How ball bar calibration can drastically improve machine accuracy and reduce part rejection:

Machining centres, horizontal or Vertical, are required to achieve consistent accuracy in their machining capabilities. With mass production requirements or intricate batch production needs, part rejections are a devastating loss. In order to achieve lesser rejection, regular calibration of machines is a must. The Ball Bar is a calibration tool that analyses the motion on a machine tool. With a circular interpolation of two axes as the centre of inspection, the tool records the motion of the axes and detects the deviations that the machine tool is making in creating the circular motion. When a program is made on a CNC machine tool to create a circular path then the same should be achieved during machining. We expect this perfection in theory but practical factors like wear, control system and machine geometry affect the radius of the test circle and its shape to deviate from the programmed circle. To measure the circularity of a machine we would have to accurately measure the actual circular path and then compare it to the program.

The tool:

Made up of a telescoping bar with precision balls at each end, the ball bar can detect the movement of the spindle through Transducers inside the bar. The tool is mounted on the table and spindle which are located in the face of each mount. With this set up, the ball bar measures detailed deviations in the radius as the machine follows a circular path as per the program. The test takes into observation two consecutive circles, a clockwise and counterclockwise direction. In theory, a machine with perfect positioning performance would move in a circular path that exactly matched the program circle. By recording this data and comparing it through the ball bar method is one of fastest and most accurate methods of checking for machine accuracy. Conducting this calibration test on a regular basis is an important preventive maintenance to ensure that your productivity is unaffected. With a ball bar test errors like Reversal spikes, Back lash, Scale miss match, Straightness, Squreness, cyclic error, stick slip, vibration, lateral play, radius change, Servo mismatch etc. can be identified and tuned. Why Ball Bar calibration is important:

• To confirm that the original build specification is maintained in the customer’s working environment
• This is a predictive maintenance tool that helps avoid the rejection of the components.
• It helps figure out the machine’s performance capabilities.
• Guarantee the process control (Cp, Cpk) for machining operation.
• Create & authenticate the error compensation parameters for the controller.

Request for a calibration test from your Micromatic service engineer at the earliest.