Press brake/shear: blanking & muting
Application limits and safety notes. This guide explains how blanking and muting are applied to safety light curtains on press brakes and shears. It focuses on what these functions permit, the hard limits you must not cross, and the records auditors expect (distance math, timing proof, wiring evidence).
Start with the safety light curtain selection range to identify documented device capabilities, then apply the specific press-brake or shear requirements. A punch-press application rule is not automatically a rule for a press brake or a guillotine.
Content updated: 2026-09-05.
1) Plain-language definitions
Blanking (masking beams)
- Fixed blanking: accommodate a defined obstruction using the device's supported configuration and presence-monitoring rules. Guard residual openings if the object is removed or moves.
- Floating blanking: permit only the interruptions specified for the selected mode. Reassess effective detection capability and safety distance; the permitted beam count alone is not a body-part safety limit.
- Partial dynamic blanking: is a model-specific capability, not a standard feature on every curtain. Require the documented profile limits and validation method.
Muting (temporary bypass)
- Automatically and temporarily suppress the protective function under specific, safe conditions (e.g., sheet feed).
- Requires a documented safety-related implementation, permitted initiation and termination conditions, fault behavior and any required status indication. Sensor number and layout are application-specific.
- Ends or enters the documented safe fault response when permitted conditions no longer hold. Recovery or override, if supported, needs its own controlled procedure; reset must not cause unexpected motion.
2) What’s allowed — and what isn’t
| Topic | Allowed | Not allowed |
|---|---|---|
| Blanking scope | An explicitly supported mode with documented effective detection capability and controlled residual openings. | A masked route through which a person can reach the hazard; hiding contamination or alignment faults. |
| Muting logic | A documented safety-rated function with machine-specific conditions and validated access prevention. | A generic two-sensor sequence or timer used to suppress protection during hazardous closing. |
| Reset behavior | The approved reset and restart interlock, with required monitoring and visibility of the safeguarded area. | Clearing a beam or an ordinary PLC reset bit causing unexpected hazardous motion. |
| Records | Approved mode parameters, effective detection capability, full stopping-time evidence, access assessment and validation results. | Undocumented changes or treating a photograph as proof of stopping performance. |
3) Press brake specifics (bending)
Typical use
- Workpieces can interrupt a front field during bending. Use only a supported blanking arrangement with residual access controlled.
- A closing-stroke mute requires the machine-specific approved conditions, which can include validated position and speed functions. Elapsed time or material presence alone is insufficient.
- Assess tooling, backgauge and workpiece movement, side/rear access and reflections as separate hazards.
Hard checks
- Validate the complete sensing-to-hazard-stop chain, including the machine's motion and stopping elements.
- Confirm the selected protective arrangement is applicable to this press brake and operating mode, not merely to a conveyor.
- Verify transitions into and out of suppression, faults and restart without exposing a person to the closing tools.
HSE's inspection guidance includes machine-specific mute checks and distinguishes bending from using power-press tooling. It is not permission to invent a general timer threshold. OSHA's press-brake interpretation addresses safeguarding under 1910.212; do not silently substitute mechanical-power-press rules.
4) Shear specifics (guillotine/plate)
- Assess the blade, hold-down clamps, stock handling and rear discharge separately; an entry curtain does not contain ejected material.
- Where a supported blanking mode accommodates a support or stock path, verify remaining openings and effective detection capability.
- Continuous feed is not automatic authorization for muting. Use a machine-specific validated arrangement that prevents a person reaching the blade or clamps.
- Rear guards, interlocks or appropriately rated presence detection require their own protective function and safe restart design; an emergency-stop circuit does not replace guarding.
5) Safety distance & timing inputs
Distance worksheet (copy)
Machine and task: press brake / shear; applicable rules and manual revision = ?
Safeguard mode and effective detection capability (mm) = ?
Worst-case total detection-to-hazard-stop time (s) = ?
Measurement start/end points = ?; missing sequential delays = ?
Avoid omitting machine stopping time or double-counting measured stages.
Applicable ISO 13855:2024 geometry / approach / additional distances = ?
Required distance and actual minimum distance (mm) = ?
