Ball-type constant-velocity universal joints are known wherein the drive member and driven member, which rotate about intersecting angles, are both formed with ball races. The ball races of one member open outwardly and the ball races of the other member open inwardly, so that balls each received halfway in a race of the one member and halfway in a race of the other member are used to transmit angular force between these two members. Such universal joints are used frequently in a motor vehicle, one at the rear end of the transmission and another at the input side of the differential at the rear axle.
Typically the halves of such a universal joint are formed by forging. Thus a workpiece blank corresponding roughly to the shape desired is fitted between a pair of forging dies which are then pressed together so as to forge the desired shape in the universal-joint half. Such cold working produces a workpiece that is very strong.
If the races are to extend along skew axes relative to the center axis of such a universal-joint half, it is impossible to form these races in the universal-joint half by forging. Forming the inside of the forging dies with grooves to form the races would be out of the question, as since these ridges would have to extend at an angle to the opening and closing direction of the dies, the forged workpiece could not be separated from the dies once completed. In fact it would be impossible to open the dies at all without damaging the workpiece or the dies. For this reason in this type of arrangement the races are machined into the forged workpiece after the forging operation.
It is, however, possible to form races in the dies by forging the races directly into the workpiece during the forging operation in situations where the races extend parallel to the opening and closing of the dies. Such an arrangement invariably leaves a ridge or rib along the closing plane of the die in each of the races. This ridge or rib must be removed completely, so that it is necessary in any case to subject the forged workpiece to a subsequent machining operation. Obviously the cost of such machining elevates the price of the finished workpiece.