City Research Online

Abstract

There are aspects of wire and tube drawing processes which have not received sufficient attention by the past workers. The equation relating drawing force and wall thickness in the tube sinking process includes terms involving the coefficient of friction at the die-workpiece interface and redundant deformation. The use of this equation necessitates estimation of the values of these parameters and often leads to significant errors.

Various workers have carried out experiments and theoretical analysis to develop and verify these equations. Unfortunately, the fundamental weakness has been determining values of the coefficient of friction, for various materials, die configurations and tribological conditions. It has been assumed that the frictional stress, T, at die-tube interface cannot be greater than yield shear stress at the interface, i.e. T = Mp k where p is the absolute radial pressure and k is the yield stress is shear. There has been doubt on the validity of the upper bound values of jU attained from the upper bound hypothesis based on plain strain theory which is far from an ideal tube sinking process. The work carried out under the research presented in this thesis includes:

1) Devising an elemental die theory to facilitate the analysis of elemental force across a conical die pass

2) The use of the elemental die theory to provide a method for theoretical and experimental accurate analysis of the coefficient of friction across a die-pass

3) Employment of the elemental die theory to prove and to assess theoretically and experimentally the redundant deformation force at the entry and exit of conical die.

From the results attained, the existence of redundant deformation was connoted and correction factors to eliminate the under-estimation by Penny’s proposed redundant deformation theory were deduced and presented. Both the elemental and the significant values of V attained were employed in conjunction with results of radial pressure experiment to check the validity of the upper bound assumption as applied to tube sinking process. It is concluded that the proposed elemental die theory can be employed to determine accurately the profile of h across a die pass and most importantly to estimate accurately the significant V value needed for accurate calculation of the total drawing force due to redundant deformation.

Publication Type:	Thesis (Doctoral)
Subjects:	T Technology > TA Engineering (General). Civil engineering (General) T Technology > TJ Mechanical engineering and machinery
Departments:	School of Science & Technology > Engineering School of Science & Technology > School of Science & Technology Doctoral Theses Doctoral Theses

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