Achieving process repeatability

The increase in the productivity of a machine tool depends on the repeatability of the process. Boosting machine tool productivity strongly also relies on the dynamic characteristics of the machine. Collet-type, hydraulic, shrink-fit, Weldon and other holders all have different dynamic properties. It might be possible to adjust the part program to account for the geometric change caused by a new holder, but changing the holder means the stable spindle speeds move and the permissible chatter-free DOCs change. It may look that for ISO- and HSK-type connections, drawbar force matters and it might seem desirable to have the drawbar force as high as possible. It is not so because a high drawbar force does increase the stiffness of the connection, but it also eliminates damping. Machine tool builders specify an acceptable range, and it is a good idea to check the drawbar force with a drawbar dynamometer. NC programming software currently allows the part program to be written considering only workpiece geometry.