Getting concentricity from centerless grinding 1

[robbiec]

We are manufacturing filament wound (fiberglass) tubes that require a +/- .001 OD and decent finish. In order to keep this product competetive we have had to switch from cylindrical grinding to centerless. This changeover took place 3 years ago and we have learned a lot about centerless grinding in that time.

Recently though we've been having a lot of concentricity issues. Our tolerances are typically .003 to .005 TIR but we've been seeing tubes come out up to .025 TIR.

Parts are run 1/8 to 3/8 above center line of wheels, typically on the top 1/3 of the blade - though we've been varying these in an attempt to clear up the TIR issues. Without luck.

We have not changed the wheels we purchase, and have not changed suppliers.

increasing/decreasing speed of the reg wheel does not seem to help.

The leading edge of the reg wheel is somewhat beat up, but I've been told this should have no effect (?!?)

Any ideas would be appreciated!

 

[BillPSU]

I believe your problem is in the unground tube. You are getting wall thickness variation in your feed tube. There was probably a change in process when filament winding or curing which is causing a problem.

 

[steveh]

By all means dress your reg wheel. It should be done regularly. A poor reg wheel dress is the cause of about 75% of geometry problems on centerless machines.

 

[waner]

hello mate,
we are currently running to sub micron manufacture using c/less technology,if you sure the rest blade hight is correct and the run-out of the control wheel is o.k check the programed plunge cut values....as the spimdle bearings wear the tir tends to increase,slow the infeed down a little on the initial approach/first cut as this doesnt load the wheel too quickly,may increase the cycle time a little,if this works increase the dressing amount/frequency to compensate then increase the infeed towards nominal....hope this helps

 

[sparkout]

Hello robbiec,

Helped a customer of ours setup their c-less to grind something similar to yours, are you infeeding or thrufeeding this part, whats the tir before grinding?
There is a possibility there is to much grinding pressure and you are distorting part in grinding process, also, it's always a good idea to keep your reg wheel cleaned up.