Maximum Thinning Rate Research Articles

Investigation of defect behavior during the stamping of a thin-walled semicircular shell with bending angle

Springback, wrinkling, and thinning typically occur during the stamping of thin-walled semicircular shells with bending angle. These defects cause poor forming accuracy of specimens and lead to assemble difficultly; consequently, the produced specimens do not meet requirements. In this work, the defect behavior during the stamping of thin-walled semicircular shells with bending angle is studied via an analytical model, experiments, and finite element (FE) simulation. First, an analytical model is established to predict springback and analyze springback trend. Second, stamping experimental tests of a thin-walled semicircular shell with bending angle are conducted. The influences of blank holder force (BHF) and stamping speed on the springback, wrinkling, and thinning of specimens are investigated. Finally, an FE simulation model is developed to investigate the deformation characteristics and springback of the thin-walled semicircular shell with bending angle. Results show that the maximum springback decreases with increasing BHF. Meanwhile, the results of the analytical model are consistent with the experimental and simulation results. The maximum thinning rate of the specimen increases with increasing BHF, whereas the wrinkling defect exhibits the opposite trend. The maximum thinning rate and wrinkling of the specimen increase with increasing stamping speed. Compared with that of BHF, the effect of stamping speed on defects is smaller.

Research on stamping forming prediction of aluminum alloy sheet based on RBF neural network

In order to accurately predict and reduce the possible defects in the stamping process of an aluminum alloy sheet, the simulation data of the sheet thickness for the 6016 aluminum alloy in the stamping process were obtained by the Hill’48 yield criterion based on finite element ABAQUS/Explicit solver. Taking blank holder force, friction coefficient, stamping speed, and die clearance as input parameters, the radial basis function (RBF) network model for predicting the maximum thinning rate of the stamping aluminum alloy sheet was established. The results show that the RBF network model constructed in this paper has high precision and can reflect the complex relationship between the stamping process parameters and the maximum thinning rate well by comparing the finite element simulation and neural network prediction results. It is of great significance to improve the optimization efficiency of the stamping process of the aluminum alloy sheet and reduce the actual experimental cost.

Study on hybrid hydroforming process of sheet metal with multi-concave and convex surface parts

By means of numerical simulation and experimental, the liquid filling forming process of an aluminum alloy double concave and convex curved sheet part was studied. The quality of forming parts, especially the thinning rate, is compared and studied during different hydroforming process. The results show that the thinning rate of the product is more than 25% regardless of the passive or active liquid filling drawing. However, the maximum thinning rate of the product is less than 20% when the hybrid hydroforming is carried out in a set of die with passive liquid filling in sequence, followed by pulsating reverse liquid filling. The method has reference significance for improving the forming quality of the parts with concave and convex surface of thin plate.

Hybrid optimisation of input process parameters of deep-drawn cylindrical cups from directional rolled copper strips

Deep drawing is a method of producing sheet metal. It is extensively used in the automobile, packaging and home appliance industries. Incorrect parameter selection might induce defects in stamped components. Trial and error can improve product accuracy, but at the expense of execution and calculation. An optimisation approach and a response surface model are used to determine the optimal parametric parameter design. This study proposes a full and efficient optimisation approach, starting with modelling by RSM (Response Surface Methodology) and concluding with optimal process parameter identification. Based on this, a neural network was developed to improve cylindrical cup deep drawing. Three characteristics of fabricating the cups are clearance, punch radius and coefficient of friction. This parameter demonstrates the resultant tool force, spring back, maximum forming limiting curve and maximum thinning rate of cylinder cups. Initially, the three inputs are varied to measure the outcome using simulation software by Altair inspire form. Then, the equations for each output are designed using quadratic-based linear model fitting. The generated objective function is then used to establish the ideal process parameters for the cylindrical cups. The proposed method is compared to real-time physical experiments. The optimised parameter microstructure at the high-stress zone and the product quality are satisfactory without defects.

