No Stock Movement

Posted by stephens on Jul 3, 2009 in Automated Transactions | 0 comments

Progressive dies must be engineered to take No Stock Movement (NSM) into account. This is the time during the press upstroke that the feeder has to wait for the die components to be clear of the coil.

Feeders have a limited amount of time to index the coil one progression. This time is measured in crank angle degrees. Most feeders have 180° of time to feed. The faster the press runs and the shorter the press stroke, the less time is available to feed material one progression.

No Stock Movement is a simple calculation. It can be expressed as:

• NSM = UDT + LDT + P +ESM

where (all values are inches or millimeters):

• NSM = No Stock Movement
• UDT = Maximum Upper Die Travel (along press stroke vector)
• LDT = Maximum Lower Die Travel (along press stroke vector)
• P = Distance Pilots extend past stripper pads
• ESM = Engineered Safety Margin (dwell time after pilots are clear of coil before feeding starts)

For example, a progressive die with an upper pad travel of 50 mm, lower lifter travel of 25 mm, pilots extending 6.3 mm past the stripper in the open position, and 3.7 mm engineered safey margin requires:

• NSM = UDT + LDT + P +ESM
• NSM = 50 + 25 + 6.3 + 3.7
• NSM = 85 mm

In other words, the feeder cannot start feeding until the ram is 85 mm from bottom dead center on the press upstroke. The feeder must have the capability to index the coil one progression before the ram is 85 mm from bottom dead center on the press downstroke.

Otherwise, the press will have to operate slower or a faster feeder will be needed to run the die free from tooling interference with the material.