Effect of Multi-Axial Stress State on the Deformation Path in Tube Flaring Process By Necking Instability Criteria

Various parts for automotive, appliance and oil industry are pro- duced from tubes that are assembled and welded. For gaining the best weight savings, durability and cost reasons (energy saving, production cost, etc) the formability of the tubular materials is very important. The overall success of deformation process heavily depends on the incoming tubular material proper- ties. In this work, formability of tubular steels is experimentally characterized and with the development of a numerical model the effect of biaxial stress state has been investigated. An experimental method has been developed to characterize the importance of multi-axial stress state on the formability of tubes. This requires the deformation in form of flaring of the tubular samples through a conical die. Damage strains are determined with the help of Hill-Swift Sheet Metal Forming Criteria and a plot of main strains occurring during the tube flaring test, after variation of the die-angle and friction coefficient has been resulted. Experimental results were then entered into the damage models of finite element program DEFORMTM-PC PRO and used to calibrate the damage model for formability so that a sizable variation of range of multiaxial state of stress could be produced. The results showed that with increasing the stress multiaxiality of tubular steels, the damage strain was reduced. This indicates that the proposed method could be used of benefit in quality control in the production of tubes specially in the monitoring and controlling of tubes production such as tube rolling, welding and annealing.

Study of tube billet reduction to obtain constant wall thickness

Analysis of material thickening process during reduction operation is presented. In order to obtain constant thickness after reduction by conical die thickness distribution of the workpiece is proposed. Workpiece with required thickness distribution is manufactured by thinning drawing. Experimental verification of proposed thickness distribution in order to obtain constant thickness after reduction operation is carried out.

Effect of Anisotropy, Temperature, Strain Rate on deep drawing using Conical Die

This paper covers the role of anisotropy, temperature, and strain rate on the flow behavior of the material when a conical die is used instead of conventional blank holder. The effect of anisotropy was investigated using Lankford’s coefficient (r) in three directions (0°, 45°, and 90°). The effect of working temperatures (Room temperature, 100°C - 300°C) on drawing stress and strain rate sensitivity on punch pressure were also investigated in detail. ANSYS APDL was used to investigate the effects of temperature, strain rate and anisotropy. The simulation results have confirmed that the strain variation in the direction of r0 and r45 are more than the variation of r90.

Influence of Deformation Conditions on the Power Regimes of the Process of Cold Crimping of a Pipe Billet in a Conical Die

An engineering technique has been developed that makes it possible to determine the power regimes of the process of crimping a tubular billet in a conical die, taking into account the effect of deformation conditions. The influence of the geometric parameters of the workpiece and tool, the crimping coefficient and non-contact deformation on the axial stress of the crimping process is studied. The main factors influencing the limiting values ​​of the workpiece crimping factor are established. Calculations are performed for the crimping process performed on an open circuit (without stop block), taking into account the friction and hardening of the material. The obtained results are in good agreement with the known experimental data and can be used in the development of the processes of crimping of pipe billets.

Influence of elongation factor on distributions of effective strain and flow stress for pushing through a conical die process of round bars made from S355 steel

The paper presents computer modelling results of researches on pushing through a conical die process of round bars. Calculations were carried out using the commercial code QFORM-2D, based on the Finite Element Method (FEM). Investigations involved the use of circular sectioned S355 (1.0577) steel segments of rods with diameter of 9 mm and conical dies with different diameter of sizing portion of a die (d = 7.1 mm; 7.6 mm and 8.0 mm). The aim of the paper is to compare distributions of effective strain and flow stress in longitudinal sections of round bars at different elongation factors (λ1 = 1.24, λ2 = 1.37 and λ3 = 1.57).