NL2030189B1 - A die pair for manufacturing a 3d-shaped plate by press forming, a die of the die pair and a press-forming method using the die pair - Google Patents

Abstract

The present invention relates to a die pair (20, 21) consisting of an upper die (20) or punch and a lower or counter die (21) for press forming plate material (10) between such upper and lower dies (20, 21), whereof at least one die (20; 21) has a profiled working surface (22) with relatively raised parts (24) and relatively recessed parts recessed parts (23). According to the present invention, the said relatively raised parts (24) are each provided with a protruding edge (30) between a top surface (31) and a side surface of that relatively raised part (24).

Description

A DIE PAIR FOR MANUFACTURING A 3D-SHAPED PLATE BY PRESS FORMING,

A DIE OF THE DIE PAIR AND A PRESS-FORMING METHOD USING THE DIE PAIR

The present invention relates to a die pair consisting of an upper die and a lower (counter) die for press forming plate material between such upper and lower dies, perpendicular to the main plane thereof, which press-forming method is also known as embossing or 3D shaping in general. Typically during such press forming, one die of the die pair is moved relative to the other die of the pair that is fixed in place, which moveable die is commonly referred to as a punch. Press-formed, i.e. 3D-shaped plates are used in many applications, such as in construction, in heat exchange devices and in electrochemical devices, in particular as so-called fluid distribution plates in such devices that are also referred to as separator plates or bipolar plates.

Typically when press forming, a flat, relatively thin plate is used as a starting material, into which corrugations are pressed perpendicular to the main plane of the plate. In particular in case of the said fluid distribution plates, these corrugations constitute a so-called flow field for fluid, composed of channels located between relatively protruding islands, ridges, etc. that are provided on a relatively fine scale in the main plane of the plate (i.e. small corrugation pitch) and on a relatively large scale perpendicular thereto (i.e. large corrugation depth/height). That is to say that a width dimension of a single channel of the plate corrugations is typically small compared to its depth or height dimension, while all of these three dimensions are multiples of the plate thickness. The starting material can be a plastic, but in many of the said applications (sheet) metal is the preferred starting material.

An early example of the fluid distribution plate for an electrochemical cell is provided by the international (patent) application publication W09516287 A1. In the electrochemical cell, the channels defined by the plate corrugations carry reactants and/or coolant along a so-called active area of the device to and from through-holes in the plate for the supply and discharge thereof. The channels of the plate corrugations allow fluid communication with an electrode or other porous layer, whereas the ridges thereof supports and fixates such porous layer in the electrochemical device.

Moreover, the plate corrugations can also serve to contain a sealing or gasket between the plate and the porous layer or between two adjoining plates. In a typical manufacturing process of the separator plate, the said through-holes in the starting material are pierced through first. Then the said plate corrugations are created by press forming the fluid distribution plate between the dies of the said die pair. Finally, the outer circumference of the fluid distribution plate is cut, for example by means of laser cutting or blanking. In particular in case of so-called fine-blanking, the punch and counter punch that are applied in such well-known fine-blanking process may serve as the presently considered die pair for 3D-shaping.

The working surface -being the surface facing and/or engaging the plate- of at least one die of the die pair is thereto provided with a surface profile defined by relatively raised and relatively recessed parts of the respective die, corresponding to the desired 3D shape of the plate. In case of so-called rubber pad (press) forming only one die of the die pair is provided with such profiled working surface. However, commonly the working surfaces of both dies of the die pair are provided with respective surface profiles that are mutually complementary to one another, such that the raised parts of one die correspond with the recessed parts of the other die and vice-versa. More specifically, such complementary die pair can be designed as a so- called closed tooling or open tooling.

