Finite element analysis of the forming process of the rectangular copper tubes of the conductor rotor to change the circular tube section

Dissertation for M.Sc master's degree

Mechanical engineering - manufacturing and production trend

Abstract

Manufacturing of square and rectangular pipes has received more attention than before due to their wide use in industries that require high pressure and temperature. There are different methods for making rectangular tubes, including extrusion, stretching and pressing. Another method that has been studied in recent years is the reshaping of rotating tubes and turning them into square or rectangular sections. In previous researches, the proposed methods are all used to produce square pipes, and it is not possible to produce rectangular pipes using those methods. The method introduced in this research is to fill the tube with bismuth and rolling it in three consecutive steps. In this research, the desired process is first simulated in Abaqus software, and then a real sample is made by experimental testing. The manufactured sample is examined in terms of dimensions and compared with the results obtained from the simulation. The results of this research show that the method of filling the tube with bismuth and passing through three rollers is a suitable method for making thin-walled tubes with a rectangular cross-section. rtl;">Introduction

1-1 Introduction

Square pipes are widely used in various industries. The inner surface of these tubes is used as a fluid movement path, electric wave conduction path, or as a freezing mold. Various methods including extrusion, stretching and pressing (cold and hot) and forging are used to prepare these pipes. Another one of these methods is roller forming the circular tube and turning it into a square tube. Through this process, a product with dimensional accuracy, mechanical properties such as greater hardness and strength can be achieved. In addition, the products obtained by this method are seamless square tubes that are obtained from cast round tubes. Despite the age and the increasing use of cold roll forming, the number of practical and research works done in this field, especially the reshaping of round to non-round tubes, is small compared to other metal forming processes.

In this chapter, first, explanations are given about the target part, and then a review of past works is made.

1-2 Introduction of the target part Review

The piece under review is a two-dimensional profile (Figure 1-1). These pipes are used in the construction of generators (Figure 1-2) and are responsible for the transmission of electric current, and on the other hand, cold air passes through them to cool these pipes. These parts are used in Mapna Engineering and Generator Manufacturing Company, which is one of the subsets of Mapna Group. So far, these parts have been imported from Ansaldo, which is an Italian company, and currently, it is necessary to compile the technical knowledge of making this part in the country. The piece under investigation is made of copper, that's why it has a high thermal conductivity and hot extrusion is difficult. Research has been done in this field, which will be explained in more detail in the following sections.

1-3 Overview of the work done

Before this, different experimental, analytical and numerical methods have been performed to investigate the process of tube roll forming. The obtained results of some of these researches show a good agreement with the experimental measurements.

Kiuchi1 has studied the effect of process variables and the pipe passing program for the case in which the primary rotating pipe with a thin wall is transformed into a square section pipe.

Kiuchi 1 has experimentally and approximately investigated the effect of process variables and tube passing program for the case in which the initial rotating tube with thin wall is transformed into a tube with a square cross-section in the case of the cold roller rolling process. The distribution of the wall thickness change in the cross section of the pipe for each stage of the forming process, the effects of the way the pipe passes through the rollers on the radius of the corners of the square cross section of the product and obtaining the minimum radius of the corners have been researched [1 and 2]. Using this, a numerical simulation method, such as the finite element method, has calculated the amount of circumferential shrinkage of the pipe in this process and obtained the initial round dimensions of the pipe. He considered the effect of parameters such as the dimensions of the final pipe, the amount of deformation in each stage, the number of stages and so on. . . has investigated on the corners of the tube [3].

Onada3 and his colleagues have discussed the deformation characteristics of round steel tubes that are transformed into square tubes by the Extrol forming process according to experimental measurements and the results calculated by the finite element method for rigid-plastic material[4,5].

Biomi 2 has presented an analytical method for producing regular polygonal metal tubes from round tubes by cold drawing by passing through a set of flat rollers and during one step (Figure 1-2). The solution is based on obtaining an admissible velocity field that satisfies the dynamic conditions for generating the strain rate components. The effects of the shape of the outlet section, the amount of friction on the contact surface of the pipe and the roller, the radius of the roller and the thickness of the wall on the amount of load on the rollers and the traction force required to carry out the process have been researched [6].

Maslimi Naini has developed a new and simple numerical simulation called FDM for the two-dimensional analysis of the elastic-plastic deformation of the pipe in the process of reshaping round pipes into round pipes. Non-round tubes have been determined using a combination of finite element method and finite difference method [7]. Leo1 has done the reshaping process of square tubes using four flat plates. In this method, the initial round tube is clamped first, and then four flat plates gradually change the shape of the round tube into a square shape. Using the finite element method, he investigated the effective parameters on this process, such as the friction coefficient, the stiffness strain coefficient, the geometric rate (R / t) on the indentation defects of the walls in the process of squaring and determining the forming force (Figure 1-3) [8, 9, 10]. Elasto-plastic finite elements have investigated the effect of parameters such as friction, geometric rate, type of pipes and the amount of height reduction on the forming force and the failure modes that occur in the conversion of square pipes from the original round pipe using V-shaped molds (Figure 1-4)]11[.

Bayoumi1 and his colleagues have investigated and determined the forming and tension forces in the conversion of round pipes to square pipes by means of four plates. This analysis was done with the help of an analytical method and with the help of the finite element method in ABAQUS and LS-DYANA 3D software, and in order to confirm and compare the simulation and analytical results, a series of experimental experiments were performed. The effect of process parameters such as roller radius, primary tube diameter, the amount of height reduction of the rollers on the rolled product has been investigated. In order to compare and confirm the simulation results, a series of experimental tests have been performed. Quantities such as energy, wall thickness and radius of the corners of the final product have been measured and presented

Abrinia and Tajyar have researched the effect of different parameters on the separating force in the reshaping of a round tube into a square and investigated the effect of different process parameters on the separating force in the reshaping process using the finite element method in ABAQUS software (Figure 7-1) [10].