Automating and integrating a tube fabrication workcell

With a wealth of tube bending opportunities available in today’s manufacturing economy and a dearth of tube bending experts, more companies are going to be looking at automated workcells to produce laser-cut and bent tube fabrications. Images: BLM Group

Manufacturers have always had an interest in making processes more efficient, more consistent, and less labor-intensive, and these interests continue to grow. The scarcity of skilled labor, increasing competition (both domestic and foreign), the cost of materials, the increasingly stringent dimensional accuracy required by many OEMs, and other factors continuously pull fabricators down a path toward greater use of equipment and less reliance on workers.

The last few years have brought huge growth in the implementation of robots and cobots. Abetted by progress in sensor technology and software, robots and cobots are becoming progressively more capable and increasingly attractive. The variety of end effectors, the sensitivity of the sensors, and the abilities of the software grow and expand more or less continuously, enabling robots and cobots to do more as time goes on.

However, this doesn’t mean that setting up an automated process with a robot or a cobot is easy. Far from it. Consider the number of steps involved in a common task—say, a worker retrieving five unique fabricated tubes from a variety of bins and packing them into a carton for shipping. The worker has to look into the first bin, locate one tube in a jumbled pile of tubes, grip it, lift it, and place it into the shipping carton. It’s a simple matter for a person, but for a robot, every one of those steps has to be programmed, which is anything but simple.

Many, many tube fabrication projects have been automated and many workcells have been integrated, but it’s a matter of finding the right opportunities and understanding the scope of the investment.

Matching Machine Capabilities to Production Necessities

“Using cobot technology in an automated cell to integrate a tube laser machine with a bender isn’t always as easy as it seems,” said Gunar Gossard, BLM GROUP’s director of sales. “The first step is finding a match between the diversity of parts made by the shop and the capacity and size of the cobot. Considering a robot that loads and unloads a press brake, usually it’s easy to go from one part to another, but it becomes a challenge when dealing with tube in a fabrication cell and changing to a new diameter or length.”

Fabricators have to consider how each part will be presented to the robot, how it will be gripped by the robot, whether or not seam detection and orientation are important to the project at an immediate stage or some subsequent stage, and how to prepare the tube to go to the next step or the next station. Variables from one production run to the next include part dimensions, contours, and weight—and every dimension counts. Diameter, overall part length, the number and lengths of straights between bends, and the overall part envelope—the amount of space it occupies along its X, Y, and Z axes—influence how the part is to be located, gripped, manipulated, and moved.

“For many fabricators, the frame of reference is an automated cell with a laser machine that makes parts from sheet,” said Robert Adelman, BLM’s North American laser product manager. “Sheet is flat so it’s easy to handle. The raw material goes from a storage tower to the laser machine and it can run 24/7. With the right unloading system, a workcell like this can run unattended overnight. This works because the number of variables is small compared with a laser for cutting tube.”

A key difference is how the material gets from storage to the machine.

“When using a sheet laser, the material doesn’t move,” Adelman said. “The sheet sits on a pallet table. The pallet table shuttles in and out of the laser, bringing raw material in and taking cut parts out.” Getting tube into a laser machine can be like that; a magazine loader might hold enough material to run several hours. However, unloading material from a tube laser is a completely different matter; each tube has to be unloaded individually.

“A fabricator might fill its loader five times a day but it has to unload two parts per minute,” Adelman said.

One of the most common applications for robots in a tube fabrication workcell is unloading tubes from a laser cutting machine.

That unloading often is performed with an incline table. The tube comes off the laser, hits the table, and gravity takes over. The tube ends up in the same location every time. Removing tube from a bender likewise tends to be easy. When the bending action comes to a stop, the tube is located in the same spot every time.

Still, tube diameter is a consideration. A small-diameter tube, especially one laying on an incline table, can be difficult for a robot to grasp. A magnetic end effector is a possibility if the tube is carbon steel or one of the 400 series stainless steels.

Another big consideration is part orientation throughout each of the steps. Consider a part that has a coped end (a fishmouth). The part is to be welded to a bore on another tube to become part of a manifold. If the part needs several features—perhaps a fishmouth in the right orientation at the other end, some bends, and a hole along the length of the tube—getting everything lined up just right is easy on paper but difficult in practice.

Bends alone can be perplexing. Long, shallow bends are forgiving, but these are rare. As manufacturing becomes more complex, everyone wants to pack ever-greater numbers of components into smaller spaces, so bends tend to become more severe over time, meaning that the weld seam must be oriented along the bend’s neutral axis to prevent splitting. For a part with several bends, proper part orientation can be a compromise, getting the weld seam as close as possible to the neutral axes of several bends. Add two coped ends and the aforementioned hole so the tube can be joined to yet another tube, and the challenges in proper orientation multiply.

