The objective of this work was the development of aMachining Control prototype system for turning, whichintegrates three fundamental aspects of Machining Controltechnology: Monitoring, Control and Optimisation. MachiningControl refers to the detection and automatic handling ofdisturbances in machining processes. Consequences ofdisturbances can be classified in three major groups:Breakdowns, production rejects and non-optimal production. Byminimising these consequences, the efficiency of the machiningprocess can be improved, which in turn will have a major impacton productivity, machining economy and product quality as well.This calls for user friendly supervisory systems that cansupport the human operator and perform monitoring, control andoptimisation tasks, i.e. Machining Control (MC) systems.
The MC system presented in this thesis is developed around aturning centre, and consists basically of a PC equipped with amodular DSP multiprocessor, sensor systems for vibration andcutting force measurements, as well as machine tool interfaces.The basic structure of the MC system allows flexibleimplementation of tasks, which can interact with the machinetool controller and other auxiliary devices. In other words,the MC system combines virtually all essential features toperform advanced real time supervision.
An important aspect in the development of this MC system wasthe access to accurate data, reflecting the underlyingmachining process. Therefore, the turning centre is equippedwith an integrated dynamometer and an acoustical sensor systemthat have access to the tool-workpiece interface. To ensurereliable cutting force measurements, a three-axis calibrationmethod has been developed that performs a transformation ofoutput signals from the force sensor system to accurate cuttingforces at the tool tip. A good knowledge of tool vibration andinstantaneous cutting forces allows the safer use of moreaggressive machining operations, thus utilising most of theavailable tool life withoutcausing costly breakdowns andproduction rejects.
Two MC functions for in-process tool condition monitoringhave been developed and are discussed from both theoretical andexperimental point of view. Classical models have been used toanalyse the dynamic behaviour of the machining system, whileparametric modelling was employed for in-process monitoring andcontrol of dynamic stability. It is shown that an efficientcontrol of dynamic stability only can be performed if propertooling is selected. Some efficient solutions for improving thedynamic properties of tooling are presented. Finally, a modulefor an automatic optimisation of cutting conditions isdescribed. This module takes advantage of all the features thatare implemented in the MC system.
This research work shows a successful application of anintegrated MC system for an effective combination betweenpeople and technology in future manufacturing systems.
Keywords:Machining Control, tool condition monitoring,in-process dynamic stability monitoring and control,optimisation of cutting conditions, MC, DSP, TCM
Stockholm: KTH , 2001. , 230 p.
Machining Control, tool condition monitoring, in-process dynamic stability monitoring and control, optimisation of cutting conditions, MC, DSP, TCM