Blank Shape Research Articles

The application of geometric-morphometric shape analysis to Middle Paleolithic bone retouchers from the Altai Mountains, Russia

Here, we apply geometric-morphometric shape analysis to Middle Paleolithic bone retouchers from Chagyrskaya Cave in the Altai Mountains of southern Siberia. The cave contains evidence of the easternmost manifestation of the Micoquian industry, associated with Neanderthals at end of MIS4 and the beginning of MIS3. Taphonomic and scar pattern analyses were performed first on random samples exhibiting appropriate characteristics. Several retouchers produced on intentionally modified blanks were identified in our sample, suggesting that some of the Chagyrskaya Cave bone retouchers can be described as formal tools. All retouchers from Chagyrskaya Cave exhibit a similar general morphology. The most variable group is comprised of complete retouchers without blank modifications. Retouchers exhibiting minor damage affect the general pattern of variability and it is not possible to identify them only by means of geometric-morphometric shape analysis. Complete retouchers with blank modifications fall within the range of variability of complete retouchers without blank modification, suggesting intentional shaping of blanks to conform to a standard template. The range of variability of the bone retouchers does not differ significantly from that of the most highly modified lithic artifacts at Chagyrskaya – plano-convex bifaces – which may indicate intentional shape control for such artifacts. Geometric-morphometric analysis indicates that the anatomical origin of bone blanks does not significantly influence the retouchers’ shape, which may point to strict blank selection and, at the same time, intentional modification. Our results raise questions regarding the integration of retouchers into a complex, multidimensional “chaine-opératoire” as well as the nature of Neanderthal cognitive abilities. Geometric-morphometric shape analysis represents a major step forward in the study of prehistoric retouchers.

Oblique/Curved Tube Necking Formed by Synchronous Multipass Spinning

In this paper, we propose a method of forming a tube into an oblique/curved shape by synchronous multipass spinning, in which the forming roller reciprocates in the radial direction in synchrony with the rotation angle of the spindle while the roller moves back and forth along the workpiece in the axial direction to gradually deform a blank tube into a target shape. The target oblique/curved shape is expressed as a series of inclined circular cross sections. The contact position of the roller and the workpiece is calculated from the inclination angle, center coordinates, and diameter of the cross sections, considering the geometrical shape of the roller. The blank shape and the target shape are interpolated along normalized tool paths to generate the numerical control command of the roller. By this method, we experimentally formed aluminum tubes into curved shapes with various radii of curvature, and the forming accuracy, thickness distribution, and strain distribution are examined. We verified that the curved shapes with the target radii of curvature can be accurately realized.

Manufacturing of a hemispherical component combining incremental forming and superplastic forming

The interest towards magnesium (Mg) alloys for the fabrication of light weight components has been continuously increasing, especially for transportation, since the payload is strictly related to the energy (fuel or electricity) consumption. Super plastic forming (SPF) and single point incremental forming (SPIF) are viable processes for manufacturing light weight parts since they allow to produce components with superior characteristics and quite complex geometries, even in the case of the poorly formable Mg alloys. But, since both the processes are characterized by stretching, thinning is a key issue to be addressed. On the other side, in order to fulfil the structural and corrosion resistance characteristics required by aerospace and automotive applications, components with a uniform thickness distribution have to be produced. Such an aspect is even more important when the shape complexity of the component increases. SPF and SPIF have never been combined or hybridized so far but, in order to produce parts with a uniform thickness distribution, a possible strategy based on the blank pre-forming by SPIF prior to the SPF has been proposed in the present paper. In particular, the initial blank shape to be obtained by SPIF was designed using a numerical optimization approach and effectively created using the sine law to predict the wall angle and design the tool path. A hemispherical component in AZ31B-H24 was used as case study. The thickness profile of the component obtained by SPF revealed to be highly uniform in a large area (the portion from the centre of the sample to its periphery corresponding to about 70%) being characterized by a thickness equal to about 0.5mm. The quality in terms of finishing of the component produced by SPF resulted to be good, irrespective of the roughness increase exhibited by the blank after the pre-forming by SPIF.

Non-sorting multi-objective optimization of flexible roll forming using artificial neural networks

The main defects due to flexible roll forming (FRF) processes include longitudinal bow and wrinkling. In this study, experimental and numerical analyses were performed using three different blank shapes to characterize the effects of the process parameters on defects in parts fabricated by FRF with and without leveling roll. Owing to the complexity of the FRF process, two algorithms were combined for its optimization. Artificial neural network-based Non-dominated Sorting Genetic Algorithm II (NSGA-II) was used to optimize the effective parameters of the FRF process, such as the sheet thickness, yield strength, and blank shape, with respect to the target bend angle to minimize the longitudinal bow and wrinkling of the product. The back-propagation neural network (BPNN) was used to identify two objective functions, while non-sorting multi-objective algorithm simulation was used to optimize the input parameters to minimize the objective functions. The results showed that the sheet thickness had the greatest effect on the minimization of the two objective functions, followed by the yield strength and blank shape, respectively.

