Effect Of Forming Processes On Mechanical Properties Of Roll-formed Square Tube

With the advantages of low material and energy consumption, high producing efficiency and reliable quality,roll formed rectangular tube has been widely utilized in various industry fields and especially in building. Generally, there are two methods to produce rectangular tube, namely Flat-strip-to-Square Forming (FRF) and Circle-to-Square Forming (CRF). There is no doubt, different forming methods lead to different roll-forming effects which means variation of yield strength, tensile strength, elongation ratio etc. after roll forming. Due to lack of theoretical and experimental researches on comparing different forming method, there are not so much guide lines to be followed for engineers to select suitable rectangular tube. In this thesis, FEM analysis and corresponding experiment are carried out to achieve the effect of different forming methods toward rectangular tube products.To study the process of different forming method, commercial FEM code ABAQUS was utilized. Through comparing, extends of affected by forming process in different area were discovered, they arranges as:angleJ1of CRF>angle J2of FRF> angle J2of CRF>angle J1of FRF>web part M2of CRF> web part M2of FRF. To observe the different effects of forming method on the production, a hole-drilling residual stress test was carried out to obtain the residual stress in the two kinds of square tubes. The results show that forming process has a significant effect on the distribution of longitudinal residual stresses. The residual stresses in the welding zone are found to be the largest through the section in both kinds of the tube. Due to the edge of circular tube was forced a larger pressure during welding process. The microstructure of welding zone was observed. The results show that heat-affected zone of CRF tube is smaller than that of FRF tube. The pressure restrains the growth of austenite when welding, which in turn fines crystalline grain after cooling.In addition, uniaxial tensile test of specimen has been conducted to obtain the mechanical performance parameters. The specimen was cut from different parts of the tubes forming in two methods, including the corners, plate and welding line. The results show yield strength of all deteced parts was increased. Except the plate part of FRF tube, all parts of tensile strength were increased. The yield ratio was also increased, while the elongation was reduced compared to base metal. Yield strength and tensile strength in corner parts were larger than plate parts. The elongation in corner parts were smaller than plate parts.