Page 49 - MetalForming-Feb-2018-issue

G—This vertical light curtain includes a remote segment protect- ing the area between the curtain and the press. Note the heavy- duty brackets and how the light-curtain elements are protected from damage during die loading; the side panels that prevent reach into the hazard behind the curtain; and how the height of the curtain prevents reach over the top or from underneath.
using the prescribed formula. Often stampers will use the edge of the bolster as a default for this line of hazard, which makes it easy to monitor—any tool that fits inside of the bolster complies with the guarding. In applications where the tooling never extends to the edge, though, it is acceptable to define the line accordingly.
Production Issues and the MOS
Too often, even when stampers factor in the stop time and brake-monitor setting, they fail to sufficiently consider production issues that may require the MOS to increase. To correctly apply light curtains, stampers must examine all of the factors required for production. For example, the work- piece material must be brought to the point of operation, and the stamped parts, as well as the scrap from punching and trimming, must exit the point of operation. The guarding must account for these actions.
The biggest mistake we see stampers make when it comes to compromising guarding is failing to factor in the need to allow scrap to escape the die area. For most presses, scrap exits the rear of the press. For example, without giving careful thought to scrap egress, a stamper might have to raise the light curtain (photo A) to allow the scrap to exit, compro- mising the guarding. Photo B illustrates a similar scenario, where the stamper installed the light curtain without con- sidering scrap egress and has blocked a very large section of the curtain to allow room for the scrap bin and for the scrap to exit, compromising the guarding. Photo C shows a similar arrangement.
An excellent option that allows proper scrap egress while continuing to protect operators is the use of a guarding zone (photos D-E). Here, physical barriers prevent access
to the hazard except through the opening between them, and light curtains scan across the opening to prevent human entry without blocking the lights. The lights are set up with manual-reset fault logic. Once interrupted, even for a moment, the lights remain in fault condition even when unblocked; an operator must use a key to reset the lights and allow the machine to run.
The next biggest offender we see in the field: improper guarding of the press where the parts exit. The opening through the guarding—whether a light curtain or physical barrier—must be large enough to allow the parts to escape. Referring again to Photo B, the stamper has adjusted the opening at the exit end of the straightside press to allow for part egress, which, unfortunately also allows an easy reach into the hazard through the window. Similarly, on gap presses, the part often exits on the side opposite the feed, which creates a similar hazard.
Cause and Solution
The underlying cause for these types of part-egress issues often traces back to using gravity to move parts away from the tooling. This necessitates an aggressive slope to the part chute that requires the stamper to locate the opening in the guard very close to the hazard. Developing a solution, the stamper must first determine the required opening; the larger the opening the further it must be from the hazard (refer to OSHA standard 1910.217 Table O). In a practical sense, the opening must be far enough away from the hazard to prevent an operator from reaching through the opening into the hazard. This, however, may result in the opening being too far away to use a chute and gravity to move parts out. The answer: Use conveyors to remove parts from the tool and through the guarding.
With a gap press, this may require additional barrier guarding extending out from the machine frame, and then forward to the front light (photo F). With a straightside, the stamper might have to add a fabricated-sheetmetal tunnel that extends out from the frame so that the opening can be located far enough away from the hazard to ensure safety (photos E and G).
Preventing Reach-In
The last issue to address involves preventing operators from reaching around the light curtain or moving between the curtain and the hazard when the light curtain has been positioned away from the press. Additional safeguarding is required, such as installing an additional section of light curtain that fills the area between the vertical curtain and the hazard. In Photo G we see side panels installed to prevent reaching around behind the curtain. And, additional sections of light curtain have been added.
Fortunately, when stampers diligently consider the issues outlined here when designing a press-guarding scheme, they will enjoy optimum productivity without sacrificing safety. MF
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