Research On The Step Action Of NC Pipe Bender And The Section Quality Of Elbow

NC pipe bender is the main machinery and equipment of tube bending forming, the advent of comprehensive national strength and competitiveness of enterprises has created higher requirement in efficiency, automation and other aspects of NC pipe bender. At present, welding-bend integrally molding process has not been automated in China, moreover, low bend efficiency is also a problem. So, in order to develop our own automation of molding equipment, it is necessary to carry out the reach of formulating the process parameters and controlling the section quality and other aspects. The step action of NC pipe bender and the section quality of elbow are carried out in this paper.The subject comes from National Technology Support Program of China(number. 2014BAF12B00). In the step action of NC pipe bender, studying mandrel adjustment, pipe installation, perform and unload pipe bend procedure demonstrates with Virtual Prototype Technology, thus it is in favor of displaying new products, further, modifying and optimizing. In the section quality of elbow, studying tube bending forming and summing up influence laws with finite element numerical simulation. In order to guarantee the elbow meet the requirements, it is necessary to obtain appropriate process parameters. Moreover it can provide guidance for other similar types of tube curved molding. The main contents and conclusion are as follows:(1) According to the subject source, this paper Introduced the virtual prototyping technology, the theory of curved molding, and the molding defects which relates to the paper. And also described the research status of the section quality of tube curved molding. Moreover explained the research background and meaning.(2) Combined with virtual prototype technology, research the process action of pipe welding-bend with NC pipe bender. First, established main components like bed, slide group and bent arm according to the structure of the machine tool; Then, assemble the major parts of the machine tool in virtual prototyping, analysis the global interference and the simulation of process motion.(3) Based on the Finite element numerical simulation, research on the elbow section quality of the common maritime pipe of model (p114mm×8.5mm×342mm. First, combine theory of pipe bending forming and the simulation model to set up a finite element model of bend forming and test it with experiment. Then, study the characteristics of stress/strain and section quality of the deformation zone. Finally, the influence of two process parameters, the extend amount of mandrel and the clearance between mandrel and tube, on the section quality after bend forming is given. The results indicated that:1) As the tube bending, stress mainly concentrated in the inside and outside of the tube, the plastic deformation area’s size and position remains unchanged, wall thickness showed that the outer wall is thinner and the inner wall is thicker; 2) The change of tangential stress which is at double side of the bend from initial region to end area is similar after bend forming. It showed that the stress near the bending point is larger and the tensile strain is larger than the press strain in magnitude. The change of outer wall thickness manifests as up-stable-down. The maximum of section distortion at bending section is in the area which bypass the tangential point of bend about 35 degrees, and the value is larger as the increasing of angle of bend; 3) The wall thinning increased obviously and cross-section distortion reduced obviously as mandrel extension length increased. Suitable mandrel extension length is 25-30mm; 4) The wall thinning reduced obviously and cross-section distortion increased obviously as clearance between mandrel and tube increased. Suitable clearance between mandrel and tube is 0.5～1mm.