Patent Description:
In the art it is suggested to improve the process speed, i.e. the production rate of the blanking process for, in particular, relatively thin metal parts by utilising a layered basic material therein. As a result, a number of metal parts is simultaneously blanked with a single stroke of the blanking punch corresponding to the number of layers of the layered basic material. This known, so-called, multi-layer blanking process is for example described in the international patent application <CIT> , on which the preamble of claim <NUM> is based.

According to this document, a counter punch is applied on the opposite side of the layered basic material relative to the blanking punch in order to render such multi-layer blanking process feasible in practice, in particular in terms of the typically required surface quality and/or shape accuracy of the cut side faces of the metal parts. This known multi-layer blanking process is particularly suited for the simultaneous manufacture of a number of sheets, i.e. individual lamina, for a laminate, such as rotor or stator laminations for electric motors.

Although representing a step forward in manufacturing technology, the practicality of the multi-layer blanking process proposed by <CIT> appears to be limited in terms of the complexity of the 2D contour of the metal parts that can be manufactured thereby. In particular, a minimum separation is required between two separate cutting lines. This is because a part of the blanking die that is located between, i.e. which separates two adjacent cutting lines requires a minimum size for the adequate strength and/or rigidity. Also in the known multi-layer blanking process, scrap or waste material, i.e. material that is cut loose from both the layered basic material and from the metal part to form a hole inside the metal parts, is held between the blanking die and the blank holder after the blanking stroke, while the metal parts are held between the blanking punch and the counter punch. Thus, after each blanking stroke the scrap material and the metal parts have to be removed from between the blanking die and the blank holder and from between the blanking punch and the counter punch, respectively. Hereto, the blanking device is opened by moving the blank holder and the blanking punch away from the blanking die and the counter punch, such that the scrap material and the metal parts become accessible from the outside of the device. The scrap material must be removed from the blanking device after each blanking stroke reliably and carefully, in particular keeping it separate from the metal parts. In practice, it can be required that the scrap material and the metal parts are removed from the blanking device sequentially rather than simultaneously, which is detrimental to the production speed of the multi-layer blanking process, i.e. which limits the blanking stroke rate of the blanking device.

The present invention sets out to address the limitations of the known multi-layer blanking process and to favourable improve the practicality thereof, in particular in terms of the process speed/production rate and/or of the complexity of the metal parts that are attainable therewith. The present invention defines a process according to the features of claim <NUM>.

According to the present invention, the metal parts are blanked in two blanking process stages that are carried out in mutual succession and whereof a first blanking stage entails the cutting-out of a hole or a number of holes in the layered basic material without utilizing a counter punch and whereof a second blanking stage entails the cutting-out of the metal parts from the layered basic material utilizing the counter punch. By not applying a counter punch in the said first blanking stage, the scrap material that is cut loose from the layered basic material therein to form the hole(s), can be favourably discarded through the cavity in the blanking die without first having to open the blanking device by moving the blank holder and the blanking punch away from the blanking die. Thus, when the blanking device is opened, the scrap material has already been removed from it and the metal parts can be removed easily and immediately after such opening of the blanking device.

Rather than exchanging the blanking tools between the said first and second blanking stages, the layered basic material is preferably advanced in-between these blanking stages from a first blanking station without a counter punch, which first blanking station carries out the said first blanking stage, to a second blanking station with the counter punch, which second blanking station carries out the said second blanking stage. Preferably, these two blanking stations are both part of a single blanking device, such that the blanking punches and/or the blanking dies of the two blanking stations are actuated in common by a single actuator of the blanking device, such as a hydraulically or mechanically actuated ram. Moreover, depending on the complexity of the metal part, two or more blanking stations of either type, i.e. respectively with and without a counter punch, can be applied to cut and form the complete 2D contour of the metal part by intermittently advancing the basic material form one blanking station to the next.

Preferably, in the said first blanking stage, pilot holes are cut out of the layered basic material outside the contour of the metal part to be blanked. These pilot holes are favourably used in the said second blanking stage to accurately place and hold the layered basic material in the second blanking station by placing these pilot holes over pilot pins fixed to and protruding from either the blanking die or the blank holder.

