Search

To obtain better quality parts in the stamping process, the important parameter is the flow of material into the die cavity. This flow is controlled by adapting appropriate blank holding force, initial blank shape, and geometry of drawbead. In this paper, a comparative study is carried out using blank holding force and different blank shapes such as rectangular, oblongated, and oval shapes on thinning of the formed part using hyperform as simulation software. From the simulation, it is observed that more thinning is in rectangular blank shapes as compare to oblongated and oval shapes. Formation of oblongated or oval shape blank required extra blanking die which adds more cost. Hence the use of rectangular blank is most preferable along with drawbead. Further research work is carried out to get an optimized solution on rectangular blank using circular drawbead. The result of drawbead with rectangular blank size will give a less thinning with minimum blank holding force compare to oval and oblongated blank shapes. The results obtained by finite element simulation are in good agreement with the experimental results with a permissible error of an average of 6.70%.

When the fine-blanking process is used, secondary grinding or processing can be omitted because the shear surface of fine-blanking parts can achieve almost zero fracture zone requirements. Fine-blanking has the advantages of high precision and high production efficiency. It was originally used on watch parts, but with increasingly refined technology, it has been widely applied in computers, consumer electronics, communication products, and vehicle parts. The primary objective of the fine-blanking process is to reduce the fracture zone depth and die roll zone width. This study used a 2.5mm thick central processing unit (CPU) thermal heat spreader as an example. Finite element analysis software was employed to simulate and optimize the main eight process parameters that affect the fracture zone depth and die roll zone width after fine-blanking: the V-ring shape angle, V-ring height of the blank holder, V-ring height of the cavity, V-ring position, blank holder force, counter punch force, die clearance, and blanking velocity. Simulation analysis was conducted using the L18 (21×37) Taguchi orthogonal array experimental combination. The simulation results of the fracture zone depth and die roll zone width were optimized and analyzed as quality objectives using Taguchi’s smaller-the-better design. The analysis results revealed that with fracture zone depth as the quality objective, 0.164 mm was the optimal value, and counter punch force made the largest contribution of 25.89%. In addition, with die roll zone width as the quality objective, the optimal value was 1.274 mm, and V-ring height of the cavity made the largest contribution of 29.45%. Subsequently, this study selected fracture zone depth and die roll zone width as multi-criteria quality objectives and used the robust multi-criteria optimal approach and Pareto-optimal solutions to perform multi-criteria optimization analysis. The results revealed the optimal fracture zone depth and die roll zone width were 0.239 mm and 1.288 mm, respectively. Finally, the experimental results verified that the fracture zone depth was 0.230 mm and die roll zone width was 1.205 mm. The findings met the industry’s fraction zone depth standard (below 12% of blank thickness) and achieved a smaller die roll zone width.

This study conducts numerical and experimental analyses to study the parameters affecting deep drawing of symmetric low-depth products, such as die geometry, punch movement, and cushioning. The methodology proposed in this paper is applied on the deep drawing of a frying pan manufactured out of AL99.9%. The finite element model (FE-model) is developed using LS-Dyna© and an experiment is carried out to validate the FE-model. The numerical and experimental results have shown minor deviation of 3.5% and 0.92% for maximum pressing load and maximum thickness, respectively. The validated FE-model is then employed to study the parameters affecting the maximum pressing load and maximum thinning. It is proved that the cushion stiffness and the initial blank thickness have the major influence, while the punch speed shows an insignificant impact. The results are justified and hence the FE-model proves to be reliable for further analyses.

A V-bending experimental setup has been designed, to analyze the impact of blank geometry and process parameters over the springback in hot-rolled high-tensile-strength sheet metals (JSH590 steel). In this setup, a hydraulic press having the ability to vary load and holding time has been used. JSH590 sheet-metal blanks with varying geometric parameters are bend to acute, right and obtuse angles. Springback in each blank is determined which is found to be varying due to the different combinations of blank geometry and process parameters. To analyze the significance of thickness, width, bend angle, applied load and holding time, analysis of variance is applied, regression model is also derived relating the parameters with the springback, and finally, Genetic Algorithm has been applied to optimize the process parameters for the minimum springback. The outcomes of the research can be used in the industry, to evaluate the outcome in very-high-tensile-strength steel sheets.

Introduction. Friction stir welding is widely used due to certain advantages of this method. Factors that reduce the strength of joints made of high-strength aluminum alloys are considered. When welding flat sheets, an effective way to increase the strength of the weld is edge thickening. The paper proposes a method for such thickening. A device is developed, calculations and experiments are carried out. Materials and Methods. Laboratory equipment has been developed to provide simultaneous thickening of two edges to be welded. The main component of this equipment is a steel roller, which is rolled along the edges of two blanks and thickens them due to plastic deformation. The same setup can be used for the friction stir welding process. To calculate the geometry of the thickened edges and the parameters of the deforming roller depending on the value of the edge settlement, a mathematical model based on the contact problem for elastic (roller) and elastoplastic (blank) bodies with a bilinear hardening law has been developed. A three-dimensional simplified geometric model of the facility with account of its symmetry has been constructed. On the contact surfaces, special contact finite elements were selected and the finite element mesh was refined. The numerical implementation of the model was carried out in the ANSYS package. Results. The theoretical model provides assessing the stress-strain state of interacting elements. On the basis of the developed finite element model, the parameters of the thickened edges are calculated, and the geometry of the thickened edges is defined. Using the developed laboratory equipment, full-scale experiments on thickening the edges of the blanks were carried out. The experimental results confirm the adequacy of the developed theoretical model and calculations based on it. The possibility of adjusting the size of the thickened edges is shown. Discussion and Conclusion. A technology for obtaining thickened edges in places of welds is proposed. It will reduce the metal consumption of structures and ensure the bearing capacity of welded joints not lower than similar characteristics of the base metal. A theoretical model of the process is developed, and a numerical experiment providing the selection of the process parameters is carried out.

The hydraulic bulging technology of tubes can provide hollow parts with special-shaped cross sections. Its manufacturing process can effectively improve material utilization and product accuracy and reduce the number and cost of molds. However, the hydraulic bulging process of parts is very complicated. The size of the tube blank, the design of the loading route, and the forming process parameters will have an effect on the molding quality. Closed tubular torsion automobile beam is considered as the research object to study hydraulic bulging die design and optimize forming process parameters. CATIA software is used to design torsion beam product structure and hydraulic bulging die. AMESim software is employed to design hydraulic synchronous control system for cylinders on both sides of the hydraulic bulging die. Mathematical control model is established and verified in Simulink software. DYNAFORM software is applied to conduct numerical simulation of hydraulic expansion. The supporting pressure, molding pressure, friction coefficient, and feeding quantity are taken as orthogonal experiment level factors. Maximum thinning and maximum thickening rates are taken as hydraulic pressure expansion evaluation indexes to complete the orthogonal experiments. Main molding process parameters are analyzed via orthogonal experiment results and optimized by employing the Taguchi method. Optimal hydraulic bulging parameters are obtained as follows: supporting pressure of 20 MPa, molding pressure of 150 MPa, feeding quantity of 25 mm, and friction coefficient of 0.075. Simulation analysis results indicate that the maximum thinning rate is equal to 9.013%, while the maximum thickening rate is equal to 16.523%. Finally, the design of hydraulic bulging die for torsion beam was completed, and its forming process parameters were optimized.

