DEFORMATION ANALYSIS OF SHEET METAL SINGLE-POINT INCREMENTAL FORMING BY FINITE ELEMENT METHOD SIMULATION

Single-point incremental forming （SPIF） is an innovational sheet metal forming method without dedicated dies, which belongs to rapid prototyping technology. In generalizing the SPIF of sheet metal, the deformation analysis on forming process becomes an important and useful method for the planning of shell products, the choice of material, the design of the forming process and the planning of the forming tool. Using solid brick elements, the finite element method（FEM） model of truncated pyramid was established. Based on the theory of anisotropy and assumed strain formulation, the SPIF processes with different parameters were simulated. The resulted comparison between the simulations and the experiments shows that the FEM model is feasible and effective. Then, according to the simulated forming process, the deformation pattern of SPIF can be summarized as the combination of plane-stretching deformation and bending deformation. And the study about the process parameters＇ impact on deformation shows that the process parameter of interlayer spacing is a dominant factor on the deformation. Decreasing interlayer spacing, the strain of one step decreases and the formability of blank will be improved. With bigger interlayer spacing, the plastic deformation zone increases and the forming force will be bigger.

Finite Element Simulation of Flexible Roll Forming with Supplemented Material Data and the Experimental Verification

Flexible roll forming is a promising manufacturing method for the production of variable cross section products. Considering the large plastic strain in this forming process which is much larger than that of uniform deformation phase of uniaxial tensile test, the widely adopted method of simulating the forming processes with non-supplemented material data from uniaxial tensile test will certainly lead to large error. To reduce this error, the material data is supplemented based on three constitutive models. Then a finite element model of a six passes flexible roll forming process is established based on the supplemented material data and the original material data from the uniaxial tensile test. The flexible roll forming experiment of a B pillar reinforcing plate is carried out to verify the proposed method. Final cross section shapes of the experimental and the simulated results are compared. It is shown that the simulation calculated with supplemented material data based on Swift model agrees well with the experimental results, while the simulation based on original material data could not predict the actual deformation accurately. The results indicate that this material supplement method is reliable and indispensible, and the simulation model can well reflect the real metal forming process. Detailed analysis of the distribution and history of plastic strain at different positions are performed. A new material data supplement method is proposed to tackle the problem which is ignored in other roll forming simulations, and thus the forming process simulation accuracy can be greatly improved.

Planar Weak Form Quadrature Beam Elements Based on Absolute Nodal Coordinate Formulation: A Structural Mechanics Approach

A planar nonlinear weak form quadrature beam element of arbitrary number of axial nodes is proposed on the basis of the absolute nodal coordinate formulation (ANCF). Elastic forces of the element are established through geometrically exact beam theory, resulting in good consistency with classical beam theory. Two examples with strong geometrical nonlinearity are presented to verify the effec-tiveness of the formulation.

Thermodynamic Modelling of Ore-Forming Mechanism of the Changkeng Gold-Silver Deposits in Guangdong Province

The Changkeng gold-silver deposits consist of a sediment-hosted, disseminated gold deposit and a replacement-type silver deposit. The mineralizations of gold and silver are zoned and closely related to the silicification of carbonate and clastic rocks, so that siliceous ores dominate in the deposit. The mineralizing temperature ranges mainly from 300 to 170℃, and K+, Na+, Ca2+, Mg2+, and Cl- are the major ions in the ore-forming fluid. Calculations of distribution of metal complexes show that gold is mainly transported by hydrosulphide complexes, but chloride complexes of silver, iron, lead, and zinc, which are transformed into hydroxyl and hydrosulphide complexes under neutral to weak-alkaline circumstances in the late stage, predominate in the ore-forming solutions. Water-rock interaction is confirmed to be the effective mechanism for the formation of silver ores by computer modelling of reaction of hydrothermal solution with carbonate rocks. The solubility analyses demonstrate that the precipitation of gold and silver-bearing minerals taking place under weak-acid conditions and near-neutral to weak-alkaline conditions, respectively, is the main or favourable factor for the ore zonation and separation between gold and silver.

APPLICATION OF INTEGRATION ALGORITHEMS FOR ELASTO-PLASTICITY CONSTITUTIVE MODEL FOR ANISOTROPIC SHEET MATERIALS

Two algorithms of computing stress increment by using the elasto-plasticity constitutive model are firstly formulated, which are the Euler integration method and the radial return method. Hill＇48 anisotropic yield criterion is used. The Euler integration method can not obtain more accurate computation of the stress increment as the radial return method unless enough subintervals are taken,by which the Euler integration method will take excessive computing time. Without docreasing any accuracy, the radial return method can save much time. Finally, a square cup deep drawing from NUMISHEET＇93 benchmarks is simulated with a self-developed code SheetForrn in order to investigate the accuracy and efficiency of the radial return method.

