Wire electric discharge machining apparatus and wire electric discharge machining method

A wire electric discharge machining apparatus, comprising a wire electrode, an upper guide assembly, and a lower guide assembly,

• wherein the upper guide assembly and the lower guide assembly are respectively provided above and below a workpiece, and the upper guide assembly comprises an upper wire guide, an upper power feed contact, and a power feed contact movement device,
• the lower guide assembly comprises a lower wire guide and a lower power feed contact,
• the wire electrode is guided by the upper wire guide and the lower wire guide and performs discharge machining on the workpiece,
• the upper power feed contact and the lower power feed contact are configured to contact the wire electrode to supply power to the wire electrode by moving in a horizontal direction from initial positions not contacting the wire electrode,
• the power feed contact movement device is configured to move the upper power feed contact in the horizontal direction from the initial position by a predetermined offset amount,
• the offset amount is set based on a machining condition, and
• the machining condition comprises at least one of a condition of the wire electrode, a condition of the workpiece, and a surface roughness required for a cut surface of the workpiece.