The Advantages & Limitations of Roll Forming
Ryan Hernden
Roll forming is an exceptional alternative to using a press brake, but there are some limitations to the process. Learn more in this article.
Roll forming is an exceptional alternative to using a press brake, but there are some limitations to the process. Learn more in this article.
Roll forming is an exceptional alternative to using a press brake if you want to make metal parts with a uniform profile or cross-section. Rather than cutting sheet into separate pieces, roll forming involves unspooling a coil and feeding it through multiple pairs of rollers. Each of these “roll stands” puts a bend into the strip or increases the bend made previously. By the time it reaches the cutoff station at the end of the forming line, the strip is shaped into a “U,” a top hat section, or something more complex.
Roll forming has many benefits, but it’s also not right for every part. This article looks at the advantages and main limitations of roll forming to give you a better understanding of the best use cases.
Roll forming is usually very cost-effective for large quantities of a profile. Once the line is set up, the strip runs between 100 and 300 feet per minute, sometimes faster (maximum speed depends on factors like strip thickness and material ductility). This is a much higher production rate than press braking and requires less labor.
Another point is that notching and hole-punching operations can be performed while the strip is running. This reduces, or even eliminates, many secondary processing operations and the associated handling and waste.
The last operation in a roll forming line is the cutoff station. Cutting the profile to the needed length virtually eliminates material waste.
In contrast, offcuts from the sheet are unavoidable when forming profiles on a press brake.
Once a line is set up, roll forming is very repeatable, producing highly consistent profiles. Standard tolerances are:
Tighter tolerances are achievable by tightening the tolerances on the forming rolls.
If you’re new to roll forming, you may be surprised by the complexity of profiles the process can achieve. Roll form tooling designers can put bends surprisingly close together and create very tight radii.
While space is needed to get the forming rolls into the profile, the process doesn’t face the same space and size constraints that limit press brake operations. It’s even possible to produce closed tubular profiles.
Not every profile design is suitable for this process. However, by understanding the limitations of this process, it’s often possible to make changes that make it feasible and economical. Here are the main factors to be aware of:
The profile being formed and the material it’s made from determine the number of roll stands and sets of tooling needed; thicker, less ductile strip is deformed less at each pair of rollers, so requires more stands than material that’s easier to work with.
Additionally, extensive grinding is often required to produce the precise dimensions and finish needed for forming rolls. Heat treatment and multiple grinding operations can result in long lead times. Requesting tighter-than-standard tolerances on the profile being formed also inevitably complicates and slows roll production.
However, there are ways around this. After many years in business, MMC Roll Form has built up an extensive tooling library. When potential customers bring designs to us, we look to see whether we have tooling available to form the needed shapes. If we can get close to the required profile, we will discuss whether there’s any scope for design modifications that will reduce the need to make new tooling.
In short, tooling can cause a delay in the production of a new profile, but don’t assume this will be the case. Let us review your design and see what options exist.
Roll forming uses coiled strip as the input material, and depending on the material used, its properties along with strip dimensions can create challenges.
Strip requires some ductility for forming, so materials like low-carbon mild steel, aluminum, and copper are preferred. Keep in mind that harder alloys, like some stainless steels, can be roll formed, but at lower feed rates.
Additionally, material hardness can vary along the length of a coil, which affects springback (the tendency of metal to move back to its initial position after bending). Tool designers can accommodate a degree of variation, but problems will arise if this becomes excessive—this is why MMC Roll Form seeks out quality strip from reputable suppliers.
Thinner material is easier to roll form. However, a bigger challenge for tool designers is variation in strip thickness and width. Thickness is usually consistent along the length, but strip can suffer from a taper across the width, depending on where it was cut from the original coil, leading to some variation in bend angles achieved.
Variations in strip width can show up as variations in the size and position of the outer edges of the formed profile. Wherever possible, this should be allowed in the design.
Sometimes, a customer may want to scale up production from press brakes to roll forming, and this may be possible depending on the profile design. However, it’s also quite likely that design changes will be needed to make this switch.
This is best approached at the initial design stage. While press brakes are ideal for small-quantity production, if future volume growth is expected, consider designing for roll forming from the outset rather than being forced into making changes after a product has launched.
Roll forming is extremely cost-effective for larger quantities of profiled section, and is often used when rigidity and low weight are priorities, as in building materials and channels. But it’s just as effective for shorter-length parts, like brackets, rails, and supports.
Despite the many benefits of roll forming, it may not be the best process in some situations. Thick materials and those with little ductility aren’t suitable, and smaller quantities can be expensive per piece.
MMC Roll Form is an industry-leading, ISO-certified roll forming manufacturer in the United States. We have over 50 years of experience manufacturing roll form parts with tight tolerances. Our additional capabilities include pre-piercing, cutoff and notching, and offline fabrication and assembly.
If you’re not sure if roll forming is the best route for your project, please contact us today for a free, no-obligation project analysis.