Structural beam cambering with throughput in mind
How to camber efficiently while keeping the process flowing in structural fabrication
A cambering station (on the right) can be integrated into a broader automated line. The material handling strategy hinges on, among other factors, available floor space and the volume and variety of beam dimensions requiring cambering.
Because gravity works, there will always be a need for beam cambering. Walk on a floor of poured concrete, and it's highly likely the beams underneath have been cambered to counteract deflection under load. Roof beams can require cambering as well. In fact, unlike floor beams, which usually have a single camber point, roof beams can require multiple points of camber. And some beams need to be cambered in specific ways to meet cosmetic requirements.
Beam cambering has always had a black magic quality to it, originating from the days when skilled fabricators wielded a rosebud torch back and forth in a careful pattern along the web to make the beam bend under its own weight. It required time, seriously experienced talent, and a lot of consumables—hence the growing dominance of another method: cold cambering.
Hot cambering still has a place for light, narrow beams with short web sections, as well as other beam geometries highly susceptible to crimping. Otherwise, most perform some type of cold cambering.
So who does the cambering within the construction value chain? As with so many processes in the fab shop, this depends on the volume of cambered beams fabricators process, the available talent, and the technology on the floor.
"There's a lot of know-how that goes into beam cambering, especially if an operation doesn't have someone dedicated to the task day in and day out,'"said Ben Morrall, vice president of sales at Voortman USA, Monee, Ill. "This is why some structural fabricators lean on the service center."
This makes sense in some supply chains. A structural fab shop might not have the volume that calls for someone to camber beams all day, every day on a dedicated machine, but a service center might. And cambering all day, every day is a good way to develop talent for what remains a subtle process. Beams bend differently depending on their web width, web thickness, and flange dimensions. They also form the hard way, on their widest and strongest axis. Springback and other forming characteristics can vary from beam to beam, especially if those beams come from different mills or heats. Bend too hard or position the beam incorrectly and the web can buckle.
One challenge with cambering lies in the handling requirements. Sure, material handling isn't really an issue with hot cambering. As a portion of the overall process time, the crane time is inconsequential.
But cold cambering changes the situation. If you consider the overall cycle of a cold cambering operation, much of that time involves tying up a crane, transporting the beam to and from the machine, as well as positioning the beam in the machine itself.
Again, this might not be an issue if, say, a service center uses cranes to move a beam in and out of inventory anyway. But as Morrall explained, automation has changed the way beams move on the floor, particularly at the structural fabricator. Today some shops minimize crane picks by sending a beam down conveyor systems through cutting, drilling, coping, and other processes before it’s picked and moved to final fabrication or shipping. It’s about beam velocity, and another crane pick to the cambering machine can slow things down significantly.
"Say you have a stand-alone unit that's not connected to your main processing line," Morrall said. "You might have a staging area where you stack beams that go to this stand-alone unit. So you need to pick a beam from the line to the staging area, then pick it again to load the machine. At best, this can require three or four extra pickups of a product. All that material handling can be expensive."
Beam velocity underlies Voortman's approach to cambering, Morrall said. Instead of relying on a crane, the company's cambering system uses a roller conveyor to feed beams into position. A single hydraulic cylinder secures the beam against two movable load points with ridges on top that hold the beam in place during the cambering cycle. From there, the cylinder pushes the beam to a reaction point—that is, the point at which the beam is bent before it springs back to a certain position (similar to the pre-springback "bent angle"made by a press brake ram).
"For the first piece [in a heat or lot], if it reacts the way we think it will, you can get it right the first time," Morrall said. "If it falls short, you'll need to bump it a little further. But the machine will remember that reaction point, so on the second beam, it will push the beam to that correct point every time.
"The machine has a system that measures where it pushes to," Morrall continued, "and as [the beam] reacts back in the opposite direction, it measures where it reacted to. It knows what the difference is, and it will push further automatically after that."
Regarding overall cambering time, especially when conveyors allow beams to roll into and out of the process, Morrall said the machine can camber a beam every two or three minutes. He added that the quick cambering cycle time, though beneficial, is only part of the story. The goal is to increase the overall beam velocity from one end of the shop to the other, and that comes through automated material handling.
"Once you've told [the automation] what beams are on the infeed, whether it's one or six machines connected together, the system automatically distributes the material from one machine to the next throughout the total process. So near the end of the total process—after [being] shotblasted, drilled, sawed, coped, and marked—the beam gets to the cambering machine. At that point the system can automatically deliver beams that need to be cambered to the cambering station. Then anything that doesn't need to be cambered goes to the other outfeed locations to get sent to fabrication."
Such throughput, Morrall said, increases the business case for in-house cambering in structural fabrication. "Cambering doesn't need to be a costly process that fabricators simply have to do as part of a job. Instead, it can be a money-maker."
Source: the fabricator