In a closed (press forming) tooling, the dies of the die pair are designed to engage the plate directly opposite one another, at least in an ultimate, i.e. fully closed position of the press-forming tooling including such die pair during the press forming of the plate. In this case, the material of the plate is compressed somewhat between the dies, such that it can plastically flow transversely thereof. Typically, the top and bottom sections of the corrugations (that typically remain essentially oriented in the main plane of the plate) are compressed in this way, such that some material thereof flows into wall sections thereof (that each extend between respective top and bottom sections at an angle relative to the main plane of the plate). This specific setup of press forming with the closed tooling can counteract a tearing of the plate material, i.e. can enable a favourably relatively sharp transition/sharp curvature between the wall sections and the top and bottom sections of the corrugations. On the other hand, the relatively high forces exerted by and between the dies of the closed tooling can result in relatively high tool wear.

The USA patent US 9,364,883 B2 describes a variant of the closed tooling. In this variant, the said wall sections of the corrugations are compressed between the dies of the die pair, rather than the top and bottom sections thereof. Hereby, potentially, the corrugation depth can be increased without tearing of the plate material. Furthermore, US 10,150,152 B2 describes a fully closed tooling, wherein both the top and bottom sections and the wall sections of the corrugations are compressed between the dies. Both these latter two variants, however, will be accompanied by even higher forces and more wear than the aforementioned, conventional closed tooling.

In an open (press forming) tooling, the dies of the die pair are designed to engage the plate only through the said raised parts of the respective working surfaces thereof, even in an ultimate, i.e. closest together position thereof in the press-forming tooling during the press forming of the plate. In this case, the plate is not compressed, but rather is bent and stretched by and around the raised parts of the dies. This specific setup of press forming can reduce tool wear. However, a known limitation of the open tooling is that the corners/transitions of the corrugations between the wall sections and the top and bottom sections thereof, cannot be as sharply curved when using the open tooling, as compared to the closed tooling. Moreover, since the top and bottom sections of the corrugations are engaged only on the (concave) inside thereof, i.e. are engaged by only one of the dies of the die pair, these will be more or less convexly/concavely shaped when using the open tooling. Therefore, if relatively sharp corrugation corners are required and/or if relatively flat top and bottom corrugation sections are required, the closed tooling is to be preferred. Nevertheless, also when using the closed tooling, the plate corrugations will necessarily deviate from a theoretically rectangular shape, due to bending contraction in press forming and/or elastic spring-back after press forming.

The present invention aims to improve upon the known press-forming method and closed tooling thereof. In particular, the present invention aims to improve upon the flatness of the top and/or bottom sections of the resulting plate corrugations, specifically in relation to relatively thin (and thus relatively easy to tear) metal plate in combination with corrugations on a relatively fine scale. In this latter respect, the present invention specifically relates to fluid distribution plates having a thickness of 0.05 to 0.5 mm, having a corrugation pitch of 1 to 10 mm and having a corrugation depth that exceeds the plate thickness by a factor of 2 to 8. Such flatness of the corrugation top and/or bottom sections is sought after as this can improve the mechanical and electrical contact between the corrugated plate and the said porous layer or another, i.e. adjoining plate.

According to the present invention, at least one of the relatively raised parts of the working surfaces of the dies of the die pair is provided with a protruding edge that protrudes beyond a central section of a top surface of that respective relatively raised part, located adjacent to such protruding edge. In other words, such central section of the respective relatively raised part is recessed relative to a corner section thereof. By this protruding edge, a respective corrugation corner is additionally compressed on the (concave) inside thereof between the dies during press forming, at least relative to a respectively adjacent top and/or bottom section of the corrugation that is engaged by the relatively lower lying central section of the top surface of that one raised part. As a result, the said bending contraction and/or the said elastic spring-back of the respective corrugation corner are favourably reduced. Hereby, the flatness of the (outside of the) top and/or bottom section of the respective plate corrugations can be favourably improved and/or the respective plate corrugations can be favourably more rectangularly shaped.

Preferably according to the present, such protruding edge is provided on both sides of that one raised part, more preferably on both sides of all of the relatively raised parts of the working surfaces of the dies in question and most preferably on both sides of all of the raised parts of the working surfaces of both dies of the die pair.

