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.

A Numerical Study on Rotational Tube Flaring Process

A substantial increase in demand on the sheet metal part usage in aerospace and automotive industries is due to the increase in the sale of these products to ease the transportation. However, due to increase in the fuel prices and further environmental regulation had left no choice but to manufacture more fuel efficient and inexpensive vehicles. These heavy demands force researchers to think outside the box. There are many advanced manufacturing processes to produce optimized part are single and double point incremental forming, Reuleaux forming, hydroforming, explosive forming, electrically assisted manufacturing. In this project, a numerical study on rotational tube flaring process will be studied. Tube flaring is one of the most commonly used processes under tube forming. In this process, a conical tool contacts and forces the end of the tube while another end of the tube is fixed. This is called conventional flaring process. In contrast to this process, a tool rotational technique was utilized for this work. The rotation and the feed of the tool will be analyzed to have the best formability of the tool. The strain path and failure will be analyzed. The strain and thinning pattern will be discussed.

Tube Buckling: An Advantage to Tube Shaping

Tube forming is one of the most common manufacturing processes to shape the tubes. Within tube forming operations the general practice is to expand and reduce the tube end cross-section and bend the tube by means of a solid mandrel. Mostly the mandrel is rigid bodies. To reduce the friction between the tube and the tool, tube hydroforming process was evolved in which the fluid was highly pressurized to expand the tube shape to the desired shape. By reducing the friction more uniform thickness could be achieved and thus increase in formability. One of the process within tube end forming process is flaring which is the focus of this paper. In tube flaring process the conical shape rigid tool flares the end of the tube. While flaring the tube, the tube buckles if proper consideration would not have been taken. In this paper, various influencing parameters such as outer diameter to tube thickness ratio, length or the tube, the strength coefficient of the tube and conical angle of the tool were analyzed. It was noted that the most important factor affect the buckling of the tube is its strength coefficient. Considering this parameter the buckling was carried out in a set die and a tube shape was formed. The advantages of this process over similar processes were discussed.

Outer Diameter to Thickness Ratio Effect on Tube Flaring Behavior

Tube forming is one of the main manufacturing techniques for processing of tubular components. This process is subdivided depending on the processing i.e., tube end forming either to expand or reduce the section. One of these tube end forming techniques is a flaring process. Most applications for flaring tube ends, utilizes a conical tool for flaring the tube either till a particular deformation to achieve a desired shape or till failure to characterize the material properties. The relationship between the flaring behavior during the process based on the outer diameter and thickness of the tube was experimentally characterized in this paper for variety of tube sizes. Further flaring limits were analyzed in these considered tube sizes. For this four outer diameter to thickness ratio were experimented and results were analyzed. Further numerical simulations were performed to match the results. A closer look on the required force-displacement curve is presented and unique regions were identified. Based on the data an empirical equation is proposed. This equation provides a concept based on material or process stiffness. It is believed that once an equation is established and variables are linked to the parameter a more better prediction can be carried out for flaring the tubes.

An Analysis on Bilayer Tube Flaring

Lightweight design for vehicle industry is not anymore an optional condition but a mandatory need to reduce the fuel consumption and adhere to environmental regulations. To achieve this goal many single parts have been removed and complex design have been implied. This includes implementation of tailored-welded blanks and multi-layer materials. Due to the increase use of dissimilar materials in a component it is also called as hybrid components. It was observed that due to use of hybrid component the part weight decrease and thus increase fuel efficiency. To continue this aspect, in this bilayer tube flaring is investigated. The metal tubular material from inside and polymer from outside is considered for flaring. The flaring behavior of the tube is analyzed and compared with the single metal layer. The strength difference and effect of that on the formability is discussed and resulted. It was observed that due to contact of lower strength material from outside the formability of the metal tube increased and failure is delayed.