فهرست مطالب hasan moslemi naeini

In this paper, using the Sobol sensitivity analysis method, which is based on variance, 11 factors affecting the optimization of the loading path of the hydroforming process are investigated, then the feasibility and validation of the results with other optimization methods such as finite element and experimental method are reported. Is Input factors include, expansion pressure, final pressure, yield time, end of expansion time, intermediate mandrel displacement, final mandrel displacement, intermediate mandrel displacement time, initial position of reciprocating mandrel, final position of reciprocating mandrel, start time of reciprocating mandrel and time The stops of the reciprocating mandrels are considered, then the effect of each of them on the minimum thickness and maximum height in the loading path of the hydroforming process to produce T-joints is investigated and reported in detail. Quantitatively and qualitatively, the optimal values are obtained for each of the 11 input factors and are calculated based on the loading paths.

In this paper, by considering the temperature, time, and process pressure, as the most important factors in producing the thermoplastic composites, an experimental design was performed. An adaptive neuro-fuzzy inference system (ANFIS) was utilized to estimate the important characteristics containing flexural strength, porosity volume ratio, fiber volume ratio, and flexural modulus. Then, the parameters of the ANFIS network were optimized by the teaching-learning-based optimization (TLBO) algorithm. For the purpose of modeling material behavior in the process, the experimental results were utilized for the training and validation of the adaptive inference system. The accuracy of the obtained model has been investigated by using different graphs, based on the statistical criteria of the mean absolute error, correlation coefficient, mean square error, and the percentage of mean absolute error. Based on the obtained results, the TLBO-ANFIS approach has been very effective in estimating the above-mentioned properties in the production process. The network error for estimating flexural strength, porosity volume ratio, fiber volume ratio, and flexural modulus in the teaching section was equal to 0.159%, 0.0003%, 1.074%, and 0.0001%, and the corresponding values were equal to 0.852%, 42.413%, 33.95%, and 4.894% in the testing section.

In this research, the twist and the longitudinal bow defects were studied by finite element analysis in the asymmetrical channel sections. Effects of the geometrical properties including the strip thickness, the web width, and the flange width were investigated on the above effects. Some experiments were performed on an industrial roll-forming machine to verify the accuracy of the finite element model. The results showed that the twist angle decreases with the increase of both strip thickness and web width. However, the twist angle increases with the increase of flanges width. Also the variations of the longitudinal bow height are similar to those of the average residual longitudinal strain of both flange edges.

The Cold roll forming is a complex forming process which quality of its products is highly dependent on the process parameters. The edge wrinkling defect is one of the common defects in the cold roll forming process of wide profiles. Edge wrinkling leads to several problems such as decrease in dimensional quality¡ wearing of forming rolls due to contact with the buckled edge and non-uniform distribution of forming forces through the production line. In order to investigate the edge wrinkling defect in this study¡ the finite element simulation and experimental tests were used. At first¡ for validation of simulation results¡ one model in exact in accordance with experimental set up and with one holding station and one forming station to produce one trapezoidal profile was created. Then by simulating this process in Abaqus software and comparing the longitudinal strain in simulation and experimental results¡ the numerical model was validated. After verifying the numerical model¡ it was used for simulating a similar profile with two channels in transversal direction and in three forming stations and then the effect of sheet material (yield stress and work hardening exponent)¡ strip thickness and distance between the roll stands are investigated on the edge wrinkling defect of products. Results of this study show that wrinkling increases with the yield stress increase¡ but decreases with increase in work hardening exponent¡ strip thickness and distance between the roll stands.

The forming limit diagram (FLD) is a useful method for characterizing the formability of sheet metals. In this paper, different numerical models were used to investigate the FLD of Tailor Welded Blank (TWB). TWBs were Co2 laser-welded samples of interstitial-free (IF) steel sheets with different thicknesses. The results of the numerical models were compared with the experimental FLD as well as with the empirical model proposed by the North American Deep Drawing Research Group (NADDRG). The emphasis of this investigation is to determine the performance of these different approaches in predicting the FLD. These numerical models for FLD are: second derivation of thinning (SDT), effective strain rate (ESR), major strain rate (MSR), thickness strain rate (TSR) and thickness gradient (TG). Results of this research show necking will happen, when the value of MSR, TSR, ESR criteria is maximum, TG ≤ 0.78 and SDT criterion has the first peak in forming process time. Weld line movement is one of parameters which influence formability of TWBs. Maximum of weld line movement of TWB base on different numerical criteria was predicted and compared with experimental results. Results of this research show that SDT criterion has a good accuracy for prediction of forming limit diagram and also weld line movement in the forming of TWB.

Cage roll forming is one of the new methods of cold roll forming process which is widely used for producing ERW pipes. In addition to less production cost and time, using cage roll forming provides smooth deformation on the strip. Few studies can be found about cage roll forming because of its complexity, and the available knowledge is more experience-based and not science-based. In this paper, deformation of pipes with small thickness/diameter ratio is investigated by 3D finite element simulation in Marc-Mentat software. Edge buckling defect in roll forming of pipes with small thickness/diameter ratio is very important. Due to direct effect of longitudinal strain on the edge buckling phenomenon, longitudinal strains at the edge and center line of the deformed strip are investigated and the high risk stands are introduced. Deformation flower pattern and curvature of the deformed strip are predicted using the simulation results and the effects of each cage forming stage on the deformed strip profile are specified. In order to verify the simulation results, circumferential length, opening distance of the two edges and forming power in different forming stages are obtained from the simulations and are compared that of the experimental data which were measured from the production line. A good agreement between the experimental and simulated results is observed.

Use of Tailor-Welded Blanks (TWBs) in production has significant advantages such as weight and cost reduction. However, their application requires processes that increase their poor formability in comparison to base materials. One of these procedures is the use of fluid pressure in sheet metal forming. In this paper hydro-mechanical deep drawing process of tailor-welded low carbon steel (St12) blanks with different thicknesses is studied using FEM and verified experimentally, and effect of fluid pressure on weld-line movement and thickness distribution is investigated. Results of FEM are in good agreement with experiments. Results show that there is an optimum value of final pressure in which the least maximum thinning occurs. Furthermore, using fluid pressure we can obtain higher drawing ratios and also reduce the weld-line movement compared to conventional deep drawing.