Furthermore and in accordance with a preferred aspect of the present invention, a height difference between the said protruding edge of a respective raised part and the adjacent, lower lying, central section of the top surface thereof, amounts to between 10% and 60% of the plate thickness, in particular to between 20% to 40% of such thickness, more in particular to about 30% such thickness. These (relative) heights of the protruding edges were found to provide the best result in terms of the reduction of the bending contraction versus required pressing force exerted by and between the dies of the die pair when press forming the corrugated plate.

In accordance with another preferred aspect of the present invention, a peak, i.e. most protruding part of the said protruding edge is shaped as a flat surface, preferably extending in parallel with a corresponding recessed part of the working surface of the opposing die of the die pair, the bottom surface of which recessed part is likewise shaped as a flat surface. By such flat peak region the protruding edge has sufficient strength for it to be formed cost-effectively by abrasively removing material at the location of the said relatively lower lying, central section of the top surface of the respective raised part, such as by milling. Alternatives to milling are, for instance, electrical discharge machining EDM and laser ablation, which latter processes typically allow the said protruding edge to be shaped with smaller and/or sharper details compared to milling.

In the following, the press forming die and the press-forming method according to the present invention are explained further and in more detail by way of example embodiments and with reference to the drawings, whereof:

Figure 1 schematically depicts a typical example of a known fluid distribution plate defining fluid channels on both sides thereof by virtue of being provided with corrugations;

Figure 2 is a schematically drawn, cross-sectional view of a part of a die pair of the known press-forming tooling prior to press forming the corrugated plate, illustrating the surface profile of the working surface of the dies thereof;

Figure 3 provides the same cross-sectional view of the known die pair as in figure 2 however in a fully closed position of the press-forming tooling; 5 Figure 4 is a photograph of a cross-section of a thin, corrugated plate that is typically obtained with the known press-forming tooling;

Figure 5 is a schematically drawn, cross-sectional view of a part of a novel die pair in accordance with the invention, illustrating the surface profile of the working surfaces thereof;

Figure 6 provides the same cross-sectional view of the novel die pair as in figure 5 however in a fully closed position of a press-forming tooling constituted thereby;

Figure 7 represents a cross-section of a thin, corrugated plate that is obtained with the die pair according to the invention; and

Figure 8 schematically illustrates several principle shapes of a protruding edge of a raised part of a die of the die pair according to the invention.

In figure 1, a generic example of fluid distribution plate 1 is illustrated, such as is used as a separator in a stack of electrochemical cells. The fluid distribution plate 1 has flat outer rim 2 and a central, so-called active area 3 that is 3D-shaped. The outer rim 2 of the plate 1 is provided with circular holes 4 for accommodating bolts that hold the stack together and with oblong holes 5 for the supply and discharge of (fluid) reactants and/or coolant to and from the said active area 3 of the plate 1. In the shown example of the fluid distribution plate 1, the active area 3 is composed of multiple channels and multiple ridges oriented in parallel. Moreover, the channels on one main side of the plate 1 represent the ridges on the other main side thereof and vice-versa.

The 3D-shape of the active area 3 of the fluid distribution plate 1, i.e. the concavely shaped channels 6 and the convexly-shaped ridges 7 thereof is typically created by press forming plate material 10 between an upper die 20 and a lower die 21 of a die pair, which dies 20, 21 are thereto moved together with the plate material 10 placed therebetween, as schematically illustrated in figures 2 and 3.

In figures 2 and 3, the dies 20, 21 of the die pair and the plate material 10 are illustrated in a cross-section of a relevant part thereof. The working surface 22 -being the surface 22 that faces and at least in part engages the plate material 10- of both dies 20, 21 is provided with a surface profile that is defined by relatively recessed parts 23 of the dies 20, 21, located between relatively raised parts 24 thereof. The working surface 22 of the dies 20, 21 are mutually complementary in the sense that the raised parts 24 of one of the dies 20, 21 can fit into the recessed parts 23 of the respective other one die. The known raised parts 24 are provided with a flat top surface and the known recessed parts 23 are provided with a flat bottom surface.

