I had knee replacement 6 weeks ago. Since that time, I have periods of profuse sweating that go into chills. I do not have a fever.?

See your doctor asap. The concern would be that you have developed what we would call a "subacute" infection -- which might involve the replaced knee or surrounding bone, but could potentially even involve the heart. You should see your primary care physician first, and you may need to see your orthopedist as well.
Possible infection. Any time a recent post-op patient experiences chills/sweating, even in the absence of fever, the primary concern is the possibility of infection. I would definitely advise evaluation by your surgeon.