Reach-over / under / around / presence behind field / reflective surfaces = ?
Configuration approval and validation record = ?Timing notes
- Measure worst-case hazard stopping performance using an approved method and competent personnel. A relay drop-out trace alone omits continuing machine motion.
- Derive any time limits from the approved function and operating envelope; also validate the required position, speed, access and fault conditions. A short timeout alone does not establish safety.
6) Logic review examples (non-executable checklists)
Blanking configuration review
REVIEW CHECKLIST — not control logic
[ ] Ordered device supports the selected blanking mode.
[ ] Obstruction movement/removal behavior matches its manual.
[ ] All residual access gaps are prevented.
[ ] Effective detection capability and distance are recalculated.
[ ] Configuration changes are controlled and revalidated.
Any missing evidence -> HOLD release; do not create a PLC bypass.Machine-specific muting review
REVIEW CHECKLIST — not a muting function block
[ ] Machine-specific suppression conditions are approved.
[ ] Safety-related position/speed/state inputs are validated where required.
[ ] A person cannot access the hazard during the permitted interval.
[ ] Entry / exit / timeout / invalid sequence / recovery are defined.
[ ] Required indication and restart behavior are tested.
Conveyor sensor count alone does not authorize a bending-stroke mute.These are evidence checklists, not PLC code or a certified function block. Do not combine raw OSSDs in ordinary logic or generate a protective bypass from these items. Use the exact manufacturer-approved safety implementation.
7) Commissioning & periodic tests
Commissioning
- Verify the documented power, protective earthing, safety input interface and required final-element monitoring using an approved safe test procedure. Do not hold a contactor on a live machine.
- Record distance worksheet and photos of mounting/angles.
- Validate the approved suppression conditions, indication, invalid sequence or state, timeout and safe recovery.
Periodic tests at the required interval
- With hazardous motion prevented, use the exact specified test piece across the entire field and boundaries. Establish intervals from the manuals and applicable inspection requirements.
- Test supported fault cases and recovery under controlled conditions, including prevention of unexpected restart.
- Review logs for parameter changes; seal critical settings.
Test log (CSV copy)
Item,Test,Expected,Actual,Result,Notes
1,Required final-element monitoring,Approved safe fault test prevents unsafe restart,,,
2,Blanking configuration,Documented mode and residual-access controls verified,,,
3,Muting conditions,Approved machine-state limits and indication verified,,,
4,Muting faults and recovery,Documented safe response without unexpected restart,,,
5,Distance and full stopping chain,Applicable method and measured limits satisfied,,,
Frequently asked questions
Can blanking create a pass-through opening for material and hands?
No. Blanking must not create an unprotected route to the hazard. For fixed blanking, follow the manual's obstruction monitoring and guard any residual openings. Floating blanking can change effective detection capability and the required safety distance; use the exact mode's documented limits rather than assuming beam pitch equals detection capability.
What's the minimum logic for muting?
There is no universal two-sensor recipe. The exact device, safety controller and machine application must support and validate the function, conditions, timing, termination, indication and fault recovery. Conveyor material-detection logic must not be copied into a press-brake closing stroke; machine-specific safeguarding conditions govern.
Do I still need EDM when using blanking or muting?
Blanking and muting do not remove any required final-element monitoring or restart protection. The design may use documented EDM feedback or another approved monitoring architecture. Do not assume every system has K1/K2 contactors or that an ordinary PLC can perform the safety reset.
General application references: IEC 62046:2026 and ISO 13855:2024. The selected device manual and machine-specific requirements remain essential.
8) Common mistakes & corrective review
| Mistake | Symptom | Fix |
|---|---|---|
| Unassessed blanking opening | Reach-through or reduced detection capability | Stop use; reassess mode, residual guards and distance before revalidation. |
| Conveyor muting copied to a press | Hazardous closing stroke becomes unprotected | Use the machine-specific approved safeguarding design; sensor count is not acceptance. |
| Missing required indication | Safeguard suppression is not properly indicated | Restore the indication and any monitoring required by the exact system. |
| Ordinary PLC used for safety reset | Restart protection is not validated | Implement approved reset logic in the safety system; use separate auxiliary status for diagnostics. |