When the dies 20, 21 of the die pair are moved towards each other the plate material 10 is permanently deformed, i.e. is plastically bent and stretched around the said raised parts 24 of the working surfaces 22 thereof. In figure 3 the dies 20, 21 of the die pair are illustrated in their ultimate position of press-forming, wherein the corrugations of the active area 3 of the fluid distribution plate 1 is completely formed. In such ultimate position of the dies 20, 21, a mutual separation S remaining there between can be larger than a thickness T of the plate material 10 indicated in figure 2 (so-called open tooling; not illustrated), or equal to or marginally smaller than such thickness T (so-called closed tooling; illustrated in figure 3).

Even though with the closed tooling that is illustrated in figure 3, the plate material 10 is somewhat compressed between the dies 20, 21 of the die pair, practical limitations apply to the shape and scale of the said plate corrugations. For example, corners 25 of the plate corrugations are stretched more during press forming than other parts thereof, such that locally the plate material 10 will contract in thickness direction, as is visible in the enlarged section of figure 3. Also, a varying amount of elastic spring-back can occur in such corrugation corners 25, which can cause the fluid distribution plate 1 to warp when it is removed from (between) the dies 20, 21 of the die pair. Moreover, a minimum bending radius and a maximum (enclosed) angle apply to the corrugation corners 25 in order to avoid a tearing of the plate material 10 during press forming. As a result, the corrugations will necessarily deviate considerably from a rectangular prismatic shape that may be theoretically preferred.

Figure 4 provides a photographic representation of a cross-section of the active area 3 of the fluid distribution plate 1 obtained in practice with the above-described, known press-forming method and press-forming tooling. In figure 4, three limitations of such known method and tooling are observable

Firstly, the arrow A indicates an area, in particular a corrugation corner 25, where a substantial bending contraction occurred in thickness direction of the fluid distribution plate 1. As a result, the fluid distribution plate 1 is locally weakened and a minimum bending radius and/or maximum angle disadvantageously applies to such corrugation corner 25 in the design of the fluid distribution plate 1.

Secondly, the arrow B indicates an area, in particular a bottom section 26’ of a respective corrugation, where the corners 25’ of that respective corrugation mutually overlap. As a result, the outside of the said bottom section 26’ is disadvantageously curved, i.e. does not include a flat middle part that is typically preferred or even required in the application. Of course, by broadening the corrugations in the design of the fluid distribution plate 1, such corner overlap can always be avoided. However, such design limitation is undesirable as a matter of principle.

Thirdly, the arrow C indicates an area, in particular a top section 26 of a respective corrugation, where the corner 25 of that respective corrugation disadvantageously shows more elastic spring-back after press forming than the corner 25’ on the opposite side of a wall section 27 of that respective corrugation. As a result, the top section 26 and the bottom section 26° of respectively adjacent corrugations are disadvantageously mutually oriented at an angle rather than in parallel.

The present invention aims to improve the known method for press forming plate material 10. In particular, the present invention aims to address the above-mentioned limitations of the known press-forming and to at least improve upon the flatness of the top and/or bottom section 26; 26’ of the plate corrugations. Hereto the present invention proposes a novel design of at least one of the dies 20, 21 of the die pair, which novel design is illustrated in figures 5 and 6. Figures 5 and 6 provide a cross- sectional view of a press-forming die pair -and of the plate material 10 that is (to be) shaped thereby- similar to those provided by figures 2 and 3, however, with the dies 20, 21 thereof being designed in accordance with the present invention.

