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 when it comes to forming metal.
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, well, roll forming.
Hot rolling is almost nonexistent in the contracted OEM roll forming world. This process is left up to the steel mills that make standard, commodity-type shapes.
So let's take a look at the ins and outs of cold formed vs. hot rolled steel:
What Is Hot Forming vs. Cold Roll Forming?
What differences make the cold process applicable for roll forming and sometimes a better choice than hot forming?
Hot forming allows for the creation of complex shapes and can require fewer rolls to thin the metal.
On the other hand, cold roll forming is a more controlled and precise process that results in stronger steel products with well-defined angles and edges. Cold roll forming also offers the advantage of not requiring the additional time and costs associated with heating and cooling the material.
Hot Roll Forming
Hot forming combines extruding and rolling using molten steel under extremely high temperatures. Some structural shapes, such as those used in holding up and reinforcing buildings, cannot be made any other way.
A classic example is having a large “plunger” 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 its shape and squeeze it down into the tolerances required for that particular shape.
It doesn’t make sense to take a steel bar and cold form it into something like an “I” shape. Hot forming can also produce coiled steel sheets as thin as 0.60”.
The challenge is that this is a very specialized mill process. Using high temperatures and molten material requires 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 experienced workers to operate the equipment.
Cold Roll Forming
True-ish to its name, cold roll forming involves making shapes at room temperature or slightly above room temperature.
It does not take a lot of high-temperature, specialized 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 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.
(Resource: Want to know more about cold roll forming? Click below to read our guide!)
What Is the Difference Between Hot Rolled and Cold Rolled Steel?
There are uses for both hot and cold forming. The properties of specific metal grades sometimes dictate whether you should have them hot or cold formed.
Differences include:
- Run speed & quality
- Structural uses
- Strength
- Size limits
Run Speed & Quality
It might take 50 rolls to thin out a hot steel workpiece with hot roll forming. That piece may require 100 passes with cold roll forming. Why? It takes more force to manipulate the metal.
However, with more rolls, you can get tighter tolerances on the piece and a higher-quality end product. This process can increase the costs because of the additional machinery and labor time required, but it may be worth it to your customer.
Structural Uses
Structural shapes like I-beams are usually hot rolled. The formula of steel used for I beams is different from that used in cold forming. It’s hard and less ductile, which makes it tougher to bend when cold, hence the use for structural shapes that carry a lot of weight!
Cold roll forming has many commercial and industrial uses. They include:
- Signposts & guard rails
- Solar
- Refrigeration
- Escalators & elevators
Click here for more information on some of the many uses of roll forming.
Strength
For similar grades, cold rolled metal can be stronger than hot rolled metal because of work hardening. When you put a piece through 100 vs. 50 passes, the strain you put on the material hardens it and makes it stronger.
If the roll formed part requires hot rolled sheets, you’ll still get some added strength. But it would be stronger if you started with standard cold rolled material.
Size Limits
As previously mentioned, steel sheets are 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 component. Hot rolled shapes are also only limited by equipment capability.
advantages of Roll Forming
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 best process for the job. Do you need to know whether your application fits with roll forming or an alternative method? Ask a manufacturer before committing to either cold or hot roll forming.
Want to Learn More About Roll Form Design?
Our Comprehensive Design Guide to Great Roll Formed Parts gives a good primer for optimizing your design for cold roll forming. Download the guide below:
(Editor's note: This article was originally published in January 2019 and was recently updated.)
Topics: OEM Roll Forming, Pros and Cons
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