"Bumper and a method of manufacturing the same" The present invention relates to a structural member such as an impact absorbing member provided with a hole for accommodating a towing hook. It further relates to a method for making a hole in the wall of a structural member such as an impact absorbing member, preferably being an extruded profile.

It is formerly known to make holes in structural members by stamping, drilling or in any other way remove material from the sidewall of the profile. This method is also known for making holes in impact absorbing members or bumper beams. The holes are necessary for enabling the attachment of a towing hook in the beam.

Due to the pressure put on the towing hook in a towing operation, the towing hook will deflect laterally or vertically from its initial position. In many cases the towing hook will get in contact with the edge of the hole through which it is inserted. The surroundings must therefore support a high amount of stress without tearing up the walls through which the towing hook is entered.

Previously, holes for entering a towing hook has been enforced by increasing material thickness of the bumper beam sidewall. Alternatively, a reinforcement part have been manufactured separately and attached to the structural member in the designated area in which holes are made.

Both methods will lead to increased material consumption and thereby overall weight of the vehicle part. The use of an extra reinforcement part leads to a more complicated manufacturing process due to the extra part.

The claimed invention presents a structural member provided with a reinforced hole having improved mechanical resistance and load bearing capacity. As the flange forms an integrated part of a member sidewall, an improved strength is obtained in

the rim of the hole compared to previously known methods for forming holes in structural members.

The invention further presents an improved method for making such reinforced holes in a structural member. This is done by forming sidewall material into a hole provided with a flange.

The hole is made by pressing out the excessive material simultaneously with removing it from the sidewall, thereby forming a hole with an integrated flange. The excessive sidewall material will provide the hole with an integrated flange. The sidewall material is removed by pressing a rotating die onto and through the sidewall surface. The friction caused by the head of the rotating die will heat the wall material locally and make excessive material flow outwards as the rotating die is pressed through the side wall, simultaneously forming the hole and the integrated flanges.

The invention will now be an example further explained by means of figures where: Fig. 1 shows a section of a bumper beam with a towing hook and a hole of prior art, Fig. 2 shows a side view of a section of a bumper beam with a hole according to the present invention, Fig. 3 shows a cross sectional view of a towing hook arrangement according to the present invention, Figs. 4-7 show the method of making a towing hook hole according to the invention.

A bumper beam 1 of prior art is shown on Figure 1. A hole 2 is made in the bumper sidewall 3. A towing hook 4 is inserted through the hole 2 and attached inside or behind the bumper beam 1, on the neighbouring structure or elsewhere on the vehicle structure where it is found appropriate.

A load is attached to the towing hook 4, normally from a vehicle being towed. As the towing vehicle and the towed vehicle are moving, the towing hook 4 will be forced in different directions putting a load on the hole edge 5 and thereby on the sidewall 3.

To avoid breakage of the hole 2, it is sometimes required to increase the dimensions of the sidewall 3 or add extra material as a flange member or the like to the hole 2.

Fig. 2 shows a section of a bumper beam 1 according to the present invention. The hole 2 is made by displacing sidewall material thereby forming a hole. The material of the sidewall 3 being displaced will form a collar or flange 6 around the hole 2.

The flange 6 will have a strengthening effect on the hole 2, thereby enabling a decrease in sidewall thickness without compromising the technical requirements for the towing hook arrangement. As the flange 6 is an integrated part of the sidewall 3, the transition between the sidewall 3 and the flange 6 will be continuous thereby creating a stress flow with low stress concentrations from the towing hook through the hole 2 into the sidewall 3.

Figure 3 shows a cross sectional view of a towing hook arrangement with a hole 2 in the bumper sidewall 3 according to the present invention. A hole 2 provided with a flange 6 according to the invention is made in one of the sidewalls 3 of the bumper beam 1. The flange 6 forms a cylindrical shape in the hole 2.

Figures 4-7 show a method for forming a hole 2 with an integrated flange 6. A hole 2'having a smaller dimension than the final hole 2 is punched in the sidewall 3. A revolving tool with a pointed head 7 is pressed down directly onto the hole 2'. As the head 7 revolves in the hole 2', the surrounding region of the sidewall 3 is heated by friction and will flow out, forming a collar or flange 6. The revolving head will thereby simultaneously form the hole and the surrounding flange.

The revolving head 7 is pressed down through the hole 2'increasing it until a hole 2 according to the invention is made in the side wall 3. The flange 6 will have a mainly cylindrical shape. The flange will normally be formed mainly perpendicular on the

sidewall surface. By pressing the revolving tool onto the surface in a predefined angle, the flange will form a different integrated shape in the sidewall of the member.

As the flange and hole are made at a low temperature raise, the method will not cause any substantial heat affected zone around the hole and flange. However, the small temperature raise, causing the side wall material to flow, also leads to a method where little pressure is put on the side wall, thereby avoiding residual stress in the area surrounding the hole and flange.

A hole according to the present invention can be made in any wall and any section of the bumper beam where reinforcement is needed.

It should further be noted that the method for forming such holes also could be used for forming holes in other structural members such as vehicle parts, where stress is lead into the structure through a hole. Such examples can be in the flange of a crash box, on the end section of a vehicle side member or other vehicle parts where enforced holes are needed.

The invention is especially suited for forming a reinforced hole in an extruded profile preferably of aluminium, but it can also be used for forming reinforced holes in structural members made of other materials such as steel or polymers.