A Panel Assembly and a Method of Assembling Panels Together

The invention relates to a panel assembly particularly, although not exclusively limited to, a panel assembly for use in an automobile.

In automobile production, automotive structures, for example body panels, must be joined together in a geometrically stable, repetitive and robust condition.

The conventional approach to joining together such panels is to provide pre- formed sheets which may have been press-formed with particular features and with punched holes therethrough. The pre-formed sheets are located in an assembly fixture and are joined together, for example, by welding, friction stir joining, riveting or adhesive bonding to form a panel subassembly or a complete assembly.

The assembly fixtures generally comprise a jig with location pins which extend through the holes pre-punched in the panels and clamps to clamp the panels together during fixing (see Fig.l). The pre-forming of the sheets often introduces internal stresses which cause one or both of the panels to adopt an incorrect position unless clamped. The clamps correct the spring-back caused during the forming process and hold the panels together in the right configuration prior to fixing.

The prior arrangement is disadvantageous for several reasons. Firstly, for each set of panels requiring assembly together, a separate jig is required. This means that at the end of a production run of a particular vehicle the entire tool must be scrapped.

Also, the requirement for locating pins and the clamps restricts access to parts of the panel assembly during fixing. Where the fixing is to be effected by welding or by riveting, restricted access is undesirable. Also, the jig tool means that the panel can only be approached from one side which reduces the fixing options.

Moreover, as the individual panels tend to be press-formed, there is potential for substantial tolerance errors to be introduced into the assembly. Press form tolerance is in the order of 0.5mm.

It is an object of the invention to provide an improved panel assembly and an improved method for assembling panels together.

According to a first aspect of the invention there is provided a vehicular panel assembly comprising a first panel having a first location formation formed by at least partially shearing it from the first panel and a second panel having a second location formation, formed by at least partially shearing it from the second panel, the first location formation co-operating with the second location formation to locate the first panel on the second panel.

In that way, the need for locating pins and/or clamps in the assembly fixture is reduced or, in certain circumstances, eliminated altogether.

As sheared formations are used to locate one panel on the other in that embodiment, the tolerance errors are substantially reduced. Shear tolerances are generally of the order of + or - 0.2mm. This reduces the tolerance build up, eliminating the fixture tolerance and controlling the panel tolerance to the aforementioned level in the panel assembly by an order of magnitude.

The principle advantage provided by the arrangement of the present invention is that the sheared formation which acts to locate and, in some cases, retain the panels together is actually formed at the mating surface itself. Thus, the retention and location are provided at the optimum position, not at a position dictated by the ability to access with a pin or clamp.

A further advantage of the present arrangement is the reduction in time before sign off of the die. Normally, when a pressing or stamping die is made it undergoes iterative redesign after trialling parts made from the die. This redesign may be

prompted by a number of factors. Firstly, the component made in the die tends to spring back out of the initial die position and the amount and effect of springback differs from material to material and shape to shape. The main effect of springback is to increase the dimensional tolerances to which the panels are subjected as the positional arrangement of pins and clamps is less predictable the greater the springback. In the present arrangement, whilst parts can spring back, the location features of two panels together reduce the dimensional tolerances substantially as described above. This tends to reduce the effect of springback as an issue and thus reduce the time to die maturity. Previously, the assembly maturation process required the part to be optimised then the assembly to be optimised. By using the present arrangement, where the location formations provide a geometrically stable location of parts together, parts can be cut incorporating a spring back correction. Thus, the assembly can be approved without previous part approval. Work on the assembly is constrained to achieving function performance rather than an intermediate geometrical standard which has no functional bearing.

Furthermore, the present arrangement provides a way in which one or both panels can be pre-stressed when assembled together, if desired.

The first location formation may comprise an aperture fully sheared out of the first panel. Alternatively, the first location formation may be partially sheared from the first panel so as to form a recess in the panel.

The second location formation is preferably sheared so as to create a projecting part, projecting from the surface of the panel. The projecting part preferably projects by a distance greater than the thickness of the first panel. Alternatively, the projecting part projects from the surface of the second panel by a distance less than the thickness of the first panel. The projecting part may have an aperture formed therethrough.

The projecting part may include a lead-in formation, for example a conical, pyramidal or otherwise tapered tip. The projecting part may be formed so as to snap- engage with the first location formation.

A plurality of first location formations on the first panel may be provided together with a respective plurality of second location formations on the second panel.

In a preferred embodiment, the location formations act to secure the panels together.

The panels of the panel assembly are preferably fixed together by welding, bonding using adhesive or riveting or hemming.

The invention also includes a vehicle body panel, a vehicle subassembly and a vehicle respectively comprising a panel assembly as set out in the first embodiment of the invention.

