Roll Forming: A Cost-Effective Parts Manufacturing Process

Mission creep is a common problem in manufacturing. The initial success of a product can trigger an unexpected level of demand, ironically leading to production volumes that are less cost-effective.
 
When this occurs, switching to a different production method may be the most prudent option.
 
Consider cold roll forming.
 
In cold roll forming, a roll set progressively bends a steel strip into a final shape. This process can produce many different profiles out of many different types of steel. It can also give the steel one or more curves as well as holes and notches. 
 
Including these additional details in one step can eliminate secondary operations, which means that when the steel comes off the line it can simply be cut off as a finished part.
 
Roll Forming vs. Brake Forming
For mid-size or large orders, roll forming has several advantages over brake forming. Roll forming accommodates much longer parts, and the capital investment in roll forming is generally less than brake forming. This is because one roll former can roll many different parts, provided it has the right tooling sets.
 
The roll forming process can produce very complex shapes, though this will increase costs. Many products are made with 12-16 passes through roll formers, but very complex shapes can require fifty passes or more.
 
“You see a lot of that in the electrical and aerospace industries,” said Thomas Brewer, president and general manager of Cargowall. “We’re starting to see parts being rolled, the pass shift in the roll form, the steel moving 3-4 feet and the pass shifting back out…basically putting a wave in the part.”
 
Multiple passes may work-harden the material, but roll forming manufacturers can use this to their advantage. “You can buy a lower yield material knowing that you’re going to work-harden it during the roll forming process,” said Brewer.
 
Roll Forming Materials
Roll forming processes can be applied to a wide variety of steels.
 
New steel alloys are considerably harder to roll form than the traditional carbon steels because of factors like increased spring back. The steel industry’s goal is achieving more strength with less weight, which means that manufacturers are pushing the envelope to 80 (KSI) or 100 (KSI) steel.
 
Brewer offers this advice: “If you’re going to try a new type of steel, it’s best to talk to a roll designer who’s worked with it before. If you don’t, you can spend 2-3 months perfecting the process to meet the specifications.”
 
Cargowall works with materials as thin as ten thousandths of an inch, measuring all the way up to 5/16ths of an inch. Depending on the facility, roll forming can be used to create parts as small as 3 or 4 inches, all the way up to rail car parts 70 to 80 feet long.
 
 
It is also possible to roll form pre-finished material. Cargowall is currently developing a part manufacturing process for the tractor trailer industry that involves rolling two different steels in the same roll forming mill.
 
The new process will wrap pre-painted steel nineteen thousandths of an inch thick around unfinished steel sixty thousandths of an inch thick.
 
“A lot of it is just bending metal,” said Brewer. “But when you start to wrap two different materials in one mill and come out with a finished product, that’s a little more interesting.”
 
Reducing Costs with Roll Forming
Three main factors impact the cost of roll forming a part:
 
Complexity of the part
Dimensions of the part
Volume of the order
Greater complexity means more passes through the roll former, and also requires longer setup times. According to Brewer, “Depending on the part and the size of the mill, you can spend eight hours setting up for a part.”
 
Complex parts also require more tooling, which impacts production costs significantly when customers own the tooling.
 
This is one reason Cargowall often elects to make the investment in the tooling themselves. “We look after the design of the roll tooling [so] the customer is happy they aren’t putting out extra money,” said Brewer.
 
A part’s dimensions will also affect its cost, though dimensions are less of a limiting factor for roll forming than for brake forming, which is restricted by the width of the press brake.
 
For cold roll forming, the size of the roll is the crucial issue.
 
“If you start rolling a part that takes 20 passes and it’s 1/4 inch material, the rolls are 22 inches in diameter. At that point, some of the rolls weigh 140-150 pounds, so you need cranes to put the rolls on,” said Brewer.
 
Even more than the other factors, the volume of the order determines whether it’s worth switching from brake forming to roll forming. “If it’s a complex part to press brake, then it’s most likely a complex part to roll form,” said Brewer.
 
But as production volume increases, brake forming becomes less cost-effective as the press brakes get closer to operating at full capacity. At that point, the manufacturer must decide whether to buy another press brake, or switch to a roll forming process.
 
Identifying that point can be difficult, but there are ways to smooth the transition.
 
“If we know what the part is fitting up to, then we can analyze what’s critical for the part and what’s not. Focusing on the critical items saves us a lot of trial and error,” said Brewer.