Multi-Objective Optimization of Process Parameters in 6016 Aluminum Alloy Hot Stamping Using Taguchi-Grey Relational Analysis

The hot stamping technology of aluminum alloy is of great significance for realizing the light weight of the automobile body, and the proper process parameters are important conditions to obtain excellent aluminum alloy parts. In this paper, the thermal deformation behavior of 6016 aluminum alloy at a high temperature is experimentally studied to provide a theoretical basis for a finite element model. With the help of blank stamping finite element software, a numerical model of a 6016 aluminum alloy automobile windshield beam during hot stamping was established. The finite element model was verified by a forming experiment. Then, the effect of the process parameters, including blank holder force, die gap, forming temperature, friction coefficient, and stamping speed on aluminum alloy formability were investigated using Taguchi design, grey relational analysis (GRA), and analysis of variance (ANOVA). Stamping tests were arranged at temperatures between 480 and 570 °C, blank holder force between 20 and 50 kN, stamping speed between 50 and 200 mm/s, die gap between 1.05 t and 1.20 t (t is the thickness of the sheet), and friction coefficient between 0.15 and 0.60. It was found that the significant factors affecting the forming quality of the hot-stamped parts were blank holder force and stamping speed, with influence significance of 28.64% and 34.09%, respectively. The optimal parameters for hot stamping of the automobile windshield beam by the above analysis are that the die gap is 1.05 t, the blank temperature is 540 °C, the coefficient of friction is 0.15, stamping speed is 200 mm/s, and blank holder force is 50 kN. The optimized maximum thickening rate is 4.87% and the maximum thinning rate is 9.00%. The optimization method used in this paper and the results of the process parameter optimization provide reference values for the optimization of hot stamping forming.

Deformation characteristics and forming force limits of multi-point forming with individually controlled force–displacement

To solve the problem of springback in traditional multi-point forming (MPF), a new multi-point forming process, namely, multi-point forming with individually controlled force–displacement (MPF-ICFD), is proposed. In this manuscript, traditional MPF and MPF-ICFD are compared. Taking the cylindrical surface as the research object, the change in the springback of a plate is analysed by experiments, and the distribution of the strain and wall thickness of the plate is analysed by numerical simulation. Theoretical analysis is used to calculate the forming window for the MPF-ICFD process, and the results from theoretical analysis are verified by experiments and numerical simulation. The results show that the springback of 1060 aluminium alloy and Q295 for MPF-ICFD can be decreased by 73.8% and 45.5%, respectively, compared with traditional MPF. In traditional MPF, the strain uniformity of the plate is poor, and the maximum thinning rate is 4.5%. For MPF-ICFD, the strain is relatively uniform, and the maximum thinning rate is 0.25%. For an aluminium alloy sheet with a wall thickness of 1.5–3 mm, the upper and lower limits of the forming force for a single head are observed to change linearly from 6.3 to 12.6 kN and from 0.5 to 1 kN, respectively.

Dual-wafer intergrinding thinning by bipolar-discharge EDM with a capacity-coupled pulse generator considering large gap capacitance and minimization of discharge energy

The noncontact electrical discharge grinding technique has the potential to effectively grind thin, increasingly large-diameter wafers. This study proposes a bipolar electrical discharge machining (bipolar-EDM) method to realize the intergrinding of dual wafers, in which both wafers serve as the working electrode. A capacity-coupled (CC-type) pulse generator generates regular and identical bipolar discharges, ensuring symmetrical and stable removal of both wafers. Thus, both the energy efficiency and wafer thinning yield are doubled. The process characteristics are evaluated through equivalent circuit analysis and experiments, demonstrating that two thinned wafers exhibit high consistency in surface integrity and material removal rate (MRR). Moreover, the dual-wafer system causes an increase in the circuit resistance and gap capacitance, leading to a much lower discharge energy. This is beneficial for precision wafer grinding and thinning by electrical discharge machining (EDM) while keeping damage minimal. As a result, two Φ20 mm 4H–SiC wafers were thinned simultaneously with a maximum thinning rate of 3 μm/min. A mirror-like smooth surface (Ra < 80 nm) was obtained under finishing conditions, demonstrating its capability for precise wafer processing.

