Forming Of Sheet Metal Parts Research Articles

Coupled effect of prestrain and intermediate annealing on mechanical properties and microstructural evolution of GH5188 superalloy

The forming of sheet metal parts with complex structures often requires multiple processing. The Co-based superalloy GH5188 sheet is taken as the research object for two-stage uniaxial tensile experiments including intermediate heat treatment, where the prestrain is 10%, 20% and 30%, respectively, in the first stage. The results indicate that the macroscopic residual stress increases with increasing prestrain, which is manifested as the increase of the initial yield strength, the deterioration of ductility and work hardening ability. The increase in dislocation density in the plastic deformation process is the decisive factor. After annealing, the number of deformed grains greatly reduces, and the grain size is refined, resulting in a corresponding reduction in dislocation density. Intermediate heat treatment can eliminate dislocation stacking and stress concentration in the alloy and reduce the influence of internal stress generated during work hardening. Furthermore, the intermediate annealing can decrease the initial yield stress and increase the elongation of the predeformed sheet, while retaining desirable work hardening ability and tensile strength, ultimately enhancing the subsequent work performance.

Experimental and Numerical Investigation on Effects of Pin Diameter on Multi-Point Forming

Multi-point forming (MPF) is an advanced and flexible method to form sheet metal workpieces. Although there are studies investigating different aspects of this method, the studies on the effects of pin diameter on sheet and pin contact on MPF are insufficient. In this study, pins with diameters of 10, 12, and 14 mm were used to investigate the damage factor, effective stress distribution, and required forming loads of three forms of aluminum 1100 parts in finite element simulations. In addition, experimental works were conducted for the 12 mm pin and the forming loads and the thinning on the contact points of pin and formed sheet metal parts were compared with the simulations. The 14 mm pin forming provided the highest effective stress distributions and the damage factors of 0.448, 0.770, and 0.329 were obtained for form1, form2, and form3, respectively. The percentage errors between experimental works and simulations using 12 mm pin forming were calculated as 7.4, 5.1, and 2.4% for all forms 1 to 3. In conclusion, pin diameter was shown to have significant effects on the MPF process. Larger diameter pins resulted in higher loads and tearing of sheet metal.

Multistage Deep-Drawing with Alternating Blank Draw-in for Springback Reduction in Transfer and Progressive Dies

Cold formed sheet metal parts made of advanced high-strength steels (AHSS) offer a high potential for a lightweight, durable and economic design. However, manufacturing dedicated, high-strength parts with cold forming technologies such as conventional deep-drawing often results in unacceptable shape deviations due to elastic springback after unloading the part from the forming tools. Therefore, various springback compensation methods have been established to ensure dimensional quality of such sheet metal parts. At the Institute for Metal Forming Technology (IFU Stuttgart), deep-drawing with alternating blank draw-in was developed in this context as a new approach to reduce springback and enhance cold forming of AHSS sheet metal parts. Presented work provides numerical sensitivity analysis as well as experimental studies about this new forming method. The asymmetric and alternating blank draw-in, which is changed within a multistage forming process sequence, results in an alternated bending over tool radii and leads to a beneficial stress superposition in the part wall area with reduced springback phenomena. Compared to conventional deep-drawn sheet metal components, springback of a benchmark part geometry could thus be reduced over 75 % by a three-stage forming process with an optimized blank draw-in kinematic.

Formability analysis on titanium grade2 sheets in multi point incremental forming process

Single point incremental forming (SPIF) is found to be a good alternative to the conventional sheet metal forming techniques and is suitable for the production of small batch and custom made parts. The major disadvantage of the SPIF process is the time required to complete the job. In this work, a multipoint incremental forming (MPIF) tool which gives better contact on the workpiece and completes the job in less time compared to SPIF is used. The present work investigates the formability and failure mechanism of titanium grade 2 sheets in MPIF process. The major operating parameters selected for the study are step depth, feed rate and speed. Formability of titanium grade 2 sheets increases with decrease in speed and step depth while keeping the feed rate constant. Based on the results it was found that the MPIF process can be effectively utilized for forming sheet metal parts.

