The Role of Tooling in Custom Roll Forming
Ryan Hernden
In this blog, you’ll learn more about the role of tooling in roll forming, the various types of tooling, and factors that influence tooling creation.
In this blog, you’ll learn more about the role of tooling in roll forming, the various types of tooling, and factors that influence tooling creation.
Roll forming puts profiles into long strips of metal, giving them the stiffness and geometry for many applications, from solar panel mounts to components for trailers, HVAC systems, and appliances. The core component of this process is the tooling mounted on the roll forming mill.
The tooling used for custom roll forming consists of pairs of profiled rollers that mount on upper and lower shafts. Each pair applies some deformation to the strip, which passes through the gap between them.
In this blog, we’ll explore some of the different tooling used in the process and how different process factors influence the type and quantity of tooling used.
A roll forming mill is usually fed with strip material supplied as a coil. (In some cases, sheet material is used instead).
This strip first passes through a straightener to remove camber and bow before entering a pre-punch press. This puts any required notches and holes into the strip at intervals to suit the product design; then, the material enters the roll forming mill.
Here, successive pairs of rollers progressively deform the strip in its longitudinal direction. For example, the rollers could bend the strip’s sides upwards to form a ‘U’ section. Once the strip has the required profile, it’s cut to length. Any required end features are added, and the final product is shipped out.
The rollers acting on the strip take an almost limitless range of forms, depending on the profile produced. A partial list includes:
“Forming rolls” is a broad term that essentially refers to all of the main tooling used in custom roll forming machines. Each forming roll gradually shapes the material into the desired profile through a series of stands, making incremental bends until the final shape is achieved.
This tooling, positioned at the beginning of the custom roll forming line, starts bending the flat material strip to establish the basic shape of the profile.
Finishing rolls are located at the end of the custom roll forming line and are used to make final adjustments and precise bends to ensure the strip achieves the exact dimensions and application requirements.
These are mounted on a vertical axis, positioned perpendicular to the main forming rolls, and push the profile inwards horizontally, ensuring consistency along the sides of the formed material.
Edge rolls specifically focus on shaping and refining the edges of the metal strip.
As the name suggests, this tooling type pushes down on the strip from above. They help control vertical dimensions and complete complex bends that can’t be achieved by bottom-up forming alone.
Underneath rolls push upwards on the profile from below. They help achieve upward bends and contours in the profile, ensuring dimensional accuracy and stability during forming.
These are groups of rolls stacked closely together and are typically used to manage intricate forming processes or to provide additional support and stability to the material being shaped, especially in complex profiles.
Cut-off dies cut the strip into set lengths. To avoid interrupting the continuous motion of the strip, these move in the direction the strip is being fed as they close.
If punching is needed, this tooling is used to put holes, notches, and other features into the strip while it’s flat. This can include a hole that tells the cut-off die when to cycle, which ensures the pre-punch features are positioned consistently from the ends of the strip.
This puts features into the ends of the cut pieces. Features could include notches and bends.
This tooling is only used in a turret-style roll forming machine. Turret roles can be quickly swapped out during production to change profiles or to replace worn rolls.
These rolls simultaneously perform multiple bending or forming functions, which is useful for complex or multi-stage forming operations.
As mentioned, the list above is not complete; additional specialty rolls may be needed for specific applications.
The type of material, how it’s finished, and the finish wanted on it all affect roll forming tooling design.
Starting with type, more ductile alloys, like most grades of aluminum and copper, bend readily with little springback. However, harder alloys like steel need more force to bend and have more springback. Addressing this means increasing the extent to which each bend is overbent so it recovers to the required angle.
Roll forming can be performed on finished and coated material as well as uncoated. This requires careful selection of tool material to avoid marking or damaging the coating. Material selection for tooling becomes even more important when the strip needs a high-quality “Class A” finish.
Roll design involves more than just the angles needed to create a profile. Bend radii are critical considerations, as this is where cracking is most likely. Asymmetric profiles are more challenging than those that are symmetrical, as stretching one region tends to compress another, sometimes resulting in undesirable effects like bowing.
When new rolls are needed, as for a custom roll forming project, some development time should be expected. For most projects, rolls are initially produced in maximum material condition and machined as needed until they produce the required deformation (it’s always easier to remove metal than add it).
As mentioned in the previous section, material selection is an essential consideration as rolls will wear in service. If large quantities will be needed, a material like tungsten carbide might be preferred, as its long life will outweigh the additional machining costs. Roll material must also be compatible with the strip, as some combinations can result in galling.
The number of bends, their angle, root radius, and the type of material determine how many rollers are needed. With high-tensile strength materials, bends are often applied progressively over several sets of rollers. Conversely, a large deformation can be applied quickly when the material has high ductility.
Deformation, profile shape, and number of rolls needed are shown in a “flower” diagram, illustrating how each pair of rolls moves the profile closer to the required shape.
Speed of deformation is important when bending metal: the grain structure needs time to adjust to the loads being applied, and trying to move too fast can cause cracking. However, running a roll forming line slower increases the cost per foot of profile.
Running faster means using more roll pairs, each applying a smaller amount of deformation. However, lines are fixed in length, so more tooling requires a bigger budget. Therefore, optimizing forming speed is a complex challenge where spending more on rolls (and the associated time to set up the line) allows a higher production rate.
Other factors to consider are the pitch between pairs of rolls, which is where the material recovers from being deformed, and the forming angle applied at each roll. Pitch is fixed for any given roll forming mill and influences the maximum speed at which a material can be run.
When discussing roll forming tooling, especially for a custom roll forming project, it’s helpful to know the number of pieces needed, the target cost, and the budget available for tooling. In general, spending more on tooling will allow for lower unit costs, because with more roll pairs, the line can run faster. Plus, harder materials will suffer less wear and last longer.
However, we understand that when the expected demand for a profile is low or uncertain, there’s pressure to minimize tooling costs. The tradeoff is to use fewer sets of rolls and run the line more slowly.
Another option is to determine if the required profile can be modified to use tooling that’s already available.
MMC Roll Forming is an established supplier of roll-formed metal products for industries ranging from automotive to consumer appliance. We specialize in custom roll forming and have an extensive in-house inventory of no-cost tooling. Our engineers can help you determine the tooling your project needs and can advise on modifications to help you save money while improving product quality.
If you need roll-formed profiles, we’d like to help. Contact us today to request a project analysis.