A new method for hydroforming of thin-walled spherical parts using overlapping tubular blanks

Tube hydroforming is an advanced metal forming processes, which is widely used to form various tubular parts. Axial feeding is usually used to avoid excessive thinning in hydroforming of a variable-diameter part. However, wrinkling defects are susceptible to occur easily under the axial loading if the wall thickness of the tube is small. A new method was proposed to enhance the expansion ratio and improve the thickness distribution for hydroforming of thin-walled spherical parts using overlapping tubular blanks. A special loading tool was created and AISI 304 stainless steel blanks were used for the experimental research. The effects of blank shapes and normal constraints were studied on wrinkling defects of the overlapping blanks. The results show that wrinkling defects at the inner layer of the overlap are prevented by using curved-edge blanks. Wrinkling defects at the outer layer of the overlap is eliminated by using normal constraints. Finally, a sound thin-walled spherical part was obtained by using an overlapping tubular blank. The maximum expansion ratio is 60% and increased by 30.2% compared with that of conventional hydroforming using a closed cross-sections tube. The maximum thinning ratio was 32.4%, which was decreased by 29.3%. In general, it is feasible to use an overlapping blank to form a variable diameter part. The maximum expansion enhances significantly and the thickness distribution improves apparently.

Effect of pre-strain on stretch flange deformation limit of steel sheets

The effect of pre-strain on the stretch flange deformation limit of steel sheets was investigated by hole expansion tests under various pre-strain conditions. Pre-strain was given by stretch forming with a cylindrical punch. The strain ratio and amount of pre-strain were controlled by changing the blank shape and forming height. The hole expansion tests were carried out with a conical punch and cylindrical punch in order to clarify the effect of the strain gradient. The effect of the strain ratio of pre-strain on the stretch flange deformation limit can be expressed by equivalent strain. In the case of higher strain gradients, the stretch flange deformation limit increased with increasing pre-strain. However, at lower strain gradients, the stretch flange deformation limit was almost constant. These results suggest that the formability of the stretch flange deformation area given by pre-strain should be determined from not only the total equivalent strain but also the strain gradient and the amount of pre-strain expressed by equivalent strain.

Optimization of initial blank shape for flexible micro deep drawing of square parts

Micro flexible tool-assisted sheet metal forming is one of the forming techniques that have increasingly attracted extensive attention of researchers. Due to its simplicity, low overall production cost, feasibility of prototyping, this forming process seems appropriate for producing micro components. This work presents an evaluation study on using flexible deep drawing process to produce micro stainless steel 304 square cups. The influence of initial foil thickness and blank shape are investigated in details. An optimization of blank shape is implemented to provide micro square products with net-shape and flange free. The finite element simulations are achieved using the commercial code Abaqus/Standard. The results showed that the initial foil thickness affects the thinning and thickening values of the formed cup wall. As well as, the optimization method is feasible to indicate the optimum initial blank shape for producing free flange- micro square parts.

Production of Hollow Alloy Blanks with Shape Memory Effect

Abstract—The manufacture of blanks from alloys based on titanium nickelide with shape memory is proposed by means of reverse extrusion with subsequent thermomechanical treatment and crimping. The alloy plasticity is analyzed as a function of the temperature and strain rate. The shaping of such blanks is investigated.

Prediction of Eight Earings in Deep Drawing of 5754O Aluminum Alloy Sheet

Earings appear easily during deep drawing of cylindrical parts owing to the anisotropic properties of materials. However, current methods cannot fully utilize the mechanical properties of material, and the number of earings obtained differ with the simulation methods. In order to predict the eight-earing problem in the cylindrical deep drawing of 5754O aluminum alloy sheet, a new method of combining the yield stress and anisotropy index (r-value) to solve the parameters of the Hill48 yield function is proposed. The general formula for the yield stress and r-value in any direction is presented. Taking a 5754O aluminum alloy sheet as an example in this study, the deformation area in deep drawing is divided into several equal sectorial regions based on the anisotropy. The parameters of the Hill48 yield function are solved based on the yield stress and r-value simultaneously for the corresponding deformation area. Finite element simulations of deep drawing based on new and existing methods are carried out for comparison with experimental results. This study provides a convenient and reliable way to predict the formation of eight earings in the deep drawing process, which is expected to be useful in industrial applications. The results of this study lay the foundation for the optimization of the cylindrical deep drawing process, including the optimization of the blank shape to eliminate earing defects on the final product, which is of great importance in the actual production process.