According to the invention, the raised parts 24 of the working surfaces 22 of the dies 20, 21 of the die pair are provided with protruding edges 30 that extend beyond a flat top surface 31 of a respective raised part 24 in the height direction thereof. With this novel design of the dies 20, 21 and when these are moved towards each other to 3D shape the plate material 10, these initially arrive in contact with the plate material 10 through the said protruding edges 30. Thus, when the novel dies 20, 21 are moved further towards each other, a force is exerted on the plate material 10 at the location of the said corrugation corners 25 and specifically on the inside, i.e. the concave side thereof. This has the effect that during such press-forming/3D-shaping, material is favourably displaced to the outside of the corrugation corners 25, whereby the said bending contraction at the outside, i.e. the convex side thereof is counteracted, at least in part. In this latter respect it is noted that, by providing the protruding edge 30 with an appropriate, in particular at least partly convexly rounded shape, such material displacement occurs not only from the inside of a respective corrugation corner 25, but favourably also from the top or bottom section 28; 26° of a respective plate corrugation.

Examples of such appropriate shapes of the protruding edge 30 are illustrated in detail in figure 8.

In figure 6 the novel dies 20, 21 of the die pair according to the present invention are illustrated in their ultimate position of press-forming, wherein the corrugations of the active area 3 of the fluid distribution plate 1 is completely formed. In such ultimate position of the dies 20, 21, a mutual separation S remaining there between, when measured at the location of the said top surface 31 of the raised part 24, is essentially equal to the thickness T of the plate material 10, whereas when measured at the location of the said protruding edge 30 of the raised part 24, such mutual die separation is smaller than such plate thickness T. In particular the example thereof illustrated in figures 5 and 6, the separation of the dies 20, 21 remaining at the location of the said protruding edge 30 in the fully closed position of the press-forming tooling amounts to approximately 50% of the plate thickness T. Thus, the height difference between the protruding edge 30 and the lower lying top surface 31 of the raised parts 24 of the dies 20, 21 of the novel die pair also amounts to approximately 50% of the plate thickness T. This latter value of 50% is on the higher end of the applicable range for the relative height of the protruding edges 30, to be able to clearly illustrate this novel design feature according to the present invention. In practice, a relative height of the protruding edges 30 amounting to between one quarter and one third of the plate thickness T will typically be optimal.

Figure 7 illustrates the corrugations that are obtainable by press forming with the die design according to the present invention in a partial cross-section of the resulting, 3D-shaped plate 1. In this particular example, the said relative height of the protruding edges 30 of the raised die parts 24 used to press form the corrugated plate 1 amounted to 0.3 times the nominal thickness T of the plate 1.

From figure 7 it appears that with such novel die design, the bending contraction at the corrugation corners 25 are, at least to a large extent, be avoided. Moreover, a thinnest and therefore most critical cross-section D of the plate 1, favourably occurs beyond the corrugation corners 25 in a flat middle part 28 of the top and bottom sections 26, 26’ of the plate corrugations. Also, these top and bottom sections 26, 26’ of the corrugations are all favourably provided with such flat middle part 28 that, moreover, extends over a predominant part of the width thereof, even for relatively narrow corrugations. Moreover, the top section 26 and the bottom section 26’ of respectively adjacent corrugations are favourably mutually oriented in parallel.

Although not illustrated in figure 7 relative to figure 4, it is noted that with the novel die design according to the invention, also a favourably small bending radius and/or a favourably large (enclosed) angle can be obtained.

Figure 8 schematically illustrates several possible detailed designs of the dies 20, 21 of the die pair according to the invention in a cross-section of the raised part 24 thereof and zoomed-in on the protruding edge 30 of that raised part 24. In figure 8, the reference numbers 33a-d indicate several principle contours, i.e. surface shapes of the protruding edge 30, as part of the working surface 22 of the respective die 20; 21 that extends between the (lower lying) top surface 31 of the respective raised part 24 and a respective side surface 32 thereof.