According to a second aspect of the invention there is provided a method of assembling vehicular panels together comprising the steps of: providing a first panel, creating a first location formation on the first panel by at least partially shearing a part of the first panel, providing a second panel, creating a second location formation on the second part by at least partially shearing a part of the second part, and assembling the first and second panels together so that the first location formation co-operates with the second location formation to locate the first panel on the second panel.

Embodiments of the invention will now be described in detail by way of example and with reference to the accompanying drawings, in which:-

Fig.l is a schematic sectional view of a prior art panel assembly method,

Fig. Ia is a schematic sectional view through the end part of the panel shown in Fig.l in the undamped condition,

Fig.2 is a schematic sectional view through a panel assembly in accordance with the first aspect of the invention.

Fig.3a and Fig.3b are schematic sectional views of a panel assembly in accordance with the first aspect of the invention and a panel assembly method in accordance with the second aspect of the invention,

Fig.4a and Fig.4b are schematic sectional views through another panel assembly and method of panel assembly in accordance with the first and second aspects of the invention,

Fig.5 is a schematic sectional view of a further panel assembly in accordance with the first aspect of the invention,

Fig.6 is a schematic sectional view through a still further panel assembly in accordance with the first aspect of the invention,

Fig.7a-d are schematic side elevations of various punch tools used to create the shear formed projections in Figs.3-6,

Fig.8 is a schematic sectional view of part of the panel assembly of Fig.3 shown to a larger scale,

Fig.9 is a schematic sectional view of a panel of a further panel assembly in accordance with the invention,

Fig.10 is a schematic sectional view of a yet further panel assembly in accordance with the invention, and

Fig.11 is a schematic sectional view of a panel assembly similar to Fig.10 with a stepped formation to create a controlled spacing.

Fig. 12a is a side elevation of a punch tool for creating a shear-formed projection,

Fig. 12b is an end elevation of the punch tool of fig. 12a looking in the direction of arrow A in fig. 12a,

Fig. 12c is an enlarged sectional view through the punch head,

Figs. 13a and b are plan and sectional views respectively of a die for use with the punch of figs. 12a to c,

Fig. 14 is a schematic sectional view of the punch and die of figs. 12 and 13 punching a formation from a metal sheet,

Figs. 15a and b are plan and sectional views respectively of the formation formed in fig. 14,

Fig. 16 is an enlarged sectional view of the formation in fig. 15,

Fig. 17 is an end elevation of another punch tool,

Figs. 18a and b are plan and sectional views through the formation formed by the punch tool of fig. 17

Figs.l and Ia illustrate a prior panel assembly as described above. In Fig.l, the panel assembly 10 comprises a first panel 12 and a second panel 14 which are assembled together by means of an assembly fixture 16.

Each panel is pre-formed from sheet material by a pressing operation. During the pressing operation, each panel 12, 14 is provided with a series of punched apertures 18.

The sheet material thickness is typically 0-5mm and the material is generally steel or aluminum.

The assembly fixture 16 which is shown schematically in Fig.l comprises locating pins 20 which are positioned and dimensioned so as to extend through the apertures 18 formed in the panels 12, 14 and clamps 22, 24 which are arranged to clamp the panels 12, 14 of the assembly 10 together. As can be seen in Fig.la, press forming of the panels 12, 14 can result in one or each panel springing away from its intended final position due to the internal stresses created in a panel at the time of pressing. The clamps 22, 24 assist to retain the panels in their final position prior to fixing.

In Fig.2, a panel assembly in accordance with the first aspect of the invention is shown. Parts corresponding to parts in Fig.l carry the same reference numerals.

A panel assembly 10 comprises first and second panels 12, 14 each of which has been press-formed prior to assembly.

The first panel 12 has a series of apertures 18 punched therethrough in similar manner to the prior art panel shown in Fig.1.

The second panel 14 has, at corresponding positions to the apertures 18 in panel

12, a series of projections 26 formed by partially shearing through the panel 14 using a punch tool (see Figs.7a-d). In Fig.2, the apertures 18 are substantially circular and the projections 26 are also circular. The diameter of the aperture 18 is arranged to be a sliding clearance fit wider than the diameter of the projection 26.

The panels 12, 14 can then be assembled together so that the projections 26 extend into the apertures 18 so as to locate the first panel 12 on the second panel 14. The projections 26 take the place of the locating pins 20 in the prior art assembly fixture. Moreover, by selecting the positions of the apertures 18 and the projections 26 on the panels 12, 14 some of the clamps 22, 24 from the prior art assembly fixture can

be dispensed with. The fit of the panels together, with the projections 26 extending through the apertures 18, is enough to hold the panels 12, 14 against springing back into the undamped position, as shown in Fig.la. The panels 12, 14 can then be fixed together, for example by welding, e.g. spot welding, riveting or by bonding.