Analysis of shape defects during flexible roll forming of steel/aluminum double-layered blanks

Flexible roll forming is an advanced sheet-metal-forming process that allows the production of parts with variable cross-sections. Double-layered blanks can have enhanced properties such as a high stiffness-to-weight ratio and high corrosion resistivity when combined with suitable materials. However, in the flexible-roll-forming process of double-layered blanks, additional shape defects and interface delamination can occur owing to their inhomogeneous mechanical properties compared with those of single-layered blanks. In this study, investigations on shape defects generated during the flexible-roll-forming process of steel/aluminum double-layered blanks were performed. Shape defects such as web-warping, wrinkling, and delamination at the interface were investigated on three different blanks with trapezoidal, convex, and concave shapes. The results show that the process-induced longitudinal strains significantly affect the occurrence of shape defects. Moreover, the longitudinal strains strongly depend on the blank shapes, their stacking order, and mechanical properties of the constituent layers.

Blank layout shape optimization of drawn part

Blank layout shape optimization of drawn part

Effects of pressure, boundary conditions, and cutting reliefs on thermo-hydroforming of fiber-reinforced thermoplastic composite helmet based on numerical optimization

Compared with layup techniques, thermo-hydroforming is shown to be a viable process for mass production of thermoplastic composite structures due to its relatively rapid cycle time and low impact on the microstructure of the material. However, unlike layup technique, thermo-hydroforming can produce wrinkles in the formed part. A research was conducted wherein ABAQUS/CAE (6.14-1) was employed to numerically study the impact of thermo-hydroforming process parameters on the formation of wrinkles in a thermoplastic helmet. The optimized properties of the fiber-reinforced polymer composite was previously determined by the authors using the preferred fiber orientation model implemented as a user material subroutine (VUMAT). To account for the interaction between different layers of the laminated composite, the cohesive zone model was employed. The objective of the study was to use the simulation tool to minimize the overall wrinkle density and wrinkle height in the formed helmet as a function of the fluid pressure, boundary conditions, and especially the blank shape and the relief cuts made in the blank.

Numerical analysis of automobile front floor forming

In this paper, DYNAFORM software was used to simulate and analyze the stamping and forming process of automobile front floor parts. In addition, through ETA post-processing software, the animation simulation of the front floor forming process, the forming limit diagram (FLD), the change of thinning rate and the flow of materials are obtained, according to the law of change, some parameters are adjusted to obtain the optimal results. Three groups of subjects were set up: blank holder force, blank shape and draw bead, by controlling the material and the friction coefficient and other parameters are the same, respectively to compare the result of the experiment data, to get the best forming solution. Through DYNAFORM simulation and analysis, the overall forming effect of automobile front floor parts is the best under the scheme of 240 tons of blank holder force, rectangular blank shape and sectionalized sectional draw bead.

Influence of Process Variables on the Stamping Formability of Aluminum Wing Nose Rib

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.

Numerical optimization of variable blank holder force trajectory and blank shape for twist springback reduction using sequential approximate optimization

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.

Effect of pin arrangement on formed shape with sparse multi-point flexible tool for creep age forming

Abstract The effect of forming pin arrangement on formed shape accuracy with sparse multi-point flexible (SMPF) tool has been experimentally and numerically investigated for creep age forming (CAF) process. An analytical method has been introduced to predict shape, stress and strain distributions of blanks loaded by SMPF tool with different pin configurations. Experiments and FE simulations of loading and CAF processes by SMPF tool with various pin number/interval conditions have been performed and the formed shapes after loading and CAF have been quantitatively analysed. The results show that increasing pin numbers in SMPF tool decreases shape errors and stress variations in the loaded blank, leading to lower deflections of the formed blank after CAF. With increasing pin numbers, the formed shape approaches the shape formed with corresponding surface tool. The shape error percentage in loaded blanks is significantly enlarged after CAF with SMPF tool, from 3% to more than 20% for singly-curved tool shapes with aluminium alloy 6082, and detailed value varies with tool shapes. Stresses in loaded blanks directly affect CAFed shapes and it has been found for the first time that there is a same stress discrepancy level between loaded blanks with SMPF tool and corresponding surface tool to achieve a particular shape accuracy after CAF with different tool shapes. It is proposed that the stress discrepancy parameter in loaded blanks can be used as a new and more efficient design criterion for pin arrangement in SMPF tool for CAF process. In addition, an asymmetric pin pattern, which reduces half of pins in SMPF tool and increases efficiency, has been proposed and its effectiveness for CAF process has been tested and discussed.

