Controls & Transformers
Questions and Answers
Weld schedules are available in the Resistance Welding Manual and AWS Standard C1.1 for many of the most frequently used materials. The information commonly provided is the proper electrode design, size and material. The weld force, weld time and weld current are also published. The minimum distance between welds is usually listed and the expected nugget or button size is shown. Tensile properties frequently are also published. Other sources are the Tuffaloy and CMW Catalogs.
A weld schedule is an instruction to set up a resistance welder for a given 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, 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 when the job started.
Force is the "P" in PCT - Pressure Current and Time.The Force component of a weld schedule is required to hold the two work pieces being welded together during the welding operation. This prevents any arcing due to the parts being loose. If not held tightly molten material would be expelled during the weld operation. It also provides a forging action as the weld solidifies and cools. This forging action greatly improves the final weld strength.
AIR CYLINDER
When welding galvanized and other coated materials a layer of oxides and brass builds up on the face of the electrode. During the first twenty five to fifty welds while this layer builds up and develops equilibrium, the welding results can be inconsistent. This period is called conditioning.
EXTREME MUSHROOMING
When a job is set up properly and the electrodes and water cooling are maintained it is still possible to have weld variation during a production day. It is very common that the line voltage at most production plants can vary during the day because of the demand on the Utility Company. The problem could be your feed to your plant or the Utility Company's main grid. It also could be overloaded power buses within the facility.
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