In the particular case of the rotor or stator laminations for an electric motor, the inner circumference of the stator sheet and/or the outer circumference of the rotor sheet is provided with -and is thus partly constituted by- radially extending slots of/in the stator of the rotor respectively. In the end-product electric motor these slots of the rotor and/or the stator sheets mutually align in axial direction between adjacent sheets of the respective lamination, to accommodate windings of electric wire and/or bars of aluminium or copper in case of an induction type electric motor. According to the present disclosure, each such circumference slot is pre-formed as a hole in the said first blanking stage, i.e. without using a counter punch, whereas the respective stator or rotor sheets are cut loose from the basic material in the said second blanking stage, whereby a respective side of each hole is removed to open up the holes and form the said slots. This particular arrangement of the multi-layer blanking process is particularly effective in case the circumference slots are provided on a relatively fine scale, in particular on a scale that is difficult or impractical to cut and form in the said second blanking stage.

Additionally or alternatively in case of the said rotor or stator lamination sheets, the rotor sheets are preferably formed from the basic material radially inside the stator sheets. In this way, efficient use is made of the basic material, since -at least for a specific end-product electric motor- the outer circumference of the rotor lamination is typically only slightly smaller than in the inner circumference of the stator lamination to maximize the electromagnetic coupling between them. Preferably in this latter setup of the multi-layer blanking process according to the present disclosure, the rotor sheets and the stator sheets are simultaneously cut loose from the basic material in a single instance of the said second blanking process stage. Although in this setup of the multi-layer blanking process a ring of scrap material is formed between the rotor sheets and the stator sheet, this ring is removed from the blanking device together with the stator and rotor sheets after separating the blank holder and the counter punch from the blanking die and the counter punch respectively. In this setup of the multi-layer blanking process, the ring of scrap material and thus also the radial gap ("air gap") between the rotor and stator laminations can be favourably small, i.e. can be relatively thin, e.g. in the order of less than one up to a couple of millimetres. In this respect it is noted that such small gap is generally preferred, because the efficiency of the electric motor is inversely related to the gap width.

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

The <FIG> illustrate a multi-layer blanking process for producing a metal part <NUM>. The <FIG> each represent a simplified cross-section of a blanking device <NUM> that is used to simultaneously, i.e. in a single stroke of the blanking device <NUM>, cutout a number of such metal parts <NUM> from a layered basic material <NUM> comprising two or more (i.e. four in the example of <FIG>) of mutually stacked strips <NUM> of basic material. The blanking device <NUM> includes four tool parts, namely 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>, <NUM>, wherein the blanking punch <NUM> and the counter punch <NUM> are contained, which cavities <NUM>, <NUM> are shaped to correspond to the metal part <NUM>, i.e. to the 2D contour thereof. This particular type of blanking process/blanking device <NUM> using a counter punch <NUM> is known per se, namely as 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 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> the actual cutting out a number of the metal parts <NUM>, as determined by the number of strips <NUM> of basic material of the layered basic material <NUM>, by the forced relative movement of the combination of the blanking punch <NUM> and the counter punch <NUM> relative to the blanking die <NUM>, is schematically illustrated. In particular in <FIG> the blanking device <NUM> is shown during the actual cutting and in <FIG> the blanking device <NUM> is shown after the metal parts <NUM> are cut completely, i.e. after these have been severed from the layered basic material <NUM>, and are still held between the blanking punch <NUM> and the counter punch <NUM> inside the said cavity <NUM> of the blanking die <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>, the layer basic material is lifted of the blanking die <NUM> and wherein the counter punch <NUM> protrudes from the blanking die <NUM> after pushing the 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..

<FIG> provide examples of the metal part <NUM> that can be suitably produced with the aid of the multi-layer blanking process discussed herein. In the example of <FIG>, the metal part <NUM> takes the form of a stator ring <NUM> for an electric motor. In the electric motor a number of such stator rings <NUM> are stacked and clamped or interconnected in axial direction to form a stator lamination. In the presently illustrated, non-limiting, example of the stator ring <NUM>, it is shown to include a series of slots <NUM> that are arranged on and along its inner circumference. These slots <NUM> serve to accommodate windings of electric wire in the electric motor. In the example of <FIG>, the metal part <NUM> takes the form of a rotor disc <NUM> of an electric motor. In the electric motor a number of such rotor discs <NUM> are stacked and clamped or interconnected in axial direction to form a rotor lamination. In the presently illustrated, non-limiting, example of the rotor disc <NUM>, it is shown to include a central hole <NUM>, for accommodating a rotor shaft that extends in axial direction through the whole of the rotor lamination while being fixed thereto, and a number of circumference holes <NUM>, for accommodating permanent magnets that extend in axial direction through the whole of the rotor lamination.

