A manufacturing method of a steel bush is provided to reduce the defective rate and to simplify process flow because the final dimension of the steel bush can be obtained through the sizing process. A manufacturing method of a steel bush is as following steps: first piercing step (S1) which forms a first through-hole on the raw material; upsetting step(S2) which forms protrusion while adding pressure to the material and making the thickness of the thickness material fixed; second piercing step(S3) which forms a second through-hole on the material in relation to the first through-hole; burring step(S5) which expands the inner circumference of the second through-hole and extends the length of protrusion at the same time; sizing step(S6) which forms the final size of the steel bush; and trimming step(S7) which separates the steel bush from the material.
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