Roll Forming
Training Objective
After watching the program and reviewing this printed material, the viewer will gain an understanding and
knowledge of the roll forming process, it’s tooling and applications.
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Roll forming processes are clearly shown
Types of roll forming stock are examined
Manufacture of the forming rolls is demonstrated
Roller machine types and lubrication methods are detailed
Roll Forming Process
Roll forming is a continuous process for forming sheet, strip or coiled metal stock into long shapes of essentially
uniform cross-section. The material is fed through multiple pairs of contoured forming rolls, which progressively
shape the metal until the desired cross section is produced.
Roll forming is typically a high volume production process but is also suited for shorter production runs as well. As
such, roll forming finds wide application in automotive, building, construction, office furniture, appliance, aircraft, and
in the HVAC industries. Both ferrous and non-ferrous metals as well as some non-metallic material can be roll
formed. Mild steel and aluminum are the most common materials used in the process. Additionally, polished, painted,
coated and plated materials can also be roll formed.
Stock to be roll formed may be either pre-cut to a pre-determined length before roll forming, or post-cut afterwards to
a specified dimension, with the latter being most common.
In the pre-cut method, material passes through the rolls at fixed speeds of 50 to 250 feet, or 15 to 76 meters per
minute. Pre-cut roll forming is commonly used for low-volume production when notching is required that cannot be
easily done using post-cut lines, or when multiple profile widths require expensive and or time consuming tool
changeover.
The more productive post-cut method typically involves a stock uncoiler, a roll forming machine, a cutoff machine,
and a runout table. Production speeds average 100 to 180 feet, or 30 to 55 meters per minute, but can be as high as
600 feet, or 185 meters per minute. Post-cutting occurs on the fly as the stock is moving. Post-cut roll forming is also
commonly augmented with a range of auxiliary equipment to perform certain operations, such as prenotching,
punching, embossing, marking, trimming, welding, curving, and die forming. By incorporating auxiliary equipment, the
post-cut method can be a complete net-shape process, fully automated or nearly so if desired. But tool cost and tool
change time are more than for the precut method.
Roll Forming Tolerances
Roll formed product dimensional tolerances are affected by variations in stock material width and thickness, the
physical properties of the material being rolled, the quality of the tooling, machine condition, and operator skill. Cross
section dimensions are commonly held within plus or minus .010 to .030 of an inch, or .25 to .78 of a millimeter, and
plus or minus one degree angularly.
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Roll Forming
Somewhat greater tolerances are necessary for gauge variations and cross-sectional features found in parts with
wide panels or deep profiles.
In general, roll forming length tolerances of plus or minus .020 to .093 of an inch, or .51 to .236 of a millimeter are
possible, depending on the length. The longer the length the greater the tolerance. Additionally, material straightness
before and after roll forming is critical. To be considered are:
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Camber, which is the deviation of a side edge from a straight line measured prior to roll forming.
Curve, also referred to as Sweep, which is the deviation from a straight line in the horizontal plane.
Bow, which is the vertical plane deviation from a straight line.
Twist, which resembles a corkscrew effect, measured in degrees.
A straightening unit installed after the final roll pass is often used to minimize or eliminate the internal stresses that
cause curve, bow and twist. In some instances though, roll forming parameters can be adjusted to produce parts with
controlled curvature.
Springback and end flare are other conditions that can negatively affect the finished part. Springback occurs when
the formed part does not stress beyond its elastic limit during forming. Springback is often compensated for by
overforming the material and then allowing it to ‘spring back’ to the required part profile. End flare occurs at the end
of the formed section and is caused by released internal stresses as the part is cut-off. Additional roll passes and
avoiding pre-punched areas at the cut-off point can control the problem.
Forming Rolls
The design of the forming rollers is dependent upon several factors including:
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Number of forming passes - As the roll forming process is progressive in operation too few passes can cause
distortion and loss of tolerance, too many passes increase the final tooling cost.
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Material width - Generally determined by dividing the finished profile into its component curved and straight
sections, and then totaling these individual dimensions with subsequent width adjustments once the part is run.
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Flower design - is a station-by-station overlay of the progressive part contours starting with the flat strip width
before forming and ending with the final desired section profile. CAD software packages are very useful in
optimizing roller design.
