October 10, 2006
Proper feeding, scrap removal, and shut height calibration are essential for good die setup.
Editor's Note: This is the second part of a two-part series that discusses proper die setup procedures for progressive dies. Part I discussed press and die cleanness, die alignment, clamping procedures, and preliminary shut height calibration. Part II wraps up the die setup procedure by establishing the process for a good die setup procedure.
Make sure that the feed line height is set correctly for the die's feeding level. Avoid feeding downward or upward into the tool. Regardless of the vertical travel of the strip, the feed line height should be set at the level at which the material is feeding. Setting the feed line height at the midpoint of the strip's vertical travel is most likely an attempt to compensate for an incorrect pilot release setup.
Setting up the feed line height correctly helps keep the material straight and flat. Straight, flat material has stiffness and is less likely to buckle during feeding (see Figure 1).
Setting up the feed line height correctly helps keep the material straight and flat. Straight, flat material has stiffness and is less likely to buckle during feeding.
The most die damage occurs when material is introduced into the die, so this procedure is one of the most critical parts of die setup.
When introducing material into the die, make sure it is properly fed up to the correct strip-starting position in the die. This starting place often is called a first-hit line. This starting place can be a solid stop, such as a pin or pitch stop block, or it might be a simple line drawn, ground, or scribed on the die.
Starting strip in the wrong location can result in half-cut or -formed parts or unnecessary loose scrap. Cutting less than half of a hole or forming less than half of a part will result in unbalanced forces in the tool.
Unbalanced forces may result in poor die alignment, shearing, or severe die damage. Figure 2shows the importance of starting the strip in the proper position, as well as a first- hit line.
Unbalanced forces may result in poor die alignment, shearing, or severe die damage.
Regardless of how progressive dies are processed and designed, it often is difficult to place a first-hit line in a position where no loose scrap is left in the die during the material feeding process.
Be sure to remove all loose scrap manually after each hit and progression. Inspect both the lower and upper dies for loose scrap. Small pieces of scrap often have a tendency to stick to the faces of cutting punches, pads, and strippers. Failing to remove loose scrap in the die will result in double metal thickness being fed through it, which can cause severe die damage.
Pilot release, often referred to as feed release, is an important part of setting up a progressive die (see Figure 3). The pilot release function on a coil feeder allows the strip being fed into the die to be released so that the pilots in the die can properly locate and register the strip in the die.
Most coil feeders use feed rollers to index the material inward. These feed rollers clamp onto the strip and rotate a given amount, causing the strip to feed one progression forward.
For the pilots to position the strip correctly, the feed rollers must unclamp the strip before full pilot entry. However, letting go of the material too soon before the pilots partially enter the strip can pull the strip out of position by the weight of the take-up loop between the feeder and the coil.
The feed release must be timed so that the bullet nose of the pilot enters the strip but the full pilot diameter does not. This point can be determined by inching the press downward until the very tips of the pilots begin to enter the strip. When you've established this point, note the degrees on the press's stroke and set the pilot release to let go of the strip at this point.
Program or adjust your pilot release so that the material or strip remains fully unclamped (feed rollers in the open position) until all of the work has been performed in the die and the strip has been brought back up to the proper feeding level (feed line height). When the strip is at feeding level, the feed rollers can clamp the strip and feed it forward one progression.
Once again, monitor this point during the press stroke and adjust the feed release with respect to the degrees during the crank stroke. Doing so correctly allows the material to move linearly inward and away from the die during the vertical travel of the lifter bars.
Incorrect setup of the feed release can cause misfeed; elongation of the pilot holes in the strip; bent, broken, or galled pilots; and poor part location and gauging.
This procedure is critical, especially for progressive dies that are making deep-drawn parts and require a great deal of vertical lift to feed forward (see Figure 3). Incorrect setup of the feed release can cause misfeed; elongation of the pilot holes in the strip; bent, broken, or galled pilots; and poor part location and gauging.
When the die is fully loaded, you might need to make a final calibration of the press's shut height. This is primarily because presses deflect when loaded with a great deal of force.
When the die is fully loaded, force is applied to both the ram and the bolster plate. Depending on the strength of the press and the load being applied, the press might flex, bow, or deflect slightly.
Lowering the ram to the proper calibrated shut height helps ensure that the die is fully closed while fully loaded. The amount of lowering depends on the condition and tonnage of the press, so it is good practice to double-check to make sure the die is fully closed. Use setup block calibration grooves and leads to make a final calibration.
Don't take the die setup process lightly. Take the time to train die setup personnel properly. A little time spent in training can save a great deal of money, headaches, and die damage.
Until next time ... Best of luck!
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