SAFE GUARDING THE FRONT ZONE OF PRESS BRAKE

SUGGESTION FOR A PROCEDURE 

⒈Survey 

● Of all parts produced on the press brakes. 

● Of all the bends on each of the parts. 

●Of the bend sequence for each part to be produced. 

● Of the distance of the fingers from the dies for each bend in each part.

⒉Classification of parts The parts to be produced with the same characteristics must be grouped together. For example: 

● Parts that require that fingers be very close to the dies in order to put them between the dies or support them during bending. 

● Parts that require handling by more than one person (dimensions, stiffness, weight, etc.). 

● Thick parts. 

● Parts that can be produced in large or small lots. 

● Parts that will require removal from the side of the die after the bend is executed.

⒊Measurements and calculations of stopping times and distances of hydraulic power press brakes to be safeguarded (see appendices) 

⒋Standardization of the height of the dies in order to simplify safeguarding of the press brake (see part 5) 5. Choice of means of risk reduction by press brake, for all of the parts produced on it:

OPENING REDUCED TO 6 MM (Intrinsic prevention)

Description 

The danger zone opening reduced to 6 mm is one solution that eliminates the risk at source. With this configuration, there is no longer any risk of introducing a part of the body into this danger zone. 

Among the definitions of the opening reduced to 6 mm, we chose to retain the definition of the Centre technique des industries mécaniques (CETIM) and the INRS, which consider the distance between the point of the upper die and the top of the sheet to be bent (definition of the Safety point, page 6):

Advantages of the opening reduced to 6 mm

⒈Immediate solution that is easy to implement since it requires few or no changes to the press. 

⒉Inexpensive solution. 

⒊Protects everyone accessing the space between the dies. 

⒋Little training and very short adaptation time for operators. 

⒌Allows the sheet to be supported by the hands. 

⒍Complies with ROHS and CSA Z142-02 if correctly installed.

Modes of operation 

Opening reduced to 6 mm at all times 

Safeguarding the press brake by limiting the opening to 6 mm at all times is foreseeable when all the parts can be introduced and removed after the bend or bends have been made, despite this reduced opening. Intrinsically, this solution is the most effective; however, it remains limited to targeted production: thin sheet, single bend, etc.

Opening reduced to 6 mm in combination with another means of safeguarding One more flexible way of using the opening reduced to 6 mm is to associate it with a safety light curtain, a laser beam device or even a two-hand control device (see pages 13 and 27).

Constraints for the opening reduced to 6 mm AT ALL TIMES

⒈This procedure applies only if the two conditions below are met: - all the parts can be introduced with an opening reduced to 6 mm above the sheet, and - all the parts can be removed after bending with an opening reduced to 6 mm either by tipping to the front or by sliding to the side.

SAFETY LIGHT CURTAIN (Protective device for everyone located in the front zone) 

REMINDER The safeguarding offered by a safety light curtain is based on the safety distance, which is mainly a function of the ram’s stopping time. It is therefore essential that this stopping time be reliable and repeatable before considering using this means of safeguarding (see Appendix 8.A). 

Description 

The safety light curtain is an electro-sensitive protective device. It consists of a transmitter and a receiver. The transmitter sends small infrared light beams (separated at equal distances) to the receiver. The distance between two beams gives the resolution of a light curtain. If a body crosses one of the beams, a signal to stop or reverse the hazardous movement is given. The resolution of the safety light curtain should be chosen by taking into account the thickness and shape (simple or complex) of the material to be bent. 

The safety light curtain is minimally active during the hazardous phase of the cycle: approach phase of the ram until the opening is reduced to 6 mm.

Bending modes 

With a safety light curtain, a bend can be executed according to two methods described in this box, depending on whether the safety light curtain is obstructed or not, before the bend is executed. Obstruction can be due either to the part (thickness, perpendicular bend), or to the hand of the operator holding the sheet. 

Insertion of the sheet before descent of the table

Possible configurations during installation 

The safety light curtain can be configured horizontally or vertically. Sometimes these devices are installed obliquely (see page 28) or in combination (see page 29). 

Curtain positioning must comply with a certain number of criteria in order to avoid their being bypassed. These criteria are stated, for example, in clause 5.3.12.2 of standard EN12622: 2001.

In all cases, its positioning must comply with a safety distance that allows the hazardous movement to be stopped before the operator can reach the zone where this movement occurs. 

Information relating to the calculation of the safety distance for the vertical and horizontal positions is presented in this document’s appendix.

Options available on a safety light curtain 

In order to alleviate some production constraints, various operating options exist for a safety light curtain. dIMPORTANT When beam blanking is authorized or the curtain’s response time is changed, recalculation of the safety distance must be considered. 

Constraint: Permanent obstruction of beams before bending is executed. Solution: Fixed blanking and deactivation of the safety light curtain at an opening of 6 mm. When the safety light curtain is used in fixed blanking mode, only the beams that were programmed to be obstructed can be obstructed. If another beam is crossed, ram movement will be impossible. Constraint: Part with multiple bends that obstructs the curtain and that cannot be inserted at 6 mm, or even when blanking at 6 mm is not programmed or not programmable. Solution: Floating blanking. 

Note: This functionality increases the system’s response time and therefore the safety distance. When the floating blanking mode is chosen, a programmed number of beams out of all those in the curtain can be obstructed. If a higher number of beams is obstructed, ram movement will be impossible.

Constraint: Preventing the safety light curtain from systematically ordering the ram to stop when it is unnecessary. 

Solution: Multiple scanning. 

Note: This functionality increases the system’s response time and therefore the safety distance. When one of the beams is crossed, the protective device memorizes it. During the next scan, if the same beam is still crossed, the protective device orders the hazardous movement to stop or to be reversed. 

Constraint: Risk of optical interference during the use of two safety light curtains near each other. 

Solution: Beam coding. 

Some safety light curtains offer the possibility of beam coding. The transmitter sends a coded light pulse train that only its receiver can interpret.