A punch unit associable with a respective punch holder of a punching machine to form a punch assembly comprises a punch tip holder mountable on the respective punch holder and a punch tip housed in, and connected to, the punch tip holder in an assembled configuration; the punch tip holder includes a connecting element coupled to the punch tip; an adapter element shaped and sized so as to be inserted and housed in the respective punch holder and provided with an inner cavity suitable to house the connecting element with the punch tip in the assembled configuration; a locking device housed in the adapter element, which can be operated manually without tools and arranged for locking or unlocking the connecting element with the punch tip to or from the adapter element.