Semi-conformable pressure application system and method for joining composite parts

A method for fusing at least two thermoplastic composite components together, the method comprising:

• placing a first thermoplastic composite component comprising a first faying surface and a first non-faying surface onto a second thermoplastic composite component comprising a second faying surface such that the first faying surface and the second faying surface contact each other, wherein the first and second thermoplastic composite components each comprise conductive fibers and a first matrix material;
• placing a separation layer over and against at least a portion of one or both of the first thermoplastic composite component and the second thermoplastic composite component;
• placing a multi-layer composite pressure pad over and in contact with the separation layer, the multi-layer composite pressure pad comprising:
• a first layer having non-conductive reinforcement and a second matrix material with a melting point that is the same or lower than a melting point of the first matrix material of the first and the second thermoplastic composite components, wherein at least a portion of the first layer contacts the separation layer, and
• a second layer having non-conductive fibers and a third matrix material with a melting point that is greater than the melting point of the first matrix material of the first and the second thermoplastic composite components, wherein the first layer is between the second layer and the separation layer;
• and
• placing an activated inductor against the second layer of the multi-layer composite pressure pad, wherein the activated inductor induction welds the first faying surface to the second faying surface.

A method for step-welding at least two thermoplastic composite components together, the method comprising:

• placing a first thermoplastic composite component comprising a first faying surface and a first non-faying surface onto a second thermoplastic composite component comprising a second faying surface such that the first faying surface and the second faying surface contact each other, wherein the first and second thermoplastic composite components each comprise conductive fibers and a first matrix material;
• placing a separation layer over and against at least a portion of one or both of the first thermoplastic composite component and the second thermoplastic composite component, wherein the separation layer is a release film;
• placing a multi-layer composite pressure pad over and in contact with the separation layer, the multi-layer composite pressure pad comprising:
• a first layer having non-conductive fibers and a second matrix material with a melting point that is the same or lower than a melting point of the first matrix material, wherein at least a portion of the first layer contacts the separation layer, and
• a second layer having non-conductive fibers and a third matrix material with a melting point that is greater than the melting point of the first matrix material, wherein the first layer is between the second layer and the separation layer;
• and
• placing an activated inductor against the second layer of the multi-layer composite pressure pad, wherein the activated inductor induction welds the first faying surface to the second faying surface via induction welding, wherein the separation layer has a higher melting point that the first matrix material and the second matrix material.