Punch Corner Radius Research Articles

Effect of Tool Shape on Hole Clinching for CFRP with Steel and Aluminum Alloy Sheet

Use of light materials such as aluminum, magnesium and carbon fiber reinforced plastic (CFRP) has been increased to achieve the light-weight car body in automotive industry. For successful multi-material design of automotive body, the joining method for dissimilar materials is required to assemble the automotive components produced by various materials. Especially, hole clinching process is effective to fasten dissimilar materials without any additional joining element. In this study, effect of tool shape on the hole clinching is investigated by FE-analysis and experiments. The parameters related to clinching tool shape are punch diameter, punch corner radius and die depth. The geometrical interlocking is evaluated by the neck-thickness and undercut. Joint strength using single lap shear test is evaluated also to verify the effectiveness of hole clinching as automotive joints.

Investigation of the Effects of Pressure Path and Tool Parameters in Hydrodynamic Deep Drawing

In recent years, hydroforming process has been applied in different industries such as aerospace, automotive and military industries due to its advantages, such as high dimensional accuracy, capability of forming complicated parts and high drawing ratio. Hydrodynamic deep drawing with radial pressure is one type of hydroforming process. In this paper, forming of cylindrical cups in hydrodynamic deep drawing with radial pressure is numerically and experimentally investigated and the effects of significant parameters such as pressure path, punch corner radius and die profile radius on the cup thickness distribution and punch force were studied. The results obtained showed that increasing the pressure affects the thickness reduction in critical regions of cup and from the certain pressure, the pressure does not have a significant effect on the thickness of part. On the other hand, increasing the pressure, increases the force needed for forming the cup. Also, it was found that by increasing the punch corner radius, the cup thickness will be more uniform and maximum punch force does not change. Results of studying the effect of die profile radius on thickness distribution and punch force showed that increasing the die profile radius has a positive effect on the cup thickness distribution and the force needed to form part.

Formability improvement and blank shape definition for deep drawing of cylindrical cup with complex curve profile from SPCC sheets using FEM

In the current work, to predict and improve the formability of deep drawing process for steel plate cold rolled commercial grade (SPCC) sheets, three parameters including the blanking force, the die and punch corner radius were considered. The experimental plan according to Taguchi’s orthogonal array was coupled with the finite element method (FEM) simulations. Firstly, the data from the test of stress-strain and forming limit curves were used as input into ABAQUS/Explicit finite element code to predict the failure occurrence of deep drawing process. The three parameters were then validated to establish their effects on the press formability. The optimum case found via simulation was finally confirmed through an experiment. In order to obtain the complex curve profile of cup shape after deep drawing, the anisotropic behavior of earring phenomenon was modeled and implemented into FEM. After such phenomenon was correctly predicted, an error metric compared with design curve was then measured.

Influence of Tool Shape on Hole Clinching for Carbon Fiber-Reinforced Plastic and SPRC440

Carbon fiber-reinforced plastic (CFRP) is a lightweight material that can potentially replace structural steel components in automobiles. The hole-clinching process is a mechanical clinching technique for joining brittle or low-ductility materials, such as CFRP, with ductile materials. In this study, the influence of tool shape on the hole-clinching process for CFRP and SPRC440 was investigated using FE-analysis and experiments. The parameters of the tool shape investigated were the punch corner radius and the punch diameter. The geometrical interlocking shapes of hole-clinched joints were characterized by neck thickness and undercut. Based on the desired joint strength of 2.5 kN, hole-clinching tools were designed on the basis of the relationship between joint strength and geometrical interlocking. FE-analysis and hole-clinching experiments were performed with the designed hole-clinching tools to investigate the geometrical interlocking shape as well as joinability, including neck fracture, undercut, and hole expansion, resulting from changes in tool parameters. Joint strength was evaluated to verify the effectiveness of hole clinching by a single lap shear test.

