Design and validation of a sheet metal shearing experimental procedure

Throughout the industrial processes of sheet metal manufacturing and refining, shear cutting is widely used for its speed and cost advantages over competing cutting methods. Industrial shears may include some force measurement possibilities, but the force is most likely influenced by friction losses between shear tool and the point of measurement, and are in general not showing the actual force applied to the sheet. Well defined shears and accurate measurements of force and shear tool position are important for understanding the influence of shear parameters. Accurate experimental data are also necessary for calibration of numerical shear models. Here, a dedicated laboratory set-up with well defined geometry and movement in the shear, and high measurability in terms of force and geometry is designed, built and verified. Parameters important to the shear process are studied with perturbation analysis techniques and requirements on input parameter accuracy are formulated to meet experimental output demands. Input parameters in shearing are mostly geometric parameters, but also material properties and contact conditions. Based on the accuracy requirements, a symmetric experiment with internal balancing of forces is constructed to avoid guides and corresponding friction losses. Finally, the experimental procedure is validated through shearing of a medium grade steel. With the obtained experimental set-up performance, force changes as result of changes in studied input parameters are distinguishable down to a level of 1%.     

板材剪切与冲裁加工实验的位移测量系统

针对板材剪切与冲裁加工的特点，设计了一种应变片式位移传感器。传感器可根据需要对量程进行调节，且相对精度不变，特别适于中小位移的测量。结合数据采集系统，在材料试验机上实现了板材剪切加工和精密冲裁实验的位移测量。     

剪板机剪切力与剪板断面形貌的关系浅析

通过观察剪板机剪板的断面形貌,分析剪板机的剪板过程,进而导出了一种剪切力的简易计算方法,该法计算结果与常用公式的计算结果近似,但方法更为简单,可作为设计计算的参考.     

杠杆式液压联合冲剪机剪板机构优化设计

就作者自行设计的液压联合冲剪机的杠杆—摇块剪板机构进行了运动和受力分析,建立了剪板机构优化设计的数学模型,并就设计结果进行了讨论。按该方法设计,一次行程剪切宽度增加了３７．７％,并使耗料大大减少,刚度增加。     

摆式剪板机刀架的有限元分析

摆式剪板机主要组成部分刀架和机架,它们强度和刚度直接决定了剪板机的刚性和剪切精度。本文以QC12Y-6×3200为例,对摆式剪板机的刀架进行建模分析,判断出关键位置和静力学性能,为改进产品结构、提高设计质量提供重要依据。     

剪板机的一种带回传功能的复合型后托料装置

介绍剪板机的一种新型后托料装置,可在剪板时托住板料,提高剪板精度,又具有回传功能,可将剪切下来的板料送到操作者手中,减小操作者劳动强度。     

高精剪—板材激光拼焊生产线上的关键设备

高精剪是近十年来随着国外大批量板材激光拼焊生产线的推广应用而研制开发的一种板料制坯专用设备。本文介绍了精密剪切的基本原理,阐述了我国研制开发高精剪的必要性和可行性,并提出了解决的几个关键技术问题。     

Formation of shearing bands in the hot-rolling process of AZ31 alloy

Three types of AZ31 alloy samples, numbered with A, B, C, with various texture and microstructure condition were hot-rolled in single pass to investigate the different mechanism of shearing bands formation. Shearing bands came into being via twinning related grain fragmentation and DRX in Sample A while via rotational recrystallization in Sample B. Twinning played the most important role in shearing bands formation in Sample C. DRX and twinning are the two major elements in the formation of shearing band in magnesium alloys. Contrastive study indicated that sharper texture would increase the influence of twining while small size would promote the recrystallization in shearing bands formation.     

Folding-shearing: Shrinking and stretching sheet metal with no thickness change

50% of all sheet metal is scrapped, mainly by trimming following deep-drawing. To combat this a novel process inspired by the mechanics of spinning is proposed and its feasibility is tested with a novel experimental rig. A sheet is first folded along its long axis and then drawn through a die-set in a state of shear to reduce its width with no average reduction of thickness. The performance and limits of the process are evaluated with a novel experimental rig and new analytical and numerical simulations. The extension from this pre-cursor process to a more general forming process is discussed.     

