The present disclosure relates to a process for the blanking of metal parts, in particular a multi-layer fine blanking process. The fine blanking process is, as such, generally known and are broadly applied in the manufacturing of metal parts, in particular for the cutting-out thereof from strip or plate shaped basic material. In the known fine blanking process at least the 2D contour of the metal part is shaped by pressing a correspondingly shaped blanking punch against and through the basic material, which basic material is clamped between a blanking die and a blank holder of a blanking device. The blanking die and the blank holder thereto define a respective cavity that is shaped to accommodate the blanking punch. An edge of the blanking die defining the contour of the cavity thereof, carves into and finally completely cuts through the basic material, as such basic material is progressively pressed into the cavity by the movement of the blanking punch relative to the blanking die. The fine blanking process is set apart from the more conventional blanking process, by the presence of the counter punch located opposite the blanking punch and pressing against the other side of the basic material as the blanking punch.

In order to increase a production rate of the former, known blanking processes, it has been proposed in the art to apply a layered basic material therein, i.e. to stack two or more layers of the basic material on top of one another prior to the actual blanking, i.e. cutting thereof. In this case, a number of metal parts can be formed with a single blanking punch in a single blanking stroke that corresponds to the number of layers of the layered basic material. The Japanese patent application publication No. S57-156657 teaches an early example of such a multi-layer blanking process, in particular of the said conventional variant thereof that does not include the counter punch of fine-blanking. According to this document, a stack of three layers, in particular composed of two metal strips with a third strip of insulating material there between, is fed to the blanking device and two mutually insulated rotor parts are subsequently blanked simultaneously from such layered basic material by the blanking punch. Additionally, S57-156657 teaches to provide the layered basic material with protrusions that protrude through all three layers thereof, in a direction perpendicular to length direction of the strip. These known protrusions are provided for preventing the individual layers of the layered basic material from sliding relative to one another when it is intermittedly advanced in the blanking device in-between each blanking stroke. In particular, such known protrusions are each formed by bending an edge section of the layered strip downwards, which edge section is defined between two relatively closely spaced incisions into a side edge of the layered strip.

The multi-layer blanking process is particularly relevant for the production of metal parts of relatively small thickness, such as individual lamina for an electric motor stator or rotor laminate, by using basic material of such small thickness. In particular by applying such layered basic material, a production rate of the blanking process can be increased, essentially proportional to the number of layers that are applied in the layered basic material. The said multi-layer fine blanking process variant of the multi-layer blanking has been proposed recently in WO2017/174215 for handling even thinner metal parts, i.e. for handling even thinner layers of the basic material than what is possible with the conventional blanking process.

According to the present disclosure, the known layered basic material can be improved upon in view of the application thereof in the multi-layer fine blanking process. In particular according to the present disclosure, the known protrusions of the layered basic material may not perform as well in the fine blanking process as in the conventional blanking process.

The present disclosure departs from and relies on the insight that the known protrusions provide an interlocking of the stacked layers, i.e. strips of the layered basic material in the plane of their main faces, but not perpendicular thereto. In other words, the known protrusions prevent the individual layers of the layered basic material from sliding relative to one another in the length and width directions thereof, but not from separating in their height, i.e. thickness direction. Moreover, the present disclosure takes into account a particular feature of the fine blanking process, namely that after the metal part is cut by the blanking punch, the layered basic material and the blanking die are moved apart to create a gap between them, through which gap the metal parts are subsequently removed from the fine blanking device. In particular, by such movement of the layered basic material relative to the blanking die, the layered basic material is no longer supported in its height direction and, typically, also vibrations occur therein in that direction, e.g. due to the said intermitted advancement thereof. As a consequence, a mutual alignment of the individual layers of the layered basic material may not be optimally maintained as a consequence.

According to the present disclosure, the layered basic material is plastically deformed locally to create an interlock between the individual layers thereof in all of the length, width and height direction thereof, prior to the section of the layered basic material with such interlock is advanced to between the blanking die and the blank holder or between the blanking punch and counter punch of the fine blanking device. The interlocks are formed outside the virtual contour of the metal parts to be blanked from the basic material, which has the advantage that the mechanical and/or electrical properties of these metal parts are not deteriorated by the said plastic deformation associated with press-locking. Also in this case, a coating provided to the individual layers of the layered basic material, such as an electrically isolating coating, is retained intact at the location of the metal parts. These latter aspects of the present disclosure are particularly relevant for the stator and rotor laminae of the electric motor.

