Projections of different sizes that make simultaneous contact will heat at different rates, leading to overheating and expulsion. Projection size or shape: When welding using multiple projections, ensure that the projections are of the same size and shape. The final projection, when it makes contact, will do so under current, meaning that an arc will occur and lead to expulsion. An overheated projection or projections can expel material. The key variables to control: alignment, projection size and shape, force follow-up, and weld schedule.Īlignment: Weld pressure must force the projections into contact simultaneously and at the same pressure, otherwise one or more projections will carry most of the current and overheat. PW, like any RW process, if not performed properly can generate weld spatter or expulsion. Due to the multitude of nut-and-bolt designs, users and standard-writing groups have not been able to collect the necessary data to form a consensus and develop a standard.Ĭan a Projection Weld Cause Spatter or Expulsion?Īnother example of projection welding-threaded spuds welded to a tank head. However, I am not aware of a standard for nut-and-bolt welding. Considering that nut-and-bolt welding comprises a large percentage of PW, it would seem that standards might be available. Several sources exist for PW schedules, some included in industrial standards and literature. Where Can I Find Weld Schedules/Parameters for Projection Welding (PW)? to form a point of contact), a weld forms at the crossing location. Note: In the case of cross-wire welding (two round wires placed together at 90 deg. The hot projections then collapse as the weld nugget forms. When the mating parts come together, the projections concentrate the current flow and generate heat in these locations. In most applications, one of the workpiece surfaces features multiple, small, formed projections-round dimples, elongated ridges or rings, or the extended corners of weld nuts. What is a Projection Weld? Projection welds developed via the resistance welding (RW) process use the design or shape of the part to make discreet individual-point contacts to concentrate the current during welding. The hot projections then collapse as the weld nuggets form. Projections (shown here on a nut) concentrate current flow and generate heat in these locations. Projection Welding-Facts and Fundamentals February 27, 2020
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