The withdrawal kanban is typically used to pull material from a Material warehouse to a production warehouse/location. If no onhand exists on that warehouse and the default order type of that warehouse is purchase + the planning principle is "requirement" then the withdrawal kanban will trigger purchase order/purchase line 1:1, which is the closes correspondence of a purchase kanban that AX Standard can support. 

(Only eBECS has an ISV add-on for Purchase Kanbans, that has improved the purchase handling.)

And another big problem in Standard AX is more in the direction of communicating the requirements automatically with the vendor and have the vendor maybe print out the kanban cards and supply the goods properly packed and sorted etc...

Purchase Kanban would make most sense in combination with some Vendor portal functionality or when using a Kanban EDI Message, that allows the Vendor to deliver with specific paperwork.