Abstract: Preimpregnated thermoplastic yarn is interwoven around spaced hex mandrels as weft members in a preformed ribbon, which may be folded into layers or cut into sheets for stacking in a honeycomb pattern in preparation for bonding. In block bonding, pressure and heat are applied to an entire fully stacked block to bond the interface facets together and form hex ducts around the mandrels, which must then be extracted, typically individually in a special pneumatic press process. In a preferred layer bonding process certain problems and limitations of block bonding are overcome by bonding each sheet as it is added to a stack buildup. An alternate layer bonding process is disclosed, which is facilitated by magnetic pressing, using electromagnets acting on ferrous mandrels to apply pressure evenly distributed along interfacial facets during thermal fusion bonding. The magnetically pressed layer bonding process is readily automated by disclosed apparatus. Heating and cooling are provided to the mandrels.