Although figure 2 shows three sets of apertures 18 and projections 26, any number of apertures and projections may be provided. For example, it is envisaged within the scope of the invention merely to replace one of the locating pins 20 by a projection 26 on the second panel 14 and to retain the clamps 22, 24.

Figs.3a and 3b show part of the panel assembly 10 of Fig.2 to a larger scale. In Fig.3a, the panel 12 has yet to be assembled onto the panel 14. The projection 26 is shown in more detail in Figs.3a and 3b and Fig.8. The projection 26 comprises a conical lead-in portion 28 and a cylindrical projecting part 30 which is partially sheared from the panel 14. Three lands 32 which are regularly angularly spaced around the periphery of the projection 26 on the undersides thereof connect the projection 26 to the panel 14. Save for the lands 32, the projection 26 is completely sheared from the panel 14.

Fig.3b shows the panel 12 assembled on to the panel 14 so that the projection 26 extends into the aperture 18. It can be seen that the projection 26 is a tight fit into the aperture 18.

Because the aperture 18 is sheared out of the panel 14 and the projection 26 is sheared out of the panel 14, the panels 12, 14 are located relative to one another with a much closer tolerance than in the prior art. The conical projecting portion 28 on the projection 26 assists the lead-in of the projection 26 into the aperture 18 so as to facilitate assembly of the panels 12, 14 together.

Turning to Figs.4a and 4b, an alternative embodiment of panel assembly is shown.

Parts corresponding to parts in Figs.1-3 carry the same reference numerals. In Fig.4a, the panel 12 is identical to the panel 12 in Fig.3 a with an aperture 18 formed

therethrough. The panel 14 has a projection 26 shear formed therefrom. However, the projection 26 in Fig.4a does not have a lead-in portion 28 and projects from the panel 14 by a distance D which is less than the thickness T of the panel 12. When the panel 12 is assembled onto the panel 14, as shown in Fig.4b, the projection 26 extends into the aperture 18 but does not project beyond the aperture 18 so as protrude from the first panel 12.

That arrangement is advantageous in circumstances where it would be undesirable for the projection 26 to project out from the panel 12. For example, in circumstances where clearance around the panel assembly 10 is an issue.

Fig.5 shows further panel assembly 10 comprising a first panel 12 having an aperture 18 formed therethrough and a second panel 14 having an annular projection 34 which is formed partially by shearing and partially by extruding side walls 36 of the projection 34. That configuration is appropriate for thinner walled material than the embodiments of Figs.2 to 4.

Fig.6 shows a further alternative panel assembly 10 which is similar in many respects to the panel assembly in Fig.5. The panel assembly 10 in Fig.6 comprises a panel 12 having an aperture 18 and a panel 14 having a circular projection 38 partially sheared and partially extruded from the panel 14. Again, panel assembly of Fig.6 is appropriate for thinner walled material than the panel assemblies shown in Figs. 3 and 4.

Figs.7a-d illustrate the punch tools used to generate the formations in the embodiments of Figs.3-6. The punch tool 40a of Fig.7a is used to generate the projection 26 shown in Fig.3, the punch tool 40b of Fig.7b is used to generate the projection shown 26 in Fig.4. The punch tool 40c of Fig.7c is used to generate the projection 34 in Fig.5. The punch tool 4Od of Fig.7d is used to generate the projection 38 in Figs.6.

Fig.8 merely shows the panel 14 of Figs.3a and 3b in more detail.

Fig.9 shows a similar panel to the panel 14 in Figs.4a and 4b with the exception that the projection 26 is sheared in such a way that the part of the circular peripheral wall which project outwardly from the panel 14 flares outwardly to create a slightly wider diameter projection at the end thereof spaced from the panel 14. The outward flaring is not particularly substantial but is sufficient to cause a snap-fit when being located in the aperture 18 of the panel 12,

Fig.lO illustrates a further panel assembly 10 in accordance with the invention. In Fig.lO the first panel 12 has a projection 42 formed therein which defines, on the underside thereof, a recess 44. Another panel 14 has a projection 46 extending therefrom, which projection is substantially similar in size and shape to the recess 44.

The projection 46 extends into the recess 44 so as to locate the panel 12 on the panel 14 as shown in the previous embodiments. Again, the projections and recesses 44, 46 are formed at least partially by shearing the panel material.

In Fig.ll, the assembly of Fig.lO has a further stepped feature 48 formed by pressing or shearing on the lower panel 14. The underside of upper panel 12 rests on the stepped feature 48 to define a spacing 50 between the panels 12, 14. This enables positional control of the panels in the "Z" direction, i.e. in the direction of shear of the formation, whilst the sheared sides of the formation 46 provide positional control in the X-Y direction of the panels, i.e. in the plane of the panels.

