Water pump and manufacturing method thereof

A water pump comprising:

• a motor housing having a shape of a container with an open upper side;
• a lower casing disposed on the upper side of the motor housing, and including a rotor accommodating part that protrudes downward and has a rotor accommodating space concave downward from an upper surface thereof, and a first side wall protruding downward along a circumference thereof for a lower end of the first side wall to be in contact with an upper end of the motor housing;
• and
• an upper casing disposed on an upper side of the lower casing to be fitted to the outside of the lower casing, having an impeller accommodating space formed therein together with the lower casing, and including a second side wall protruding downward along a circumference thereof for a lower end of the second side wall to be in contact with the upper end of the motor housing,
• wherein the upper end of the motor housing, the lower end of the first side wall, and the lower end of the second side wall are fusion-coupled with one another,
• the motor housing has a concave insertion groove positioned along a circumference of the upper end,
• the lower end of the first side wall and the lower end of the second side wall are inserted into the insertion groove,
• the motor housing is made of a laser-transmitting material,
• the lower casing or the upper casing is made of a laser-absorbing material, and
• the part where the insertion groove, the first side wall, and the second side wall are all adjacent to one another is fused to form a fused part.