This work provides numerical and experimental investigations of blanking process, where the shear-enhanced Lemaitre’s damage model is fully characterized and successfully applied in blanking process to predict the cutting force and cutting edge geometry under different blanking process parameters. Advanced high strength steel DP1000 and an aluminum alloy Al6082-T6 are selected for series of experiments. To obtain the damage parameters in Lemaitre’s damage model the flat rectangular notched specimens tensile test was conducted and the inverse parameter identification procedure was performed. For characterizing the crack closure parameter h in the shear enhanced Lemaitre’s damage model, an in-plane torsion test with novel specimen design was conducted. The finite element model (FEM) of this test was established with the minimum mesh size of 0.01 mm which was consistent with the minimum mesh size in the shear zone of the FEM for blanking process simulation. The longitudinal strain distributions of four kinds of initial notch radius or central-hole specimen were measured and compared with simulation results to validate the FEMs for these four tests. Deformation analysis of blanking of a circular work piece also was performed under three clearances. The effects of blanking conditions on sheared part morphology were detected. Stress triaxiality distribution of the blank sheet was revealed taking advantage of the successfully established FEM. The availability of the testing method and the determination method of the parameters was investigated.

This study focuses on the Bubnov-Galerkin finite element model used to obtain the stresses and pressure fields set up at various cross-sections of a blank during the metal forming process. Four Lagrange quadratic elements were assembled to represent the various blanks. The governing equation adopted is a one-dimensional differential equation describing the pressures and stresses exerted on the forming process. In conducting the analysis, the various blanks are divided into a finite number of elements and further applying the Bubnov-Galerkin-weighted residual method to obtain the weighted integral form; the finite element model is obtained in a matrix form, from the weighted residual boundary conditions which are now applied to obtain the pressure distribution across the cross-section of the various blanks. Finite element results are obtained for a value of the coefficient of friction, die angle, length, and blank radius. Solution of the finite element method was compared with the exact solution, along with an experimental test known as press-fit analysis using Ansys Workbench, a program-controlled mesh of polar hexahedral elements which was utilized to further validate the result. Furthermore, the use of a computer-aided software assists in visualizing the solution of the tube sinking problem. The results were all presented in both tabular and graphical modes. This study shows that there are potentials for using this approach in engineering practices to ensure that the strength of materials be considered before usage in design and fabrication. These results are expected to improve advance knowledge in manufacturing processes.

Punch–die misalignment is one of the factors that can contribute to drawn cup defects such as thinning and tearing. Deep drawing is a closed-die process, and defects can be identified only after the drawing is finished. In this work, the effect of punch–die misalignment severity on the drawing force and wall thickness distribution of electrolytic zinc-coated steel blank (SECC) was investigated. The stress–strain diagram and forming limit diagram of SECC material was determined and simulated using the Hill’48 model. Two conditions of punch–die misalignment were studied: single-axis and multi-axis misalignment. A high punch–die misalignment severity contributes to the increment in the drawing force. Furthermore, wall thickness distribution becomes non-uniform, and the thinning pattern increases due to the greater misalignment severity. For validation, an experiment was conducted on a universal tensile machine.

Machining distortion control is of great concern to the manufacturing of slender aerospace components. Simulation models for distortion prediction enable forecasting potential distortion as material is removed and bulk stresses released. These models, either analytical or numerical, require accurate residual stress data as it varies from one machining blank to another. The on-machine layer removal method is a promising technique for fulfilling the task due to its low requirements on equipment, labor expertise, and computation time, which enable industrial application. Besides, the method can be applied to ribbed geometries allowing to measure the stresses and obtain the final component from the same bulk, just by taking certain assumptions related to its geometry. Nevertheless, under these assumptions the method does not consider the bucking of the ribs or their specific position within the components, which decreases its accuracy in ribbed geometries. In this paper, the influence of equivalent bending stiffness in the characterization of residual stresses of machining blanks for ribbed components is investigated. The formulation considers through-thickness bulk residual stresses and machining-induced residual stresses in two spatial directions, as well as the initial curvature of the machining blanks. A semi-analytical formulation establishes the quantitative relation between source and distortion for ribbed part geometries. Finally, simulations are contrasted with experimental data in a Al 7050-T7451 demonstrator.

Blank wrinkling is the most frequently encountered material processing failure in spinning. Design of toolpath profiles and selection of process parameters are important in preventing wrinkling. Existing studies employ simplified toolpath profiles and rely on the calculation of maximum and critical stresses of the blank to determine the onset of wrinkling, often requiring time-consuming Finite Element simulations. To overcome these limitations, this paper develops an analytical wrinkling prediction model integrated with toolpath design in developing multi-pass conventional spinning. The toolpath design is parameterised for concave, convex and linear profiles and a wrinkling-wave function using a concave profile is developed to capture geometrical characteristics of a wrinkled blank. The forming depth is introduced as a critical variable in designing a toolpath profile to control wrinkling. Material plastic deformation is analysed by employing the Donnell-Mushtari-Vlasov theory and wrinkling initiation is predicted by the occurrence of the instability of the blank as a doubly-curved thin shell. Experimental tests of first-pass conventional spinning using concave, convex and linear toolpath profiles are performed to validate the developed wrinkling prediction model. The experimental validation confirms that the proposed critical forming depth of toolpath profile is an accurate and effective measure in predicting the onset of wrinkling. The results show the significant effect of the design of toolpath profile, blank thickness, spin ratio and feed ratio on the onset of the wrinkling. The wrinkling prediction model is capable of producing processing maps of these key parameters to prevent wrinkling for the spinning process development in practical applications.

