Bridgeport introduces effective thermal compensation

Citation

(1999), "Bridgeport introduces effective thermal compensation", Aircraft Engineering and Aerospace Technology, Vol. 71 No. 2. https://doi.org/10.1108/aeat.1999.12771bab.015

Bridgeport introduces effective thermal compensation

Bridgeport introduces effective thermal compensation

Keywords Bridgeport, Machining

Bridgeport announces what is believed to be a technological leap forward in providing higher standards of excellence in the machining of components.

In response to the demand by users of machine tools for more consistent levels of machining accuracy, Bridgeport has developed a thermal frame compensation system, which is now being fitted as standard on all models from the VMC 600 through the range to the largest VMC 2000.

Thermal distortion is a natural occurrence in all machine tools, the biggest generator of heat being the spindle assembly. This can cause quite severe inaccuracies in machined components over a period of time as the frame absorbs the heat. The problem has been addressed at Bridgeport in a number of ways.

Bridgeport have minimised errors owing to heat generation by fitting the latest specification, high-efficiency, digital spindle motors from Siemens, which reduce heat transfer by 25 per cent and by isolating it from the main structure of the machine.

Heat generation has been reduced by re-designing the spindle itself with the introduction of ABEC 7 class ceramic bearings on 10K spindle assemblies.

On the portal frame Bridgeport machines, models VMC 1500 and VMC 2000, refrigerated spindle motor chillers have been incorporated to reduce thermal effects generated by the in-line spindle motor assemblies. This allows most of the heat within the spindles to be regulated and kept constant, which is an important factor, say the company.

While all of these measures have reduced thermal effects significantly, residual heat is further compensated for by the introduction of an innovative temperature measuring system, which uses a mapping technique to check thermal growth in the Y and Z axes in every standard frame.

These data are then fed into the computer control which automatically effects mechanical compensation for any heat generation. The system works on the basis that, as the heat generated in the spindle head can vary according to spindle speeds, and also the heat generated in the ballscrew will differ depending on duty cycles, it is important to have a dynamic system of measurement that can take into account these differing heat sources.

The system uses four temperature sensors, three on the machine spindle head and one to measure the ambient temperature. Temperature rises in the structure are constantly measured and the data fed back to the Heidenhain control.

From temperature rises monitored by the sensors, a calculation in the control is made based on the mathematical model unique to the particular machine type and consequent levels of distortion determined. The values are then fed into the relevant axes as offsets to counter any unwanted thermal effects.

Further details from Bridgeport Machines Ltd. Tel: +44 (0) 116 2531122; Fax: +44 (0) 116 26399960.