Modelling and simulation of contact force in cold rotary forging

Cold rotary forging is an advanced and complex metal forming technology with continuous local plastic deformation.Investigating the contact force between the dies and the workpiece has a great significance to improve the life of the dies in cold rotary forging.The purpose of this work is to reveal the contact force responses in cold rotary forging through the modelling and simulation.For this purpose,a 3D elastic-plastic dynamic explicit FE model of cold rotary forging is developed using the FE code ABAQUS/Explicit.Through the modelling and simulation,the distribution and evolution of the contact force in cold rotary forging is investigated in detail.The experiment has been conducted and the validity of the 3D FE model of cold rotary forging has been verified.The results show that: 1) The contact force distribution is complex and exhibits an obvious non-uniform characteristic in the radial and circumferential directions; 2) The maximum contact force between the upper die and the workpiece is much larger than that between the lower die and the workpiece; 3) The contact force evolution history is periodic and every period experiences three different stages; 4) The total normal contact force is much larger than the total shear contact force at any given time.

Influence of variables in deep drawing of AA 6061 sheet

Deep drawing is one of the most important processes for forming sheet metal parts.It is widely used for mass production of cup shapes in automobile,aerospace and packaging industries.Cup drawing,besides its importance as forming process,also serves as a basic test for the sheet metal formability.The effect of equipment and tooling parameters results in complex deformation mechanism.Existence of thickness variation in the formed part may cause stress concentration and may lead to acceleration of damage.Using TAGUCHI's signal-to-noise ratio,it is determined that the die shoulder radius has major influence followed by blank holder force and punch nose radius on the thickness distribution of the deep drawn cup of AA 6061 sheet.The optimum levels of the above three factors,for the most even wall thickness distribution,are found to be punch nose radius of 3 mm,die shoulder radius of 8 mm and blank holder force of 4 kN.

Simulation of bulk metal forming processes using one-step finite element approach based on deformation theory of plasticity

The bulk metal forming processes were simulated by using a one-step finite element(FE)approach based on deformation theory of plasticity,which enables rapid prediction of final workpiece configurations and stress/strain distributions.This approach was implemented to minimize the approximated plastic potential energy derived from the total plastic work and the equivalent external work in static equilibrium,for incompressibly rigid-plastic materials,by FE calculation based on the extremum work principle.The one-step forward simulations of compression and rolling processes were presented as examples,and the results were compared with those obtained by classical incremental FE simulation to verify the feasibility and validity of the proposed method.

Expression changes and roles of matrix metalloproteinases in a rat model of traumatic deep vein thrombosis

Objective：To study the expression changes of matrix metal loproteinases （MMPs） in traumatic deep vein thrombosis （TDVT） in a rat model with the aid of gene chip technology and to explore the roles of MMPs in TDVT.Methods：Totally 150 Sprague Dawley rats were randomly divided into control group （n=10） and model group （n=140）. Rat models of TDVT were established by clamping the femoral vein and fixing the bilateral hind limbs. Then fixation of the hip spica with plaster bandage was conducted.According to the observation phases and/or biological situations of the femoral vein thrombosis, the model rats were further divided into 7 groups. Vascular tissues were obtained from each group through noninvasive incision into the femoral vein at corresponding time points. We adopted the Trizoi one-step method for total RNA extraction,Affymetrix RAT 230 2.0 array for detection of RNA expressions and fold change （FC） analysis for changes of differential expressions of MMPs in each group. The main outcome parameters measured included expressions of MMP-2,MMP-3, MMP-7, MMP-8, MMP-9, MMP-10, MMP-11,MMP- 12, MMP-13, MMP- 14, MMP- 16, MMP-23 and MMP-24. Gene array data of these MMPs were analyzed by the Affymetrix Microarray Analysis software （Version 5.0）.Results：FC analysis showed differential expressions of MMPs in each group during the course of TDVT. At the initial period of thrombosis, MMP-2, MMP-3, MMP-7,MMP-8, MMP-9, MMP- 10, MMP-11, and MMP-24 had significantly high expression, while MMP-12, MMP-13,MMP-14, MMP-16 and MMP-23 had relatively low expression. MMPs were all highly expressed at the peak time of thrombosis. In the process of thrombus resolution,MMP-2, MMP-10, MMP-16 and MMP-24 have relatively low expression, while MMP-12, MMP-13, MMP-14,MMP-16 and MMP-23 have significantly high expression.Conclusion：MMPs may affect the process of TDVT through transcription regulation of the fibrinolysis-anti-fibrinolytic system during the course of thrombosis and thrombus resolution.