Counter Punch Research Articles

A new tube forging process for manufacturing hollow parts with inner flange at an arbitrary location

The forging of hollow parts faces a great challenge as folding and buckling always occur during the forging process. To overcome these problems, a novel tube forging process combining upsetting and shear forging is developed to manufacture hollow parts with an inner flange at an arbitrary location. Firstly, two flow modes are introduced to analyze the deformation behavior of a hollow cylinder during internal thickening by upsetting, where the geometric limits associated with different deformation modes and the critical upsetting ratio with no folding defects are determined. The results clearly show the occurrence of a mode transition for some cylinders during the upsetting process; furthermore, the cylinder is less prone to folding in some cases due to the appearance of a third deformation zone located mid-way up the cylinder. Then, the forming mechanism of this novel process is analyzed, and its feasibility is demonstrated through finite element simulations and experiments. Results show that the flange can be moved to an arbitrary location on the inner wall in the height direction by controlling the stroke of the punch, and shear deformation can enhance the strength of the flange. Additionally, it is found that the shear depth, corner radius of the counter punch, and supporting force on the counter punch are the key parameters affecting the product quality.

The effect of differential lubrication and counter punch on hydroforming of 5A02 thin-walled aluminum alloy Y-shaped tube

The effect of differential lubrication and counter punch on hydroforming of 5A02 thin-walled aluminum alloy Y-shaped tube

Quality comparison of Y-shape joints by tube hydroforming with and without counterforce

The design capability, strength, and structural rigidity provided by tube hydroforming (THF) are successfully used in many applications to produce high-strength parts and assemblies with improved mechanical properties, optimized service life, and weight features. In tubular metal forming, output parameters such as branch height, distribution of tube wall material thickness, distribution of damage factor, metal flow, effective stress, and effective strain significantly affect the quality of the product after the forming process. Therefore, this paper aims to evaluate the manufacturing quality of Y-shape joints from AISI304 material steel tube through output parameters of THF process with and without counter punch force on numerical simulation base. The Finite Element Method (FEM) has become an established feature of metal forming technology. The objective of FEM is to replace costly and elaborate experimental testing with fast, low-cost computer simulation. The simulation study uses finite element method-based virtual prototyping techniques to characterize output parameters, gain insight into strain mechanics, and predict mechanical properties of shaped components. The research results are presented clearly and unambiguously through the evaluation of 7 criteria to compare the quality of the specimens hydroformed by two surveyed cases and optimize the crucial input process parameters. And these data can be applied in experiments, more efficient product and process design, calculation, and control of input parameters avoiding costly trial and error in industrial production. The findings can help technologists optimize process parameters in the hydroforming process of products with protrusion from a tubular blank

Design Guidelines for interlocked stator cores made of CoFe sheets

CoFe lamination stacks used for high-performance electric motors can be manufactured economically in high volumes by interlocking. In order to ensure sufficient joint strength with minimized sheet thickness, a comprehensive knowledge of the influences of various process parameters, such as embossing depth, clearance and counter punch force, is essential. To analyze these parameters, which also influence the magnetic properties, experiments are carried out and resulting joint strengths are determined in top tensile tests. The negative influences of the cutting process on magnetic conductivity and thus hysteresis losses due to residual stresses and plastic deformation are well known. In the subsequent stacking step, an influence of embossing and pre-stresses on the material properties is expected. In addition, local electrical contacts between the sheets may occur due to the interlocking process, causing additional eddy currents. Loss measurements are conducted to investigate the effect of the joining process on the magnetic properties of the stack. In doing so, the influence of process parameters such as the embossing depth and clearance on eddy current power losses is analyzed.

