Applied Mechanics and Materials Vols. 809-810

Abstract: Thickness variation is a major defect of the drawn parts made from sheet metals that influences the intensity of part defects. In the case of mini deep drawing, the sheet thickness variation along parts profile has the following effects on the drawn part geometry: increases the non-uniformity of the part diameter variation; influences the values of springback parameters (part edge radius deviations and angle of wall inclination); influences the intensity of wrinkling; causes the part cracking and fracture. Hence, the main objective in the mini scale deep drawing processes must be to increase the drawn part accuracy by minimizing the thickness variation in the drawn parts, i.e. to minimize the values of thinning and thickening. The present paper analyses the results of investigations made to minimize the thickness variation and hence to increase the accuracy of the mini drawn parts by determining the optimal values of the working parameters from the application of the Genetic Algorithms method.

Abstract: The present paper analyses the results of investigations concerning the size and effects of sheet wrinkling in the case of mini cylindrical drawn parts made from aluminium alloy sheets. The wrinkling occurs in the mini drawn part walls when the blankholder is missing from the die structure or it is driven with an excessive force. By comparing to macro scale processes, the manufacturing of mini parts usually involves new concepts concerning the establishment of the following parameters: tool clearances, tool dimensional parameters, blank dimensions, working process parameters etc. In the case of mini deep drawing such objectives cannot be simply achieved by reducing the process from macro to mini scales. The present work was devoted to study the particularities of the wrinkling that occur during mini deep drawing processes and affect the quality of the mini drawn parts. The experimental investigations were performed using a mini tool having the following main components: punch with a flat bottom, die and an annular blankholder plate. The tool was installed on a mini deep drawing device having the following main components: mobile grip - connected to machine mobile head; fixed grip; helical spring - used to regulate the blankholder force and placed between the fixed grip plate and punch support. The simulation was performed using the DynaForm software and the applied criterion of plasticity was the Barlat 89 criterion.

Abstract: The goal of this paper is to study the time-dependent properties of multi-walls carbon nanotubes (MWCNTs)-filled polypropylene (PP) composites using the instrumented indentation technique. Two types of the indentation test, the 3-step and the 5-step indentation tests, were considered to investigate the creep response during sharp indentation. In order to characterize the state of distribution of MWCNTs, the Scanning Electron Microscopy (SEM) technique was used. It was found that the maximum indentation depth decreases with the increase in the MWCNTs concentration. At lower MWCNTs concentration, the effect of injection pressure on the creep displacement is not significant. Comparison of the creep displacements from 3-step and 5-step loading histories indicates a noticeable decrease in creep displacement when the 5-step loading history is used.

Abstract: Deep drawing is one of the most important processes for forming sheet metal parts. Besides its importance as a forming process, cup drawing also serves as a basic test for the sheet metal formability. This article investigates the influence of the die punch clearance, the average velocity in the active stage and the lubrication on the deep drawing quality expressed by the thickness evenness on the finished product surface. In order to minimize the number of experimental trials, a fractional factorial design was developed together with an orthogonal array, thus analyzing the contribution of the three parameters under study to the quality of the deep drawing process. Using TAGUCHI’s signal-to-noise ratio, we determine that ram velocity has a major influence, followed by the clearance between the active elements, while the contribution of lubrication is negligible. The results of the research are useful in developing a sensible design of experiments.

Abstract: In case of sheet metal forming the main dimensional errors are caused by the springback phenomena. The present work deals with numerical simulation related to draw bending and springback of U - shaped part made from magnesium alloy. The current paper is trying to prove out the important role of the blank holder force with respect to the forming process. Though novel approaches relating to the formality of magnesium alloy sheets, the change of springback due to the characteristic of each process should be verified by finite element method. Springback refers to the elastic recovery of deformed parts. Springback occurs because of the elastic relief from the bending moment imparted to the sheet metal during forming. Springback is mainly influenced by the sheet thickness, the punch and die profile radii, initial clearance between punch and die, friction conditions, rolling direction of the materials, blankholder force and by material properties. In this study, the magnesium alloy strips with two types of material having the thickness of 1mm, are used to investigate springback characteristics in U-shape bending. The Dynaform 5.6 software was used to simulate the forming process, in which the blank holder force takes values between 15 and 35 kN. In this study, the springback was analyzed by U-forming at room temperature conditions with different blank holder forces. Springback decreased with the increase of the blank holding force. Excessive holding force cause irregular thinning of the material, especially in the radius area.

