Carriage assembly with asymmetrical swage bosses and associated methods

A carriage assembly for a hard disk drive, the carriage assembly comprising:

• a head stack assembly comprising a carriage arm, the carriage arm comprising a carriage-arm tip that comprises a swaging hole centered about a swaging axis and passing through the carriage-arm tip from a first side of the carriage-arm tip to a second side of the carriage-arm tip that is opposite the first side;
• a first head-gimbal assembly, comprising a tension baseplate on the first side of the carriage-arm tip and comprising a tension swage boss located within the swaging hole, wherein the tension swage boss is annular, is centered about the swaging axis, has a tension-boss inner diameter, and has a tension-boss outer diameter;
• and
• a second head-gimbal assembly, comprising a compression baseplate on the second side of the carriage-arm tip and comprising a compression swage boss located within the swaging hole and spaced apart from the tension swage boss along the swaging axis, wherein the compression swage boss is annular, is centered about the swaging axis, has a compression-boss inner diameter, and has a compression-boss outer diameter;
• wherein:
• the tension swage boss comprises an uppercut that extends radially outward, away from the swage axis, from a first backbore diameter to a second backbore diameter and has an uppercut depth, in a direction parallel to the swaging axis;
• and
• the compression swage boss is asymmetrical relative to the tension swage boss.

A method of coupling a head-gimbal assembly to a carriage arm, the method comprising:

• positioning a tension baseplate of a first head-gimbal assembly on a carriage-arm tip of a carriage arm such that a tension swage boss is located within a swaging hole, on the carriage-arm tip and concentric with a swaging axis of the swaging hole;
• positioning a compression baseplate of a second head-gimbal assembly on a carriage arm tip of a carriage arm such that the carriage arm tip is sandwiched between the tension baseplate and the compression baseplate, a compression swage boss located within the swaging hole and concentric with the swaging axis of the swaging hole and the compression swage boss spaced apart from the tension swage boss along the swaging axis;
• and
• inserting a swaging ball axially through the swaging hole in an insertion direction and plastically deforming the tension swage boss and the compression swage boss to form an interference fit between an outer periphery of the tension swage boss against an inner periphery of the swaging hole and an interference fit between an outer periphery of the compression swage boss against the inner periphery of the swaging hole.
• wherein:
• the tension swage boss comprises an uppercut extending radially outward, away from the swaging axis, from a first backbore diameter to a second backbore diameter and has an uppercut depth, in a direction parallel to the swaging axis;
• and
• the compression swage boss is asymmetrical relative to the tension swage boss.