Deep Drawing Characteristics of Square Cups through Conical Dies

This paper studies the deformation characteristics of a newly developed process for increasing the drawability of square cups. The process has a simple tooling set in which a circular blank can be easily deformed by a flat headed square punch through a conical die with a square aperture. Finite element analysis (FEA) was used to study the influences of the geometric parameters on the formability of square cup in order to find out the optimum setup dimensions of the present process. The effects of die fillet radius, die corner radius, die throat length, punch profile radius; punch corner radius, punch shape factor, relative die clearance and blank thickness on the drawability of square cup were mainly investigated. Cup drawability was also studied with the change of material strain hardening exponent, n, strength coefficient, K, average anisotropy, R, and friction coefficients between die-sheet-punch to find the best operating conditions. The limiting drawing ratio (LDR) was used to evaluate the effects of all these parameters on the square cup drawability. The LDR's, maximum drawing loads, cup thickness, cup height and modes of failure were predicted. The analysis reveals that the determination of the optimum setup dimensions of our developed process has increased the drawing ratio up to 3.1 for brass alloy (67/33 Cu-Zn) and 3.15 for aluminum (Al99.5w) in a single-drawing stroke. Experiments have been also done in order to compare and verify the FE-predictions. Successful square cups with drawing ratio of 3.07 for brass and 2.93 for aluminum were produced. These LDR's are significantly higher than that of the improved conventional methods with blank holder.

Influence of process parameters in mechanical clinching with extensible dies

The influence of clinching tool design in joining metal sheets by the clinching process with extensible dies is investigated. The material flow during the clinching process was examined experimentally and numerically. The geometrical and mechanical characteristics of joints produced under different processing conditions, that is, forming loads, were used to calibrate and validate a 3D finite element model of the clinching process. Then, the model was utilized to evaluate the influence of clinching tool design parameters, namely the punch diameter, the punch corner radius, the fixed die depth, the fixed die diameter, and the die corner radius. The effects of design parameters on the cross section of a clinched joint, the required forming load and the joint strength were analysed and the appropriate processing window was determined. According to the achieved results, the main benefits and drawbacks of each configuration are discussed.

Thickness of Magnesium Alloy Cylindrical Cup in Pressure-Lubricating Deep Drawing

Forming process of AZ31B magnesium alloy cup parts in pressure-lubricating deep drawing was simulated by Dynaform at room temperature. The technological parameters which influence the wall thickness difference of cup parts were investigated in this paper, including internal pressure, blank holder force and punch corner radius, etc. Compared with the deformation behaviors of magnesium alloy in mechanical deep drawing and pressure-lubricating deep drawing, the wall thickness distribution of cup parts was discussed. The result shows that preferable deformation behaviors can be obtained in pressure-lubricating deep drawing when adopted adaptive technological parameters.

유한요소법을 이용한 초고강도 판재 굽힘에 따른 후변형의 정량적 분석: Spring-back or Spring-go

A major source of difficulty in die design for high strength steel is the high level of elastic recovery during unloading. The degree of elastic recovery is affected by factors such as material strength, bending angle, punch's corner radius and sheet thickness. Finite Element Method was used in the present work to quantitatively analyze the elastic recovery for various combinations of these parameters. In some cases elastic recovery happened in reverse direction. This phenomenon, which we call spring-go, was explained via changes in stress distribution in the panel occurring in the forming process.

Blank Optimization in Elliptical-Shape Sheet Metal Forming Using Response Surface Model Coupled with Reduced Basis Technique and Finite Element Analysis

The present study aims to determine the optimum blank shape design for the deep drawing of Elliptical-shape cups with a uniform trimming allowance at the flange i.e. cups without ears. This earing defect is caused by planar anisotropy in the sheet and the friction between the blank and punch/die. In this research, a new method for optimum blank shape design using finite element analysis has been proposed. Present study describes the approach of applying Response Surface Methodology (RSM) with Reduced Basis Technique (RBT) to assist engineers in the blank optimization in sheet metal forming. The primary objective of the method is to reduce the enormous number of design variables required to define the blank shape. RBT is a weighted combination of several basis shapes. The aim of the method is to find the best combination using the weights for each blank shape as the design variables. A multi-level design process is developed to find suitable basis shapes or trial shapes at each level that can be used in the reduced basis technique. Each level is treated as a separated optimization problem until the required objective – minimum earing function – is achieved. The experimental design of RSM method is used to build the approximation model and to perform optimization. MATLAB software has been used for building RSM model. Explicit non-linear finite element (FE) Code Abaqus/CAE is used to simulate the deep drawing process. FE models are constructed incorporating the exact physical conditions of the process such as tooling design like die profile radius, punch corner radius, etc., material used, coefficient of friction, punch speed and blank holder force. The material used for the analysis is Stainless steel St12. A quantitative earing function is defined to measure the amount of earing and to compare the deformed shape and target shape set for each stage of the analysis. The cycle is repeated until the converged results are achieved. This iterative design process leads to optimal blank shape. So through the investigation the proposed method of optimal blank design is found to be very effective in the deep drawing process and can be further applied to other stamping applications.

