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Cold Roll Forming Process

For 100+ years, the cold roll forming process(aka rolling metal process) has provided strong parts — quickly and cost-effectively — for numerous industries.
Roll Forming Basics: What is it? Process, Benefits, Metals Used, 7 Applications, 5 Types, Design Guide

What is Cold Roll Forming?

Roll forming video from Dalarna University:
“What exactly is Roll Forming?”
Find out the basics…watch this short instructional video produced by Dalarna University.

Cold Roll Forming Process(rolling metal process) is a kind of cold bending processing, also called profile sheet bending, is a reliable, proven approach to metal shaping, and is an efficient, effective shaping that delivers tight tolerances on complex profiles, which is ideal for modern applications.

A method of rolling relating to the continuous bending of a long strip of sheet metal (typically coiled steel) into a desired cross-section is roll forming. In the roll-forming process, permanent deformation is achieved by subjecting the material to high compressive stress by allowing the material to pass through the gap between two rotating cylindrical rolls, also spelled as roll-forming or roll forming.

The rolls may be flat or grooved and are kept at a fixed distance apart from each other. The rolls are rotated in opposite directions by means of the electrical drive system (motor, gearbox, spindle, and couplings).

Cold roll forming is the process of gradually bending a flat strip or coil of metal into a longitudinal, uniform profile. the cold roll forming process uses a continuous bending operation where long metal strips, typically coiled steel, are passed through consecutive sets of rolls at room temperature. Each set of rolls performs incremental parts of the bend to produce the desired cross-section profile. Cold roll forming is a cold-forming process that doesn’t require heating up the metal. High-temperature, specialized equipment isn’t necessary to produce cold-rolled shapes.

Unlike other metal shaping methods such as plate rolling, the cold roll forming process is inherently flexible. Secondary processes can also be integrated into a single production line, other than roll formation, a variety of metalworking tasks are performed by these machines, including material cutting and roll punching. Roll-forming machines operate in a continuous cycle, for the most part. The material is fed into the system where it constantly works its way through each operation’s phases, finishing with the product completed.

Why is the roll forming process important?

The rolling process is the most important metal-forming process, more than 95% of ferrous and non-ferrous metals and alloys are processed to their usable shapes by rolling. Usable shapes of rolled metals are plate, sheet, strip, foil, and different sections like rail, beam, channel, angle, bar, rod, seamless pipe, etc.

The 5 features of the roll forming process

  1. Using a number of stations, a roll forming machine bends metal at room temperature where fixed rollers both guide the metal and make the required bends.
  2. As the strip of metal travels through the roll forming machine, each set of rollers bends the metal a little more than the previous station of rollers.
  3. This progressive method of bending metal ensures that the correct cross-sectional configuration is achieved while maintaining the cross-sectional area of the workpiece.
  4. Roll forming machines, typically operating at speeds between 30 to 600 feet per minute, are a good choice for producing large quantities of parts or very long pieces.
  5. Roll forming machines are also good for creating precise parts that require very little, if any, finishing work. In most cases, depending on the material being shaped, the end product features an excellent finish and very fine detail.

What can cold roll forming do?

The cold roll forming process can be used to shape galvanized steel, non-galvanized steel, stainless steel, and copper. It is the production of a profile from the metal strip in a continuous process, where material passes along a series of stations on the production line through sets of rollers, manipulating it to the required form.

What are the raw materials for cold roll forming?

Raw material can be either flat or coiled sheets. It’s possible to use hot rolled steel in sheet form as the raw material in cold roll forming. 

Roll forming metal is a very common practice, so let’s start there. While mild steel may be the most common raw material for roll forming, any ductile metal is considered fair game. Traditional materials include:

  • Galvanized and galvannealed steel
  • Stainless steel
  • Aluminum
  • Copper
  • Brass
  • Bronze

But every so often we hear about using different source material. Here are some rules to keep in mind:

Don’t Use Anything That Has Poor Ductility

You can check out our metal properties PDF chart for a look at ductility and common roll-formed materials.

The top priority for most projects is to build something that’s structurally reliable and won’t fall apart (and fall on people). What makes a material unsuitable for roll forming really comes from a formability standpoint.

It Can’t Be Too Brittle; It’s Got to Be Malleable

Anything hard or brittle, like cast metal or certain metals that are heat-treated to increase hardness, isn’t formable.

