Experimental investigation of the cutting force reduction during the blanking operation of AHSS sheet materials

Within the manufacturing process of sheet metals, blanking represents an essential process operation. As the industrial application of high-strength multi-phase steels grows, the blanking process must consider high blanking and shear forces which are characteristic of these materials. This paper presents possibilities for reducing these forces. Experiments were performed utilizing a novel tool concept which can correlate necessary blanking forces to the punch stroke in three dimensions and in direct force path. Results from three different AHSS materials are presented showing the variation of decisive blanking parameters such as clearance, shearing angle and sheet positioning angle.     

Failure Analysis of a Sheet Metal Blanking Process Based on Damage Coupling Model

In this paper, a blanking process of sheet metal is studied by the methods of numerical simulation and experimental observation. The effects of varying technological parameters related to the quality of products are investigated. An elastoplastic constitutive equation accounting for isotropic ductile damage is implemented into the finite element code ABAQUS with a user-defined material subroutine UMAT. The simulations of the damage evolution and ductile fracture in a sheet metal blanking process have been carried out by the FEM. In order to guarantee computation accuracy and avoid numerical divergence during large plastic deformation, a specified remeshing technique is successively applied when severe element distortion occurs. In the simulation, the evolutions of damage at different stage of the blanking process have been evaluated and the distributions of damage obtained from simulation are in proper agreement with the experimental results.     

倾斜板料冲裁的冲裁力研究

倾斜板料冲裁的冲裁力计算是一个尚待研究的课题。本文对倾斜板料圆孔冲裁的冲裁过程进行了探讨，将其分为板料包容冲头和板料不包容冲头两种类型和三个冲裁阶段，导出了每种类型各冲裁阶段冲裁力的计算公式，分析了冲裁力随行程的变化规律，研究了最大冲裁力和板料厚度、圆孔直径、板料倾斜角度的关系，获得了一些有价值的结论。     

A New Method to Calculate Threshold Values of Ductile Fracture Criteria for Advanced High-Strength Sheet Blanking

A new approach is presented in this paper to calculate the critical threshold value of fracture initiation. It is based on the experimental data for forming limit curves and fracture forming limit curves. The deformation path for finally a fractured material point is assumed as two-stage proportional loading: biaxial loading from the beginning to the onset of incipient necking, followed plane strain deformation within the incipient neck until the final fracture. The fracture threshold value is determined by analytical integration and validated by numerical simulation. Four phenomenological models for ductile fracture are selected in this study, i.e., Brozzo, McClintock, Rice-Tracey, and Oyane models. The threshold value for each model is obtained through best-fitting of experimental data. The results are compared with each other and test data. These fracture criteria are implemented in ABAQUS/EXPLICIT through user subroutine VUMAT to simulate the blanking process of advanced high-strength steels. The simulated fracture surfaces are examined to determine the initiation of ductile fracture during the process, and compared with experimental results for DP780 sheet steel blanking. The comparisons between FE simulated results coupled with different fracture models and experimental one show good agreements on punching edge quality. The study demonstrates that the proposed approach to calculate threshold values of fracture models is efficient and reliable. The results also suggest that the McClintock and Oyane fracture models are more accurate than the Rice-Tracey or Brozzo models in predicting load-stroke curves. However, the predicted blanking edge quality does not have appreciable differences.     

Description of numerical techniques with the aim of predicting the sheet metal blanking process by FEM simulation

A numerical formulation of the blanking process in 2D is presented in this article. A finite element software called BlankForm has been developed to simulate the blanking process. Several approaches to model ductile damage and fracture have been investigated and are presented in this paper. In particular, some details are provided about a discrete cracking method that has been developed to take the propagation of one or several cracks into account. Our formulation is evaluated on an axisymmetric blanking experiment. The importance of remeshing is demonstrated. Coupled and uncoupled damage models are benchmarked, and two methods for fracture simulation are analysed, namely the previous discrete cracking method, and a widely used method in blanking applications, the element kill method. It is shown that more realistic results are obtained when the discrete cracking method is used.     

A novel process for transforming sheet metal blanks: Ridged die forming

Up to 20% of all sheet metal produced is scrapped as blanking skeletons. A novel process is therefore designed and examined, aiming to transform tessellating ‘pre-blanks’ in-plane into the real blanks required for stamping. Prior to blanking, the sheet is formed with a set of ridged dies, from which pre-blanks are cut and then flattened into true blanks. Several different approaches to designing ridged dies are evaluated by simulation and experiment, and the best results demonstrate a potential reduction in blanking yield losses for can-making from 9.3% to 6.9%.     