Investigation on deformation of DP600 steel sheets in electric-pulse triggered energetic materials forming

Electric-pulse triggered energetic materials forming (ETEF) is a high-speed manufacturing process, which utilizes the chemical energy released by energetic materials (EMs) triggered by underwater wire discharge to plastically shape metals. ETEF is not fully understood, particularly in research on the discharge characteristics of energetic materials triggered by metal wires and the deformation process of metal sheets. The above two problems were investigated in this paper using experimentation and numerical simulation. For the pulse discharge characteristics, the peak values of voltage and current were reduced during the triggering process of energetic materials, and the triggering energy consumption of energetic materials was quantified to be about 200 J. The matching parameters of different capacitor-voltage devices may be insensitive to triggering the energy release of energetic materials. The maximum major strain and thinning rate of the bulged specimen under ETEF conditions were significantly reduced when compared to the quasi-static specimen with the same bulging height, and the specimen’s deformation uniformity and strain distribution were improved. The simulation results showed that the addition of energetic materials significantly improved the plastic strain energy of the blank. The deformation of the blank in ETEF can be divided into two stages: the initial chemical energy action stage and the inertia action stage. The bulging height of sheet metal increased by nearly 301% in inertia action stage, accounting for 80% of the total deformation time, and the effective plastic strain distribution was more uniform.

Research on the active pressurized forced lubrication deep drawing process and evaluation of the lubrication effect

Friction and lubrication are important parameters that affect the quality of sheet metal forming; excellent lubrication conditions and less harmful friction can reduce local thinning, delay fracture, and improve surface quality. Aiming at the poor friction conditions and difficult lubrication in the flange area during deep drawing, an active pressurized forced lubrication deep drawing (FLDD) process was proposed in this paper. A hydraulic system was employed to flush high-pressure lubricating oil into the contact gap between the die and sheet in the flange area. The high-pressure hydrostatic oil film in the contact gap can reduce the real contact area and effectively improve the lubrication conditions. The equipment is simple, the cost is low, and the lubricating oil pressure can be measured and controlled. Under the conditions of 20-kN, 35-kN, and 50-kN blank holder force (BHF), FLDD testing of box parts was carried out with 5-MPa and 9-MPa pressure using water-based lubricating oil. The horizontal comparison experiment was conducted with vegetable oil and water-based lubricating oil under the same process conditions. The test results illustrated that the lubrication effect of vegetable oil was the worst, whereas the lubrication effect of water-based mineral lubricant was significantly improved after pressurization. The maximum forming height was increased by 17.97%, the maximum forming force was reduced by 8.9%, the maximum wall thickness thinning rate was decreased by 7%, and the lubrication effect at 9-MPa pressure was superior to that of 5 MPa. The FLDD process has definite application value in improving the production environment, pollution control, and automatic production.

Process parameter optimization for thin-walled tube push-bending using response surface methodology

In this paper, the response surface methodology (RSM) and finite element (FE) simulation were applied to optimize the push-bending process parameters of the thin-walled tube with polyurethane mandrel. The objective of the present work is to predict the optimal set of process parameters including the length to diameter ratio of the mandrel (L/D), the friction coefficient between die and tube ( $${\mu }_{1}$$ ), the friction coefficient between polyurethane and tube ( $${\mu }_{2}$$ ), and Poisson’s ratio of polyurethane ( $$\upsilon$$ ) to obtain qualified bent tubes. Three empirical models were developed to describe the relationship between process parameters and quality parameters of the bent tubes. In addition, the significant factors affecting the forming quality were analyzed using analysis of variance (ANOVA) of each model. Response surfaces were constructed to study the effect of each process parameter on the quality of the bent tubes. Finally, the process optimization window with the maximum thinning rate ( $$\varphi$$ ) less than 20%, the maximum thickening rate ( $$\psi$$ ) less than 17%, and the maximum cross-section ovality ( $$\xi$$ ) less than 5% of the bent tube was established. Qualified bent tubes with diameter of 144 mm, wall thickness of 2 mm, and bending radius of 280 mm were formed experimentally by following the established process window.