Typically, the dimension of the stator ring <NUM> and/or of the rotor disc <NUM> in axial direction, i.e. its thickness that corresponds to the thickness of the strip <NUM> of basic material, is chosen small to minimise eddy current losses in the electric motor. However, in practice, a smallest achievable, i.e. minimum thickness applies from a process economics point of view, as well as in terms of the technical capability of the blanking process. Nevertheless, by utilising the above-described multi-layer fine blanking process such minimum thickness is smaller than what is achievable with the so-called conventional or progressive blanking process, wherein the counter punch <NUM> is omitted from the blanking device <NUM> and a blanked metal part <NUM> is discharged via the cavity <NUM> of the blanking die <NUM>.

In particular compared to the conventional blanking process, the said multi-layer fine blanking process comes with the limitation that after the cutting out of the metal parts <NUM>; <NUM>, <NUM>, the scrap material from the cut slots <NUM> of the stator ring <NUM> or from the cut holes <NUM>; <NUM> of the rotor disc <NUM>, as well as the blanked metal parts <NUM>; <NUM>, <NUM> themselves are still held between the upper tool parts <NUM>, <NUM> and the lower tool parts <NUM>, <NUM> of the blanking device <NUM>. As a result, complications arise in the extraction step illustrated in <FIG>, i.e. when removing all of the layers of the said scrap material and the metal parts <NUM> from the blanking device <NUM>, in particular to remove these reliably, quickly and without damage. Removing the scrap material <NUM> and the blanked metal parts <NUM>, <NUM>; <NUM> in the said extraction step becomes even more complicated, almost impractical, when the rotor disc <NUM> is formed radially inside the stator ring <NUM>, as illustrated in <FIG> in a frontal view of the layered basic material <NUM>. In this nested arrangement of the rotor disc <NUM> and the stator ring <NUM>, additionally a thin ring <NUM> of scrap material is to be removed from between them, further complicating the said extraction step. Still, such a nested arrangement is preferred in principle to optimise the utilisation rate of the strips <NUM> of basic material of the layered basic material <NUM>.

As an improvement of the above-described known multi-layer fine blanking process, it is presently proposed to precede it by a multi-layer conventional blanking process. In other words the present disclosure provides for a novel multi-layer blanking process that is schematically illustrated in <FIG> by way of a blanking device <NUM>, which novel multi-layer blanking process is executed in at least two stages I and II.

In a first stage I of the novel multi-layer blanking process, a part or parts of the contour of the metal parts <NUM> is cut from the layered basic material <NUM> by conventional blanking, i.e. without applying a counter punch opposite a first blanking punch <NUM>. In a second stage II of the novel multi-layer blanking process, a remaining part or parts of the contour of the metal parts <NUM> is cut from the layered basic material <NUM> by fine blanking, i.e. with applying a counter punch <NUM> opposite a second blanking punch <NUM>. The contour part or parts that are cut in the said first stage I by the first blanking punch <NUM> represent holes <NUM> that are formed in the layered basic material <NUM> by removing correspondingly shaped pieces of scrap material <NUM>. These pieces of scrap material <NUM> are removed from the layered basic material <NUM> by being ejected through the blanking die <NUM>. In the said second stage II, the circumference of the metal parts <NUM> is formed, at least is completed by the second blanking punch <NUM>. The thus finally formed metal parts <NUM> are extracted from between the second blanking punch <NUM> and the counter punch <NUM> after opening the blanking device <NUM> (see also <FIG>). In between the two blanking stages I, II, the blanking punches <NUM>, <NUM> are retracted in the blank holder <NUM> and the layered basic material <NUM> is stepwise advanced in the direction from the first blanking station <NUM> towards a second blanking station <NUM>.