Blanking tool wear modeling using the finite element method

One of the main objectives of the numerical process design in metal forming is to develop adequate tool design and establish process parameter in order to increase tool life and to improve part quality and complexity while reducing manufacturing cost. The prediction of tool wear in sheet metal blanking/punching processes is investigated in this paper using the finite element method. A wear prediction model has been implemented in a finite element code in which the tool wear is a function of the normal pressure and some material parameters. A damage model is used in order to describe crack initiation and propagation into the sheet. The distribution of the tool wear on the tool profile is obtained and compared to industrial observations. Furthermore, a numerical investigation has been carried out to study the effect of tool wear on the burr formation.     

冲裁件二维排样优化

分析了整体板料对单一冲裁件的排样,以有限长,宽的整体板料上所能冲裁出最大 样件个数目标,给出单一冲裁件排样的数学模型及相应的优化算法。／     

Self-piercing riveting process: An experimental and numerical investigation

The self-piercing riveting is a young technology for joining sheet metals in automotive structures. In this paper, the riveting process has been simulated numerically using the finite element code LS-Dyna. A 2D axisymmetric model was generated including two sheets to be joined, rivet and tools. The rivet and tools geometries are based on the Böllhoff standards. An implicit solution technique with r-adaptivity has been used. The advantages and the limits of using r-adaptivity in this class of metal forming process are discussed. In addition, parametric studies on important parameters for the forming process, i.e. friction, mesh size and failure criteria are presented. In order to validate the numerical simulation of the riveting process, a new test device was developed in order to record the force applied on the rivet during the riveting process. An extensive experimental program on specimens made of aluminium alloy 6060 in two different tempers, T4 and T6, has been used as a database for the validation of the numerical simulations. The results show the capability to simulate the riveting process for different combination of plate material and rivet geometries.     

板材冲挤复合成形模拟与裂纹预测

板材冲挤复合成形是一种厚板近净形成形工艺,在汽车零部件精密成形制造中有着广阔的应用前景。文章采用刚塑性有限元法对板材冲挤成形工艺进行了模拟,确定了板材冲挤变形的速度场、等效应力场和等效应变场,揭示了板材冲挤工艺的成形特点。基于J.W.Hancock与A.C.Mackenzie提出的断裂判剧和数值模拟分析,预测了板材冲挤成形裂纹产生位置和主要影响因素。通过实验测定板材冲挤成形中裂纹产生情况,验证了模拟分析结果,对于板材冲挤复合成形工艺设计有指导意义。     

可减少条带数的矩形件二维下料算法

从板材上切割矩形件的过程通常包含两个阶段:第1阶段用大型刀具将板材切成条带;第2阶段用小型刀具将条带切成所需要的矩形件.第1阶段的切割成本随着下料方案中条带数的增加而增加.针对矩形件二维下料问题,提出一种可减少条带数的下料算法,其优化目标是最小化材料成本和切割成本之和.首先,建立该问题的整数线性规划模型;然后,构造T型...     

基于响应曲面法的QSTE460板料冲裁工艺参数优化

以冲压零件作为分析对象,基于响应曲面法设计板料冲裁的模拟试验,利用DEFORM-2D模拟软件对板料的冲裁变形过程进行有限元模拟,建立了冲裁工艺参数与冲裁断面光亮带长度之间的数学模型。通过模拟结果的分析得知:冲裁间隙与模具刃口圆角半径对光亮带长度的交互式影响最大。将冲裁速度、冲裁间隙以及模具刃口圆角半径作为设计变量,以光亮带长度作为优化目标,利用Design Expert软件对响应曲面模型进行优化,得到板料冲裁的优化参数:冲裁速度为14.04 mm·s-1,冲裁间隙为8.99%t(t为板料厚度),模具刃口圆角半径为1.25%t,光亮带长度的响应值为0.834 mm。此外,利用冲压模具进行试验验证,试验值与响应值之间的相对误差为11.8%,验证了响应曲面法应用于板料冲裁工艺参数优化的准确性。     

Rotary blanking: tool materials

The growing globalization leads to an increasing demand on competition between industrial companies. The manufacturing processes using innovative operations and advanced materials make it possible to develop a competitive power with a high level productivity. In this paper the process of rotary blanking is introduced as an innovative manufacturing method. It enables users to work more efficient and to reduce product costs with a high process speed. In order to understand this modern manufacturing technology, it is needed to analyze process parameters. In particular it is necessary to determine which materials are preferable for the rotary blanking. Therefore, the influence of different tool materials on the part quality was investigated through experiments. Experimental results of the rotary blanking from different tool materials are discussed and they are compared with the results of finite element simulations in this paper.     