Sheet Bulk Forming of Thin-Walled Components with External Gearing through Upsetting Using Controllable Deformation Zone Method

Sheet-bulk metal forming (SBMF) is a promising process for manufacturing complex sheet components with functional elements. In this study, the entire forming process for a typical thin-walled component with external gearing is investigated, including sheet forming and bulk forming processes. Deep drawn cups are prepared during sheet forming; subsequently, upsetting is performed on the sidewall to form external gearing. The upsetting method performed is known as upsetting with a controllable deformation zone (U-CDZ). Compared with the conventional upsetting method, a floating counter punch with a counter force is used in the U-CDZ method such that the forming mechanism is changed into the accumulation of the deformation zone instead of deformation throughout the entire sidewall. The effects of the counter force and material flow are investigated to understand the mechanism. The forming quality, i.e., the formfilling and effective strain distribution, improved, whereas a high forming load is avoided. In addition, a punch with a lock bead is used to prevent folding at the inner corner during the experiment.

Numerical simulation and optimization of fine-blanking process for copper alloy sheet

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. The primary objective of the fine-blanking process is to reduce the fracture zone depth and die roll zone width. This study used a 2.5-mm-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 multicriteria quality objectives and used the robust multicriteria optimal approach and Pareto-optimal solutions to perform multicriteria optimization analysis. The results met the industry’s fraction zone depth standard (below 12% of blank thickness) and achieved a smaller die roll zone width.

Effect of various shearing shape conditions for the scrap-used coining method on tensile residual stress on sheared edge

Application of high strength steel for automobiles is required to achieve fulfilment of the CO2 emission regulation and improvement of collision safety. Nevertheless, high strength steel has the problem that hydrogen embrittlement and fatigue cracks are likely to occur especially on sheared edge. The previously proposed scrap-used coining method could reduce tensile residual stress on sheared edge using the scrap generated by shearing as the coining tool with a counter punch. However, the conditions this method could reduce tensile residual stress effectively were not clarified. In this report, the effects of the following shearing shape factors on residual stress on sheared edge were investigated, the size of shearing line curvature using punches with a diameter of 10 and 20 mm, positive and negative sign of curvature by testing both of the product and scrap part, and the flat and dome shape of counter punch head. Residual stress on sheared edge could be reduced in the 10 and 20 mm of punch diameter regardless of the product or scrap part. FEM analyses showed that the change of stress distribution in processing area during the scrap-used coining is caused by the shearing hole expansion and reduction and the sheared edge compression by contact of the product and scrap and these mechanisms are common to both of the parts. The dome shaped counter punch is able to reduce the coining load in addition to almost the same amount of residual stress as the flat shaped one. Thus, the tool cost decreases because the cushion pin required to get the reaction force for coining could be reduced.

Double-action bending for eliminating springback in hat-shaped bending of advanced high-strength steel sheet

This paper presents a novel technology called ‘double-action bending (DAB)’ to eliminate springback in hat-shape forming of advanced high-strength steel sheets (AHSS). It consists of four steps: (1) clamping of a sheet between an inner punch and a counter punch, (2) U-bending under a constant clamping force, (3) pushing-up the sheet by the counter punch from the bottom end, and (4) bending of the flange by an outer punch. A great advantage of this technology over other hat-bending processes, such as draw bending and crash forming, is that perfect hat-shaped channels are easily obtained for any type of AHSS just by determining two controllable process parameters, namely, the bottom pushing-up force and outer-punch stroke in flange bending. An accurate finite element (FE) simulation allows us to determine these process parameters prior to experimental tryout. The validation for this process was shown by performing the hat-shaped DAB experiments on a dual-phase 980-MPa AHSS and the corresponding FE simulation.

Increasing the Hole Expansion Ability of High Strength Steel Sheet by Improving the Pre-Hole Shearing Process

The hole expansion process is a forming process that the fracture easily occurred on the hole edge. Therefore, many research papers presented various processes to make a precision pre-hole shearing to a hole expansion process such as wire cut, EDM, and laser cut. The purpose of this work is to increase a hole expansion ratio on the high strength steel sheet. The conventional piercing by piercing punch and piercing with a counter punch was used to make a pre-hole shearing process in this research paper. The high strength steel grade 590 and 980 MPa of 1.2 mm of thickness were used in the experiments. From experimental results, it was found that the pre-hole shearing by piercing with a counter punch can be increased a shear surface on cutting edge of workpiece. Moreover, the used piercing with counter punch can improve the hole expansion ratio more than the conventional piercing process because sheared surface around the hole edge was increased.