Preferably and as illustrated in <FIG>, the said two blanking stages I, II are carried out in subsequent blanking stations <NUM>, <NUM> of the single blanking device <NUM> and the respective blanking punches <NUM>, <NUM> are operated in common relative to the blanking dies <NUM>, preferably by means of a single ram <NUM> of the device <NUM>. In <FIG> the ram <NUM> is shown to act on and thus to move the blanking punches <NUM>, <NUM>, while the blanking dies <NUM> are fixed in place. However, since only the relative movement between the blanking punches <NUM>, <NUM> and the blanking dies <NUM> is of concern, the ram <NUM> can just as well act on the blanking dies <NUM>, while the blanking punches <NUM>, <NUM> are fixed in place. Moreover, the blanking device <NUM> may also be embodied with separate rams for moving the respective blanking punches <NUM>, <NUM> and/or the respective blanking dies <NUM> (embodiment not illustrated).

Further in relation to <FIG> it is noted that, generally speaking, in any blanking process the cut edges are formed relatively sharply on one side (the so-called burr side) of the blanked metal parts <NUM> and relatively smoothly/smoothly curved (the so-called rollover side) on the respective opposite side thereof. However, these burr and rollover sides are typically located on opposite sides of the metal parts <NUM> between the conventional and the fine blanking processes. In particular, in the first, conventional blanking stage I of the novel multi-layer blanking process, the rollover is formed on the side of the metal parts <NUM> facing upward in <FIG>, i.e. towards the blank holder <NUM> and/or the first blanking punch <NUM> and the burr is formed on the side of the metal parts <NUM> facing downward towards the blanking die <NUM>. On the other hand, in the second, fine blanking stage II of the novel multi-layer blanking process, the rollover is formed on the side of the metal parts <NUM> facing downward in <FIG>, i.e. towards the blanking die <NUM> and/or counter punch <NUM> and the burr is formed on the side of the metal parts <NUM> facing upward towards the blank holder <NUM> and/or the second blanking punch <NUM>.

In <FIG>, the novel multi-layer blanking process is schematically illustrated in a top view of the layered blanking basic material <NUM> in a first possible application thereof for the manufacture of the rotor disc <NUM>. In the first stage I of the novel multi-layer blanking process, scrap material <NUM> is removed from the layer basic material <NUM> by the first blanking punch <NUM> to form the central hole <NUM> and the circumference holes <NUM> of the -still to be finally formed- rotor disc <NUM>. In the second stage II of the novel multi-layer blanking process, the rotor disc <NUM> is formed while being supported by the counter punch <NUM>, by the second blanking punch <NUM> cutting its outer circumference <NUM>.

In <FIG>, the novel multi-layer blanking process is schematically illustrated in a top view of the layered blanking basic material <NUM> in a second possible application thereof for the manufacture of the stator ring <NUM>. In the first stage I of the novel multi-layer blanking process, scrap material <NUM> is removed from the layer basic material <NUM> by the first blanking punch <NUM> to pre-form the slots <NUM> of the -still to be finally formed-stator ring <NUM> as separate, radially oriented holes <NUM>. In the second stage II of this second possible application of novel multi-layer blanking process, the stator ring <NUM> is finally formed while being supported by the counter punch <NUM>, by the second blanking punch <NUM> simultaneously cutting both the inner circumference <NUM> and the outer circumference <NUM> thereof. In this second stage II, the radial holes <NUM> representing the pre-formed slots <NUM> are opened up by the cutting of the inner circumference <NUM> of the stator ring <NUM>.

It is noted that the said first stage I of multi-layer conventional blanking and possibly also the said second stage II of multi-layer fine blanking can be subdivided into two or more sub-stages of the respective stage I, II. In such arrangement of the novel multi-layer blanking process a blanking sub-station is provided for each sub-stage. In particular in case of an end-product having a relatively complicated 2D contour it can be convenient or necessary even to carry out a respective stage I, II in two or more subsequent steps, i.e. sub-stages. For example, in case of the rotor discs <NUM> and the stator rings <NUM> of a specific end-product electric motor, these cannot easily be blanked from the layered basic material <NUM> in a mutually concentric placement, as is preferred in principle. This limitation occurs not only because the shape or 2D contour of these parts can be too complex to be fully incorporated into only the said first and second blanking punches <NUM>, <NUM>, but also because the scrap ring <NUM> has to be accurately formed -and removed from- between the rotor disc <NUM> and the stator ring <NUM> to provide a radial gap there between in the end-product electric motor. In <FIG> it is illustrated to subdivide both the first stage I and the second stage II of the novel multi-layer blanking process into three sub-stages I-<NUM>, I-<NUM>, I-<NUM> and II-<NUM>, II-<NUM>, II-<NUM>. This particular, illustrated setup of the overall novel blanking process is, however, only an example: other subdivisions are conceivable.