EFFECT OF VELOCITY ON DUCTILITY UNDER HIGH VELOCITY FORMING

The ring expansion procedures over various forming velocities are calculated with ANSYS software in order to show the effect of forming velocity on ductility of rate insensitive materials. Ring expansion procedures are simplified to one-dimensional tension by constraining the radial deformation, with element birth and death method, fracture problem of circular ring are considered. The calculated results show that for insensitive materials of 1060 aluminum and 3A21 aluminum alloy, fracture strain increases corresponding to the increase of forming velocity. This trend agrees well with experimental results, and indicates inertia is the key factor to affect ductility; With element birth and death methods, fracture problems can be solved effectively. Experimental studies on formability of tubular workpieces are also conducted, experimental results show that the formability of 1060 aluminum and 3A21 aluminum alloy under electromagnetic forming is higher than that under quasistatic forming, according to the characteristics of electromagnetic forming, the forming limit diasrams of the two materials tube are also built respectively, this is very important to promote the development of electromagnetic forming and guide the engineering practices.

PREDICTION OF MICROSTRUCTURE EVOLUTION DURING HOT EXPANDING-EXTRUSION FORMING OF RESTRAINING RINGS

A mathematic model for dynamic and static recrystallization of Mn18Cr18N steel is presented.Hot expanding extrusion forming and air cooling process of 600 MW retaining ring has been simulated by the combination of thermos coupled rigid viscoplasitic FEM with this model,and grain size distribution on cross section of ring is shown.The essential results can be provided for use of the new technique.

Microstructure evolution of laser solid forming of Ti-Al-V ternary system alloys from blended elemental powders

Morphology evolution of prior β grains of laser solid forming （LSF） Ti-xAl-yV （x 11,y 20） alloys from blended elemental powders is investigated. The formation mechanism of grain morphology is revealed by incorporating columnar to equiaxed transition （CET） mechanism during solidification. The morphology of prior β grains of LSF Ti-6Al-yV changes from columnar to equiaxed grains with increasing element V content from 4 to 20 wt.-%. This agrees well with CET theoretical prediction. Likewise, the grain morphology of LSF Ti-xAl-2V from blended elemental powders changes from large columnar to small equiaxed with increasing Al content from 2 to 11 wt.-%. The macro-morphologies of LSF Ti-8Al-2V and Ti-11Al-2V from blended elemental powders do not agree with CET predictions. This is caused by the increased disturbance effects of mixing enthalpy with increasing Al content, generated in the alloying process of Ti, Al, and V in the molten pool.

Effects of Mo Contents in Matrix on Microstructure and Properties of Vanadium Carbide Coating Formed by Thermal Diffusion Treatment

Thermal diffusion salt-bath vanadizing was finished for Crl2MoV die steel, in order to investigate the properties of vanadium carbide coatings related with the Mo contents in Crl2MoV die steel. Scanning electron micro- scopic observation reveals that Mo can decrease the growth rate of coating as a carbide forming element. Besides, Mo element can promote grain refinement of the coating. X-ray diffraction analysis shows that the different Mo contents have no influence on the phase structure of the coatings. Energy dispersive spectrum analysis and mechanical properties test show that Mo can diffuse into the coating and make a strengthening effect on the coating.

Research on deformation characteristics of JCOE forming in large diameter welding pipe

In the present work, the JCOE forming is inves- tigated using the finite element （FE） method. A two- dimensional FE model is established for the plane strain condition by FE code ABAQUS, and the FE model is vali- dated by experiments. The aim of this research is to inves- tigate forming quality states in the JCOE forming process; in particular, the effects of technological parameters on form- ing quality are evaluated. Taking the JCOE forming process of X80 steel φ1 219 mm × 22 mm × 12 000 mmwelding pipe for instance, the deformation characteristics of JCOE forming are analyzed, in which the geometry of the formed pipe, residual stress distributions and effects of process parameters on JCOE forming quality can be obtained. Thus, the presented results of this research provide an effective approach to improve welding pipe forming quality.

Vibration Analysis of Timoshenko Beams on a Nonlinear Elastic Foundation

The vibrations of beams on a nonlinear elastic foundation were analyzed considering the effects of transverse shear deformation and the rotational inertia of beams. A weak form quadrature element method （QEM） is used for the vibration analysis. The fundamental frequencies of beams are presented for various slenderness ratios and nonlinear foundation parameters for both slender and short beams. The results for slender beams compare well with finite element results. The analysis shows that the transverse shear deformation and the nonlinear foundation parameter significantly affect the fundamental frequency of the beams.