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ANSYS/LS-Dyna Analysis of a Valve Actuator for Stanley Bostitch

     

Stanley Bostitch was designing a new valve actuator for their next generation of pneumatic power tools.  However, early tests indicated a problem with valve timing, showing inadequate opening times at the desired frequency.  Engineers at Stanley Bostitch needed a design tool that would allow them to quickly evaluate the effects of changes to the geometry, material, o-rings, and spring stiffness on valve timing.  They had determined that testing alone could not provide the insight and rapid turnaround they needed.  CAE Associates was asked to develop the design tool, which they hoped would help them to improve valve timing without adversely affecting other critical design criteria.

CAE Associates chose to develop this tool using the ANSYS/LS-Dyna software because of its strengths in modeling high speed transient contact events.  The tool consisted of axisymmetric models of the valve, including contacting parts, springs, and o-rings (Figure 1).  The models featured complex pressure-time loads, Mooney-Rivlin material models for the rubber o-rings, and multi-body contact.  A static phase was included for preloading the o-rings and the springs.  Model results showed realistic kinematic behavior and valve timing (Figure 2) that agreed with their test results.

Stanley Bostitch was able to use the models to evaluate modifications to their valve design.  Ultimately, the models showed that they could not get the desired valve timing with their current design, which was supported by test results.  However, the models provided very useful information regarding the damping effect of the o-rings and the striker geometry which they could not readily obtain through testing.  This information proved invaluable in designing the final valve which was incorporated into their latest generation of pneumatic power tools.