Stability Analysis of Turning Process in the Presence

Document Sample
Stability Analysis of Turning Process in the Presence Powered By Docstoc
					                  Tehran International Congress on Manufacturing Engineering (TICME2007)
                                     December 10-13, 2007, Tehran, Iran

           Stability Analysis of Turning Process in the
                      Presence of Tool Wear

                  H. Moradi1, M.R. Movahhedi2 and G.R. Vossoughi3
          Manufacturing Engineering Group, Mechanical Engineering Department,
                 Sharif University of Technology, Azadi Ave.,Tehran, Iran

Chatter suppression is an important topic in any type of machining process. In this
paper, orthogonal cutting process is modelled as a single degree of freedom
dynamic system. A nonlinear delay differential equation is presented that models
flank wear of the tool. Results of stability analysis for two distinct cases of a sharp
tool and a worn tool are presented and compared. In addition, the effect of some
machining parameters such as tool wear length and cutting velocity is discussed in
this analysis. It can be shown that in the case of a worn tool, dynamic system is
more stable.

Keywords: Regenerative Chatter, Nonlinear Model, Tool Wear, Stability analysis

1 Introduction
Chatter is an undesirable phenomenon in machining processes which can result in
reduction of material removal rate (MRR), poor surface finish and increase in tool
wear. In the early works of the subject [1-4], modelling of the dynamic process,
structural aspects and stability limit aspects have been studied. Machine tool chatter
can be classified into regenerative and non-regenerative chatter. The former is due
to the interaction of the cutting force and the workpiece surface undulations
produced by preceding tool passes. Non-regenerative chatter is due to other
phenomena, such as mode coupling, and usually occurs when there is no interaction
between the vibration of the system and undulated surface of the workpiece, such as
in threading. The regenerative type is found to be the most detrimental phenomenon
in most machining processes. The most common approach to avoid undesirable
chatter vibration is through the adjustment of operational parameters, i.e., cutting
conditions [5-8]. Stability lobes are usually obtained to find sets of cutting conditions
while maintaining high production rate.
Tool wear is an important factor in machining with a significant effect on high rate
production. The complex nature of tool wear is regarded as a major obstacle in
achieving of manufacturing automation. Many efforts have been done to find a
correlation between machining parameters and the tool wear [9-12]. Since the force
signals are highly sensitive to the status of machining process, measuring the
amplitude of cutting forces is an effective technique for indirect detection of the
extent of the tool wear [13-15].

    - Graduate Student
    - Associate Professor
    - Associate Professor