DETERMINATION OF BLANK HOLDER FORCE IN SHEET METAL DEEP DRAWING PROCESS

Blank holder force (BHF) is an important measure to control the sheet metal forming. BHF is identified quickly using artificial neural network (ANN) on the basis of its analytical description. And critical rupture and wrinkle BHF curves are given. A close-loop control system is established to finish the forming process.

Prediction of Earing in Deep Drawing of Roll-cast Aluminium Alloy Sheets

Commercial aluminium alloy sheets are presently sem ic ontinuously, direct chill casting billets that are hot and cold rolled to the fi nal gauge. Interest has been shown in continuous methods which eliminate the ho t rolling step through rapid solidification of the molten metal to the final sla b. Accordingly, sheets are produced by homogenization, cold rolling, intermedia te and final annealing of these roll-cast slabs. The problem of earing is of gr eat concern as it causes frequent interruption of production runs and leads to m aterial wastage. Therefore, it is quite desirable that earing can be predic ted and consequently necessary measures be taken to minimize or eliminate this u nwanted phenomenon. It is accepted generally that, the principal source of earing is the crystallogr aphic anisotropy arising from non-random distribution of crystal orientations i n the material. Accordingly, several attempts have been made to correlate the m echanical and crystallographic properties of the materials to the earing behavio ur for predictive purposes. Some of these are based on continuum concepts which concentrate on the macroscopic rather than the microscopic aspects of the mater ials. To accommodate the microstructural features of the material, some models have been developed. A more recent approach which provides a connection between texture and plastic anisotropy parameters of the material is the Continuum Mech anics of Textured Polycrystals (CMTP) method proposed by Lin et al. A simplifie d version of this method has been suggested by Chan with promising accuracy for aluminium and copper sheets. AA3105 and AA8011 aluminium alloy sheets were used in this investigation. The a s-cast slabs were cold rolled to the final thickness of 1.0 mm. Different anne aling temperatures in the range of 420 ℃ to 540 ℃ produced a range of R-value s. Circular blanks of 60 mm diameter were machined and deep drawn using a cylind rical flat-bottom punch of 33 mm diameter. The heights of the drawn cups were measured at 0, 45 and 90° to the rolling direction, with the aid of a microme ter accurate to 10 -2 mm. The earing percentage was then calculated usin g the following formula: % earing=h p-h v1/2(h p+h v)(1) where h p is the distance between the bottom of the cup and the peak of ear , and h v is the distance between the bottom of the cup and the valley of t he ear. For the measurement of plastic strain ratios (R-values), tensile specimens cut at 0, 45 and 90° to the rolling direction were photogridded with 1mm square s. These specimens were then stretched in the range of uniform deformation and the dimensional changes were measured with the aid of a travelling microscope. The strain ratios, whether R 0, R 45 or R 90 were determined from the following equation: R θ=dε wdε t=dε wdε l+dε w(2) where Θ refers to the specimen orientation and dε w and dεl refer to the transverse and longitudinal strains of the gauge section, respectively. The av erage strain ratio, R, and the parameter ΔR were then calculated from: R=14(R 0+2R 45+R 90)(3) ΔR=12(R 0-2R 45+R 90)(4) where R 0, R 45 and R 90 values are determined using specimen s cut at 0, 45 and 90° to the rolling direction, respectively. Finally, a continuum mechanics approach using different yield criteria is employ ed for the prediction of earing behaviour under different conditions of the mate rials. Instead of using texture data, the yield stress values are obtained by d ifferent anisotropic yield criteria such as; Hosford, Hill, and Zhou. The predicted earing profiles are compared to the experimental data and the suit ability of different yield criteria is discussed.

Hot Granules Medium Pressure Forming Process of AA7075 Conical Parts

High strength aluminum alloy plate has a low elongation at room temperature, which leads to the forming of its components need a high temperature. Liquid or gas is used as the pressure-transfer medium in the existing flexible mould forming process, the heat resistance of the medium and pressurizing device makes the application of aluminum alloy plate thermoforming restricted. To solve this problem, the existing medium is replaced by the heat-resisting solid granules and the general pressure equipments are applied. Based on the pressure-transfer performance test of the solid granules medium, the feasibility that the assumption of the extended Drucker-Prager linear model can be used in the finite element analysis is proved. The constitutive equation, the yield function and the theoretical forming limit diagram（FLD） of AA7075 sheet are established. Through the finite element numerical simulation of hot granules medium pressure forming（HGMF） process, not only the influence laws of the process parameters, such as forming temperature, the blank-holder gap and the diameter of the slab, on sheet metal forming performance are discussed, but also the broken area of the forming process is analyzed and predicted, which are coincided with the technological test. The conical part whose half cone angle is 15° and relative height H/d0 is 0.57, is formed in one process at 250℃. The HGMF process solves the problems of loading and seal in the existing flexible mould forming process and provides a novel technology for thermoforming of light alloy plate, such as magnesium alloy, aluminium alloy and titanium alloy.

Epigenesis of Pb-Zn Deposits in the Xicheng Ore Field,Western Qinling

Abstract: It was previously considered that all of the Pb-Zn deposits in the Xicheng orefield belong to Devonian hydrothermal-sedimentary deposits or their reworked ones. Study proves that the host strata, besides the Devonian, include the Palaeoproterozoic. The super-large Changba-Lijiagou Pb-Zn deposit occurs in the Palaeoproterozoic strata. The deposits in this district are not hydrothermal-sedimentary deposits or their reworked ones, but Yanshanian-Himalayan epigenetic hydrothermal deposits. The modes of occurrence, sizes and positions of all the deposits in the Xicheng orefield are completely controlled by the choula (draw)-thrust sheet. Therefore the previous grounds for the model of the Qinling-type Pb-Zn deposits cannot hold good. The authors propose that the Changba-type and Bijiashan-type Pb-Zn deposits be used to represent two mineral deposit models with different characteristics in the Xicheng orefield.