Durability. Flexibility. Cost-effectiveness. Adaptability for a variety of industrial and commercial applications. You’ve probably wondered at some point how hot forming and cold forming compare in these categories.
Although hot rolled steel shapes comprise the highest volume of rolled items in the United States, did you know that contract roll forming only uses cold rolling? So, to us, cold roll forming is just … roll forming. Hot rolling is basically nonexistent in the contracted OEM roll forming world. This process is left up to the steel mills making standard, commodity-type shapes.
So, when it comes to hot forming vs. cold roll forming, what are the differences that make the cold process applicable and sometimes a better choice than hot forming?
What Is Hot Forming Vs. Cold Roll Forming?
Hot forming is a combination of extruding and rolling using molten steel under extremely high temperatures. Some structural shapes, such as those used in holding up and reinforcing buildings, really cannot be made any other way than hot forming.
A classic example is having a large “plunger” that is filled with hot steel, which extrudes a shape used for an I-beam in structural applications. It then goes through a series of rollers that fine tune the shape and squeeze it down into the tolerances required for that particular shape.
It doesn’t make sense to take a bar of steel and try to cold form it into something like an “I” shape. Coiled steel sheet down to a certain thickness (0.60”) can also be produced with hot forming.
The challenge is that this is a very specialized mill process. The use of high temperatures and molten product require the use of huge furnaces, which aren’t exactly in abundance. It’s a huge investment to buy the machinery needed to safely manage molten steel, and to find the experienced manpower to operate the equipment.
True-ish to its name, cold forming involves making shapes at room temperature or slightly above room temperature.
It does not take a lot of high-temperature, specialized cold roll forming equipment to produce cold rolled shapes. The two forms of raw material typically fed through roll forming machines are flat and coiled sheets.
It’s possible to use hot rolled steel in sheet form as the raw material in cold roll forming. You just wouldn’t form it “hot off the presses,” so to speak -- it would be room temperature for days by the time your roll former works with it.
So, What Are the Big Differences?
There are uses for both hot and cold forming. The properties of certain metal grades sometimes dictate whether you should have them hot or cold formed. So, what are the big differences between hot rolled steel and cold formed steel?
Run Speed & Quality
With hot steel, it might take 50 rolls to thin a workpiece out, while that same piece may require 100 passes with cold roll forming. Why? It takes more force to manipulate the metal.
However … with more rolls, you can also get tighter tolerances on the piece and a higher-quality end product. This can increase the costs because of the additional machinery and labor time required, but it may be worth it to your customer.
Structural shapes like I-beams are usually hot rolled. The formula of steel used for I beams is different than used in cold forming. It’s less ductile and harder, which makes it tougher to bend cold, hence the use for structural shapes that carry a lot of weight!
Cold roll forming has many commercial and industrial uses. They include:
Sign posts & guard rails
Escalators & elevators
For similar grades, cold rolled metal can be stronger than hot rolled metal because of what’s called work hardening. When you put a piece through 100 vs. 50 passes, the strain you put on the material actually hardens it and makes it stronger.
If hot rolled sheet is specified for a part that will be roll formed, you’ll still get some added strength. But it won’t match the strength you would have received if you started with standard cold rolled material.
As we mentioned, steel sheet is only hot rolled up to a certain thickness. You can’t buy 20 gauge hot rolled sheets. At that point, you’ll have to use cold rolled.
Since roll formed parts are usually produced from coiled material, product length is limited only by the amount of material in the coil and the handling of the finished part. Hot rolled shapes are also only limited by equipment capability.
Roll Forming Makes Senses … Usually
Cold roll forming usually results in better, more attractive finished surfaces with closer tolerances. It can be formed into a wide variety of shapes that can be easily galvanized, painted, or powder coated during the forming process.
The point, of course, is to use the process that is right for the job. If you need to know more about whether your application fits with roll forming or an alternative process, it’s best to ask a manufacturer first before marrying yourself to either process.
“What is metal roll forming?”
Even design engineers with 20+ years of experience still Google this question. Despite its efficient and industrious nature, roll forming is a niche manufacturing process known to few and understood by even fewer.
When it comes to metal fabrication processes, roll forming is one of the most affordable available.
People not familiar with roll forming usually need some education regarding the machines’ capabilities and limitations – even people who regularly work in sheet metal roll forming. There’s a reason skilled roll form engineers are a coveted resource – this is complicated stuff.