Statistical weld process monitoring with expert interpretation

A statistical weld process monitoring system is described. Using data of voltage, current, wire feed speed, gas flow rate, travel speed, and elapsed arc 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. For purposes of quality control, the control limits required for acceptance are specified in the weld procedure acceptance specifications. The control charts then provide quality assurance documentation for each weld. The statistical data trending analysis performed by the SPC program is not only valuable as a quality assurance monitoring and documentation system, it is also valuable in providing diagnostic assistance in troubleshooting equipment and material problems. Possible equipment/process problems are identified and matched with features of the SPC control charts. To aid in interpreting the voluminous statistical output generated by the SPC system, a large number of If-Then rules have been devised for providing computer-based expert advice for pinpointing problems based on out-of-limit variations of the control charts. The paper describes the SPC monitoring tool and the rule-based expert interpreter that has been developed for relating control chart trends to equipment/process problems.