Corrugated Metals: Metal Tips
Roll Forming Tutorial - Part 3
Materials and Tolerance Expectations
To help our site visitors understand the roll forming process, Corrugated
Metals has included this roll forming tutorial. Part 3 addresses Materials
that can be roll formed and Tolerance expectations.
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. Corrugated Metals
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.
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 (Commercial Quality)) 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
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
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
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. [could
use an illustration here!]
-
Twist
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 and some of the operating
parameters of the roll forming process. 
Roll Forming Tutorial Sections
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