Surface Contact calc

[Dabble]

Hello all I am designing some tooling that will have a 7.938 spherical radius going into a 8mm concave radius. Is there any way Alibre can tell me what the amount of surface contact will be ?

 

[OTE_TheMissile]

Well, in the CAD world, placing a smaller sphere inside a larger arc results in a single infinitely small point of contact, since CAD assumes all "material" to be completely rigid... :?

 

[cclark440]

As stated before placing a smaller sphere into a larger sphere, there will only ever be a single contact point.

 

[Dabble]

Any way of determining how large of an area wil be contacting? LOl sorry if not making any sense I will post a picture of model and maybe you can see what information I am looking for.

 

[MilesH]

As the others said, for Alibre the spheres will have single point contact. The "surfaces" will be perfectly smooth and uniform and there will be no deformation from gravitational force! So, the answer to your question is that, in Alibre, the area of contact will be infinitely small :wink:

 

[Dabble]

Oh Ok I think I get it lol. The tooling I was speaking of is an Electrode used in resitence welding My ball spherical radius is 7.938 mm I am trying to come up with the best possible surface contact I can get ( most surface covered) from electrode to ball bearing without having to make a special ball end mill to do the job. Previously we were using a 5/8" ball end mill which is approx 15.875 mm I am trying to decide if it will change my surface contact area enough to go a 16 mm end mill. There are other factors involved of course like the depth that we are inserting the ball mill and the angle we are cutting on the outside of the electrode. So I may have not been asking my question correctly in the first place.
Thanks for all the help. I will still upload the picture to binaries so you can get a look at what I am doing and maybe someone could suggest some type of similation software I could use.

 

[MilesH]

Maybe carry on with the 5/8" and use the ball bearing as a hone?

 

[Dabble]

Duh, I did a cad drawing of it and it finally got through my thick tired skull guess I couldnt see the forest through the trees.

 

[Dabble]

Maybe carry on with the 5/8" and use the ball bearing as a hone?

Thats not a bad idea we farm these out to an outside vendor but you did give me an idea maybe load the bearing and electrode into a press (electrode is c17510) and force the electrode to conform to the bearing surface. Maybe aplly certain amount of pressure for a certain lenggth of time.

 

[indesign]

Or you could always have someone like me grind a ball endmill to what you want. :wink:

 

[RobtHoyt]

Oh Ok I think I get it lol. The tooling I was speaking of is an Electrode used in resitence welding My ball spherical radius is 7.938 mm I am trying to come up with the best possible surface contact I can get ( most surface covered) from electrode to ball bearing without having to make a special ball end mill to do the job. Previously we were using a 5/8" ball end mill which is approx 15.875 mm I am trying to decide if it will change my surface contact area enough to go a 16 mm end mill. There are other factors involved of course like the depth that we are inserting the ball mill and the angle we are cutting on the outside of the electrode. So I may have not been asking my question correctly in the first place.
Thanks for all the help. I will still upload the picture to binaries so you can get a look at what I am doing and maybe someone could suggest some type of similation software I could use.

Classic hand calculations are from Hertz, and will give both contact area and stresses due to elastic deformations. Theoretical contact between rigid surfaces would be a point, but the loaded elastic reality is a spot, larger if the diameters are nearly identical. See Formulas for Stress and Strain by Roark (in the Seventh edition, Chapter 14, case 1c for formulas and appropriate coefficients, but any of the editions will have this, In the Fouth edition it is in a different chapter). Similar equations exist for cylindrical line contact, or contact between two cylinders. FEA software like FEM Designer should also work with Alibre models.