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Does your roll formed section look like this?
Most problems with twist are usually attributable to mistakes made during setup. The following is a list of some of the problems that I run into while serving our customer’s needs, as well as some remedies for the roll form operators.
Entry Guide Stand
Sometimes an improperly aligned entry guide stand can cause twist in your part. Do you fight with the straightener, twisting it back and forth trying to eliminate twist but nothing happens? Check the entry table and make sure the material is perpendicular to the rolls. Make sure the stand is in good working order (twist can be induced if the stand is allowed to move off one side to the other). If the sides are not aligned properly, use a 24” scale and place half of it on the front or flat face of the first pass (Figure 1). Align the guide parallel to the scale and tighten the stand. This is a quick and easy way to potentially minimize twist.
Excessive Pressure on the Inboard or Outboard Side of the Tooling
This is a common mistake that operators make when adjusting the rolls. Usually the operator adjusts the tooling with no material in the machine and runs the material all the way through the mill, which can lead to twist, down bow, up bow, etc. In order to remedy this, gauge the roll form tooling without the material and check the rolls using a mirror to view between each pass. This will ensure you that the rolls are matched properly. Then start the material through the first pass and re-gage the rolls. Set the roll gaps based on the actual material thickness you are running. Then jog the mill about one inch and check the gap, you may need to do this a few times to get the proper gap. Continue this process for the remaining passes.
Improper Roll Match
I have been on many service calls in which the rolls were not matched properly. Matching the roll form tooling should be a procedure during setup. After you have the tooling set up and gaged to the material thickness, you should make a habit of checking the match between top and bottom rolls. Take a mirror and a sheet of white paper and hold the paper at a slight angle between the rolls (Figure 2). On the other side of the roll, look in the mirror and check the outline of the rolls where the material will be formed. You should have equal clearance or gap around the form and just a small amount (0.005-0.010”) of clearance between the top and bottom rolls.
If you do not have the proper roll match after performing this step (Figure 3), re-check the setup and/or the machine spindle alignment.
When you have the tooling gauge property and the spindles are aligned, you will be ready to install the material. At this point, you should have roll form section with little or no twist. (see figure 4)
Lack of Lubrication
This is something that may not have crossed your mind when you have issues with twist. These days, we are asked to design and manufacture tooling for very difficult profiles. These profiles can involve multiple material thicknesses and types. At the same time, we are asked to do all of this with one set of tooling. Depending on the tooling design, there may be issues with the material fighting drag with the all compression and stretching as it is being formed. Sometimes just a little bit of lubricant works wonders. If the product cannot have lubricant on it, there are many types of vanishing oil that dissipate after the product has been formed.
Roll Forming Tooling Design
Sometimes you just can’t design tooling with the section in the ideal orientation due to pre-punch, post-punch and cutoff concerns. In this case, we can install anti-twist fixtures that can move the material as it comes through the roll former to help minimize twist in the section. Sometimes a simple cam follower can be used to minimize twist.
Author: David L. Rostocil Sr., Director of Product Applications
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