During manufacturing nuts of increased height, a problem of obtaining correct cylindrical form of the hole for thread and overall geometrical parameters arises. To solve the problem it is necessary to know regularity of the blank forming process. Results of the study of a technological process of high hexahedral nuts forming presented. The nuts were M18 of 22 mm height, M16 of 19 mm height and M12 of normal height 10 mm according to GOST 5915–70, accuracy class B, steel grade 10 according to GOST 10702–78. The volumetric stamping was accomplished at the five-position automatic presses of АА1822 type. It was determined, that unevenness of the metal flow in the process of plastic deformation of blanks of increased height nuts was caused by different stress conditions by their sections. To simulate the mode of deformation, the program complex QForm-3D was chosen. The complex ensured to forecast with necessary accuracy the metal flow in a blank, as well as to define the deformation force and arising stress in the working instrument. The simulation showed the presence of regularity between preliminary formed buffle and deviation of dimensions and form of a blank wall after its finishing piercing, which can be expressed by a nonlinear dependence. The limit values of the relative height of the buffle С/D = 0.56–0.588 defined, exceeding which will result in rejection of the finished product. Accounting the limit values of the relative height of the buffle will enable to correct a mode of technological operations and technological instruments at stamping of high hexahedral nuts.

A prediction model for machining deformation considering machining-induced residual stress (MIRS) and initial residual stress (IRS) of the blank is proposed in the present study based on the equivalent stiffness numerical calculation and elastic mechanics. The deflections of six thin-walled parts (includes two thin-walled specimens designed in the present study and four cases in the literature [1]) are predicted using the proposed model, and the corresponding finite element analysis (FEA) and experiments are implemented to verify the model. The machining deformation can be ultimately expressed by MIRS and IRS with the influence coefficients on the basis of the proposed model, and the effects of MIRS and IRS on the machining deformation are analyzed. It is shown that the predicted deformation by the proposed model has a good consistency with the FEA and experiment results. By comparison with the model only considering IRS in literature [1], the prediction accuracy visibly increases when both MIRS and IRS are considered. The contribution ratio of MIRS and IRS on the machining deformation is affected by the stress magnitude and depth, equivalent bending stiffness, and material removal rate. Also it can be easily gotten based on the proposed model.

Prefabricating blank ends into special shape is the most effective and commonly used method to eliminate end-face cavities for realizing cross-wedge rolling (CWR) without stub bar. A hot rotary shearing forming method based on metal-plastic forming together with its implementing mechanism for the manufacturing of special-shaped ends blank was proposed in this paper. The hot rotary shearing forming method was firstly investigated by finite element simulation, and the forming process of the special-shaped end with the movement of the shear blade is analyzed. Then the implementing mechanism characterized by the combination of a differential elliptical gear train with conjugate cam was designed. To obtain the structural parameters that can make the shear blade move as designed, kinematics model of the mechanism was deduced by analyzing its working principle. Based on the model, a computer-aided analysis program for the hot rotary shearing mechanism, using MATLAB, is developed. Finally, one application example was conducted. The experimental results revealed that the dimension of the special-shaped end blank obtained by this method was close to the designed dimension. The research result verifies the correctness of the kinematic model and the feasibility of the forming method.

The increase in economic and technological competitiveness means that the automobile industry seeks constant innovation in its production methods and processes, in order to produce lighter, safer and more efficient vehicles. Products with greater mechanical resistance, better conformability, thickness combinations of plates / materials are sought with a focus on reducing mass and increasing the rigidity of the vehicle body. In this scenario, Tailor Welded Blank (TWB), which is a top welding technique (by unconventional processes) of sheets of different specifications (materials, thicknesses and / or coatings), appears as a solution, as it allows localized distribution of mechanical properties, mass, optimizing the relationship between structural rigidity and the total weight of the vehicle body. The great challenge of this technique is to combine two processes with completely different demands, welding and mechanical forming. Due to the complexity of forming TWBs, the use of simulations has been widely adopted. In this review, different results of the numerical simulation methods used for a Tailor Welded Blank are compared, focusing on the details and the influence of the parameters used.

In order to reveal the influence of different processing procedures on the machining deformation of the whole structure of aviation frame type, a prediction model for the deformation of frame type integral structure caused by initial residual stress was established based on finite element. According to the deformation law of frame parts caused by initial stress of blank, the deformation of whole structure parts based on aviation frame is minimized. The influence of processing process on deformation of frame structure is studied. The results show that when removing the frame material, the deformation of the workpiece can be slowed down by first removing the area with large deformation and relatively concentrated material. And symmetrical removal of the frame material can also slow the deformation of the workpiece.

Variable-thickness rolled blank (VRB) technique is one of the most effective methods to improve the level of lightweight and stiffness characteristics of car body. The shape of thickness transition...

In the field of automotive lightweight manufacturing, the advanced high-strength steel (AHSS) sheet gets a pivotal position owing to a good match between the plasticity and superior strength. However, in the complex multi-step loadings, the twist springback phenomenon generated by irregular and curved stampings has arisen great concerns. In this article, the material DP500 is adopted for the twist springback analysis in a two-step loading experiment. First, the large bone-shaped specimen is deformed to 4% strain along the rolling direction. Subsequently, the forming blank, cut from the large specimen at different directions, is stamped in a die to form a 3D curved channel. Meanwhile, the simulation analysis of the two-step loading procedure is built for twist springback prediction. An advanced distortional hardening model incorporated with an attenuated modulus model is applied for exactly capturing the deformation features under mutative strain path. A deep analysis with regard to the residual stress and elastic modulus distribution is conducted to evaluate the pre-strain's influence on the twist springback of this curved part. The result shows that mutative strain path induced by the change of the pre-strain axis has a significant impact on the twist springback. Keywords: Twist, DP steel, Multi-step loading, Strain path change

The aim of the study is to evaluate the quality of the marginal gap of the frames of artificial crowns made with the use of CAD/CAM system and by casting method. Materials and methods. The article presents an assessment of the quality of the edge fitting of artificial crown frames made by means of CAD/CAM system KaVo ARCTICA on digital images of dentition created by intraoral laser scanner iTero Cadent and frames made of Co-Cr by the method of casting. The Image J computer program was used to study the quality of the marginal gap of artificial crown frames. For statistical analysis of the obtained data nonparametric Wilcoxon-Mann-Whitney test was used for the evaluation of the related samples. Results. We found that the average value of the marginal gap between the tooth stump of the experimental model and the frames of artificial crowns made in the KaVo ARCTICA Engine milling and grinding machine from the titanium blank Titan-Blank is 21.79 microns. The average value of the cement gap of the frames of artificial crowns made by the traditional casting method is 77.18 microns. The value of the marginal gap of artificial crown frames made by using the CAD/CAM system KaVo ARCTICA was 2.8 times less than the value of the marginal gap of frames made by the traditional casting method with a significance level of р 0.05 (V-Wilcoxon criterion for related samples = 0, р = 0.001). Conclusion. The results of our study indicate that the frames of artificial crowns made with the use of CAD/CAM system KaVo ARCTICA have a greater dimensional accuracy of the marginal gap compared to the frames of artificial crowns made by the traditional casting method.