The most common material we repeatedly see specified even though it’s unsuitable for roll forming is a heat-treated aluminum alloy used for extrusions – 6061. When you’re specifying a T6 or, to a lesser extent, T4, you’re losing bendability, making it harder for your manufacturing to avoid cracking the metal.

That’s why metal extrusion is usually the process of choice for 6061-T6: You need to form and heat treat it at the same time. That’s not possible with a roll-forming line.

How to choose the right material?

Judging a metal (or other material) requires an understanding of the roll forming process itself as well as the properties of the material.

  • Thickness
  • Mechanical properties
  • Surface quality
  • Uniform flatness tolerances
  • End-use requirements

What is cold roll forming capability?

Typical cold roll forming mills can accommodate material gauges ranging from .010″ up to 0. 250″ thick. The bend radius is largely determined by the ductility of the metal. However, 180-degree bends are commonly achieved with the right material. Roll forming easily accommodates the integration of secondary operations such as welding, punching, and precision laser cutting to optimize production efficiency.

Advantages

  • Rollforming is optimal for profiles with long lengths and large quantities
  • Delivers consistent and accurate results
  • It’s suitable for a variety of metals
  • It is environmentally friendly
  • Ideal for custom product design and manufacture
  • The curvature radius corresponds to the thickness of the metal strip.
  • Lightening the weight of structures by roll-forming steels with high elastic limits.
  • Ease of implementation in assemblies with welding, riveting, bolting and gluing.
  • Variety of possible delivery lengths of steel profiles, up to 30 meters.
  • Diversity of surface conditions such as hot roll, pickled, cold rolled, prepainted, and galvanized.

Available roll-forming materials

Cold roll forming can form a wide variety of metals, including:

  • Cold rolled steel: High material hardness, resistant to flattening and deformation. It also is abrasion and erosion resistant, offers good breaking resistance, and has high toughness.
  • High-strength, low-alloy steel: High-strength, low-alloy (HSLA) steels have nearly the same composition as plain carbon steels. However, they are up to twice as strong and their greater load-bearing capacity allows engineering use in lighter sections.
  • Steel/ Stainless Steel: contains a high percentage of chromium, which lends it high staining and corrosion resistance.
  • Hot rolled, pickled, and oiled steel: It has been processed to remove surface impurities. When traditional hot-rolled steel is pickled and oiled, it becomes more durable and rust-resistant.
  • Galvanized / Galvannealed Steel: the surface of the metal features a bonded coating of zinc-iron alloy.
  • Aluminum: a soft, malleable, and lightweight metal with excellent resistance to corrosion.
  • Brass: a copper and zinc alloy featuring a bright, gold-like color and a high resistance to corrosion.
  • Copper: a ductile metal noted for its electrical conductivity.
  • Bronze: Highly ductile, low friction.
  • Composites: materials engineered from two or more materials.

7 cold roll forming applications in disguise

Cold roll-formed shapes are advantageous due to their ability to be produced at a rapid pace while maintaining design accuracy. Yet it’s also ideal for parts with multi-bend profiles, or those that require high-end finishes.

Hole punching, bending, and cutting to length are all easy to fit into one continuous process, rather than separate steps. In all of these cases, it’s simply more cost-effective and productive to use this tried-and-true method of metal forming.

  • Power distribution components
  • Warehouse & data storage
  • Commercial food storage
  • Solar
  • Trains
  • Trailers & trucks
  • Guard rails & signposts

4 Types of Roll Forming processes

Every roll forming manufacturer uses a unique set of rolling processes to create their products. Some specialize in tubing, while others produce roofing and siding. 

  1. Roll Bending: It can be used for thick large metal plates. Three or four-roll plate bending machines roll bending the plate to produce the desired curve. The placement of the rollers determines the exact bend and angle, which is controlled by the distance between the rollers.
  2. Flat Rolling: The basic form of roll forming is when the end material has a rectangular cross-section. In flat rolling, two working rollers rotate in opposite directions. The gap between the two rollers is slightly less than the thickness of the material, which is pushed through by the friction between the material and the rollers, which elongates the material due to the decrease in material thickness. The friction limits the amount of deformation in a single pass making several passes necessary.
  3. Profile Roll Forming: Shape rolling cuts different shapes in the workpiece and does not involve any change in the thickness of the metal. It produces molded sections such as irregular-shaped channels and trims. Shapes formed include I-beams, L-beams, U-channels, and rails for railroad tracks.
  4. Ring Rolling: In ring rolling, a ring of a small diameter workpiece is rolled between two rollers to form a ring of a larger diameter. One roller is the drive roller, while the other roller is idle. An edging roller ensures that the metal will have a constant width. The reduction in the width of the ring is compensated for by the diameter of the ring. The process is used to create seamless large rings.

