Connecting structure for covered wires

A method of producing a connecting structure for covered wires, the method comprising the steps of:

• preparing a first covered wire having a first conductor covered with a first resinous cover and a second covered wire having a second conductor covered with a second resinous cover;
• preparing upper and lower resin tips, one of the upper and lower resin tips being provided, on an entire periphery of a butt thereof to be abutted against the other resin tip, with a projecting rim and the other of the upper and lower resin tips being provided, on an entire periphery of a butt face thereof to be abutted against the other resin tip, with a recessed rim;
• overlaying the second covered wire on the first covered wire cross each other;
• interposing respective overlapping portions of the first and second covered wires between the upper resin tip and the lower resin tip;
• integrating the upper and lower resin tips by engaging the projecting rim with the recessed rim;
• and
• oscillating the upper and lower resin tips with ultrasonic waves while compressing the upper and lower resin tips from the outside, whereby the first and second resinous covers of the first and second covered wires are molten for removal thereby to bring the first conductor of the first covered wire into electrical contact with the second conductor of the second covered wire and simultaneously, the upper and lower resin tips are mutually welded to each other thereby to seal up an area surrounding a contact between the first conductor and the second conductor.