Deformation Behaviors of AZ31B Magnesium Alloy Sheets in Hydraulic Deep Drawing

Magnesium alloy sheets have poor formability at room temperature, and the hydraulic forming may be a choice to improve its formability. Experiments were conducted to investigate the deformation behaviors of AZ31B magnesium alloy sheet in radial pressure deep drawing, one of the hydraulic forming technologies. The influence of hydraulic pressure, die dimension, blank dimension on the limit drawing height (LDH) of the drawn workpieces is investigated, and the location, evolvement and pattern of the fractures are also analyzed. The research results show that the obtained LDH increases with the hydraulic pressure when the punch corner radius is large enough, the formability can be improved only under a proper moderate hydraulic pressure when the punch corner radius is small; moreover, the location of the fractures may be around the corner, on the flange and the sidewall of the drawn workpieces, which appears different evolvement directions and patterns through cross-section.

Numerical Simulation and Sensitivity Analysis for Tube Hydropiercing Quality Based on Experiments

In the present work, the ductile fracture process of hydropiercing is simulated using Rice and Tracey ductile fracture criterion by means of the user subroutine VUMAT of ABAQUS. The simulations at different loading pressures coincide well with the experiments. Based on this criterion, the processes of hydropiercing at different technical conditions are simulated with orthogonal design and the sensitivity analysis of parameters is conducted. The sensitivity analysis shows that internal pressure plays the most important role in controlling quality of the hydropierced products, namely the sheared zone length, roll-over depth and whole coefficient Y. High pressure and better lubricant are better for all the three indexes. Large punch corner radius is better for sheared zone length and Y but worse for roll-over depth. Additionally, it is found that internal pressure and punch corner radius could be intensified each other at conditions of both larger values.

중공 박판의 기계적 프레스 결합에 관한 해석

본 논문은 중공을 가진 판재 두 매를 결합하기 위하여 중공 주위를 따라 기존 레이저 용접법 대신 기계적 프레스 결합법을 적용하는 것에 관한 연구이다. 이를 통해 레이저 용접을 적용했을 때 불가피하게 발생하는 열 변형을 효과적으로 없앨 수 있다. 유한요소해석을 통하여 중공형 판재를 기계적으로 결합시킬 수 있는 금형 설계 방법을 제안하였다. 기계적 결합력을 최대화시키는 데 관련 있는 다섯 가지 설계인자를 선택하여 다꾸치 실험법을 적용한 결과 성형 깊이와 펀치모서리 반경이 가장 크게 영향을 미치는 인자로 나타났다. This study is to apply the mechanical press joining method to join two kinds of sheet metals with circular holes by mechanical pressing instead of laser beam. Usage of the mechanical pressing avoids the thermal deformation of sheet metals which occurs inevitably in laser joining. A die design has been proposed to make the mechanical press joining applicable with finite element analysis. Five design factors related to the joining force have been selected and applied to the Taguchi method for optimization. Among five factors, 'Forming Depth' and 'Punch Corner Radius' have been revealed to be the most influential ones.

