Safe use of machinery factsheets : Power presses machine guarding
Improper use of mechanical power presses cause a large number of workplace amputations. Crushing injuries and fractures to the fingers, hands and arms are also common injuries.
Power Presses are machines that shear, punch, form, or assemble metal or other material by means of tools or dies attached to slides. Power presses can be mechanical, hydraulic or pneumatic. In mechanical power presses, tools and dies are mounted on a slide or ram, and move away from the stationary bed containing the lower die. The upper and lower dies press together to punch, shear or form the work piece.
Employers have a legal responsibility under the Health and Safety in Employment Act 1992 to provide a safe working environment and this includes the safe use of machinery. Under Regulation 17 of the HSE Act’s 1995 Regulations, provision must be made for the safe cleaning, maintenance and repair of machinery. This includes guarding, lockout mechanisms, and a training programme for safe work procedures.
Types of Power Presses
A full revolution (positive clutch) power press once activated, cannot be stopped until it completes the press cycle - lowering and raising of the slide or ram. Presence-sensing devices will not work on these machines, and operators must be protected by fixed guards or mechanical interlock guards during the entire press operating cycle.
A part revolution or the friction clutch power press can be disengaged at any time before it completes the down stroke, and can be guarded with presence-sensing devices.
Power Press Hazards
- Trapping by the tool and die;
- Trapping by other moving parts of the machinery;
- Projectile hazards from tool failure;
- Entanglement by rotating parts.
- Use of the closed tool method (enclosed tool);
- Fit with emergency stops;
- Adequate training and supervision of operators;
- Reduced force of the press;
- Increased clearance to remove pinch point;
- Automated material handing or robots.
Two-handed controls may be suitable as a backup safety system, but cannot be used as a replacement for other more effective guarding systems.
Mechanical power presses
During operation, ensure that the interlock guard is locked in a closed position without any gaps for access, and remains locked until the crankshaft has completed at least one revolution and stopped.
Provide an anti-free fall device, independent of the normal cyclical working of the friction brake, on the press to prevent involuntary descent of the ram, and/or any other slide due to over-run or fall-back of the crankshaft or by gravity.
Ensure the power press is suitably guarded to prevent access. Fit the machine with an interlock safety device to ensure the machine stops when the guard is lifted.
Presence-sensing devices can only be used on hydraulic power presses that are designed and constructed to meet the requirements of the relevant standards that are listed in this factsheet.
Provide mechanical back-up protection for an electrical interlock. If this is not practicable, use two independent electrical circuits and monitor regularly.
Anti-free fall devices to prevent ram free-fall should also be provided where this is a hazard.
Maintenance and Servicing
- Power presses and their safety systems should be inspected and checked daily.
- Carry out regular maintenance as per the manufacturer’s instructions
- Establish a safe die-setting procedure using an inch or jog safety device together with lockout/tag out procedures.
- Guards must be in place before testing the press’s automatic mode.
- Use energy control precautions - safety blocks or lock-out the disconnect switch. An inch or jog device will not provide protection for gravity fall of the slide/ram.
Common Guarding Mistakes
- Using a guard with excessive opening size.
- Two-hand controls that are mounted within the safety distance of the press without any other guarding.
- The machine can be started before the interlocked guard is fully engaged.
- Interrupted feeding rhythm and operator’s hands are placed in the danger area while riding the foot pedal.
- Mechanical failure of linkages, electrical control relay, and components.
- Using normally open switches that can be overridden by the operator.
- Ineffective lock-out/tag-out procedures during maintenance.
Available at www.standards.com.au
AS 4024.3001-2009 Safety of Machinery –Material Forming and Shearing – Mechanical Power Presses
AS 4024.3002-2009 Safety of Machinery –Material Forming and Shearing – Hydraulic Power Presses
AS4024.2601-2008 Safety of Machinery-Design of Controls, Interlocks and Guarding-Two Hand Control Devices-Functional Aspects and Design Principles
AS 1219 - -1994 Power Presses Safety requirements
Excessive opening size in fixed frontal guard leading to accident
Mechanical power press guarded with hinged interlock guard and anti-free fall device
References and Further Reading
- Machinery - Guidelines for Guarding Principles and General Safety for (Department of Labour, 1995)
- Machine Guarding - The Ergonomics of (Department of Labour, 1979)
- Electrical Interlocking for Safety in Industrial Processes - Guidance Notes for (Department of Labour, 1994)
The Department of Labour would like to acknowledge the Victorian WorkCover Authority (WorkSafe Victoria) for allowing the reproduction of their material in this Guidance Sheet. Further information can be obtained at www.worksafe.vic.gov.au.
Note: This material is also only intended to provide general advice and does not constitute legal advice. You should make your own judgement about action you may need to take to ensure you have complied with your workplace health and safety obligations under the law.