Method of Executing Hemming Process

The present invention relates to a method of executing a hemming process for folding a hem flange of an outer panel and combining an inner panel therewith and an apparatus for implementing this method in the course of manufacturing an external plate body like a hood, fenders, side-doors, and a luggage room, of an automotive body, for example.

For instance, when processing an external plate body such as a hood, fenders, side-doors, or the like, available for assembling an automotive body, a hem flange formed at an edge of an outer panel is folded in the backward direction to cause the folded hem flange to nip an edge of an inner panel in order to combine both panels with each other. Conventionally, this method is called the "hemming process". Concretely, as shown in FIG. 7, a hem flange 11a is previously formed at an edge of an outer panel 11 by erecting it at a substantially right angle. Next, an edge of an inner panel 12 is superposed on the inner surface of the hem flange 11a, and then a preliminary folding process is executed against the superposed hem flange 11a by a predetermined folding angle by operating a preliminary-folding blade 13. Finally, the hem flange 11a is regularly folded by means of a regular folding blade 15.

However, when executing a hemming process, generally, how to process corner domain of the hem flange 11a is an important problem. This is because, in the course of folding corner domain of the hem flange 11a backward in the direction of an edge of an inner panel, a certain excessive substance is naturally generated to inevitably result in the generation of numerous creases. Once numerous creases are generated, it not only spoils external appearance, but it also causes part of the creases to protrude from the contour of the corner domain to eventually generate a security problem. Furthermore, deformation may be generated on the external surface of an outer panel.

To prevent those critical problems from occurrence, as shown in FIG. 8, conventionally, the dimension of corner domain 11a1 is reduced so that depth S3 of the hem flange 11a can extremely be contracted from the other depth S4 of peripheral domains other than the corner domain 11a1, thus decreasing the amount of excessive substance of the corner domain 11a1.

Furthermore, as shown in FIG. 9, any of those conventional folding methods terminates the preliminary folding process without further executing a regular folding process against the corner domain 11a1.

Nevertheless, according to such a conventional method cited above, although a crease can be prevented from occurrence in the corner domain, since this conventional method deletes the regular folding process, special treatment is discretely needed in order to fill up clearance between the corner domain 11a1 and the inner panel 2a with sealing agent or paint, thus increasing an additional step. Desirably, such an additional step should be eliminated.

Therefore, the object of the invention is to fully solve those technical problems cited above in the course of processing the corner domain of a hem flange during the hemming process.

The hemming process according to claim 1 is consummated by sequentially executing those steps described below. Initially, a hem flange formed at an edge of an outer panel is preliminarily folded in the direction of an edge of an inner panel. Next, a regular folding process is executed against the preliminarily folded hem flange by further exerting pressurized force thereto. Finally, the hem flange of the outer panel is folded backward in order to nip the inner panel. Only partial domain of the corner substance is deformed by locally exerting pressurizing force to it at the initial stage of the preliminary folding process executed against the corner domain.

The hemming apparatus according to claim 2 is provided with a preliminary-folding blade for preliminarily folding recessed and rounded corner of a hem flange formed at an edge of an outer panel, where the preliminary-folding blade has a pressurizing surface which is provided with recessed and rounded shape having curvature substantially being equal to that of the corner domain and projected initial pressurizing domain formed thereon.

As a result of a variety of tests carried out by the Applicant of the invention, it was confirmed that creases caused by surplus amount of substance were always present in such domain where the substance initially incurred deformation. It was also confirmed that, whenever applying such load that might facilitate growth of creases, these creases grew themselves by way of solely concentrating on the domain where the substance initially deformed. Probably, this is because, since the yield point of specific domain incurring initial deformation to the substance is lowered from the yield point of other domains, when such a domain comprising surplus substance receives pressure, certain forces aiming to be out of pressurized surface concentrates on the domain containing lowered yield point. In other words, by locally lowering the yield point of specific domain of the substance during the initial stage of the pressurizing process, it is possible that creases can be generated and grown by way of concentrating on this specific domain.

