Fabricating Tech Tips: Press feeding basics
- August 31, 2015
Tips on how to avoid short feeds
If you listed all the issues reported by stamping manufacturers related to feed equipment, short feeding would be at the top of the list.
If this is not immediately corrected it can cause damage to your die, scrap material, lost revenue and possibly result in late deliveries. To avoid misfeeds and their adverse impact it’s important to understand what causes them and how to fix them.
Slippage is usually caused by misalignment between the die and feed system. It is crucial when you load and thread a coil into the press that material is centered and square through the feed rolls and die. Make sure you set the die correctly. It should always be centered and square to the press bolster plate.
• Centering: When loading a coil on the reel make sure it is centered on the mandrel. Most mandrels are equipped with 1:2 increment scales with “0” at the centerline. Example: If your coil is 21-inches wide, make sure both edges of the coil are at 21-inches. Also, it’s important to utilize the feed edge guides. They should be against the material on both sides to help guide the material square into the die. Make sure they are calibrated to the center of the die.
• Pilot Release: Feed or pilot release helps thematerial flow square through the die. Pilot release momentarily releases the material so it can align itself by the die’s pilot pins. Momentarily opening the rollers allows for stress in the material caused by camber or slight misalignment to be relieved. The pilot pins correct slight misfeeds by pulling the material into final position. Pilot release timing is critical. If the pins are not engaging the material when released, the material can fall back due to the weight in the loop causing short feeds.
• Support: Lack of support between the feed rolls and die can contribute to short feeding. Without support the material can buckle or sag causing short or long feeds. Also, the feed line height must be set correctly to the die height. If set too high or low, the material will feed uphill or downhill causing drag against the die.
Here are five tips that will help determine the cause of short feeds.
The “One Revolution” test can determine the accuracy of the servo motor. Calculate the roll circumference (roll diameter x 3.1416). Remove material from the feed. Enter the circumference into the feed length. Scribe a line on the driven pulley of the feeder and another line on the side plate for reference. Single stroke the press several times. If the lines match up every time, the scaling parameters are correct. If they do not match, contact the equipment manufacturer for the correct parameters.
Check the pilot timing. Turn the pilot release off then single stroke the press. If this improves accuracy the pilot release press output is not timed correctly.
If excessive roller pressure is required, there may be a slippage problem. Contact the equipment manufacturer for the correct setting.
Use the edge guides to check for an alignment problem. Move the feed edge guides against the material. Cycle the press several times. Check if either guide roller is hard to turn indicating an alignment problem. If the material pushes hard against one of the guide rollers move both edge guides towards the pressure until they turn freely.
Excess following errors or drive faults may indicate the feeder is being overworked due to an alignment problem.
Bottom line: It’s important to take a little extra time to make sure your setup is correct. Dies must be centered and square to the press bolster plate, coil centered on the mandrel, feed edge guides against the material and centered to the die. SMT
Matt Trethewey is a service manager and John Kwiatkowski is a Coe certified manager with Coe Press Equipment Corp.