In <FIG>, in sub-stage I-<NUM> the slots <NUM> of the stator ring <NUM> are pre-formed as radial holes <NUM>, in sub-stage I-<NUM> the circumference holes <NUM> of the rotor disc <NUM> are formed and in sub-stage I-<NUM> the central hole <NUM> of the rotor disc <NUM> is formed. In each such step of punching, the respective holes <NUM>, <NUM>, <NUM> are formed by means of a blanking punch, but without applying a counter punch. Also in <FIG>, in sub-stage II-<NUM> the rotor disc <NUM> is blanked by cutting its outer circumference <NUM>, in sub-stage II-<NUM> the scrap ring <NUM> is blanked by cutting its outer circumference <NUM> that corresponds to the inner circumference <NUM> of the stator ring <NUM> and in sub-stage II-<NUM> the stator ring <NUM> is blanked by cutting its outer circumference <NUM>. In each step of blanking, the respective part <NUM>, <NUM>, <NUM> are formed by means of and while being held between a blanking punch and a counter punch.

As mentioned hereinabove, <FIG> represents only one possible embodiment of the novel blanking process. In particular some of the sub-stages illustrated in <FIG> could possibly be combined with another one, or could possibly be divided into further sub-stages. For example, the forming of the central hole <NUM> of the rotor discs <NUM> could potentially be included in either one of the sub-stages I-<NUM> and I-<NUM>. Moreover, at least the final two sub-stages II-<NUM> and II-<NUM>, however ideally all three of the shown sub-stages II-<NUM>, II-<NUM> and II-<NUM> of the second blanking stage II are preferably carried out simultaneously, i.e. in a single blanking stroke.

If the final two sub-stages II-<NUM> and II-<NUM> that are illustrated separately in <FIG> are combined into one, it is preferable that the stator rings <NUM> are held between the second blanking punch <NUM> and the counter punch <NUM> and the scrap rings <NUM> are held between the blank holder <NUM> and the blanking die <NUM>, rather than the other way round. In this case, the thin scrap rings <NUM> are preferably removed from the blanking device <NUM> before the stator rings <NUM>. In particular, departing from the state of the blanking device <NUM> corresponding to <FIG>, first the upper tool parts <NUM>, <NUM> of the blanking device <NUM> are moved relative to and away from its lower tool parts <NUM>, <NUM>, however, without raising the counter punch <NUM> relative to the blanking die <NUM>. In this state of the blanking device <NUM> the scrap rings <NUM> can be removed, e.g. by a forced air flow. Only thereafter, the counter punch <NUM> is moved relative to the blanking die <NUM>, to raise the stator rings <NUM> above the blanking die <NUM>. In this state of the blanking device <NUM> that corresponds to the state illustrated in <FIG>, the stator rings <NUM> can be removed, preferably carefully for example by means of a mechanical gripper.

If all of the three sub-stages II-<NUM>, II-<NUM> and II-<NUM> that are illustrated separately in <FIG> are combined into one, it is preferably that both the stator rings <NUM> and the rotor discs <NUM> are held between the second blanking punch <NUM> and the counter punch <NUM>, rather than between the blank holder <NUM> and the blanking die <NUM>. In this case and as part of the second blanking stage II, the scrap rings <NUM> are preferably removed first from the blanking device <NUM> in the above manner, i.e. by opening the blanking device <NUM> without raising the counter punch <NUM> relative to the blanking die <NUM>. Thereafter, the stator rings <NUM> and the rotor discs <NUM> are preferably removed from the blanking device in succession by successively moving the counter punches <NUM> associated with the stator rings <NUM> and the rotor discs respectively and thus successively raising these above the blanking die <NUM> for their successive removal from the blanking device <NUM>.

