The life of every driver depends on how safe his brakes are.

Brake discs have become a global mass product, but one that makes enormous demands on safety. In the end, the life of every driver depends, often more than just once every day, on the safety of his brakes.  At present, 600 million passenger cars travel the roads and byways of the world. Let us assume that during the 10 to 14 years of the life of a car the brake discs are being replaced at least once – and that a quarter of all passenger cars are still equipped with drum brakes – and we arrive at an annual global requirement of approximately 400 million discs.

Before, it had been customary to use at least four interlinked VSC machines for the complete-machining of brake discs. A new aspect of this particular solution was the attempt to achieve the same result with a line of just three machines. The problem faced was an obvious one: required capacity. The task was to produce 200,000 brake discs for passenger cars per annum – of the same type, not internally ventilated (owing to the speed limit in the country), in a material comparable to grey cast iron, with a disc diameter of 300 mm. The finish-machining operation was to be cross-grinding, to achieve a better surface finish. Other requirements were dry machining, balancing, a test certificate, and the components finish-machined, ready for despatch. The required cycle time: less than 100 seconds, all inclusive. This type of disc makes greater demands on the manufacturing technology, as it is less stable during machining than the ventilated variety. Brake discs are also increasing in size, but are not supposed to get heavier. Larger diameters achieve a higher braking torque. The braking area is moving further away from the centre. As a result of these changes the discs are getting thinner and sometimes tend to flutter. This is as much a problem during machining as it is later during braking. Those drivers clamouring for greater comfort and a quieter car do not take kindly to braking noises and fluttering. Ergo, the brake discs must be manufactured to the highest precision.

The two VSC 400s and one VSC 500 are linked up by automation equipment from Heilig (also part of the EMAG Group). This forms a continuous, fully automated line from collection of the workpieces stored in skeleton containers via turnover stations to the component’s final destination – packing. The fist station (a VSC 400) turns, drills, taps and gauges the first side of the component. The rough machining operation uses KM special heads that accommodate single and twin tool tips coated with silicon nitride (Kyon 3400). The coating increases tool life by about 30%. Combination drilling and chamfering tools plus threading tools complete the tooling equipment for the first station. The second station (also a VSC 400) turns, drills and gauges the second side of the component. Equipment: the same as station 1, plus solid carbide step drills and solid carbide fraises, the latter chucked in live tool holders using expansion chuck technology from Kenna. The third station (a VSC 500) turns, grinds, balances and gauges and also generates a protocol. The result of including all these operations in a complete-machining cycle that requires only a single set-up is a considerable leap in component quality. The deviation in the thickness of the discs is below 3 µm, the surface finish below Rz 6.3 µm, with parallelism/runout also being in the µ-range. The tooling used for the finishing-operations consists of an NC twin cutter head KM50 for the simultaneous machining of both brake surfaces, a further NC twin cutter head KM50 for the machining of the contact surface of the cup, and two CBN grinding wheels for the cross-grinding of the brake surfaces. The final tool in the third station is a solid carbide balance fraise.