Evaluation of and Compensation for Thermal Deformation in a Compact CNC Lathe

Because heat sources for compact Computer Numerically Controlled (CNC) lathes are likely to be closely arranged, they may cause large and complicated thermal deformation. Previously, we developed a CNC lathe with its heat sources arranged so as to reduce thermal deformation. This lathe achieved highprecision work under stable temperatures in continuous operation. However, in some cases, it could cause rapid thermal deformation. Previously, we proposed a simple method to compensate for the thermal deformation in CNC lathes by measuring temperatures at only a few points. By developing amodified compensation method capable of estimating minute and complicated thermal deformation and applying this method to the current lathe, processing accuracy will become more precise. Thus, we evaluated the thermal deformation of a compact CNC lathe. As a result, we found that the thermal deformation of the lathe was caused not only by movable parts, such as the spindle motor, but also by non-movable parts, such as the hydraulic unit. We therefore approximated the thermal deformation caused by the non-movable parts and estimated the change in the deformation caused only by the movable parts. This enabled us to express the thermal deformation by a simple linear equation, the form of which was same as that used for previous lathes. From these results, we were able to compensate for the thermal deformation using approximate equations for both movable and non-movable parts and we applied this method to the current lathe. We confirmed that the work error can be reduced under stable conditions using this method.