This study presents the experimental results and the comparison of different analytical models for springback evaluation of bent thin sheets. Three types of advanced high strength steels (from the group of dual phase steels, namely DP600, DP800 and DP1000) and a mild steel (DC04) were used to investigate the sheet profile after rectangular V-die bending. Uniaxial tension-compression tests were also carried out formerly to lay the basis of the precise theoretical examinations. Striving to consider all possible circumstances, the change of the elastic modulus with the increase of the plastic strain, as well as plane strain state with the corresponding yield stress were assumed during the springback prediction. In certain cases, the effect of the sheet thickness variation was also taken into account. In many practical stampings, these variables can be at least partially neglected, but the presented models also can lead to poor accuracy, even though they are more complicated. According to our experiences, both the circular approximation and the moment-equilibrium based general formulae predict under the measured springback angles, but the punctuality can be developed by precise material behavior modelling. The phenomenological approach extended with fitting parameters gives the most accurate estimation obviously, but the physical meaning of the added parameters remain a question. The uncertainty is being more enhanced at the tailor-welded blanks (TWBs) where the interaction of the components should not be negligible as well, i.e. a subsequent variable, namely the distance from the weld line comes into the focus. Laser beam welding was applied to joint each DP steels to the mild steel component and then the sheets with different widths were bent perpendicular to the weld line. Due to the doubled effect on the deforming or restraining action of the different sides, the final shape and thus the curvature shift towards the weld line from the blank’s edge. It means that new viewpoints need to consider at the analytical springback evaluation of TWBs.

Aiming at the existing problems, e.g. cracking, many forming passes, difficult control of dimensional accuracy, in thin-walled pipe fittings hot extrusion forming process, a innovative forming on thinning and thickening of thin-walled pipe fittings by three-roll skew rolling with a pair of molds is being proposed in this paper. Based on the analysis of the movement principle of the three-roll skew rolling hollow reduction process, the three-roll diameter reducing and end-thickening forming of thin-walled pipe blank with 1.5mm wall thickness is simulated by Simufact Finite Element software. The law of metal flow, strain field and rolling force are analysed, and the forming mechanism is clarified. The product meeting the production specifications is obtained by comparing the simulation results of the end wall thickness distribution and the wall thickness of pipe forming. The results show that the diameter reducing and end-thickening forming process of thin-walled pipe fittings by three-roll skew rolling is feasible. This study lays a theoretical foundation and new idea for the diameter reducing and end-thickening high-efficiency precision forming of thin-walled pipe fittings such as aircraft control rods.

Relevance. A new technical solution of bent-closed profiles relating to light steel thin-walled structures (LSTS), which have high technical and economic indicators and are widely used in industrial and civil construction, is presented. Aim of the research. The characteristics of thin-walled structures can be further enhanced by shaping the modification of profiles, combining in its composition the outlines of closed and open outlines. Methods. By means of developmental studies and optimization and design calculations for bent-closed profiles, their new technical solution was developed, the originality of which was confirmed by patent examination. Results. New curved closed profiles (CCP) consist of a tubular part of a single thickness and a double-thickness rib. For their manufacture without welded, bolted or riveted joints, the sheet blank is made along the entire length with serrated longitudinal edges, the teeth of which are arranged relative to each other in a staggered manner and mutually bent in grooves between themselves after the curved profile is closed along its edge. The bends of the gear fasteners increase the thickness of the collapse and provide an increase in the shear strength of the joints of thin-walled elements. With equal dimensions in height and width of the CCP, they are optimized by the criterion of uniform stability, which is the same from the plane and in the plane of the supporting structure. Additionally, a series of pentagonal, triangular and trapezoidal profiles are presen- ted, in which the lateral faces are inclined relative to the vertical at angles of 45 and 60 degrees.

The challenging problem of ensuring the accuracy of sizes in bending followed by elastic springback of angle parts, which form a wide class of aircraft elements, i.e., stringers, stiffening ribs, and lattice wheel and wing elements, is considered. The purpose of this work is to develop a technique for engineering estimation of the angle error in bending an angle blank in a tool die. The proposed technique reflects the physical features of springback in bending in a tool die, is characterized by simplicity, and provides the accuracy of estimating the angular error that is sufficient for engineering practice. This technique can be used to solve a number of practical problems.

The steel-concrete (SC) or steel-concrete-steel (SCS) composite structures are widely used in large-scale structures like immersed tunnels, protection structures, etc., due to their superior performances in capacity, ductility, waterproofness, construction efficiency, etc. The steel plates in these structures are usually stiffened with ribs to increase the out-of-plane rigidity and to improve the local buckling performance. While there have been several applications, the buckling design of the composite stiffened plates, based on the methods for steel structures, is still immature and conservative. To deal with this problem, a selected series method (SSM) based the energy theory is proposed, which could both be utilized in composite stiffened plates and steel stiffened plates. The special series shape functions, which could efficiently and accurately represent the 3-dimentional spatial buckling deformation of the stiffened plates with multiple stiffeners, are selected. The explicit high-order solutions for the buckling stress of stiffened plates are derived. Furthermore, a finite element model (FEM) is established. Based on the FEM, a numerical database including most common design parameters is derived, and extensive numerical analyses are conducted to modify and verify the proposed SSM. It is found that, for steel structures, the SSM has a 10%–20% improvement in accuracy compared with the existing methods, and for composite structures, the SSM fills the blank in this area and has acceptable accuracy for design. Finally, from the above studies, the design suggestions are given and discussed.

Springback in hot-rolled, high tensile strength sheet-metals (JSH440) are measured to evaluate the influence of blank geometry and process parameters over the springback outcomes. Sheet-metal thickness, width, bend angle, applied load and holding time are considered as controllable factors, whereas, other factors are kept constant. Analysis of Variance (ANOVA) and sensitivity analysis Are applied to observe the significance of controllable factors over the springback magnitude. Analytical models considering all the controllable parameters have been developed to predict the springback in JSH440 sheet-metals, whereas, simplified analytical models based on bend angles are also developed for different geometries of sheet-metals. Finally, the Genetic Algorithm has been applied for the determination of optimal applied load and holding times are determined for the minimum springback in different geometries of the JSH440 steel-sheets. This research can be used in the industry to predict the springback, optimize the blank geometries and process parameters for the minimum springback in JSH440 sheet-metals.

