Is there a function in DB2 as400 that masks a string or number?

Is there a function in DB2 as400 that masks a string or number?
in exemple,
I have the NUMBER= 20120821

I would like a function: masks( NUMBER, '9999-99-99') that returns a string = 2012-08-21

This because I have a field decimal 8,0 (YYYYMMDD, ISO)
and I have to traslate it in a date field

Thanks

Release as400 V5R4M0