It is noted that such interlocking method by plastic deformation is generally known per se for the interlocking in all three dimensions of two sheet metal layers and is referred to as press-locking hereinafter. In the art, such press-locking method and/or variants thereof are also referred to as clinching. Press-locking of more than two sheet metal layers is not practiced, because of the excessive (plastic) deformation that would be necessary in the known applications thereof. However, according to present disclosure and in the specific context of multi-layer fine blanking, press-locking was surprisingly found to be suitable also for joining and interlocking three or more layers of sheet metal, provided that these layers have a combined thickness in the range from 0.2 mm to 1 .2 mm and that their individual thickness lies in the range from 0.1 mm to 0.3 mm and preferably does not exceed 0.2 mm.

The known press-locking method requires a press-locking punch and an anvil that are located on opposite sides of the layered basic material and that are pressed together to plastically deform the layered basic material there between into an keyed connection that is referred to herein as the interlock. In combination with the known multi-layer fine blanking process, the known press-locking method has the advantage that the movement of the press-locking punch relative to the anvil, can be favourably coordinated with the movement of the blank holder or of the blanking punch relative to the blanking die, i.e. with the opening and closing of the blanking device. Preferably, these relative movements are not only mutually coordinated but also jointly actuated. In other words, pressing joining can be advantageously integrated in the multi-layer fine blanking process, thus creating the novel multi-layer fine blanking process according to the present disclosure.

Further according to the present disclosure, a number of interlocks are created simultaneously, by using a number of simultaneously actuated pairs of press-locking punches and anvils. This has the advantage that the interlocking of the individual layers of the layered basic material is more stable without detriment to the production rate of the blanking process and/or blanking device.

In the following, the multi-layer fine blanking process and device according to the present disclosure is explained further by way of example embodiments and with reference to drawing figures, whereof:

Figure 1 is a schematic, plan view of a typical blanked metal part, being a single lamina made from electrical steel for a stack of lamina, i.e. laminate, for a rotor of an electric motor;

Figures 2A to 2F schematically illustrate a multi-layer blanking device and process for forming metal parts;

Figure 3 is a schematically drawn cross-section of a layered basic material used in the multi-layer blanking process, which layered basic material is provided with an interlock between the individual layers thereof;

Figures 4A and 4B schematically illustrate a simplified press-locking device and process for interlocking the individual layers of the layered basic material;

Figure 5 is a schematically drawn perspective view of an alternative embodiment of the interlock between the individual layers of the layered basic material; and

Figure 6 is a schematic representation of a novel multi-layer blanking process including a process step of press-locking.

Figure 1 provides an example of a metal part 10 that can suitably be produced with the aid of a blanking process, in particular the multi-layer blanking process discussed herein. In this example the metal part 10 takes the form of an individual rotor disc 1 1 for a rotor laminate, i.e. stack of rotor discs of an electric motor. In this particular example, the rotor disc 1 1 is provided with a primary or central hole 12 and a number of secondary holes 13 that are arranged along its circumference. The outer contour, i.e. perimeter of the rotor disc 1 1 as well as the contours of the central and secondary holes 12, 13 thereof are formed, i.e. are cut out of a basic material, in particular electrical steel, either simultaneously in one cut, i.e. with a single stroke of a blanking device 90, or in a number of subsequent partial cuts in separate stages of the blanking process. In the electric motor, the central holes 12 of (the stack of) the rotor discs 1 1 accommodate a rotor shaft and the said secondary holes 13 thereof accommodate magnets. Often an electrically isolating layer is provided between the individual rotor discs 1 1 in the rotor stack in order to reduce so-called Eddy current losses, possibly in the form of an electrically isolating coating applied to at least one side of the basic material for the rotor discs 1 1 before blanking.

It is noted that the exact size or the exact contour of the rotor disc 1 1 illustrated in figure 1 is not relevant within the context of the present disclosure. Rather, the present disclosure is also applicable to not only differently shaped rotor discs 1 1 , but also the stator ring component (not illustrated) of the stator laminate of the electric motor and even to metal parts 10 in general, as long as these parts 1 1 are at least partly formed in the multi-layer fine blanking process that is described hereunder.

