Statistical process control application to weld process

A statistical weld process monitoring system is described, Using data (voltage, current, wire feed speed, gas flow rate, travel speed, and elapsed arf time) collected while welding, the welding statistical process control (SPC) tool provides weld process quality control by implementing techniques of data trending analysis, tolerance analysis, and sequential analysis, The SPC system computes the mean, standard deviation, and range of each of the parameters sampled by the data collection system, Changes in the mean, standard deviation, and range are displayed using control (or trend) charts, The control chart displays a function of a parameter with respect to the ordering of the weld records (for a single weld) or weld number (for multiple welds), The SPC tool also permits plotting tolerance charts of the mean, standard deviation, and range for each of the sampled parameters, The tolerance chart is plotted versus the record number (or weld number) and consists of a vertical line for each record (or weld number) showing the minimum and maximum value of that parameter for that record (or weld number). The upper control limit (UCL), lower control limit (LCL), and nominal value may also be displayed on the tolerance chart printout, The SPC also performs sequential analysis, which allows the user to examine the process as it goes along, which ire turn may permit the user to locate a possible change in the process before it goes out of control, Sequential analysis makes use of the running average and running standard deviation. Simply stated, tide mean and standard deviation are constantly being updated as new values are read into the list, By examining each new value versus the accumulated information concerning previous values, a determination can be made of any suspect nature of the weld just completed, Work directed toward developing an expert interpreter of the voluminous statistical output generated by the SPC is also described.