The effect of structure and properties of steel 30KhGSA on the shaping of round blanks using plastic bending

The influence of the structure and properties of 30KhGSA steel on the shaping of round-shaped blanks using the method of plastic bending is studied. Bending of the initial steel rod sample results in the sample fracture. Methods of mechanical tests and metallographic analysis used in the study showed that the steel sample in the initial satate has a structure of lamellar perlite. A comparative evaluation of the structure and properties of the steel samples prior to and after additional heat treatment (spheroidizing annealing) revealed that annealing enhanced the plastic properties of the sample and changed the sample structure from lamellar to globular perlite. Formation of the granular perlite structure indicates to the devision of the plates into smaller particles and their further spheroidization due to transferring carbon through the surrounding solid solution. Thus, additional cyclic heat treatment of steel in the state of delivery, allowed us to solve the problem of the rod fracture upon subsequent plastic bending. As a result of the research, the values of the mechanical properties of steel were obtained experimentally, which ensure the process of bending the rod into a round shaped blank without destroying it. The proposed mode of cyclic heat treatment (spheroidizing annealing) can be used to improve the plasticity characteristics of the metal upon shaping by the method of plastic bending.

Basic Characteristics of Sheet Hydroforming

Recently, tube hydroforming is appreciated for its contribution to improving fuel economy and crash safety. For further complex shapes, sheet hydroforming has some advantages because sheet blank shape can be designed freely. In this paper, the basic forming characteristics of punchless sheet hydroforming are investigated on the basis of the results of experiments and finite element (FE) analysis. The main conclusions are as follows. (1) In hydroforming, panel dent resistance is improved compared with that in stamping, because larger strain can be induced and work hardening occurs in the punch bottom area in hydroforming. (2) Fractures and wrinkles occur in the stamping drawing test. On the other hand, wrinkles do not occur in the hydroforming drawing test, because, in hydroforming, circumferential stress at the lower area of the side wall shifts in the tensile direction compared with that in stamping and sheets are supported by internal pressure, which suppresses the out-of-plane deformation. (3) The formable range of the drawing test in hydroforming is greater than that in stamping, since relatively large strain can be induced in the entire specimen in the equibiaxial strain state in hydroforming.

Blanking immediately after heating and ultrasonic cleaning for compact hot-stamping systems using rapid resistance heating

To produce ultra-high-strength steel parts for improving fuel consumption and collision safety of automobiles, a compact hot-stamping process having resistance heating was developed. In this process, a blanking operation was introduced immediately after heating to deal with non-rectangular blanks in resistance heating. By blanking, not only were the blank shapes optimised for stamping but the formability was also improved by removing both non-heating edges in contact with the electrode. A rectangular quenchable steel sheet was resistance-heated; the sheet was immediately blanked into the desired shape, and the blank was hot-stamped. In addition, reinforcements used for a body-in-white were hot-stamped using the proposed process to examine the applicability. The reduction in thickness of the hot-stamped reinforcement using a hot-blanked sheet was reduced compared with that using a rectangular blank. The formability was improved by blanking immediately after heating. Moreover, ultrasonic cleaning with diluted hydrochloric acid removed the thin oxide scale caused by resistance heating, and the spot-resistance weldability and electrodeposition paintability were improved. Blanking immediately after heating and ultrasonic cleaning are useful for practical hot-stamping processes using resistance heating.

Synchronous multipass spinning of oblique-bottom shape

Recently, various methods for the metal spinning of noncircular shapes have been proposed to overcome the limitation of its application range. In this study, a metal spinning method for noncircular shapes with oblique bottoms is proposed. This method is a combination of synchronous spinning and multipass spinning, in which the roller is synchronized with the mandrel rotation to track a noncircular cross section while the workpiece is gradually deformed without much thinning through some paths of the roller. The roller trajectory is calculated by linear interpolation in the radial direction and axial direction between the inclined blank shape and the inclined cross section of the product. A circular cup and square cup with an oblique bottom and vertical side walls are successfully spun using this method. As the wall thickness locally increases at the side edges of the square cup, the thickness distribution is equalized by using an intermediate circular shape. This method interpolates the roller trajectory between the blank shape and intermediate shape and between the intermediate shape and the product. The difference in the wall thickness is reduced since the square shape is formed via a cylindrical shape. In addition, the effect of the process parameters on the forming results is experimentally investigated.