Rapid traverse

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Efficient turning and milling with rapid traverse

Rapid traverse is a tool speed intended for empty runs without component contact. It is used to move the tool to the desired position. The rapid traverse must always be precisely calculated, otherwise there is a risk of serious machine damage.

Machining processes on modern lathes and milling machines

The process of machining a turned or milled part takes place in the following two main phases:

  • Roughing
  • Finishing
  • Finishing

Roughing or broaching refers to the rapid removal of as much material as possible. Tolerances and adherence to the exact geometry are not yet important during roughing. Only a few tools are required for roughing. A standard milling cutter or chisel is usually sufficient to form the desired raw geometry from the workpiece.

Roughing is followed by finishing. In this machining step, the pre-roughed workpiece is brought to its desired geometry while maintaining the required tolerances. This requires considerably more tools.

Finally, the finishing operation follows. Here, threads are cut in prepared holes, chamfers are formed or burrs are removed. Today, this is also largely automated and done in the same operation.

Time factor tool change

CNC machines only work profitably if they can produce a sufficient output of workpieces. This makes the machining time per workpiece a critical factor. This time can be shortened considerably with the rapid traverse. As soon as a machining operation is finished and a tool change is due, the spindle retracts completely from the workpiece. It then moves at rapid traverse - i.e. at up to 100 m/min - to the tool changer. There, the desired tool is already waiting to be picked up. The new workpiece then moves again at rapid traverse to the next machining point. The previously lengthy process of tool changing has been reduced to a few seconds by the rapid traverse.

Limits of rapid traverse

Theoretically, rapid traverse speeds of up to 1400 m/min are possible on machine tools today. However, these high speeds must always be braked again just as effectively. This causes the machine to vibrate, and the tolerances can suffer as a result.

The greatest danger of rapid traverse, however, is workpiece contact. If the workpiece enters the solid steel block at full speed, a so-called "crash" is inevitable. The damage is not only to the workpiece and the tool. The entire machine is also affected by a crash. This makes the exact calculation of the rapid traverse an indispensable matter.