Stainless steel hollow balls can be divided into hollow balls without openings and hollow balls with openings. Hollow balls without openings are to punch the steel plate into two hemispheres with cold extruding and weld together. Hollow balls with openings are to punch the steel plate into the cup bottom with cold extruding and close up, there are no welds in this way. Of course, the closing method can be rolling and can also be cold extruding. The upper mold is concave spherical, making it more efficiently and regularly. First, the material has to be calculated. Finally, there must be follow-up processing to achieve the final requirements.