石墨碳块复合加工机床的防护设计

石墨碳块加工过程中会产生多种形态的尘屑,这些尘屑对加工刀具寿命、零件的加工精度及机床精度保持性产生很大的影响。为消除石墨碳块的尘屑对机床的影响,给出了在设计石墨碳块加工机床时应采取的防尘措施及石墨尘屑的收集方法。     

Revisiting the empirical relation for the maximum shearing force using plasticity and ductile fracture mechanics

Combination of plasticity with ductile fracture mechanics in a simple plastic flow model for sheet metal cutting provides a new level of understanding of the empirical relation between the maximum shearing force F_max and the ultimate tensile stress σ_UTS of the workpiece. The constant C in F_max = C σ_UTStL, where t is the sheet thickness and L the total surface length of the cut contour, is shown to be determined either (a) by the load to cause plastic instability in shear with separation (cracking) occurring subsequently or (b) by the load to cause cracking when that occurs at a punch displacement smaller than that at plastic instability in which case no instability occurs. The usually encountered range of empirical values for C, viz.: 0.65 < C < 0.85, is shown to correspond with the load for instability and depends on the work hardening index, with less-ductile materials having C at the lower end of the range. Whether cracking can precede the instability depends on the toughness/strength ratio (R/k₀) of the material and the workpiece thickness, where R is the fracture toughness and k₀ the yield stress in shear. The thicker the sheet and the less ductile the material, i.e. the lower the (R/k₀), promotes ductile fracture at a load smaller than that for plastic instability.     

An analytical force model with shearing and ploughing mechanisms for end milling

An analytical force model with both shearing and ploughing mechanisms is established for the end milling processes. The elemental forces are defined as the linear combination of shearing and ploughing forces in six cutting constants. The analytical model for the total milling forces in the angular and frequency domain are derived by convolution approach and Fourier transform respectively and are expressed as the superposition of the shearing force component and ploughing force component. This dual-mechanism model is analyzed and discussed in the frequency domain and compared with the lumped shear model. An expression is derived for identifying the cutting constants of the dual-mechanism model from the average milling forces. Explicit inclusion of ploughing force in the model is shown to result in better predictive accuracy and yields a linear force model with constant cutting coefficients. Experiments verify the accuracy and the frequency analysis of the dual-mechanism model and show that cutting constants for the dual-mechanism model are fairly independent of chip thickness.     

Identification of shearing and ploughing cutting constants from average forces in ball-end milling

This paper presents an analytical model for the direct identification of global shearing and ploughing cutting constants from measured average cutting forces in ball-end milling. This model is based on the linear decomposition of elemental local cutting forces into a shearing component and a ploughing component. Then, a convolution integral approach is used to obtain the average cutting forces leading to a concise and explicit expression for the global shearing and ploughing cutting constants in terms of axial depth of cut, cutter radius and average milling forces. The model is verified by comparisons with an existing force model of variable cutting coefficients. Cutting constants are identified through milling experiments and the prediction of cutting forces from identified cutting constants coincides with the experimental measurements. A model for identifying the lumped shearing constants is obtained as a subset of the presented dual mechanism model. Experimental results indicate that a model with dual-mechanism cutting constants predicts the ball-end milling forces with better accuracy than the lumped force model.     

A study of high-rate shearing of commercially pure aluminum sheet

The effect of shearing speed on the quality of shape and edge-face of the sheared-off products is studied. The tested material is a commercially pure aluminum. The maximum shearing speed is 10 m/s. It is evidenced that the shape quality of the sheared-off parts is better when a smaller clearance and a higher rate of shearing are applied. A thin ring of almost complete rectangular cross-section, i.e. 1.5 mm in width and 10 mm in height, whose edge-face is glossy, is successfully produced by the high-rate shearing process using a constraint tool set at the outer periphery of the sheet blank. It is demonstrated clearly by the pictures of microstructure that the material flow is concentrated within a very narrow band, showing even a recrystallized structure. A theoretical analysis proves that the band is the so-called adiabatic shear band (ASB), and that even melting of material takes place within it. In the shearing process, first an ASB evolves, followed by melting in the early stage of shearing. The major stroke of the punch is occupied by an easy simple shearing in a melted state.     

Punching of ultra-high strength steel sheets using local resistance heating of shearing zone

A punching process using local resistance heating of a shearing zone was developed to shear ultra-high strength steel sheets. The shearing zone was heated by passing electric current between the sheet holder and the knockout in order to decrease the flow stress in the shearing, and the heating of the die and punch was prevented by no contact with the sheet during the heating. Electrode pins having an individual spring were employed to attain uniform heating of the shearing zone. The welding resistance of the heads of the electrode pins to the sheet by the heating was examined for Ag-W, Cu-W, Ag + WC and W. The Cu-W pins having the highest welding resistance were employed in a punching experiment of 980 MPa level ultra-high strength steel sheets. The punching load was considerably reduced by the heating, e.g., about 1/5 of the cold punching load at 800 °C. As the heating temperature increased, the depth of the shiny burnished surface on the sheared edge increased and that of the rough fracture surface decreased.     