Spatially Resolved Forming Mechanisms Detection in Single Point Incremental Forming Using Synchrotron Based Texture Analysis

Despite the ongoing success of understanding the deformation states in sheets manufactured by single-point incremental forming (SPIF), the unawareness of the spatially resolved influence of the forming mechanisms on the residual stress states of incrementally formed sheet metal parts impedes their application-optimized use. In this study, a well-founded experimental proof of the occurring forming mechanisms shear, bending and stretching is presented using spatially resolved, high-energy synchrotron x-ray diffraction-based texture analysis in transmission mode. The measuring method allows even near-surface areas to be examined without any impairment of microstructural influences due to tribological reactions. The depth-resolved texture evolution for different sets of forming parameters offers insights into the forming mechanisms acting in SPIF. Therefore, the forming mechanisms are triggered explicitly by adjusting the vertical step-down increment Δz for groove, plate and truncated cone geometries. The texture analysis reveals that the process parameters and the specimen geometries used lead to characteristic changes in the crystallites’ orientation distribution in the formed parts due to plastic deformation. These forming-induced reorientations of the crystallites could be assigned to the forming mechanisms by means of defined reference states. It was found that for groove, plate and truncated cone geometries, a decreasing magnitude of step-down increments leads to a more pronounced shear deformation, which causes an increasing work hardening especially at the tool contact area of the formed parts. Larger step-down increments, on the other hand, induce a greater bending deformation. The plastic deformation by bending leads to a complex stress field that involves alternating residual tensile stresses on the tool and residual compressive stresses on the tool-averted side incrementally formed sheets. The present study demonstrates the potential of high-energy synchrotron x-ray diffraction for the spatially resolved forming mechanism research in SPIF. Controlling the residual stress states by optimizing the process parameters necessitates knowledge of the fundamental forming mechanism action.

Experimental analysis and smoothed particle hydrodynamics modeling of electrohydraulic forming of sheet metal parts

One of the considerable advantages of high velocity forming methods i.e. Electrohydraulic Forming method is improvement in the formability of the materials in comparison to conventional methods. In this study, the electrohydraulic forming method is used to free-form circular plates and to study the effect of some process parameters such as discharge energy, stand-off distance and electrode gap size on the deformed part. In addition, the process was simulated using Arbitrary Lagrangian Eulerian (ALE) and Smoothed Particle Hydrodynamics (SPH) methods and the results were compared with the experimental data. It was shown that the numerical approach overestimated the experimental results. This was happened due to the dissipated energy of electrical circuit in the experimental test. Higher discharge energies caused larger dome heights and enhancing the stand-off distance declined the dome height. On the other hand, the electrode gap size had an optimum value which provided the maximum dome height. It was found that, the implemented method of applying discharge energy for simulation reduces the differences between the experimental and numerical results lower than 10%. It was noticed that the utilizing the SPH method in the simulation of the EHF process is a very promising method and could be beneficial in the research work and industrial application.

Developments of New Sheet Metal Forming Technology and Theory in China

Developments of new sheet metal forming technology and theory in China are reviewed in detail in this paper. Advances of crystal plasticity on the deformation mechanism of Mg alloy are firstly described, especially its applications on the prediction of sheet forming process. Then, a new macroscopic constitutive model is introduced, which possesses an enhanced description capacity of tension/compression anisotropy and anisotropic hardening. In order to take into account the twinning process of hexagonal close-packed material, a modified hierarchical multi-scale model is also established with adequate accuracy in a shorter computational time. The advanced forming limit of sheet metal, mainly about aluminum alloy, is also investigated. Besides the above theory developments, some new sheet metal forming technologies are reviewed simultaneously. The warm forming technology of Mg alloy is discussed. New processes to form sheet parts and to bend tubes are proposed by using hard granules. On the other hand, a new kind of ultra-high-strength steel based on typical 22MnB5 by introducing more residual austenite and Cu-rich phase to increase the elongation and strength and its novel forming method that integrates hot stamping and quenching participation are proposed. Progresses in sheet hydroforming, press forging and electromagnetic forming of sheet metal parts are also summarized.

