It is the responsibility of every metal fabricator, including rolling plate operators, to create and keep up-to-date with a list of guidelines, tips, tricks, safety shortcuts, and rules for every metalworking process and operation they perform.
Metalworking is an art, and serious manufacturers treat it that way, learning and applying skills that create near-perfect parts every time. When press brake/plate rolling machine operators continually build and refer to their personally compiled list of “rules of the road”, their ability to reliably perform any bend required to achieve the correct angle in any type of metal is greatly enhanced.
The plate rolling machine operators also need to maintain such a checklist – a “roll rule”, so to speak – to ensure the proper radius is obtained for any job they encounter. Guides for better rolling can be obtained in a number of ways: by being instructed by an expert rolling operator; learning books and videos about rolling procedures; or just simple trial and error.
There’s a lot to learn (and practice) along the way to becoming a truly skilled plate rolling machine operator, such as understanding how different metals behave under pressure, the math involved in rolling jobs, or preventing rolling operations from failure. As a metal worker learns and grows in these various fields of knowledge, he or she will transform from a mere plate rolling machine operator to a true metal craftsman.
Be a plate rolling artist
A fabricator doesn’t need to seek a bachelor’s degree in engineering or materials science followed by graduate studies to gain a working knowledge of rudimentary metallurgy—all it takes is a passion for metals and a willingness to study. Understanding the basic properties of all the metals that will potentially be used at a shop will greatly benefit a metalworker who will have to cut, roll, bend, or otherwise fabricate them.
How Metal Reacts During a Bending Process
A person with a basic metal fabricating background is going to be much more aware of how the metal reacts during the bending process. For instance, someone with metal forming experience understands that as a material is being formed it moves along a stress-strain curve, which has peaks and valleys. Eventually, the operator gets to the point where he is able to apply just enough stress on the material, and the process moves down the valley, where it becomes much easier to move the material. But as the operator comes out of that valley, the material becomes much harder to manipulate.
This is not an uncommon problem in heavy fab shops where someone is rolling a plate back and forth on a manual machine, gradually bringing the plate down to the needed diameter. When the operator gets close, he brings the bending roll up just a hair, but the diameter gets too tight. The operator has no idea how the material moved so much after being so resistant. Experience would have had him be much more aware of dramatic material changes after having worked it so much in the rollers. A scrapped cylinder made of ½-in. carbon steel is bad news for everybody.
The operator also needs to recognize that differences exist in what might be considered the same material. Different aluminum alloys have different characteristics, with some considered softer and easier to form than others. Also, material properties can change as it ages. For instance, if a shop is just stacking laser-cut aluminum blanks and the workpieces at the bottom are not used because newer blanks are always stacked on top of it, a plate rolling machine operator has to be cognizant that the older aluminum blanks at the bottom are likely more hardened than the more recently cut blanks.
A person with press brake experience might be the closest a shop can come to find that person with metal forming experience, but it’s not exactly the same as plate rolling. In press brake forming, bending is static. It’s a little easier to measure the load that it takes to get the metal to a certain point. Plate rolling is a constant process where the material and bending rolls are moving simultaneously. It’s a little more complicated. But someone with that press brake experience at least has some familiarity with how the metal reacts when it is under bending stress, so he may be a bit more cautious when working with much more expensive material.
Simple plate rolling mathematician
There’s no getting around it—expert fabricators need to understand math. While the advent of CNC plate bending machines has greatly simplified metal forming processes, there is no substitute for a metalworker being truly adept at his or her craft. Tales abound in the industry of a job being saved from ruin by a knowledgeable fabricator spotting an error that was entered into a program by mistake.
In plate rolling operations, indispensable math skills run from the elementary to the complex. Some examples include:
The minimum internal diameter of a part that can be rolled or pre-bent is based on a multiple of the diameter of the top roll of the machine in question and varies according to the thickness of the workpiece.
In procuring the correct blank to create a cylinder, the ability to calculate the centerline arc of the rolled part is necessary (subtracting the thickness of the material from the outside diameter of the cylinder), then multiplying that number by pi (3.1416) to give the length of the needed plate.
Roll bending a plate into a conical surface requires understanding the different radii along the length of the finished cone, along with other factors, such as the angle of the axis of the upper roll in relation to the axes of the side rolls at each step of the operation.
The Math Behind Plate Rolling
The plate rolling process entails two groups of important variables. The first group hinges on the machine, such as the number of rolls, their diameter, position, and how they move. All these depend on the machine being used. The second variable group deals with the workpiece involved, such as the maximum plate width (W), maximum plate thickness (Th), and the minimum workpiece diameter (Ø), as well as the type of metal and its yield strength (YS). These variables can be plugged into an equation: W x Th2 x YS/g = K, where K is the constant and g is a parameter that takes into account the workpiece diameter and the Sheet Metal Rolling Machine geometry.
Applying such equations requires detailed application information, of course, but the important takeaway here is the factor Th2. Note that the sheet thickness value is squared, implying that a small change in thickness can have a dramatic effect on roll parameters.
Plate Rolling tips in Tribal Knowledge
In most companies, there is a large amount of knowledge about products, customers, and processes that are only known to certain employees. This information is called tribal knowledge and it is a problem that many companies are either unaware of or unconcerned about.
Think about when you first learned that a quick and effective way to check the radius of a rolled part—while it’s still on the plate roll—was by using a precut template you could hold against the inside diameter. While such knowledge might have been gained from an article like this one or through an instructional video, it is much more likely that the trick was taught to you by a mentor, either on the job or in a class.
The best learning will always take place in the presence of experts who are willing to impart what they know while answering any questions that arise during the instruction. Likewise, as you gain skills and knowledge, be ready to share it with others at your workplace and elsewhere in the coming months and years.
As fabricators share the various techniques that they’ve learned to make jobs easier, safer, and of better quality, they are increasing the tribal knowledge within their organization—and likely also within the local industry—that will hopefully be passed down through many generations of future metalworkers.