FIG. 1a is a perspective view of the corner domain of a hem flange related to the invention;

FIG. 1b is a plan of the corner domain shown in FIG. 1a;

FIG. 1c is a sectional view of the corner domain along line c--c shown in FIG. 1a;

FIG. 2a is a perspective view of a preliminary-folding blade related to the invention;

FIG. 2b is a plan of the preleiminary folding blade shown in FIG. 2a;

FIG. 2c is a sectional view of the preliminary-folding blade along line c--c shown in FIG. 2a;

FIG. 3a is a perspective view of the corner domain of a hem flange at the initial stage of preliminary folding process related to the invention;

FIG. 3b is a sectional view of the corner domain along line b--b shown in FIG. 3a;

FIG. 3c is a sectional view of the corner domain along line c--c shown in FIG. 3a;

FIG. 4a is a perspective view of the corner domain of a hem flange at the final stage of preliminary-folding process related to the invention;

FIG. 4b is a sectional view of the corner domain along line b--b shown in FIG. 4a;

FIG. 4c is a sectional view of the corner domain along line c--c shown in FIG. 4a;

FIG. 5a is a perspective view of the corner domain of a hem flange at the final stage of the regular folding process related to the invention;

FIG. 5b is a sectional view of the corner domain along line b--b shown in FIG. 5a;

FIG. 5c is a sectional view of the corner domain along line c--c shown in FIG. 5a;

FIG. 6 is a plan of the prelimiary-folding blade according to another embodiment of the invention;

FIG. 7 is a conceptive view denoting a general aspect of the hemming process related to the invention;

FIG. 8a is a perspective view of the conventional corner domain of a hem flange;

FIG. 8b is a sectional view of the conventional corner domain along line b--b shown in FIG. 8a; and

FIG. 9 is a sectional view denoting the final stage of a conventional method of processing the conventional corner domain of a hem flange.

Referring now to the accompanying drawings, a novel method of executing a hemming process according to an embodiment of the invention is described below.

FIG. 1 schematically illustrates the corner domain 1a1 of a hem flange 1a formed at an edge of an outer panel 1. The hem flange 1a is previously formed along an edge of the outer panel 1 by way of being erected at a substantially right angle. As shown in FIG. 1b, the corner domain 1a1 of the hem flange 1a is of recessed and rounded shape having a radius of curvature R1. As shown in FIG. 1c, the flange depth S1 is slightly less than the other flange depth S2 of peripheral domains other than the corner domain 1a1. Although an embodiment of the invention decreases the substance of the corner domain 1a1 in the same way as is conventionally done, the decreased amount of the substance is not as much as that of the conventional practice.

FIG. 2 schematically illustrates a preliminary folding blade 3 which is used for preliminarily folding the corner domain 1a1. As shown in FIG. 2b, the preliminary folding blade 3 comprises a recessed and rounded surface 3a drawn by a radius of curvature R2 of the corner domain 1a1 and a projected initial pressurizing domain 3b (cusp) which is integrally formed in the substantially center domain of the pressurizing domain 3a. Although the initial pressurizing domain 3b shown in FIGS. 2a and 2b has triangular section and extends in the direction of the depth of the pressurizing surface 3a, the structure of this domain 3b is not solely limited to the one described above.

FIG. 3 schematically illustrates the initial state of the preliminary folding of the corner domain 1a1 of the hem flange 1a via operation of a preliminary folding blade 3 by causing the recessed and rounded pressurizing surface 3a of the preliminary folding blade 3 to pressurize the projected and rounded corner domain 1a1 in order to preliminarily fold the corner domain 1a1 by a predetermined folding angle .theta.1 onto an edge of an inner panel 2. Since a projected initial pressurizing domain 3b is formed on the pressurizing surface 3a of the preliminary folding blade 3, only the initial pressurizing domain 3b comes into contact with the corner domain 1a1 during the initial stage of the preliminary folding process. In consequence, as shown in FIG. 3b, the corner domain 1a1 is locally pressurized by the initial pressurizing domain 3b, thus causing only the pressurized domain A to incur deformation (a cuspal crease).

FIG. 4 schematically illustrates the final state of the preliminary folding process executed by the preliminary folding blade 3. By continuously exerting pressurizing force against the preliminary folding blade 3 further from the state shown in FIG. 3, the pressurizing surface 3a of the preliminary folding blade 3 comes into contact with the corner domain 1a1 to pressurize the entire corner domain 1a1. Upon receipt of the pressurizing force from the pressurizing surface 3a of the preliminary folding blade 3, the corner domain 1a1 is folded in the direction of an edge of the inner panel 2 by a predetermined folding angle .theta.1. Concurrently, deformation slightly grows in the pressurized domain A after initially being pressurized by the initial pressurizing domain 3b.

