Robotics

Any kind of welder will do.

A stick welder will do and would be the best technique to learn first, but requires you to cleanup every weld.

A MIG is the easiest as it's almost like holding a metal glue gun, but proper welds require some practice.

A TIG welder is in my opinion the most peaceful technique, but requires the most amount of practice.

If it's for production runs of multiple gym equipment, MIG is the fastest technique.

Get whatever suits your price range and practice, practice

Thanks for your kind information, Well currently we are using the stick welding so that we are facing the complaints of blow holes, spatters and etc.

co2 MIG welding robot

Proper application of the process chosen is more important than the process itself. As stated, any of the weld processes will work. The results you are getting are most likely due to some deficiency present in the process you have in place. Pinholes and excess spatter can be a sign of cleanliness of the base metals, improper electrode selection, poor weld technique, or any combination of the above.