Furthermore, the above-discussed combinations of the sub-stages II-<NUM>, II-<NUM> and II-<NUM> of the second blanking stage II, can be facilitated by either one or both of the following detailed features of the novel multi-layer blanking process according to the present disclosure.

A first such detailed feature is illustrated in <FIG>. This first detailed feature entails the extension of a number of the radial holes <NUM> that are cut in the first blanking stage I in radial inward direction. In particular, such an extended radial hole <NUM>' is dimensioned to fully, or at least almost fully, bridge the radial gap between the stator ring <NUM> and the rotor disc <NUM> that will be cut later in the second blanking stage II. It is noted that in the illustration of the second blanking stage II in <FIG>, the holes <NUM>, <NUM>' formed in the first blanking stage I are drawn in solid black.

In this particular arrangement of the multi-layer blanking process, when the outer circumference <NUM> of the rotor disc <NUM> and the inner circumference <NUM> of the stator ring <NUM> are cut, the ring-shaped scrap material between the rotor disc <NUM> and the stator ring <NUM> does not form a closed ring, but rather one or more scrap ring sections or fragments <NUM>'. According to the present disclosure, such scrap ring fragments <NUM>' are easier to remove from the blanking device <NUM>, i.e. from in-between the blank holder <NUM> and the blanking die <NUM>, than a closed ring that can hook around an edge or other protruding part of the blanking device <NUM>. Obviously, the number of scrap ring fragments <NUM>' formed in the second blanking stage II corresponds to the number of extended radial holes <NUM>' applied in the first blanking stage I. Preferably, the extended radial holes <NUM>' are approximately equally distributed amongst the total number of radial holes <NUM>. Preferably also, the number of extended radial holes <NUM>' is between <NUM> and <NUM>. Obviously, with only <NUM> extended radial hole <NUM>', only one scrap ring fragment <NUM>' is formed that is still relatively unfavourable to remove from blanking device <NUM>. However, as the number of extended radial holes <NUM>' increases, the scrap ring fragments <NUM>' formed become smaller, which can complicate the removal thereof as well.

A second detailed feature of the novel multi-layer blanking process according to the present disclosure is illustrated in <FIG>. This second detailed feature entails the provision of radially extending reinforcement ribs <NUM> to a relatively thin, cylindrically-shaped tool part (or tool parts) <NUM>' of the blanking device <NUM> that acts against the layered basic material <NUM> in the radial gap between the stator ring <NUM> and the rotor disc <NUM> to be formed, i.e. which blanking tool part <NUM>' supports the said scrap rings <NUM> (or the scrap ring fragments <NUM>') as these are cut loose from the rest of the layered basic material <NUM> in the second blanking stage II. Thus, in the above-mentioned arrangement of the blanking device wherein the scrap rings <NUM> are held between the blank holder <NUM> and the blanking die <NUM>, the said blanking tool part <NUM>' provided with the reinforcement ribs <NUM> corresponds to at least a part of either the blank holder <NUM>, the blanking die <NUM> or both. However, in principle, it is also possible to arrange the second blanking stage II of the novel multi-layer blanking process such that the scrap rings <NUM> are held between the second blanking punch <NUM> and the counter punch <NUM>, in which case the reinforcement ribs <NUM> are provided to either one of the second blanking punch <NUM>, the counter punch <NUM> or both.

As illustrated in <FIG>, in a cross section of the blanking device <NUM>, the relatively thin, cylindrically-shaped part <NUM>' of the blank holder <NUM> is located between two second blanking punches <NUM>', <NUM>" of the second blanking station <NUM> that respectively act on the rotor discs <NUM> and on the stator rings <NUM>. The said cylindrically-shaped blank holder part <NUM>' thus supports the scrap rings <NUM> in the second blanking stage II. A further part <NUM>" of the blank holder <NUM> encloses all three aforementioned blanking tool parts <NUM>', <NUM>", <NUM>' of the blanking device <NUM>. Axially opposite the cylindrically-shaped blank holder part <NUM>', a likewise thin and cylindrically-shaped part of the blanking die <NUM> is located (not shown). The thickness of these cylindrically-shaped parts <NUM>' of the blanking holder <NUM> and the blanking die <NUM> respectively, are bound to a minimum by the required strength and rigidity thereof, such that the (minimum) width of the scrap ring <NUM> and the radial gap between the rotor and stator laminations are similarly bound.

