A METHOD OF FABRICATION OF AUTOMOBILE PARTS

The present invention relates to methods of fabrication of automobile parts such as body panels, sills and metal interior folded parts.

In the manufacture of panels for conventional automobiles, restrike tools are often used to increase panel form definition. Restrike tooling can be very expensive.

In a first aspect the present invention provides a method of fabricating a structural panel of an automobile by shaping a metal sheet using a die tool wherein: the structural panel is formed with one or more lines of curvature running therealong; the panel is provided with a plurality of form-holding features in each of which plastic strain applied to the metal sheet during shaping is greater than in adjoining areas of the panel; and the form-holding features are provided at spaced apart intervals along at least one of the lines of curvature and extend transversely across the line of curvature.

The formation of sills for an automobile often involves investment in stretching and bending tools.

In a second aspect, the present invention provides a method of fabricating an arcuate sill for an automobile which comprises welding at least three components together to form the sill, with the at least three components comprising two end components each welded onto one or more

central component (s) to form angled joints between the end components and the central component (s) and thereby to form the arcuate sill each end component having an end surface which abuts a respective end surface of the central component (s) and each abutting surface is inclined relative to a principal axis of the relevant component.

The various aspects of the present invention will now be described with reference to the accompanying drawings, which shows : -

Figure 1 is a plan view of a hood inner, laid flat, the hood inner having form-holding features;

Figure 2 is a view of a part of the hood inner of Figure 1, showing the holding form features in greater detail;

Figure 3 is a perspective view of the part of the hood of shown Figure 2, the Figure 3 perspective view showing more clearly the holding-form features illustrated in Figure 2; Figure 4 is a cross-section through the hood part of

Figures 2 and 3, showing radii of curvature of the lines of curvature of the panel;

Figure 5 is a perspective view of a body panel having form-holding features; Figure 6 is a cross-section through the Figure 5 body panel, showing radii of curvature;

Figure 7 is a plan view of a three part welded sill; Figure 8 is a side elevation view of the sill of Figure 7 ; and Figure 9 is a perspective view of the sill of Figures 7 and 8 ;

Figure 10 is a cross-section through the sill of Figures 7 to 9;

Figure 11 is a simplified version of Figure 7; and

Figure 12 is a simplified detail view of a joint in a sill of Figures 7 to 10, showing angles at the joint.

Restrike tools are often used in vehicle panel manufacture to increase panel form definition. This can be an expensive process. In order to avoid this the present invention proposes adding form-holding features of shape and configuration to form the panels in order to enhance the plastic strain of the panel and therefore hold panel shape. This is illustrated with reference to Figures 1 to 4 which show a hood inner panel and figures 5 and 6, which show a different vehicle body panel.

In Figure 2 there can be seen the addition of form- holding features 21 to a panel 20 (see Figure 1) which allow the panel 20 to hold its form and negate the need for the use of restrike tools. The added form-holding features 21 are "bird beaks" in outline and are formed during the initial forming of the panel 20 from a flat metal sheet. There can also be seen form-holding features 25 which are sausage-shaped. The material of the panel plastically deforms in the region of the added form-holding features 21 and 25 shown in Figure 2. Form-holding features 21 are added solely for the purpose of creating extra plastic deformation in order that the formed panel 22 retains its shape after forming. The features 21 and 25 are form- holding features in that they hold the rest of the panel in shape. They are all domed protrusions from the metal sheet which have an outline in the shape of a bird's beak or a

sausage. They are smoothly curving features in the panel. A smoothly curving form-holding feature is desired because some materials, e.g. aluminium, can split if the shape of the form-holding feature is not "soft" in nature.

The form-holding features 21 and 25 are formed simultaneously with the other features of shape and configuration of the panel as it is formed by drawing in a die. The form-holding features are chosen to span lines of curvature e.g. 100, 101, 102 in Figure 3 in the formed panel to hold the shape of such areas of curvature in the panels. Lines of curvature are lines recognisable in the formed panel which are deformed by localised curvature of the panel. A consistent localised radius of curvature along a path across the panel gives rise to a line of curvature.

Figure 4 shows a cross-section through the lines of curvature 100, 101, 102. The figure shows a radius of curvature of 9.43mm for the line 100, a radius of curvature of 15.04mm for the line 101 and a radius of curvature of 15.07mm for the line 102.

Figure 5 shows a body panel 500 having sausage-shaped form-holding features 501 spanning lines of curvature 502 and 503. Figure 6 is a cross-section through the panel of Figure 5 and shows that the line 502 has a radius of curvature of 9.21mm and that line 503 has a radius of curvature of 15.78mm.

The form-holding features of the present invention preferably span lines of curvature with radii of curvature

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in the range 5 to 20mm, or more preferably 7.5 to 17.5mm or most preferably 9 to 16mm.

A plurality of discrete separate and spaced apart form- holding features will be provided along at least one line of curvature of a panel to hold the shape of the panel, e.g. in Figure 3 the form-holding features 21 are spaced apart along the line 100 crossing transversely across the line 100; this can also be seen with the spaced apart form-holding features 25 along the line 102.

