Patent Description:
The 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 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. Within this context, 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 and fine 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 known 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 multi-layer fine blanking process variant of the multi-layer blanking has been proposed recently 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.

<CIT> and <CIT>, on which the preamble of claim <NUM> is based, provide further examples of 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 these documents, a stack of two layers, i.e. of two metal strips 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. Further according to these documents, an interlock is created between the individual layers of the layered basic material in all of the length, width and height or thickness direction thereof, which interlock is created by plastic deformation in a section thereof that corresponds to the metal parts to be blanked. Such interlock is thus created before the said section of the layered basic material with that 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. This has the advantage that not only the layered basic material is favourably held together as an integral part when it is advanced in, i.e. relative to the blanking device, but also the metal parts are held together in this way after blanking, i.e. after these have been cut out of the layered basic material by the blanking device.

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. 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. It is further noted that 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.

In fact, <CIT> concerns and is limited to a specific type of interlock, i.e. a specific press-locking method. Namely, in <CIT> a rectangular section of the two layered stack of basic material is pushed below the two layers thereof, by bending the short sides of such rectangular section, whilst shearing-off its long sides. Hereby, a rectangular cavity is formed in the two layers of the basic material, whilst a rectangular bulge is formed below these. Because the bulge is compressed between the press-locking punch and the anvil, it is expanded sideways, i.e. in a direction that is parallel to the short sides of the said rectangular section. As a result, the long sides of the bulge catch, i.e. hook on the long sides of the cavity, such that the layers of the layered basic material cannot be separated in the height or thickness direction thereof.

Further, according to <CIT>, after a set of two metal parts containing such interlock are simultaneously blanked from the layered basic material, a laminate is assembled from several of such sets of blanked metal parts by pressing the bulge of the interlock of a first set of blanked metal parts in the cavity of the interlock of an adjacent set of blanked metal parts in the laminate. Hereby, the said bulge is elastically compressed to fit into the said cavity that is elastically stretched, such that an interference or press fit is created between such neighbouring sets of blanked metal parts. Of course, as a consequence of creating the press fit, the keyed connection between the individual layers, i.e. between the metal parts of a set is lost.

According to the present disclosure, the above known process for manufacturing the laminate can be improved upon. The present invention provides such an improved process with a method according to the features of independent claim <NUM>.

In the laminate manufacturing process according to the invention, the layered basic material is not only provided with the interlock, but also with a hole that is therein as part of the multi-layer blanking process step. This hole serves to receive the bulge of the interlock of the said adjacent set of blanked metal parts in the laminate. Hereby, the bulge of the interlock is not compressed in the laminate, or at least to a lesser extent than what is taught by <CIT>, and favourably remains hooked on the (long) side of the cavity of that same interlock. Moreover, the method according to the invention favourably allows for other known types of interlock than the rectangular interlock to be applied. Further, press-locking was surprisingly found to be suitable also for joining and interlocking more than two layers of sheet metal, provided that these layers have a combined thickness in the range from <NUM> to <NUM> and that their individual thickness lies in the range from <NUM> to <NUM>, preferably does not exceed <NUM>.

In the following, the laminate manufacturing process according to the present invention is explained further by way of example embodiments and with reference to drawing figures, whereof:.

<FIG> provides an example of a metal part <NUM> 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 <NUM> takes the form of an individual rotor disc <NUM> for a rotor laminate, i.e. stack of rotor discs of an electric motor. In this particular example, the rotor disc <NUM> is provided with a primary or central hole <NUM> and a number of secondary holes <NUM> that are arranged along its circumference. The outer contour, i.e. perimeter of the rotor disc <NUM> as well as the contours of the central and secondary holes <NUM>, <NUM> 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 <NUM>, or in a number of subsequent partial cuts in separate stages of the blanking process. In the electric motor, the central holes <NUM> of (the stack of) the rotor discs <NUM> accommodate a rotor shaft and the said secondary holes <NUM> thereof accommodate magnets. Often an electrically isolating layer is provided between the individual rotor discs <NUM> 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 <NUM> before blanking.

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

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

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

In <FIG> the blanking device <NUM> is shown after the blank holder <NUM> and the blanking die <NUM> have been moved towards each other to clamp the layered basic material <NUM> between them.

In <FIG> the blanking device <NUM> is shown after the blanking punch <NUM> and the counter punch <NUM> have been moved towards each other to also clamp the layered basic material <NUM> between them.