Enhancement of the residual stresses of cold full‐forward extruded parts by application of an active counter punch

AbstractDer Einsatz eines gesteuerten Gegenstempels als aktives Element kann die Qualität und die Beanspruchbarkeit kaltfließgepresster Produkte signifikant verbessern. Durch konventionelle Prozessführung mittels Voll‐Vorwärts‐Fließpressen hergestellte Bauteile weisen hohe Zugeigenspannungen an der Oberfläche sowie einen steilen Spannungsgradienten auf. Neben der Gefahr des Verzugs beeinträchtigt dieser ungünstige Eigenspannungszustand das Ermüdungsverhalten. Von den Autoren wurde ein System entwickelt, das während des Fließpressvorgangs mit einem aktiv eingesetzten Gegenstempel eine Druckkraft auf das zu umzuformende Bauteil ausübt und eine signifikante Verbesserung des Spannungszustands des Endprodukts bewirkt. Der positive Effekt wird durch eine Homogenisierung der Deformationen im Bauteil während des Fließpressens bewirkt. Zur Prozesssimulation wurde ein Finite‐Elemente‐Modell in Simufact Forming® entwickelt. Die Simulationsergebnisse zeigen, wie sich die durch den aktiven Gegenstempel aufgebrachte Kraft auf den endgültigen Spannungszustand auswirkt. Die Validierung der Simulationsergebnisse erfolgte anhand von Versuchen mit den beiden austenitischen Stählen 1.4307 und 1.4404. Ein weiterer Schwerpunkt bildet die Entwicklung geeigneter Messstrategien zur röntgenographischen Eigenspannungsanalyse mit dem sin2Ψ‐Verfahren, um trotz grobkörniger und anisotroper Werkstoffzustände die Qualität der Messergebnisse sicherzustellen. Die Ergebnisse aus Simulation und Experiment belegen das Potenzial der entwickelten Umformstrategie. Die Produktqualität lässt sich ohne Änderung der Prozesszeit erhöhen.

A binding scheme to minimize thinning of formed tailor welded blanks

Weld line movements (WLM) and thinning in draw bending and deep drawing of Tailor Welded Blanks (TWBs) constitute major defects in automotive applications. The present work aims at the development of a binding scheme that improves sheet thinning and eliminates WLM. This is achieved by using controlled blank holding segmented binders (blank holders) at the boundaries of the parent sheets of the TWB and counter pins at the weld lines. Analytical models for the 2-D draw bending and 3-D deep drawing are developed to predict the required blank-holder/counter-pin forces that insures identical elongation (deformation) on both sides of the TWB and thus eliminates the WLM. The 2-D model is validated by a series of draw-bending laboratory experiments. The experimentation of the proposed force scheme produced identical elongations on both parent sheets and consequently zero weld line movement (WLM) as targeted by the analytical model and hence the feasibility of the proposed scheme is proved in practice. Additional draw-bending/box-drawing experiments are conducted to compare the proposed scheme with separate use of either segmented blank holders, weld line clamping pins or counter punch. The results showed improved reduction in thinning and elimination of WLM when the binding forces of the process are controlled as proposed by the developed model.

Metal flow control during hot forming of square cups with local-thickened plates and varied friction conditions

Obtaining square cups with the radius at the bottom corner lower than the thickness of original plate via a single-step hot forming process is a challenge. In this paper, a processing way was proposed by combining local-thickened plate and friction control, to manufacture square cups with small corner radii. Through finite element (FE) simulations, the metal flow during hot forming of square cups was optimized by varying the shape of the local thickened section and adjusting the friction conditions at the interfaces between blank and tools. It was found that the filling ratio of the bottom corner can be significantly improved by increasing the friction coefficient at the interfaces between the blank and the upper punch, and that between the blank and the central zone of counter punch. The established flow dividing surface (FDS) model is capable for describing the variation of metal flow with the friction coefficients. Base on the simulation results, hot forming experiments were also carried out, and square cups with small radii of 2mm at the bottom corners were successfully manufactured.