FIG. 5 schematically illustrates the final stage of the regular folding process executed by a regular folding blade 5 having a conventional structure. The corner domain 1a1 is fully folded by activating the regular folding blade 5 to further exert pressurizing force against the corner domain 1a1 previously being folded by the preliminary folding blade 3 by a predetermined folding angle .theta.1 before the corner domain 1a1 is eventually folded back onto the edge of the inner panel 2 to implement a regular folding process. When the corner domain 1a1 is fully folded backward, the edge of the inner panel 2 is nipped by the fully-folded corner domain 1a1 to combine the outer and inner panels 1 and 2 with each other. As shown in FIG. 5b, creases generated by surplus substance of the corner domain 1a1 concentrically grow themselves in the pressurized domain A which was initially pressurized and deformed by the initial pressurizing domain 3b during the initial stage of the preliminary folding process. The pressurized domain substantially curves inwards. Surplus substance of the corner domain 1a1 mildly continues from the pressurized domain A by way of curving itself in the outward direction. It was confirmed that no crease was generated in other domains. In consequence, compared to the conventional effect, the combined outer and inner panels 1 and 2 proved a far better appearance, and yet, fully solved the security problem mentioned earlier.

It is acknowldged that the wider the curved angle .theta.1, the greater the amount of surplus substance generated in the corner domain 1a1. Upon receipt of pressurizing force from the regular folding blade 5, the surplus substance aims to be out of the pressurized surface 5a. The force aiming to be out of the pressurized surface 5a concentrically acts as contracted stress upon a specific domain which initially generated creases (in other words, deformation) to cause creases to grow furthermore. In this way, creases are generated in the specific domain A of the corner domain 1a1 during the initial pressurizing stage to cause creases to continuously grow themselves in the specific domain A in association with furtherance of the regular folding process. In consequence, the regular folding process is properly executed without causing creases to be generated in other domains at all.

Another embodiment shown in FIG. 6 provides curvature (concretely, radius of curvature R3) for the pressurizing surface 3'a of a preliminary folding blade 3', where the curvature R3 is greater than the other curvature (concretely, radius of curvature R1) provided for the corner domain 1a1. This embodiment generates such functional effect identical to that is generated by the preceding embodiment by causing the substantial center domain 3'b of the pressurizing surface 3' to solely come into contact with part of the corner domain 1a1 during the initial stage of the preliminary folding process. Therefore, whenever operating the preliminary folding blade 3', the center domain 3' of the pressurizing surface 3'a serves as the initial pressurizing domain which initially pressurizes to partly deform domain A of the corner domain 1a1.

As shown in FIG. 1a, those embodiments described above respectively take off part of the susbtance of the corner domain 1a1. Alternatively, the invention also permits to execute those sequential processes described below by way of deleting execution of the removal of part of the substance of the corner domain 1a1, in other words, by way of maintaining a state of the flange depth denoted by S1=S2. Even when the flange depth S1 and S2 are equal to each other, the invention can still achieve such functional effect identical to that which is achieved by those preceding embodiments described above. The essential content of the invention is to eventually cause creases to be generated and grown concentrically in a specfic domain by locally lowering the yield point of this domain of material susbstance at the initial stage of the preliminary folding process. Therefore, for example, it is theoretically possible to generate such functional effect identical to that is achieved by the invention by previously forming extremely fine slits in the flange-protruding direction in such a case in which the corner domain contains fine slits in external corner and thin thickness.

As is apparent from the above description, the object of the invention is to concentrically generate and grow numerous creases from surplus substance of the corner domain of a hem flange in partial domain of the corner area by defining this partial corner by solely and locally pressurizing it during the initial stage of the preliminary folding process executed against the corner domain. Therefore, according to the invention, even when executing the regular folding process without extremely contracting flange dimension of the corner, the resulting product can be provided with far better appearance than any of those conventional products. At the same time, the method according to the invention can securely eliminate faulty effects such as unwanted protrusion of part of creases from the contour of the corner domain or unwanted generation of abnormal deformation on the external surface of the outer panel, or the like. Furthermore, the method according to the invention dispenses with such an additional step otherwise needed to fill up clearance between the corner domain and the inner panel with sealing agent or paint normally needed to implement any conventional method because the conventional method terminates the corner-domain processing work as of the preliminary folding process. In consequence, the novel method according to the invention securely promotes operating efficiency as well.