Welding method

A welding method of welding a first composite material and a second composite material, each of which contains a carbon fiber base material and a thermoplastic resin, the method comprising:

• a sheet disposition process of disposing a first protection sheet such that the first protection sheet comes into contact with a first bonding surface of the first composite material, disposing a second protection sheet such that the second protection sheet comes into contact with a second bonding surface of the second composite material, and disposing an energization sheet such that the energization sheet comes into contact with the first protection sheet and the second protection sheet;
• an electrode disposition process of disposing a pair of electrode portions such that the electrode portions come into contact with a pair of end portions of the energization sheet;
• and
• a welding process of applying a voltage to the pair of electrode portions and welding the first composite material and the second composite material,
• wherein each of the first protection sheet, the second protection sheet, and the energization sheet contains the carbon fiber base material oriented unidirectionally and the thermoplastic resin,
• the energization sheet contains only the carbon fiber base material oriented in a first predetermined direction connecting the pair of electrode portions,
• the first protection sheet and the second protection sheet contain only the carbon fiber base material oriented in a second predetermined direction that substantially perpendicularly intersects the first predetermined direction,
• the first protection sheet is disposed to be in direct contact with a first surface of the energization sheet, and
• the second protection sheet is disposed to be in direct contact with a second surface of the energization sheet,
• in the sheet deposition process, the first composite material is installed above the first protection sheet after bonding the first protection sheet, the second protection sheet, and the energization sheet to the second composite material by heating a part or all of the first protection sheet, the second protection sheet, and the energization sheet and heating the matrix resin contained therein to a temperature that is equal to or greater than the melting point.