Automobile manufacturers using tailor welded blank (TWB) technology carryout forming operations for curved shape components by orienting multiple welds. This process results in the formation of inflection point at the welded joints, leading to fracture during forming. The study of the effect of curvilinear weld profile on formability aspects with regard to stamping/deep drawing operations is limited. Curvilinear welds decrease the number of weld requirements, scrap material and avoid imperfections whenever two welds intersect. In this work, the effect of different shapes of weld profiles viz. circular, elliptical and spline shapes on the weld line movement (WLM) was studied. WLM is one of the primary concerns in the manufacture of tailor welded blanks, because it affects component assembly and also leads to wrinkling and tearing during forming. Simulation results showed that the spline curve weld profile has a considerable effect in reducing WLM with improved formability compared to straight welds.

The shape dimensions of die corners and surface textures of blank holders are important in the effective control of twist springback. For predicting springback accurately, a mixed hardening model is presented for a thin-walled S beam made from TRIP780. Based on a proposed evaluation index for twist springback, the experiments of stamping and twist springback for TRIP780 are carried out. The twist springback angle is gauged by a three-coordinate measure instrument. A Response Surface Model (RSM) between the parameters of the mixed hardening model and the twist springback angles is established, and the parameters are inversed. The progressive die corners are designed for the twist springback compensation based on the stress distribution of the thin-walled S beam after stamping, and the die corner radius is optimized by the RSM and an Ant Colony Algorithm (ACA). Meanwhile, the macro textures of blank holders including longitudinal texture and transverse texture are designed. Based on the compensation analysis, a comprehensive compensation method which combined the progressive die corners with the longitudinal texture of the blank holder is proposed. The results show that the springback angle is reduced by 33.6%, proving the proposed comprehensive compensation method is effective.

The industrial demand for products with better quality and lower production costs have encouraged the widespread application of the finite element analysis (FEA) in the development and optimization of sheet metal forming processes. To ensure that the FEA solutions are reliable and robust it is important to take into account the uncertainties that inevitably arise in a real industrial environment. In this context, a numerical study on the influence of the material and process uncertainty in the stamping results of a square cup is presented. In this analysis, it is assumed uncertainty in the elasticity properties, hardening law parameters, anisotropy coefficients, blank thickness, friction coefficient and in the blank holder force. The effect of the uncertainty in these input parameters is evaluated in the punch force, equivalent plastic strain, thickness and cup geometry. Firstly, quasi-Monte Carlo method was used to evaluate the variability in the simulation outputs, considering the uncertainty of the input parameters. This analysis shows that the geometry is the output most sensitive to the uncertainty of the input parameters. Afterwards, a variance-based sensitivity analysis was carried out to identify the input parameters that most influence the output variability. It was concluded that the hardening law parameters and the anisotropy coefficients have the most influence in the stamping results variability of a square cup.

Finite element simulation has become an important tool of process and production design in various fields, especially in the automotive industry. The calculation of forming processes in the early concept phase of new cars allows virtual adaptions, which can reduce costs of later phases in the product development significantly. Therefore, the precise characterization and modelling of the material behavior is necessary to ensure a robust and reliable numerical process design. The mechanical properties of numerous materials are highly influenced by the rolling or extrusion direction in the production process. This necessitates the characterization of materials in different loading directions. However, depending on the dimensional aspects of the semi-finished product, the manufacturing of specimens can be challenging or even impossible. Thus, in this investigation, an innovative, indirect approach for the identification of the Lankford coefficient in transversal direction is presented. Based on numerical and experimental data of layer compression tests the Lankford coefficient is determined by inverse modelling of the resulting specimen contour. Due to the characteristics of the layer compression test, it can even be used for semi-finished products with small transversal dimensions like extruded profiles. The presented methodology is on the one hand verified by conventional uniaxial tensile tests for aluminum as well as steel blank material. On the other hand it is used to determine Lankford coefficients for an aluminum extrusion hollow profile and the inversely identified material model is validated by comparison of strain distributions of experimental and numerical square tube bending tests.

Physical and computer modeling of continuous shaping is described. In the experiments, strip workpieces undergo continuous shaping on a TESA 10-50 pipe-electrowelding system for pipe of diameter 50 mm with wall thickness 1 mm. The pipe blanks are shaped in horizontal and vertical shaping stands, with estimation of the geometric parameters. Single-radius grooves are used on the rollers. The forces affecting the geometry of the pipe blank are determined. Analysis of the workpiece geometry reveals defects of corrugation type on its right edge between the second edging stand and the third shaping stand. A similar defect appears on the left edge in the section between the third shaping stand and third edging stand. To eliminate defects in the shaping section, the horizontal stands are adjusted so that the forces at the drives are the same. Then the relevant forces are again determined: the tractional forces of the drives; the resistance to strip motion in the stands; and the vertical shaping forces. In calculating the forces, the basic parameters are determined by two methods. In the first, the geometric parameters of the pipe blank and the parameters in the bending section are taken into account, with allowance for deformation outside of the contact zone. In the second, the contact interaction of the pipe blank and the shaping tool over the deformation cross section is taken into account. The discrepancy between the calculation results and the experimental data is 8–12%. After correcting the shaping parameters and adjusting the roller grooving, defect-free pipe blanks are shaped. According to comparison of the calculated and experimental trajectories of the edges of the workpiece over the height and width in the stands, the discrepancy is 6–9%. In investigating the geometric parameters of the deformation region, the bending zones with and without contact are taken into account, as well as the springback section. The shaping parameters of the pipe blank are calculated in uniform and roller shaping zones. Analysis of the results shows that shaping of the workpiece corresponds to the assumptions regarding the change in its geometry in roller grooves.

This paper describes a multi-point receptance coupling substructure analysis (RCSA) technique for tool point receptance prediction. The portion of the tool inside the holder is coupled to the portion of the holder that clamps the tool at multiple points along the insertion length. The coupling can be rigid or flexible-damped. The procedure is described analytically and then experimental results are presented. The tool point receptances, or frequency response functions, for four carbide tool blank diameters are tested at multiple extension lengths and compared to predictions for an ER32 collet connection. Stiffness matrices are identified for each of the tool blank diameters and reported. Given the predicted tool point receptances, milling process models can be used to select optimized operating parameters at the process planning stage.

The cylindrical die forced throughfeed rolling process for gears was proposed to overcome an end-effect behavior of the standard radial-feed gear rolling process which can result in pitch variation and excessive axial end-flow. In the rolling process, the workpieces are pushed through the gap of the rolling tools to form the gear teeth. Understanding of material flow is important for grasping the cause of defect formation and improving the quality of formed gears. In this paper, the material flow behavior of the gear forced throughfeed rolling process was studied on the flow velocity and displacement of key locations by using finite element analysis (FEA). The experiment was also conducted and its blank was sliced to thin pieces, and the grid pattern (GP) was utilized to track the trajectory of flowing materials. The results show that the end-flow is located at the root rather than the tooth crest of the formed workpiece, because the compressive forces from rolling tool mainly take effect at the root of the formed workpiece. The asymmetry of circumferential flow displacements with respect to the gear teeth results in the asymmetrical flanks defect, and this is due to the meshing between teeth of rolling tool and workpiece. The local displacement in the radial direction is larger than that in the circumferential direction.

