For many metal shops, finding a sheet metal rolling specialist is difficult, so it makes sense to train one yourself. Photos provided
If you want to learn how to drive a car, you can go to your nearest parking lot and practice entering parking spaces, turning, reversing, different speeds, and emergency braking. If you want to learn how to drive a race car, you will need more practice, the right equipment, the right track and a team behind you. In other words, it’s a big leap from driving a family sedan in an empty mall parking lot to driving Kevin Harvick’s Ford on a NASCAR track.
The same idea applies to working on a sheet metal press. Anyone can load material into the machine and press a button on the CNC controller to start it. However, this does not mean that things are going smoothly.
Even in the era of advanced CNC machines, sheet rolling remains an art form. The thickness and hardness of the material can vary from sheet to sheet but still be within specified tolerances, adding variety to an already complex job. Careful execution of operations helps maintain a safe work environment and promotes accurate work, but shops are always under pressure to increase productivity. In an era where “set it and forget it” control technology has appeared in everything from laser cutters to automated press brakes, experienced press brake operators are always welcome.
Unfortunately, experienced operators are not always available. There are not many sheet metal shops, so the industry simply does not produce a large number of qualified sheet metal machines. In fact, in some cities you will see a good operator jumping from one manufacturer to another, demanding a small raise at each stop because the company values the skills the employee possesses.
Businesses wishing to enter the flat steel industry may be forced to develop their own specialists. This isn’t necessarily a bad thing, since the company knows more about the machine operators it might like than an unknown number of other manufacturers. With that in mind, here are some recommendations for shops that may be looking to add plate rolling experience to their ranks.
Someone with experience in metal fabrication will have a better understanding of how metal reacts during the bending process. For example, those experienced in metal forming know that as a material is formed, it moves along a stress-strain curve that has peaks and valleys. Eventually, the operator can apply enough pressure to the material and the process moves downward, making it easier to move the material. But as operators leave this valley, the material becomes increasingly difficult to manipulate.
This is not an uncommon problem in heavy factories where someone rolls the sheet back and forth on a hand-held machine, gradually reducing the sheet to the desired diameter. As he approached, the operator pulled the bent roll a little, but the diameter became too small. The operator had no idea how the material could move so much with so much resistance. After so many falls, experience helps him become more aware of dramatic changes in materials. Scrap metal cylinder made from 1/2-in. Carbon steel is bad news for everyone.
Operators also need to be aware that there are differences between materials that may be considered the same material. Different aluminum alloys have different properties, with some considered softer and easier to machine than others. In addition, the properties of the material change with age. For example, if a shop is simply stacking laser-cut aluminum blanks and the parts below are not being used because new blanks are always stacked on top of them, the press brake operator needs to understand that the old blank underneath may be stronger than the newly cut blanks.
A person with press brake experience is probably the closest thing to a person with metal forming experience, but it’s not quite the same as sheet metal rolling. When forming with a press brake, the bending is static. It’s a little easier to measure the load required to bring the metal to a certain point. Sheet rolling is a continuous process in which the material and bending rollers move simultaneously. The situation is a little complicated. But someone with press brake experience has at least some understanding of how metal reacts to bending stress, so they can be more careful when using more expensive materials.
Typically, training on a newly purchased sheet metal rolling machine is conducted on the first shift, with future sheet metal equipment operators also present on site. It doesn’t matter if the company only has one shift. But if the company introduces second and third shifts, then the operators of these shifts will also need to participate in training. And the fact that the third shift operator will be late for two additional hours over two days does not count.
When rolling a sheet on a machine of this size, the job must be done correctly. The workshop has no right to reject workpieces that do not meet customer requirements.
Rolling a steel sheet with a grain structure requires less effort than rolling against the grain because the ductility of the material is easily stretched when the sheet is produced in a rolling mill. The problem is that the computer on the sheet bending machine cannot determine the direction of the grain of the sheet loaded into the drum. This is determined by the operator.
But bottom-up processes can help. Instead of simply cutting blanks and laying out parts in a random order, regardless of the grain pattern, the operator can take the time to ensure that each laser-cut blank is laid out so that the grain pattern on each part moves in the same direction. This way, the sheet metal operator can load stock and expect the sheets to be somewhat similar in shape without worrying about random sheets causing him to roll against the grain.
When purchasing a new sheet metal rolling machine, many people rely on a tape measure to check the radius. Literally, this means that the rolled plate is removed from the machine and inspected using a tape measure.
It makes more sense to create a template. The manufacturer has a plasma or laser cutter nearby, so he should cut the template to the specified radius. The template can then be attached to the rolled sheet while the template is still in the drum. If the dimensions are incorrect, you can run the machine to add the finishing touches to the rolled out shape.
For those new to sheet rolling, four-roll machines are easier to work with. First, loading panels into the machine is easier than loading panels into a three-roll machine because the bending roller can be used as a backstop on the shears.
When the sheet is loaded into the machine, the operator lifts the back bending roller and moves the material until it reaches the center of the back bending roller, straightening it just like a brake brake operator would do with the workpiece and back gauge as it was done. The bottom roller then rises to clamp the material. With this four-roller design, the material is held in place by the rollers throughout the bending process.
Now, four-roller casters are less versatile than three-roller casters because the space between the top and bottom of the four-roller is limited. In addition, when material is clamped in a four-roll machine, the equipment exposes the sheet to the crown of the roller. (The rollers are convex, which helps withstand deflection during bending.) A four-roll machine will almost inevitably give the material some odd shape, although in most cases a barrel or hourglass shape will still be appropriate. Work permits.
If budget is not an issue, manufacturers are interested in processing 16 GA. For materials up to 0.5 inches thick, you can purchase a four-roll bender with an 18-inch diameter. The rolls are straight, not convex. (Straight rolls can handle deflections because they are much larger than conventional rolls on machines that can roll the same thickness of material.) However, the reality is that few companies are interested in purchasing larger machines with straight rolls. Most shops have different applications in mind when purchasing a sheet metal rolling machine, so they want to get the most out of their investment.
Plate rolling works best when an experienced operator can supervise the operation, but this does not mean that a less experienced operator cannot produce quality parts. If management can put someone in place who is willing to understand the molding process and is familiar with the controls, which are similar to a cell phone interface, the company has a good chance of success.
Early training from the machine supplier will not cover all situations that a manufacturer may encounter when using a new press brake, but the supplier should be available for immediate consultation. Difficulties are to be expected. Fortunately, they make press brake operators more capable and better prepared for the next challenge that eventually arises.
Advances in modern control software and hardware have made it easier than ever to produce uniform quality sheets, but dedicated operators are also an integral part of the process.
Post time: Oct-23-2023