Quick Mold Change (QMC) magnetic work holders improve mold changeover times but require process engineers to apply them within their safe operating limits.
In the quest for reducing mold or die changeover times, molders have sought to obtain efficiencies in the clamping process by using magnetic work holders in lieu of manually operated or semi-automated mechanical clamps. But to apply Quick Mold Change magnets effectively, molders need to integrate them into their processes within widely accepted guidelines.
General Guidelines for QMC Magnet Applications
In general, QMC magnets have been safely and efficiently applied in thermoplastic injection molding where (1) the press size is over 50 tons, (2) the mold base operating temperatures do not exceed 250 degrees F, (3) the daylight of the press allows for the thickness of the magnets, (4) variable mold sizes are produced, (5) there’s need for failsafe operation, (6) the fast switching of the work holder is required, and (7) there’s uniform holding force over the entire mold base surface.
All technologies have limitations and Quick Mold Change magnets are no different. But knowing their limitations can allow molders to engineer their processes in a manner to work around these limitations. Maximum operating temperatures during the molding process is an important limitation because some rare-earth magnet materials are affected by excessively high temperatures. In cases where resin is used in the non-magnetic areas between the magnetic poles, high temperatures can cause the resin to expand above the pole surface, which can reduce holding force.
Another limitation is the maximum holding force. In the event that a press generates a force greater than the clamp force, the mold will move. During most operating conditions, QMC magnets have more than adequate clamping force; however, certain dynamic conditions can cause overloads. These include over packing the mold, applying excessive nozzle force, and over-stroked ejector rods.
Other Guidelines for Safe Application of QMC Magnets
Other factors to consider for the safe application of QMC magnets include:
Maximum Operating Temperatures: The grade and type of the raw magnet material determines over temperature risks. Special magnets exist for hotter applications. Always refer to the manufacturer’s specifications for maximum operating temperatures.
Safety Interlocks: All magnets should be interlocked directly to an emergency stop. Interlock logic should include (1) enabling only when the mold is in contact before activating, (2) machine guards are closed before activating/deactivating, and (3) preventing magnet disabling during a production cycle.
Pole Design: The magnet’s poles should be designed such that the mold base absorbs most of the magnetic field and stray fields are kept close to the magnet surface.
Power Supply: All Quick Mold Change magnets are controlled by permanent-electro magnetic technology, which only requires electrical power to switch on or off, giving the magnet a failsafe operation. Ensure the power supply to the magnet’s controller is within maximum voltage and current ratings. Since reliable control is critical, the isolation of the controller’s supply from the normal supply is recommended.
Post time: 12-27-2016