How automating deslagging on plasma

The LISSMAC SBM-M D2 in O’Neal Manufacturing Services’ Greensboro, N.C., facility removes the slag from plasma-cut plate with metal pins attached to rubber belts that move across the belt as the part flows through the machine. Images: O’Neal Manufacturing Services

O’Neal Manufacturing Services’ Greensboro, N.C., is a busy place. The 226,000-sq.-ft. facility produces various parts, some reaching more than 400 lbs., for the nation's largest equipment manufacturers. For one particular customer, the fabricating facility is shipping about five to six trucks of metal parts each day.

The shop has an impressive lineup of cutting equipment: four fiber laser cutting machines, three CO2 lasers, five plasma cutting tables (with one also have oxyfuel cutting capability), an oxyfuel cutting table, and two laser tube cutting machines. That's creating a lot of blanks for downstream processes or delivery to final part staging. It also can create a lot of pressure for others on the shop floor to keep up.

That was the case in early 2017. The plasma cutting tables were overwhelming the parts cleaning operation nearby. Plasma-cut parts needed to be deslagged coming off the table and finished in a way to meet customer specifications. (For instance, some holes had to be ground to create a specified profile.) Thirty-two parts cleaners were doing the job manually, but they couldn't keep up. The plasma-cut parts were unloaded off the table and stacked near the parts cleaning area, waiting to be mechanically finished.

A conveyorized line with automated deslagging and edge preparation equipment installed later that year rectified the situation. The results experienced at the Greensboro facility have been noticed by other general managers in the OMS family, and the success has demonstrated just how automation technology can help a metal fabricator make the most of its labor situation while simultaneously minimizing the risk of injury.

There was plenty of motivation to minimize the amount of manual parts cleaning being done. The first thing anyone watching this cleaning action would notice is the constant picking and placing of heavy parts. Heavy parts were placed on the ground and had to be picked up and placed on a grinding table, removed when the finishing was complete, placed on the floor until it was moved to the next step, picked up once again, and placed on the appropriate carts for delivery downstream. With this type of activity comes the risk of injury, which is something every shop wants to minimize.

The largest of the parts—about 48 by 72 in. and weighing about 430 lbs.—posed the biggest risk to the parts cleaner. With no real easy way to flip the part, because both sides needed to be deslagged, company engineers came up with a table that supported the part and allowed underneath access to the parts cleaner. The part didn't need to be flipped, but someone still had to climb underneath the table to finish the cleanup job.

"That's hard for anyone having to do that, and we made about 40 of those a day," said Matt Moon, the current general manager for the OMS Greensboro operation.

The manual deslagging process was cumbersome, and the repeated motions associated with the finishing process strained parts cleaners’ muscles.

Then there's the people issue. Parts cleaning is an entry-level job at the Greensboro shop, and frankly at most metal fabricating companies, and it can be hard to find people that want to tackle that chore. It's probably even more of a chore to have them stay at it for a while. When a company is trying to employ more than 30 to do that type of job, finding parties interested in the work is incredibly challenging.

"Obviously, it's hard to find any people wanting to do this, so anything that you can do to reduce the number of people involved, you have to take advantage of," Moon said.

The SBM-XL G2S2 has grinding belts—two at the top and two at the bottom of the unit—that refine part surfaces and belts with edge-rounding blocks—two rows on top and two rows at the bottom—that remove the parts’ razor-sharp edges.

Manually cleaning the parts over three shifts increased the risk of injury for employees. It was a problem that needed serious attention.

To address this, OMS added a safety technician to oversee the parts cleaning activities for each shift. That spurred the company's decision to purchase an automated answer for this risky work process.

OMS purchased a LISSMAC SBM-M D2 deslagging machine, a SBM-XL G2S2 grinding and edge preparation machine, and approximately 125 ft. of conveyors to minimize part handling and greatly reduce the number of manual parts cleaners that would be needed for the job. The conveyor is right next to the plasma cutting table where parts can be loaded directly from the table. They move along to a ball bearing table where they are spun and a conveyor feeds them into the deslagging machine. From there, the parts are picked up by another segment of motorized conveyor and fed straight into the grinding and edge-rounding machine. After exiting that, a conveyor delivers the parts to final parts holding, where about three days’ worth of parts are held for customers. If you were to look at the conveyor setup, it would be shaped like a lightning bolt, according to Moon.

The deslagging machine features a metal pin system that removes the slag from the parts. The pins are attached to rubber belts that move across the parts as they feed into the system. Two sets of belts with metal pins clean the top of the part, and two sets of belts do the same beneath. This means that the parts never have to be flipped over during the deslagging process.