In <FIG> and <FIG> the step of cutting out the metal part <NUM> from each strip <NUM> of the layered basic material <NUM>, by the forced movement of the combination of the blanking punch <NUM> and the counter punch <NUM> relative to the blanking die <NUM>, is illustrated. In particular in <FIG> the blanking device <NUM> is shown during such cutting-out and in <FIG> the blanking device <NUM> is shown after the metal parts <NUM> have been completely cut out, i.e. have been severed from the layered basic material <NUM>, but are still held between the blanking punch <NUM> and the counter punch <NUM>.

In <FIG> the blanking device <NUM> is shown in a second open state, wherein the blanking punch <NUM> is fully retracted into the blank holder <NUM> and wherein the counter punch <NUM> protrudes from the blanking die <NUM> after pushing the blanked metal parts <NUM> upwards out of the cavity <NUM> of the blanking die <NUM> to allow the extraction thereof from the blanking device <NUM>. After such extraction, the blanking device <NUM> returns to its first open state shown in <FIG> etc. <NUM>.

As illustrated in <FIG>, the blanked metal parts <NUM> are extracted individually, or at least as individual, i.e. loose parts in the second open state of the blanking device <NUM>.

In order to be able to extract the blanked metal parts <NUM> from the blanking device as a whole, it is known to interlock these in all of the length, width and thickness directions thereof (i.e. in all <NUM> spatial/physical dimensions) by the local plastic deformation of the strips <NUM> of the layered basic material <NUM> within the contour of the metal parts <NUM> to be blanked. In particular such an interlock <NUM> is created by so-called press-locking, before the layered basic material <NUM> is inserted between the blanking punch <NUM> and the counter punch <NUM> of the blanking device <NUM>.

A possible embodiment of such interlock <NUM> is schematically illustrated in <FIG> in an enlarged cross-section of the layered basic material <NUM>. In this example of the interlock <NUM>, it is essentially shaped predominantly rectangular. In particular a rectangular bulge <NUM> is formed on the layered basic material <NUM> by bending down the two short sides <NUM> of the rectangle and shearing-off its two long sides <NUM>, whilst leaving a rectangular cavity <NUM> in the plane of the layered basic material <NUM>. In this realization of the interlock <NUM>, the relative movement in thickness direction of the individual layers of the basic material <NUM>, i.e. strips <NUM>; <NUM>-T, <NUM>-B is blocked by the sheared long sides <NUM> of the bulge <NUM> at a top layer <NUM>-T of the layered basic material <NUM> catching the sheared long sides <NUM> of a bottom layer <NUM>-B of the layered basic material <NUM> and thus forming a keyed connection there between. In the practical realization of this particular embodiment of the interlock <NUM>, the width of the bulge <NUM> between the said long sides <NUM> typically exceeds such width of the cavity by at least <NUM>%.

In <FIG>, an example of a press-locking method, in particular the press-locking method for forming the interlock <NUM> of <FIG> is schematically illustrated. In a first step of this particular press-locking method -that is illustrated in <FIG>- the layered basic material <NUM> is inserted between a press-locking punch <NUM> with a projection <NUM> and an anvil <NUM> defining a hollow <NUM>. In a second step of the press-locking method -that is illustrated in <FIG>- the projection <NUM> of the press-locking punch <NUM> is pressed into the layered basic material <NUM> -whereby the rectangular cavity <NUM> is formed therein (see <FIG>)- and the basic material <NUM> is displaced downward into the hollow <NUM> in the anvil <NUM> - whereby a protruding bulge <NUM> is formed thereon (see <FIG>). Because the depth of the hollow <NUM> is somewhat less than the thickness of the layered basic material <NUM>, the said bulge <NUM> is expanded sideways, somewhat beyond and thus catches the (long) sides <NUM> of the cavity <NUM>.

In <FIG> the known multi-layer blanking process including the process step of press-locking is schematically illustrated in a plan view of the layered basic material <NUM>, i.e. looking downward in the height direction H thereof. Firstly, in a press-joining stage PJS of the known multi-layer blanking process, multiple (here: four) interlocks <NUM> are formed within the contour of the metal parts <NUM> to be blanked. Once formed, the interlocks <NUM> are transported together with the layered basic material <NUM>, by the said intermitted advancement thereof, to the blanking stage BS. In the blanking stage BS, the metal parts <NUM> (that are depicted as rotor discs <NUM> in <FIG>) are cut out of the layered basic material <NUM> in two subsequent partial cuts. In the first partial cut the central hole <NUM> and the secondary holes <NUM> are cut and in the second partial cut the outer circumference <NUM> of the metal part <NUM> is cut thus finally separating the metal parts <NUM> from the layered basic material <NUM>. By providing the interlocks <NUM> within the contour of the metal parts <NUM>, these are favourably held together after being cut out of the layered basic material <NUM> in the blanking stage BS. In this way, a stacked set of a number of blanked metal parts <NUM> is created, which number of parts <NUM> corresponds to the number of individual layers <NUM> of the layered basic material <NUM>. Moreover, the known interlocks <NUM> promote the synchronising and the mutual alignment of the individual strips <NUM> of the layered basic material <NUM> when it is (intermittedly) advanced as part of the multi-layer blanking process.