Research on High Temperature Stamping Forming Performance and Process Parameters Optimization of 7075 Aluminum Alloy.

The stress strain curve of 7075 aluminum alloy in the temperature range of 310 °C to 410 °C was obtained by Gleeble-3800. By Nakazima test, the isothermal thermoforming limit diagrams of 7075 aluminum alloy at different deformation temperatures and stamping speeds were acquired. Moreover, the parameters of automotive S-rail hot stamping process were optimized by GA-BP neural network. The results show that the forming limit curve of 7075 aluminum alloy increases as the deformation temperature and stamping speed increase. The predicted optimal parameters for hot stamping of automotive S-rails by GA-BP neural network are: stamping speed is 50 mm/s, friction coefficient between die and blank is 0.1, and blank holder force is 5 kN. The maximum thinning rate at this process parameter is 9.37%, which provided a reference for 7075 aluminum alloy automotive S-rail hot stamping.

Numerical simulation for expansion of preform and optimization of preform in thermoset composites

The expansion of preform and the optimization of preform have become important steps in the molding process. At present, there are some questions in the expansion of thermoset composite material preform and precompression, for example, the inaccurate dimensions, cracks, and wrinkles. For the expansion of preform, the finite element inverse algorithm is used as the expansion algorithm, and then the initial solution is optimized by the arc length mapping method, the expansion of preform is realized by the iterative equation which is solved by the ABAQUS solver. The effectiveness of the expansion of preform is verified through the comparison between the finite element inverse algorithm with DYNAFORM. The optimization of the precompression process is researched in order to solved the problems of cracks and wrinkles in the integral precompression method of preform. Firstly, the precompression sequence is adjusted by the precompression method, and then the precompression direction is optimized by the genetic algorithm. Through numerical simulation, the maximum thinning rate is reduced to 13%, and the maximum thickening rate is reduced to 6%, which improve the problems of cracks and wrinkles of preform, and the effectiveness of the optimization method is verified.

A novel method of processing sheet metals: Electric-pulse triggered energetic materials forming

• A novel high-velocity sheet metal forming method is proposed: ETEF. The energetic materials (EMs) were introduced into the EHF system, and the electrical explosion of metal wire ignited EMs and released energy. • The EMs under the 10 wt.%Al/90 wt.%AP conditions exhibited the highest energy release efficiency, the energy grade of EMs was determined to be 3.04 kJ/g in this work. Under discharge voltage of 3 kV, the bulging height of DP600 specimen from ETEF was increased by 162 % relative to that from EHF. • Compared with that of EHF/7 kV, the strain concentration area of the sheet under the ETEF was wider (about 60 mm). The maximum major strain and maximum thinning rate of the specimen under the 2 g/3 kV/10 wt.% Al/90 wt.% AP conditions were reduced by 10.6 % and 13.1 %, respectively. • The dynamic deformation of the DP600 specimens during ETEF were presented for the first time by LS-DYNA. The EMs were ignited by electric explosion of metal wire to realize the coupling of two kinds of energy. To improve the formability of sheet metals at room temperature and overcome the limitation of the upper limit of energy storage in electrohydraulic forming (EHF), a novel sheet metal forming is proposed: electric-pulse triggered energetic materials forming (ETEF). The power to deform a metal sheet originates from the electrical explosion of a metal wire in a liquid chamber and that releasing chemical energy from the energetic materials (EMs) being triggered. Equi-biaxial stretching tests of DP600 were carried out through ETEF with different weight ratios and changing grams under a low discharge voltage. The final profiles, strain and thickness distribution of the sheet were analyzed. The energetic materials with 10 wt.%Al/90 wt.%AP had an energy level of 3.04 kJ/g, and the bulging height of the deformed specimen was 34 mm, which was higher than the energy levels obtained under other testing conditions. Compared with that of the 7 kV specimen of the same bulging height (34 mm) obtained by EHF, the strain concentration region of the specimen processed under the 2 g/3 kV/10 wt.% Al/90 wt.%AP conditions widened by 52.5 %, and the maximum major strain and maximum thinning rates were lower by 10.6 % and 13.1 %, respectively. The dynamic deformation characteristics of the DP600 specimens during ETEF were presented for the first time by LS-DYNA. The values obtained for the DP600 sheet were as follows: maximum bulging height, 32 mm; maximum effective strain rate, 1521/s; and maximum speed, 258 m/s.