Abstract: By plastic deformation processing techniques is possible to achieve parts with complex geometric configuration and superior mechanical characteristics required in many industries such as aerospace, energy, transport etc. These parts are subjected to high loads or involves a special safety in operation and therefore can not be achieved by empirical design techniques. In addition, industrial development requires obtaining parts with smaller dimensional deviations without defects from expensive materials which are manufacturing in smaller series. To cope with these trends in the currently processed by severe plastic deformation is necessary to apply plastic deformation simulation using finite element method. Aluminum flow simulation is necessary for plastic deformation predetermination the total force, which is used to choose the machine deformation. Also through flow simulation aims to determine contact stress material - deformation tools, necessary stress dimensioning tool, in this case the active plate, punch and counterpunch.

Abstract: The Single Point Incremental Forming Process (SPIF) is a forming technique of sheet material based on layered manufacturing principles. The forming tool is moved along the tool path while the edges of sheet material are clamped. The finished part is manufactured by the CNC machine. SPIF involves extensive plastic deformation and the description of the process is more complicated by highly nonlinear boundary conditions, namely contact and frictional effects have been accomplished. However, due to the complex nature of these models, numerical approaches dominated by the FEA are now in widespread use. The paper presents the data and main results of a study on effect of using cover blank in SPIF through FEA. The considered SPIF has been studied under certain process conditions referring to the test work piece, tool, etc., applying ANSYS 11.0. The results show that the simulation model can predict an ideal profile of processing track, spring back error of SPIF, the behavior of contact tool-work piece, the product accuracy by evaluation its thickness and strain distributions, the contact status and chattering among surface interface tool-work piece.

Abstract: Magnesium alloys were being increasingly considered for sheet forming applications because of their low density and high strength. Therefore, the main areas of research focused on the deformation mechanisms, improving ductility, and possible forming applications [1]. Published results on deformability and springback prediction of magnesium alloy stripes are minimal. The rolling direction of the materials with respect to the deformation direction can greatly influence on springback as well as formability. Though novel approaches relating to the formality of magnesium alloy stripes are available, the change of springback due to the characteristic of each process should be verified by finite element method [2]. In this study, the magnesium alloy strips having the thickness of 1mm, are used to investigate springback characteristics in U-shape bending. The Dynaform 5.8 software was used to simulate the forming process, in which the rolling directions of the material vary with respect to the main deformation axis. There are three different cases: RD0^o, RD45^o and RD90^o. The springback phenomenon is simulated using the same software, but a different module. The following aspects stand out from the simulation tests of the influence of rolling direction on springback parameters: the material rolling direction perpendicular to the deformation direction (0^o) leads to reduction of springback intensity; the thickness of the material in case of RD0^o is reduced in comparison with the one of RD90^o. It can be considered that the results generated by the analysis of springback phenomenon using finite element method are sufficiently accurate and can be considered valid.

Abstract: There is a continuing interest in using laminated materials for the production of lightweight parts, the resulting parts having the same functionality and even an increased stiffness and length of operation compared to conventional materials. The present paper aims to study the forming behavior of the laminated materials that requires the unfolding of tests to determine the tensile mechanical properties and the intrinsic properties, determining the forming limit curves by means of the Nakajima test and the analysis of the behavior at unconventional incremental forming.

Abstract: Processing errors in the process of stamping, represent some of the most important aspect that requires attention when you want to process parts with a simple configuration. Reducing errors increase the quality of stamped parts, therefore the processing industry of blanks from metal sheets attaches great importance to them. Given the international quality standards it is required to study in detail the problem of eliminating these errors. As a result the results of researches on the establishment of a special portable device to eliminate the clearance between the sheet metal and the guidance rulers of the material in die in order to reduce the deformations of the sheet metal trough successive actions dies. Are presented the proposed constructive solution, its advantages and experimental measurements at stamping with the use of the proposed solution.