This invention relates to wheel rim manufacture.

A wheel rim, particularly for the wheel of a car or other road vehicle, is conventionally manufactured by cutting steel strip to the required length, forming the strip into a hoop so that the two ends abut one another, and joining the ends together by a butt weld. Subsequent process operations include shaping or forming the hoop to form the flanges, bead seats and well of the rim, forming a hole in the rim for receiving an inflation valve, and testing the butt weld for any leaks.

Some of the subsequent process operations need to be carried out at particular locations on the rim and the butt weld is used as a datum. Thus the butt weld has to be located accurately.

One method of locating the weld comprises shining a narrow light beam at the rim, receiving the reflected beam and detecting when the reflected beam is disturbed by the butt weld. However sometimes the reflected beam is disturbed by a foreign body on the rim such as dirt or a patch of oil with the result that the subsequent operations which are required to be carried out at locations accurately measured from the weld are not so carried out. The rim is thus manufactured in a faulty condition and has to be rejected .

One method of overcoming this problem was to form the hole for receiving the valve in the rim immediately after the butt welding had been carried out, the hole being located at an accurate predetermined distance from the weld, and the hole rather than the weld being used as the datum. However subsequent forming operations can cause distortion of the hole causing it to be unsuitable so again the rim has to be rejected.

It is an object of the present invention to provide a method of manufacturing a wheel rim which substantially overcomes the aforementioned

disadvantages.

In accordance with the invention, a method of manufacturing a wheel rim comprises cutting steel strip to the required length, applying a mark to the strip at an accurately predetermined distance from an end of the length of strip and using the mark as a datum in any subsequent manufacturing operation required to be carried out at an accurately determined position on the rim with respect to the end.

The mark may be applied after the end has been joined to the other end of the strip.

The mark may be in the form of a small indentation applied to a surface of the strip which is preferably the radially outer but may also be the radially inner surface of the finished rim. The indentation may be applied by any suitable indentation tool such as a punch or a drill. The indentation is preferably detectable by an eddy-current detector or other suitable device. Alternatively the mark may be in the form of an ink dot or line applied to the surface. The ink may be a magnetic ink so the mark is detectable by a suitable magnetic detecting device.

One embodiment will now be described by way of example only with reference to the accompanying drawing of a wheel rim manufactured according to the invention.

As shown in the drawing a wheel rim 10 comprises a well 12, two bead seats 14, 15 and two flanges 16,17. During the course of manufacture a mark in the form of a small indentation 18 is applied to the outer surface of the rim in the well 12 at an accurately measured distance e g 20 mm from the weld joining the two ends of the length of steel strip from which the rim is formed. The indentation is applied by means of a small indenting punch.

At a later stage in the manufacture of the rim the position of the indentation is detected accurately by means of an eddy-current detecting

device and the rim then rotated by a predetermined amount so that the point at which it is required to form a hole (not shown) for an inflation valve is moved beneath a hole forming tool, and the hole formed. The point for the hole is often diametrically opposite the weld so the point is thus half the rim well circumference ± 20 mm (depending on the direction of rotation of the rim) away from the weld.

The last stages of the manufacturing process include various control checks, for example checking to ensure that the weld does not leak. In order to do this the mark is detected by an eddy-current detecting device, one side of the rim is pressurised and the leak detector placed 20 mm circumferentially from the detected mark i.e. immediately adjacent the weld.