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Roll material - Several types of materials are used in the manufacture of the forming rolls with the most common
being oil-hardened tool steels. For extended tool life, hardened high-carbon, high-chromium tool steels are used.
On extremely tough forming applications involving high temperatures and or abrasive materials,
aluminum/bronze or carbide rolls may be required. Where it is important to maintain pre-finished material
surfaces, chrome plated rolls, or plastic rolls made from materials such as nylon or Teflon are used.
Single rolls are often manufactured in multiple sections called split rolls. These have the advantage of lighter weight
and ease of machining. They are also used when a tool set is intended for a family of roll formed parts.
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Roll Forming
Roll Forming Machines
Roll forming machines typically have a number of individual dual-spindle roll forming units mounted on a baseplate.
In set-up, rolls are mounted and aligned on these dual-spindle roll forming units. Spacers are used to fix the rolls in
exact position on the spindles. Vertical adjustment of the top shaft position fine tunes it to accommodate specific rolls
and material thickness. There are many styles of spindle support for roll forming machines, with the most popular
type being outboard-style spindle support machines. Outboard machines have housings supporting both ends of the
spindle shafts. The outboard housing is generally adjustable along the spindles, lessening the distance between
supports to accommodate small shapes of thick gage.
The manner in which roll forming units are mounted on a common baseplate largely determines the types of shapes
formed on a particular machine. The most common types of roll forming machines include:
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Single-duty machines, which are made for one particular cross-sectional profile or tool set and are not normally
designed for convenient roll change.
Standard/conventional machines, which have their outboard supports that are easily removed, permitting tool
change to produce various profiles.
Side-by-side machines, which accommodate multiple profiles by having more than one set of roll tools mounted
on the spindle shaft at the same time.
Double-head machines, which have two separate sets of housings and roll shafts that face one another. The
housings are mounted on an adjustable plate mechanism so that they can be shifted to change overall width
while maintaining the same profile for edge formation.
Rafted machines have housings and spindle shafts with one particular set of roll tools mounted to it. However,
several forming units are on rafts or subplates that are removable from the roll-former base. On tool change,
these individual rafts are removed and replacement rafts installed holding tooling that has been set-up off-line.
There are numerous drive systems for roll forming machines with the most flexible being universal-drives. Universaldrive machines have a series of worm-driven gear boxes with outputs that transfer the power source to the individual
roll shafts through a double-jointed universal coupling.
Various lubricants and lubricating systems are used in roll forming. These lubricants can be classified as
evaporative compounds, chemical solutions or synthetics, micro-emulsions or semi-synthetics, macroemulsions or water solubles and petroleum-based lubricants. Application methods include air or airless
spraying, wiping, roll coating, dripping or flooding and the systems can be highly automated.
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Roll Forming
Review Questions
1.
The operative word that best describes the roll forming process is:
a. die forming
b. progressive
c. coining
d. profiling
2.
The most desirable materials used in roll forming is/are:
a. spring steel
b. chrome-molybdenum steels
c. non-metallics
d. mild steels and aluminum
3.
The most common cutting method of roll forming is:
a. sawing
b. parting
c. pre-cutting
d. post-cutting
4.
Pre-cut roll forming production speeds are:
a. 600 to 800 feet/183 to 244 meters per minute
b. up to 1,000 feet/300 meters per minute
c. 100 to 300 feet/30 to 90 meters per minute
d. 50 to 250 feet/15 to 76 meters per minute
5.
Camber refers to deviation from a straight line in the:
a. side edge before roll forming
b. vertical plane
c. horizontal plane
d. side edge after roll forming
6.
Springback occurs when the material:
a. is stressed beyond its elastic limit
b. does not stress beyond its elastic limit
c. is too hard
d. is too soft
7.
The flower design is:
a. the part’s finished profile
b. the total number of formed bends
c. a station-by-station overlay of progressive part contours
d. the finished profile divided into component bends and straight sections
8.
The most common material used to produce forming rolls is:
a. chrome steels
b. aluminum
c. carbide
d. oil hardened tool steels
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Roll Forming
Answer Key
1. b
2. d
3. d
4. d
5. a
6. b
7. c
8. d
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