Although the embodiments described comprise substantially circular apertures and projections 18, 26, 34, 38, 44, 46, it is envisaged that alternative shapes may be used. For example, the aperture 18 and the projection 26 may be rectangular in shape or another appropriate polygon. The aperture may comprise a slot having semicircular ends and the projection 26 may comprise a circular projection running in the slot or another appropriate shape running in the slot.

IQ figs. 12a to c, a punch tool 51 for creating a shear-formed projection in a vehicular panel in accordance with the invention comprises a punch body 52 and a

punch head 54. The punch body 52 has a waist portion 56 and a recess 58 to allow it to be secured to a driving mechanism (not shown). The punch head 54 comprises an elongated cylindrical part extending from the body 52 via a tapered portion 60. The tool is generally cylindrical and has an axis X. An end face 62 of the punch head 54 has three shear cutters 64 which extend radially and are equally angularly spaced relative to the other. Each shear cutter 64 extends around 15 degrees and each cutter 64 is spaced from its neighbour by approximately 105 degrees. The shear cutters 64 stand proud from the rest of the surface of the end face 62.

Figs. 13a and b show a punch die 66 for use with the punch tool shown in fig. 12.

The punch die 66 is generally cylindrical and has a bore 68 extending from one end into a larger bore 70 which extends to the other end of the die 66 via a shoulder 72.

Fig. 14 illustrates the punch tool 51 forming a location formation in a vehicular panel 74. The panel 74 is arranged between the die 66 and the punch tool 51 and the punch tool 51 is pressed against the panel 74. The diameter of the punch head 54 is slightly smaller than the diameter of the bore 68 and the die 66. As the punch tool contacts the panel 74, the shear cutters 64 (not shown in fig. 14) contact the panel 74 first. That pushes part of the panel 74 into the bore 68, deforming the panel 74 around the die 51. Because of the relative geometries of the bore 68 and the punch head 53, the shear cutters 64 partially shear through the panel 74 as shown in fig. 14 and 76. The remaining part of the panel engaged by the punch tool 51 which is not engaged by one of the shear cutters 64 is press formed as shown at 78 in fig. 14.

The arrangement of the punch tool 51 and die 66, when applied to vehicular panel

74 produces a panel 74 as shown in figs. 15a and b. The panel 74 has a projection 80 which is circular in plan and conical in section. Three die cutters 64 produce three strips of material from the panel 74 which extend from the centre point of the projection 80 radially outwardly therefrom at the equal angular spacings. Those portions 82 are at least partially sheared, as shown in fig. 15b, from the rest of the panel 74. They are retained on the panel 74 by means of lands 84 which correspond to the portions of the face 62 of the punch head 54 between the shear cutters 64.

In fig. 16, the vehicular panel 74 has been assembled together with another panel 86 which has an aperture 88 formed therein. The aperture 88 has a diameter which is selected to be an interference with the outer diameter of the projection 80 defined by the radially outer extent of the partially sheared portions 82.

The conical shape of the projection 80 acts as a leading portion as the panel 74 is placed against the panel 86. The shear formed portions 82 abut the inner wall of the aperture 88 to provide a very precise fit between the panel 74 and the panel 86.

Fig. 17 is an end elevation of another punch tool 88. The punch tool 88 has a punch body 90 which is generally cylindrical. Punch head 92 is lozenge shaped in section and the end face 94 of the punch head 92 has two semi-pyramidal projections 96, 98 extending therefrom spaced apart by a recess 100. When the punch tool 88 flies to a vehicular panel 102 against the die (not shown), the panel 102 obtains a projection 104, as shown in figs. 18a and b. The projections 104 is lozenge shaped and has two strip-like, shear-formed portions 106, 108 at opposite ends thereof. The projection 104 can be arranged in the correspondingly lozenge shaped recess or aperture in another panel (not shown) to provide securing of the panel 102 to the panel (not shown) and to provide resistance against rotation of the panels relative to each other.

A polygonal-shaped projection located in a correspondingly polygonal aperture has the advantage that that serves to locate the panel against two degrees of freedom. That can reduce the overall number of aperture and projection pairs required to locate the panel prior to fixing.

Any of the projections could be arranged to co-operate with an appropriate aperture which may be machined from a casting.

As mentioned above, one of the advantages of the present system is that the location between the panels is provided by the panels themselves rather than by a separate jig/fixture. This reduces tooling costs as well as assembly time. Also, the

present invention may allow multiple different panel assemblies to be assembled using the same assembly fixture since only minimal location/support will be required to hold the panels in a particular place prior to welding or other fixing method. That, in turn, opens up the possibility that a single assembly fixture station could be used on a production line to join multiple different panel designs and improves the opportunity for tooling reuse at the end of a production run of a vehicle.