A method and apparatus for determination of the ultrasonic-assisted forming limit diagram

It was recently demonstrated that ultrasonic vibrations could result in lower forming forces and a better surface finish in a wide range of metal forming processes. The Nakazima stretch-forming test is a long-established experimental procedure for the formability evaluation of sheet metals. Today, the development of a standard test is critical for assessing sheet metals’ formability enhancement due to ultrasonic vibrations, which can potentially unlock the material selection limit in various manufacturing applications. This study aims to present a method and apparatus for effectuating the forming limit diagram (FLD). At the same time, high-frequency ultrasonic vibrations are combined with the movement of the forming tool. Taking St14 steel as an example, the mechanical and microstructural properties such as formability, Micro-Vickers hardness, and grain sizes were systematically investigated. Furthermore, the conventional FLD, as well as the novel “Ultrasonic-Assisted Forming Limit Diagram” (UA-FLD), were attained and compared with a nonlinear regression-based approach. The results have indicated that superimposing ultrasonic vibrations with the amplitude of 15µm at the frequency of 20 kHz to the tool would cause a notable enhancement in forming limit diagram, a maximum of 28% increase in hardness, and a 23% reduction in average grain size of the specimens.

Investigation of mechanical and micro structural properties of ST14 steel sheet joints by friction stir welding process

High strength and ductility are considered as the superior features of ST14 steel, which have resulted in the extensive usage of this material in the automotive and aerospace industries. Friction stir welding (FSW) is one of the new methods of solid-state welding with preferable mechanical properties for joining steel components. In this study, the mechanical and microstructural properties of 1.5 mm thick ST14 steel sheets in FSW process are investigated. The results revealed the highest tensile strength of 305 MPa for the welded specimen at the rotational speed of 800 rpm and linear speed of 80 mm/min. In addition, higher separation rate of the tungsten carbide particles from the tool as a result of higher heat input to the piece was realized from the metallographic test with the use of sample with rotational speed of 1000 rpm and linear speed of 50 mm/min. Moreover, regarding the results of micro hardness test, an increased hardness to 115\(\pm\)1 HV in the stirred zone (SZ) was acquired in this sample. Furthermore, the presence of the tungsten carbide particles were observed in this area.

Investigation of mechanical and micro structural properties of ST14 steel sheet joints by friction stir welding process

High strength and ductility are considered as the superior features of ST14 steel, which have resulted in the extensive usage of this material in the automotive and aerospace industries. Friction stir welding (FSW) is one of the new methods of solid-state welding with preferable mechanical properties for joining steel components.In this study, the mechanical and microstructural properties of 1.5 mm thick ST14 steel sheets in FSW process are investigated. The results revealed the highest tensile strength of 305 MPa for the welded specimen at the rotational speed of 800 rpm and linear speed of 80 mm/min. In addition, higher separation rate of the tungsten carbide particles from the tool as a result of higher heat input to the piece was realized from the metallographic test with the use of sample with rotational speed of 1000 rpm and linear speed of 50 mm/min. Moreover, regarding the results of micro hardness test, an increased hardness to 115H1 HV in the stirred zone (SZ) was acquired in this sample. Furthermore, the presence of the tungsten carbide particles were observed in this area.

Investigation of mechanical and micro structural properties of ST14 steel sheet joints by friction stir welding process

High strength and ductility are some of reasons that make ST14 steel one of the most widely used steels in automotive and aerospace industries. FSW is one of the new methods of solid-state welding that is proposed as a method with desirable mechanical properties.In this study, mechanical and microstructural properties of 1.5mm thick ST14 steel sheets were investigated in the friction stir welding process. The results showed that the welded specimen with rotational speed of 800 rpm and linear motion speed of 80 mm/min had the highest tensile strength of 305MPa. In addition, results of metallographic test showed that the sample with 1000 rpm rotational speed and 50 mm/min linear motion speed had the highest heat input to the piece, and therefore the tungsten carbide particles were separated from the instrument and entered the stirred zone. Also the results of micro hardness test showed that in the welded specimen with rotational speed of 1000 rpm and linear motion speed of 50 mm/min, hardness increased to 115H1 HV in the stirred zone, which is higher than hardness of other samples in same region. It can be claimed that tungsten carbide particles are present in this area.

