Energy efficient usage of CNC machines

DAMRC has though several years performed productivity optimizations at various companies in Denmark. This is done by stability optimization though modal analysis. From this work, it is known that machining at unstable conditions increases cutting forces dramatically. Based on the knowledge of machining stability and cutting forces, it is expected that machining stability affects the energy consumption of the machining process, and that increased stability and productivity will have a positive impact on the energy consumption.

This hypothesis has been tested in this project through comparative studies, where energy consumption has been recorded pre-and post-stability and productivity optimizations. This have been studied though internal experimental studies at DAMRC Technology Center and furthermore with industrial tests at multiple machining companies across Denmark, using true production parts.

The power consumption has been measured for a specific process/part, where the parameters has not been optimized. The parameters have then been optimized via modal stability analysis and cutting forces analysis to obtain productivity improvements. Secondly a similar machining process has been conducted and the power consumption has been measured again. These measurements are converted into actual power consumption per process/part, and such the consumption can be compared before and after optimization to understand the influence of power on the optimization via stability- and cutting force optimization.

Both measurement from the industrial partners on real production as well as the lab-tests at DAMRC has shown that.

• When productivity is increase, the power consumption is increased – however not proportional.
   
• When machining time is reduced as a consequence of the productivity optimization, the power consumption is reduced per part – resulting from the NON-proportional relation between productivity increase and increase of power consumption.

This leads to the conclusion, that productivity optimizations achieved via stability optimization is most likely to reduce energy consumption per part.

Results from pre-studies show as much a 40% reduction in energy consumption per part, when all processes have been optimized via modal stability analysis. Similar, however not as large effects are seen in industry cases, where a typical reduction in energy consumption per part is between 0-10% compared to reference consumption before optimization. The interesting aspect of these numbers is, that they “allow” to reduce energy consumption per part, or to produce more parts using the same total amount of energy.

In a situation with a theoretical full national implementation of modal stability- and tool path optimization, an accumulated national saving between 5-50 mio. kWh might be possible. Settling at just 1% full implementation the accumulated national saving would still be in the range of 0,5-5 mio. kWh.

Originally it was believed that machining at optimal stability conditions would yield a reduction in energy consumption. However, the studies have indicated that the main driver for energy reductions is most likely the reduced machining time. This outlines one of the most important findings of this project – how small portion of the total energy consumption that is used on pure machining.

The results of this project – coupled with findings from similar projects carried out by DAMRC, as well as Aarhus University, has established a foundation for a future project to which funds will be sought. This project aims to study the power consumption of auxiliary processes and stand-by modes of machine centers, with the goal to find possibilities for energy reductions, as studies show that these uses up to 90% of total energy consumption.

Further, the results will ongoing be communicated by DAMRC as a method to work sustainable with energy consumption per part which also benefitting economically