What is a cold roll forming machine?

The cold roll forming machines make specific configurations out of long strips of metal, most commonly coiled steel. They have more group-forming rollers to control the localized processing of the material to prevent folding and wrinkling during the process, it is designed to meet the needs of metal bending. As the workpiece passes along the line, each roller further reduces its thickness by a specified percentage until the piece reaches the desired thickness.

In most applications, the cross-sectional profile is usually tailored to the specific needs of the customer for the roll forming machine to bend the metal as necessary

The two benefits of roll forming machines

  • Energy-efficient because roll forming machines do not expend energy to heat material—the metal shapes at room temperature
  • An adjustable process and applicable to projects of varying time duration so results in a precise, uniform part.

6 components of the cold roll forming machine

  1. Infeed Section: The Infeed Section is mainly used for loading and feeding the material, which is mostly in the form of continuous cut sheets or in continuous coils depending on the final product to be processed.
  2. Roll Forming Section: The Roll Forming Section is mainly for the processing of the incoming sheet. It contains a roll forming system with multiple rollers, as well as drives, power systems, and infrastructure. The main purpose is to continuously process the profiles that pass through the roll forming section to achieve the desired metal component.
  3. Shearing Section: After the continuous processing of the profile, the profile is cut to the required nominal length according to the specified length.
  4. Exit Section: After the complete processing procedure has been realized, to prevent the finished product from falling, a table is added to carry out the storage of the finished profile.
  5. Control System: A PLC control system is used to achieve a fully automated production model and to realize processing accuracy and cutting precision.
  6. Additional Kit: When carrying out production, there may be many additional needs, such as printing logos, straightening, embossing, etc.

Top 11 Design Guides of the Roll Forming Process

  1. Design a symmetrical shape wherever possible. This allows an equal amount of forming to be done on each side of the vertical centerline and equalizes the stresses imparted by the forming process as the strip progresses through the forming rolls.
  2. Suggests that you avoid cross-sections with extreme deformations. The strains produced by roll forming (moving metal) are greatest around the arc of the bend and at the edges of the strip.
  3. Try to avoid sharp bends. The ductility of the metal will determine the minimum bend radius possible. The roll-formed radius should be at least equal to the metal thickness.
  4. Recommends that the minimum practical leg length, including the bend, should be three times the metal thickness.
  5. Whenever possible, avoid air forming (a bend or area that is not in direct contact with the roll-forming tools). Dimensional accuracy is more difficult to control with this type of design.
  6. Suggests that when faced with wide, flat areas, consider adding ribs or grooves to hide potential waviness.
    Try to position notches, slots, holes, etc., away from the bend line and the edge. Be aware that these openings may become distorted in size and shape during roll-forming.
  7. When a part is pre-cut (cut before roll forming), the leading end and trailing end are both likely to be distorted and flared. The pre-cut method may be advantageous to pocket areas and mitered edges.
  8. In contrast, a part may be post-cut (cut after roll forming), with a flying cut-off die shaped to fit the profile. Post-cutting produces somewhat less end-cut distortion. This method is the most common and efficient.
  9. Depending on the gauge and metal tolerance, cross-section tolerances of +/- .015 and angular tolerances of +/- 2 degrees are typical. Length tolerances of +/- 1/8″ per 12 feet are routine. Tolerances may be designed tighter as required.
  10. A). Bow and Camber: The deviation from a straight line in the vertical plane.
    B). Lateral or curve or sweep: The deviation from a straight line in the horizontal plane.
    C). Twist the deviation from vertical and horizontal lines in a corkscrew shape: “propeller effect”.
    Bow and Lateral are typically held to +/- 1/8″ per 10 feet. The twist is typically held to 5 degrees per 10 feet. These conditions can be caused by variations in metal hardness and thickness, slitting pressures, burrs, and stretching. Tighter tolerances can often be held with appropriate tooling design.
  11. Spring back occurs when the elastic limit of the metal is not exceeded during a bending operation. In effect, the stock returns partially to its original pre-bent shape. Spring back can be countered by proper design of tooling that intentionally stretches the stock beyond the elastic limit and then, at another step, sets the correct shape by finish forming.

Resource: MP Metal Products