Patent ID: 8093526

Claim:
A wire electric discharge machine that generates an electric discharge between a wire electrode and a workpiece by application of a voltage thereby machining the workpiece, the wire electric discharge machine comprising: the wire electrode which moves with respect to the workpiece; a machining power supply which supplies a machining current between the wire electrode and the workpiece; a power feed contact comprising a first power feed contact and a second power feed contact that respectively feed power by contacting the wire electrode at at least two points, said points are on lower and upper sides of the workpiece which is positioned between the at least two points; a first machining-current loop comprising the machining power supply, the first power feed contact, the wire electrode, and the workpiece, where in the first machining-current loop, a first machining current of the machining current flows from the first power feed contact toward the workpiece; a second machining-current loop comprising the machining power supply, the second power feed contact, the wire electrode, and the workpiece, and where in the second machining-current loop, a second machining current of the machining current flows from the second power feed contact toward the workpiece; an impedance switching circuit positioned in one of the first machining-current loop and the second machining-current loop, where the impedance switching circuit has a variable impedance; and a control unit which controls a flow ratio of the first machining current and the second machining current by changing the impedance of the impedance switching circuit the control unit controls such that the first machining current is substantially equal to the second machining current when making a difference between a machining dimension on a side of the first power feed contact and a machining dimension on a side of the second power feed contact small, the first machining current is smaller than the second machining current when making the machining dimension on the side of the first power feed contact greater than the machining dimension on the side of the second power feed contact, and the first machining current is greater than the second machining current when making the machining dimension on the side of the first power feed contact smaller than the machining dimension on the side of the second power feed contact.