Engineering practice classical approach in the machine tool design follows the aspect of the possibly highest machine frame static stiffness achievement. Besides the need of reaching high stiffness at the tool centre point (TCP), the mentioned principle takes into account commonly applied method of position measurement in locations relatively distant from the TCP as well. With the prerequisite of the TCP positioning control based on the mentioned measuring method the need of the position error minimization between the measuring scale and TCP arises. Fulfilment of such requirement has been until now usually attained by means of static and dynamic stiffness enhancement of the machine tool parts. Using steel and cast iron, materials commonly applied in the machine tool design, leads to the design of quite heavy structures. Decisive amount of the material applied is used to meet the stiffness criterion, whereas only a small fraction of the material provides kinematical functionality of the machine tool. Machine tool heavy movable parts consequently require feed drive design with appropriate dimensioning of its components and sufficiently powerful motor.
Mass of the machine structure and motor power decides the overall energy demands of the machine tool operation. Energy consumed by the motor during the machine operation is besides the force spent to counteract the cutting forces proportional to the passive resistance forces magnitude and force applied to accelerate or decelerate the machine tool components. Acceleration forces component becomes very important especially with the high speed cutting (HSC) processes, for which increasing number of new machine tools are being designed. Appropriate capacity of the cooling and lubrication systems relates to the motor power and size of the machine tool components as well, whereby energy consumption of those systems represents another part of the machine tool overall energy budget.
Until now there has not been much attention paid to the question of the energy consumed during the machine tool operation. Considering the still increasing energy prices and with respect to the environmental protection issues, machine tool energy efficiency can become one of the important qualitative parameters applied with the machine tool assessment.
Author: Ing. Matej Sulitka, PhD. www.rcmt.cvut.cz
