Page 28 - MetalForming April 2010

Tooling Technology
Setting the blowoff cam from 170 to 230 deg. should be sufficient. Optimally, aim the air so that the part blows straight off; some operators place one line on either side of the part. While this can work, if one air line has more pres- sure than the other or if only one side has air, the part will likely try to exit the die away from the center. The air must be controlled evenly so that the part leaves the die straight.
Small spring-loaded lifters or plungers also can be used to help eject the part after cutoff, especially if the lifters or plungers are located under the back of the part so that gravity will help the part fall out of the die. Also, some dies are designed to allow the feeding of the strip to help eject the part. While this also can work, it invites a host of prob- lems, such as lifting or cambering the strip if the part stays in the die.
Dies that produce more than one part at a time or right- and left-hand parts require some attention on the exit
side as well. In the case of right- and left- hand parts, each part must be con- tained apart from the other, and each side can create its own ejection prob- lems such as those mentioned above. There are several methods to detect parts exiting the die, whether single or multiple and blanked or ejected.
Finding a Sensor Solution
Photoelectric sensors work well for part-out applications. If the part pass- es through the beam or, in the case of a diffuse-reflective sensor, reflects the beam back at the sensor, the sensor changes state. For blanked parts, using a through-beam sensor is very effec- tive, especially if the press is pro- grammed to look for a change in sensor state only during certain angles. If a part were to hang up inside the cavity, the sensor would detect it by staying on longer than expected. The press con- troller then would send a stop signal to the press.
Ring sensors find use in monitoring part ejection from the press. Here, an inductive ring sensor tracks the suc- cessful ejection of drill bits as they pass through a hose.
Retro-reflective sensors obviously will not work very well mounted under the die shoe, because finding a way to protect the polarized reflector from the rigors of die handling would be difficult. Also, fitting a part conveyor or chute under a reflector would be difficult. One method to detect parts is to embed a diffuse-reflective switch in the shoe underneath the cutoff-die section. As long as the opposite side of the cavity does not cause the sensor to switch and there are no dead spots where the part can miss the beam, this can be one of the best ways to detect parts after cutoff. Mounting the sensor between the shoe and the die section protects it from damage, and the section can still be maintained without any danger of cut- ting a wire. A bit of milling on the shoe is necessary to provide room for the sensor and wires.
Inductive sensors also can effective- ly detect parts, as long as the parts exit the die within range of the sensor. Parts blanked off the end can be monitored by using a block-style proximity sensor underneath a nonmetallic ramp. Depending on the size of the part, an inductive ring can be used effectively if the part can be directed through it by the use of controlled air or a transpar- ent tube.
Regardless of the method used to detect parts, the method should always be thoroughly bench-tested. If a die- protection application fails just one time at the press, then it can’t be trust- ed to be effective at all. MF
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26 METALFORMING / APRIL 2010
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