October 15-17, 2024 at Orange County Convention Center in Orlando, Florida
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Tuesday Oct 15 9 AM — 5 PM
Wednesday Oct 16 9 AM — 5 PM
Thursday Oct 17 9 AM — 4 PM

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Orange County Convention Center

9800 International Drive
Orlando, Florida 32819

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North America's largest metal forming, fabricating, welding and finishing event heads to Orange County Convention Center in October 2024. FABTECH provides a convenient "one stop shop" venue where you can meet with world-class suppliers, see the latest industry products and developments, and find the tools to improve productivity, increase profits and discover new solutions to all of your metal forming, fabricating, welding and finishing needs.

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North America's Largest Metal Forming, Fabricating, Welding and Finishing Event

From the Blog

Selecting a Plasma Arc Cutting System

By Jennifer Dallos on on
Consider the factors presented here to make sure you purchase cutting equipment that will meet your expectations for doing the job at the right price. Based on an article from Hypertherm Reprinted with permission: The Welding Journal  Selecting a new plasma arc cutting (PAC) system is a lot like selecting a new truck. Plasma systems, like trucks, range from light-duty, personal use models to heavy-duty industrial models, with specialized versions available to meet specific customer needs. All share certain attributes, but within each class there are other features that are unique to the specific model. In the end, what really matters is which one meets the customer’s needs most efficiently and most cost effectively.
Welding-Cutting System

A typical plasma arc cutting system at work.

