| 摘要 |
PROBLEM TO BE SOLVED: To vary the chamfer dimensions and chamfer angles extending over the whole periphery of an opening edge part of a port and to easily obtain a sectional form of a curved surface such as a rounded shape or the like by applying chamfer working to the open edge part of the port by a non-contact working method. SOLUTION: Chamfer working for the opening edge part 8b of an exhaust port 8B is performed using a discharge machining electrode 20. In this case, by accumulation of discharge scars produced by high frequency pulse-like discharge current generated from the chamfer working surface 23, the opening edge part 8b is cut to form a chamfered part 10 of desired dimensions, angle and shape. Simultaneously, by accumulation of discharge scars caused by high frequency pulse-like discharge current generated from the coarse working surface 25, the inner peripheral surface of the exhaust port 8B heightens the diffusion effect of air-fuel mixture in a cylinder bore (combustion working chamber) to promote atomization of fuel. Further, a suitable roughened surface having projecting and recessed parts 10μm-30μm high for heightening the cooling effect of the cylinder is automatically formed.
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