The Influnce of Some Parameters on the Quality of Deep Drawing of Cylindrical Cups without a Blank Holder

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

An automated solution for fixtureless sheet metal forming

Manual forming of sheet metal parts through traditional panel beating is a highly skilled profession used in many industries, particularly for sample manufacturing or repair and maintenance. However, this skill is becoming gradually isolated mainly due to the high cost and lack of expertise. Nonetheless, a cost-effective and flexible approach to forming sheet metal parts could significantly assist various industries by providing a method for fast prototyping sheet metal parts. The development of a new fixtureless sheet metal forming approach is discussed in this article. The proposed approach, named Mechatroforming®, consists of integrated mechanisms to manipulate sheet metal parts by a robotic arm under a controlled hammering tool. The method includes mechatronics-based monitoring and control systems for (near) real-time prediction and control of incremental deformations of parts. This article includes description of the proposed approach, the theoretical and modelling backgrounds used to predict the forming, skills learned from manual operations, and proposed automation system being built.

Effects of K Factor on the Length of Aircraft Sheetmetal Material Preparation under Unfolding State

To prepare materials for sheetmetal unfolded based on CATIA software became an important link in processing and forming of sheetmetal parts. In this paper through the research of practical problem encountered in the process of sheetmetal unfolding preparation in aircraft manufacturing enterprises, introduce and prove the influence of sheetmetal unfolding coefficient on the preparation of raw materials; through analysis of external factors like the characteristics of materials and ductility of sheetmetal, developed a suitable method to calculating the length of sheet metal stocks. It greatly enhanced the level of sheetmetal manufacturing in aircraft manufacturing enterprises, meet the requirements needed on sheetmetal processing, and bring about the technology expand from theory to practice.

Modeling of electrohydraulic forming of sheet metal parts

Electrohydraulic forming (EHF) is based upon the electro-hydraulic effect: a complex phenomenon related to the high voltage discharge inside the water filled chamber. The resulting shockwave in the liquid is propagated toward the blank, and the mass and momentum of the water in the shock wave accelerates the sheet metal blank toward the die. Methodology of numerical simulation of EHF processes was developed based upon LS-DYNA commercial code using Arbitrary Lagrange–Eulerian (ALE) Multi-Material formulation. The model incorporates energy deposition inside the plasma channel, expansion of the channel driven by high pressure inside of it, propagation of the pressure pulse through the water filled chamber in contact with the rigid walls of the chamber and with the sheet metal blank being deformed. Comparison of the numerical and experimental results was performed on maximum pressure measured on the wall of the cylindrical chamber employing the membrane method.The model was used to simulate multistage EHF of a complex geometry automotive part. Analysis of the results showed the complex nature of multistage EHF process: a clearly recognizable wave picture during the initial stage of the channel expansion which transitions to almost incompressible water flow during later stages.

Hot Stamping Technology for Door Impact Beam

In response to the increasingly stringent environmental requirements and collision regulations, the high strength steel has become the mainstream trend of the automotive materials. This study used door impact beam as the experimental vehicle, applied CAE simulation analysis, and conducted experimental verification to discuss how to reduce the thinning condition of the formed sheet metal parts. Then, the hardness test, thinning rate analysis and 3D curved surface scanning were performed to check the mechanical properties and external dimensions of the finished products of hot stamping. The results are used as the reference for door impact beam forming die design.

A comprehensive blank development method for forming sheet metal parts

For some shortcomings in the use of standard radial length development in the blank development for forming sheet metal parts, an improved radial length normal spreading approach considering outside normal direction is developed to resolve blank development in sheet metal forming. Moreover, a comprehensive spreading method, which combines radial length normal spreading and orthogonal length development method, is presented in this paper to avoid the overlapping problem which happens sometime in the spreading process related to severely curved sheet parts. To deal with holes and gaps which exist in some sheet metal parts, dummy elements are used to calculate the intercepting line’s length precisely. Finally, a multistep spreading and merging strategy is adopted to handle some special sheet metal parts with vertical free edges that should be jointed or not. Through practical applications, the effectiveness and the usefulness of this approach are evaluated, and the unfolded result is more reasonable; meanwhile, the obtained blank shape should be a better initial guess in the application of the so-called one-step quick analysis for sheet metal forming simulation.

Research and Design of an Equipment for Multi-Point Press Forming Sheet Metal Parts

The premise of the flexible multi-point die stamping processing is that each punch can be adjusted to required position. Using numerical control technique, punches can be adjusted by stepping motors through driving screw rods. But each punch requires a stepping motor in this equipment. This kind of equipment is much expensive. In addition, the distance between adjacent punches is much big. Thus, this kind of equipments is not suitable for processing some small and medium-sized sheet metal parts. A new kind of equipment for press forming sheet metal parts is presented. Only two DC motors are needed to adjust punches of male and female moulds in this kind of equipment. Punches can be arranged more closely. This kind of equipments can be used to process small and medium-sized sheet metal parts.

