|
The purpose of this thesis is to use the model of elasto-
plastic incremental finite element to analyze the influence of
manufacturing parameters in axisymmetric sheet stretching and
drawing process. The formulation of this CAE system is based on
ULF (updated Lagrangian formulation). A special feature is to
extend the r_{min} method, which is used to determine the punch
increment, to the judgement of the element elasto-plastic
transient, contact or separation of the node at tool-metal
interface, and the confinement of maximum element strain and
rotation. The Coulomb friction model is modified to calculate
the friction coefficients at the interface of die and nodal.
The fractured thickness of speciment in tension experiment is
adopted as the criterion of fracture. That is, if the sheet-
thickness of the stretching or drawing process is less than
this value, then the fracture of material in this region will
happen. Using the simulation of finite element method, the data
of the whole deformation history of stretching and drawing can
be obtained. The data includes diagrams in deformation stages,
relations of punch and stroke, thickness variation of sheet and
limit of fracture. The simulation results agree with the
results from experimental tests. This verifies the reliability
and accuracy of finite element program developed in this
thesis. In the drawing process, the following conclusions cab
be also obtained: (1) The formability of solid lubricant (Zinc
Stearate) is better than liquid lubricant (press oil). (2) From
the analysis of five different radii (R=4.8 mm, 8.0 mm, 10.0
mm, 12.0 mm, 14.0 mm), it can be found that the larger die-
radius the better formability. (3) In the three different die-
punch clearances (c=1.04t, c=1.15t, c=1.22t), the formability
of c=1.15t is the best. The same results can be obtained in the
experimental tests.
|