Projection Welding
Questions and Answers
A weld schedule is an instruction to set up a resistance welder for a specific job. It includes all of the specific settings of the machine, control settings, tools, electrodes, forces, times, rates and all other pertinent data related to a job. It also includes the information about the part itself including material, thickness, number of welds, weld locations, quality requirements, and precleaning. This information is stored and can be used to set up the job on it’s next run. It also can be used as a ground zero if parameters have changed and you want to go back to where you started.
Electrodes are available in many sizes and shapes to fit most needs in industry. To choose many considerations come to mind. The first decision would be full size vs cap electrode. Are you a job shop or highly automated usually decides this.
All spot welding electrodes mushroom during use and when this happens the resultant weld eventually is unacceptable. Before this happens most operations either dress or change the electrode to get the face back to original operating conditions.
EXTREME MUSHROOMING
Back up electrodes are used for projection welding electrodes. They are normally used on the lower side and are flat faced. There is no need for a defined weld face since the projection concentrates the weld current and heat into a desired spot for nugget creation.
Some resistance welding applications call out forces above the limits of tapered electrodes. The RWMA Manual Fig 18.3 shows force vs taper. It shows that above 2400 Lbs force tapers are not viable. Above this force specially designed High Pressure/High Force Electrodes must be used. These electrodes can be straight shanks, threaded or flanged electrodes. They are available from several manufacturers. Contact your electrode supplier for assistance.
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