Oasys LS-DYNA Environment 8.1 VOLUME 3 ... - Oasys Software

Oasys LS-DYNA Environment: User Guide (Version 8.1)
17.0 SHEET METAL FORMING SIMULATIONS
LS-DYNA has been used extensively for sheet metal forming simulation for many years. The
solver includes many features specifically for simulating manufacture by draw die, although
many other sheet metal processes such as tubular hydro forming, fluid cell forming, roll forming
and superplastic forming can also be simulated. The goal in any such simulation is to confirm
that the proposed manufacturing process will give a successful end result, thereby reducing press
try out time and hence producing cost savings. An efficient modelling strategy is required to
achieve an effective contribution to production operations. The following notes are intended to
draw attention to some of the features of LS-DYNA which should be considered when setting
up a draw die simulation.
SEQUENCE OF OPERATIONS
The complete sequence would be:
` gravity wrap
` blank holder closure or wrap
` forming operation (stretch, draw, flange, etc)
` trimming
` springback
Multiple draw operations can be simulated by looping this sequence. It is often preferable to
conduct each of these phases as separate calculations with restarts used to move to the next
phase; this allows parameters to be set up optimally for each operation.
In previous versions of LS-DYNA, two options were available for calculating springback after
forming; dynamic relaxation or output of a file for submission to LS-NIKE3D (using the
*INTERFACE_SPRINGBACK keyword). These methods have now been superseded by the
addition of the implicit solver options within LS-DYNA itself. The implicit mode can be
activated in two ways. A simulation can be run entirely in implicit mode using the
*CONTROL_IMPLICIT_GENERAL keyword; the input file for this can be automatically
created by LS-DYNA at the end of the forming phase using the
*INTERFACE_SPRINGBACK_DYNA3D keyword. Alternatively an explicit simulation may
be seamlessly switched into implicit mode at a specific time using the
*INTERFACE_SPRINGBACK_SEAMLESS keyword. Several other *CONTROL_IMPLICIT
keywords have been added to LS-DYNA to control the implicit analysis; default values have
been carefully selected to minimise user input.
The implicit analysis capability within LS-DYNA also now allows it to be used for the gravity
wrap and blankholder wrap stages of the forming sequence, allowing more efficient and more
accurate calculation of these quasi-static stages.
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