Typically, e.g. in case of the electric motor, the end product laminate contains fare more layers (e.g. several hundred layers) than the two layers <NUM> that are included in the said set of blanked metal parts <NUM>, or at more than that can conceivably be cut simultaneously with the multi-layer blanking process. Thus, in practice, a large number of such sets are placed on top of one another in a subsequent process step to form the laminate, whereto the bulge <NUM> of the interlock <NUM> of a first set of blanked metal parts <NUM> is pressed into the cavity <NUM> of the interlock <NUM> of an adjacent, second set of blanked metal parts <NUM>. Hereby, an interference fit is created between these first and second sets of blanked metal parts <NUM>, however at the expense of the positive, i.e. keyed connection between the blanked metal parts <NUM> within each such set.

According to the present invention, this latter disadvantage of the known multi-layer blanking process can be overcome by the novel multi-layer blanking process that is schematically illustrated in <FIG> in a plan view of the layered basic material <NUM> corresponding to that of <FIG>, however, composed of four layers <NUM> of the basic material <NUM> stacked on top of one another. According to the present invention, the metal parts <NUM> are provided with tertiary holes <NUM> in the blanking stage BS. In particular, one such tertiary hole <NUM> is cut for each interlock <NUM> that has been created within the circumference <NUM> of the metal part <NUM> in the preceding press-joining stage PJS. Each such tertiary hole <NUM> is shaped and sized to be able to receive the bulge <NUM> of a respective interlock <NUM>, whereas the number of such tertiary holes <NUM> is at least equal to the number of interlocks <NUM>.

It is an optional feature to also provide one or more interlocks <NUM>-o outside the contour of the metal parts <NUM> to be blanked, as illustrated in <FIG> as well. By this latter feature, the synchronising and the mutual alignment of the individual strips <NUM> of the layered basic material <NUM> is favourably enhanced further, e.g. also after the set <NUM> of metal parts <NUM> has been separated therefrom in the blanking process step.

In <FIG> two stacked sets <NUM>; <NUM>-<NUM>, <NUM>-<NUM> of blanked metal parts <NUM> obtainable with the novel multi-layer blanking process of <FIG> are schematically illustrated, both in a plan view and in a side elevation. In the side elevations, the tertiary holes <NUM> are indicated by a pair of dashed lines each, whereas the central hole <NUM>, the secondary holes <NUM> and the cavity <NUM> of the interlocks <NUM> are not indicated therein for clarity.

In accordance with the present invention, the bulges <NUM> of the interlocks <NUM> of the first set <NUM>-<NUM> of blanked metal parts <NUM> are aligned with the tertiary holes <NUM> of the second set <NUM>-<NUM> of metal parts <NUM> before these are placed on top of one another to (at least partly) form the laminate. Hereby, the bulges <NUM> of the interlocks <NUM> of the said first set <NUM>-<NUM> are inserted in the tertiary holes <NUM> of the said second set <NUM>-<NUM> neighbouring it, favourably without exerting a substantial compressive force on the interlock <NUM>, in particular on the said bulge <NUM> thereof.

Preferably, the blanked metal parts <NUM> of each set <NUM>-<NUM>, <NUM>-<NUM> are identically shaped, such that these can be manufactured cost-effectively with only one blanking device <NUM>. In this case, the interlocks <NUM> and tertiary holes <NUM> are arranged in a regular geometric pattern, for example equally spaced on the circumference of a virtual circle. The embodiment of the rotor disc <NUM> that is illustrated in <FIG> satisfies such preference, since a first set <NUM>-<NUM> of metal parts <NUM> is identical to a second set <NUM>-<NUM> of metal parts <NUM> after it has been rotated over an angle α of <NUM> degrees clockwise (or a positive or negative odd multiple thereof).