According to the present disclosure, the strength and rigidity of at least the blank holder <NUM> and preferably also the blanking die <NUM>, can be favourably improved by providing the respective cylindrically-shaped part <NUM>' thereof with radially oriented reinforcement ribs <NUM>, whereof a tangential placement corresponds to that of the radial holes <NUM> that were cut in layered basic material <NUM> in the first blanking stage I to pre-form the radial slots <NUM> on the inner circumference of the stator discs <NUM>. This second detailed feature is schematically illustrated in <FIG>, whereof <FIG> does not include the said two second blanking punches <NUM>', <NUM>" to make visible the layered basic material <NUM> located there below.

Obviously, the reinforcement ribs <NUM> are highly advantageous in strengthening the blank holder <NUM> and thereby allow the cylindrically-shaped part <NUM>' thereof to be provided with a minimal width, which favourably translates to the scrap ring <NUM> and the air gap likewise having a minimal width. This second detailed feature makes favourable use of the two stage approach of the novel multi-layer blanking process according to the present disclosure. Preferably, the reinforcement ribs <NUM> are each dimensioned somewhat smaller than a corresponding radial hole <NUM> to avoid interference with the cut edges thereof. Moreover, not every radial hole <NUM> needs to utilised this way, i.e. the number of the reinforcement ribs <NUM> may be smaller than the number of radial holes <NUM>, as is indeed the case in <FIG>.

Claim 1:
A process for the blanking of metal parts (<NUM>; <NUM>, <NUM>) provided with one or more holes (<NUM>, <NUM>) and/or one or more slots (<NUM>) from a layered basic material (<NUM>), wherein the metal parts (<NUM>; <NUM>, <NUM>) are blanked from the layered basic material (<NUM>) with the aid of a blanking station (<NUM>), which blanking station (<NUM>) is provided with a blank holder (<NUM>) and with a blanking die (<NUM>), each of which defines a cavity (<NUM>; <NUM>) with a contour shape corresponding to that of the metals parts (<NUM>; <NUM>, <NUM>) to be blanked and with a blanking punch (<NUM>) and a counter punch (<NUM>) contained therein, whereof the blank holder (<NUM>) and the blanking die (<NUM>), on the one hand, and the blanking punch (<NUM>) and the counter punch (<NUM>), on the other hand, are movable with respect to each other, to which end the layered basic material (<NUM>) is first clamped between the blank holder (<NUM>) and the blanking die (<NUM>) on the one hand and the blanking punch (<NUM>) and the counter punch (<NUM>) on the other hand and, thereafter, the blanking punch (<NUM>) is moved through the successive layers (<NUM>) of the layered basic material (<NUM>), while this is supported by the counter punch (<NUM>), and thereby cuts loose a single metal part (<NUM>; <NUM>, <NUM>) from the surrounding basic material (<NUM>) per such layer (<NUM>), characterized in that, prior to such cutting loose of the metal parts (<NUM>; <NUM>, <NUM>), one or more holes (<NUM>; <NUM>, <NUM>, <NUM>) are punched into the layered base material (<NUM>) with the aid of a further blanking station (<NUM>), which further blanking station (<NUM>) is likewise provided with a blank holder (<NUM>) and with a blanking die (<NUM>), each of which defines an opening with a contour shape corresponding to that of the holes (<NUM>; <NUM>, <NUM>, <NUM>) to be punched and with a further blanking punch (<NUM>) contained therein, whereof the blank holder (<NUM>) and the blanking die (<NUM>) are movable with respect to the further blanking punch (<NUM>), to which end the layered base material (<NUM>) is first clamped between the blank holder (<NUM>) and the blanking die (<NUM>) and, thereafter, the further blanking punch (<NUM>) is moved through the successive layers (<NUM>) of the layered basic material (<NUM>) and thereby cuts loose a piece of scrap material (<NUM>) from the surrounding basic material (<NUM>) per such layer (<NUM>) without utilizing a counter punch.