WELDING JOURNAL 25 However, if an operator is not properly trained in the operation of a retraction feature, or if it’s not properly adjusted, additional pinch point dangers can result when the machine comes out of retraction. OSHA requires guarding against pinch point injury to be passive. This means that there can be no way to defeat the protection system and that safety of the welding machine cannot be dependent upon operator adjustments. Since the gap between electrodes can vary depending on the setup, at present the only way to meet this OSHA requirement is by use of a system called “Soft Touch.” Press-Type Resistance Welding Machines A vertical-action press-type spot welding machine can be operated much like a rocker arm and initiation with a shrouded foot switch is generally acceptable if both hands are used to hold the part being welded — Fig. 3. Again, using the Soft Touch system and/or reducing the gap between the tips to ¼ in. are recommended, as are adjustable and retractable stroke welding machine cylinders to make loading and unloading easier. Hand-loading projection welded nuts or weld studs exposes the operator to Fig. 1 — A growing trend is to completely guard the pinch point of a resistance welding machine. In addition to a physical enclosure, this vertical-action pedestal-type spot welding machine includes a light curtain to ensure that the operator’s hands are outside the pinch point area after loading the assembly to be welded into a tooling nest. When the operator initiates the machine with a foot switch, a door automatically closes the opening in the enclosure and shields the operator from weld flash. Fig. 2 — A — A rocker-arm spot welding machine with a prominently displayed pinch point warning sign; B — a close-up view of a warning sign. For info, go to www.aws.org/ad-index — continued from page 22 A B
Welding Journal | January 2014
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