Point contact constraint

[DaSalo]

Hello,
First time posting to this forum. I am an experienced unigraphics/NX user who has very recently taken a job at a company that uses CATIA V5R20. So far the adjustment has been relatively painless but there are a few things that I used to do all the time with NX (and solidworks before that) that I can not seem to find anyway to accomplish with CATIA. Any help as to how to think about this problem or workflow differently to better adapt to CATIA would be very welcome:

- I work with molded parts composed of all freeform surfaces. The tooling for these parts almost always uses a 6 point nest for location. Occasionally we will get a tool from another shop that is really not what it is supposed to be and we need to reverse engineer the datum structure to figure out exactly where the gage points would touch on a nominal part. In NX I would simply take the CMM inspection data for the fixture, move the gage points in the model to the actual locations as determined by the CMM, and then create point contact constraints between the spherical surfaces of the gage points and the part surfaces. 6 constraints and the part is fully constrained in the nest. Then I can create intersection points at the points of contact for each gage point and I have my new datum structure.

In CATIA it does not seem possible to create a point contact constraint between a spherical surface and a freeform surface. I am totally at a loss as to how I can constrain the part into the nest and determine the exact contact points. This is a 10 minute job in NX and I have been struggling for many hours now trying to figure out some way to accomplish this. I'm pretty convinced that this can't really be done using assembly constraints so I am wondering if there are tools in the kinematics module or some other module that might be helpful. Any advice would be very much appreciated.

Thanks in advance!

NX 7.5.5.4 mp01, NX 8.0.1.5
Tecnomatix Quality 8.0.1.3
PC-DMIS 2011 MR1

 

[itsmyjob]

An offset surface of that freeform surafce should pass by the center of the spherical surface.

There are other ways but too complex for a quick answer.

Eric N.
indocti discant et ament meminisse periti ​

 

[cadddict]

I would create a part that represents a sphere.Create an intersection curve passing through the centre plane, then Add a point using the extrenum feature in gsd.
Next I would place points on the freeform surface part wherever the gauge points would touch.
Then in assembly use a coincidence constaraint between the points created on the sphere and freeform surface.

 

[DaSalo]

"Next I would place points on the freeform surface part wherever the gauge points would touch."

This is the root of the problem. I don't know where the gage points will contact the freeform surfaces. That is what I need to figure out. This task is very easy if the contact points are known, as when designing a tool from scratch based on a defined datum structure. I simply create points on the part surfaces at the defined datum locations. Then I create lines that use the datum points as their endpoints, are normal to the part surfaces, and are the length of the sphere radius. Now the endpoint of the line that is hanging out in space is equal to the center of the spherical surface of the gage point so I can use a point-to-point coincidence constraint.

The difficulty is going at this from the other end. I know where the gage points are but I do not know exactly how the part will fit into the existing nest and exactly where the gage points will contact the part. I need to be able to constrain the part into in the nest so that it has exact single point contact on each of the 6 spherical surfaces and then I can determine exactly where those points of contact are.

"An offset surface of that freeform surface should pass by the center of the spherical surface."

This might work. So you are suggesting that I create an offset surface the distance of the sphere radius and then use a point-to-surface coincidence constraint? I'll try that when I get to work.

Thanks for the help! I'm sure I'll have plenty more questions in the coming weeks.

CATIA V5 R20
PC-DMIS 2011 MR1

 

[DaSalo]

"An offset surface of that freeform surface should pass by the center of the spherical surface."
This did not work for me. As far as I can tell there is no way to create any kind of assembly constraint between a point and a freeform surface.

CATIA V5 R20
PC-DMIS 2011 MR1