A method for joining a cover layer to an object in a continuous joining process using mechanical vibration energy and a joining material based on a thermoplastic polymer being liquefied or at least plasticized with the aid of the mechanical vibration energy, the method comprising the steps of: providing the cover layer and the object, the cover layer and the object each comprising a contact surface, the two contact surfaces facing each other in a joint to be established, and the joining material being arranged to constitute at least part of one of the two contact surfaces, arranging the cover layer and the object with the contact surface of the cover layer and the contact surface of the object facing each other, bringing the contact surface of the cover layer in contact with the contact surface of the object, preheating the joining material in a contactless manner, pressing the cover layer against the object and applying mechanical vibration energy to an outer surface of the cover layer for a time sufficient for liquefaction or at least plastification and possibly dislocation of the joining material, consolidating the liquefied or plasticized and possibly dislocated joining material by stopping application of the mechanical vibration energy and still pressing the cover layer against the object for a time sufficient for the joining material to re-solidify, wherein the method further comprises a step of providing a susceptor or absorber being one of integrated in the joining material, being arranged or arrangeable in the vicinity of the joining material, and being constituted by the thermoplastic polymer base of the joining material, and wherein the step of preheating comprises exciting the susceptor or absorber with electromagnetic energy and heating the joining material by electric or magnetic induction, characterized in that the preheating of the joining material is carried out for a time sufficient for raising the temperature of the joining material to above its glass transition temperature at least, in that the step of pressing and applying mechanical vibration energy is carried out after the step of preheating, and in that the method comprises a step of conveying the cover layer and object in a continuous manner in a conveying direction throughout the steps of arranging, of bringing into contact, of subjecting to preheating, of pressing and applying vibration energy, and of consolidating. providing the cover layer and the object, the cover layer and the object each comprising a contact surface, the two contact surfaces facing each other in a joint to be established, and the joining material being arranged to constitute at least part of one of the two contact surfaces, arranging the cover layer and the object with the contact surface of the cover layer and the contact surface of the object facing each other, bringing the contact surface of the cover layer in contact with the contact surface of the object, preheating the joining material in a contactless manner, pressing the cover layer against the object and applying mechanical vibration energy to an outer surface of the cover layer for a time sufficient for liquefaction or at least plastification and possibly dislocation of the joining material, consolidating the liquefied or plasticized and possibly dislocated joining material by stopping application of the mechanical vibration energy and still pressing the cover layer against the object for a time sufficient for the joining material to re-solidify, wherein the method further comprises a step of providing a susceptor or absorber being one of integrated in the joining material, being arranged or arrangeable in the vicinity of the joining material, and being constituted by the thermoplastic polymer base of the joining material, and wherein the step of preheating comprises exciting the susceptor or absorber with electromagnetic energy and heating the joining material by electric or magnetic induction, characterized in that the preheating of the joining material is carried out for a time sufficient for raising the temperature of the joining material to above its glass transition temperature at least, in that the step of pressing and applying mechanical vibration energy is carried out after the step of preheating, and in that the method comprises a step of conveying the cover layer and object in a continuous manner in a conveying direction throughout the steps of arranging, of bringing into contact, of subjecting to preheating, of pressing and applying vibration energy, and of consolidating.