The figures 2A-2F schematically illustrate a multi-layer blanking process for producing the rotor discs 1 1 or the metal part 10 in general. The figures 2A-2F each represent a simplified cross-section of the blanking device 90 that is used to cut-out such metal parts 10 from a layered basic material 51 comprising two or more (here: four) of mutually stacked layers, i.e. strips 50 of basic material. The blanking device 90 includes a blanking punch 30, a counter punch 40, a blank holder 70 and a blanking die 80. The blank holder 70 and the blanking die 80 each define a respective cavity 71 , resp. 81 , wherein the blanking punch 30 and the counter punch 40 are contained, which cavities 71 , 81 are shaped to correspond to the (contour of the) metal part 10. This particular type of blanking process/blanking device 90 using a counter punch 40 is known per se, namely as a fine-blanking.

In figure 2A, the blanking device 90 is shown in a first open state, wherein the blanking punch 30 is fully retracted into the blank holder 70, the counter punch 40 is fully retracted into the blanking die 80 and wherein the blank holder 70 and the blanking die 80 are separated from one another, at least sufficiently for allowing the layered basic material 51 to be inserted and/or advanced along its length direction relative to the blanking device 90, as schematically indicated by the dashed arrow.

In figure 2B the blanking device 90 is shown after the blank holder 70 and the blanking die 80 have been moved towards each other to clamp the layered basic material 51 between them.

In figure 2C the blanking device 90 is shown after the blanking punch 30 and the counter punch 40 have been moved towards each other to also clamp the layered basic material 51 between them.

In figures 2D and 2E the step of cutting out the metal part 10 from each strip 50 of the layered basic material 51 , by the forced movement of the combination of the blanking punch 30 and the counter punch 40 relative to the blanking die 80, is illustrated. In particular in figure 2D the blanking device 90 is shown during such cutting-out and in figure 2E the blanking device 90 is shown after the metal parts 10 have been completely cut out, i.e. have been severed from the layered basic material 51 , but are still held between the blanking punch 30 and the counter punch 40.

In figure 2F the blanking device 90 is shown in a second open state, wherein the blanking punch 30 is fully retracted into the blank holder 70 and wherein the counter punch 40 protrudes from the blanking die 80 after pushing the blanked metal parts 10 upwards out of the cavity 81 of the blanking die 80 to allow the extraction thereof from the blanking device 90. After such extraction, the blanking device 90 returns to its first open state shown in figure 2A etc.

As illustrated in figure 2F in the second open state of the blanking device 90, but actually also in the said first open state thereof, the individual strips 50 of the layered basic material 51 tend to separate from each other in their thickness direction, i.e. in the height direction H of the layered basic material 51 . As a result, the mutual alignment of the individual strips 50 in their length and width directions can become compromised, or at least the blanking device must be equipped with additional means (not illustrated) for supporting and guiding the layered basic material 51 when it is lifted from and/or advanced relative to the blanking die 80. Furthermore in the second open state of the blanking device 90 and as also illustrated in figure 2F by the solid arrow, the blanked metal parts 10 are extracted individually, or at least as individual, i.e. loose parts.

According to the present disclosure, the former multi-layer blanking process can be improved upon. In particular, a synchronising and a mutual alignment of the individual strips 50 of the layered basic material 51 can be favourably realised by mutually interlocking these strips 50 in all of the length, width and thickness directions thereof (i.e. in all 3 spatial/physical dimensions) by the local plastic deformation of the strips 50, i.e. by creating an interlock 1 there between by so-called press-locking, before the layered basic material 51 is inserted between the blanking punch 30 and the counter punch 40 of the blanking device 90.

A possible embodiment of such interlock 1 is schematically illustrated in figure 3 in an enlarged cross-section of the layered basic material 51. In this example of the interlock 1 , it is essentially shaped as a dovetail-shaped joint 3 that is circularly symmetric, such that it prevents the strips 50 from relative movement in all three dimensions.

In figure 4A and 4B, an example of a press-locking method, in particular the press locking method for forming the interlock 1 of figure 3 is schematically illustrated. In a first step of this particular press-locking method -that is illustrated in figure 4A- the layered basic material 51 is inserted between a press-locking punch 101 with a projection 102 and an anvil 103 defining a hollow 104. In a second step of the press-locking method - that is illustrated in figure 4B- the projection 102 of the press-locking punch 101 is pressed into the layered basic material 51 -whereby an indentation 2 is formed therein (see figure 3)- and the basic material 51 is displaced not only downward into the hollow 104 in the anvil 103 -whereby a protruding bulge 4 is formed thereon (see figure 3)-, but also sideways, whereby the said dovetail-shaped joint 3 is formed.