Prediction of slug carry-up by the punch in blanking by air-blow of the slug

Blanking is one of the press working operations most often encountered in sheet-metal processing. The punched part or slug which should fall down through the die cavity was occasionally brought upward by the punch and dropped on the strip stock which will hinder the following blanking operation. Though there are many ways to reduce this problem, however, this phenomenon still exists when stamping a very thin gauge strip in a high-speed press. Methods which can help us predict the occurrence of the slug suck-up by the punch in blanking are thus important. In this study, a prediction method is proposed for the occurrence of the phenomenon by air-blow of the slug. Parameters like material tensile strength, punch/die clearances, punch chamfer degree, punch corner radius were considered in organizing the experiment plans. The results showed that the slug carry-up forces measured from direct air-blow of the slug can be adopted as a criterion for the occurrence of the phenomenon. The best and worst parameter combinations were also identified by this method.

알루미늄 합금을 이용한 후방압출에 의한 캔 성형시 성형 조건이 표면확장과 접촉 압력에 미치는 영향

This paper is concerned with the analysis on the surface expansion of AA 2024 and AA 1100 aluminum alloys in backward extrusion process. Due to heavy surface expansion appeared usually in the backward can extrusion process, the tribological conditions along the interface between the material and the punch land are very severe. In the present study, the surface expansion is analyzed especially under various process conditions. The main goal of this study is to investigate the influence of degree of reduction in height, geometries of punch nose, friction and hardening characteristics of different aluminum alloys on the material flow and thus on the surface expansion on the working material. Two different materials are selected for investigation as model materials and they are AA 2024 and AA 1100 aluminum alloys. The geometrical parameters employed in analysis include punch corner radius and punch nose angle. The geometry of punch follows basically the recommendation of ICFG and some variations of punch geometry are adopted to obtain quantitative information on the effect of geometrical parameters on material flow. Extensive simulation has been conducted by applying the rigid-plastic finite element method to the backward can extrusion process under different geometrical, material, and interface conditions. The simulation results are summarized in terms of surface expansion at different reduction in height, deformation patterns including pressure distributions along the interface between workpiece and punch, comparison of surface expansion between two model materials, geometrical and interfacial parametric effects on surface expansion, and load-stroke relationships.

A study on the springback in the sheet metal flange drawing

Abstract The flange drawing process is used to make flanges from the sheet metal blank using the die, punch and blank holder optionally with the supporter. This process is being applied in many sheet metal industries. One of concerns of this process is that the flanged section formed is mostly not parallel with the original blank due to the springback occurrence, which could affect the quality of the formed part. This study has focused on the evaluation of springback occurring in the sheet metal flange drawing process by controlling some process factors like the punch corner radius (PR) and die corner radius (DR), the blank-holding-force (BHF), the supporting-force (SF), the lubrication and so on. The springback phenomenon in the flange drawing process has been studied first using the finite element method (FEM) in order to understand what the main causes of springback are. The distribution pattern of local x -component of stress along the longitudinal direction of the blank has been revealed to be very important in predicting the final shape of the flange. This fact has been backed up by the experimental results carried out with the developed test dies. The Taguchi table L 18 has been used to determine which of the process factors of the flange drawing is the most influencing to make the flanged section parallel with the original blank in spite of springback occurrence. The results show that the punch corner radius (PR) is the most important factor of the process.

박판 스프링용 재료의 기계적특성과 굽힘가공성 평가 연구

This study examined the mechanical properties and bending formability evaluation of spring strip materials(SK5 CSPH, STS 301 CSP-EH, C7701-H). The hardness test and tensile test were performed at room temperature() for mechanical properties. The U-bending test were carried out at various conditions of punch corner radius(Rp), ratio of punch comer radius/thickness(Rp/t) and ratio of clearance/thickness(Rp/t) and ratio of clearance/thickness(C/t) for bending formability evaluation.

