Rotary friction welding

A joining method for joining a first steel member and a second steel member through a joining metal, said method based on rotational friction, said method comprising:

• positioning said first steel member and said second steel member at neighboring positions with an end surface of said first steel member and an end surface of said second steel member opposing each other;
• manufacturing a void which straddles the end surface of said first steel member and the end surface of said second steel member, said void having a rotational axis, said void also having a side peripheral surface and having a bottom and a rotationally symmetrical shape;
• inserting the joining metal into said void, said joining metal having a rotationally symmetrical body;
• generating friction by rotating said joining metal around said rotational axis with a contact portion between a tip of said joining metal and said bottom of said void under a pressing force;
• generating molten metal near said contact portion by utilizing frictional heat from said friction;
• filling said molten metal into a gap between said peripheral surface of said joining metal and said peripheral surface of said void by utilizing said pressing force and rotational motion generated at the tip of said joining metal;
• and
• subsequently stopping said rotational motion, thus allowing said molten metal to become solidified and be integrated with the steel members near said gap, thus joining said first steel member and said second steel member.

A joining method for joining a first steel member and a second steel member through a joining metal, said method based on rotational friction, said method comprising:

• positioning said first steel member and said second steel member at neighboring positions with a back surface of said first steel member and a front surface of said second steel member opposing each other;
• manufacturing a void which has a side peripheral surface and a bottom and a rotationally symmetrical shape in line with a straight line running through a back surface of said first steel member and a front surface of said second steel member, said void having a rotational axis;
• inserting the joining metal into said void, said joining metal having a rotationally symmetrical body;
• generating friction by rotating said joining metal around said rotational axis with a contact portion between a tip of said joining metal and said bottom of said void under a pressing force;
• generating molten metal near said contact portion by utilizing frictional heat from said friction;
• filling said molten metal into a gap between said peripheral surface of said joining metal and said peripheral surface of said void by utilizing said pressing force and rotational motion generated at the tip of said joining metal;
• and
• subsequently stopping said rotational motion, thus allowing said molten metal to become solidified and be integrated with the steel members near said gap, thus joining said first steel member and said second steel member.

A joint structure of steel members joined by rotational friction, wherein said steel members are joined by a method comprising the following:

• positioning a first steel member and a second steel member at neighboring positions with a surface of said first steel member and a surface of said second steel member opposing each other;
• manufacturing a void which has a side peripheral surface and a bottom and a rotationally symmetrical shape, said void having a rotational axis;
• inserting the joining metal into said void, said joining metal having a rotationally symmetrical body;
• generating friction by rotating said joining metal around said rotational axis with a contact portion between a tip of said joining metal and said bottom of said void under a pressing force;
• generating molten metal near said contact portion by utilizing frictional heat from said friction;
• filling said molten metal into a gap between said peripheral surface of said joining metal and said peripheral surface of said void by utilizing said pressing force and rotational motion generated at the tip of said joining metal;
• and
• subsequently stopping said rotational motion, thus allowing said molten metal to become solidified and joining said first steel member with said second steel member.