Hole Making Process of Metal and Composite Sheets by Impact Hydraulic Pressure

Abstract Hole making process of metal and composite sheets using impact hydraulic pressure is investigated. The sheet is mounted in contact with the die face that locates at the bottom end of the cylinder. The piston at the top end is impacted by a drop-hammer with 10 m/s velocity, by which very high pressure is put on the sheet face to induce shear force at die edge. The die hole is circular, square or rhombic. The test materials are pure aluminum and its alloy, pure titanium, stainless steel and carbon fiber reinforcement plastic (CFRP) sheets. The cut surface is rather rough and the shear drop is larger compared with that in conventional punching. Burr generation is successfully suppressed for the metallic materials. Interlaminar fracture of CFRP sheet occurs in the hole vicinity. Corner radius of the square and rhombic holes is rounded. Counter punch in the die cavity is useful for improving shape accuracy.

Investigation of the Relationship between Material Flow and Rollover in Double-Sided Shearing Using Image Processing

Shearing is the cutting of a sheet material with a punch and a die. The cut surface obtained by shearing is composed of rollover, a sheared surface, a fracture surface and burr. It has been reported that rollover is formed by the insufficiency of material and material flow in the lateral direction. However, the rollover in the sheet material on the die and that in the sheet material under the punch have not been evaluated individually in previous studies. In this report, the relationship between the material flow and the formation of rollover in the sheet material on the die is discussed on the basis of experimental results obtained by image processing. The relationship between the material flow and the formation of rollover in the sheet material under the punch also is discussed. Double-sided shearing with a counter punch was carried out. The deformation of the sheet material was observed through reinforced glass using a high-speed CCD camera. The image processing was carried out to investigate the material flow. The results were as follows. When the clearance is small, the material flow in the clearance is toward the sheet material on the die. When the clearance is large, the material flow in the clearance is toward the sheet material under the punch. The area of rollover in the sheet material on the die is equal to the sum of the amount of material flow in the clearance and that in the lateral direction. On the other hand, the area of rollover in the sheet material under the punch is equal to the sum of the amount of material flow in the lateral direction under the punch, that in the clearance and the insufficiency of material. These findings are useful for considering the relationship between the material flow and the formation of rollover in the case that the rollover in the sheet material on the die and that in the sheet material under the punch are evaluated individually.

The multi-objective optimization of the loading paths for T-shape tube hydroforming using adaptive support vector regression

The objective of this study is to introduce adaptive support vector regression, whose accuracy and efficiency are illustrated through a numerical example, to determine the Pareto optimal solution set for T-shape tube hydroforming process. A validated finite element model developed by the explicit finite element code LS-DYNA is used to conduct virtual T-shape tube hydroforming experiments. Multi-objective optimization problem considering contact area between the tube and counter punch, maximum thinning ratio, and protrusion height is formulated. Then, the Latin hypercube design is employed to construct the initial support vector regression model, and some extra sampling points are added to reconstruct the support vector regression model to obtain the Pareto optimal solution set during each iteration. Finally, the ideal point is used to obtain a compromise solution from the Pareto optimal solution set for the engineers.

A Kriging-based non-probability interval optimization of loading path in T-shape tube hydroforming

In this study, the interval optimization method, in which the bounds of uncertain parameters are only required and knowing their probability distributions are not needed, is introduced to deal with limited information in T-shape tube hydroforming. The contact area between the counter punch and the tube is taken as the objective function and the protrusion height and maximum thinning ratio as constraints. To control the possibility degree of failure associated to each constraint, the reliability-based possibility degree of interval method is adopted to evaluate the reliability of T-shape tube hydroforming process. Before optimizing the process, the finite element model is validated against experimental results, and Taguchi method is employed to screen key factors from a number of potential factors. In addition, to improve computation efficiency, the Kriging model is adopted to construct the surrogate model, and the performance of the resulting surrogate model is validated using cross-validated method. Finally, the Kriging based on interval optimization method is applied for loading path design in T-shape tube hydroforming, and the results show that the robustness and reliability of the process can be guaranteed.

