A method for welding parts formed of polymeric resins having different melt-index grades. The method may include the steps of selecting a tube formed of a first thermoplastic in an extrusion process, selecting a first flange formed of a second thermoplastic in an injection molding process and having a containment region sized to receive an end of the tube, inserting an end of the tube within the containment region of the first flange, and welding the tube to the flange by inducing relative rotation between the flange and the tube. The containment region may have a depth more than two times the wall thickness of the tube. Moreover, the containment region may maintain its shape and support friction pressure on a significant portion of melted material within the weld zone, so the material may continue to generate heat and conduct the same to the less easily melted material.