The present invention relates to a method for manufacturing a cage culture lower frame which is suitable for mass production and in which a net is more easily coupled, step； A main frame bending step of bending the main frame coupled with the first and second double pipes in a rectangular shape and welding the ends to each other； An elbow forming step of forming an elbow at a corner portion of the main frame by double injection； An intermediate frame joining step of joining a plurality of intermediate frames to the main frame between the second double pipes by welding； And a TiBe forming step of forming a TiBe by a double injection on a connecting portion between the main frame and the intermediate frame, wherein the TiBe forming step is performed by using a heater, A preheating step is added, and a second preheating step of raising the temperature of the connecting portion between the main frame and the intermediate frame is performed using a heater immediately before the TiBe forming step. The heater is composed of an upper cover and a lower cover formed in a vertically symmetrical configuration And heat is applied to the inside of the upper cover and the lower cover to apply heat to the surface of the metal main frame exposed to the outside.Therefore, according to the present invention, the main frame and the intermediate frame made of metal are completely sealed by the pipe made of synthetic resin, thereby preventing corrosion by seawater and extending the lifetime of the cage farm. In addition, since TiVo and elbow can be formed by double injection and heat fusion, manufacturing cost and manufacturing time can be saved, which is more economical and suitable for mass production.본 발명은 대량생산에 적합하며 그물의 결합이 더욱 용이한 가두리 양식용 하부틀의 제조방법에 관한 것으로, 일자형의 메인프레임 외측에 복수의 제1이중파이프 및 제2이중파이프를 결합하는 이중파이프 결합단계； 상기 제1이중파이프 및 제2이중파이프가 결합된 메인프레임을 사각형의 형상으로 절곡하고 끝단을 용접하여 결합하는 메인프레임 절곡단계； 상기 메인프레임의 모서리 부분에 엘보를 이중사출에 의해 성형하는 엘보 성형단계； 상기 제2이중파이프 사이의 메인프레임에 복수의 중간프레임을 용접에 의해 결합하는 중간프레임 결합단계