The complexity and specificity of the three-cylinder crankshaft lead to under-filling in the balance slider. Normally, way of the precision of the crankshaft is to increase the blank diameter or the bridge size of flash, which result in high forging load, low service life of die, and material utilization. Therefore, a preformed dressing is designed in the balance slider of the pre-forging die. During the pre-forging period, a dressing will be formed in the balance slider, which is used to ensure the precision of the three-cylinder crankshaft in the final forging period. First, CAD models of the die and billet are established, then which are simulated by the Deform-3D software. The forging load and die wear depth are analyzed, and the area of the balance slider is under-filling. Second, a new pre-forging die is designed with a preformed dressing by the CAD software. Third, response surface analysis (RSA) and finite element technology are combined to optimize the pre-forging die of the three-cylinder crankshaft. According to variance analysis, the preformed dressing is not a significant influence factor on the die wear depth and load. Optimized factors’ R, D, H of the pre-forging die are 19 mm, 84 mm, and 6 mm, respectively. Fourth, the flash height of the final forging die is optimized, and the balance slider is filled well, and the die wear depth is reduced. Finally, physical experiment and practice forging are carried out to verify the optimal scheme of the finite element method (FEM), and the results of the experimental and finite element have a good consistency.

Isogeometric analysis (IGA) has been used with great success when combined with incremental methods to simulate sheet metal forming. In this paper, we present the development of one-step inverse IGA based on the total deformation theory of plasticity . For a large number of industrial stamping parts, the membrane effects are dominant. Thus, we adopted an isogeometric membrane element to predict the flattened contour of the initial blank from the energy-based initial solution estimation approach. In addition, we used the Newton–Raphson algorithm for nonlinear plastic iterations to evaluate the thickness and equivalent strain and stress of the final stamping parts. We applied our framework to square box and S-rail surface models for demonstration. The results for these two examples illustrate the performance of one-step inverse IGA and its applicability to the integrated design of sheet metal forming.

The gear rolling process using a conical gear roller was developed recently and has been proved to be feasible for forming cylindrical gears. However, the rabbit ear defect, which is normally present in the traditional rolling process, still exists. Therefore, an innovative structure for the conical gear roller is proposed to prevent rabbit ear defects. The size of the dedendum circle during the tooth forming stage is determined according to the height of the growing tooth on the blank at each moment, and the volume of the roller pressed into the blank is equivalent to that of the objective gear’s tooth space. Both simulations and experiments are carried out to investigate the effects of the revised rollers on the rolling process. The results show that the formation of the tooth profiles can be effectively confined to the desired volume cavity, so that there is no extra space for the formation of rabbit ears. The tooth is fully filled, and the rabbit ear defects are obviously reduced. The experimental results agree well with the numerical simulation. The present study can help in improving the integrity and accuracy of the formed teeth for the gear rolling process.

The working capacity of the logging and wood processing equipment feeding mechanisms is determined by the achievable coupling of the roller’s working elements with the movable blanks. The coupling stability depends significantly on the geometry specified in the design and implemented in manufacturing and physicochemical properties of the materials of tenons that capture, hold and continuously move the blanks into the processing zone. During operation, the geometrical parameters of tenons are changing due to wearing out, which is a result of a complex set of mechanical, chemical, thermal and other influences that accompany friction and deformation interaction of working elements of feeders and movable wood. Worn down tenons do not provide reliable movement of a blank, due to its slippage, which causes quality reduction of final products and leads to intensification of the cutting tool wearing out. At the same time the features of influence of tenon geometrical form on the mating forces of feeding rollers with movable blanks in conditions of development of the tribotechnical characteristics, which provide their working capacity, are not studied sufficiently for the practical use. Therefore, the research purpose is to clarify the conditions of friction-mechanical interaction of working elements of rollers with wood and to identify patterns of wearing out of tenon working surfaces, which allows theoretically substantiate their rational geometrical shape and requirements for the physicochemical characteristics of recommended materials. The acting load’s principles realized in the zone of contact of the metal surfaces of tenons with wood at displacement of blanks are considered for these purposes. The process of the force interaction change of tenons with blanks is shown beginning with the moment of contact of a certain tenon until it leaves the coupling. Its analysis showed that already at the beginning of the contact the shock bending load begins to act on the top of a tenon. The load in case of peak values often leads to wearing out by crumbling sufficiently large microvolumes of the feeding tenons. The probability of development of such fracture pattern is the greatest with insufficient strength of the using material and pre-sence of structural defects, especially unfavorably located microcracks, and the action of dangerous tensile residual stresses. These factors also significantly affect the corrosion-mechanical wearing out of the working surfaces of tenons and their resistance movement in wood. Thus, the main factor of effective transportation of a blank to the processing zone and achievement of high wearing resistance of feeding rollers is optimization the tenon geometry, properties of the assigned materials and technology of strengthening treatment of the concerned details. For citation: Pamfilov E.A., Pilyushina G.A., Sheveleva E.V., Prozorov Ya.S., Pyrikov P.G. Improving the Feeder’s Working Capacity of Timber Processing Equipment. Lesnoy Zhurnal [Forestry Journal], 2019, no. 2, pp. 102–110. DOI: 10.17238/issn0536-1036.2019.2.102

Ribs are the forming components of the framework of an airplane wing. The nose ribs studied have a U-shaped geometry that consisted of a flat plate, a curved flange with various radius of curvature, and straight flange, and were produced by a stamping process. During stamping, some defects such as thinning, thickening, wrinkling, and springback may occur. To design a forming tool that produces good quality, it was essential to understand the influence of process variables. This study evaluated the influence of stamping process variables on the formability of the nose rib for prevention of excessive thinning and control of the springback phenomenon. Three important process variables namely, blank holder gap, die corner radius, and clearance between the die and the punch were analyzed during an Al-2024-O nose rib stamping. The stamping simulation was a nonlinear problem in nonlinear behavior of solid materials and contacts, which was applied to an elastic–plastic material employed with contact behavior conditions. A DOE design matrix was generated by a full factorial design with every combination of the design variables. The main process variables affecting the multi-objective function, i.e., thickness reduction ratio and springback amount were suggested through main effect analysis, along with the stamping simulation. An experiment was performed to verify the validity of the simulation results. Results indicated that the thickness reduction rate and the springback amount predicted by the simulation were in good agreement with the experimental results. The locations where the maximum thickness reduction occurred, the maximum deformation amount caused by springback, the blank holder force, and the initial blank shape were suggested in this paper. The influence of the process variables will be considered as a reference for improving the quality of the nose rib.

