lamination. Furthermore, there is less need for hardening of the blanking or cutting edge, as the effects of work hardening are minimal or non-existent.

Instead of the energy storage arrangement or capacitor arrangement, it is also possible to use any energy source that enables a brief high current to be generated rapidly to heat the blanking edge locally.

It is also within the concept of the disclosure if the energy storage arrangement, i.e. for example the capacitor arrangement, is used in order to be combined with the blanking machine in such a way that the blanking edge is heated and softened in a locally delimited manner by the generation of a brief high-amperage current, such that the objectives and advantages described above can be achieved.

Disclosed in a further aspect of the invention is an electrical sheet that is produced using the blanking machine, in particular according to one of the designs described above, and the method, in particular according to one of the applications described above. The advantages mentioned above in relation to the blanking machine described above and the method described above can be achieved in a similar manner with the electrical sheet.

In particular, the electrical sheet is produced as a lamination that can be used, in particular, in electric motors. Envisaged in particular in this case are electric motors in motor vehicles such as, for example, cars, lorries (trucks), buses, vans, etc.

Further advantageous details and effects according to the disclosure are explained in greater detail below with reference to a representative embodiment, shown in the figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A, 1B, 1C, and 1D illustrate a blanking machine configured to perform a method according to the disclosure for producing blanks.

FIG. 2 shows a perspective, oblique top view of a blanking machine and electrical sheet positioned between a punch and die.

DETAILED DESCRIPTION

As required, detailed embodiments are disclosed herein; however, it is to be understood that the disclosed embodiments are merely representative of the claimed subject matter that may be embodied in various and alternative forms. The figures are not necessarily to scale; some features may be exaggerated or minimized to show details of particular components. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a representative basis for teaching one skilled in the art to variously employ the present invention.

In the various figures, parts that are the same are in each case denoted by the same reference designations, for which reason they are also generally described only once.

FIG. 1 shows a blanking machine 1. The blanking machine 1 has a punch 2 and a die 3. The punch 2 represents the inner mold, while the die 3 has a correspondingly suitable opening 4. Depending on the structural design of the tool, the punch 2 may be either the upper or the lower part of the blanking machine 1. In the representative embodiment represented, in the plane of the drawing the punch 2 is the upper part, which is moved into the opening 4 of the die 3 from above.

Electrically connected to the blanking machine 1 is an energy storage arrangement 6. This, by way of example, is in the form of a capacitor arrangement and is electrically connected to the blanking machine 1. The energy storage arrangement 6 is referred to below as the capacitor arrangement, but this is not intended to be limiting.

On the one hand, the capacitor arrangement is electrically connected to the punch 2. On the other hand, the capacitor arrangement is electrically connected to the die 3. Electrical lines 9, 11 are provided for electrical connection. There is a closed-loop control unit 12 arranged in one of the electrical lines 9, 11, for example in the electrical line 9 for connecting the capacitor arrangement to the punch 2.

The closed-loop control unit 12 is to be understood as being purely schematic. Control unit 12 may provide closed-loop feedback control of current and voltage as well as process forces. For this purpose, a control unit is preferably provided, but is not explicitly illustrated, which controls and monitors the blanking machine 1 and the capacitor arrangement, and which is adapted to the required heating profile and to the material. The control device, which is communicatively connected to the blanking machine and the capacitor arrangement, may be provided for this purpose, and controls the application and level of current, voltage and process force, depending on the required and given parameters. This allows the process to be controlled and information on quality to be obtained. The control unit, which may also be referred to as a central control unit, may comprise stored software, an integrated input unit and an output device for checking the parameters (such as voltage, current, process force, etc.).

The capacitor arrangement may be composed of a single capacitor or of a plurality of capacitors, for example two, three or four or even more capacitors. If a plurality of capacitors make up the capacitor arrangement, the capacitors may be connected in parallel.

By means of the blanking machine 1, which is electrically connected to the capacitor arrangement, blanks 13 can be punched out of a main body 14. The main body 14 may be an electrical sheet of a thickness of less than 2 mm, in particular of a thickness of 100-350 μm. If the main body 14 is an electrical sheet, the blanks 13 produced may be laminations for use in an electric motor.

For this purpose, in a first step, the main body 14 is inserted into the blanking machine 1, namely into a gap 16 between the punch 2 and the die 3. At the same time, or even beforehand, the capacitor arrangement is charged. This is represented in FIG. 1A, which is at the top left in the plane of the drawing. The charging of the capacitor arrangement is known per se, and is not represented in FIG. 1A.

Once the capacitor arrangement is charged and the main body 14 is inserted into the blanking machine 1, the blanking machine 1 is preloaded. In the exemplary embodiment represented, the punch 2, arranged at the top of the plane of the drawing, is moved in the direction of die 3 and is stopped when both the punch 2 and die 3 contact the mutually opposite surfaces of the main body 14. Pressure is thereby applied to the main body 14, such that it is clamped between the punch 2 and the 3. The pressure in this case is such that the main body 14, in the region in which the punch 2 is in bearing contact, extends just above the opening 4 of the die 3. In this step, the main body 14 is thus advantageously clamped in the blanking machine 1 with a slight bend. The punch 2 and the die are arranged and aligned in relation to each other. This is represented in FIG. 1B, which is at the top right in the plane of the drawing.

Once the main body 14 is clamped in the blanking machine 1, the closed-loop control unit 12 is closed. The capacitor arrangement discharges. The capacitive discharge causes a high-amperage current to be introduced very rapidly, via the punch 2 and the die 3, into the main body 14, heating the edge 17 to be punched, as the latter closes the circuit between the punch 2 and the die 3. At the same time, the punch 2 is moved into the die 3 to produce the blank 13. This is represented in FIG. 1C, which is at the bottom left in the plane of the drawing, in which there are ellipses drawn around the blanking edge 17 to highlight the heating of the blanking edge 17 by means of the brief capacitive discharge current. Furthermore, the movement of the punch 2 into the opening 4 of the die 3 is indicated by the force arrow F. The capacitive discharge of the capacitor arrangement takes only a few milliseconds, in particular 50 ms or even just 10 ms.

Following the capacitive discharge of the capacitor arrangement, the closed-loop control unit 12 is opened again. The punch 2, however, is moved further into the die 3, such that the blank 13 becomes fully separated, along its blanking edge 17, from the main body 14. This is represented in FIG. 1D, which is at the bottom right in the plane of the drawing.

The capacitor arrangement could ideally be recharged immediately once the closed-loop control unit 12 is opened again.

FIG. 2 shows a perspective, oblique top view of a blanking machine as a detail. In this design, there is electrical insulation 18 on the side of the punch 2 that is orientated towards the main body 14. The electrical insulation 18 is arranged over a large area on the respective contact surface of the punch 2, and is such that a surrounding peripheral region 19 remains electrically uninsulated. Such an electrical insulation may also be arranged on the die 3.

The electrical insulation 18 may be in the form of a pad or ceramic inlay, this being cited merely as an example. This discloses a further measure to optimally guide the electric current only along the blanking edge 17, such that the current can flow here in a targeted manner and heat the blanking edge.

While exemplary embodiments are described above, it is not intended that these embodiments describe all possible forms of the invention. The words used in the specification are words of description rather than limitation, and it is understood that various changes may be made without departing from the spirit and scope of the claimed subject matter. Additionally, the features of various implementing embodiments may be combined to form further embodiments that may not be explicitly described or illustrated but will be understood by those of ordinary skill in the art based on the disclosure.