Analytical and numerical investigation of hot free bulging process of aluminum tube

Dissertation for M.Sc master's degree

Mechanical Engineering-Manufacturing and Production

Abstract

Nowadays, according to the need of high strength and low weight parts, the method of manufacturing parts has become important. Hot gas forming[1] is a new process that, due to the elimination of side operations such as welding, the overall weight of the parts is reduced, strength is increased, and finally production time is reduced.  Due to the limitation of the internal pressure range of the fluid (forming pressure) and the ease of material flow in the gas forming process, the need to heat the forming tube [2], which ultimately leads to a successful bulge, becomes important. In this process, instead of the fluid pressure of water or oil inside the tube, which ultimately leads to its shaping, air pressure is used to shape the part. In hot tube free bulging [3], heating is done at the tube bulging area during the process.

In this research, for the first time, the analytical and numerical solution of the hot tube free bulging process, in order to investigate the effect of the important input parameters of the process such as the thickness of the tube, the length of the tube bulging area, the outer radius of the tube, the radius of the mold corner, the working power and the strength coefficient on the height of the deformed tube bulging as one of the most key output factors, was carried out. became. Also, the forming pressure that leads to tube bulge is air pressure. In this thesis, with the help of theoretical methods and equations governing the forming of metals, the influence of the mentioned input parameters on the height of the aluminum alloy tube bulge was discussed. Then, by analyzing the mathematical relationships and programming it in the form of MATLAB software[4], the resulting diagrams were extracted. After that, the finite element simulation [5] of the process was presented with the help of Abaqus [6] software.

The results of the theoretical solution and simulation of the finite elements of the process show that the increase in the length of the tube bulge, the outer radius of the tube and the hardness of the material increases the height of the deformed tube bulge. On the other hand, increasing the tube thickness and mold corner radius decreases the height of the deformed tube bulge. Also, the results obtained from the analytical solution had an acceptable convergence with the results obtained from the numerical solution.

Key words: hot gas forming - theoretical solution - finite element simulation - fluid internal pressure - bulge height

Chapter One: Introduction

1-1 Introduction

With the ever-increasing advancement of technology and the competition of the trade market, the automotive industry has turned towards reducing the cost and time of production, producing lighter, more energy-efficient products with high quality and a flexible production system, for this reason, the use of advanced production processes such as hydroforming [1] and hot gas forming has become the focus of industrialists' attention. This method is based on forming hollow parts with the minimum possible steps. Today, the mentioned methods are considered quite advanced and successful for making complex parts. The success that makes this production method superior to other forming methods is the excellent surface quality and high precision of the production parts, which are affected by the hydraulic pressure of fluids instead of using rigid tools. The basis of the work in pipe hydroforming is that by applying internal fluid pressure and axial feeding on the raw pipe, shaping is done, so the said pipe reaches the desired shape by contact with the surface of the mold. The general principles of pipe forming with gas pressure are the same as forming with water pressure, but in terms of the forming pressure range, heating and several other factors, it has differences with the hydroforming method, which are discussed in detail in the following chapters.

1-2 chapters review

In the first chapter, an introduction to the process of hydroforming and hot gas forming and the history of their origin, as well as a summary of the scientific and practical research that has been carried out on these processes until today. At the end, an introduction to the goals of the thesis is presented.

In the second chapter of this research, the introduction of the process of hydroforming and hot gas forming, their classification, process characteristics, advantages and disadvantages, and the parameters affecting the process are discussed.

In the third chapter, firstly, the analytical analysis of the said process is presented with the help of theoretical relations and mathematical equations governing the forming of metals, then the process design and its programming in the software. MATLAB will be discussed.

In the fourth chapter, Abaqus software will be introduced and a brief history of it will be presented. Finally, the simulation of the process using the finite element method will be presented with the help of Abaqus software. A comparison of the results obtained from both analytical and numerical solutions will be presented.

In the sixth chapter, general conclusions and suggestions for further work will be given.

1-3 History of hydroforming and gas forming

According to archaeologists, the initial signs of the metal forming industry are 6000 years old. It goes back to BC. The first findings of archaeologists were large pieces of copper that were shaped by a large and heavy object. Archaeologists also discovered that the history of melting metals by human hands dates back to 4000 BC. At first, the shaping of metals by human hands was based on methods such as forging, pressing, and casting, but later, new methods such as deep drawing, powder metallurgy, shaping with the help of water or gas fluid replaced the traditional methods. The principles of the process of hydroforming and forming with the help of fluid pressure have been noticed since the beginning of the 20th century, and at the beginning of the work, depending on the time and the country where this method is used, it took on different names, among which we can mention pipe bulging forming, forming with hydraulic or hydrostatic pressure, bulging forming with liquid, forming with internal pressure. As mentioned, hydroforming technology dates back to a long time ago and the only reason that caused this method to be abandoned and the development and utilization of this method was delayed was the lack of accurate control systems to manage the produced pressure and precise and momentary control of the process due to the presence of mechanical control equipment instead of electronic control equipment. It was in the second half of the 1950s that modern electronic and pressure control systems paved the way for the more and more practical development of the hydroforming process. Finally, in 2001, a new method was proposed to perform the hydroforming process at high temperature. In this method, instead of water or oil, gas was used as the internal pressure factor to prevent the evaporation of the fluid inside the pipe. In this way, a new method called hot gas forming was born, which together with its older brother, hydroforming, presented a new style of metal forming. Pipe hydroforming is introduced. Then, the history of the hot gas forming process is examined.

Nader Asnafi and his colleagues in their 1999 article discussed the effect of the important input factors of the free tube bulging process, such as the dimensions of the tube and the material of the tube, on the applied pressure which ultimately leads to the barreling of the tube. Considering the axial nutrition, they presented a model to avoid tearing and wrinkling [1]. Also, in 2000, they introduced the mathematical model of the pipe free bulging process based on theoretical relationships, and based on this model, they were able to establish a relationship between the input parameters such as geometric dimensions, internal pressure, workability, strength factor and output parameters such as the height of the bulge, stress distribution [2].

Tisukloski[2] and his colleagues in 2000 published an article entitled Evaluation of pipe ductility and material characteristics in hydraulic bulge testing Pipe provided. In this article, they related the effective parameters in the process such as the radius of the mold corner and the thickness of the material with the internal pressure of the fluid, then by extracting the stress-strain curve, they investigated the thickness of the pipe in different pressure paths in both simulation and laboratory modes [3].