Between the side surface 32 of the raised part 24 and a highest, i.e. most protruding part P of the protruding edge 30 thereof, the respective part 33a of the contour 33a-d of such protruding edge 30 is preferably convexly curved. Beyond such most protruding part P of the protruding edge 30, i.e. descending towards the top surface 31 of the raised part 24, the contour 33a-d thereof can be convexly curved as well, as illustrated by the dashed-dotted line 33b in figure 8. Nevertheless, the protruding edge 30 is preferably created by abrasively machining (e.g. milling) the respective raised part 24 at the location of the top surface 31 thereof. In this case, the contour 33a-d of the protruding edge 30 will descend from the most protruding part P thereof towards the top surface 31 of the respective raised part 24, relatively steeply, as illustrated by the solid line 33c in figure 8. In particular in this case, a machining radius, i.e. the radius of concave curvature of that solid line 33c, preferably amounts to between 50% and 250% of a radius of curvature of the said convexly curved part 33a of the contour 33a-d of the protruding edge 30.

Moreover and irrespective of the shape of the descending part (33b; 33c) of the contour 33a-d thereof, the highest part P of the protruding edge 30 is preferably represented by a flat part 33d of such contour 33a-d, extending in the width direction thereof, i.e. essentially in parallel with the top surface 31 thereof. By such flat part 33d the mechanical strength and/or wear resistance of the protruding edge 30 is remarkably increased, as may be required for the said milling of the raised part 24 and/or for the actual use of the die 20; 21 in press forming. Nevertheless, the extend of such flat part 33d in width direction can remain relatively small. In particular in this case, such extend of the flat part 33d preferably amounts to between 5% and 50% of the radius of curvature of the said convexly curved part 33a of the contour 33a-d of the protruding edge 30.

The present invention, in addition to the entirety of the preceding description and all details of the accompanying figures, also concerns and includes all the features of the appended set of claims. Bracketed references in the claims do not limit the scope thereof, but are merely provided as non-binding examples of the respectively claimed feature. The claimed features can be applied separately in a given product or a given process, as the case may be, but it is also possible to apply any combination of two or more of such features therein.

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

Claims (8)

CONCLUSIONS 1. An assembly of two stamps (20, 21) for converting, in particular pressure forming, plate material (10) between them, at least one stamp (20; 21) of which is provided with a profiled working surface (22) with protruding parts ( 24) between lower parts (23) thereof, characterized in that at least one protruding part (24) of the respective one punch (20; 21) is provided with a raised edge (30) between a top surface (31) and a side surface ( 32) thereof. The set of punches (20, 21) according to claim 1, characterized in that all projecting parts (24) thereof are provided with the raised edge (30) on both sides of their respective upper surfaces (31). The set of stamps (20, 21) according to claim 1 or 2, characterized in that a height difference of the size of 10% to 60% of a nominal thickness (T) of the sheet material (10) to be formed. The set of punches (20, 21) according to claim 3, characterized in that said height difference is between 20% and 40% of said nominal plate thickness (T) and is preferably approximately equal to 30% of that nominal plate thickness (T). The set of stamps (20, 21} according to claim 1 or 2, characterized in that a contour (33a-d) of the raised edge (30) at least at the position of a most protruding part (P) thereof is provided with a flat contour portion (33d). The set of punches (20, 21) according to claim 5, characterized in that the contour (33a-d) of the raised edge (30) between said flat contour part (33d) thereof and a side face of the respective projection (24) is provided with a convex curved contour part (33a). A method for manufacturing profiled sheet (1} by means of pressure molding and with the aid of the set of punches (20; 21) according to any one of claims 1 to 6, in which the two punches (20, 21) face each other. be moved towards them with the sheet material (10) therebetween, until a distance between the top surfaces (31) of their respective projections (24) is substantially equal to a nominal thickness (T) of that sheet material (10). A punch (20; 21) for the set of punches (20; 21) according to any one of claims 1 to 6 and comprising a profiled working surface (22) with projections {24) between lower parts (23) thereof, characterized in that at least one of the protruding parts (24) is provided with a raised edge (30) between a top surface (31) and a side surface (32) thereof.