how often need to change the nozzle and lens for laser welding machine?

Razortek laser welding &cleaning machine with 10-20 pcs protect lens,1-2 pcs welding focus lens for standard .
some client ask how often to change the lens and nozzle.
Hanwei welding nozzle 

in fact, if the laser beam in center,the nozzle can not damage .so one box nozzle is enough. several days to change the protect lens, cleaning or change,
several month to change the focus lens,we can offer the spare parts with factory price.

Suplaser nozzle

welding focus lens

protect lens