Wire electrical discharge machining apparatus, wire electrical discharge machining method, and wafer manufacturing method

A wire electrical discharge machining apparatus that generates electrical discharge between a plurality of cutting wire parts that are running and a workpiece to perform electrical discharge machining on the workpiece with energy generated by the electrical discharge, and simultaneously cuts out a plurality of wafers from the workpiece, the wire electrical discharge machining apparatus comprising:

• a wire electrode including the plurality of cutting wire parts spaced apart from each other in parallel and facing the workpiece;
• a machining power supply to generate electrical discharge between the plurality of cutting wire parts and the workpiece;
• a pair of machining fluid flow rectifying plates having conductivity connected to the machining power supply and provided in contact with both sides of the workpiece so as to sandwich the workpiece;
• a pair of nozzles in which the plurality of cutting wire parts are inserted, the pair of nozzles including a plurality of machining fluid ejection holes that eject a machining fluid toward a space sandwiched between the pair of machining fluid flow rectifying plates to supply the machining fluid to a gap between the plurality of cutting wire parts and the workpiece;
• a cutting feed stage to move the pair of machining fluid flow rectifying plates upward and downward relative to the plurality of cutting wire parts;
• a workpiece retaining unit to hold the workpiece to be divided during cutting from above the workpiece and the plurality of cutting wire parts;
• and
• a lower workpiece holding portion having conductivity to come into contact with the workpiece from below to hold the workpiece, wherein
• the pair of machining fluid flow rectifying plates comprises:
• a first machining fluid flow rectifying plate provided so as to be in contact with one end surface of the workpiece in a wire parallel direction that is a direction in which the cutting wire parts are disposed in parallel, and connected to the machining power supply;
• and
• a second machining fluid flow rectifying plate provided so as to be in contact with another end surface of the workpiece in the wire parallel direction,
• the lower workpiece holding portion is fixed to a facing surface of the first machining fluid flow rectifying plate, the facing surface being a surface of the first machining fluid flow rectifying plate facing the second machining fluid flow rectifying plate, and
• the lower workpiece holding portion comprises:
• a thin plate side surface holding portion provided over upper and lower regions of a machining end portion that is a portion where cutting of the workpiece by the cutting wire parts is completed in an upward and downward direction thereof and fixed to the first machining fluid flow rectifying plate in a state of being in contact with an outer peripheral side surface of the workpiece.