Panel assembly of hemmed panels and its method of manufacture

Abstract: Production of a satisfactory outer profile for a hemmed joint is often difficult due the bending of a hem being conducted without anything to provide back resistance to the bending motion. A first inner panel 4 and a method for joining the first inner panel to a second outer panel 8 are disclosed. A hem 22 of the second panel 8 is wrapped around an edge 2 of the first panel provided along at least a part of its length with a die cast bead 14 to secure the edge of the first panel within a channel 34 formed thereby in the second panel. The die cast bead 14 provides a back resistance during this bending of the hem portion about the lip of the bead.

Description: The present invention relates to a motor vehicle door panel as defined in claim 1. It is known to join panels together by hemming. In this method, an outer panel is provided beneath an inner panel. The inner panel is provided with a flat edge where it is desired to join the panels together. The outer panel extends beyond each edge that it is desired to hem. The extending portion or hem of the outer panel is bent around the flat edge of the inner panel and flattened to the inner panel to form a "U" shaped groove around the edge of the outer panel in which the inner panel is located. Production of a satisfactory outer profile for the joint is often difficult due the bending of the hem being conducted without anything to provide back resistance to the bending motion. In addition such a joint is not particularly secure. When the joint is twisted, for example, the inner panel may be withdrawn from the groove. Further processes are often employed in order to ensure that the joint will be durable. However, such operations clearly add to the cost and time involved in the production of the joint. Futher, obtaining a consistently reproducible joint of satisfactory quality is difficult. US-A 5 237 734 shows according to the preamble of Claim 1 a known method of solving these problems in which a raised portion is provided along the edge of the inner panel. However, in this method it is necessary to have a special tool, provided with a slot corresponding to the raised portion. If the slot is not present, the raised portion will be flattened and the advantaged gained by providing an inner panel with a raised portion is lost. DE-A-197 08 369 shows a similar arrangement applied to a vehicle sunroof where a pressed U-section bead is formed at the outer periphery of an inner panel and where a hem bent over the bead is secured by welds. It is an advantage of the present invention that it provides for a reproducible secure hemmed joint without the need for specially adapted tooling or further processing of the joint. According to the invention, there is provided a motor vehicle door panel comprising a first, inner, panel and a second, outer, panel wherein the first and second panels are joined together at a hemmed joint comprising a hem of the second panel bent around a peripheral edge of the first panel to secure the edge of the first panel within the second panel, the peripheral edge of the first panel including a bead having an outer surface which interlocks with the inner surface of the hem, characterised in that the bead is solid and is at the outermost peripheral edge of the first panel. Since the channel formed by the hem wrapping around the bead has a mouth narrower than a thickness of the bead, it will not be possible to pull the first panel from the second without damaging the channel. Preferably, the bead extends along the entire length of the edge of the first panel. Preferably, the bead is an integral part of the edge of the first panel. Preferably, the first panel is a die cast member. This has the advantage that the panel and bead can be produced to a high tolerance with regard to dimensional accuracy. When the hem is bent around the bead, the profile formed will be accurate, consistent and more tightly formed than has previously been possible. Preferably, the bead takes the form of a ridge extending out from a surface of the first panel. The invention will now be described, by way of example only, with reference to the accompanying drawings, in which Figure 1 shows a side view of an edge of a first panel and an edge of a second panel for joining together by the method of the present invention; Figure 2 shows a side view of the edge of the first panel and the edge of the second panel joined together by the method of the present invention; and Figure 3 shows a detail of Figure 2. Referring to the Figures, there can be seen an edge portion 2 of a first inner panel 4 and an edge portion 6 of a second outer panel 8. The edge portion 2 of the first inner panel 4 has an upper surface 10 and a lower surface 12. A bulbous profile or bead 14 is provided extending along at least a part of the edge portion of the first inner panel. The bead 14 extends from the lower surface 12 of the first inner panel above the upper surface 10 of the first inner panel to form a ridge or lip 16 along that part of the edge of the first inner panel. The first inner panel 4 is conveniently manufactured by die casting, though any other suitable method may be used. The first inner panel is conveniently manufactured from cast steel, though any other suitable material, for example aluminium, may be used. The edge portion 6 of the second outer panel 8 has a main portion 20 and a hem portion 22. The main portion of the edge portion has an upper surface 24 and a lower surface 26. The hem portion 22 is provided at an angle to the main edge portion and forms an acute angle therewith by way of a curved intermediate portion 28. The angle may be formed during the manufacture of the second outer panel or subsequent thereto. The hem portion 22 is provided with an inner surface 30 and an outer surface 32. The second outer panel 8 is conveniently manufactured from sheet steel, though any other suitable material, for example aluminium, may be used. The method of joining the first inner panel 4 and the second outer panel 8 will now be described. The second outer panel 8 is placed with the lower surface 26 of the main edge portion on a locating die (not shown). The first inner panel is then placed with the lower surface 12 on the upper surface 24 of the main edge portion of the second panel such that the bead 14 is located adjacent the intermediate portion 28 of the edge of the second panel. In this position the hem portion 22 of the second panel extends over the lip 16 of the bead 14 of the first panel (Figure 1). A hemming punch (not shown) is then used to stamp the hem portion 22 of the second outer panel to the edge portion of the first inner panel. The punch impacts the outer surface 32 of the hem portion 22 causing the hem portion to bend around the lip 16 of the bead 14 of the first panel such that the inner surface 30 of the hem portion comes into contact with the upper surface 10 of the first panel. The bead 14 provides a back resistance during this bending of the hem portion about the lip of the bead. This allows the hem portion 22 to be tightly wrapped around the bead 16 to form a channel 34 at the edge of the second outer panel 8 having a narrow mouth 36 extending along the hemmed edge of the second outer panel. The edge 2 of the first inner panel 4 in this way becomes trapped inside the channel 34 formed by the second outer panel 8 since the bead 14 of the first inner panel 4 cannot pass through the mouth 36 of the channel 34 without distorting the channel.

Claims: A motor vehicle door panel comprising a first, inner, panel (4) and a second, outer, panel (8) wherein the first and second panels are joined together at a hemmed joint comprising a hem (22) of the second panel bent around a peripheral edge (2) of the first panel to secure the edge of the first panel within the second panel, the peripheral edge of the first panel including a bead (14) having an outer surface which interlocks with the inner surface of the hem, characterised in that the bead (14) is solid and is at the outermost peripheral edge of the first panel (4). A door panel according to claim 1, characterised in that the bead (14) extends along the entire length of the edge (2) of the first panel (4). A door panel according to claim 1, characterised in that the bent-over hem (32) extends over a surface portion of the first panel inwards of the bead (14). A door panel according to any previous claim, characterised in that the first panel (4) is a die cast member. A door panel according to any previous claim characterised in that the bead (14) takes the form of a ridge (16) extending out from a surface of the first panel (4).

Inventors: MAY ROBERT HINDLEY, MAY, ROBERT HINDLEY, May, Robert Hindley, 8 Renoir Close
Applicants: LAND ROVER GROUP LTD, LAND ROVER GROUP LIMITED
Application year: 1999
Main classification: B21D39
IPC codes: B21D39