Numerical Analysis on the Extruded Volume and Length Ratios of Backward Tube to Forward Rod in Combined Extrusion Processes

This paper is concerned with forward rod extrusion combined simultaneously with backward tube extrusion process in both steady and transient states. The analysis has been conducted in numerical manner by employing a rigid-plastic finite element method. AA 2024 aluminum alloy was selected as a model material for analysis. Among many process parameters, major design factors chosen for analysis include frictional condition, thickness of tube in backward direction, punch corner radius, and die corner radius. The main goal of this study is to investigate the material flow characteristics in combined extrusion process, i.e. forward rod extrusion combined simultaneously with backward tube extrusion process. Simulation results have been summarized in term of relationships between process parameters and extruded length and volume ratios, and between process parameters and force requirements, respectively. The extruded length ratio is defined as the ratio of tube length extruded in backward direction to rod length extruded in forward direction, and the volume ratio as that of extruded volume in backward direction to that in forward direction, respectively. It has been revealed from the simulation results that material flow into both backward and forward directions are mostly influenced by the backward tube thickness, and other process parameters such as die corner radius etc. have little influence on the volume ratio particularly in steady state of combined extrusion process. The pressure distributions along the tool-workpiece interface have been also analyzed such that the pressure exerted on die is not so significant in this particular process such as combined operation process. Comparisons between multi-stage forming process in sequence operation and one stage combined operation have been also made in terms of forming load and pressure exerted on die. The simulation results shows that the combined extrusion process has the greatest advantage of lower forming load comparing to that in sequence operation.

An Analysis on the Surface Expansion of Aluminium Alloys in Backward Can Extrusion Process

This paper is concerned with the analysis on the surface expansion of AA 2024 and AA 1100 aluminum alloys in backward extrusion process. Due to heavy surface expansion appeared usually in the backward can extrusion process, the tribological conditions along the interface between the material and the punch land are very severe. In the present study, the surface expansion is analyzed especially under various process conditions. The main goal of this study is to investigate the influence of degree of reduction in height, geometries of punch nose, friction and hardening characteristics of different aluminum alloys on the material flow and thus on the surface expansion on the working material. Two different materials are selected for investigation as model materials and they are AA 2024 and AA 1100 aluminum alloys. The geometrical parameters employed in analysis include punch corner radius and punch face angle. The geometry of punch follows basically the recommendation of ICFG and some variations of punch geometry are adopted to obtain quantitative information on the effect of geometrical parameters on material flow. Extensive simulation has been conducted by applying the rigid-plastic finite element method to the backward can extrusion process under different geometrical, material, and interface conditions. The simulation results are summarized in terms of surface expansion at different reduction in height, deformation patterns including pressure distributions along the interface between workpiece and punch, comparison of surface expansion between two model materials, geometrical and interfacial parametric effects on surface expansion, and load-stroke relationships. It has been concluded from the present study that the geometrical condition of punch is the most significant factor among the parameters employed in this study. It is also known from the simulation results that the difference in surface expansion according to different material properties is not more or less significant.

Material Flow Characteristics on the Forward and Backward Solid Extrusion Process

FE simulations were carried out to analyze the influence of die geometry and process condition on the material flow. Deformation pattern and its characteristics in a combined forward and backward solid extrusion process were analyzed in terms of forming loads as the primary parameter, volume ratio of backward solid to forward solid and die pressure between tool-workpiece interfaces. Major parameter is the outer diameter ratio (ODR) of backward solid radius to forward solid radius with constant outer diameter of forward solid. Furthermore, extensive simulation works were conducted to investigate the effect of minor design parameters on stable material flow such as punch corner radius. The deformation pattern of material flow in a combined solid extrusion process is also presented. The results from the process simulation predict the flow modes of workpiece material and the die pressure occurring at the contact surface between workpiece and punch. The process of a combined forward and backward solid extrusion was analyzed using a rigid plastic finite element code to get information about the forming load and die pressure distribution, etc.

박판 성형공정 유한요소 해석용 마찰모델

In order to find the effect of lubricant viscosity, tool geometry, forming speed, and sheet material properties on the friction in the sheet metal forming, friction tests were performed. Friction test results show that as the lubricant viscosity becomes lower, the friction coefficient is higher. When surface roughness is extremely low or high, the friction coefficient is high. The bigger die corner radii and punch speed are, the smaller is the friction coefficient. From the experimental observation, the friction model which is the mathematical expression of friction coefficient in terms of lubricant viscosity, roughness and hardness of sheet surface, punch corner radius, and punch speed is constructed. By comparing the punch load found by FEM using the proposed friction model with that obtained from the experiment in 2-D stretch forming, the validity and accuracy of the friction model are demonstrated.