Year

1998

Degree Name

Doctor of Philosophy

Department

Department of Mechanical Engineering

Abstract

With the expanding use of automation in machining technology, the modern manufacturing aims toward achieving high productivity without close human supervision. This aim requires reliable machining processes. The chip control is one of major concern in automated machining system. It is essential for the safety of the machining operation, the maintenance of good surface finish on the machined parts, the convenience of chip disposal, and the possible power reduction.

This thesis major deals with theoretical modelling for the 3-D chip curling process, including geometry and mechanics consideration. These models are then used to develop a computer animation system to simulate the process of chip curling in 3-D metal cutting. Hence the work described in this thesis is devoted to developing an effective theoretical technique for chip control in automated machining systems.

Firstly, a new method to describe the development process of 3-D chip curling is developed in accord with the mechanics and kinematics characters of chip curling in 3-D machining. This analysis divided the process of 3-D chip development into different stages based on the deformation mechanism and characteristics, i.e. chip forming stage, chip curling stage, chip breaking stage, and the kinematical characters according to whether the curled chip, after leaving the rake face, hits the backwall of breaker/groove, or/and workpiece, or/and backface of tool, or/and extends along the chip breaker. Then new basic chip curling forms, up-curling, side-curling and twisting, are proposed based on the continuum mechanics theory. It reveals that a 3-D curling chip body m a y undergo longitudinal bending, transversal bending and torsional deformations. The analysis provides the fundament for the theoretical modelling of the 3-D chip curling and breaking.

Secondly, a general geometric model of 3-D chip curling generated by typical chip breakers is developed by introducing the three-dimensional deformation state of the chip curling. The model, so developed, can be used to predict the 3-D chip curling forms. The prediction includes a group of criteria for the effects of ωx, ω ʸ, ωz and ηo on the chip forms/shapes. The varying tendency of the chip radius and chip pitch with varying ωx, ω ʸ, ωz and ηO is further discussed based on a sensitivity analysis the results of which are summarised graphically. The sensitivity analysis provides a quantitative assessment of the significance of three basic chip curling forms, namely up-curling, side-curling and twisting to the general helical chip form.

Thirdly, a set of 3-D mechanics models of chip curling with chip breaker for the internal resisting forces is developed for the 4 basic chip deformation cases of chip curling process based on the structural mechanics theory, These internal forces, in particular the bending moments and torques are expressed as variations along the length of the curled chip. The set of models considers a spatial force system including the longitudinal bending moment, transversal bending moment and the torsional torque. Then the distribution of the bending moments and torques along the chip body are discussed based on graphically presented calculated results. The models reveal, in theory, new insights into the chip breaking mechanisms. More importantly it provides a new approach to theoretically asses the curling chip breakability. Notably it is shown that the bending moment and torque are the main causes of chip breaking. Furthermore the bending moment and torque in the chip body are caused by the chip breaker and the obstacle the curling chip contacts.

Finally, a computer animation system for 3-D chip curling in machining process is developed based on the 3-D chip curling developing process, geometry model and mechanics models of 3-D chip curling presented in the research work. The 3-D chip animation integrates the chip flow equation, chip curling patterns, chip geometrical features and mathematical expressions for the 3-D helix surface. Based on the input conditions (namely chip breaker parameters and cutting conditions), a computer program is developed to convert the parametric prediction into a series of dynamic graphs demonstrating the chip formation process. Then the animation results are analysed and compared with the experimental observations. The methodology presented will provide assistance for machine operators to select machining conditions or for process planning designers to confidently and thoroughly plan the cutting process, control chip breakage and evaluate the chip control effect.

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