Elimination of springback of high-strength steel sheet by using additional bending with counter punch

This study proposes a new technique to eliminate the springback of high-strength steel (HSS) sheets in the U-bending process. In this technique, the bottom plate is additionally bent with a counter punch at the final stage of the U-bending process. In an experiment, a flat-headed punch with a shallow hollow on the punch head was employed in combination with a counter punch. The U-bending process consists of four sequential steps: (1) clamping of a sheet between a punch and a counter punch, (2) U-bending under a constant clamping force, (3) bottom pushing-up by the counter punch, and (4) final unloading process. From the experiment on a 980Y HSS sheet, an appropriate combination of the clamping force and the final bottom pushing-up force that eliminates springback entirely was found. To investigate the mechanism of the reduction in springback in this process, an FE simulation of this process was conducted using the Yoshida–Uemori model, an advanced kinematic hardening model. The simulation result showed that the major mechanism of springback elimination is the “spring-go” induced by the release of the negative bending moment generated by bottom pushing-up.

A single-step hot stamping-forging process for aluminum alloy shell parts with nonuniform thickness

In this study, a single-step hot stamping-forging process using a counter punch was proposed to produce pan-shaped shell parts with nonuniform thickness distributions, which are often used in satellites. Through FE simulations, the effects of die temperature, counter punch initial interposition length and counter force on the part thickness were examined. It was found that the material flow is divided at a flow dividing surface (FDS) which moves in the wall during forming. The maximum bottom thickness and nonuniformity were found to be closely related to the counter force and initial interposition length. Base on the simulation results, experiments were carried out using sheet blanks with initial thicknesses of 4mm. After stamping-forging deformation, the part bottom was successfully thickened to 4.3mm while the wall was thinned to 2.5–2.7mm.

The optimization of the loading path for T-shape tube hydroforming using adaptive radial basis function

The success of the T-shape tube hydroforming process requires a combination of internal pressure and axial and counter punch actions. The objective of this study is to introduce the adaptive radial basis function and demonstrate its accuracy and efficiency through a numerical example, to determine the optimal loading parameters in T-shape tube hydroforming process. The finite element model is developed with the explicit dynamic finite element code LS-DYNA and validated against the experimental work. The Taguchi method based on variance of analysis technique is used to screen the important loading parameters, which have a significant effect on the forming quality, such as the maximum thinning ratio, protrusion height and contact area, etc, from a number of potential loading parameters. The contact area is considered as the objective while the maximum thinning ratio and protrusion height are regarded as the constraints, and then the optimal loading parameters are obtained by adaptive radial basis function after several iterations. The results show that a significant improvement in the contact area is achieved while the results of the minimum thickness and protrusion height do not become worse.

Comparative Efficiency of Artificial Neural Network to Predict Spring-Back Value in U-Bending Process of High Strength Steel

High strength steel (HSS) was used as raw material in the automotive industry, which required lightweight and high strength, such as chassis and etc. However, the strength and hardness of the steel are relatively high, leading to the low permeability and large spring-back occurring after forming operation. As a result, the work piece is not shaped desire. This research proposes neural network for predicts the spring back values, in U-bending process, that the materials were differences in mechanical properties, such as SPFH590 (JIS) and SPEC980Y (JIS). In the experiment, the input factors for predictable data consists as the punch radius (RP), die radius (Rd), clearance (Cl) and counter punch force (Fc). After that, the input data were analyzed relation with spring-back values by the Pearson Correlation of One-tailed. Next, It was selected by Leave-one-out and k-fold Cross validation (K-fold and LOOCV), to improve efficiency of the prediction process. Moreover, the result was a measurable performance with Root Mean Square Error (RMSE) technique, equal to 0.788 and 2.10 respectively. In the final analysis, the neural network is effective to predict the Spring-back values of SPFH590 (JIS) rather than SPEC 980Y (JIS) in U-bending process.