A South Carolina manufacturer of fertilizer distribution systems has realized benefits from the use of a 'high density' plasma cutting process. In this case study, the benefits of the precision process are explored.

Calhoun Trading Company, St. Matthews, South Carolina, manufactures commercial fertilizer distribution systems under the "Yella Bear" brand name.

InnerLogic's FineLine 200 PC power supply supplies the arc to the MG "Promaster."

Typical carbon steel cut parts.

Cut parts like this perforated plate require no secondary machining operations.

These bent pieces exhibit good edge quality and precision holes.

Proprietor Tatum's office overlooks the cutting machine station. He can program the system from his computer without leaving his office.

Close-up of plasma cutting arc. Note the the pneumatic marking and pneumatic drilling tools to the right of the torch tip. They're available if and when needed.

Rural St. Matthews, SC, is not the most likely spot to find state-of-the-art plasma cutting equipment, but Calhoun Trading Company had no problem being among the first to introduce a new process that improves quality, speeds production, eliminates secondary processing, and which can open up new markets.

Father and Son Team

Father and son Tatum and Sidney Gressette operate this third generation company that produces large commercial fertilizer distribution systems under the "Yella Bear" brand name. In the past, much of Calhoun's production had been accomplished with manual processes and involved a lot of shop floor intervention by the Gressettes. While the need to implement more modern production methods was evident, Tatum also recognized that if he was to maintain engineer son's interest in the business, he needed to think in ways would be seen as interesting and challenging. Looking for a better way to process carbon steel and stainless steel sheet and plate, they initially considered investing in laser cutting technology. Additional research, however, led them to the conclusion that precision "high density" plasma cutting provided everything they hoped for, while requiring a substantially smaller investment.

Plasma Cutting
Plasma cutting has been around since the 1950s. It was initially viewed as a tool for processing metals that could not be cut with conventional flame cutting torches. Both hand held and mechanized versions were typically called upon as a more costly but necessary option when non-ferrous metals needed to be cut. The process saw widespread use among specialty metals warehouses and fabricators processing metals such as aluminum and stainless steel.

Plasma cutting technology progressed in the early 1980s with the introduction of lower amperage air plasma systems which simplified operation and performed quite well in sheet metal processing applications, both hand held and mechanized. Offering speed and convenience on virtually any type of metal, the air plasma process radically changed the way thin metals are processed. Air plasma found ready acceptance in industries as varied as HVAC duct manufacturing, maintenance, auto body, job shops, and field repair operations. Of course, these low amperage systems did little for those who needed to production cut heavier plate.

Oxygen as Plasma Gas
Recognizing that the market for processing thicker carbon steels was vastly larger than the nonferrous market, plasma equipment manufacturers developed newer technology in the mid 1980s that utilized oxygen as the plasma gas. Oxygen, combined with technology introduced in the early 1990s that solved the inherent problem of rapid electrode erosion when using oxygen, opened up an entirely new and huge market for mechanized plasma cutting. The dramatic increases in speed made possible with oxygen plasma cutting of carbon steel, as compared to traditional flame cutting, yielded economic statistics that strongly favored plasma in many high volume operations. This is especially true since labor continues to be the dominant cost factor in sheet and plate cutting operations. Use of oxygen as the plasma gas also provided cleaner, weldable cut edges.

Plasma cutting did not previously provide weldable edges because of the nitriding that occurred when nitrogen or air was used as the plasma gas. Conventional oxygen plasma also provides carbon steel cuts that exhibit less dross than processes using other plasma gases. Post-cutting operations to clean up cut edges were eliminated in many cases.

The Varied Kerf Problem
One problem with the conventional plasma process that remained was that cut edges exhibited a wider kerf at the top of the cut than at the bottom. The resultant beveled edge often required secondary operations to square up the part. This problem can be improved upon by close control of torch height (arc voltage). Even then, materials under ¹ /4 in. exhibited considerable bevel, often in the 5-10° range.

Further development in the early 1990s yielded technology that produced considerably higher current densities by restricting the plasma column through a smaller nozzle bore. While conventional plasma processes typically produce arcs of 30,000 --35,000 Amperes per square inch (A/in. ² ) , this new process produces arcs of 50,000 (or more) A/in. ² This "high density" arc was found to provide even higher operating speeds in plate cutting while improving cut edge squareness. In fact, cut edges with as little as 2° or less of bevel are normal for this process throughout its thickness range of gage through 1-in. These improvements in squareness with "high density" plasma cutting are evident on non-ferrous metals as well.

Precision "High Density" Process
The precision "high density" process has taken plasma cutting to a level that compares favorably to laser cutting in many applications. It is accomplishments such as these, coupled with the equipment's relatively low cost and simple operation, that led the Gressettes to choose precision "high density" plasma for Calhoun Trading.

They decided in 2001 that if they were to succeed in an ever more competitive market, they needed to look at ways to improve quality, lower operating costs, and to take advantage of the things that the latest technology can provide.

Tatum likes to put things in perspective by noting a question that he previously asked prospective employ-ees - what is half of ⁵ /16? The answer may seem basic to many, but Tatum found that many job applicants did not readily know the answer. That litmus test now plays a far smaller role in his interviewing process since they have taken the burden of critical layout procedures from the shop floor and placed it in the office. Tatum and Sid are now more concerned about a prospective employee's mechanical aptitude and willingness to follow procedures than about his math skills.

"High Density" Plasma Solution
After a very thorough evaluation of all of their options, Tatum and Sid purchased an InnerLogic FineLine 200PC precision "high density" plasma system fitted to an MG "Pro-Master" platform. This 200 A system eliminated many secondary operations such as drilling, shearing, and grinding; and has reduced set-up time from hours to minutes.

Sid says a typical part that would have taken half a day to layout, cut, and clean up now can be produced in a few minutes. The system has also helped lower overhead by minimizing shop floor layout, and it has eliminated the need for other machinery such as the shear and ironworker that they previously depended upon.

The nesting of expensive stainless components offers additional economies, as compared with the sizeable amount of scrap produced when shearing was used extensively. An unanticipated secondary benefit involved the first time use of a CNC machine at Calhoun Trading.

This new operation prompted management to adapt computeraided design (CAD) into the table's x-y layout capability. Newly implemented computer technology has had farreaching results and has improved methods and procedures throughout Calhoun Trading.

New Markets
Not only has the precision "high density" process improved quality and made their operation more cost effective, but it has opened up some new markets as well. For the first time in company history, Calhoun Trading has begun to do work for other companies in their area.

Interestingly, some of the new business they are enjoying is coming from shops that have only laser cutting capability. They are seeing considerable growth in contract cutting, and that is becoming a more important part of their business. Such work is of great benefit not only from a revenue standpoint but also because it helps smooth out the seasonal fluctuations that are normal in their core business.

Tatum states, "In this economy, you simply cannot be competitive without one of these machines. I don't know how a smaller shop not having such a plasma can continue to exist."

Tatum and Sid are so pleased with their new production tool that they continue to thank InnerLogic's distributor — Fabrication Automation, Concord, NC, for having convinced them to implement the process.

According to Tatum, precision "high density" plasma has become so important to their operation that "it would be hard to imagine operating without it".

Edited from information supplied by Innerlogic, Inc., Charleston, SC. For additional information contact Brian O'Hara, national sales manager, InnerLogic, Inc.: Phone (843) 795-4286; fax (843) 795-8931; email: bohara@innerlogic-inc.com, or visit www.innerlogic-inc.com