What’s the difference between Hot Forming and Cold Roll Forming?
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 roll forming compare in above 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 what are the differences that make the cold process applicable for roll forming and sometimes a better choice than hot forming?
WHAT IS HOT FORMING VS. COLD ROLL FORMING?
Hot 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 investmentto buy the machinery needed to safely manage molten steel, and to find the experienced manpower to operate the equipment.
Cold Forming
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 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.
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 Uses
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:
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 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.
Size Limits
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.
Original Text: WHAT’S THE DIFFERENCE BETWEEN HOT FORMING AND COLD ROLL FORMING?
Frequently Asked Questions
Can I use hot rolled steel sheet as the raw material for a cold roll forming machine? ›
Yes, hot rolled steel in sheet form can be used as raw material for cold roll forming. The key detail is that the material must be at room temperature before it enters the roll former—it is not formed ‘hot off the mill.’ The hot rolled sheet sits for days or longer until it cools completely, then runs through the cold roll forming machine like any other coiled or flat sheet input.
Why is hot forming not typically used in contract or custom OEM roll forming work? ›
In the contract roll forming world, cold roll forming is the standard process; hot forming is essentially nonexistent for this type of work. Hot forming is performed by steel mills that make standard, commodity-type shapes, such as I-beams for structural applications. The extreme heat and specialized mill equipment required for hot forming are not practical for the custom, smaller-batch profiles typically associated with OEM roll forming projects.
What are the primary trade-offs between hot forming and cold roll forming in terms of production passes and tolerances? ›
The trade-off centers on speed versus precision. Hot forming can require fewer rolling passes—for example, about 50 passes to thin out a piece—because the metal is more malleable at high temperatures. Cold roll forming typically requires more passes, potentially around 100, because it takes more force to manipulate room-temperature metal. However, the additional passes in cold roll forming allow for tighter tolerances and a higher-quality, more precise finished product.
How does cold roll forming affect the strength of the metal compared to hot forming? ›
Cold rolled metal is generally stronger than hot rolled metal of similar grade due to work hardening. The strain placed on the material during the cold forming process—especially with the higher number of passes—actually hardens the steel, increasing its strength. Even if you start with hot rolled sheet but form it cold, you will get some added strength, though it will still be less than what you would achieve starting with standard cold rolled material.
When would a structural I-beam still need to be made through hot forming rather than cold roll forming? ›
Structural shapes like I-beams are a classic example of parts that generally must be hot formed. The steel formula used for I-beams is less ductile and harder than what is typically used in cold forming, making it extremely difficult to bend cold. These shapes are designed to carry heavy loads, so the material properties and geometry required are usually only achievable through the hot extruding and rolling process used at steel mills.
Does the page explain the thickness limits that dictate when to use cold rolled instead of hot rolled sheet? ›
Yes, the page notes that steel sheet is only hot rolled down to a certain thickness—specifically, you cannot buy 20-gauge hot rolled sheets. When you need material that thin, you have to use cold rolled steel. This makes cold roll forming necessary for many thinner-profile applications, regardless of the production method’s other advantages or disadvantages.