For a part like this, the laser machine needs a built-in weld seam detector. Coping the ends and making the hole in the proper location relative to the coped ends and relative to the weld seam is no challenge—this is what lasers do, all day, every day. Offloading the part onto an incline table so it ends up in the same location every time likewise is a simple matter. Getting it to the bender probably isn’t much of a problem, but rotating the tube to the proper orientation is now critical. Depending on the precision of the application—say, a part for a fluid delivery system in a machine or perhaps an aircraft—just a tiny amount of rotation, as little as two degrees, might render such a part useless.

Options? Another seam detector might work. Using a vision system to detect the hole in the tube wall is probably a more precise and less expensive way to go. If the tube doesn’t have a feature that’s easy to find, another option would be to use the laser itself, at low power, to add an orientation mark to the tube’s OD.

This is just one scenario involving one tube. Add a dozen more part numbers, some with more features and therefore more complexity, and the challenges in setting up the cell multiply exponentially.

Another facet is efficiency. The planning stage involves mapping out each production step and the flow.

“If a process is worked out to be single-piece flow, the benefit is that the shop floor isn’t cluttered with carts of work in progress,” Gossard said. “The downside is that every machine runs only as fast as the slowest machine, which means the laser usually has a lot of idle time.” That’s good for establishing a streamlined flow, but terrible for the laser’s return on investment.

“It’s really a matter of what the manufacturer wants to accomplish,” Adelman said. “In conventional manufacturing, a laser cutting machine might make a part every 10 seconds.” That’s dazzling, but unless the subsequent stages can process parts that fast, a pile of WIP is going to stack up next to that machine. “In a fully automated and integrated cell, the output might be one part every two minutes,” he said.

An important and related point that Gossard stressed is that a worker provides the ultimate level of versatility, and it’s unmatched by any robot or cobot. A robot can handle simple, repetitive tasks quickly and efficiently and never takes a sick day, but it simply can’t match a worker’s ability to process inputs and make the decisions needed to carry out a series of tasks. Stated another way, a robot imposes limits. Nobody wants to consider limiting the productivity of a tube laser cutting machine or a tube bender, but there is no way to get around it.

This doesn’t mean that big, grand plans can’t be achieved. Often the limit isn’t the technology but the cost.

“In part, it’s a matter of how much a fabricator wants to spend,” Gossard said. “Often these projects start out as big plans, but then it’s a matter of making a few compromises so the project matches the budget.”

Staying on Top of the New Workcell

With this level of investment, fabricators want to ensure that the automation is working as intended. That’s where digital connectivity can make a big difference.

Greg Klemme, vice president and general manager of operations for Mittler Bros. Machine & Tool, has been involved in robotic applications and automation projects all over the map, including some involving tube lasers. Even when his company’s technicians are not on-site in fabricating facilities, they are not that far away.

Klemme said Mittler Bros. has used virtual private networks (VPNs), a secure, encrypted channel between two devices that acts as a private tunnel for data and communications exchange over the internet, to stay engaged with customers that need consulting on their equipment, without forcing a technician on the road. If a fabricator has trouble with the workcell, a technician can access the machine control via the VPN to diagnose error codes or even review machine programs. Expert troubleshooting is only an internet link away.

Sometimes seeing is better, so the digital connectivity is taken to the next level, and cameras are installed on the equipment.

“We had a customer that had a huge piece of equipment, and we requested they put cameras on their cell. So if there were issues, we could go back and look at the footage to find out exactly what happened and how to prevent it from happening again,” Klemme said.

Fabricators interested in keeping tabs on their workcells can access dashboards that are created to pull performance information directly from the machines. Managers can track something as simple as machinery starts and stops to get an idea of just how efficiently the cell is operating. Maintenance technicians get accurate data on machine wear.

This digital connectivity helps to ensure the ultimate potential of the automated workcell—unattended operation while still meeting customer specifications and deadlines. It particularly comes in handy as the targeted fabrication work becomes more complex.

Klemme said his company is just starting to quote work on workcells with not only tube laser cutting, but also tube bending. Meanwhile, Gossard estimated that of the equipment sold by BLM, about 60% concerns automation projects involving sheet lasers and press brakes, and just 5% involves integration of a tube fabrication cell.

Tube fabricating is an area ripe for more automation investment. It’s just a matter of seeing what companies are going to take the lead.