Method for forming a sound attenuation structure provided with s-shaped cells

A method for manufacturing an acoustic resonator panel for an aircraft propulsion assembly nacelle, the acoustic panel including adjoining acoustic cells which form a cellular center, each cell extending along an axis of acoustic propagation of sound waves and including inside the cell, at least one partial obstacle which extends transversely with respect to the acoustic propagation axis and which forms an internal passage off-center with respect to a center of the cell to increase a length of a path traveled by the sound waves through the cell,

• the method for manufacturing the acoustic panel comprising:
• a step of forming at least one perforated metal sheet according to a regular pattern to form said internal passages, a center of each internal passage being separated from a center of the adjacent internal passages by a distance corresponding to the width of the acoustic cells, and each internal passage having a size smaller than the size of each acoustic cell measured in a plane perpendicular to a main direction, the main direction being parallel to the acoustic propagation axis,
• a step of stacking, in the main direction, a plurality of cellular cores made of thermoplastic resin and at least one of said at least one perforated metal sheet, two successive cellular cores being separated by one of said at least one perforated metal sheet, each cellular core including a plurality of honeycomb cells joined in a plane orthogonal to the main direction and forming, in combination with adjoining cellular cores on either side of said at least one perforated metal sheet, corresponding portions of said adjoining acoustic cells of said cellular center in the main direction, and each honeycomb cell of a cellular core facing one of said internal passages of said perforated metal sheet, said one internal passage and a central axis of the honeycomb cell not being aligned in the main direction,
• a compaction step during which a compaction pressure is applied in the main direction on either side of the stack obtained following the stacking step,
• and a thermoplastic welding step carried out while maintaining the compacting pressure.