Metal Tips Roll Forming Tutorial – Part 3 Materials and Tolerance Expectations

To help our site visitors understand the roll forming process, Corrugated Metals, Inc. has included this roll forming tutorial. Part 3 addresses Materials That Can Be Roll Formed and Tolerance Expectations.

Materials That Can Be Roll Formed

Almost any material that can tolerate bending to a desired radius can be roll formed. The more ductile a material is, the better it will roll form. The roll forming process can handle ferrous, nonferrous, hot rolled, cold rolled, polished, plated, or pre-painted metals producing excellent results.

Materials as thin as 0.005″ and as thick as 0.750″ can be roll formed. Material pieces as narrow as 1/8″ and as wide as 72″ (or more) can be roll formed, depending on your vendor’s machinery. CMI roll forms to a final width of 63″.

The length of the finished roll formed part is only restricted by the length that can be functionally handled after the finished part exits the roll forming machine.

Sometimes, several sections can be formed from a single strip or several strips can be fed concurrently and united to produce a combined section. There is only one absolute material requirement for composite forming. The material must be capable of being formed at room temperature to the desired radius.

Tolerance Expectations

Typically, four tolerances are critical to successful roll forming operations. These include dimensional cross-sectional, length tolerances, angular, and material straightness.

Dimensional cross-sectional tolerances from ±0.010 to ±0.031″ can be achieved with roll forming equipment. If tighter tolerances are required the roll former must buy materials that can hold the increased tolerances.

Length tolerances are totally dependent on the thickness of the material, the length of the part, the speed of the roll forming line, the quality of the equipment, its condition, and the type of measuring and cutoff system used by the roll former.

It is advisable when ordering roll forming material to obtain material with somewhat tighter than Commercial Quality (CQ) tolerances. Ordering this upgraded material will eliminate many dimensional problems from occurring.

Angular tolerances of ±1° are typical in the roll forming process.

Material straightness is another tolerance consideration. Factors that establish material straightness include camber, curve or sweep, bow, and twist. The terms camber, curve, and bow are many times interchanged when describing material straightness, but they actually have slightly different meanings. A formed part’s horizontal and vertical planes are determined by their position in the roll forming process.

Material straightness terms include:

  • Camber is the variation of a side edge from a straight line. Extreme camber contributes to curve, bow, and/or twist in the finished part.
  • Curve, or sweep is the variation from a straight line in the horizontal plane measured after the part has been roll formed. Causes of curve or sweep included incorrect horizontal roll alignment and uneven forming pressure.
  • Bow is the variation from a straight line in the vertical plane. It can be either cross bow or longitudinal bow. Bow is often caused by the existence of irregular vertical spaces on symmetrical sections and from uneven forming areas on unsymmetrical sections.
  • A formed part is said to have twist when it resembles a corkscrew effect. This is often caused by excessive forming pressure in the final formed part. For most roll forming operations, twist is typically less than 5° in 10 feet of formed parts.

Next: Part 4 of the Roll Forming Process that provides a quick overview of springback and end flare, a quick list industries that use products from the roll forming process, some notes on roll form tooling, and a quick look at some of the operating parameters of the roll forming process.

Roll Forming Tutorial Sections