Iranian Journal of Materials Forming
Volume:4 Issue: 2, Summer and Autumn 2017

In recent decades, one of the challenges in sheet metal forming was production of two-step bending surfaces without mechanical tools and external force or by a combination of heat source and mechanical tools. Forming with a heat source such as laser beam has the potential for forming arbitrary 3D shapes such as two-step bending surfaces. In this paper a novel method for laser forming of complicated two-step bending dome shaped part is proposed. The initial sheets are made from mild steel with thickness of 0.85 mm. In this method, combination of simple straight lines leads to production of a two-step bending dome shaped part. The results of this paper show that the proposed method is a powerful irradiating scheme for production of two-step bending dome shapes with considerable deformations and symmetries. In addition, using an analytical study the mechanics of plate deformation is precisely investigated. All of investigations are performed experimentally and numerically and it is shown that numerical results are in good agreement with experimental observations.

In this work, a support vector machine (SVM) model was developed to predict the hot deformation flow curves of AZ91 magnesium alloy. The experimental stress-strain curves, obtained from hot compression testing at different deformation conditions, were sampled. Consequently, a data base with the input variables of the deformation temperature, strain rate and strain and the output variable of flow stress was prepared. To develop the support vector machine (SVM) model, the overall data was divided into two subsets of training and testing (randomly selected). Root mean square error (RMSE) criterion was used to evaluate the prediction performance of the developed model. The low RMSE value calculated for the developed model showed the robustness of it to predict the hot deformation flow curves of tested alloy. Also, the performance of the SVM model was compared with the performance of some previously used constitutive equations. The overall results showed the better performance of the SVM model over them.

The grain size refinement of AISI 422 martensitic stainless steel in the temperature range of 950-1150 ºC was investigated by hot deformation tests. The deformed specimens were held at deformation temperature with delay times of 5 to 300s after achieving a strain of 0.3. The austenite grains exhibit a considerable growth at temperature higher than 1050˚C, while the grain coarsening is negligible at lower deformation temperatures. Therefore, it is a difficult task to achieve a fine grain structure at these high deformation temperatures. In the second stage of this work, the grain growth behavior of the deformed alloy at temperature range of 940-1020 ºC was investigated to obtain a fine austenite grain in the final deformation step. A uniform and fine-grain structure, with average grain size less than 30 µm, can be obtained by considering the appropriate temperature and strain per pass. At 1020˚C a relatively fine and uniform recrystallized grain, mean grain size of about 28 µm, is obtained with an applied strain of 0.4, while at 980˚C after strain of 0.2 a nearly equiaxed grain with the same mean grain size is achieved.

Cutting processes can be used in batch production of polygonal bars with special features. In this paper, a new form of broaching process for cutting of hexagonal bars from raw round bars is discussed. Due to lack of rolled or drawn raw material, the final product is made of AISI 316L stainless steel bars having appropriate initial size. In this method, a fixed die is used as a tool, and by applying pressure to the raw bar and passing it through the die, it is cut hexagonally. To study this process, different empirical tests have been conducted with different dies. Based on the empirical data, the process is simulated by finite element method. To determine optimal features of the tool, the simulation results in the design and development (i.e., tool making) stages have been used. Among the studied rake angles, the 15 degree angle can be introduced as the most suitable rake angle. In order to evaluate the amount of work hardening, micro hardness tests have been carried out. Quality of final surfaces of machined samples in terms of material and angles of the simulated dies were acceptable and experimental measurements indicated a slight increase in micro hardness of surface layers of the samples.

In this work, incremental sheet forming of a complicated shape is investigated experimentally. Two point incremental forming with negative and positive dies are employed for manufacturing of a complicated shape with positive and negative truncated cones. The material is aluminum alloy 3105 with a thickness of 1 mm. The effects of process parameters such as sequence of positive and negative forming processes, step depth (incremental depth) and rotational speed of the tool on the maximum achievable outer and inner heights for the proposed specimen are investigated. The selected ranges for the step depth and rotational speed are 0.2 mm - 0.6 mm and 0-1000 rpm, respectively. The results show that both maximum achievable outer and inner heights of the specimen are increased with change of Positive/Negative variant to Negative/Positive variant. Also, the results prove that both maximum achievable outer and inner heights are increased with decreasing in the step depth and increasing in the rotational speed of the tool. An optimum parameter combination (Negative/Positive, step depth = 0.2 mm and rotational speed = 1000 rpm) is obtained to get the both maximum achievable outer and inner heights using the signal to noise ratio analysis.

Welding method and its parameters has an important effect on the formability and mechanical properties of tailor welded blanks(TWBs). In this study gas tungsten arc welding(GTAW) is used to joint aluminum TWBs. Aluminum TWBs consist of 6061 aluminum sheets with different thickness of 1mm and 2mm. Main parameters of GTAW consist of welding current, pressure of shielding gas, welding speed and diameter of filler material are investigated. Design of experiment based on the Tauguchi method is used to investigate the effect of each parameter and also parameters interaction. Erichsen formability test which is an out-of-plane forming test is used for formability investigation of aluminum TWBs. Forming height of Erichsen test is used as a criterion to study the effect of GTAW parameters on the quality of aluminum TWBs. Results of present study shows that shielding gas pressure and welding speed have the greatest impact on the formability of aluminum TWBs.