Optimum design of axial feeding pressure curve in hot hydroforming process of tee pipes

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Mechanical Engineering

Abstract:

Today, the use of aluminum and magnesium alloys in the automotive and aerospace industries is increasing due to the high strength of these alloys and their light weight. Since the forming ability of these alloys is low at ambient temperature, forming these alloys at high temperatures improves their formability. Therefore, in this research, the forming of AA7075 aluminum alloy in the hot hydroforming process of a three-way pipe at high temperatures has been investigated. For this purpose, the process has been simulated in ABAQUS finite element software and to ensure its correctness, the results have been compared with experimental test data presented in existing articles. In the following, the effect of temperature on the forming of aluminum tube has been investigated. The results show that increasing the temperature in the hot hydroforminic process of the tee tubes improves the thickness distribution and increases the height of the protrusion in the tee tube. Also, in the hot hydroforming process, it is possible to produce a tube with a more uniform thickness distribution and a higher projection height with a lower internal pressure compared to the cold hydroforming process. In this research, the Taguchi test design method was used to obtain the data required for the input and output variables of this process. A number of 32 tests were conducted using finite element simulation of the process at 150°C for AA6063 alloy. Linear regression model was used to fit the experimental data. Linear regression model was used as the objective function to optimize the process input variables with the aim of producing pipes without wrinkle and burst defects. The results of the finite element simulation performed using optimal quantities show the achievement of the optimization goals. 1-1 hydroforming process [1]: Hydroforming is a metal forming process that uses high pressure fluid (liquid or gas) instead of hard tools such as mandrels and molds to change the plastic shape of pipes or sheets. Figure 1-1 shows the pipe hydroforming process.

Using this method, parts with complex shapes can be made with lower cost and greater strength compared to forging, casting, etc. produced The cost-effectiveness of this method is due to the fact that the forming steps in this method are reduced to one step. Figure 2-1 shows some cases of using the hydroforming method for the production of car parts [1]. 1-2 Hydroforming method history and classification: The history of using fluid to shape metals goes back more than a hundred years. The primary applications of this process were for the production of steam boilers and musical equipment. But the principles and basis of hydroforming were established in 1940 [2]. The first recorded industrial application of hydroforming was the production of kitchen faucet by Milton Garvin [2] of the Shibel Company of Cincinnati [3] in 1950 [1]. Until 1990, the hydroforming process was mostly used to produce copper pipes. After 1990, the hydroforming process advanced rapidly due to advances in computer control and hydraulic systems. The hydroforming process can be divided into two main groups: sheet and tube hydroforming

Hydromechanical deep drawing process does not have a core mold, but hydraulic pressure is applied when the mandrel is lowered. The counter pressure of the fluid is controlled by the self-adjusting valve [4]. Nakamura and his colleagues [3] investigated hydromechanical deep drawing experimentally and showed that the stretching limit in this process increases due to the presence of counter pressure of the mandrel, and the part of the sheet that is attached to the mandrel is not stretched during the process. rtl;">Figure 6-1 shows a sheet high pressure hydroforming process. The sheet placed in the sheet holder after a traditional deep draw forming step fills the mold cavity in a second step by fluid pressure.. For the hydroforming of the double-layer sheet shown in Figure 1-7; After the two sheets are formed in the first stage of traditional deep drawing, fluid is pumped between the two sheets and the mold cavity is filled with fluid pressure so that the sheets are formed into an upper and lower cavity [1].

Nowadays usage of aluminum and magnesium alloys is increasing in car industry and aerospace because of the high strength and low density. Since the hydroformability of these alloys in ambient temperature is low,

Therefore in this research the forming of the aluminum alloy, AA7075, is considered in the hydroforming process of one T-tube in high temperature. For this purpose the process is simulated in a finite element software - "ABAQUS". Then in order to have the confidence, the results are compared with experimental data given in available articles. After that, the influence of the temperature on the formation of the aluminum tube is studied. The results show that in the hot hydroforming of the T-pipe process, the increase of the temperature improves the thickness distribution and enhances the height of the bulge in T-tubes. Also it is possible to produce tube with better thickness distribution and height of bursting in the hot hydroforming process by the low internal pressure in comparison with cold hydroforming.

In this research Taguchi experiment design method is used to obtain data which is necessary to extract relation among internal and external data. Thirty two (32) experiments are carried out for aluminum alloy, AA7075 by finite element simulation in 150 °C. Regression method is used to process experimental data. For optimization of the internal data of the process in order to achieve tube production without wrinkle and bursting defects regression method is used as an objective function. Results of finite element experiments are indicating optimization purpose by optimized quantity.