3DDave
Aerospace
- May 23, 2013
- 11,183
In this article:
is the observation that It would be much more convenient if the part could be inspected in the free state, and then have the data compensated to reflect the proper restrained condition."
I've mentioned before that a huge blind spot for Dimensioning and Tolerancing is that it doesn't seem to involve the stress engineering group. The suggestion "Perhaps the point cloud gathered by the CMM or other 3D metrology device could be processed to “unbend” and “untwist” it, to simulate the deformation that would occur if the part was physically restrained." isn't likely to directly produce a usable result.
One could feed in the offsets from the ideal mating condition as forced displacements into an FEA analysis of the part and from that gain the resulting offsets due to strain of all the features of interest; their displacements would be in the opposite direction of those the actual part will see, assuming the displacements are small enough to retain linearity. Since the restrained condition should not require plastic deformation of the part, this assumption seems reasonable.
It's possible that an integration with a FEA modeler that would generate the stiffness matrix and the CMM that would measure the displacement and an intermediary software that would find the minimum displacements to satisfy the constrained condition could be made - with the ridiculously cheap memory and CPUs available now it's not a stretch to think this could be a near real time operation. A further refinement of the notion is that RFS features could be analyzed against their mating boundaries to estimate contact pressure and deformation of surrounding material as a free-floating constraint.
is the observation that It would be much more convenient if the part could be inspected in the free state, and then have the data compensated to reflect the proper restrained condition."
I've mentioned before that a huge blind spot for Dimensioning and Tolerancing is that it doesn't seem to involve the stress engineering group. The suggestion "Perhaps the point cloud gathered by the CMM or other 3D metrology device could be processed to “unbend” and “untwist” it, to simulate the deformation that would occur if the part was physically restrained." isn't likely to directly produce a usable result.
One could feed in the offsets from the ideal mating condition as forced displacements into an FEA analysis of the part and from that gain the resulting offsets due to strain of all the features of interest; their displacements would be in the opposite direction of those the actual part will see, assuming the displacements are small enough to retain linearity. Since the restrained condition should not require plastic deformation of the part, this assumption seems reasonable.
It's possible that an integration with a FEA modeler that would generate the stiffness matrix and the CMM that would measure the displacement and an intermediary software that would find the minimum displacements to satisfy the constrained condition could be made - with the ridiculously cheap memory and CPUs available now it's not a stretch to think this could be a near real time operation. A further refinement of the notion is that RFS features could be analyzed against their mating boundaries to estimate contact pressure and deformation of surrounding material as a free-floating constraint.