Effects of forming parameters on the forming limit of single-point incremental forming of sheet metal

In this paper, experimental and numerical simulation studies on the forming limit diagram of single-point incremental forming (SPIF) were described. We proposed a novel method for evaluating the forming limit in incremental forming. The proposed method utilizes the forming limit angle and the maximum thinning rate. The effects of the forming and processing parameters on the forming limit of an aluminum sheet during incremental forming were investigated using a combination of simulation analysis and experimental verification. The obtained results show that the forming limit is large for 1060Al and 6061Al when the initial thickness is 1.5 mm for a single parameter change for SPIF. For 1060Al, the step size is in the range of 0.8–1.5 mm. When the step size is 0.8 mm, the incremental forming limit is large and the forming precision is high. For 1060Al and 6061Al, the incremental forming limit is at the maximum level when the tool radius is 6.0 mm, and when the tool radius is 5.0 mm, the best forming precision can be achieved. It is of great theoretical significance and practical engineering value to study the effects of various forming parameters on the forming limit of metal sheet SPIF.

Design of Hydraulic Bulging Die for Automobile Torsion Beam and Optimization of Forming Process Parameters

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.

Effects of process variables optimization on the quality of parts processed in high speed single point incremental sheet metal forming by ranking algorithm

Single point Incremental shaping (SPIF) is a metal forming process which rose to unambiguous quality toward the commencement of the 1990 s. ISF is an exceptionally limited twisting procedure in which a device, modified to take after in a specific direction, moves over a sheet metal and structures the coveted shape and a prosperous process to manufacture sheet metal parts that is well adapted for prototypes or small batch production. On contrast with the traditional sheet forming technologies this is relatively a slow process and is only profitable for the above mentioned production types but it can be used in different applications in automotive and aircraft industries, in architecture engineering and in medical aids manufacturing. SPIF is a die less method of forming which offers high formability. In this study the SPIF, process parameters such as the spindle Speed 1000/1500/2000 (Rpm), Feed 100/300/500 (mm/min), Tool Diameter 8/10/12 (mm) and step down 0.2/0.4/0.6 (mm) at the specimen interface greatly influence in the Cone shaped Mechanical quality such as Maximum Thinning rate (%), Surface roughness (µm), spring back (%) & formability of Forming for Aluminium alloy AA 8011. The aim of the present work is to study these parameters to build up a cone quality, formed by VMC and to carry out a detailed study of these parameters, experiments were conducted by using the L9 orthogonal array. The output parameters such as affecting mechanical and forming quality were analyzed by TOPSIS and ranking was analyzed.

Effect of Process Parameters on the Automobile Part in Hot Stamping Process

In this study, the influence of variables, including friction coefficient and initial blank temperature, on the formability in the hot stamping process of steel was analyzed. The formability indexes have maximum thickness thinning rate and springback. The friction coefficient is chosen between 0.05 and 0.4. The range of initial blank temperature varies from 825 to 995 °C. The combination of central composite design and response surface method was used to analyze the relationship between the variables and indexes. The maximum thinning rate of the hot formed part increases obviously with the increase of the friction coefficient. The maximum thinning rate increases slightly with the decrease of the initial blank temperature. The springback increases with the decrease of the friction coefficient significantly. The initial blank temperature affects the springback slightly.