"These metal pins act like a person with a chisel," said Brett Mandes, LISSMAC's senior sales manager. "The metal pin strikes the edge of the part or the corner where the slag is. When it impacts the slag, it knocks it off just like if you were to hit it with a metal chisel."

If a metal pin breaks, they can be replaced without having to replace the whole belt. They are attached to the belt with one bolt and can be unscrewed, removed, and replaced with another pin.

Once the part exits the deslagging area, a motorized table picks up the part and continues it down the conveyor to the next stage. Parts follow through one after the other and side by side.

Mandes said the maximum part width for the system is 59 in. The maximum part thickness is about 4.75 in. The smallest part that can be sent through this system is about 6 in. long and 2 in. wide.

The second LISSMAC machine works in much the same way as the deslagging process. The first set of belts, oriented across the incoming feed, not with the direction in which the part flows, grinds the tops and bottoms of the parts to further refine the surface and create a slag-free part. Two sets of grinding belts are located at the top of the unit, and two are located at the bottom.

From there, the parts feed into the edge rounding portion of the machine. Again, belts with edge rounding blocks—two rows on top and two rows on the bottom—encounter the parts as they pass between the cross-belt movement of the belts.

Mandes said that in the OMS application the edge rounding is more of a "softening" of the edge. Any razor-sharp edge is removed by the blocks. The user can adjust the degree of edge rounding, from very light to heavy. As a result, the edge rounding blocks are adjusted so that they actually apply enough pressure to remove only enough material to create the desired edge.

Mandes added that the machine has a photo eye that monitors the trim life of the abrasive blocks. Sensing that the blocks are being worn down because of usage, the machine automatically adjusts the belts positioning to ensure that the edge rounding blocks are producing a consistent and repeatable result with little to no manual adjustment.

"The machine intermittently moves those blocks as they wear, so you don't have to rely on a person to monitor that," Mandes said.

Moon said that since the deslagging and edge preparation line was installed, the parts cleaning operation attached to the plasma cutting table has been transformed from a monumental manufacturing challenge into an efficient production process that is catching the eye of others within the OMS family. He mentioned that at a recent gathering of other OMS general managers at the Greensboro facility, most of the visiting guests wanted to check out the LISSMAC conveyor and a couple of nearby blasting cabinets, which are used to finish plate before cutting and plasma-cut parts right off the table, depending on just what customer specifications dictate.

"I might be jinxing us, but I couldn't tell you the last time we had an injury in parts cleaning," Moon said. (The Greensboro plant received the Fabricators & Manufacturers Association's 2022 Safety Award of Merit in April.)

One of the best ways to minimize the risk of injury in a process is removing those that might be injured from the process. That's what the automated finishing line has allowed OMS to do. Whereas it once needed 32 people to tackle deslagging and edge preparation with manual grinders, only two to six people are needed today. If the parts are on the larger size, two people can handle the transfer of parts from the plasma table to the conveyors. If the parts are small, six people might be needed in feeding the conveyor table.

Moon added that the parts cleaners still are involved with some manual deslagging, but it's much more of an easy clearing of easy-to-remove slag that might be hanging from the plate surface, much like clearing a large icicle from a roofline with the snow shovel. He said this is aimed at extending the life of deslagging, grinding, and edge rounding consumables.

Obviously minimizing manual parts cleaning helps to reduce the chance of ergonomic strains and potential cuts and eye injuries, but the presence of the conveyors also has eliminated a considerable amount of lifting, which could lead to back issues. Moon said workers have gone from a minimum of five lifts, which were required to move parts around before the conveyors and automated finishing equipment was installed, to just two lifts—one to move parts from the plasma cutting table to the conveyor and another to remove the parts from the conveyor and place them in the appropriate racks.

"Things are totally different in our parts cleaning area now," Moon said. "The group we have in there now are not trying to get out of parts cleaning. They like running the LISSMAC. It's been a dramatic improvement there."

Recounting the past several years with the equipment, Moon remembered the simple thrill of just removing the more than 30 power cords that littered the shop floor in the parts cleaning area and the potential tripping hazards they created. "You just don't think about those things when they are gone," he said.

Now that other general managers have seen the Greensboro facility's finishing technology in action, they know what automated finishing equipment can do for them. These other facilities might not do as much plasma cutting as Greensboro, but a lot of them are cutting metal with high-powered fiber laser cutting machines, which have a tendency to create slag when the machines are pushed to maximize productivity instead of slowing things down to deliver less slag and more precise edges.

Moon is OK with the knowledge sharing. He thinks every facility in the OMS family can improve their operations just by learning from each other.

"You should always steal the great ideas," he said.