Tempdb growing, however it has a lot of free space
What is the autogrow model for the TempDB files? Tiny increments will incur many small autogrowths whereas large increments will incur fewer, but more intensive, growth routines.

Presumably TempDB is growing because queries that are running on the server are constructing a lot of temporary tables, table variables, or cursors and so on?

Is it known what queries are running, and do you have historical baseline to compare the autogrowths and sizes to?

If things have suddenly changed, and the organisation has not grown the amount of actual data it uses significantly, I would guess that a developer or reporting user has changed the way in which they run their queries.

I think we need a bit more information from you, regarding the above.