Speed or Velocity? The difference between speed and velocity is that velocity is speed with a direction. Often, velocity is represented by a lower case “v” with an arrow over it to indicate direction. Most of the time, we’re looking at a roll former running in the forward direction. In any event, for most people dealing with a roll forming application in their day-to-day lives, you may treat velocity and speed as interchangeable. Don’t get hung up on the terminology.
For a constant speed and time, any distance can be calculated. This formula is useful when determining how much material will be used when the machine is running at a constant speed. It can also be used to calculate where punch or shear targets will be with respect to different tooling or physical locations on the machine.
Most of the time, a roll former is treated as if it is always running at a constant speed for a specific period of time. This formula is the basis for most of the other formulas used to describe material motion.
s · t = d
s = speed in either feet per minute or inches per second*
t = time in either minutes or seconds*
d = distance in either feet or inches*
*Unless you’re calculating throughput or examining a roll former from the perspective of an overall process, you’ll use inches per second, seconds, and inches to troubleshoot problems.
A roll former is running at 350 fpm (70 ips). The cutoff press requires 0.25 seconds to stroke through the material and back out.
70 ips · 0.25 s = 17.5 in.
The cutoff die must travel 17.5″ during the cut process.
A roll former runs at 200 fpm. Assuming two shifts per day, 5 days per week, 40 hour work weeks with 30 minute breaks, and a runtime average of 50%. How many feet of product can we expect in a month from this machine?
8 hours = 480 minutes – 30 minutes (breaks) = 450 available runtime minutes
average runtime minutes = 450 · 2 (shifts per day) · 5 (days per week) · 50% = 2250 runtime minutes per week
200 fpm · 2250 minutes = 450,000 feet per week
A roll former is producing a product at 100 fpm (20 ips) within the overall length tolerance of ± 0.032″. The punch hole distance is varying by ± 0.25″. What is the timing variance in the punch?
0.5″ (total punch variance) ÷ 20 ips = 0.025 s
The variance is probably due to a sticky valve or a blown seal on the punch press.