As recently as 40 years ago, the process of fabricating ductwork was incredibly time-consuming. Skilled tradesman known as “tin knockers” individually laid out each galvanized component using templates made of plywood, metal, or cardboard. They’d take a template and sketch out the location of parts on the raw steel before wielding hand and electric tin snips to cut the parts out.
This made the arrival of CNC controlled air plasma systems in the late ‘70s and early ‘80s a welcome addition. Though the capital costs were prohibitive for a smaller company, the larger and more progressive companies understood they’d quickly see a return on their roughly $30,000 investment.
Though these early systems had a learning curve and weren’t all that reliable, the ability to design, cut, and label the raw galvanized and stainless steel used for commercial and residential ductwork systems using CNC plasma was a major time saver. The new systems could typically produce more parts in a day than four to five “tin knockers” could in a week, and as an added benefit, the product was cut more accurately.
Today, the vast majority of HVAC shops now use a CNC duct cutting machine. Unlike the early systems, these systems are highly reliable, more capable than ever before and, when adjusted for inflation, less expensive than the original designs.
Cutting beds are typically 5’ x 10’ in size to fit a standard 5 x 10 sheet of steel though busier shops might feed a large continuous coil of galvanized steel to a larger 5’ x 20’ cutting bed for more efficient production. The CAD/CAM software powering these systems is better than ever. It’s easy to learn and use so that comprehensive shops can go from design to forming and fabrication.
Most companies are powering their machines with an air plasma system like Hypertherm’s Powermax brand with the Powermax45 XP and Powermax65 among the most popular models. Some of these machines also include an add-on tool like a high-speed rotary spindle to accurately cut the duct liner and insulation materials in addition to the sheet metal. The cut quality is very good; however, most HVAC fabricators are more focused on speed since faster cut speeds provide the ability to produce more product in less time. Typically, cut speeds when using a 30 or 40-amp system on single phase power with standard shop air are in the 350 to 400 inch per minute (IPM) range while larger 60 and 80-amp systems boast cutting speeds in the 650 to 700 IPM range.
There are also lighter and smaller options for field use, including systems with built-in air compressors that can run on a standard 20-amp, 120-volt power outlet or even on a generator. They really are the fastest way to cut galvanized steel in the field using a handheld torch placed right on the metal surface being cut. This allows technicians to drag the torch along the side of a straight edge or template for very accurate cutting of additional duct or branch holes that are so often necessary. Though less common, a few companies also take on heavier metal fabricating jobs using a high-definition or even X-Definition class plasma such as an XPR300.
The critical plasma torch to material distance is held with either a plate rider sled or better still, a system that uses more accurate arc voltage feedback. The torch design and consumables are much improved. While the nozzle and electrode in early systems would get through 100 or so duct fittings or three to six sheets of galvanized steel before needing replacement, the consumables on modern systems last 10 times as long.
Along with the additional capabilities, ease of use, and higher productivity levels of the CNC duct cutting machines on the market today keep in mind that plasma cutting technology has advanced as well. There are opportunities to upgrade just the plasma system on your existing CNC machine or to add this technology for the field installation crews to improve their productivity and versatility.
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