Advanced feature detection algorithms for incrementally formed sheet metal parts

New advanced algorithms for the detection of detailed features in parts formed by single point incremental forming (SPIF) were developed. The features were detected in STL part specifications that took into account the geometry, curvature, location, orientation and process parameters to detect 33 different features within an expert CAPP system for SPIF. The detection process was facilitated by using multi-level edge segmentation routines that first created a frame of edge features. Within this frame, the remaining features were then detected using region growing algorithms. The results show successful detection for a number of test cases. A case study for a double curved hemisphere illustrates the generation of optimal tool paths using compensation for the detected features in the part. These tool paths lead to the improvement in the accuracy of the formed sheet metal parts.

반구형 극소 드로인 제품의 두께분포 비교

Meso-scale or micro-scale forming of sheet metal parts has been recently considered as one of the important forming technologies with growing demand on meso/micro products for electric or medical devices. Experimental investigation on the cylindrical meso-cup drawing with hemispherical punch is carried out to examine the limit drawing ratio and thickness distribution of drawn cups. The working parameters chosen in this study are blank diameter, die-corner radius and blankholding force. It is found from the experiments that the limit drawing ratio of 2.4 can be achieved in the case of hemispherical cup drawing and uniform thickness distribution in wider region can be obtained compared with the results of conventional cup drawing.

Influence of variables in deep drawing of AA 6061 sheet

Deep drawing is one of the most important processes for forming sheet metal parts. It is widely used for mass production of cup shapes in automobile, aerospace and packaging industries. Cup drawing, besides its importance as forming process, also serves as a basic test for the sheet metal formability. The effect of equipment and tooling parameters results in complex deformation mechanism. Existence of thickness variation in the formed part may cause stress concentration and may lead to acceleration of damage. Using TAGUCHI's signal-to-noise ratio, it is determined that the die shoulder radius has major influence followed by blank holder force and punch nose radius on the thickness distribution of the deep drawn cup of AA 6061 sheet. The optimum levels of the above three factors, for the most even wall thickness distribution, are found to be punch nose radius of 3 mm, die shoulder radius of 8 mm and blank holder force of 4 kN.

Development of ultra high performance concrete dies for sheet metal hydroforming

The paper concentrates on investigation results dealing with ultra high performance concrete (UHPC) dies for the use in sheet metal hydroforming. A special mixture of UHPC for these tools with its mechanical properties and its manufacturing is presented. The developed UHPC features a compressive strength of approx. 250 MPa and a Young’s modulus of approx. 50 GPa. Applying internal pressure, the UHPC die (without confinement or reinforcement) failed between 80 and 96 MPa. The forming test proved a good shape accuracy of the sheet metal parts but revealed critical tribological conditions. Drawing foil and already formed sheet metal parts were tested successfully as interlayer and led to an appropriate material flow and surface quality of the sheet metal parts.

An integrated numerical technique in determining blank shape for netshape sheet metal forming

A new blank design method is proposed based on iterative FE sheet metal forming simulations. An algorithm is introduced to approximately develop both CAD design and FE-virtually formed sheet metal parts onto a 2D plane. The errors between the original CAD design and the FE simulated parts can be characterised in both 2D and 3D spaces. An integrated numerical procedure for the netshape sheet metal forming process is detailed in the paper and a U-type channel part is taken as an example in the investigation.

Analysis of surface roughness for parts formed by computer numerical controlled incremental forming

Surface roughness tests were performed on computer numerical controlled (CNC) incrementally formed sheet metal parts using various tool depth increments and spindle speeds. A non-contact method using white light interferometry was selected to avoid scratching the material surface. All parts were formed from annealed Al 3003 sheet to a shape with a flat 45° wall section for testing. A relationship was defined between peak-to-valley roughness and depth increment, which was then compared to theory for shear forming. The surface quality of modern incremental methods and shear forming was shown to depend on similar settings, and the defined relationship allows for knowledgeable control of surface roughness in future work on such applications as reflective surfaces.