In addition to being rotated relative to the said second set <NUM>-<NUM>, the said first set <NUM>-<NUM> can also be flipped upside down before being placed against the said first set <NUM>-<NUM> to (at least partly) form a laminate <NUM>. Hereby, not only the bulges <NUM> of the interlocks <NUM> of the said first set <NUM>-<NUM> are inserted and/or received in the tertiary holes <NUM> of the said neighbouring, second set <NUM>-<NUM>, but also vice versa. In principle every other set <NUM>-<NUM> in the laminate <NUM> can be flipped in this way, which particular mutual arrangement of the two types <NUM>-<NUM>, <NUM>-<NUM> of sets <NUM> of metal parts <NUM> is schematically illustrated in <FIG>. Alternatively, the laminate <NUM> (or a section thereof) can be started (or finished) with a starting set <NUM>-s of metal parts <NUM> that is not provided with the interlocks <NUM>, such that no bulges <NUM> protrude to the outside of the laminate <NUM>, while a relative rotation between favourably all sets <NUM>; <NUM>-<NUM>, <NUM>-<NUM>, <NUM>-s thereof is still limited to a clearance between the bulges <NUM> and the tertiary holes <NUM> that can be small. This particular arrangement of the laminate <NUM> is schematically illustrated in <FIG>. However, for the same purpose of realising that the bulges <NUM> do not protrude to the outside of the laminate <NUM>, it is also possible to either:.

Either one of these latter two arrangements favourably avoids an interference between the bulges <NUM> of the said starting set <NUM>-s and those of the said other neighbouring stack <NUM>-<NUM>*.

As mentioned above, the surface area of the tertiary hole <NUM> should be large enough to receive the bulge <NUM> of the interlock <NUM> that is to be inserted therein. A mutual bonding and/or fixation of the sets <NUM> of metal parts <NUM> relative to one another in the laminate <NUM> can in this case be realised by gluing or welding, or, at least in case of the rotor discs <NUM>, by inserting the rotor shaft through the central holes <NUM> of the metal parts <NUM>. Ideally, however, the bulges <NUM> are received in the tertiary holes <NUM> with an interference fit, such that not only the relative rotation between all sets <NUM>; <NUM>-<NUM>, <NUM>-<NUM>, <NUM>-s of metal parts <NUM> in the laminate <NUM> is favourably prevented, but also their relative displacement in the height direction of the laminate <NUM>, i.e. in a stacking direction. Such interference fit F can, for example, be realised by at least locally providing the tertiary hole <NUM> with a breadth B that is somewhat smaller than a local width W of the bulge <NUM>, as is schematically illustrated in <FIG>. Quantitatively speaking, such local width W of the bulge <NUM> preferably exceeds the local breadth B of the hole <NUM> by <NUM> to <NUM>%, more preferably by <NUM> to <NUM>%. Hereby, a tearing of the hole <NUM> is prevented, even for the presently considered relatively thin layers <NUM> of the layered basic material <NUM>.

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 <NUM> of the layered basic material <NUM> in all three dimensions by the targeted, i.e. local and controlled plastic deformation thereof. In this respect, <FIG> schematically illustrates a possible alternative embodiment of the interlock <NUM> in an enlarged cross-section of the layered basic material <NUM>. In this example of the interlock <NUM> is realised by an essentially dovetail-shaped joint <NUM> that is circularly symmetric, such that it prevents the strips <NUM> from relative movement in all three dimensions. In this latter embodiment of the interlock <NUM>, its cavity <NUM> is provided with a relatively small dimension in the plane of the layered basic material <NUM> relative to such dimension of its bulge <NUM>. Also in this latter embodiment of the interlock <NUM>, its cavity <NUM> extends over only a part of the height of the layered basic material <NUM>.

Claim 1:
A method for manufacturing a laminate (<NUM>) of mutually stacked metal parts (<NUM>; <NUM>) by means of a multi-layer blanking process, wherein in the multi-layer blanking process successively several layered sets (<NUM>; <NUM>-<NUM>, <NUM>-<NUM>, <NUM>-s) of such metal parts (<NUM>; <NUM>) are cut from a layered basic material (<NUM>), in which subsequently the laminate (<NUM>) is assembled from several such sets (<NUM>; <NUM>-<NUM>, <NUM>-<NUM>, <NUM>-s) of the metal parts (<NUM>; <NUM>), by stacking these, and in which, prior to the multi-layer blanking process, the individual layers (<NUM>) of the layered basic material (<NUM>) are interconnected by plastically deforming them, whereby a bulge (<NUM>) is formed on the layered basic material (<NUM>) within the outer circumference (<NUM>) of the, still to be cut, metal parts (<NUM>; <NUM>), characterized in that the metal parts (<NUM>; <NUM>) are provided with a hole (<NUM>) that is cut in the multi-layer blanking process and that extends completely through the layered basic material (<NUM>) and in that when the laminate (<NUM>) is assembled, the bulge (<NUM>) of a first set (<NUM>; <NUM>-<NUM>) of the metal parts (<NUM>; <NUM>) is inserted into the hole (<NUM>) of a second set (<NUM>; <NUM>-<NUM>) of the metal parts (<NUM>; <NUM>).