This paper proposes an approach for twist springback reduction using variable blank holder force (VBHF) trajectory that the blank holder force (BHF) varies through the stroke. In addition, the blank shape is optimized. Therefore, design optimization of VBHF trajectory and blank shape for twist springback reduction is performed. Springback of U-shaped product is a simple deformation, whereas the one of S-rail-shaped product shows more complicated behavior due to twisting. As the result, compared with the springback of U-shaped product, it is difficult to evaluate the twist springback. A novel evaluation method for the twist springback is proposed, and the optimal VBHF trajectory and blank shape for the twist springback reduction are determined under several design constraints. Numerical simulation of the S-rail-shaped product is so intensive that response surface approach is valid. In particular, a sequential approximate optimization that the response surface is repeatedly constructed and optimized is used to determine the optimal VBHF and blank shape. Through numerical result, the validation of the proposed approach is examined.

The increasing use of aluminum alloys in automotive industry brings new challenges regarding formability and springback. Servo presses and servo hydraulic cushions can accurately control ram motion and blank holder force during the forming process, reducing the difficulties encountered in forming Al alloys. This study presents an experimental and numerical analysis of springback and residual stresses induced during the U-channel drawing of Al 5182-O. During the U-channel drawing, the draw-in of the sheet material into the die cavity is controlled by blank holder force. So, the material is under stretch bending condition when it slides around the die corner radius. When the material passes the die corner radius it unbends. The reverse loading resulted from the unbending process provides heterogeneous stress distribution through the sheet thickness in the wall section. The effect of post stretching, applied by the use of a servo hydraulic cushion, on reduction of residual stresses and springback at the wall is investigated. The benefit of using servo hydraulic cushion for reducing springback and residual stresses has been demonstrated experimentally. Results illustrate a significant reduction of residual stresses and springback when post stretching is applied.

Origami-based sheet metal (OSM) bending is an extension of rigid origami technique, where the final 3D structure is created from a single 2D flat pattern by bending. The key aspect of OSM is material discontinuity (MD), which helps achieve a unique dieless bending process. MD is a feature along bend line of blank sheet and it can be fabricated using laser or water jet cutting. Even though a number of successful implementations of OSM bending have been found, these cases are limited only to product development and industrial application. The mechanics of OSM bending with respect to parameters that define MD, blank sheet, as well as the bending process have not been studied. Thus, this study identifies parameters and investigates the effect of identified parameters associated with OSM bending. Parameters studied in this work include design parameters and process parameters. Design parameters are kerf-to-thickness (k/t) ratio, web-to-width (w/b) ratio, and thickness of sheet (t). These are associated with MD design. The process parameters are related to OSM bending process, and they include punch placement (t+g), offset distance (s), and punch radius (RP). Finite element analysis (FEA) is performed to investigate the effect of these parameters on the OSM bending process. The simulated OSM bending cases resulted in successful bending without using a die. The general recommendation is provided for selecting parameters of OSM bending based on results. In addition, the shape of MD is an important factor when designing the OSM bending process.

Ultra-high-strength steels (UHSS) offer exceptional opportunities in car body manufacturing regarding the improvement of passenger safety as well as the reduction of total vehicle weight. However, springback represents a serious problem when forming such sheet metal materials. In this context, a new approach that can be used for significant reduction of springback was developed at Institute for Metal Forming, University of Stuttgart (IFU). The uniqueness of this approach is the alternating draw-in of blank during the deep drawing process. This paper shows research results regarding the influence of tool radii on springback by forming with an alternating blank draw-in of this kind. In these investigations, an ultra-high-strength steel sheet of the grade DP 980 was used. Firstly, a finite element (FE) analysis was conducted for a hat channel part geometry using the simulation code LS-Dyna. In order to describe the material behaviour in simulation as exactly as possible, additional tests were provided for determining the strain level dependent change of the elastic modulus as well as Bauschinger effect parameters of the used sheet material. Initial simulation results showed that use of smaller tool radii generally lead to reduced springback amount when forming with alternating blank draw-in. In order to validate these simulation results, experimental work was carried out with the same geometrical and technological parameters as in simulation. Afterwards, the part shape deviations occurred in the experiments were measured by using the optical measurement system GOM ATOS 5M. At the end, the simulation results were compared with the experimentally obtained results and a satisfying consistency was found.

The manufacturing accuracy of the thin-walled parts is significantly affected by the residual stress in the blank and the resulting machining deformation. In recent years, the prediction and control of the machining deformation have received extensive attentions. A semi-analytical machining deformation prediction model is proposed for the thin-walled parts in terms of the equivalent bending stiffness calculated by finite element method (FEM) simulation and theory of plates and shells. Machining deformations of seven typical study cases are predicted by the semi-analytical model. Corresponding experiments and FEM simulations are conducted to validate the proposed model. Then, the influences of the initial residual stress and equivalent bending stiffness on the machining deformation are investigated based on the quantitative results of the proposed model, which is difficult to be obtained by the previous FE models. The results suggests that 1) improving the bending stiffness of the part can effectively reduce the machining deformation; 2) decreasing the stresses in the top part of the blank and in the length direction is more advantageous to reduce the deformation than other parts and directions; 3) the final machining deformation is basically determined by the residual stress within a certain thickness under the blank surface when the residual stress symmetrically distributes along the mid-plane in thickness direction.

In order to further improve crashworthiness and reduce weight, tailor-welded blanks (TWBs) have been widely applied in auto-body design. In this paper, the discrete optimization design of TWBs structures with top-hat thin-walled section subjected to front dynamic impact is performed by using Taguchi-based gray relational analysis. Material grades and thicknesses with three levels are taken as discrete design variables. The total energy absorption (EA), the total weight (Mass) and the peak crashing force (Fmax) are chosen as optimization indicators. Considering the uncertain weight ratio of responses, four different cases would be analyzed. In order to determine the optimal parameter combination more accurately and eliminate errors from range analysis, the analysis of variance (ANOVA) would be performed. The optimized results demonstrate that it is feasible to increase the crashworthiness of TWBs by increasing the gray correlation of the structure. Compared to initial structure, case 1 (w(Fmax):w(EA):w(Mass)= 1/3:1/3:1/3) has the largest improvement among the four cases, i.e., the Fmax and the Mass are reduced by 29.3% and 2.7%, respectively, while the EA is increased by 3.5%. The discrete optimization method with only 27 iterations is a low computing cost or cost-effective and provides some guidance for some similar structural design. More comprehensive studies are essential to optimize performance of multi-components with more discrete variables.