Numerical simulation and optimization of clearance in sheet shearing process

1　INTRODUCTIONThesheetmetalshearingprocessisverycompli catedduetoitsdeformationandfracture .Duringtheprocess,thefiercedeformationandlimitstrainaremuchgreaterbeforefracturethananyotherprocess .So ,uptillnow ,theintricateappearancesduringtheshearingprocesscannotbeexplainedproperly .Withregardtodeformation ,shearingprocessismorecomplicatedthanotherformingprocessessuchasdeepdrawing ,bending ,bulging ,andburring .Inanalysisofformingprocesses ,thepredictionandeval uationofstress ,strain ,veloc…     

Machining accuracy for shearing process of thin-sheet metals—Development of initial tool position adjustment system

In the shearing process, clearance has a significant effect on machining accuracy. However, the relationship between uneven clearance caused by misalignment of tool position and machining accuracy remains unclear. This is attributed to the fact that, previously, the effect was small because the thickness of the workpiece was not so thin, and a method for precisely measuring and adjusting the tool position had not been established. Therefore, in the present study, a new method of adjusting the initial tool position is developed. In addition, punching experiments are conducted under the condition that the initial tool position is adjusted to an accuracy of 2 μm or better, and the effects of clearance on machining accuracy, shape of cross-section, and diameter of hole, are investigated in three types of materials. From these results, the importance of adjusting the initial tool position is clarified.     

Estimation of machine tool feed drive inclination from current measurements and a mathematical model

Leveling is an important part of a machine tool installation process because it significantly influences the product quality, machine tool accuracy, and machine lifetime. Conventional leveling procedures are performed by skilled engineers using leveling instruments such as spirit or electronic levels. It is difficult to monitor the level of a machine tool because an accurate leveling instrument is expensive and difficult to install. Therefore, a novel methodology for estimating the inclination angle of a machine tool feed drive is proposed in this paper to overcome the difficulties of leveling. The proposed methodology utilizes motor current measurements and a new mathematical model of the machine tool feed drive that considers the inclination. Experimental results showed that the proposed method successfully estimates the inclination angle and enhances the accuracy of the machine tool feed drive model by considering the inclination effects.     

Development of an analytical scheme to predict the need for tool regrinding in shearing processes

This paper describes an analytical scheme for the prediction of the tool wear and the need for tool regrinding in the sheet metal shearing process. The finite element program developed is used for the analysis of the shearing process in this study. In order to predict tool wear, Archard's wear model is reformulated in an incremental form and then the wear depth on the tool is calculated at each step in the deformation using the result of finite element analysis, taking consideration of the sliding velocity and normal pressure over the contact area. In general, the need for regrinding of the shearing tool is determined on the basis of allowable burr height on the final product. Therefore, based on this criterion, the analysis of the shearing process is iteratively performed using the worn profile on the tool in order to predict the need for tool regrinding. To analyze the quantitative wear of the tool, the parameters included in the wear model are determined by the result using a wear test, such as a pin-on-disk wear test for the material of the shearing tool and sheet metal. The effectiveness of the proposed scheme is verified by comparison with experimental results. It is shown that the simulation results are in good agreement with those obtained experimentally and the need for regrinding of the shearing tool can be determined for an allowable burr height.     

Analysis of loads on the shearing edge during electrohydraulic trimming of AHSS steel in comparison with conventional trimming

In order to achieve further weight reduction in automotive components, the technology of manufacturing of automotive panels from advanced high strength steels is being developed. Electrohydraulic trimming technology eliminates the necessity of accurate alignment of the shearing edges in trimming operation. Analysis of loads on the tool during high-rate EH trimming process has been performed. In order to investigate the effect of the process on the shearing edge performance, a dedicated finite element analysis procedure combining 3D shell and 2D solid models was developed. EH trimming experiments were carried out to validate the simulation model where elastic plastic deformation of the shearing edge was taken into account. The effects of the die geometry and number of trimming cycles on the tool contact loads and tool's plastic deformation were analyzed. This analysis was based on numerical simulation of deformation and fracture of the blank being trimmed in contact with the deformable shearing edge. Numerical analysis of the shearing edge deformation was performed in elasto-plastic formulation for the D2 tool steel inserts used in the experimental study and also in elastic formulation to define the maximum stresses which tool material needs to withstand to avoid its plastic deformation.