Numerical Simulation and Multi-Objective Optimization of Partition Cooling in Hot Stamping of the Automotive B-Pillar Based on RSM and NSGA-II

In this study, the simulation and optimization of the partition cooling in the hot stamping process was carried out for an automotive B-pillar through minimizing the maximum thickening rate and the maximum thinning rate located in the rapid and slow cooling zones. The optimization was implemented by investigating the process parameters such as friction coefficient, sheet austenitizing temperature, holding time, heating zone temperature, the upper binder force and the lower binder force. The optimal Latin hypercube design (OLHD), the response surface methodology (RSM) and the non-dominated sorting genetic algorithm (NSGA-II) were combined to establish the relationship between process parameters and form quality objectives. After multi-objective optimization, the maximum thickening rate and the maximum thinning rate of the slow cooling zone and rapid cooling zone were 11.1% and 12.4%, 4.7% and 7.1%, respectively. Afterwards, the simulation was performed according to the optimized parameter combinations to analyze the temperature field, microstructure, tensile strength, hardness, thickening rate and thinning rate, and forming quality. Moreover, the hot stamping test and experimental results showed that the microstructure of the ferrite and pearlite structure was uniformly distributed in the slow cooling zone, and its tensile strength reached 680 MPa, the elongation was 11.4% and the hardness was 230.56 HV, while the lath martensite structure was obtained in the rapid cooling zone, with tensile strength of up to 1390 MPa, elongation of about 7.0% and hardness reaching 478.78 HV. The results of thickness, microstructure, tensile strength and the hardness test correspond well with the simulation results.

Hybrid reliability analysis and robust optimum process design as applied to hot stamping of steel sheets

In the process of hot stamping of steel sheet, there may appear crack and wrinkling defects. Therefore, in the early stage of die design, it is necessary to evaluate the reliability of its quality and optimize the original design. Considering that there are both random and fuzzy factors in the stamping process, the entropy invariance principle is used to transform the fuzzy factors to the random ones, and the equivalent hybrid reliability model of anti-defect is established. Then, the reliability index is taken as constraints in robust optimization. Finally, the stamping process of bulge formed joint is taken as an example, the maximum thinning rate is taken as objective, and the reliability of anti-crack and anti-wrinkle is taken as constraints in reliability-based robust optimization (RRDO). The results show that the standard deviation obtained by robust optimization is 77.5% less than the standard deviation obtained by deterministic optimization and the reliability obtained by RRDO is higher. Compared with the experiment result, the result obtained by RRDO is more in line with engineering practice.

Study on Gas Bulging Forming and Contradictive Cooling Bonding of AZ31/Al7475 Bimetal Composite Tube

Mg/Al bimetallic tubes can give full play to the excellent properties of magnesium alloys and aluminum alloys, such as light weight, high strength and good corrosion resistance. In this study, gas bulging forming and contradictive cooling bonding process was used to form AZ31/Al7475 hexagonal section composite tubes and showed a good result. In addition, the finite element analysis method was utilized to simulate the process and optimize the forming parameters. The results show that the process could be divided into four stages: free bulging stage, sidewall sticking stage, fillet filling stage and contradictive cooling stage. The maximum thinning rate and fillet radius of AZ31/Al7475 composite tube were 10.60% and 7.00 mm, respectively, at 450 °C, 6 MPa, and 600-720 s. And the interface between the inner and outer layers was closely combined. The bonding force of the rounded corner part of the forming part was 2.04, and 2.30 MPa for the straight wall part. The experimental value of the binding force was about 28% higher than the maximum theoretical value.