The elbow push-bending process involves pushing a tube between a die and a mandrel to bend a tubular blank into an elbow shape. In this study, the yield was improved by minimizing the cutting loss at the ends of the elbow tube. This was achieved by developing an optimized method for the design of the tubular blank. The design method is based on the deformation behaviors during the push-bending process and was formulated to minimize the cutting loss. An analysis was done to develop design rules for determining the intrados and extrados lengths and the inclination angles at both ends. Given a radius of curvature and the target dimensions of an elbow tube, it is possible to provide the optimum dimensions of the tubular blank to be bent in the push-bending process. The proposed method was successfully implemented in an actual production line and showed improved dimensional accuracies with reduced cutting losses.

In order to reduce the die-roll size in the fine-blanking process, a modified die structure was proposed, which an indenter arranged along the die profile was set on the cutting edge. The indenter can be defined by four structure parameters. To investigate the effect of these four die structure parameters and evaluate their degree of importance on the die-roll size, three different levels of each die structure parameter were applied in the fine-blanking process of a specially designed triangular tooth using FEM. The optimized die structures were determined considering the effect of reducing die-roll size, the die lifetime and the prevention of crack on the cutting surface. Extra simulations were carried out to verify the effect of the modified die. To explain the mechanism of the modified die, a theoretical model was established according to the features of die structures. The former FEM results were taken as examples to demonstrate the theoretical model. To test the feasibility of this modified die, experiments were performed on the part of automobile synchronizer slipper. In addition, the relationship between the blank holder force and the die-roll sizes in the different fine-blanking processes was studied during the experiments.

Assembly and operational reliability of machines and mechanisms are significantly depending on the accuracy of sizes, forms, and positioning of parts. Systematic or accidental errors from set accuracy indexes define the error of edge metalwork. Related elastic displacements of edge and blank unit plus set movements of flexible system elements lead to change in the set trajectory of edge movement, causing shaping errors. In this paper, there are statistical and dynamic parts of errors resulting from reversible deformations. In this paper, there is provided calculation methodology for errors caused by reversible deformations under the impact of cutting forces. In this paper, there are considered the errors caused by uneven radial flexibility by the turn angle of the system spindle – boring bar caused by preliminary out-of-roundness of the bored hole concerning the spindle axis. There are provided the correlations for calculation of total errors upon boring stepped holes. In this paper, there are calculated dynamical errors based on the determination of amplitude of forced oscillations upon boring smooth and stepped holes. Computer programs were created to calculate separate component parts and also the total reversible error. This paper studies the dependency of influence indexes from geometrical parameters of console boring bars and also comparative results of statistical and dynamic errors.

Damped braces (DBs) can be an easy and not expensive retrofitting solution of reinforced concrete (r.c.) framed buildings, in order to attain a designated seismic performance for a given intensity of the ground motion. Most of the current displacement-based design (DBD) procedures of DBs only consider the capacity curve of an initially undamaged structure. However, structures may be initially damaged by previous earthquakes, so the proportioning of DBs should include the effects of the cumulative damage induced by previous loading cycles. In this study, a displacement-damage-based design (DDBD) procedure of hysteretic damped braces (HYDBs) is implemented in an automated application named DAMPERS. It is divided into six electronic sheets, each one having blank boxes editable by the user and grey boxes showing the outcome of the automated evaluation. A six-storey r.c. framed building, representative of the Italian residential housing stock constructed during the 1990s, is retrofitted with HYDBs designed through the proposed DDBD procedure with the support of DAMPERS tool. In order to assess the relevance of damage due to previous earthquakes, the retrofitting solutions are also obtained with a simplified DBD procedure. Three structural configurations are considered for the original and retrofitted structures: i.e. bare frame, with nonstructural MIs; infilled frame, with a uniform in-elevation distribution of structural MIs; pilotis frame, with no MIs at the ground floor and structural MIs at the other floors. To check the effectiveness of the HYDBs, nonlinear seismic analysis of the test structures is carried out using the computation platform OpenSees.

In the present paper, contact between blank and tools is studied, in predicting cylindrical cup deep drawing of AA2198 Al-Li alloy, in order to investigate the influence of friction on the quality of the final product. For this purpose, finite element analysis is used, and a three-dimensional model was simulated using the FE-package ABAQUS software. ABAQUS permits investigating models of real processes including different emphasis produced by complex friction, large deformations and material non-linearities.

The countersinking process is consisted to enlarge a pre-hole using a conical punch in order to allow rivets and screws to sit flush with the surface of the assembled sheets. The geometry of the pre-hole had many effects on this process. The main goal of this study is to characterize the effects of the pre-hole geometrical parameters on the obtained countersunk hole. Their effects on the forming kinematics and the loads were investigated. A finite element model was developed using ABAQUS/Standard. The adopted model was performed with an elasto-plastic behavior and an isotropic hardening rule for the workpiece. A configuration with a maintained blank holder has been adopted for this study. The results from simulations analysis provided one good explanation for the complexity of the observed forming kinematics. The comparison between the simulations and the experimental results confirmed the validity of the adopted finite element model for predicting the loads and the final shape of the countersunk workpiece.

A design of the device for studying plastic compression of long cylindrical specimens under conditions of a linear stress state is presented. The device is developed to study the properties of metals under plastic deformation in conditions of nonmonotonic loading. The goal of getting the accurate experimental data entails the necessary of carrying out tests using one long-length cylindrical sample, with the calculated length being more than five diameters. To prevent flexure of the long-length sample upon compression, the support conical sectors made by cutting truncated cone shaped blank into 6 or 8 equal parts with a central longitudinal hole having a diameter equal to the diameter of the test sample are used. The sectors are coupled by two pairs of semirings. A transcendental equation is obtained for determination of the taper angle of those sectors on the basis of kinematic analysis of the mobile links. This angle depends on the total weight of the sectors and sliding friction coefficients in the corresponding kinematic pairs of the device. For the considered device, the taper angle of the sectors is 36°. This device is designed and manufactured for compression testing of the samples with a diameter of 16.5 mm and a gaged length of 135 mm. Samples from steel 45 are tested with a goal of the flow curve construction and experimental verification of the strain diagrams under conditions of cyclic tensile-compression. Comparison of the calculated and experimental data proved the satisfactory accuracy of the stress determination, which makes it possible to recommend this device as a testing tool to be used in mechanical laboratories of the universities and research institutes.