Update ticket with values coming from the Account

Update ticket with values coming from the Account

When a ticket is created I'd like to update a Ticket's custom field with a valu coming from an Account custom field.

Something like that: 

When I a Ticket is created
Look for Account_Type  value (in Account) associated with the Ticket_Account (in ticket) 
Update Ticket_Account_Type (in ticket) with Account_Type value (in Account)

I was thinking about using a workflow rule, but I can only assign static value, not dynamic values...

I also looked at the custom functions but I'd a beginner and can't figure it out. Is it possible?