Resistance Welding Keep It Safe

If you target resistance welding as a way to boost profits, make sure you practice the value-added operation safely.

  • Pinch-point risk is a common operator risk around resistance welding in the absence of necessary safety practices or provisions.
  • Several pinch-point risks exist, including weld cylinders, clamps, moveable tooling and production parts.
  • The most common risk in most machines comes from the welding electrodes.
  • Weld electrodes come together with a very high force and are clamped against a body part, especially with pointed electrodes, that force can crush bone.
  • To minimize the risk, set the electrodes 1⁄2 in. or closer to the part in the separated state, for part load or unload. This helps prohibit fingers or hands from becoming pinched between the electrodes.
  • Once the weld cycle starts, in many machines it cannot be interrupted.
  • Should something foreign accidentally become pinched between the electrodes, the weld cycle continues until it completes. Are you looking for welding companies in Brisbane? You can contact Kennedywelding.com.au. If a body part has been partially pinned during an initial weld-gun closure, the operator’s first reaction may be to immediately step off of the foot pedal or release the palm button, to try to release the pressure.
  • In those types of machines, the pressure will continue to rise, aggravating the injury, until the weld cycle completes.

Warning about Older Weld Controls

  • Some older welding controls might still be running without electromechanical relays or other suitable pinch-point control features. As a result, they are susceptible to false, uninitiated weldgun or other pinch-point closure.
  • The presence of such a control should be examined with the suspicion that it may increase pinch-point risk and require correction.
  • If an operator ever sees an uninitiated electrode or pinch-point closure, he should seek immediate assistance.
  • Maintenance should confirm that the electrical pinch-point control connections meet electrical code.
  • These connections usually involve electromechanical relays for pinch-point control, and proper electrical grounding.
  • Maintenance personnel should consult with the manufacturer of the welding control or the machine.
  • Electrical codes and specifications identify common methods of inhibiting false initiation or unwanted electrode closure during operator loading or unloading.

Pinch from Power Up or Down

  • Powering up or powering down any energy source to a resistance-welding machine can initiate a pinch-point hazard or inhibit a pinch-point safety function.
  • When the air is left off, the operator initiates the machine, and the platen does not move. Then someone turns the air on. When the pressure builds, the platen closes. In some cases this can happen even if the initiation button or pedal no longer is depressed. If the operator’s hands are in a pinch point, the operator could be injured from the delay in the closing of the platen.
  • Unexpected and dangerous machine functions that can cause pinch, bump or pinning risk can occur from any of the following:
    • Electrical power on or off.
    • Weld-control power on or off.
    • Machine-sequence control power on or off.
    • Machine air pressure on or off.
    • Cooling water on or off.
    • Hydraulic pressure on or off.

Stored Energy an Immediate Risk

  • An unexpected release of energy and a pinch point can occur during power-up or -down from the storage of any energy source. Examples include:
    • A heavy platen or tool lifted above the floor may settle.
    • A surge tank filled with air pressure may bleed down, closing a platen.
    • Any mechanical spring compressed from a mechanical action, as well as an air or hydraulic cylinder action, can release, closing a platen or weld gun.
  • Experienced personnel pay close attention to pinch points when any of the energy sources of a resistance-welding machine power up or down.
  • In many machines a greater risk is the energy release some time after power switches on or off.
  • Not all machines make unexpected moves; many can become unpredictable with the removal or connection of an energy source.
  • Some resistance-welding machines automatically lift the electrode or platen when any fault occurs. Some machines will hang up mid-cycle from a fault.
  • Resetting the control or circuit breaker may be necessary to lift the electrode or platen. In some machines, that reset can initiate other functions that could add risk.
  • A pinned body part between the electrodes may cause a weld control fault and a breakdown stop.

Out-of-Reach Safety Controls Require Two People Present

  • Circuit breakers or controller resets are remote from the operator job location.
  • Many times, manufacturing shops require the presence of two or more people in a production area.
  • Previous descriptions of risks included pinching from power on or off; that same set of risks also applies to getting bumped or pinned from tooling or parts transfer with power on or off. If parts are suspended or shuttled due to the presence of an energy source, they can fall upon removal of the energy source.

Robot Hazards

  • In addition to automation, more resistance welding is done today using industrial robots for part loading or unloading, or for handling of portable weld guns.
  • Any operator that gets close to moving robots, presses or transfer lines should create a mental exercise that includes planning an escape route in case of a run-away, buckle or anything else that could invade the work area.
  • Robot run-away is especially dangerous since a malfunctioning robot may be able to reach beyond its programmed work zone.
  • It could enter an operator’s work zone and collide with the operator. Things break with moving automation. Unforeseen events can occur.
  • Failing to take the necessary safety precautions for entering the press—energy removal and lockout— he moved the part and the press cycled, with fatal results.

 

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