Constitutive Modelling of an Industrial Rolled Sheet for a DIN 1623 St14 (DC04) Steel

The comprehension of the anisotropy impacts on mechanical properties of the rolled steel sheets was investigated using a non-quadratic anisotropic yield function. In this study, experimental and modelling determination of behavior of an industrial rolled sheets for a DIN 1623 St14 steel were carried out. The yield stresses and Lankford r-values in uniaxial were experimentally determined but the balanced biaxial tension stress states and rb were assumed. The parameters of the associated yield equation, derived from the three orthotropic yield functions proposed by Hill48 and Yld2000-2d, were determined. Predictions and the evolution of normalized yield stress and normalized Lankford parameters (plastic strain ratio) obtained by the presented investigative are considered. In order to describe the path of equivalent plastic behavior, the isotropic hardening function is described using the following various empirical standard formulae based on: Hollomon, Ludwick, Swift and Voce model.

Genetic Algorithm optimization of initial blank shape in deep drawing of a stepped work piece

This study considers the effect of forging direction on the initial shape of sheet to create a stepped work piece. The purpose of this study is to consider rolling direction in 0°, decreasing the waste while producing workpieces and so decreasing total cost of process. To this end, the assumed workpiece was made of a low carbon and anisotropic st14 steel sheet. To find the most appropriate direction and the shortest modification steps for final shape, the expansion level of the sheet was first imaged in the rolling direction and then the piece was shaped by the geometry. This approach was based on the coupling between the simulation and Genetic Algorithm. A Genetic Algorithm based approach is developed to optimize dimensions through integrating a finite element code running to compute the objective functions for each generation. Those points with a few materials modified through Genetic Algorithm yielded better results.

Effect of Punch Profile on Thickness Distribution in Hydromechanical Deep Drawing of Conical-Cylindrical Parts

Hydro-mechanical deep drawing assisted with radial pressure (HDDRP) is used in industry to produce complex parts from sheet metals. This process is affected by parameters such as : pressure path, geometrical parameters of punch and die, friction between punch and sheet, etc. Investigating these parameters to acquire optimal parameters to produce the desired part is essential. In this study, the effects of the radius of punch tip and the radius of the transition zone from conical to cylindrical geometry, on forming and thickness distribution of parts have been studied. In performing the investigation, a specific geometry was considered for punch and different radiuses for punch tip and the transition zone were selected. The type of the sheet material examined is St14 steel. First, the process was simulated by the finite element simulation software, ABAQUS 6.9, and then some experiments were done to check the accuracy of the simulations. There is an acceptable conformity between the results. The results showed that the radius of punch tip is more effective than that of the transition zone, so with increasing the radius of punch tip, the minimum thickness increases and thickness distribution becomes more uniform.

Study of the Effect of Material Properties and Sheet Thickness on Formability of Conical Parts in Hydro-Mechanical Deep Drawing Assisted by Radial Pressure

Conical parts have a lot of usage in industries. Therefore, it is important to form these parts with high accuracy. In sheet forming processes, producing conical parts is one of the most difficult aspects. The two major problems that occur in the production of conical parts are rupturing and wrinkling. Among the forming processes for producing conical parts, the most capable one is hydroforming deep drawing. In this study, the effects of material properties and initial sheet thickness on forming and thickness reduction of the part were examined by using hydro-mechanical deep drawing assisted by radial pressure. For investigating these two parameters, pure copper and st14 steel are used. In experimental evaluation, sheets with thicknesses of 2.5 mm were used. In the simulation study, the thicknesses of 0.5, 1, and 2 mm were also examined. There is a good agreement between experimental and simulation findings. The results showed that for thinner sheets, the thickness reduction is less, and thus, a more uniform thickness distribution curve was obtained. Also, it was illustrated that for St14 steel sheet the thickness distribution curve will be more uniform compared with that of pure copper sheet.