Figure 7, 8, 9, 10, 11 and 12 show an arcuate sill 50 for an automobile. It is common for such arcuate sills to be manufactured by stretching and bending tools. However, this involves significant investment. Instead, the arcuate sill 50 is made of three straight components 51,52,53 which are welded together to create a component of arcuate form that can be best seen in the isometric view of Figure 9. The end components 52 and 53 are not parallel to the central component 51 and instead incline away from the curved component 51 at an angle. They both extend away from the component 51 in the same direction away from the component 51 when the component 51 is viewed in plan view and the inclination is considered in a lateral sense perpendicular to a side face of component 51. The component 52 is formed with a end face surface which abuts an end face surface of the component 51 and is welded along the abutment. The end face surfaces of the components 51 and 52 are both angled with respect to the side faces of the components 50 and 52 (i.e. they are not perpendicular to the side faces) as can be seen in Figures 11 and 12. The abutting surfaces must both be cut at the same or a similar angle so that the

abutting surfaces are of the same length. The three components 51, 52, 53 will be set in a welding fixture (akin to a "jig") and then welded to ensure good alignment. In a similar fashion the component 53 has an angled end face which abuts an end face of the component 51 and defines a junction which is welded. Again, both of the abutting end faces of the component 51 and the component 53 are inclined with respect to the side faces of the components. In this way a vehicle sill formed from straight components but for the vehicle is arcuate when viewed in plan view as in figure 10, in that the component arcs from ends 54 which are more inboard of the vehicle than the central portion 51.

Each of the arrangements 51, 52, 53 is typically a straight extrusion, typically in an alloy of aluminium The invention allows use of extrusions without the need for a bending operation to bend the extrusions to a chosen arcuate shape. Each could be section cut from a common extrusion and Figure 10 shows a cross-section transversely taken through each component 51, 52, 53, in such a case. The cross-section shows that each component 51, 52, 53 is hollow, but has internal webs 200, 201 extending across. Three voids 202, 203, 204 are shown. The section of sill forming the void 204 tapers from a greater width at the web 201 to a lesser width at an end surface 205 of the sill. The thickness of metal in the webs is less than the thickness of the metal in the remainder of the component.

Whilst each of the components 51, 52, 53 could be of a common cross-section, gauge and material, in some circumstances it may be preferable to use components of differing properties, e.g. a high strength thicker gauge

section could be used for the front of the three sill components, to help with crash performance of the sill, whilst the other two sections could be formed of a thinner gauge material for lightness. The type of alloy used in each component could be different, e.g. different extrusion grades could be used for each section, high strength in the front, lower strength at the rear.

In the Figure 9 there can be seen holes 60 in a laterally-facing side surface of the sill. These holes enable the joining of body panels to the sill.

In Figure 12 the angled joint between the components 51 and 52 is shown schematically so that the relevant angles can be seen: the same angles will exist in the angled joint between components 51 and 53. The angle β is called the leg angle; it is the angle between a line (or plane) coincident with a side face of the component 51 and a line (or plane) coincident with a side face of the component 52 (equally well an angle between a principal axis of the component 51 and a principal axis of the component 52, which may be more appropriate since the side faces may vary along their lengths if the components 51 and 52 are shaped) . The angle Y is a cut face angle; it is the angle between a line (or plane) exactly perpendicular to the side faces of the component 51 (or equally well perpendicular to the principal axis of component 51) and the end face of the component 51.

The angle ^ is also a cut face angle; it is the angle between a line (or plane) extending perpendicular to the side faces of the component 52 (or equally well perpendicular to the principal axis of the component 52) and

the end face of the component 52. The angle ^ is also a cut face angle; it is the angle between a line (or plane) extending perpendicular to the side faces of the component 52 (or equally well perpendicular to the principal axis of the component 52) and the end face of the component 52. The angle γ is the joint angle; it is the sum of the two cut face angles Y and ^ . The leg angle β is also the sum of

the two cut face angles γ and ^ . Examples of typical angles are given in the table below:

The leg angle is preferably in the shape 20° to 70°, more preferably 30° to 50°.

Whilst above the sill has been described as a sill fabricated out of extruded aluminium and the method of the invention is ideal for such a purpose, the invention could also be applied to steel tubing, hollow section steel arrangements (e.g. rectangular or square for section components) and also rolled steel components.

Whilst above the sill has been described as a sill fabricated out of three components, a sill can alternatively

be made of more than three components. In particular, the sill can be formed from five components. A five component sill may be formed by adding an additional component to the front and rear of a three component sill.

The components 50, 51 and 52 have been described above as "straight" - this means that they each have a linear (i.e. central) axis. It may have a linear principal (i.e. central) axis. It may be that they have straight sides as well, but the sides may be shaped.

The invention also comprises manufacture of an automobile in which a structural panel is made in the way described above and a sill also made in the manner described above.