薄板精密冲裁的变形过程和机理研究

本文构建了料厚为0.3mm的薄板精密冲裁变形有限元模型,运用该模型研究了薄板精密冲裁变形过程,分析结果显示冲裁断面质量与生产实际非常接近.论文分析了薄板精密冲裁变形过程中的静水应力的分布特征、影响机理.研究表明,强压边条件增加了静水压应力区域的范围和程度,从而延迟了裂纹的初始和发展,提高了冲裁断面的质量.     

A novel laboratory blanking apparatus for the experimental identification of blanking parameters

High-quality blanking depends on several blanking parameters that are difficult to investigate with industrial blanking presses. In this research, a novel laboratory blanking apparatus that allows quasi-static and dynamic blanking at different blanking speeds is presented. With a clear focus on the dynamics of the blanking process, the inertial correction of the punch force, the surface velocity and the surface temperature of sheet-metal are researched. In addition, measurements of the punch–die misalignment and the punch–die inclination-angle are discussed. The apparatus is also able to perform a partial penetration of the punch to a selected depth with an accuracy of better than 10 μm. The apparatus was shown to offer us a new insight into the blanking process that can increase our understanding and therefore result in better numerical models and better products.     

Two calculations concerning the critical aluminium content in Fe20Cr5Al alloys

Alloys for high temperature applications rely on a protective oxide layer formed by selective oxidation. In Fe20Cr5Al type alloys the useful lifetime is governed by the depletion of aluminium by oxidation down to a critical aluminium content. Following spallation of the oxide scale the bare metal is exposed to air and catastrophic failure due to breakaway oxidation occurs if the aluminium content is too low. In this paper a model for the calculation of the critical aluminium content is presented. Based on Wagner's ideas on selective oxidation in ternary alloys, the critical aluminium content is calculated as that corresponding to the transition between external and internal oxidation. The resulting aluminium contents are temperature dependent and cover the range of values 0 to 3.5 wt.% reported in the literature. In the second part of the paper aluminium depletion profiles in Fe20Cr5Al plates have been calculated assuming a parabolic growth law for the oxidation process. The solution of the differential equation is an extension of the one dimensional solution presented by Whittle and coworkers for chromium depletion in FeCr sheet material, to three dimensions. Because of the increased consumption of aluminium at the corners of the sample, the critical aluminium content is first reached there. Based on the calculation, the reduction in lifetime, due to premature breakaway oxidation at the corners can be estimated.     

铝合金不粘锅复合模具设计

介绍了铝合金不粘锅复合模具的设计及成型工艺，复合模能在压力机一次行程内，完成落料，冲孔，拉深，胀形等多道工序，工艺先进，设计采用聚氨脂凸模的复合模具。     

Condition-based maintenance in punching/blanking of sheet metal

This paper provides a review and proposal for condition-based maintenance (CBM) in blanking of sheet metal. To date, little research on this topic can be found in literature, which is probably due to the complex nature of the process. Previous statistical, artificial intelligence (AI) and model-based approaches are analysed. Special attention is given to inherent assumptions and other sources of inaccuracy. In addition, it is demonstrated how the signature of the force–displacement relation changes significantly with increasing tool wear in a typical configuration of sheet steel blanking. An analysis follows as to how such behaviour could be used in CBM. A practical implementation of CBM in sheet metal blanking is proposed based on a hybrid solution.     

金属材料冲裁过程的有限元模拟

介绍了利用弹性有限元对金属冲裁加工模拟的基本原理,包括弹塑性大变形木匠,裂破坏模拟以及网格重划分等技术,利用商业化有限元程度DEFORM－2D^TM对不锈钢（AISI304）板料的冲裁工艺进行了模拟,模具采用刚体模型,工件采用弹塑性模型,材料断裂破坏采用Cockroft-Latham破坏准则,分析了冲裁过程中裂纹生成、扩展以及材料断裂分离的过程,冲载力的变化等,模拟结果中的材料断裂和冲裁力的变化与已发表文献中的实验结果一致。     

毛细管铝封无搭边级进冲挤技术

将挤孔——切连皮——落料——空心件正挤压4种工序巧妙地复合在一套模具上，而且模具结构并不复杂，成功地在400kN冲床上实施了该工艺，使空心毛细管铝封片级进挤压工艺生产率达到每分钟60件，大幅度提高了生产效率。本还在落料工序中采用无搭边新技术，一改冲裁落料中有搭边的常规模式，减少了搭边损耗，大大提高了铝板材的利用率。