Inter alia, it is noted that the exact realization of the press-locking method is not relevant within the context of the present disclosure. Rather, the present disclosure relates to any press-locking method that realises a mutual interlocking of the individual layers/strips 50 of the layered basic material 51 in all three dimensions by the targeted, i.e. local and controlled plastic deformation thereof. For example, also a press-locking method is known that utilizes a planar anvil, in which case a ring is placed with some radial clearance around a press-locking punch. In this realization of the press-locking method, in the said second step thereof, the basic material 51 plastically flows sideways and upward between the press-locking punch and the said ring, forming an annular bulge there between. Also, it is known to remove the bulge 4 of the interlock 1 in a further process step of the press-locking method by compressing the layered basic material 51 at the location of the bulge 4 between two planar surfaces. Moreover, the interlock 1 need not be formed with a circular symmetry, but may for example also be formed with a predominantly oval, square or rectangular, shape. In particular in case of the rectangular interlock 1 , a rectangular bulge 4 is formed by bending its short sides 6, whilst shearing- off its long sides 5. In figure 5 such rectangular interlock 1 is schematically illustrated in a cross section thereof. In this realization of the interlock 1 , the relative movement of the individual layers 50; 50-T, 50-B in their thickness direction is blocked by the sheared long sides 5 of the bulge 4 at a top layer 50-T of the layered basic material 51 catching the sheared long sides 5 of a bottom layer 50-B of the layered basic material 51 . Although, in figure 5 the layered basic material is illustrated with two individual layers/strips 50-T, 50- B, the illustrated rectangular interlock 1 is suitable for joining more than two layers/strips 50.

Preferably, the above-described press-locking methods are carried out as part of, i.e. as a process stage in the multi-layer fine blanking process. In this case, the first press-locking step (figure 4A) is synchronized with the first multi-layer fine blanking step (figure 2A), whereas the second press-locking step (figure 4B) is preferably synchronized with the cutting of the metal parts 10 out of the layered basic material 51 (figure 2D). Such novel multi-layer blanking process including press-locking is schematically illustrated in figure 6 in relation to the rotor disc 1 1 illustrated in figure 1.

As illustrated in figure 6 in a plan view of the layered basic material 51 , i.e. looking downward in the height direction H thereof, two interlocks 1 (1 a, 1 b) are provided therein in a press-locking stage of the novel multi-layer blanking process. Once formed, the interlocks 1 are transported together with the layered basic material 51 , by the said intermitted advancement thereof, to the blanking stage. In this blanking stage, the metal parts 10 (that are depicted as rotor discs 1 1 in figure 6) are cut out of the layered basic material 51 , either entirely in one complete cut (not illustrated), or -depending on the complexity of the (contour of the) metal part 10- in two or more subsequent partial cuts. In particular, as illustrated in figure 6, in a first partial cut, the central hole 12 and the secondary holes 13 of the rotor discs 1 1 are formed, where after, in a second partial cut, the outer circumference 14 of the rotor discs 1 1 is formed, whereby the rotor discs 1 1 are cut loose from the layered basic material 51 , leaving the space 15 therein. During, in between and after these first and second partial cuts, the individual layers 50 of the layered basic material 51 are favourably held together as one, by way of the interlocks 1 . In accordance with the present disclosure, the interlocks 1 are formed outside the outer circumference 14 of the metal parts 10 that thus favourably remain unaffected thereby.

The present disclosure, in addition to the entirety of the preceding description and all details of the accompanying drawing figures, also concerns and includes all of the features in the appended set of claims. Bracketed references in the claims do not limit the scope thereof, but each merely provide a non-limiting example of a respective feature. Separately claimed features can be applied separately in a given product or a given process, as the case may be, but can also be applied simultaneously therein in any combination of two or more of such features.

The invention(s) represented by the present disclosure is (are) not limited to the embodiments and/or the examples that are explicitly mentioned herein, but also encompass(es) straightforward amendments, modifications and practical applications thereof, in particular those that lie within reach of the person skilled in the relevant art.