There are no industry standards for comparing PAC systems, so customers are left with confusing and contradicting information from the manufacturers. Historically, cutting capacity and initial purchase cost have been the key considerations for selecting a system. While capacity and price contribute to the decision-making process, additional factors should also be considered. The operating cost — the actual cost of ownership — should be the most important cost consideration. There are often significant differences in operating cost among various systems, and in a year of cutting these differences can really add up. This article presents a set of questions as a guide for selecting the best system for your needs, a list of some attributes that all PAC systems share with an explanation of why each is important, and an easy to use method for calculating operating cost. Getting Started The first step in selecting a system is to decide what you will be using it for, i.e., what you want to cut, and how you want to cut it. Becoming familiar with the industry terminology will help you ask the salesperson the right questions to get you headed in the right direction. The following checklist will provide a good starting point. Cutting Capacity. Usually quoted in inches at full output on mild steel, cutting capacity is a frequently misunderstood figure because each manufacturer may list it differently. Most use a recommended and a maximum, while some add in a severance capacity. Capacity ratings are only meaningful when coupled with a cutting speed. Some manufacturers use 10 in./min (inches per minute) as their recommended capacity, others use 20.
  • The recommended capacity is the target thickness of steel that allows for good productivity and cut quality. The general rule of thumb is that 80% of the cutting should be at this thickness and below.
  • At the maximum capacity, a good quality cut is still possible, but reduced productivity means that no more than 20% of cutting should be in this thickness range.
  • The severance capacity indicates the thickness that can be reasonably severed, but generally with poor cut quality and at very slow speeds, usually at 5 in./min or below.
The output current is only one determinant of cutting capacity. The output voltage and torch dynamics also contribute significantly to the overall productivity of a system. Like the horsepower rating for trucks, true cutting power in a plasma system is determined by output power, expressed in kilowatts. Systems may have similar output currents but different output voltages. For example, a 40-A system with a 110-V output has a 4.4-kW output power; a 40-A system with 140-V output voltage has a 5.6-kW output power — 27% higher. When both current and voltage are considered together, a more complete picture of the system’s capability emerges. Consumable Life. Often overlooked in the selection process, part life is a major contributor to operating cost. Plasma cutting consumables generally include four parts: electrode; nozzlel; swirl ring (or gas distributor); and cap. In addition to the upfront costs, consider the durability of these parts and their life in arc-hours, especially for the most frequently replaced parts — the nozzle and electrode. Primary Input Power. This refers to power at the wall or line power source, in voltage, phase, and available current. Each plasma system will have a required input current at maximum output. It is essential to know the power that is available when selecting a system. Some systems are limited to specific voltages, while others are designed to operate at multivoltage configurations. Several newer systems feature autovoltage. The multi- and autovoltage models should be considered should you plan to use the system at multiple job sites. Gas Supply. While generally not something that varies much from system to system within a given power range, the amount of air pressure and flow required is still significant in evaluating shop setup. Most air plasma systems require either air or nitrogen as a gas source, either from a high-pressure gas cylinder or, most often, an air compressor. Operating pressures vary slightly from one power range to another, but all systems have both a required pressure (lb/in.2) and a required flow rate (ft3/min). Some larger systems can use other gases, such as oxygen or argon-hydrogen mixtures. Oxygen is usually used for higher cutting speeds on mild steel, while inert gases are used on aluminum and stainless steel to prevent oxidation on the cut edge. Duty Cycle. The duty cycle is the overall operating time that can be dedicated to actual cutting before the system overheats. It is stated as a percentage of actual arc-on time at a given ambient temperature. For instance, a system with a 50% duty cycle rating can cut at full output for 5 min continuously within a 10-min period at X°F before requiring rest. Unfortunately, as with cut capacity, there is no agreed upon industry standard when it comes to determining duty cycle. Some manufacturers will cut at maximum capacity using a high ambient temperature (104°F for Hypertherm units) to determine duty cycle, while others may cut thinner metal at a lower ambient temperature like 70°F. Because of this, it is important that you, as a purchaser, ask the manufacturer exactly how the duty cycle was calculated. If you’re looking at a machine with a 1-in. recommended cut capacity and the manufacturer tells you the duty cycle was determined while cutting 1⁄2-in. material at 70°F, you’ll likely be hard pressed to reach the stated duty cycle. Other Considerations The factors above should help narrow your search, but they are not the only things to evaluate when considering a new system. Here are a few additional attributes that you should consider in choosing the right system for your specific needs. Cut Quality. The cut quality you require will be an important factor in deciding which system is right for you. Cut quality refers to the cut edge’s bevel angle and smoothness, dross or slag formation on the top or bottom of the cut, and kerf width, which is the width of the metal removed by the plasma arc. Cut quality is affected by a number of factors, including material type, thickness, operator skill, gas supply, and torch dynamics. Some manufacturers offer various torches (straight, angled, short, long, etc.) and specialized consumables, while other manufacturers use a one-size-fits-all philosophy. Application Type. Choosing the right tool not only impacts cut quality but also the ease with which you can get the job done. If you need to gouge out an old weld for example, you might want to choose a straight torch to position your hand farther away from the work surface. If you cut a lot of metal on the ground, you may want a torch that is several feet long so you don’t have to bend down as much. If you need to cut an oddly shaped piece with deep grooves, then you may prefer long, tapered consumables designed to cut in hard to reach areas. Portability. Plasma systems vary greatly in size and weight. If you plan to move the system from site to site, or even around your shop, you’ll likely want to choose a smaller and lighter system for increased portability. Most PAC systems can be easily moved by one or two workers. Larger systems, usually with capacity ratings above 1 in., may require a lift truck or hoist. Cutting Method. Plasma cutting can be done manually using a hand torch or automatically using a machine torch on a CNC table, track burner, or pipe beveler. Many systems are designed for either hand or mechanized use, but some offer both types of torches, as well as CNC interface capabilities, allowing customers to use the same unit for both applications. Conclusion Many of the factors that determine which system is right for you will become obvious when you see the system demonstrated in your own shop. Pay particular attention to cut speed, cut quality, and ease of use. Find the system that delivers the performance you want at the price you want to spend. Though the initial price is always an important consideration, take the time to calculate the operational costs to make sure you purchase cutting equipment that will meet your expectations for doing the job at the best price in the long run. Calculating Operating Cost Once your list is narrowed down to two or three systems, it’s time to determine the operating cost of each. This includes daily expenses for fuel, maintenance, and consumable parts. All of the data needed for these calculations are available from the product literature and the manufacturer. For example, let’s compare two hypothetical Systems A and B (reference the table above). Both are rated at 40 A and 1⁄2 in. Initially, System B may seem to be the better choice since it costs $500 less. However, System A has some distinct advantages. Its higher output voltage yields a higher maximum cutting speed, it offers longer consumable life, plus a longer duty cycle. To determine how much these factors will affect the operating cost, it’s only necessary to make a few calculations. List Price                       (A)$2500             (B)$2000 Output current                    40 A                 40 A Output voltage                   140 V                110 V Duty cycle                           50%                  40% Nozzle cost                       $4.00                $4.00 Electrode cost                   $8.00               $8.00 Maximum speed on 1⁄2-in. mild steel      24 in./min       12 in./min Nozzle/electrode life, in arc-h  2.00 h      1.50 h 1. Total Cost per Work Hour A. The first step is to calculate the consumable cost per arc hour. The nozzle + electrode cost for both systems is the same: $12. To find the consumable cost per arc hour, divide $12 by the life, in arc-hours. B. Next, calculate the total cost per work hour factor in the duty cycle to adjust for the time actually worked. To do this, divide the consumable life per arc hour (calculated above) by the duty C. Then, add in the labor costs. These are specific to the buyer’s business, and should include wages and overhead. For this example, we used a labor rate of $30/h. 1A Total consumable cost         (A)$12.00         (B)$12.00 Consumable life                           2.00 h                 1.50 h Consumable life/arc-h            = $6.00              = $8.00 1B Consumable life/arc-h          $6.00                    $8.00 Duty cycle                                   50%                       40% Consumable cost/work-h    = $3.00              = $3.20 1C Consumable cost/work-h       $3.00                  $3.20 Labor rate                            + $30.00            + $30.00 Total cost/work-h              = $33.00             = $33.20 2. Total Feet Cut per Work Hour A. Now we need to calculate the total number of feet each system is capable of cutting in an hour, the feet per arc-hour. Multiply the stated cutting speed by 60 min, then divide by 12 in. B. Since the systems cannot cut 100% of the time, adjust this potential ft/h number by the duty cycle to get the number of feet the system can cut in an hour. 2A in. cut/h (max speed × 60)  (24 in./min × 60) = 1440 in.  (12 in./min × 60) = 720 in. Divide by 12                                    12                                                          12 ft cut/h                                      = 120                                                      = 60 2B ft cut/h                                     120          60 Duty cycle                               50%      40% ft cut/work-h                        = 60       = 24 3. Total Cost per Foot Now that we have both the total cost per work hour and the total feet cut per work hour, we can calculate the total cost per foot. To do this, we divide the cost by the feet cut. Total cost/work-h               (A) $33.00         (B)$33.20 Total ft cut/work-h                            60                       24 Total cost/ft                               = $0.55              = $1.38 4. The Bottom Line As these calculations show, there can be significant differences in cost per foot between outwardly similar systems. In just a year of cutting, these differences can really add up. In a typical fabrication shop that cuts 5 ft/day, the cost savings can be significant. In just one year of use, System A, that cost $500 less initially, would cost $1079 more in operating expenses than System B. Total Cost/ft                      (A) $0.55        (B) $1.38 Daily Cost @ 5-ft/day          2.75             6.90 Weekly Cost                        13.75            34.50 Annual Cost to Operate   $715.00         $1794.00

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