Better plasma cutting on stainless steel
Steel distributor finds new technology provides the edge it needs
Penn Stainless Products, Quakertown, Pa., wanted to upgrade its plasma cutting operations so that it could cut thicker stainless steel plate. It found that plasma technology advancements could deliver the thicker cut and additional benefits as well.
When it comes to cutting stainless steel, plasma cutting isn’t the first method that comes to mind for most metal fabricators. Odds are they aren’t cutting a lot of stainless steel plate, however.
Penn Stainless Products does just that. From its 200,000-square-foot facility in Quakertown, Pa., the company processes and distributes stainless steel sheet, plate, bar, structural, pipe, and tubular products—some of them very large and very thick. To process these large products, the company has invested in some very robust cutting technologies.
For example, during the past year the company installed a heavy-duty laser cutting machine with a 13- by 63-ft. cutting bed and capable of cutting 1.25-in. stainless steel plate. Shortly before that installation, the steel distributor installed its largest waterjet with a 10- by 20-ft. table and the power to cut in excess of 8-in. stainless steel plate.
With these upgrades, Penn Stainless noticed a gap in its service offerings. Many metal fabricating customers wanted high-quality plasma-cut parts in thicknesses that the distributor just couldn’t accommodate with its existing plasma cutting technology. Sure, it could supply waterjet-cut blanks if necessary, but some customers didn’t need the high tolerances a waterjet produces or want the additional expense. Also, the laser cutting machine just couldn’t process parts as thick as 6 in. efficiently.
“We wanted to upgrade the equipment to better technology,” said Jason Martineau, national sales manager, Penn Stainless Products (see Figure 1). “We also were limited to about 4-in.-thick material.”
A few competitors had the ability to plasma-cut up to 6-in. and thicker stainless steel plate. To step up and serve more diverse customers in fields such as petrochemical and power generation, Penn Stainless needed that capability too.
Putting Plasma in Place
In the second half of 2012, Penn Stainless installed two new Koike Aronson Versagraph Millennium series plasma cutting machines. The installation features two cutting gantries, each powered by a Hypertherm HPR800XD® power source, operating on one shared rail system that creates a cutting envelope of 10 by 65 ft. for each cutting head (see Figure 2). A downdraft table helps to keep the smoky grit of plasma cutting out of the atmosphere.
“They basically can have two cutting machines running the whole time. That’s what it comes down to,” said George Kazmierczak, senior sale engineer, Koike Aronson Inc.
While having two plasma cutters on the same rail is not the norm, according to Kazmierczak, it’s hardly unusual. Koike Aronson actually has installed three gantries on the same rail for customers.
If anything, this sort of mechanical setup did take a little longer, but Penn Stainless required one table to be functioning at all times. Kazmierczak said the entire installation took about three weeks.
With the new cutting capability, Penn Stainless now can cut stainless steel plate up to 6.25 in. It’s getting additional benefits as well.
“This is a faster cut for sure,” Martineau said.
Kazmierczak agreed. Older plasma technology used to be able to cut 1-in. plate at 20 inches per minute (IPM); today’s technology can deliver similar cutting capability at 65 IPM.
Efficiency can be further pushed with the power source’s piercing functions. The technology can deliver maximum stainless steel pierce capability up to 4 in. with 800 amps. Hypertherm’s PowerPierce® and a controlled motion process during piercing make this possible.
Steve Liebold, plasma process engineering leader, Hypertherm, described the PowerPierce advancement as involving a liquid-cooled shield technology for the torch. Because the front end of the torch is liquid-cooled, it can better withstand the heat generated during the piercing process. In addition, the cooled front end helps to prevent molten slag from adhering to the torch.
This approach worked well for piercing mild steel with 400 amps, Liebold said, enabling robust piercing performance—a minimum of 300 pierces on the same set of consumables—up to 2 in. thickness. The push to extend the piercing capability for thicker stainless steel, in the 3- to 4-in. range, came as field reports suggested that people actually were using a set of “sacrificial” consumables just to make the pierce and then switching out to the cutting consumables.
To meet customers’ interest in working with thicker stainless steel, Hypertherm developed a controlled motion pierce process that eliminates the problems that a stationary pierce has in evacuating molten material while keeping the torch as far as possible from the molten activity, preserving consumables.
“We actually start off at a relatively fast speed, almost at a gouge speed, creating a trough into the top of the material. Again, the torch is far away,” Liebold said.
“Once we have the trough established, then we slow to a creep speed, slower than what we would be cutting the material at. At this point we are evacuating the material up through the trough that we established.”
As the pierce gets deeper, Liebold added, the torch gets closer to the plate, far enough away to sidestep any blowback but within the distance to maintain optimum voltage. This results in a clean pierce and less abuse to the plasma cutting consumables.
While 300 pierces with the same consumables is not possible at these thicknesses and harsh conditions, Liebold said that customers have indicated that the 25 to 50 starts they can expect are dramatically better than what they had been able to achieve with conventional plasma cutting systems—if they could pierce at those thicknesses at all.
Kazmierczak added that the plasma cutting advancements also contribute to increased throughput of parts for Penn Stainless because secondary processing is minimized. In the past, conventional plasma cutting left black carbonization that need to be grinded off before any machining or welding could take place. Now a mix of hydrogen and argon eliminates the need for secondary cleanup.
Additionally, modern plasma cutting has advanced so that “virtually no dross” exists when compared to older technology, Kazmierczak said. Grinding the edges and bottoms of plasma-cut parts is not as necessary as it once was.
“They can cut a part and sell a part. There are no secondary processes needed,” he said.
A Nice Cut
Martineau recognizes the improved appearance of the plasma-cut stainless steel parts (see Figure 3), even if he isn’t responsible for working the table each day. He does see some of the parts as they go out the door.
“It’s a beautiful cut, and I know that’s never very scientific-sounding. It looks a lot nicer than what we had in terms of the surface condition,” Martineau said. The plasma cutting system’s advanced controls and ability to maintain tight tolerances are making a huge impact on final part quality.
When it comes to stainless steel, appearance is one of the more important factors in determining if the part meets quality objectives. This plasma cutting technology has made the cut as a suitable fabricating tool for stainless steel plate.
The FABRICATOR is North America's leading magazine for the metal forming and fabricating industry. The magazine delivers the news, technical articles, and case histories that enable fabricators to do their jobs more efficiently. The FABRICATOR has served the industry since 1971.